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5-12-1987
Characterization of ion implanted antimony
Michael J. Cumbo
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CHARACTERIZATION OF ION IMPLANTED ANTIMONY
by
MI chae 1J. Cumbo
A Thesis Submitted
In
Partial Fulfillment
of the
ReQul rements for the Degree (\ f
MASTER OF SCIENCE
In
Electrical Engineering
Approyed by:
Prof
Name Illegible
(Thesis Adylsor)
Prof ________
Prof
Prof
Lynn
Fuller
______
__
~
Name Illegible
Swaminathan Madhu
(Department Head)
DEPARTMENT OF ELECTRICAL ENGINEERING
COLLEGE OF ENGINEERING
ROCHESTER INSTITUTE OF TECHNOLOGY
ROCHESTER, NEW YORK
MAY, 1987
May 12, 1987
I hereby outhorize Rochester Institute of Technology to release my
Moster's thesis, "Chorocterizotion of Ion Implonted Antimony," for
reproduct ion.
Michael J. Cumbo
Michael J. Cumbo
FOREWORD
The experimental
development
the Device
described In this thesis
work
project
during my
Technology
Lab
of
assignment es a process engineer In
the Electronic Research
Eastman Kodak Company. This facilitated the
semiconductor
processing
with a number of well
applications.
wish
to
testing
use of modern
equipment and provided me
defined goals In the form
of actual
device
for my employer.
the technical
acknowledge
Rochester Institute
addition, I
and
Laboratories,
This was an enjoyable experience for me and, I hope, a
useful project
I
was undertaken as a
of
guidance of
Technology, during the
received a great
deal
Prof. R.
past
three
Turkman,
years.
of encouragement and support
Eastman Kodak Company;
an
In
from
Incomplete list Is:
many
employees of
Mr. M.
DeMay, Mr. M. Guldash, Mr. J. Hach, Mr. J. Hoover, Dr. J. Lavlne,
Dr. S. T. Lee (SIMS Analysis), Mr. J. Russell, Mr. A. Scribanl and
Dr. J. Taylor. I
em also
assistance with
grateful
for the
Indebted to Mr. K.
Ion Implantation
patience of
Chasey, Varian SEG, Inc., for
equipment.
my wife, Judy.
-11-
Finally, I
am
especially
CHARACTERIZATION OF ION IMPLANTED ANTIMONY
by
Michael J. Cumbo
Electronics Research Laboratories, Eastman Kodak
Company
Rochester, New York
ABSTRACT
Ion Implanted antimony
In single crystal
(100)
(121Sb) Is
characterized as an n-type
oriented silicon.
equipment and critical parameters are
procedures used
data
on
The
required
device
that
n-type
dopant,
perspective.
require a
silicon.
experimental
In this study are presented along with the resulting
dopant distribution
heavy
Implantation
discussed. The
and crystal
damage
annealing.
The tradeoffs between antimony and arsenic, the
used
dopant
are examined
The context of this
heavily
Results of a
more
from both
commonly
a process end a
comparison
is In applications
doped layer beneath a thin deposit of epitaxial
specific
buried layer process characterization
are Included.
-Ill-
TABLE OF CONTENTS
Page
LIST OF TABLES
v
LIST OF FIGURES
vi
LIST OF SYMBOLS
lx
I.
INTRODUCTION
1
II.
ION IMPLANTATION AND MICROELECTRONICS
5
A.
Process Features
7
B.
Ion Implantation Systems
9
III.
ANTIMONY IMPLANTATION INTO SILICON
13
A.
Review
B.
Equipment Issues
30
IV.
EXPERIMENTAL PROCEDURE
38
V.
PROCESSING DETAILS AND RESULTS
45
VI.
SUMMARY
85
REFERENCES
86
APPENDIX 1:
of
the Literature: Processes and Devices
Derivation
of
13
the Mass Separation
92
Relationship
APPENDIX 2: Equipment and Materials
-iv-
Listing
94
LIST OF TABLES
Page
1. Atomic masses, tetrahedral
misfit
bonding
lattice
radii and
25
factors of n-type dopants in SI
2. Target features
of
Sb Implanted layers
after
drive-In
40
47
3. Optimum
source parameters
4.
Summary
of
Sb oxidation retarded diffusion study
66
5.
Summary
of
Sb buried layer
77
for Sb Ionization
process parameters
-v-
LIST OF FIGURES
Page
1. Block diagram of the
"generic"
2. Schematic of a Varian/Extrion CF4/DF4
medium current
Ion Implenter
3.
2
planer process sequence
10
Intrinsic dlffuslvltles
4. Cross-sectional representation
bipolar transistor
dopants in SI
of n-type
with a
burled
of a vertical
14
NPN
19
collector
5. Cross-sectional representation of a CMOS structure
with a retrograde
N
20
well
6. Vapor pressures of Sb and As
22
7. Solid solubilities
24
8. Projected
of n-type
range of
dopants in SI
Sb and As In SI
27
9. Projected standard deviation of Sb and As In Si and
10.
Ratio of lateral and
vertical straggle of
S102
28
the n-type
dopants In SI
29
Vaporizer equipped Ion source
31
1 2.
Photograph of a solid source vaporizer core
33
13.
Photograph of a standard gas fed Ion source and a
1 1
.
34
vaporizer equipped source
-vi-
Page
14.
Beam
current end mess separation vs. extraction
voltage
36
15.
Ion source mass spectrum
48
1 6.
Sb beam
49
17.
SIMS profiles: Sb Implanted Into SI
51
18.
SIMS
52
19.
Ion Implanted As Isochronal RTA data
54
20.
Ion Implanted Sb Isochronal RTA data
55
21.
Oxide thickness vs. Sb dose (Version B)
58
22.
Sb
oxidation retarded
vs.
dose
Sb
oxidation retarded
23.
profiles:
profiles
24.
Sb
current vs.
energy
Sb Implanted Into
diffusion: sheet resistance
59
(0
=
5
diffusion: SRP
concentration
61
1013/cm2)
x
oxidation retarded
profiles
S102
diffusion: SRP concentration
(0= 5 x 1014/cm2)
25.
Oxide thickness
26.
Sheet resistance
ns.
62
Sb dose (Version A)
vs.
dose after drive-In (E
68
=
90 keV,
70
Version A)
-vll-
Page
27.
Sheet
resistance vs.
dose after diive-ln (E
=
140
keV,
Version B)
28.
Sheet
71
resistance vs.
dose
after
drive-in (E
=
190 keV,
72
Version B)
oxide"
29.
Sheet
30.
Sb: Version A SRP concentration profile (E
0
31
.
=
3
resistance vs.
x
dose: "zero
74
screen
=
190
keV,
75
1015/cm2)
contour
map
78
resistance contour
map
79
Version A sheet resistance
32.
Version B sheet
33.
As: SRP
34.
As: Version B burled layer SRP
concentration profile
82
35.
Sb: Version B buried layer SRP
concentration profile
83
concentration profile after
-vlll-
Version B drive-in
81
LIST OF SYMBOLS
x
Vertical distance Into the
n(x)
Density
0
Ion dose; the
Rp
Projected range; the
Impurity
of
ARp
atoms as a
number of
Into the substrate
substrate measured
by
function of
Implanted ions
average
distance
from the
vertical
surface.
distance.
per unit area.
of vertical penetration
Implanted Ions.
Projected standard deviation (vertical straggle); the
statistical
fluctuation In Rp.
AR]
Lateral standard deviation (lateral straggle); the statistical
fluctuation In the lateral penetration
of
the substrate
by
Implanted Ions.
qe
Magnitude of the
m
Mess
Vx
Ion
h
Charge
r
Radius of
of an
charge of an electron.
Ion.
source extraction voltage.
state of an
Ion ( 1
curvature of
,2,3,...)
the beamline
-lx-
within
the analyzer.
B
Magnetic field
Ef
Final Ion
Va
Voltage drop
Ib
Ion beam current.
A
Target
R8
Sheet
D
DlffusWIty.
DN
DlffusWIty
Dj0
Intrinsic diffusion
strength of
the analyzer.
energy.
across
the accelerating tube.
area over which
the Ion beam is
scanned.
resistance.
in
a
nonoxldizing
atmosphere.
coefficient associated with neutral
vacancy
Interactions.
Dj"
Intrinsic diffusion
coefficient associated with negative
vacancy
Interactions.
n
Extrinsic
nj
Intrinsic carrier
IS1|1|
Concentration of SI Interstltlals In a nonoxldizing ambient.
[SI,]
Concentration of SI Interstltlals In an
D0
carrier concentration.
concentration.
oxidizing
Pre-exponentlal factor associated with Dj0.
-x-
ambient.
Dq"
Dj"
Pre-exponential factor
Q^
associated with
Activation energy associated
with
Dj.
Activation energy associated
with
D|~.
Q|"
-xi-
I. INTRODUCTION
The various microelectronic process technologies
fabrication
three
of monolithic
Integrated
used
In the
circuits can be classified
into
main groups:
1.) Bipolar technology.
2.) MESFET (metal-semiconductor field
effect
transistor)
technology.
3.) MOSFET (metal-oxide-semiconductor field
effect
transistor)
technology.
Each of these technologies
planar
processing
sequence
substrates, usually In
Iterations
this
Is
sequence
in
each
of a
semiconducting
In Figure 1. The details
"generic"
of each
may vary considerably between the
technology, but the
As depicted In the block diagram,
always used
on
Iterations
form. A block diagram of the
shown
of a given process
unchanged.
aluminum
to produce devices
wafer
planar process sequence
element of
relies upon successive
a
overall
doping
form
process
remains
is
not
Iteration. (The deposition and patterning of an
Interconnect layer is an example of this.)
-1-
'GENERIC'"
PLANAR PROCESS SEQUENCE
Wafer Clean
X
Oxidation
and/or
Thin Film Deposition
I
Photolithographic
Pattern Definition
I
Pattern Etch
No
Doping
I
Figure 1
-2-
One feature
of
the planer process 1s the ability to
modify the
electrical properties of select regions of the
substrate. This Is achieved
dopants Into the
substrate
by
the Introduction of substitutional
lattice. Precise
three-dimensional distribution
semiconducting
of
control of
dopant atoms 1s a
the
key
to
successful
device fabrication. The lateral dopant distribution Is determined
primarily by the
while
the
vertical
process used and
The
objective of
used
photolithographic
distribution depends
any
subsequent
A
the
etching processes,
particular
use of
doping
high tempereture exposure.
of some silicon
doping
process
based microelectronic devices.
ion implanted antimony (121Sb) es an n-type dopant
Is examined, emphasizing
layer
upon
and
this work Is to characterize a specific
In the fabrication
Namely, the
patterning
applications
requiring
e
heavily
doped buried
structure.
generalized
a review of
Is
by
the technical literature on Sb Implantation end device
applications.
process
discussion of the role of Ion Implantation Is followed
Next, the engineering
considered.
The
of an Implanted
Sb burled leyer
experimental procedures are
-3-
described In
detail, Including
techniques.
common
post-Implantation
By way
heavy
properties of
and wafer evaluation
of comparison with arsenic
n-type
Sb
annealing
dopant, the
(75As),
range statistics end
are presented.
-4-
the more
annealing
II. ION IMPLANTATION AND MICROELECTRONICS
Ion Implantation Is the technique
Ionized atoms Is directed upon
penetration of the target
by
which an energetic beam of
e solid
terget, resulting in the
the Incident atoms. The
by
range of energies
encountered In most applications are such that the Incident Ions ere
eble
to penetrate beyond the
before coming to rest,
the target
neer surface region
without
eltering the
(of the
structure of
order of
the
50
)
nuclei of
atoms.1
Ion Implantation as applied to microelectronic device fabrication Is
the technique of choice for
common renge of
doping
semiconductor
atoms per unit area of
wafer, the dose, Is usually between
end
101
]
dose are the two fundamentel
any Ion implantation doping
As
an Individual
The
Ion energies In contemporary processes Is 5 to 500
keV. The number of Implented
energy
wefers.2
and
1017
the terget
atoms/cm2.
parameters used
The
to specify
process.
Implanted Ion
propagates
Into the target wafer, It
loses energy via a multitude of scattering Interactions with the
-5-
electrons and nuclei of the target atoms. This
large ebsolute
density
statistics to predict
atoms.
The
most
of
=
coupled with the
Incident ions, mandates the
adequately the final distribution
elementery treatment
Gaussian distribution function
n(x)
fact,
of
of
use of
of
Implanted
this problem results In e
the form
{0 / [/(2ff )ARp]} exp {-0.5[(x
-
Rp) / ARp]2}
(1)
where x Is the vertical distance Into the terget
wefer, Z Is the
Rp Is the projected range (the everage normal
penetretion
ARp Is the projected standard deviation (vertical
dose,
depth)
and
straggle).3
In the absence of crystellographlc channeling effects, the Geussien
distribution function is
ectuel
the
peek of
dopent profiles. However, beceuse of the dependence of
momentum transfer
their
a reasonable approximation neer
relative
etoms can
masses, forward
occur4
not predicted
between implanted
by
This
results
or
in
atoms and
backscattering
e skewed
target etoms
of
the Implanted
dopant profile
which
the Gaussian function. Three end four moment
distribution functions heve been fitted to experimental data
permitting
more accurate process
modeling.5'6
-6-
on
Is
The utility
of
these
more complex
distribution functions becomes
significant In situations where the redistribution of Implanted atoms
due to any subsequent high temperature
processing Is
Thus, If the
a given
cumulative
/(Dt)
implantation step is
function Is sufficient for
usually the
case
product of
the processing
which
follows
than ARp, then the Gaussian
much greater
most process
negligible.
engineering
problems.
In SI processing. The range statistics
of
the
This is
shallow
level Impurities of SI and GaAs have been extensively studied end are
widely
There
published.
are
many desirable features
technique as
compared with
of
furnace
Ion implantation as a
predeposltlon.
doping
The most
Important are listed below:
1. Cleanliness: Ion Implantation takes
environment, with the pressure
place
In a high vacuum
typically 1
x
10"6
torr or
lower. All Implanters utilize some form of magnetic mass
separation
to
produce a
2. Flexibility: Magnetic
chemically
pure beam of
mass separation means
Ions.
that one
Implanter can be used for many dopants. The wide range of
achievable
Ion doses frees the process
-7-
engineer
from the
thermodynamic
constraints encountered In furnace
predeposltlon. Since most Implanters are designed to maintain
low
wafer
temperatures
are useful as masks
(<100C),
a
host of alternate materials
for selective doping.
3. Profile Control: The
ability to adjust the ion energy
control of
the Implanted dopant profile shape to
which Is not possible
by any
other selective
a
enables
degree
doping
process.
4. Uniformity: Typical three-sigma dose
uniformity
specifications of a
(a) Within
available
commercially
a wafer:
are also several
a medium current mechine
high
current machine
price
0mQX
(lmox
=
vacuum
wafer
mechanism.
from
about
$400,000 for
mA).
a complicated ensemble
components, sensitive
transport
1.505?
1 mA) up to $2,000,000 for
=
10
2. Complexity: An ion implanter Is
high
<
drawbacks to Ion Implantation:
1. Cost: Ion Implanters range In
a
are7
3s<3.75S
(b) Wafer to wafer, day to day: 3s
There
Implanter
of
electrical subsystems and a
Maintenance requirements are
-8-
significant,
with
downtimes
of
25*
not unusual.
3. Crystal Damage: An unavoidable by-product
into
single crystal material
of
Ion Implantation
Is disruption of the lattice. High
temperature annealing Is required to
repair
the damage. This
requirement conflicts with the trend In VLSI device fabrication
toward lower thermal budgets to
lateral
achieve smaller vertical and
structures.
The basic layout of most
commercial
Ion Implanters Is
schematic of a common medium current
The flight path of the dopant
1. A D.C. gas
plasma
atoms
unit8
similar.
The
Is shown In Figure 2.
Is traced below:
is used to Ionize dopant atoms In the source.
torr*
The Internal
2.
Ions are
pressure of
extracted
energy between 5
3. The
90
field
the
that the
*
A
more
through
and
source
Is about
an aperture
analyzer magnet.
trajectory
of
10~3
In the source, at
an
25 keV, Into the beamllne.
bend In the beemllne Is nested
of
has the
the
Ions
of
The field
sources
-9-
the
strength
the desired
seme radius of curvature es
detailed discussion of
within
uniform
Is
adjusted so
cherge-to-mass ratio
the bend In the beamllne.
Is In Chapter III.
0
C
0
H
P
c
u
H
u
O
u
U*
o
Q
iA
CH
fa
rH
J-1
4-J
X
UJ
c
ft
H
S-l
>
o
J
c
o
J-J
Oi
14-1
<D
The charge-to-mass
by*
Is given
ratio
qe/m
=
2VX / (hrV)
where h is the charge state of the ion
the charge
of an
electron,
m
,
(2)
qe
is the mass
Is the megnltude of
of
the
Ion,
Vx
is the
extraction voltage applied to the Ion
source, r Is the radius of
curvature of the
beamllne
and
B is the field strength
of
the
enalyzer megnet.
4. After
being
filtered
by
the enelyzer magnet, the Ion beem
pesses through e veriable eperture to adjust the current level.
The beam is then accelerated ecross the high
which
boosts the energy
of
Is the
voltage
voltage end of
accelerator
10~4
Vfl)
Ef hqe(Vx
?
drop
the ecceleretor tube. The high
ecross
(3)
the beamllne between the
tube is maintained
torr, corresponding to
a
derivation.
-11-
source and
at a pressure of
e mean
i
See Appendix 1 for
tube,
the Ions to the final value, Ef.
=
V0
voltage
the
approximately
free peth of 50 cm.
5. The next
section of
the beamllne contains
quadrupole triplet lens for beam
horizontal
target
One
feature of the scan
key
offset voltage applied
the beam
by
about
the beam that
the high
greater
6. The
Ion beam
wafer.
suppress
is
The
enters
to deflect
from
ions traverse
exchange
pressure
to a
lead to
supplied
the end
mean
station and
wafer resides within a
electron
any secondary
otherwise
which
tube because the
which corresponds
is a D.C.
plates
exchange as
the
Is
not an
Is kept
free
path of
than 10,OOOcm.
scanned
target
torr,
across
neutral atoms
any
the beamllne. Charge
accelerator
10"6
below 5 x
eliminates
from charge
voltage end of
Issue pest the
system
between the horizontal
7. This
result
plus vertical and
to raster the beam uniformly
scan plates
wafer.
focusing
an electric
significant
to the
wafer
Faraday
emission,
dose
to
errors.
Impacts the
cage
to
which would
The
neutralize
electron current
the Implanted ions
between
Is Integrated to determine the dose. The relationship
the
dose, the
scanned
0
aree,
=
A,
and
the beam current,
(|lbdt)/(hqeA)
-12-
lp, Is
(4)
III. ANTIMONY IMPLANTATION INTO SILICON
Many
microelectronic devices require localized regions doped with an
n-type
of
Si, the
see
a
that diffuses slowly In the host lattice. In the
Impurity
n-type
dopants that Mill this
Figure 3. These two materials
diffusion furnace
Before engaging In
be some
As and Sb
when
rich
heavily
Oleszek has
doped,
Sb ion Implantation, there should
seek an alternative
chemically
to
chemical
Si, Is the formation
predeposited on
defects celled "rosettes". The
R. A. Mollne's
doped layers beneath
characterized a
rosette
predeposited in
As and Sb. This problem, which Is common to both
rosettes was one goel of
form
be chemically
Sb;
the fact that a materials problem originally
In the field to
predeposltlon of
requirement are As and
Ion Implanted.
consideration of
mention of
caused workers
Impurity
or
can
case
ellminetlon of
work on
epitaxial
implanter10
uA)
-13-
e
As Induced
Ion Implanted As to
SI.9
Similarly, G. M.
technique for the formation
free, Sb buried leyers using
of
low
current
of
heavily
Omox= 25
c
c
-Q
TJ
c
ro
X
>*
o
o
0
cn
0
c
-C
u
o
o
CM
0)
Eh
u
0
LO
4-J
u
a
o
c
n
c
If)
o
o
Q.
o
O
>
E
CD
D
H
CO
E
QJ
CD
zz
cn
o
o
CD
CJ5
o
u
c
c
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
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o
o
o
o
o
o
o
o
,
.
o
o
O
y
i
o
o
<
co
CO
C^
cn
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OJ
Ion implantation
of
Sb Into SI has been
fundamentally characterized
In the range of energies between 10 keV
and 60 keV
Using
SIMS analysis, the
about
0.3 ( 20%). (The determination
reportedly too
extraction
nuclear
by
E.
of
higher moments Is
this method.) For process modeling,
LSS*
a modified
potential was fitted to the data.
Guerrero.12
SIMS
and
of
30 keV to 120 keV has been
RBS measurements
determine the dopant profiles before and
found to precipitate
were used
after annealing.
at concentrations above
6 x
Sb
1019/cm3
If the
exceeded 800C. For samples with high
Implant doses (0
1015/cm2),
=
3
x
an
anomalously high
to
was
annealing temperature
(2X)
1
sensitive to experimental noise for an accurate
scattering
by
Chu.1
W.K.
ARp/Rp ratio was found to be constant at
Sb Implantation In the energy range
studied
by
oxidation rate
was observed.
Most Ion Implantation Into SI
surface oxide
LSS:
wafers
Is done through a thin layer of
to minimize crystal channeling effects and to protect
Llndhard, Scharff
original paper on
and
Schlott,
Ion Implantation range
-15-
Reference 3, the
theory.
authors of
the
underlying
(from
Interface
x
by forward
either the Implanter apertures or
The behevlor
(5
SI from contamination
of
Implanted As
was analyzed be G. A.
1014/cm2)
were
thin oxide layer (100
temperatures
sticking
and
of
done
).
900 to
at
masking layers
Sb In the vicinity
Sal-Halasz.13
of
on
the
S1-S102
low energies (40 to 50 keV) through
a
1000*C, both dopants have
S1-S102 Interface until
an
essentially unity
2 x
1014/cm2
Is
This trapped dopant Is electrically inactive.
implented Sb
was published
Hall-effect meesurements
active
by
end
A. Nylandsted
goes out of solution
of
1020/cm3
for 700C
ion
Using RBS,
Mossbauer spectroscopy, the
further annealing, this "supersaturated
low annealing
Lersen.14
Sb concentration (incorporated
sites) was found to be 4.5 x
Sb
the wafer).
Moderate dose implants
A more rigorous Investigation of the activation properties
electrically
Impurities
RBS data Indicated that for
annealing
coefficient et the
segregated.
scattered
meximum
on substitutional
enneallng.
solution"
cen
With
be reduced. The
Into Sb-Si vacancy complexes at low doses end
temperatures,
and
Into Sb precipitates et high doses and
high temperatures.
-16-
The effect
of
the furnace tube atmosphere on the
SI has been studied
and angle
an
the
which
In
1s unique among SI
are concerned with
bipolar
e
and n-well
dry 02
is 40 to
the oxidation time.
dopants, Indicates that Sb
annealing studies,
on specific epplicetions.
devices thet
require a
CMOS devices
In the cese of the
heavily
collector
and
thin (2 to 20 um) deposit of
applications.
use of e
non-oxidizing
with vacancies exclusively.
have been published
beneeth
upon
(SRP)
that Sb diffusion
shown
coefficient in
N2, depending
Sb in
of
resistance probe
atmosphere relative to a
Beyond the basic Sb implantation
papers
Spreading
100C, the diffusion
value obtained
This behavior,
diffuses
Mlzuo.15
oxidizing
atmosphere. At 1
of
S.
lap-end-stein measurements heve
Is retarded In
50*
by
dlffuslvlty
doped buried
are
heavily
most
vertical npn
collector
Many
doped
epitaxial silicon.
the
e number of
commonly
of
these
n-type
layer
Vertical npn
cited
bipolar transistor, the
layer reduces the series
resistance, permitting a lower collector-to-emltter voltage
In
saturation mode.
of
the
parasitic
The buried layer
also minimizes
pnp transistor formed
-17-
by
the
base,
the
current gain
collector and
See Figure 4. 16
substrate*
The benefit
burled layer in CMOS devices lies in
latch-up
If the n-well Is diffused down through
a p-type
of a
immunity.17
epl-layer Into a
n-well profile
heavily
doped n-type burled layer, a retrograde
Is achieved.
transistor formed
by
the
By degrading
the
the parasitic pnp
gain of
p+
source/drain,
n-well and
substrate,
*
latch-up Immunity Is improved
J. P. Gallllard Investigated
process
heavily
using Ion Implanted
crystal orientation on
annealing.
See Figure 5.
Sb.18
doped burled layers In a bipolar
He considered the role of substrate
the effectiveness of post-Implant furnace
TEM study Indicated that residual defects ere more
difficult to
eliminate
recrystalizetlon of
formation of
In (11 1) SI than
the Implant
(100) SI. During
generated amorphous
mlcrotwlns was observed
region, the
only In (1 1 1) SI. The
injection efficiency Is reduced due to the
Increased base Gummel number. Furthermore, the transport factor
of the parasitic base Is degraded by the built-in electric field
The
parasitic emitter
associated with
base
the
retrograde
doping
width.
-18-
profile and
the Increased
Vertical NPN Bipolar Transistor
p+
p+
n epi
\
/
/
?
V^-^p-
v"^.nv
-
n+
;
n+
rj \
y
n e
nepi\
_*
-*-
buried layer
p
-
substrate
Figure 4
-19-
J
p+
/
n epi
N Well CMOS Structure
cF^; ^^
m^
pepi
p+ substrate
Figure 5
20-
microtwins are
1200C,
and
apparently
stable at
anneellng temperatures
of
up to
lead to defective epl-layers.
An unexpected benefit of burled layer structures is the elimination of
defects
epl-leyer
results of a
effective
vie extrinsic gettering.
bipolar process gettering
denuding
which were within
100
study.19
defects
of epitaxial
urn of an
G. A. Rozgonyl hes published
This demonstrated the
(primerily
stacking faults)
Implanted Sb buried collector
island.
M. L. Hammond has considered the problem of autodoping
epitaxial growth with respect
layers
near
of
the
As and
Autodoping
original wafer surface
evolution of
which
Sb20
to localized confinement
the dopant into the
depends
unwanted
upon
spreading
vertical and
the
of
of
buried
Is the redistribution of dopent
during
epl-leyer
deposition due to
epl-reactor atmosphere.
vapor pressure of
the dopant,
This effect,
can result
in
the localized buried layer islands in the
lateral directions
es well as cross contamination of
adjacent wafers In a batch reactor.
are shown
during
In Figure 6. The lower
The
vapor pressures of
vapor pressure of
-21-
As and Sb
Sb, especially
at
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typical epl-reactor temperatures (1050C to
1200C), Is the
overriding
for Its use as a burled layer dopant.
reason
If a buried leyer with a
very high peak
than 5
10j
x
doping
9/cm3) is necessary, Sb is no
to As because
of
solubilities of
concentration
longer
(greater
a viable alternative
its lower solid solubility in Si. The
solid
the common n-type dopants are shown in Figure 7 and
their tetrahedral
bonding
radii are
listed In Teble 1.
Sb has found other applications In SI devices beyond buried layer
Beceuse
structures.
(121:28),
proper
the lerge atomic mass
of
implantation
dose
of
amorphous
1
x
conditions.
1014/cm2,
SI layer
two Implents
dose level
at a
high
the
without
any
technique.21
dose, 3
amorphous
x
1015/cm2. The
thet the
layer.
However, the
-23-
After
Implanting
Sb
Implanted Into the
profile was
energies of
moderate
the
completely
Normally, P Implanted
preamorphlzation results
after annealing.
the
under
A. Schmitt has evelueted Sb
phosphorus was
were chosen such
contained within
In the SI
Sb relative to SI
It can very effectively emorphlze single crystal SI
Implantation as e preamorphlzation
et a
of
at
this
In dislocation loops
dose Sb
0
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Table 1: Atomic Masses, Tetrahedral Bonding
Radii and Lattice Misfit Factors of
n-Type Dopants in Si
Dopant
Atomic Mass
Sb
of
As
P
121.8
74.9
31.0
1.36
1.18
1.10
0.153
0.0
0.068
Most
Abundant Isotope
(amu)
Tetrahedral
Bonding
Radius (A)
Lattice Misfit Factor
Reference:
Ghandhi,
The
Theory
S.
K.
of
Microelectronics,
New
York,
1968.
-25-
p.
6,
and
Practice
Wiley,
preamorphlzation implant enables defect free recrystellzatlon of the
heavily
doped layer.
One approach to
fabricating
reliable short channel
(1 Mm) NMOSFETs
requires the use of a source/drain extension Implent. Known as a
low-doped-draln
extension of
gate.22'23
necessary
(LDD),
the usuel
this places
G. A. Sal-Halasz has outlined a method of
shallow
chosen as
See Figures 8, 9
Junction (100
and
make It useful for
8)
extensions with
A1-S1
moderately low
vertical end
range es compared with
As.
10.
values of
the
Rp and ARp for 1on Implanted Sb
Schottky
barrier heights of metel-SI
published results on
100 mV to 150 mV barrier height
metal
the
(200 Q/D to 500 0/D) 24'25 Ion Implanted
lowering
diodes. W. K. Chu has
doped lateral
fabricating
the LDD dopant because of Its reduced
The comparatively low
to
lightly
source/drain regions under the edge of the
lateral straggle for a given projected
prior
shallow,
n+
sheet resistance values
Sb Is
a
deposition.26
T1W-S1
lowering using
S. Ashok has
diodes.27
-26-
diodes,
shallow
with a
Sb Implants
reported similar results on
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There are two
key
equipment
Issues
to Implant Sb: the method of
which must
ionizing
Sb
be addressed in order
atoms and
the mass
separation of Sb Ions. Since these are equipment specific
remainder of this discussion Is based on a
current
widely Installed
Implanter, the Varian/Extiion Model 200 CF4,
machine available
The Ion source
magnetron
for this
Issues, the
medium
which was
the
work.
system used
In the CF4 Implanter Is
a
hot cathode
unit; see Figure 11. The cathode Is a tungsten filament
through which a high current (150 A) Is forced, causing thermionic
emission of electrons.
electrostatic
(usually
60 V). As the
field of the source
filament
current.
by increasing
As a
their
source gas
about
10"3
(This
path
magnet and
serves
to
by
electrons
magnetic
the
circular
enhance
length In the
a plasma
Is
forces due to the
field Induced
by
the
arc chamber.)
established.
-30-
drift across the
their Ionization efficiency
Is bled into the arc chamber,
torr,
to an
difference between the
potential
chamber, their path Is deflected
axial
to
electrons are subjected
force due to the
cathode and anode
arc
The
Increasing
If
B, P,
or
the pressure
As Ions are
J*
c
c
.0
c
01
o
o
o
CO
s
o
o
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73
a
1
a
in
-
u*
Q
3
SX
cr
K
u
Qi
N
c
o
a
X
C
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rrj
>
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QJ
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C
QJ
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OJ
u*
0)
ct
needed,
direct
a
gas
fed
source
is possible using
BF3,
PH3 or AsH3,
respectively. If a gaseous form of the desired element is not
available,
a more complicated approach
Is necessary to generate Ions.
In the case of a low vapor pressure solid (such as
heated
oven can vaporize
Sb),
a
reslstlvely
the solid and direct the vapor Into the
An inert gas such as Ar must be used to maintain a
chamber.
arc
plasma.
A photograph of the vaporizer oven assembly used in the CF4
implanter Is shown In Figure 12. A graphite crucible containing the
desired solid source
around which
material
Is located Inside a boron nitride tube,
tungsten heater wire is wound. The crucible
temperature Is monitored be a type K thermocouple Inserted into the
side of
the BN tube. The heater and thermocouple are in a closed
temperature control
160C to 800C. The
standard
system with regulation
vaporizer
to 1C
over
assembly fits Into the
loop
the range of
center of
the
CF4 gas fed Ion source. A standard Ion source and a
vaporizer equipped source are shown In
Positively
charged
a vertical slit
Ions are
In the front
extracted
surface of
-32-
Figure 13.
from the source plasma through
the arc
chamber.
The
potential
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difference between the
the extraction electrode Is
arc chamber and
the extraction voltage, Vx.
The CF4 Implanter
magnet
75
the radius of curvature fixed and the magnetic field maximized,
the extraction voltage Is necessary to extend the range
of mass separation.
current
analyze
that the
extraction voltage must
75As+.
The Implication is that the
beam current
be
results
in a beam
achieved with
possible with a
is defined
amu=
since the Ion beam
extraction voltage.
This
what would
1
penalty Is Incurred
121Sb+.
50 % for
emu
a
In Figure 14,
data from a CF4 Implanter Illustrates the tradeoff.
evident
121Sb+
However,
Is strongly dependant on the
empirical
1
to
the maximum extraction voltage, 25 kV. From equation 2,
a reduction of
It Is
In this work Is equipped with an analyzer
designed to mass separate singly charged Ions from 1
amu at
with
used
1.66 x
es
1/12
10"27
of
Vx
larger
the
current
=
-35-
degradation of nearly
maximum value of
16 kV Is only about half of
analyzer magnet and
mass of
kg.
be limited to 16 kV to
the '*C atom;
Vx
=
25 kV.
CD
CT
ro
o
>
x
.
ro
s
E E
ro
5
c
o
o
ro
L-
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LU
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ro
k_
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CD
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D.
CD
ID
CT
CO
to
co
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v
k_
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c
CD
ZO
O
m
The excessive
size and mass
(4000 lb)
of
the analyzer
replacement with a larger magnet prohibitive as
implanter's
wafer
throughput is acceptable
at
long
make
as
Its
the
the reduced beam
current.
Two Isotopes
of
isotope ratio Is
unambiguous
Sb
exist:
57/43,
121Sb
and
123Sb.
respectively.28
Identification
of
The naturally occurring
These facts
permit
the correct Ion species
implanter is tuned to Implant Sb. The
121Sb
when an
Isotope yields the
greater Ion beam current due to Its reletive preponderance.
Given the availability
published
of a suitable solid vaporizer
Information on implanted Sb range statistics and annealing
properties, the development
a straightforward
centered around
of an
ion source and the
of a
engineering
the
buried leyer
exercise.
characterization of
Sb buried layer
process.
discussed in the literature are
doping
The balance
process should
of
this work is
two device specific versions
Verification of the basic properties
attempted
-37-
be
along the
way.
IV. EXPERIMENTAL PROCEDURE
The characterization
of
any Ion Implantation
necessity Intimately tied to the
process.
doping)
Having
and
subsequent
defined the substrate
the required features
of
process
properties
peak
(orientation
experimental procedure
supply
2. Verification
of
statistics as
of
the
of
end
after
concentration,
sheet
Is as follows.
1. Optimization of the Ion source performance to
and stable
Is
furnace annealing
the Implanted layer
annealing (dopant type, junction depth,
resistance, etc.), the
doping
provide a pure
the desired dopant Ions.
correct
Ion
species and
their range
implanted.
3. Determination
of
the
annealing/diffusion properties of
the
implanted dopent.
4. Characterization
requires
the
of
diffusion. This
ion dose as well
the dopant distribution.
optimization of Implantation and
acceptable
after
evaluation of sheet resistance vs.
as measurement of
5. Final
the implanted layers
diffusion parameters for
integration with subsequent processing.
-38-
In this
thesis,
4-1nch diameter 40-Ocm boron doped (100) CZ
wafers
are used for all experiments.
Incidence
with respect to
Two versions
features
of en
Wafers
are
the Ion beam
of
Is a
fairly
Sb
are required.
junction depth,
and peak concentration are achleveble
Optimization
p-type
SI,
NBC
*
3
x
Veiian/Extiion. The final
curves29
sheet reslstence
10 1 4 / cm3).
for the lonlzetlon of Sb
straightforward task. Baseline source
by
The terget
In the specified background
of a vaporizer equipped source
parameters ere provided
off normel
listed in Teble 2. Irvln's
Indicete that these comblnetlons
(for 40 Ocm
7
Implantation.*
during
Sb buried layer process
of eech version are
concentration
tilted
operating
the Implanter manufacturer,
result of
this effort takes the form of a
mass spectrum of the ion source output, which Is obtained
by plotting
beam current vs. analyzer magnetic field. This spectrum qualifies the
purity
of
the solid Sb source
materiel and
the carrier gas (Ar).
i
This Is generally the standard St wafer orientation during Ion
Implantation since axial channeling effects are minimized. Without
a parallel beam
scanning configuration,
eliminated.
-39-
axial
channeling
cannot be
Table 2:
Target Features
of
Sb Implanted Layers
After Drive-in
Feature
Version A
Version B
600
250
5.00
1.75
Implantation Screen
Oxide Thickness
(A)
Junction Depth
(^lm)
<5xl0
(atoms /
<5xl0
cm3)
Sheet Resistance
(ohms /
18
19
Peak Concentration
<20
<400
square)
Post-Diffusion
>4000
Oxide Thickness
(A)
-40-
3000
The range
statistics of
using SIMS
analysis.
Implanted Sb in SI and
Concurrence
sufficient verification of the
with
S102 are determined
the published data Is
Implanters high
voltage calibration.
SIMS also provides an Independent identification
atoms and permits a crude evaluation of
of
the Implanted
dose control.
An understanding of the annealing and diffusion properties
of
Ion
Implanted Sb In SI Is vital for successful process Integration. An
Important
parameter
amorphous surface
is the
layer In
ton Implantation damage
critical
single crystal
can
Isochronal furnace annealing
measurements
As.30
In this
obtained
be
using Isochronal
by
four
In terms
0C
of
8C.
of
point probe sheet resistance
B. L. Crowder to determine
values of
of an
Si. Generally, annealing
characterized
and
have been used
thesis, the
dose (0C) for the formetlon
corresponding to As
rapid thermal
annealing (RTA)
0C
and
and
for
Sb
are
four
point probe measurements.
*
RTA Is a
different
useful
tool for annealing a large
conditions
(I.e. temperatures
-41-
number of samples under
and/or
times).
The degree
Interest
of oxidation retarded
fundamentally
diffusion (ORD)
because none
of
of
Sb Is of special
the other SI dopants exhibit
this behavior SRP measurements are used to characterize Sb ORD In
Version B (see Table 2) layers diffused In either
02*
N2 or dry
facilitate accurate process simulation, any
necessary
the SUPREM III default diffusion parameters are
To
adjustments of
determined.31
this point, furnace diffusion schedules which are consistent (to
At
1st
order) with the requirements listed In Table 2 can be formulated.
Electrical characterization
requires
energy
the
of
Implanted Sb layers after diffusion
generation of sheet resistance vs.
curves.
The uniformity
of
implantation dose and
the combined Implantation and
diffusion processes Is easily evaluated with contour maps of sheet
resistance
It seems
data
at
the
wafer
to mention here the Importance of substantial
appropriate
oxide growth
during
level.
buried layer diffusion In some applications.
Assume that the buried layer implant is selectively masked by a
thick Initial oxide ( > 50008) and the subsequent diffusion and
is
oxidation process
Initial oxide. It Is
layer
regions
oxidation.
perimeter
performed without removal of
clear
the patterned
that more SI Is consumed In the buried
than In the masked regions
by
this post-Implant
step Is formed on the S1 surface around the
of the buried layer Islands. This step may be a useful
Therefore,
alignment eld
for
a
subsequent photolithographic patterning.
-42-
The redistribution
(autodoping)
Integration
was
of a
of
buried layer dopant up Into the epl-leyer
discussed In Chapter III. This is the
key
Issue In the
burled layer sequence Into a device fabrication
process.
There ere
enhance
a
limited
number of process variables
can
the abruptness of the buried layer to epl-leyer
In terms of the burled layer
be minimized (I.e.
e
features,
sequences after
The
epl-layer
the
reduction of autodoping.
maximum
requirements should
In low
be
compensate
eutodoplng.32
profile.
In
high temperature process
should
be minimized.
the
The
minimum reactor
consistent with crystal
used.
The
enhanced ges
temperature
with
epl-layer
As buried
doping
layers33
profile
during
and
quality
diffusion
pressure epi-reectors offer some
autodoping, especially
of
doping
deposition process Itself offers some opportunity for
deposition rate
encountered
all
buried leyer diffusion
be altered to
the peak concentration should
deeper junction) to reduce
general, the collective Dt product of
tailoring
that
rates
Improvement In
In some applications,
deposition to
for eutodoplng from the buried leyer may be possible.
-43-
The autodoping
problem
similarly implanted
and
Is eddressed in this work
diffused Sb and As "Version
(see Table 2). The Sb buried layer
an epl-layer
structure
is
in
structure
pressure reactor.
by depositing
With
similar
are used
"best
case"
to determine the
B"
buried layers
achieved
by depositing
The As burled leyer
a similar epl-leyer In a reduced
thermel cycles end Identical
deposition rates, this represents e "worst
scenario and a
Is
an atmospheric pressure reactor.
achieved
by comparing
As eutodoplng
doping
Sb autodoping
scenario.
profiles.
-44-
case"
SRP
measurements
V. PROCESSING DETAILS AND RESULTS
The Initio!
at
optimization of
the solid viporizar
un d^ce
the lowest anticipated 121Sb+ ener
y (50 keV).
crucible with
10 grams
of
Sb shot (2 mm
the source is pumped down to about 2
x
diameter,
A^
ter charging the
5 nines purity),
10"7torr. As
outlined
Chapter III, the extraction voltege Is reduced to 16 kV,
1s established In the arc chamber end then the
Is ramped up to 700C
et e rate of
Is conducted
en
vaporizer
in
Ar plasma
temperature
10C/m1nute.
At this point, the various source parameters (Ar flow, vaporizer
temperature, fllement
current, source megnet current and arc
current) ere adjusted to maximize the Sb scenned beam current. As
might
flow
be expected, the
of
vapor.
maximum current
Ar, thereby sustelnlng the
This Is
caused
source Insulators.
If a
condensation
Induced
decreases
about
by
by
obtained
source plesma
However, frequent discharging
results.
is
of
solely
the extraction
undeslred condensation of
moderate
discharging
by stopping
with
Sb
voltege
Sb vapor
on
flow of Ar Is restored, the
ceeses
but the beam current
13*. This tradeoff Is necessary to ensure a
-45-
the
the
reliable and stable supply of Sb ions. The measured source parameter
values are
listed In Table 3.
The Ion source
corresponding to singly
doubly
and
ions are labeled. The absence
demonstrates the purity
integrity
current
qualification of
any
the Sb
^Ar, ,21Sb end ,23Sb
other significant peeks
end
Ar end
also verifies
the
vaporizer
ion
source
Ion energy (I.e. accelerating voltege) on
Is
The
meesured.
140 keV Is 155
uA.
dissipation
during
155 uA, A
90.9
on
of
of
charged
the
of the vacuum system.
As a final
effect of
Is shown In Figure 15. The peeks
mass spectrum
=
the Freon
See Figure 16. The
cm2).
The
wafer
this
oxidized
dose of 1 x 1015/cm2. The Sb
beam
for energies In excess of
mW/cm2
(E
=
190 keV, I
=
temperature remains below 50C
power
range statistics of
thermally
121Sb+
maximum possible power
Sb Implantation 1s 325
cooled platen at
To determine the
wafers and
maximum current
performance, the
(6000
level.34
Ion Implanted
121Sb+, bere
&)
Implanted
wefers are
concentration profiles
-46-
In S1 end
with a
S102
Table 3:
Optimum Source Parameters For
Sb Ionization
Ion Source Parameter
Value
Pressure (as measured at the
source diffusion pump inlet)
8x10 torr
Vaporizer Temperature
780C
Extraction Voltage
16 kV
Extraction Current
-6
3.0
mA
Arc Voltage
60 V
Arc Current
1.0 A
Filament Current
150 A
Source Magnet Current
1.2A
-47-
\
CO
/
CN
r^
o
-V
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3
u
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-H
p*,
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(J
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CD
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t
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f-
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it <
b-
o
=L.
o
o
00
o
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ON
are
then measured using SIMS.
In Figure
17,
profiles are shown for
100 keV and 190 keV implants into Si. The
corresponding
in Figure 18. The values
S102 ere shown
of
profiles
Rp end ARp determined
from these profiles agree with the published data (see Figures 8
9) to
15%.
within
determined
by Integrating
wefers ere used
the concentration profile end the actual
The Implantation energy is
The doses
to
Each Implanted
Is
'2*Sb*
end
to be 50 keV
heavily
1013/cm2
from 1 x
wafer
75As*
chosen
yield a more
range
all cases.
for the Isochronel RTA determlnetlon
the sake of comperison, both
are expected
and
Additionally, the difference between the dose
Implanted dose Is less than 25% in
Bere
in
Implents
ernealed 1vr
60
x
0C. For
ere studied.
since higher energies
damaged leyer et a
to 1
of
given
dose.
1015/cm2
seconds
1r
No
at a
temperature between 500*C and 850C using a Tamarack 180 fl
Incoherent
the
lamp
annealer.
polished side of
the
In this unit,
wafer.
An
Infrared energy emitted from the
redlent
energy is directed
optlcel pyrometer meesures
unpolished side of
-50-
the
wefer
upon
the
to
>
CD
o
o
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II
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LO
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d
d
infer the temperature.
The sheet resistance
four point
probe.
plotted vs.
RTA
of
the of the annealed layers Is measured
In Figure 19 ths sheet r ^stance of As
temperature,
corresponding Sb data Is
There
are several
For doses ebove e
Implan
r
plotted n
Interesting
critical
F
dose
tne
575C
and
while
elecricei ectlvatlon of
850C. For doses less then
The Interpretation
of
8C
es
layer in the Si Is
temperature
the Increase In
over
the
ectivetion
Is
entire range.
the dose necessery to form an amorphous
now
discussed. If the Implantation dose is
surface
during enneallng
(SPE) from the underlying
0C,
temperature
that a completely demeged
recrystellzetion
1
the activation Increeses marginally between
Increesing
such
The
to Figures 19 end 20.
cmmon
value, Bc, abrupt
more uniform with
surface
Is
parameter
the dopent etoms occurs consistently at a relatively lo
(about 575C),
!o; ers
20.
lure
feetures
es
with a
layer is
can occur
by
formed, then
solid phase
single crystel materiel.
-53-
SPE,
epltexy
which occurs
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cn
t
T
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T
tn
T
^
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LU
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1
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1
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Ji
+
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co
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LO
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o
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<
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h-
CD
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ro
c
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cn
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4
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i
Q)
r>
co
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c
ro
E
c
o
To
E
CO
CC
in
i
at
temperatures
es
low es 550C In
Implanted Group V donor
atoms
SI, effectively
beceuse
Indistinguishable from neighboring SI
co-
mechanism Is
incorporation
region
ied36
:e;
proceed
up to the
slmul'
Lattice recrystelllzatlon and dopant
aneously from the
of
SI vacancies end Interstltlals and there
.he
corresponding
factor
of
and
lone
res
or*
range
hlqhe
regrowth.37
n2
is identified as the
o~
values ere a
the derr. ge
Incorporation of the dopent atoms -eq
From Figures 19 end 20, 1 x 10'4/c
while
undamaged Interior
damage Is not sufficient to
0C, the implantation
annealing temperatures than for SPE
for As
vltuelly
etoms as far es the regrowth
completely destroy the lattice. Repair
migration of
ere
wefer surface.
If the dose is below
substitutional
they
activates
value
twe less than p e
Sb is 5
*ous,y
velue of
x 1013/cm2.
These
published result *
TO
40 keV imp'sants
end
30
minute
furnace
Wafers for the study of Sb ORD are
screen oxide
layer Is
annealing*0
Initially
cleaned end a
12,Sb+
thermelly
grown.
-56-
250
Is Implented
0C
et
1
or
50 keV with doses between 2
furnace diffusions, besed
1200C for two hours In
For the group dlffusec in
or an elllpsometer
shown in
8C
(5
x
Version B tergets,
either
N2
dry 32,
or
dry
x
1015/cm2
ore conducted at
02.
the oxide thicknesses are measured
a slight
Increase In oxldetlon
1013/cm2). The total
oxide
for
thickness variation
are
then used to determine the sheet
resistence of each Sb layer. The results, plotted in Figure
Indicate
a
Based
on
22,
10 to 20% Increase In the sheet resistance of the
diffused layers
5
rate
the range of doses considered is less than 5%.
Four point probe measurements
Sb
The
to jetermine any variation with Implant dose. As
Figure 21, there Is
doses ebove
over
on
1013/cm2and 1
x
relative
to the
N2 diffused
layers.
the Version B sheet resistance target
concentration profiles of wafers
x1013/cm2
are measured
velue
(< 400 0/D), the
that received a dose of
using SRP. To determine any
-57-
02
extrinsic
LO
T
+
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CD
CO
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Q.
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,_
diffusion effects, SRP
that received
Figures 23
a
measurements are also performed on wefers
dose of 5
and 24.
x
1014/cm2. The
results are shown 1n
It Is clear that ORD causes about
in the junction depth of the Sb leyers diffused in
the layers diffused In
SUPREM simulation
of the
III39
by
models
first using
the Sb
in a nonoxiatzing atmosphere es the sum of two terms:
=
D|
+
(5)
Df(n/nt)
1s the Intrinsic diffusion coefficient associated
charge state
vacancy Interactions
coefficient associated with
Interactions. The
vacancy
as compared with
Sb ORD results Is executed
DN(Sb)
D|
12% decrease
N2
the default dlfftsin c^flcisnts. SUPREM
dlffusivlty
02
a
singly
(n/n*,) factor
concentration
due to
and
Df
Is the Intrinsic diffusion
charged negative
accounts
chenges
with neutral
for
changes
vacancy
In the charged
In the Fermi level.
Simulation of Sb diffusion In en oxidizing ambient is complicated
the
recombination of vacancies with
-60-
by
1nterst1tiel3 injected into the
in
oj
OJ
CO
o
in
fc
a.
OJ
E
c
o
ro
fc_
c
CD
O
c
o
E
+ CO
-O
CO
LU
Lo
CO
CM
CM >
fl)
T-
CD
o
O
3
o
LO
CL
DC
LO
CO
d
Q
CE
o
3
q
d
CO
+
LU
co
E
I
CO
CD
lm
o
E
o
CL
c
o
+
^
9
LU
CO m
ro
CM
c
r-
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CD
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CD
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LT
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CC
o
-O
co
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+
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CO
"x
E
bulk from the
oxidizing Si
nonoxldizing
Sb
In the corrective
nonoxldizing
In
an
oxidizing
Simulations
dlffusivlty
of
factor,
=
the
(6)
Is the concentration of Interstitiels in
(S1(J Is the
concentration of Interstltlals
amtlent.
the 3RD experiment, using the aVault values
compor n is, predict
deeper than indicat d
by
SRP
5 to 10% lower than he four
junction depths that are
and sheet resistances
point probe
concentrations are also overestimated
The depth accuracy
the four point
of
SRP40
Is
within
probe measurements
National Bureau of Standards
by
about
the Sb
20%
ere ebout
up to 140% relative to the
N2 and 02
3% and the
Is
within
traceabllity for
-63-
thet
of
data. Simulated peak Sb
SRP profiles. These errors occur for both
of
of
DN(Sb)[S1|jy[S1,]
[Si|]|
emoient and
The SUPREM III correction
to model ORD Is of the form:
dlffuslvlty
D(Sb)
a
surface.
R8
diffusions.
absolute
accuracy
2%. On the
<
other
3000 0/D.
hand, the
confidence level In the absolute carrier concentration
values obtained from SRP profiles Is not
very high, particularly
near
the SI surface. Therefore, In
adjusting the SUPREM parameters, the
goal
Is to simulate correctly ihe junction depth
resistance of the Sb
layers,
while
and
permitting the
the sheet
peak
Sb
concentration to vary.
The two Intrinsic diffusion
explicitly by
expressed
along
with
an
coefficients
Arrhenlus
=
=
equation.41
(5)
These
can each
be
equations
D0
exp(-Q|/kBT)
((0.214)exp(-3.65eV/kBT)]cm2/sec
expt-Q^/kgT)
=
=
[(15.00)exp(-4.08eV/kBT)]cm2/sec
Is the Boltzmann constant, 8.62 x
temperature
(7)
D0"
Dj"
kB
equation
their default values In SUPREM III are:
Dj0
where
In
(In K). If T
D^
=
Df
=
=
1200C
7.02
10"5
(1473K),
then
x 10"14cm2/sec
1.66 x 10"13cm2/sec
-64-
eV/K and
(8)
T is the
Since
is tie dominant component of the Sb
Df
the pre-exponentlal term
Is decreased
at
1200C,
D0~
should be modified to fit the SUPREM III
model to the ORD experimental data.
value
diffuslvity
By
until an acceptable
trial and error, the default
fit Is achieved. The
value of
D0"
that yields
D0'(mod1f1ed)
=
an acceptable
fit Is 2/3
By
virtue of
the default
10 cm2/sec. The experimental values
junction depth, sheet resistance and
Table 4 along
of
with
the default
value:
of
Sb layer
peek concentration are
listed In
and modified simulation results.
the ORD and Isochronal RTA studies, the annealing
properties of Ion Implanted Sb In SI are
sufficiently defined to
continue with electrical characterization
(Rs vs
EO for implant
energies In excess of 50 keV. The maximum furnace temperature
employed In the ORD study,
temperature for both
1200C, is certainly
versions of
an adequate
drive-In
the burled layer process. The higher
keV.*
energy
values chosen are
90, 140
and
190
._
^
With
The
Vx
=
16
maximum
kV, the
maximum
energy
the CF4 Is about 19C
e/
Is realized If the energy Is at leett .40
Ince lent of 50 keV (end therefore 90 keV)
beam curren
keV. This defines an
of
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Wafers for the higher energy Sb
Initially
cleaned and a 600
This oxide thickness Is
&
electrical characterization are
screen oxide
chosen to match
layer Is
the
thermally
projected range of
the Intermediate energy (140 keV). 121Sb+ Is Implanted
of
doses (5
10
x
14
sheet resistance
to 6
10
x
following
1200C for
over a range
5/cm2) appropriate for the Version A
of
wafers are split
eny Sb
etoms et or neer
Into two identical
then
groups are
eight
hours In
dry
recomblned and
the
groups
SI-SIC^
Immediately
6C0
screen oxide are evaluated
which indicate i
of doses considered
annealed et
thicknesses of the wafers thet retained the
st-anneal oxide
The results,
furnace
02.
The p
*
at
Implantation. The screen oxloe Is removed from one group
The two
only.
Sb
terget value (< 20 0/D).
In order to examine the role
Interface, the
]
grown.
(not
to determine eny dose dependence.
25% thickness
Including
the 8
Figure 25.
-67-
=
variation over
0 control), are
the
range
shown
In
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The sheet resistance
Figures 26, 27
and
of
28
the each of the Sb layers Is plotted vs. dose In
corresponding to implantation
140 and 190 keV, respectively. The curves
are
energies of
labeled
90,
with respect
to the removal
or retention of
diffusion. It Is
obvious that a significant amount of Sb Is lost If the
screen oxide Is removed
dependent
of
To Investigate the
this loss is
prepared
case
is much less significant.
mechanism of
Sb loss, another group of wafers Is
for Implantation. However, the screen oxide Is
removed from half of this group prior to
Implantation, ensuring that
the total dose resides In the SI. The wafers
121Sb+
of
to
the sheet resistance characteristic curves for the
of retained screen oxide
similarly
before diffusion. The degree
prior
the Implantation energy. However, the
energy
upon
dependence
the screen oxide layer
are
Implanted
with
keV*
at
90
and
the
same range of
doses as the preceding
experiment and are annealed under the same conditions.
n
The
choice of
90 keV
evaporation of
should maximize
Sb Into the furnace
any loss due to the
ambient
because
of
Its closer
proximity to the wafer surface as Implanted relative to the higher
energy Sb profiles.
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The resulting
data for the "zero
sheet resistance
comparison Is
plotted
oxide"
screen
In Figure 29. Note that the shift In sheet
resistance values Is only 10 to 20* as compared with the huge change
(300 to 400%) induced by
Implantation
fraction
of
and/or at
as shown
removal of the screen oxide after Sb
1n Figure 26. This suggests that a large
the Implanted Sb that Is trapped in the
the
screen oxide
S1-S102 Interface readily segregates Into the
Si
during
the annealing process.
Based on the Version A sheet resistance target value, the Sb
the wafers that received a dose of
concentration profile of
3
x
1015/cm2
measured
and retained
using SRP. The
virtually Identical. The
shown
The
the
screen oxide
profiles
profile of
all
diffusion are
three energy
values are
the wafer Implanted et 190 keV Is
In Figure 30.
characterization of
Ion Implanted Sb Is
process parameter speclflcatt jn.
preceding experiments, pararr
layer
for
during
versions
With the
Based
iters can
exceotnn of
-73-
on
now at
the point of
the data
obtained
In the
be defined for both buried
the Junction depth, the Version
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LU
in
r-~
i
A
targets
are satisfied 1f 8 2 3 x
maximum wafer
throughput, 140 keV
energy (see Figure 16). With
deoth. the Version B targets
E
=
1015
cm2
is
and
E
loser, as
a sim11?rexct it
are satisfied if
3
n
5
2
90 keV. For
the Version A
n '.ne junction
>
IC 3/cm2
and
50 keV.
Since the peak concentration
critical parameters of a
and
as a
the measured junction depths
ere
values
The complete
Is
are
burled layer, the specification
depth target Is Intended only
target
the sheet resistance
first
order guideline.
the two
of a
junction
The fact that
nearly 10* less than the
original
of no real
listing
of
Sb buried layer process parameters is found
In Table 5. Although no uniformity targets are explicitly defined for
f
the*
version of
jnerated
are
for many of the wafers processed in the preceding
experiments.
shown
the Sb process, sheet resistance ccntour maps
Typical
maps of Version
In Figures 31 and
32,
A end Version B layers are
respectively.
based upon preliminary SUPREM
modeling which was conducted using the default Sb dlffuslvlty.
The
original
target values
were
-76-
Table 5:
Summary
of
Ion Implanted Buried
Layer Process Parameters
Process Parameter
Version A
Version B
600
250
140
50
Implantation Screen
Oxide Thickness
(A)
Implantation
Energy
(keV)
Implantation Dose
15
13
3x10
5x10
1200
1200
8
2
(ions/cm2)
Furnace Anneal
Temperature (C)
Anneal Time
(hours)
Anneal Ambient
Dry
-77-
Oxygen
Dry
Oxygen
Version A Sheet Resistance Contour
Map
121 Sb
E
=
+
14OkeV,0=3El5/cm2
a
/
y
Average Sheet Resistance
=
Standard Deviation
Contour Interval: 0.09
17.3
=
0.07
ohms/square
ohms/square
(dark contour)
(0.4%)
ohms/square per contour
Figure 31
-78-
(0.5%)
Version B Sheet Resistance Contour
121 Sb
E
=
50
keV, 0
=
Map
+
5E13/cm2
\
./
/
;
/
/
/i
i
.
I
:
+
'.
1
!
+
,
\
!.
i
4-
Average Sheet Resistance
=
Standard Deviation
Contour Interval: 1.9
371.7
=
3.2
ohms/square
ohms/square
(dark contour)
(0.85%)
ohms/square per contour
Figure 32
-79-
(0.5%)
The Version B Sb
process
Is selected for an
autodoping
evaluation
since a minimal transition width from the buried layer to the
epi-layer Is required. Wafers are
(600
I)
with
to Ion Imoltitetlon. He,lf
prior
121Sb+
the othe
and
energy
and
Initially
s arc
dose (50 keV, 5
x
K
of
Inplanted
i:/cm2\
cleaned and oxidized
the
wafers are
with
with
the
same
SRP is used to verify that
the As concentration profile after diffusion is
see
75As+
implanted
similar
to that
Sb;
of
Figure 33.
A 2 um thick p-type epl-layer Is deposited on both sets of
reduced pressure
(80 torr) deposition
process
wafers.
The
concentration profiles of
burled layer structures,
Figures 34
and
35,
The burled layer
again obtained
A
Is used for the As doped
wafers while an atmospheric pressure process
doped
wafers.
Is used for the Sb
the resulting As and Sb
using SRP,
are shown
in
respectively.
profiles
Indicate virtually no difference In the
epl-layer
to buried layer transition
epi-layer
thickness. The need for
therefore eliminated
width or
the
homogeneously
reduced pressure
If Sb Is substituted for As.
-80-
epitaxy Is
However, the
doped
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combination
of reduced pressure
epitaxy
useful In the control of pattern washout and
than relying
necessary
upon
with
As buried
the Si
distortion42
the epl-reactor pressure to
freedom In the deposition
surface of
Sb burled layers
and
layers), It Is
process
to
reduce
-84-
be
Rather
autodoping (as Is
available as an extra degree of
preserve
substrate.
can
any
steps on
the
VI. SUMMARY
Ion Implanted
Fundamental
121Sb+
was characterized as an n-type
dopant In SI.
properties such as the two moment range statistics and
the critical dose for amorphlzotlon were determined
at energies
which were anticipated for eventual eevize applications.
oxidation retarded
diffusion
temperature sufficient to
Sb was quantified
of
realize
Electrical characterization
of
et a
The
furnace
typical buried layer Junction depths.
implanted and diffused Sb layers
conducted over Intermediate and high dose ranges as mandated
distinct
rate of
process applications.
Si
was also
parameters
Finally,
have been
of
Sb
effect of
determined In the
a comparative
suitability
The
specified
study
as a buried
of
Sb
and
-85-
two
Process
applications.
As
layer dopant
pressure epl-layer deposition process.
by
Sb dose on the oxidation
same dose ranges
for both
was
was used
to
establish
with an atmospheric
the
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-86-
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r
4
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"Antimony
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-87-
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18. J. P. Gollllard, M. Dupuy, M. Garcia, J. C. Roussin
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1 9 1 0- 1 9 1 5, December, 1976.
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Walker, D. L. Critchlow
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1359-1367, August, 1S3C
Walker, J. F. Shepard
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590-596, April, 1982.
Sal-Halasz,
Junctions,"
"Implant-Defined Shallow FET Source/Drain
IBM Technical Disclosure
Bulletin, Vol. 26,
pp.
3018-
3019, 1983.
25. G. A. Sal-Halasz and H. B. Harrison, "Device-Grade Ultra-Shallow
Antimony,"
Junctions Fabricated with
Vol.
EDL-7, No. 9,
pp.
IEEE Electron Device
534-536, September, 1986.
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Letter
i,
26. W. K. Chu, M. J. Sullivan, S. M. Ku
Antimony
Implantation In Silicon: II. Applications to
Barrier Diode Adjustment
27. S. Ashok and B. J.
Al-Slllcon
to Ion-Implanted
end
Radiation Effects, Vol. 47,
pp.
Schottky
Diode
pp.
of
Energy
Schottky
Resistors,"
1980.
7-14,
Ballga, "Effect
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Antimony
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on
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1237-1239, 15 August, 1984.
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p.
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and
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"Annealing
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n-Type
Vol.
31. C. P
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14,
No.
10,
pp.
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-
SUPREM
Characteristics of
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313-315, 15 May, 1969.
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Installa
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F. F. Y.
37. J. D.
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27,
Processes In
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196
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Applied
APPENDIX 1:
The
90
of
v
velocity
of
the
In a
analyzer electromagnet.
tr s Lorentz force
h Is the
The
Ion of
motion of an
field B is determined
uniform magnet
by
the
magnetic
equation:
F
where
Relationship
tend In the beamline of a CF4 ion Implanter Is nested within
the field
term
Derivation of the Moss Separation
=
(10
hqevx9
the ion and
charge state of
qE
s ihe magnitude of
the
chare, of an electron.
Referring
to the
to
Flgur-
plane of
the
source, then the
:
If the direction
centripetal
mass m
into
the
magnetic
the direction of Ion
s<etch and
vector relation reduces
F
The
of
to
scalar
fie
.j
is
normal
motion out of
the
form:
(1l8>
hqevB
=
force necessary to bend the
coincidence with
the
trajectory
of
radius of curvature of
ions of
the beamllne,
rjs
Fc
=
mv2/r
(12)
centripetal force to Ions
Since the magnetic force must provide this
-92-
of
the desired charge-to-mass
ratio,
hqevB
If this is solved
mv2/r
(13)
The kinetic energy
of
03a)
(hqerB/m)2
=
the Ions is
KE
=
mv2/2
=
2hqeVx/m
=
(14)
hqeVx
forv2,
v2
Equating
have
forv2
v2
Again solving
=
we
(14a)
13a and 14a, and solving for qe/m,
qe/m
Ions extracted
out of
the
source
=
2VX
we obtein
the result
/ (hr2B2)
that do
not
(2)
satisfy this relationship
beamllne*
collide with
*lons
the
walls of
the
90
bend of the
with a charge-to-mass ratio greater
than the right hend
side of
(2) collide with the Inner surface of the bend (i.e. their
trajectory is deflected too much by the magnetic force). Conversely,
equation
ions
with a cherge-to-mass ratio
equetion
(2)
collide with
the
less than the right hand side
outer surface of
-93-
the bend.
of
APPENDIX 2:
Equipment:
1.
Ion Implanter: Varian/Extrion Model 200-CF4
2. Solid Vaporizer: Varian/Extrion Model 200-20A2F
3. Rapid Thermal Anneal er: Tamarack Scientific Model 180-M
4. Sheet Resistance
Mapping
System: Prometrix Model 11 IB
Materials:
1. Solid Sb Shot: Alfa Products Stock '800209
-94-