HIGH PRODUCTIVITY FOR WELL IMPLANT APPLICATIONS
VARIAN MEDIUM CURRENT POSITION PAPER – Rev. 1 (5-13-05)
Abstract - As devices have scaled below 100nm gate length, all transistor parametric implants
such as deep and shallow well implants as well threshold control (Vt) implants have migrated to
normal incidence implant. While the initial motivation was solely based on avoiding shadowing
and increase packing density, other factors such as defect reduction and reduced process
complexity are also becoming important factors. The architecture of the VIISta 810XE medium
current implanter and VIISta 3000 high energy implanter provides the unique ability to cover the
entire dose-energy requirements of the channel and well doping with true zero degree implants.
In this paper we will illustrate how this capability can be leveraged to maximize the utilization of
medium current and high-energy implanters and lower the overall cost of ownership. In addition,
we describe the complete process transferability across the VIISta implanters with a case study of
a typical CMOS recipe set.
I. INTRODUCTION
The IC industry is now undertaking the aggressive adoption of deep sub-micron CMOS devices
fabricated on 300mm wafers. Leading edge IC manufacturers are in high volume production on
300mm wafer production on the 130-150nm IC technology node, with 90-110nm and 65-70nm
technology nodes following soon [1]. The traditional dose and energy requirements to meet the
needs of these emerging applications are changing. There is a trend in reduced dose and energy
requirements for the latest generation of devices. This is altering the applications space that was
formally covered by high energy implantation. In the well applications area many of the implants
that were formally covered by high energy implantation can now be readily handled by this new
breed of medium current implanter.
1
As a new breed of medium current ion implanters are introduced and a paradigm shift occurs, the
ability to extend the traditional operating range into the high energy operating space has been
provided. The result of this extension in operation for medium current machines provides a high
level of productivity for well implant applications. As well implant recipes move to medium
current implanters the number of high energy implanters can be reduced. This also provides
greater flexibility as a high energy implant back-up. The reduced operating costs of the medium
current machine offer substantial benefits in terms of capital productivity [2].
The key challenges faced in delivering this additional capability fall into a number of categories.
Extended energy range operation must be provided which guarantees robust performance for
single charge boron up to 300 keV and double charge boron up to 600 keV. Also, robust
performance for single charge phos up to 300 keV, double charge to 600 keV and triple charge to
900 keV. Long term stability in this extended operating range is critical to delivering reliable
process performance.
Substantial increases in productivity must be provided in order for the migration of well implant
recipes to medium current machines to make economic sense. Delivering increased productivity
at a lower cost of ownership will be a key figure of merit.
The operation at higher power levels for well implant applications creates additional issues when
photoresist wafers are utilized. The generation of an ion beam and its impact into photoresistmasked wafers will have an adverse effect on the vacuum of a medium current ion implanter.
This is particularly significant when implanting with higher energies and higher beam current
through thick photoresist. Compensation methods must be provided to deal with Rs shift due to
photoresist outgassing. The ability to deliver a production-worthy solution to minimize Rs shift
under varying recipe and photoresist conditions will be required.
2
There are some additional device fabrication challenges that have implications for equipment
selection as well. For well and channel formation, device scaling is driving n+/p+ spacing, low
doping concentration in the well/channel region and symmetrical well junction profiles. There
are implications for high energy ion implanters (and medium current as well) where advanced
devices can no longer tolerate shadowing effect and angle variation associated with a non-zero
degree well implant [3]. These are requirements for well implant technology that will impact ion
implanter architecture considerations. It is critical that the equipment be able to provide precise,
zero degree implant capability to satisfy well implant requirements.
There are two major limitations of current well implant capabilities. The first is that increasing
well concentrations results in new challenges. For smaller devices, substrate concentration needs
to be increased to maintain adequate isolation characteristics. Also, increased well concentration
BV (V)
results in increase junction leakage and junction capacitance.
N +S / D t o P - W e l l
14
12
10
8
6
4
2
0
Low D ose
H ig h D o s e
0 .0
0 .1
0 .2
0 .3
N + - N W S p a c in g ( u m )
0 .4
Frequency (σ )
N +/ P - W e l l j u n c t i o n l e a k
2 .0
1 .0
0 .0
- 1 .0
Low D ose
H ig h D o s e
- 2 .0
1 .E - 1 1
1 .E - 1 0
1 .E - 0 9
J u n c t io n L e a k ( A )
1 .E - 0 8
Figure 1 : Well concentration and junction leakage requirements.
3
There area additional limitations associated with tilted implants limiting device scaling. Tilted
implantation degrades inter-well isolation due to shadowing. The impact is more severe with
higher aspect ratios and thick photoresist.
P + Implantation (N-well)
Non-
1
Resist
STI
'encroachment'
8
B
V 6
(V 4
Minimum
Spacing
Shadowe
2
0
-
0.
0.
0.
N+-NW Spacing
B + Implantation (P-well)
0.
N
Resist
N
N+
STI
N+
P-
N-well
P-well
NW
'shadowing'
Resist edge
Resist edge
0
0.5µ
7 Degree Tilted Implant on
Test Structure
Figure 2 : Limitations of tilted implant device scaling.
One of the issues associated with batch implanter technology is that true zero is not achievable.
A batch system will experience angular variation that exceeds the critical angle. The systems
must be run in quad mode at non-zero degree (~3-7 deg) to achieve desired uniformity. In this
mode the batch system cannot deliver the benefits of true zero degree implants.
Cone Angle
Beam
Beam
Batch Disk with Pedestals
at Offset Angle
(Cone Angle)
Induces Tilt Angle
4Variation
Uniform, zero
degree implant
Differential Channeling
due to cone angle effect
Junction Depth
VIISta 3000HP
Batch HE System
1406.7 Ω /
4.946%
1282.3 Ω /
0.568%
Figure 3 : Cone angle effect on batch system implanter.
It is critical to provide a parallel beam with precise angle control to achieve a true zero degree
implant. The precise control of the ion beam and beam parallelism will be required to maintain
uniform distribution within the wafer as depicted in Figure 4 below.
5
VIISta 3000
Sheet Resistance
of N-well
650
600
10
9
8
7
6
395Ω
415Ω
410Ω
405Ω
400Ω
σ=7.7Ω
σ=1.8Ω
Conventional Batch
2.0
1.5
1.0 Parallel Beam
0.5
0.0
0 1 2 3 4 5 6 7 8
Wafer Tilt (degree)
Conventional Batch
400Ω
Breakdown Voltage
(n+—n-well=0.6μm)
Uniformity (%)
R ( Ω/sq.)
B+, 200keV
700
12V
13V
13V
12V
12V
11V
11V
σ=0.6V
9V
10V
σ=1.0V
“Device Isolation Challenges for 65 nm Technology Node”, Dr. Takashi Kuroi, et.al. Mitsubishi, Dec. 2002
Figure 4 : Precise control requirements in order to obtain uniform distribution within the wafer.
The critical angle is small for the higher energy implants such as the P 600 keV application
outlined below. The critical angle being defined as the maximum angle variation to achieve a
uniform channeled implant. As can be seen, the higher energy results in a smaller critical angle.
1/ 2
⎛ Z1Z 2e 2 Ndp ⎞
⎟⎟
θ c = k ⎜⎜
E
⎝
⎠
Where Z1, and Z2 are the atomic numbers of the
incident ions and the target atoms respectively, e is the
electronic charge, N is the density of target atoms, and
dp is the separation between the planes of atoms that
form the channel walls
Critical angle for P, 600keV = 0.5 deg.
Source: Robert Simonton and Al F. Tasch, “Channeling
Effects in Ion Implantation into Silicon”, in ION
IMPLNATATION: Science and Technology 6th Edition,
293-308
Figure 5 : Critical angle requirements for a typical well implant recipe.
6
As outlined in the angle control summary below the total angle variation for the batch systems
will not meet the device requirements. The 1.5 degree disk is larger than the critical angle.
Total Angle Variation on High Energy Implanters
- Batch vs. Single -
Crystal Orientation
Beam Divergence
Beam Parallelism
Mechanics
4.0
Cone Angle
Angle Variation [deg]
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Batch HE - Regular
Batch HE w/ 1.5 deg
VIISta 3000HP
Figure 6 : The total angle variation on batch vs. single wafer systems.
Since the device fabrication requirements are becoming more challenging even a 0.5 degree angle
variation has a significant impact on the well profile. The critical channeling angle becomes
small as the energy increases. Even a small angle variation can cause ion de-channeling.
7
Critical angle for P, 600keV = 0.5 deg.
1050206020 Varian/J.Olson, slot 1, overlay
0 deg
1E+18
0.75 center
0.75 bottom
0.75 right
0.75 top
0.75 left
1E+17
0.25 center
0.25 bottom
0.25 right
0.25 top
0.25 left
1E+16
0.5 deg
1E+15
1E+14
0
5000
10000
15000
20000
25000
30000
35000
DEPTH (Angstroms)
Angle Variation on a Typical Batch Implanter
Figure 7 : Angle variation requirements vs. batch system performance.
II. WELL IMPLANT APPLICATION SPACE
There are an increasing number of well applications that will fall under the energy range and dose
capability of medium current ion implantation as shown in Figure 8. The use of triple well
architecture for most planar CMOS fabrication has necessitated the use of MeV implants for the
n-tub that contains both the shallower n and p-wells. These MeV implants has been the major
workhorse for cost effective substrate isolation schemes for both DRAM and Flash memory
8
manufacturing. Until recently, high energy ion implantation, unlike most of the low and medium
dose applications, have used so called batch systems, where several (13-17 wafers) are loaded on
to a disc that rotates at high speed during the ion implant process. The mechanics of wafer
scanning through the ion beam and the design limitations inherent to this approach result in a
variation of 1-1.5° across the wafer [3]. Due to this reason, conventional batch disc high-energy
ion implanters are primarily dedicated to the somewhat angle insensitive deep triple wells, while
the more sensitive threshold voltage, well, and pocket implants are all processed on the single
wafer parallel beam system. The higher cost of high-energy ion implanter coupled with the
limited process steps on these tools naturally has an adverse effect on the cost of ownership. For
example, in a typical implant sequence for DRAM and flash memory only 2-3 steps are in the
unique energy regime of high energy implanter (beyond the capability of medium current
machine), while for most logic chip manufacturing this reduces to one. With the trend in
reduction of energies for the next technology node it can be seen in Figure 9 that future well
applications will fall within the extended operating range of the medium current implanter.
The introduction of VIISta 3000HP single wafer implanter has thus for the first time enabled chip
manufacturers to maximize the utilization of high-energy systems. Both the VIISta 3000 and
VIISta 810XE implanters deliver a parallel, uniform ion beam across a 200 and 300mm wafer by
employing a corrector magnet and high speed electrostatic ion beam scanning technologies with
the details being reported elsewhere [4,5]. These features along with the patented Varian
Positioning System allows for an angle control across the entire operational energy range.
Identical dose control and glitch recovery mechanisms are used in these implanters and allows for
complete transfer of implant processes across these machines for all critical layers. In addition,
the single wafer architecture now enables high tilt pocket and halo implants (up to 60° tilt) to be
processed on both the high energy and medium current implanters. As device geometries scale,
required defect control in terms of elimination of foreign material has accelerated; both VIISta
9
3000 and VIISta 810 series of implanters demonstrate identical low levels of particle and metal
contamination for all process steps. In addition, the common control system used on the VIISta
platform allows identical interface of these tools to factory automation systems thus allowing for
easy integration of implant process steps and process transferability.
D o p in g A p p lic a t io n s S p a c e – 9 0 n m
1 .0 E + 1 7
H /C S p a c e
90nm
1 .0 E + 1 6
G a te
B -G a p
Eng.
Dose (atoms/cm2)
G e, C , N
SD E E ng
1 .0 E + 1 5
B , B F 2, A s ,
C , X e, F , N , S b
B , P , G e, As
S /D
M /C S p a c e
B , B F 2, P , A s
C o n ta c t
/P lu g
H /E S p a c e
BF2, P
Is o la tio n
1 .0 E + 1 4
B, P,
H A L O /P o c k e t
B , B F 2 , P , A s , In
1 .0 E + 1 3
C h a n n el E n g .
B , P , B F 2 , A s , In , S b
T w in W e ll
D /W e ll
P
B, P
1 .0 E + 1 2
CCD
B, P
1 .0 E + 1 1
0 .1
1
10
100
1000
10000
E n e rg y (k e V )
Figure 8 : An overview of the process applications space covered by high energy and medium
current ion implantation.
Device Type
n-well
p-w ell
deep-well
Customer 1
Logic
500/2E13
175/2.5E13
Customer 2
Logic
650/5.2E13
360/1E14
Customer 3
Logic
600/4E12
420/1.4E13
Customer 4
Logic
500/4E13
300/3.5E13
Customer 5
Logic
600/4.6E13
305/1E14
Customer 6
DRAM
800/1E12
400/2E13
1200/1E13
Customer 7
DRAM
500/2.5E13
260/1.5E13
1500/5E13
Customer 8
DRAM
500/2.5E13
260/1.5E13
1500/1.5E13
Customer 9
FLASH
600/5E12
420/2E13
2000/2E13
Customer 10
FLASH
700/7E13
360/1E13
1900/1E13
Customer
2000/2E13
Falls w ithin curre nt e nergy range (B+ = 270 keV, P++ = 540 ke V)
Falls w ithin VIISta 810XE exte nde d energy range option (B+ = 300 keV, P++ = 600 keV)
W ill likely fall within VIISta 810XE ex tended ene rgy range option at next technology node
Figure 9 : A typical process recipe list for n-well and p-well applications and the relevant trends
in reduced energies as the next technology node is approached.
10
III. PROCESS TRANSFERABILITY
Process transferability between VIISta 3000 and 810 series of implanters are shown over the
common energy range with Secondary Ion Mass Spectroscopy (SIMS) and four point probe
measurements. Implants were conducted on crystalline n or p-type 300mm wafers either at
normal incidence (referred to as 0° tilt) or at high tilt. SIMS measurements were conducted on
as-implanted wafers, while these were annealed in a RTP system at 1100°C; 10 seconds for four
probe point measurements.
Utilization of implanters and the advantages of process transferability were modeled for a typical
flash memory and low power logic recipe set with a proprietary bay capacity model.
IV. PROCESS RESULTS
Figure 10 is a plot of SIMS profiles obtained from 3 points across the wafer (center, and +/- 3mm
from the edges with all three points on a line corresponding to the fast scan direction) for a
540keV B+ implant at zero degree tilt angle on a VIISta 3000 and VIISta 810. The two major
components of the dopant profiles are formed due to dechanneled and channeled ions. The
relative populations of these peaks are dependent on the incident angle of the ion beam, as the
beam incident angle deviates away from normal incidence, the relative population of channeled
boron ions is reduced and that of dechanneled ions increases. These ratios substantially change as
the incident angle is varied by as little as 0.2 degrees. The complete overlap of the SIMS profiles
at all points across the wafer and between VIISta 810 and 3000 arise from the total control of
incident angle in a closed-loop fashion. In contrast, for a traditional batch implanter typical angle
variation of 1-1.5 degrees is reported and this precludes the implementation of true zero degree
implants. In similar vein, SIMS profiles for a typical n-well implant are shown in Figure 11 [6].
Again for this zero degree phosphorus implant, the SIMS profiles are identical between the two
implanters.
11
3
Concentration (atoms/cm )
1E+18
1E+17
1E+16
1E+15
1E+14
0.0
0.5
1.0
1.5
Depth (microns)
2.0
2.5
Figure 10 : SIMS profiles of a B+, 540keV, 5E13cm-2 implanted at a nominal tilt of zero degree
on VIISta 810 and VIISta 3000. Profiles are obtained at center and 3mm from the edge (left
and right) for wafers processed on both implanters
1E+19
Concentration (atoms/cc)
1E+18
1E+17
1E+16
1E+15
1E+14
0
0.5
1
1.5
2
2.5
Depth (um )
Figure 11 : SIMS profiles of a n-well implant (P+, 400keV, 1E13cm-2) implanted at a nominal tilt of zero
degree on VIISta 810 and VIISta 3000. Profiles are obtained at center and 3mm from the edge (left and
right) for wafers processed on both implanters
12
1.00E+19
Concentration (atoms/cc)
1.00E+18
1.00E+17
1.00E+16
1.00E+15
1.00E+14
0
100
200
300
400
500
600
700
Depth (nm)
Figure 12 : SIMS profiles of a high tilt implant (B+, 35keV, 2E13cm-2 at 30 degree tilt) on VIISta 810
and VIISta 3000 Profiles are obtained from three points at center left and right as in Figure 10
As already mentioned single wafer architecture enables high tilt implants employed in
applications such as pocket and halo doping. In Figure 12, SIMS profiles obtained for a B+,
35keV at a 30º nominal implant angle from both VIISta 810 and VIISta 3000 are plotted. The
dopant profiles produced by these implanters are identical, and thus demonstrate the ability to
transfer these layers across these tools.
In Table 1, sheet resistance values for some typical dechanneled, channeled, and high tilt implants
are listed. These values are obtained without conducting a dose matching exercise between the
machines. As can be seen from these values, the implanters are well matched and this arises from
the architectural and dose control commonality designed into the VIISta platform.
13
Table 1: Sheet Resistance Values for Typical Implants
Sheet Resistance (ohms/sq)
+
-2
B , 400keV, 5E13cm , 7°/23°
B+, 400keV, 5E13cm-2, 7°/23°
P+, 400keV, 1E14cm-2, 7°/23°
B+, 540keV, 3E13cm-2, 0°/0°
B+, 70keV, 3E13cm-2, 0°/0°
B+, 45keV, 2E13cm-2, 30°/0°
P+, 50keV, 1.5E13cm-2, 25°/0°
VIISta 3000
VIISta 810
780
829
406
665
1145
2200
1401
783
827
410
660
1148
2198
1420
V. OPTIMIZING FOR PRODUCTIVITY
The equivalent process performance of the VIISta 810 and VIISta 3000 allows for complete
process transferability in the overlapping energy and dose regime. This range is 10-300keV for
boron, 10-900keV for phosphorus/arsenic implantation and is determined by common productive
regimes of these machines. For energies below 10keV, all medium and low dose applications are
dedicated to the VIISta 810, while at higher energies such as up to 300keV for boron and 600
KeV for phosphorous, there are substantial throughput benefits when running recipes on a
medium current machine. As can be seen in Figure 13 and Figure 14 there are major productivity
gains realized in the B300 and P600 range with the VIISta 810XE operating at mechanical limit
for the recipes shown. This represents a significant throughput advantage over traditional high
energy machines. Also, compared to medium current machines which lack the extended energy
range capability, there can be a 4X to 8X gain in productivity.
In addition, for double charge Boron (> 300 KeV) and triple charge Phos (> 600 keV), the VIISta
810XE system can provide reasonable throughput performance to provide high energy back-up
capability.
14
300keV 3.5E13 Boron
450
400
Throughput (WPH)
350
300
250
200
150
100
50
0
Competitor HE System
Competitor MC System
VIISta 810XE
Figure 13: A productivity comparison between conventional HE or MC machines and the VIISta
810XE system for a Boron 300 keV P-Well implant.
600keV 1E13 Phos
450
400
Throughput (WPH)
350
300
250
200
150
100
50
0
Competitor HE System
Competitor MC System
VIISta 810XE
Figure 14: A productivity comparison between conventional HE or MC machines and the VIISta
810XE system for a Phos 600 keV N-Well implant.
15
V. DOSE COMPENSATION CAPABILITY
There are additional challenges faced when running photoresist wafers under the recipe
conditions referenced above. High energy impact of primary ions into the photoresist generates
significantly higher levels of outgassing than implants performed at more traditional low energies
(< 200 keV). Although this effect is intuitively obvious, it has significant ramifications for the
design of a beam line, process chamber and compensation algorithms. In particular, it is critical
that the control of photoresist outgassing be ensured to prevent undesired energy contamination,
non-uniformity and dose shifts during implant.
The impact of photoresist outgassing on dose control performance is realized from the faraday
reading not measuring the entire dopant flux. The degree of outgassing oscillates as the ion beam
interacts with varying photoresist areas. This results in compromised dose uniformity. The
VIISta 810XE product offers a unique dose compensation algorithm that controls dose shift (Rs
shift) when operating under challenging conditions of photoresist wafers (see Figure 15)
subjected to high powered beams.
% Rs Shift
P + + 5 0 0 k e V 5 E 1 3 V e r t ic a l D i a m e t e r S c a n
B e a m C u rre n t - 5 2 0 p u A
1 .0 0 %
0 .5 0 %
0 .0 0 %
-0 .5 0 %
-1 .0 0 %
-1 .5 0 %
-2 .0 0 %
-2 .5 0 %
-3 .0 0 %
-3 .5 0 %
P R W a fe r – D o s e C o m p O n
B a r e W a fe r
P R w a f e r , w ith 8 1 0 X E im p r o v eP
mRe nW
ts a fe r – D o sbea rC
e owma fpe rO ff
0
10
20
30
4 0 P R w a fe5r0
60
D ia m e te r S c a n - W a fe r M e a s u r e m e n t P o in ts
Figure 15: Dose compensation performance with photoresist for a P++ 500 keV, 5E13 recipe
condition.
16
The VSEA approach to dose compensation provides a simple, well characterized method to
compensate for photoresist outgassing. Since the technique involves the direct measurement of
current, there is no need for experiments to derive the charge exchange cross section variables.
There is also no requirement for real time pressure measurement which can be inherently unstable
and subject to data corruption by system electrical disturbances.
A one-time system characterization has been performed at the factory and is independent of
species, dose and energy range. The compensation applied is insensitive to absolute pressure and
photoresist conditions. The compensation algorithm (see Figure 16) is recipe selectable, allowing
for flexibility in determining when the compensation shall be applied.
IB
Determine
Effective
Dose Rate
Dose Control
Algorithm
Recipe
Selectable
Feature
Compensation parameters
fixed
One-Time Characterization
of System Requirements at VSEA
• Species
• Dose
• Energy Range
Figure 16 : A simplified overview of the Dose Compensation System algorithm utilized on the
VIISta 810XE..
VI. HIGH ENERGY TO MEDIUM CURRENT PROCESS TRANSFERS
In Figure 17, a typical allocation for a 300mm manufacturing facility with a combination of Flash
and Logic devices is shown. The flash implant recipe set consists of 22 low and medium dose
implants with only one implant that is in the exclusive process regime of the VIISta 3000, while
other implants can be achieved either on the VIISta 3000 or VIISta 810, albeit with different
productivity levels. A similar distribution of recipes also applies to the Logic manufacturing
17
process. In general, especially in the medium dose regime, the VIISta 810 provides better
productivity with lower cost of ownership. The number of high-energy implanters required as the
capacity is scaled from 1000 wafers/week to 6000 wafers/week remains constant. As the capacity
is scaled upward, more and more implants are transferred to the lower cost medium current
implanter. In all cases, the ability of VIISta 3000 to process all medium current implants enable
the reduction in the number of medium current implanters required, while maintaining
manufacturing redundancy by incorporating at least 2 implanters of a kind at all times in
production. In addition to the direct benefits in reduced number of processing tools, there are also
significant benefit and savings due to commonality of tool components, parts, and training. This
ability to optimize two different processing tools naturally reduces initial capital outlay, overall
cost of ownership, and increases manufacturing flexibility in the era of rapid changes due to
market demand fluctuations.
9
8
VIISta 810
VIISta 3000
Total Number of Implanters Required
7
6
5
6
5
4
4
3
3
2
2
2
2
2
2
2
2
1K
2K
3K
4K
5K
6K
2
1
0
Wafer Starts per Week
Figure 17 : Model for number of medium current and high energy tool required as a function of
wafer starts for a 50% logic/flash manufacturing. The bottom part of each bar shows the number
of VIISta 3000’s required. The top part of each bar shows the number of VIISta 810’s required.
18
VI. CONCLUSIONS
In this paper we have reviewed how the new breed of medium current VIISta 810XE implanter
allows for transferability of recipes which were formerly considered as dedicated to high energy
machines. A paradigm shift has occurred in the way in which traditional medium current and
high energy recipes have been dedicated to their respective tool sets. There is now greater
flexibility provided in selecting which tool set the high energy recipes can be run on. Specifically
for twin well applications there are significant productivity gains which can be realized by
employing this new strategy. The process flexibility in turn allows for maximum utilization of
the implanters and a reduced capital investment requirement for a given fab capacity. There are
also device fabrication requirements which should be considered when examining trade-offs
between single wafer vs. batch ion implanters for well applications.
REFERENCES
[1] ITRS Roadmap for Semiconductors 2002 http://public.itrs.net/files/2001itrs/home.htm
[2] V. R. Chavva, S. Norasetthekul, Y. K. Kim, J. Flanagan, and N. Variam, “Optimization of
Well and Channel Implants for Maximum Productivity: Process Transferability of Low and
Medium Dose Implants.”
[3] T. Yamashita, M. Kitazanwa, Y. Kawasaki, H. Takashino, T. Kuroi, Y. Inoue, M. Inuishi
“Advanced Retrograde Well Technology for 90-nm node Embedded SRAM by High Energy
Parallel Beam,” Japanese Journal of Applied Physics , Part 1, Vol.41, no.4B p.23999-403..
[4] J. C. Olson and A. Renau, “Control of Channeling Uniformity for Advanced Applications,”
Proc. of 13th Int. Conf. on Ion Implantation Technology, Alpbach, Austria, October 2000: pp.
670-673.
[5] J. Weeman, J. Olson, B. N. Guo, U. Jeong, G. C. Li, and S. Mehta, “Precise Beam Incidence
Angle Control on the VIISta 810HP,” Proc. of 41th Int. Conf. on Ion Implantation
Technology, Taos, New Mexico, September 2002: pp. 276-278.
[6] N. Variam, S. Mehta, S. Norasethekul, and B. N. Guo, “Seamless Transferability of Doping
Processes between the VIISta Platform of Ion Implanters,” Proc. of 14th Int. Conf. on Ion
Implantation Technology, Taos, New Mexico, September 2002: pp. 1283-286.
19