The New Concept for Particle Remove in Wet Bench Cleaning
Sheng-Hsiung Chen1, Shen-Li Chen 2, Long -Yeu Chung 1, and Wen-Kuan Yeh3
1
Department of Electrical Engineer, Tung Fang Institute of Technology, NO.110, Tung Fang RD,
Hu-Nei Shang, Kaohsiung, Taiwan, R.O.C.
2
Department of Electronic Engineering, National United University, 1, Lien-Da, Kung- Ching Li,
Miaoli 360, Taiwan, R.O.C.
3
Department of Electrical Engineering, National University of Kaohsiung, Taiwan, R.O.C.
Tel: 886-7-6939632 ext 107, Fax: 886-7-6937610, E-mail: [email protected]
Abstract
For the manufacturing of submicron or deep
submicron ULSIs, it is important to completely suppress
particles and contamination created on the silicon wafer
surface. The tradition concept for cleaning need was used
chemical content (APM, ammonia and hydrogen peroxide
mixtures) to play a major role. Unfortunately, the SC-1
(APM) had negative effect on surface damage. In recent
years, it has been modified to incorporate a more dilute
solution in order to reduce surface micro-roughness caused
by ammonium hydroxide. In this paper, a new thinking was
proposed to use DI water quick dump rinse (QDR) mode
change from conversation set-up to an improvement mode.
A modified recipe with modified using DIW can totally
remove the particle during process.
1. Introduction
As semiconductor device feature size continues to
shrink. There is a need to understand the particle removal
mechanisms and recognize the advantages and their
limitations. In this paper, some particle removal models are
modified to be able to remove soft particle deformation. A
modified RCA wafer cleaning with / without mega-sonic
energy enhancement and various rinsing techniques are
investigated for use in deep sub-micron semiconductor device
manufacturing.
The need for wet-cleaning, proposing a particle-free
substrate for use in semiconductor process has become
increasingly more important. As semiconductor devices are
scale down, the sensitivity of silicon and silicon dioxide
substrates to contamination increases. Especially, in
manufacturing processes of sub-micrometer and deep
submicron ULSI’s, surface microstructure and surface
cleanliness of substrates are going to increase their
significance as crucial for device performance and reliability.
This paper also presents a comprehensive study using
surface analysis and inspection techniques to test particle
removal rate under various cleaning recipe including (1)
Mega-sonic-on and (2) quick dump rinse (QDR) model
modified. A higher level quality of clean process was
proposed to show DI water is a good median for particle
removing. Besides, a more high effectiveness’ monitor action
was also studied by detailed design.
1-4244-0206-9/06/$20.00 ©2006 IEEE
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2. Background:
As semiconductor devices are scale down, ultra clean
surface becomes even more important. In device fabrication,
conventional RCA cleaning process and slightly changed one
have been continuously used for past three decade [1-3]. The
need for clean, particle-free substrate for use in
semiconductor processing has become increasingly
important. As device dimensions are reduced, the sensitivity
of silicon and silicon dioxide substrates to contamination
increases.
Minimizing electrical effects caused by cleaning are
extremely important in controlling contamination. Clean and
surface and precise patterns are necessary for high yields and
increased process efficiency reproducibility. Minimizing
defect density (contaminant/ area) yield loss is a key mission
of semiconductor fabricators.
An understanding of particle adhesion is imperative to
efficiently removing particles in surface cleaning process.
There are several types of forces acting to hold particulate
contamination on a wafer, which are including: (1) Van der
Waals force, (2) electro-double layer force, and (3)
deformation induced forces.
As the later dimension device is scale down, the vertical
dimension is also direct reduction. So, when the techniques
roll up, chemical (including CAROS, APM, HPM, and HF)
dip time are required to reduce for silicon damage prevents. If
ultra cleaning surface is necessary, but chemical dip time is
under limited. The option is to select mechanical method for
particles removal successful.
3. Experimental:
An 8 inch Si (100) P-type Epi wafer was used as
substrate for particle removal efficiency experiments. For
intentional particle contamination, the bare silicon wafers
were prepared by covered with thick oxidized wafer (>1000
A) and dipped in HF solution. The detailed process of C/W
with fall-on particle is as Figure-1.
The wafers were then intentionally contaminated by
dipping in as below procedure.
Proceedings of 13th IPFA 2006, Singapore
PRE = (1 −
Oxide C/W
Bare C/W
HF Dip
Bare C/W with Fall
on Particle
Fig.1 The procedure for C/W prepared with fall on particle for
this experimental.
The prepared control wafers are with particles about
200 ea as Fig.-2. The fallen on particles were with water
flow-like type distribution map on silicon surface.
The control wafers with fallen on particles were
preparing for the study of particle removal efficiency (PRE).
This method for control wafers with fallen on particles
was first time proposed using a sample and low cost
procedure. We had proved that the fallen-on particles have
same characteristics as other methods.
particles afterclean ing − particles beforeclea ning
particles beforeclea ning
) × 100
4. Results and Discussion
Figure 3 shows the SEM pictures of fallen-on particles
and are about 0.08-1 um diameter in size. In this study,
particles of 0.09-1.0 um diameter in size were used.
Generally, even in such an ultra-clean environment, particles
brought into the bath of an immersion-type wet bench by the
to-be-cleaned wafers themselves will dissolve and
accumulate in the chemical solution, though particles brought
into the bath are eventually filtered out by a circulating
particle-filtering system equipped in the wet bench.
Fig. 3 The SEM picture of fallen-on particles
These particles content are analyzed by EDS spectrum
measured. From the EDS analysis, the fallen-on particles are
composed with C and O elements as Figure-4.
Fig.2 The map of C/W prepared with fallen on particles.
For particle removal efficiency evaluation the prepared
wafers were cleaned by various techniques, including (1)
mega sonic-on and (2) quick down rinsing model modified.
All the experimented wafers were processed in Kaijo clean
module tool at room temperature. Particle levels on the wafer
before and after the processes were measured by SP1 with
TBI function. (>0.08 um in size).
The before/after processed wafer were used in order link
KLA and SEM (JEOL JWS 7500). First, KLA and SEM were
used to inspect wafers which were rinsed with/without
mega-sonics in DI water.
Particles levels evaluation was measured before and after
cleaning experiment by wafers’ particle counts. And, particle
removal efficiency (PRE) was calculated using:
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Fig. 4 The EDS spectrum analysis of fall-on particle.
In this work, the effect of mega-sonic turned-on is first
used to study. Both SC-1 (APM, NH 4 OH tank) and final
rinse tank’s megasonic functions are all turned-on as Figure-5
shown.
APM
HQDR
MegasonicMode:1~7
Power:150W~600W
HPM
HQDR
F/R
Mg/D
MegasonicMode:1~7
Power:150W~600W
Fig. 5 The experimental details of megasonic-on
Particle Removal Efficiency (%)
The mega sonic output powers are varied from 150 Watt
to 600Watt spliced up five levels. It is same as well known
that megasonics safely removes particles. Figure-6 shows that
when the megasonics output power increasing, the particle
remove rate is also increasing. As Heui-Gyun Ahn,
Sang-Young Kim, and Jeng-Gun Lee, reported [4] that the
megasonics beam is parallel to the wafer surface. Patterned
wafer cleaning can be modeled as a mass transfer in wafer
surface. In general, turning on megasonic power can improve
particle remove rate increasing around 6~28% in various
output power. Especially, the megasonic power output
implemented on particles removal will have an optimal
condition at megasonic power of 450W.
mixtures such as surface roughness, contamination, and
chemical cost. Tung Ming Pan et al, had reported [6-7] that by
preparing a surfactant (TAAH) and a chelating agent (EDTA)
into the NH 4 OH alkaline aqueous solution, the efficiency of
the particles and metals and the electrical characteristics of
capacitors are significantly improved.
But, we proposed that evaluation a new recipe to replace
the role of ammonia and hydrogen peroxide mixtures.
So, we start to evaluate the ability of using various modes
DI water. The varied parameters including (1) water
temperature, (2) idle time, (3) shower type, (4) cycle times.
We found that modified quick down rinse model is also
effective for particle removal.
The DI water has five potential characteristics to act as a
best candidate for particles, contamination, and electrostatic
charges removal material: (i) H 2 O is a polar medium to
dissolve particles and keep electrostatic charges stable, (ii)
easily control the temperature, (iii) more safe in
manufacturing process, (iv) low cost, (v) easily co-operate
with other chemical for wet bench cleaning.
A more effectively modified recipe for particle
remove is necessary. From figure-6 data show that quick
down rinse modified is another factor for particle removal
rate improvement. Mode A is conversation recipe using
HDIW (hot DI water) and Mode B is a modified recipe in this
work. The detailed difference between recipe content were
shown in Fig. 7. Besides, there is an extra step of stand-by (10
seconds) in Mode B recipe.
70
60
AMode
50
40
30
BMode
Particle
removerate
rate
remove
20
Up
flow
10
0
0W
ColdDIW
150 W 300 W 450 W 600 W
Shower
Hot DIW
Quick
Dump
Fig. 7 The comparison of QDR (Quick Dump Rinse) between
mode A and mode B.
Megasonic Power (Watt)
Fig. 6 The results of megasonic-on experimental.
Due to megasonics turn-on will have some risk to come
out pattern loss issue. The understanding of particle adhesion
is imperative to efficiently remove particles in wet bench
cleaning. Particles adhesion on wafer surface were occurred
as follows: first , long-range attraction forces draw the
particle toward to wafer surface until the contaminant
particles and wafer touch at one point of contact. Then, the
short-range attraction forces (such as: Van Der Waals)
dominate near the surface and the contact area increases [5].
In order to get a suitable for next-generation
semiconductor manufacturing using, it is necessary to reduce
the negative effect of APM, ammonia and hydrogen peroxide
139
Figure-8 shows that Mode B have more effective
particle remove rate than Mode A. As previous study, the
particle remove rate is dependent on the charge
recombination; using same duration with differential cycle is
also a little bit improvement for particle remove.
As our practical experience can concluded that four
cycles shower combined with 10 seconds shower time and
added an extra idle step are not only a optimal conditions but
also reasonable for QRD’s recipe. The reason is that using
more cycle will have more cost.
PRE (Particle Remove Efficiency (%)
[6] Tung Ming Pan, Tan Fu Lei, Fu Hsiang Ko, Tien
Shewng Chao, Tzu Huan Chiu, and Chih Peng Lu,
IEEE Transactions on Semiconductor Manufacturing,
vol. 17, NO. 3, Nov., (2004), p. 470-476.
[7] Tung Ming Pan, Tan Fu Lei, Chao Chyi Chen, Tien
Sheng Chao, Ming Chi Liaw, Wen Lu Yang, Ming
Shih Tsai, C. P. Lu and W.H. Chang, IEEE Electron
Device Letters, vol. 21, NO. 7, Jul., (2000), p.
338-340.
100
80
60
Acknowledgement
40
A mode
Particle
B mode
20
0
The authors would like to thank for the National Ministry
of Education of Taiwan, R.O.C., under Contract No. NME
94 -002, support this work
1 2 3 4 5 6
cyclecyclecyclecyclecyclecycle
Cycle numbers (#)
Fig. 8 The results of QDR experimental were with A mode
and B mode.
4. Conclusions
In this work, a new method which prepares lots of
fallen-on particles on control wafer surface was first
proposed.
Besides, the efficiency of megasonics in APM and
final rinse step have been investigated. In general, turn on
Megasonic can improve particle remove rate increasing
around 6~28%.
If using the modified recipe of QDR Mode B which
is some differences than conversation recipe (Mode A)
including: (i) added idle time of 10 sec and (2) using Cold
DIW. The modified recipe is more effective than
conversation recipe for particle remove. The PRE (particle
remove rate efficiency) is over 94% using modified QDR
mode B recipe.
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