A Comparison of Resist Selectivity

1
A Comparison of Resist Selectivity Etch
Profiles on Silicon Processed by the Plasma Therm
and STS ICP

• Presented by

Rochelle Hamby Jaclyn Murray
NNIN RETs Summer 2007
2
Objectives

• Assess the resist selectivity and profiles of two
  ICP (Inductively Coupled Plasma) etchers
• Evaluate resist pre-bake time on resist
  selectivity and etch profiles
• Determine the effects of post-baking on resist
  selectivity and etch profiles

3
Tools

• CEE Model 100CB Spinner/Hotplate
• Karl Suss MA-6 Mask Aligner for pattern exposure
• Tencor P-15 Profiler and Alpha Step 500 for
  resist and etch profiles
• STS PT ICP for Si etching
• Hitachi SEM for profile analysis

4
Spin Coating

• CEE Model 100CB Spinner
• HMDS
• Adhesion Promoter
• Recipe
• 3000 RPM, 1000 RPM/s, 20 s
• SPR 220-7.0 Photoresist
• (Rohm Haas)
• Expected Thickness 8 mm
• Actual Thickness 6.5 8 mm
• 2 Cycle Recipe
• 250 RPM, 1000 RPM/s, 5 s
• 2000 RPM, 500 RPM/s, 40 s

5
Baking

• Bake Times _at_ 110 C
• Pre-Bake Only
• 5 min
• 20 min
• Pre- and Post-Bake
• 130 min pre 5 min post
• 130 min pre 10 min post
• 12 wafers each

6
Pattern Exposure

• MA-6 Parameters
• Exposure Time 150 s
• Alignment Gap 25 mm
• Pre Vacuum 10 s
• Full Vacuum 30 s
• WEC Off 0
• WEC Type Contact
• Vacuum Purge 15 s
• Channel 2 405 nm

• Karl Suss MA-6
• Mask Aligner

7
Developing

• Developer MF 319
• Submerge wafer in developer
• Shook submerged wafer
• Develop time varied
• Completion when rainbow film disappeared

8
Resist Profiling

• Profiling with the Tencor Alpha Step 500

9
PlasmaTherm ICP Parameters

• Bosch Process Cycles
• 1. Deposition Step
• 2. Etch A
• 3. Etch B
• 10 min etch 50 cycles
• 30 min etch 150 cycles

Deposit. Etch A Etch B
Pressure (mTorr) 15 15 15
Time (s) 4 2 6
Gas 200 70 0.5 0.5
SF6 200 0.5 50 100
O2 100 0 0 0
Ar 100 40 40 40
RF1 1 9 9
RF2 800 800 800
10
STS ICP Parameters
Gases Etch Flow (sccm) Passivation Flow (sccm)
C4F8 0 50 100 5
SF6 130 50 0 5
O2 13 50 0 5
Ar 0 5 0 5
Base Pressure 0.1 mTorr Coil RF 600 W/etch
600 W/pass Platen RF 10 W/etch 0
W/pass
Recipe Module 1 10 min etch 33 cycles 30 min
etch 100 cycles
11
Profile, Strip, Profile

• 1. Profile the photoresist and etch depth.

• 2. Strip the wafers with 1165.

3. Profile the etched silicon.
12
Scanning Electron Microscope
Preparation for Edge Profiling Snapped the
samples for edge on imaging Selected a similar
cross-section Gold coated the samples

• Pictures
• Same feature selected
• Feature located at the center of the whole wafer
• Magnification 1,200 x

13
THE RESULTS
14
Profiles on the Alpha Step 500
Post-Bake Profile Height of center 22.42
mm Height of bumps 23.02 mm Width
492 mm
Pre-Bake Profile Height 37.9 mm
Width 176 mm
15
Selectivity
a
a - b
PR
PR
PR
PR
c
d
Silicon
Silicon
Etch Rate of PR Etch Rate of Si Selectivity
Ratio Etch Rate Si Etch Rate of PR

• a Photoresist Height
• b Etched Photoresist
• c Post Etch Height
• d Stripped Etch Height
• b a-cd

16
130 Minute Pre-Bake
PT ICP Post-Bake Selectivity
500 min Post-Bake 1000 min Post-Bake
10 min Etch 221 71
30 min Etch 291 61
17
PT ICP Pre-Bake Only Selectivity
500 min Pre-Bake 2000 min Pre-Bake
10 min Etch 381 71
30 min Etch 331 61
18
STS ICP Post-Bake Selectivity
130 Minute Pre-Bake
500 min Post-Bake 1000 min Post-Bake
10 min Etch 291 131
30 min Etch 441 131
19
STS ICP Pre-Bake Only Selectivity
500 min Pre-Bake 2000 min Pre-Bake
10 min Etch 561 191
30 min Etch 551 191
20
Measuring Profiles
Dq

• Wall Height (WH)
• Trench Floor Difference
• (TFD)
• Wall Angle (Dq)

WH
TFD
21
PT ICP Profiles
Selectivity 231 WH 13 mm TFD 1.55 mm Dq
0.69
Selectivity 231 WH 13.42 mm TFD 2.40
mm Dq 1.40
130 min pre bake 500 min post bake 1000 minute
etch
Selectivity 271 WH 35.5 mm TFD 6.9 mm Dq
1.74
Selectivity 271 WH 35.6 mm TFD 6.6 mm Dq
1.26
130 min pre bake 500 min post bake 3000 minute
etch
22
PT ICP Profiles
130 min pre bake 1000 min post bake 1000 min
etch
Selectivity 71 WH 14.12 mm TFD 1.86 mm Dq
7.53
Selectivity 61 WH 42.0 mm TFD 6.1 mm Dq 0
130 min pre bake 1000 min post bake 3000 min
etch
23
PT ICP Profiles
Selectivity 361 WH 11.65 mm TFD 3.1 mm Dq
2.98
Selectivity 361 WH 11.87 mm TFD 2.8 mm Dq
2.94
500 min pre bake 1000 minute etch
Selectivity 311 WH 33.8 mm TFD 7.9 mm Dq
1.91
Selectivity 311 WH 34.6 mm TFD 8.1 mm Dq
4.98
500 min pre bake 3000 minute etch
24
PT ICP Profiles
2000 pre bake 1000 min etch
Selectivity 71 WH 13.25 mm TFD 3.32 mm Dq
3.7
Selectivity 61 WH 40.3 mm TFD 5.4 mm Dq --
2000 pre bake 3000 min etch
25
STS ICP Profiles
Selectivity 291 WH 13.35 mm TFD 1.35
mm Dq 2.95
Selectivity 291 WH 13.05 mm TFD 1.45
mm Dq 5.59
130 min pre bake 500 min post bake 1000 minute
etch
Selectivity 471 WH 37.8 mm TFD 1.4 mm Dq
1.52
Selectivity 471 WH 37.6 mm TFD 1.2 mm Dq
5.82
130 min pre bake 500 min post bake 3000 minute
etch
26
STS ICP Profiles
130 min pre 1000 min post 1000 min etch
Selectivity 131 WH 13.08 mm TFD 0 mm Dq 0
130 min pre 1000 min post 3000 min etch
Selectivity 131 WH 38.7 mm TFD 0 mm Dq 0
27
STS ICP Profiles
Selectivity 621 WH 12.64 mm TFD 1.2 mm Dq
3.75
Selectivity 621 WH 12.67 mm TFD 1.29
mm Dq 1.23
500 minute pre bake 1000 minute etch
Selectivity 551 WH 38.1 mm TFD 2.4 mm Dq
2.02
Selectivity 551 WH 38.1 mm TFD 2.5 mm Dq
1.84
500 minute pre bake 3000 minute etch
28
STS ICP Profiles
Selectivity 191 WH 13.04 mm TFD 0.92 mm Dq
2.40
2000 min pre bake 1000 min etch
Selectivity 191 WH 37.4 mm TFD 4.1 mm Dq
0
2000 min pre 3000 min etch
29
Conclusions

• Selectivity
• Less bake time (pre- and post-) offers higher
  selectivity
• Profiles
• Post-bakes provide trench bases with flatter
  bottoms and sharper corners
• STS ICP trench quality (vertical horizontal) is
  improved compared to that of the Plasma Therm ICP

30
Summary Extensions

• Bake time affects the hardness and chemistry of
  the photoresist.
• Post-bake bumps created more vertical walls which
  could result in altered gas flow patterns.
• Future work could include a repetition of the
  process with various photoresists, additional
  etchers, and different pre-bake and post-bake
  times.
• Include a profile analysis using the SEM of the
  photoresist and etch.

31
MENTORS

• Janet Cobb-Sullivan
• Cristina Scelsi
• Kevin Martin, PhD
• Nancy Healy, PhD