1

SU-8 Testing (v1l)

Thin SU8 on glass slide

Test:

Soft Bake (SB) and

Post Exposure Bake (PEB)

2

“Control” Recipe1. Spin Coating: 10 s @ 500 rpm; 30 s @ 2000 rpm

– expected thickness: 600 nm

2. Soft Bake (SB): 60 s @ 93°C

3. Exposure: 8 s @ 275 W setting (power meter readings: (11.3±0.1) mW/cm2 - done before set #1 and after set #5)

4. PEB: 60s @ 93°C

5. Develop: 4 min in SU8 developer

6. SU8 developer rinse

7. IPA rinse/Nitrogen Dry– 1, 3, 6, 7 are the same for all “tests”

– 5 is also the same for tests 1-3, and for test 4: 1 min2

3

1st Set of Tests

• 4 samples; 8 devices/sample

• 4 Wells (W)+4 Blanks (B)/sample

• S1: “Control”: Misaligned (see next slide); All shorted; R(W) ~ 8.6 Ω; R(B) ~ 10 Ω

• Test Parameters for S2-4:

– SB (RT Evap) and PEB @ 60°C, same times for each

• S2: 8 min:

• R(W) = (2.7±0.8) Ω; R(B) = (11±0) MΩ; C(B) = (15.0 ± 0.1) pF

• S3: 13 min: Also misaligned (see next slide)

• R(W) = (4.9±?) Ω; R(B) = (6 ± 8) MΩ; C(B) = (17.0 ± 0.5) pF

• S4: 15 min:

• R(W) = (4 ± 1) Ω; R(B) = (11±0) MΩ; C(B) = (17 ± 0) pF

• Cracking patterns seen in S2, S3, S4

3

4

Findings/Discussion 1st Set• “Control”: All shorted

– The “misalignment” ONLY causes 1. Top contacts don’t fully overlap guide circles on bottom that could result in

the top contact not covering the well (is this the case? If not say so) – will NOT cause short

2. Top contacts touching two exposure regions

– either single + double exposures (normal) – NOT cause short,

– or single + no exposures (should not happen but may - according to Mark, but microscopy can tell us – presence of a well – check to confirm and revise here …) – MAY cause short (ONLY no exposure)

• RT Evap + PEB @ 60°C at various times: All good– All Wells are shorted with a narrow range of R

– All Blanks have good Cs also with narrow range1. Next thing to do is to estimate thickness from geometry from C

1. The two longer time ones exhibit ~10% larger C (difference in dielectric constants or thickness?)

2. All three show undesirable cracking patterns (under baked/sticky surface or over baked – low solvent, bubbling etc.?)

5

2nd Set of Test Samples

• 4 samples• 2 “Controls”: S5-6• Test Parameters for S7-8:

– 1 min PEB @ 93°C and Vary SB time @ 60°C

• S7: SB: 2.5 min• S8: SB: 5 min

5

6

2nd Test Results - “Control 1” S5Device Capacitanc

e(pF)Resistance(Ω)

Type

1 -1 29.4 B

2 -1 0.5 W

3 9.38 3.7x106 B

4 -1 24 W

5 -1 24 B

6 -1 7 W

7 -1 421 B

8 -1 17 WSummary: W: 4/4 Shorted B: 3/4 ShortedR(W): (12 ± 10) ΩExcluding #3 R(B): (158± 230) ΩC(B,#3) – very low (9.38 pF) compared to 1st set but comparable to S6 (also a Control - next slide).

13

S5 “Control” 100x

13

7

“Control 2” S6Device Capacitanc

e(pF)Resistance(Ω)

Type

1 Damaged 9.7 4.6x106 W

2 9.33 8.3x106 B

3 Damaged 9.61 3.04x105 W

4 9.4 1.05x107 B

5 -1 142 W

6 9.25 1.1x107 B

7 -1 46 W

8 10.3 1.2x104 B

Summary: W: 2/4 Shorted (2 Damaged by high voltage – 1V) B: 0/4 ShortedR(W): (94± 68) Ω; C(B): (9.6± 0.5) pF

11

S6 “Control” @ 20x

This image size is good (covering the entire crossbar) – perhaps larger ones covering up to the reference dots would be even better; at the current stage, there’s no need to have too many zoomed in images.

11

12

S6 “Control” 100x

12

8

2.5 min SB S7Device Capacitanc

e(pF)Resistance(Ω)

Type

1 -1 13.4 W

2 -1 428 B

3 -1 10.8 W

4 -1 294 B

5 -1 3.7 W

6 -1 5.7 B

7 -1 4.1 W

8 -1 11.6 BSummary: All Shorted

R(B): (185 ± 211) Ω; R(W): (8 ± 5) Ω

14

S7 2.5min SB 100x

14

9

5 min SB S8Device Capacitanc

e(pF)Resistance(Ω)

Type

1 -1 4.8 W

2 -1 16 B

3 -1 1.9 W

4 -1 44 B

5 -1 4.3 W

6 -1 ? B

7* 15.16 Very High W

8 15.25 0.57x106 BSummary: W: 3/4 Shorted (why not 4/4?) B: 3/4 ShortedR(Blank): (30 ± 20) Ω (#8 excluded)R(Well): (3.7 ± 1.6) Ω (#7 excluded)7*: Re-measured and consistent with capacitance

15

S8 5min SB 100x

15

10

Findings/Discussion for 2nd Set (S5-S8)

• The two “Controls”: – S5 is essentially all shorted, but R(B) > 10R(W)

– S6 is nominally good aside from the 2 damaged devices. But, the 2 shorts are too resistive (~90 Ω) compared to the “benchmark” Set 1 (~few Ω).

– C(B) are ~ 9.5 pF rather than 15-17 pF for set 1 (thicker, lower dielectric constants, etc?)

– The “Control” recipe is at best marginal thus unreliable (2 shorted and one nominally good out of 3 samples in sets 1 and 2) – consistent with prior Si wafer work (Matt)

• S7 and S8 are all shorted, but 20R(W) < R(B) and R(W)<10Ω, These are more consistent with Set 1 aside from being all shorted.

• The one good blank out of S8 has capacitance consistent with Set 1 capacitances (S2).

10

16

3rd Set of Test Samples

• 2 samples• Test Parameters for S9-10:

– 1 min PEB @ 93°C and Vary SB time @ 60°C (longer SB compared to 2nd set)

• S9: SB: 8 min• S10: SB: 12 min

16

17

• Back Contact not continuous – visually can’t see where it’s broken

• Measured Cs (can measure 2-terminal R)• W: 2/4 Shorted B: 1/4 Shorted• C(B): (19.3 ± 0.6) pF (excl. #2)

Device Capacitance(pF)

Resistance(Ω)

Type

1 -1 W

2 -1 B

3 12 W

4 19 B

5 -1 W

6 19 B

7 19 W

8 20 B

8 min - S9

18

12 min - S10Device Capacitanc

e(pF)Resistance(Ω)

Type

1 -1 4.5 W

2 -1 18 B

3 -1 6.7 W

4 -1 121 B

5 -1 3.9 W

6 -1 127 B

7 -1 5 W

8 -1 118 BSummary: W: 4/4 Shorted B: 4/4 Shorted

Avg Well Resistance: 5.0± 1.2Ω Avg Blank Resistance: 96± 52Ω

Double Exposed (16s)

19

Discussion/Findings of Set 3

• S9: – pretty much all open circuit– C(B) slightly higher than Set 1: 19 pF vs 15 and

17 pF– Current measurements unreliable because the

back contact is not continuous without visual “flaws”

• S10:– All shorted– 10R(W) < R(B)– Consistent with Set 2

20

4th Set of Test Samples

• 3 samples• Test Parameters for S11-13:

– 10 min PEB @ 60°C and Vary SB time @ 60°C– Develop: 1 min in SU8 developer (different from

previous)

• S11: SB: 2 min• S12: SB: 5 min• S13: SB: 10 min

20

21

2 min SB S11Device Capacitanc

e(pF)Resistance(Ω)

Type

1 Not Exposed -1 - B

2 Not Exposed -1 - W

3 -1 2.4 B

4 -1 11.4 W

5 -1 9.5 B

6 -1 1.7 W

7 -1 12.4 B

8 24.06 - W

• Summary: B: 3/3 Shorted; W: 2/3 Shorted, 1/3 openR(B): (8 ± 5) Ω; R(W): (7 ± 7) Ω

• Not exposed – “operator error” by Matt• 1 Well open circuit – not fully opened (due to shorter

developing time?)

22

5 min SB S12Device Capacitanc

e(pF)Resistance(Ω)

Type

1 13.99 - W

2 15.66 - B

3 -1 2.8 W

4 15.53 - B

5 -1 3.2 W

6* -1 0.21 B

7 -1 7.2 W

8 -1 6.2 B

Summary: W: 3/4 Shorted (#1 bad); B: 2/4 Shorted (2/4 good) R(W): (4 ± 2) Ω; R(B): (3 ± 4) Ω

C(B): (15.6 ± 0.1) pF; C(W): (14 ± 0) *Device 6: looked different – mixed cracking and not cracking - could be partially developed away.

23

10 min SB S13Device Capacitanc

e(pF)Resistance(Ω)

Type

1 -1 6.2 W

2 -1 140.7* B

3 -1 6.1 W

4 -1 1.5 B

5 Not Exposed - - W

6 -1 4.3 B

7 -1 6.0 W

8 -1 3.6 B

Summary: All ShortedR(B): (37 ± 70) Ω; R(W): (6.1± 0.1) Ω

*Exclude?

24

Discussion/Findings of Set 4

• All have cracking– Similar to Set 1

– PEB @ 60°C is the possible cause

• Nearly All shorted (S11-13)– S11:

• All blanks short circuit

• R(W) ≈ R(B)

– S12:• R(W) ≈ R(B)

• C(B) ≈ C(B:Set1) ≈15pF

– S13:• R(B) > 6 R(W)

• Only 1 “high” R with the rest equal to R(W)

26

Distribution of Resistances for “Shorted” Wells for Sets 1-4

• All devices with C = -1, i.e. Test 1-4• Stats: …

27

Distribution of Resistances for Shorted Blanks (all devices)

• All devices with C = -1, i.e. Test 1-4• Stats: …

25

SB @ RT PEB @ 60

T1

E-good

SB @ 60 PEB @ 93

T2-3

SB @ 60 PEB @ 60

T4

SB @ 93 PEB @ 93

“Control” T1-3

inconsistent

Cracking No-cracking

E-n

o g

ood

Next set:SB @ RT PEB @ 90

Keep track of time

E-?Crack?

Next set:SB @ 90 PEB @ 90

“pseudo Control” Keep

track of time

E-?Crack?

Consistency?

28

5th Set of Test Samples

• 3 ‘pseudo-control’ samples: S14-16– softbake and PEB @ 90°C for 1 min– vary the ‘cooling’ time after PEB

• S14: Cooling time: ~40s• S15: Cooling time: 3min• S16: Cooling time: 2min

• 3 BS @ RT for various times• two ‘lost’ – one dropped and another misaligned• S17

• softbake @room temp. for 10min• PEB @ 90°C for 1min• Cooling time: ~1 min

23

S14Device Capacitanc

e(pF)Resistance(Ω)

Type

1 -1 6.2 W

2 10 - B

3 -1 18 W

4 -1 1 B

5 -1 3 W

6 -1 0.9 B

7 -1 11 W

8 -1 130 B

Summary: (1/4 open blanks) (4/4 shorted wells)R(B): (44 ± 75) Ω; R(W): (10 ± 6) ΩC(B): (10 ± 0) pF

23

S15Device Capacitanc

e(pF)Resistance(Ω)

Type

1 -1 13 W

2 14 - B

3 -1 18 W

4 -1 0.2 B

5 -1 22 W

6 -1 59.6 B

7 -1 16 W

8 14.6 - B

Summary: (2/4 open blanks) (4/4 shorted wells)R(B): (30 ± 42) Ω; R(W): (16 ± 4) ΩC(B): (14.3 ± 0.4) pF

31

S15 device 7 (well)5x

23

S16Device Capacitanc

e(pF)Resistance(Ω)

Type

1 -1 145 W

2 12.5 - B

3 -1 10 W

4 12 - B

5 -1 14 W

6 -1 5 B

7 -1 341 W

8 10 - B

Summary: (3/4 open blanks) (4/4 shorted wells) R(B): 5 Ω; R(W): (127 ± 155) Ω C(B): (12 ± 1) pF

33

S16 device 6 (blank)5x

23

S17Device Capacitanc

e(pF)Resistance(Ω)

Type

1 -1 * W

2 9.7 ** B

3 -1 18 W

4 -1 10 B

5 -1 22 W

6 10.7 - B

7 -1 16 W

8 -1 10 B

Summary: (2/3 open blanks) (3/3 shorted wells)R(B): (10) Ω; R(W): (19 ± 3) ΩC(B): (10.2 ± 0.7) pF * not exposed** double exposed

35

S17 device 3 (well)5x

24

Discussion/Findings of Set 5• Wells have higher resistances than previous samples

• S14 (40 s wait)

– R(B) ≈ 4R(W), but R(B) has high standard deviation

• 1/4 Blanks Good C(B): 10 pF

• S15 (3 min wait)

– R(B) ≈ 2R(W), but R(B) has high standard deviation

– 2/4 Blanks Good C(B): (14.3 ± 0.4) pF

• S16 (2 min wait)

– R(W) > R(B), but R(W) has high standard deviation ?

– 3/4 Blanks Good C(B): (12 ± 1) pF

• S17 (SB:RT/PEB:90°C)

– R(W) ≈ 2R(B),

– 2/3 Blanks Good C(B): (10.2 ± 0.7) pF

• Summary:

– All samples have cracking – around the crossbars

– Double exposed areas (off crossbars) seem to have less ‘cracking’

– Blanks have inconsistent capacitance C = (12 ± 2) pF

37

Additional Questions Raised by Series 5

• What’s causing the cracking in the “pseudo-control” samples? Initial “controls” (S5, S6) have no cracking.

• Comparison of some parameters/results– Exposure settings the same. Same Dose: 90 mJ/cm2

– Develop time the same

– Slightly lower SB/PEB temp:

non-cracking/cracking: (93/90)°C

– C(S6): (9.6± 0.5) pF, C(S14-16): (12± 2) pF

• RT SB 60°C vs 90°C– Both cracked. So PEB temp doesn’t heal cracking

– R(W:60°C) < R(W:90°C); 5 Ω vs 18 Ω

– C(B:60°C) > C(B:90°C); 16 pF vs 10 pF