SU-8 Testing ( v1l)

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SU-8 Testing (v1l)

Thin SU8 on glass slideTest:Soft Bake (SB) and Post Exposure Bake (PEB)

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

– expected thickness: 600 nm2. Soft Bake (SB): 60 s @ 93°C3. 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°C5. Develop: 4 min in SU8 developer6. 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 min

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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

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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 range

1. Next thing to do is to estimate thickness from geometry from C1. 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.?)

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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

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2nd Test Results - “Control 1” S5Device Capacitanc

e(pF)Resistance(Ω)

Type

1 -1 29.4 B2 -1 0.5 W3 9.38 3.7x106 B4 -1 24 W5 -1 24 B6 -1 7 W7 -1 421 B8 -1 17 W

Summary: 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).

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S5 “Control” 100x

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“Control 2” S6Device Capacitanc

e(pF)Resistance(Ω)

Type

1 Damaged 9.7 4.6x106 W2 9.33 8.3x106 B3 Damaged 9.61 3.04x105 W4 9.4 1.05x107 B5 -1 142 W6 9.25 1.1x107 B7 -1 46 W8 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

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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.

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S6 “Control” 100x

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2.5 min SB S7Device Capacitanc

e(pF)Resistance(Ω)

Type

1 -1 13.4 W2 -1 428 B3 -1 10.8 W4 -1 294 B5 -1 3.7 W6 -1 5.7 B7 -1 4.1 W8 -1 11.6 B

Summary: All ShortedR(B): (185 ± 211) Ω; R(W): (8 ± 5) Ω

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S7 2.5min SB 100x

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5 min SB S8Device Capacitanc

e(pF)Resistance(Ω)

Type

1 -1 4.8 W2 -1 16 B3 -1 1.9 W4 -1 44 B5 -1 4.3 W6 -1 ? B7* 15.16 Very High W8 15.25 0.57x106 B

Summary: 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

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S8 5min SB 100x

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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).

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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

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• 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 W2 -1 B3 12 W4 19 B5 -1 W6 19 B7 19 W8 20 B

8 min - S9

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12 min - S10Device Capacitanc

e(pF)Resistance(Ω)

Type

1 -1 4.5 W2 -1 18 B3 -1 6.7 W4 -1 121 B5 -1 3.9 W6 -1 127 B7 -1 5 W8 -1 118 B

Summary: W: 4/4 Shorted B: 4/4 Shorted Avg Well Resistance: 5.0± 1.2Ω

Avg Blank Resistance: 96± 52Ω Double Exposed (16s)

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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

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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

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e(pF)Resistance(Ω)

Type

1 Not Exposed -1 - B2 Not Exposed -1 - W3 -1 2.4 B4 -1 11.4 W5 -1 9.5 B6 -1 1.7 W7 -1 12.4 B8 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?)

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e(pF)Resistance(Ω)

Type

1 13.99 - W2 15.66 - B3 -1 2.8 W4 15.53 - B5 -1 3.2 W6* -1 0.21 B7 -1 7.2 W8 -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.

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e(pF)Resistance(Ω)

Type

1 -1 6.2 W2 -1 140.7* B3 -1 6.1 W4 -1 1.5 B5 Not Exposed - - W6 -1 4.3 B7 -1 6.0 W8 -1 3.6 B

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

*Exclude?

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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)

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

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

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Distribution of Resistances for Shorted Blanks (all devices)

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

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SB @ RT PEB @ 60

T1E-good

SB @ 60 PEB @ 93

T2-3

SB @ 60 PEB @ 60

T4

SB @ 93 PEB @ 93

“Control” T1-3

inconsistentCracking No-cracking

E-no

goo

d

Next set:SB @ RT PEB @ 90

Keep track of timeE-?

Crack?

Next set:SB @ 90 PEB @ 90

“pseudo Control” Keep

track of timeE-?

Crack?Consistency?

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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

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S14Device Capacitanc

e(pF)Resistance(Ω)

Type

1 -1 6.2 W2 10 - B3 -1 18 W4 -1 1 B5 -1 3 W6 -1 0.9 B7 -1 11 W8 -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

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e(pF)Resistance(Ω)

Type

1 -1 13 W2 14 - B3 -1 18 W4 -1 0.2 B5 -1 22 W6 -1 59.6 B7 -1 16 W8 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

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S15 device 7 (well)5x

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e(pF)Resistance(Ω)

Type

1 -1 145 W2 12.5 - B3 -1 10 W4 12 - B5 -1 14 W6 -1 5 B7 -1 341 W8 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

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S16 device 6 (blank)5x

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e(pF)Resistance(Ω)

Type

1 -1 * W2 9.7 ** B3 -1 18 W4 -1 10 B5 -1 22 W6 10.7 - B7 -1 16 W8 -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

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S17 device 3 (well)5x

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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

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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

SU-8 Testing ( v1l)

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