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Thin SU8 on Glass Slide Testing Results and Discussion

This study presents testing and analysis of SU8 thin film on a glass slide, evaluating soft bake, post-exposure bake, misalignment effects, cracking patterns, and resistance measurements. The findings and discussions of multiple sets of tests are discussed in detail.

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Thin SU8 on Glass Slide Testing Results and Discussion

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  1. SU-8 Testing (v1j) • Thin SU8 on glass slide • Test: • Soft Bake (SB) and • Post Exposure Bake (PEB)

  2. “Control” Recipe • Spin Coating: 10 s @ 500 rpm; 30 s @ 2000 rpm • expected thickness: 600 nm • Soft Bake (SB): 60 s @ 93°C • Exposure: 8 s @ 275 W • PEB: 60s @ 93°C • Develop: 4 min in SU8 developer • SU8 developer rinse • 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 2

  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 • 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 • 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 • Next thing to do is to estimate thickness from geometry from C • The two longer time ones exhibit ~10% larger C (difference in dielectric constants or thickness?) • 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” S5 Summary: W: 4/4 Shorted B: 3/4 Shorted R(W): (12 ± 10) Ω Excluding #3 R(B): (158± 230) Ω C(B,#3) – very low (9.38 pF) compared to 1st set but comparable to S6 (also a Control - next slide).

  7. “Control 2” S6 Summary: W: 2/4 Shorted (2 Damaged by high voltage – 1V) B: 0/4 Shorted R(W): (94± 68) Ω; C(B): (9.6± 0.5) pF

  8. 2.5 min SB S7 Summary: All Shorted R(B): (185 ± 211) Ω; R(W): (8 ± 5) Ω

  9. 5 min SB S8 Summary: W: 3/4 Shorted (why not 4/4?) B: 3/4 Shorted R(Blank): (30 ± 20) Ω (#8 excluded) R(Well): (3.7 ± 1.6) Ω (#7 excluded) 7*: Re-measured and consistent with capacitance

  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

  11. “Control 2” @ 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. “Control 2” 100x 12

  13. “Control1” 100x 13

  14. 2.5min SB 100x 14

  15. 5min SB 100x 15

  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. 8 min - S9 • 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)

  18. 12 min - S10 Summary: 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 S11 • Summary: B:3/3 Shorted; W: 2/3 Shorted, 1/3 open • R(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 S12 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 S13 Summary: All Shorted R(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)

  25. Next set: SB @ RT PEB @ 93 Keep track of time E-? Crack? Next set: SB @ 90 PEB @ 90 “Control2”Keep track of time E-? Crack? Consistency? SB @ RT PEB @ 60 T1 E-good SB @ 93 PEB @ 93 “Control” T1-3 inconsistent SB @ 60 PEB @ 60 T4 SB @ 60 PEB @ 93 T2-3 Cracking No-cracking E-no good

  26. Distribution of Resistances for “Shorted” Wells • 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: …

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