-------------------------------------------------- Jun 7 2011 Cleaned 2-inch SSP wafer (doping unknown, surplus) with presaturated Texwipe (70% IPA / 30% DI water), air dried. Spin coated with ~0.25 ml of Emulsitone Tantalumfilm. Adhesion was good but numerous pinholes were observed due to surface contamination. Edges of wafer were not completely covered, not enough Tantalumfilm was used for a good coating. Baked wafer in air for 1 hour at 200C. Film evenness appeared to have slightly improved but pinholes were still present. Cleaved wafer perpendicular to flat, broke smaller piece parallel to flat and created 7 dies ~2mm square from resulting piece. Placed in gel box #5, positions A1-A7. Initial inspection at 10x/30x. A1: Very uneven coating, some large holes, but a few good areas. Yellow plus some purple rings. A2: Lots of midsized pinholes. Pink to orange. A3: Pretty even, lots of medium-small pinholes. Yellow. A4: A few large holes, some small ones. Deep purple. A5: One large hole, a few small ones. Even coating. Yellow. A6: Very even, a few medium-small holes. Yellow. A7: Extremely uneven (edge of wafer). Larger pinholes. Purple. Coating appears relatively thick - 150-200nm. Etched die A2 in 3% HF for 5 minutes at room temperature. No detectable thinning of film. Etched die A2 in 3% HF for 5 minutes at 50C (water bath). Most of the film was removed, some traces left in thicker areas. After another 5 minutes all but the thickest spots are gone. More heat is probably advisable for future etches. Prepared developer - 550mg NaOH in 50ml distilled water. Spin coated die A6 in Shipley SP24 photoresist. Exposed 15um half-pitch test pattern for 12 minutes using 40x objective and microscope halogen lamp. Developed, looks pretty sharp. Etched hardmask on A6 in 3% HF for 5 minutes in 65C water bath. Poor photoresist adhesion observed, hardmask not entirely etched. Baked wafer on hot plate for 5 minutes in hopes of improving adhesion of remaining resist. Many of the stress patterns disappeared, indicating successful increase in adhesion. (Photoresist was later found floating in Rinse 1 bath indicating thermal shock from heated HF to cold rinse as a possible source of adhesion problems.) Returned A6 to HF for 3 minutes. Hardmask is not quite gone in surrounding areas, needs a little more time. Etched hardmask for another 3 minutes. Hardmask still not fully penetrated, but PR is flaking off still. Aborted processing and returned A6 to gel box for future analysis. -------------------------------------------------- June 8: Cleaved several more dies out of Ta2O5-coated wafer. Placed in gel box #5, positions A8 - C2. Cell B2 was skipped due to poor adhesion. Prepared 30% KOH / 15% IPA / 55% distilled water etchant: 7.5 ml 99% IPA dissolved in 27.5ml distilled water, followed by 15 g KOH under low heat. Spattering from stirrer was observed, beaker was removed from heat and spatter removed from hot plate surface. After cooling, beaker was gently reheated to 65C while stirring slowly. Etched die B7 for 5 minutes at 65C (expected etch depth 2.5um). Returned to heat at 80C for another 5 mins to ensure a deep etch (expected depth 6.25um, total 8.75 um). No agitation during etch. Very nice etching observed, snapped a few pictures. Placed water bath on hot plate to preheat before etching. Stripped hardmask with 3% HF in 70C water bath for 15 minutes. Some traces of hardmask left in thick spots but almost entirely removed. Processing on B7 completed, ready for SEM imaging. Returned to gel tray. Removed B3-B6 from gel tray (all are similar condition; yellow with a few pinholes) and spin coated with SP24 resist for ~30 sec. Soft baked at 85C for 30 seconds. Most dies stuck to carrier wafer and were scratched during removal. Exposed first die for 30 sec using new 1W UV LED. Developed, severely underexposed. Placed in gel tray at B3. Exposed second die for 60 sec. Developed, also underexposed. Placed in gel tray at B4. Exposed third die for 5 mins. Developed, most fine features obliterated. Looks overexposed. Placed in gel tray at B5. Might try etching later since the FOV ring is intact. Exposed fourth die for 2 mins. Looks slightly out of focus; UV method definitely needs some tweaks. Hard baked B6 at 110C for 60 sec. Wet etched in 3% HF in 75C water bath for 15 minutes. Serious bubbling of photoresist observed but it stayed mostly intact. Stripped photoresist in acetone. Die now appears almost blank, looks like hardmask is gone. Returned B6 to die tray and stopped work for the night. -------------------------------------------------- June 9: Placed die A3 (fairly even gold color) in petri dish containing colloidal silica and rubbed against bottom of dish for 1 minute. Film was slightly abraded but far from removed. Some pinholes grew in size. Returned to die tray. Cleaved a small piece of <100> SSP Si from a 2-inch wafer. Cleaned in acetone and IPA, baked on hot plate at 80C for 2 min. Prepared a solution of 2 drops Tantalumfilm in 5 drops denatured alcohol; spin coated one drop onto test wafer at maximum speed. Coating had pinholes due to surface contamination. Stripped coating by rubbing with denatured alcohol and a Texwipe. Some traces remained around edges but center was clear. Cleaned wafer in acetone and IPA; baked on hot plate at 110C for 2 min. Spin coated using 2:5 dilution of Tantalumfilm in denatured alcohol. A deep blue-violet film resulted, changing to brown as the solvent evaporated. Estimated film thickness 65nm. Baked in air for 1 hour at 200C. No significant color change. Placed in 2-inch cassette for future processing. Diced wafer and placed in die tray at C5 - E5. Initial visual inspection of film quality: some pinholes but overall quite good. -------------------------------------------------- June 11: Etched die D3 in 3% HF for 5 mins at 35C (bath had not been allowed to heat adequately). No etching observed. Waited for bath to heat to 55C and etched for 5 minutes. Light brown areas of coating were completely removed; thicker areas remained in part. Returned to die tray. Spin coated die C8 in SP24 photoresist; soft baked on hot plate for 30 sec at 100C. Exposed companion cube test mask for 15 minutes using halogen-exposure process and 40x objective. Did not develop properly for reasons unknown. Stripped resist in acetone and re-coated. Soft baked for 15 sec. Exposed 10um pitch ruler as contact mask for 5 mins using 1W UV LED. Developed and hard baked for 90 sec on 110C hot plate. Etched in 3% HF for 5 mins at ~80C. Photoresist still severely damaged. Stripped in acetone, all features obliterated. Returned C8 to die tray. Spin coated C9 in photoresist, soft baked for 30 sec. Exposed 400um pitch ruler as contact mask for 5 mins using 1W UV LED. Developed, etched for 2 mins in 3% HF at ~80C. No excessive PR damage observed. Stripped PR in acetone. Unsure if hardmask was completely etched or not, coating is very thin and hard to observe. Wet etched in KOH for 2 mins at ~60C. Looks like hardmask was not completely penetrated. Returned C9 to die tray. -------------------------------------------------- June 13: Spin coated die C10 in SP24 resist (slow speed for thick coating), soft baked 90 sec at 80C. Exposed 15 minutes using halogen microscope lamp and developed. Hard baked 5 mins at 125C. Slight bubbling was observed. Allowed to cool, baked another 3 mins at 130C. No additional bubbling observed, looks like resist is adequately outgassed. Wet etched 2 mins in dilute HF in 85C water bath. Some etching observed but some PR degradation. Much improved over previous etches, more baking might help more. Returned to HF for 4 minutes. Can't tell if hardmask is etched through. Stripped resist in acetone, pattern was almost obliterated. Returned C10 to die tray. Spin coated D2 in SP24 resist at low speed, soft baked 60 sec at 130C with silicon spacer. Exposed cross pattern for 5 minutes using UV LED. Developed but did not hard bake, returned to die tray for future processing. -------------------------------------------------- June 16: Spin coated five dies (D6-7-8-9, E4) in SP24 resist. Preparation: acetone rinse, IPA rinse, dehydration bake for 3 min on 140 C hot plate. Used low speed for thick film. Soft baked all dies for 60 sec on 120 C hot plate, moved to hot carrier wafer for 2 min, let cool. Exposed all dies for 8 mins using UV LED and contact mask, developed. No hard bake. Prepared five etch tubes: A - distilled water B - 3% HF C - HCl solution diluted to same pH as HF D - 3% HF buffered to near-neutral pH with NaOH E - 3% HF Heated all tubes but E in 61C water bath, etched 5 mins. Suctioned etchants, rinsed, imaged. A - no visible damage. Returned to die tray, D6. B - lots of small bubbles, one big chunk cracked off. Returned to die tray, D7. C - No visible damage. Returned to die tray, D8. D - completely obliterated, no trace of resist. Returned to die tray, D9. E - lots of big chunks broken off. Returned to die tray, E4. -------------------------------------------------- June 17: Scribed several more dies out of blank <100> wafer, placed in die tray (E7:F3). Spin coated E7 in SP24 resist, soft baked 60 sec, exposed companion cube 15 mins under microscope at 10x objective, developed. No hard bake. Spin coated E7 and E8 in 2:5 dilution of Tantalumfilm in denatured alcohol. Tested un-baked Tantalumfilm on E8 for acetone resistance, no degradation observed. Inspected E7 under microscope, good lift-off profile visible. Lifted off E7 in acetone with gentle rubbing of a cleanroom swab. Sonication would be preferable but no ultrasonic cleaner was available and this was just a test. Results were very good, took several images. Baked E7 at 200C for 1 hour, returned to die tray. -------------------------------------------------- June 18: Etched E7 in 30% KOH / 15% IPA for 5 mins at 85C. Visually inspected under microscope, some black contamination (not sure what). Etch isn't that deep, stuck it back in the KOH for another 5 mins. Stripped hardmask in 3% HF for 5 mins in water bath. Contamination still present, not identified. Returned E7 to die tray. -------------------------------------------------- June 19: Spin coated E9 and E10 in SP24 resist, soft baked 60 sec at 80C. Preparation: 90 sec dehydration bake at 80C, acetone rinse, blow dry. Exposed darkfield companion cube mask on E9 through camera tube with Mag-Lite for 15 minutes using 10x objective, developed. Some areas underexposed due to uneven illumination, imperfect focus, but most features resolved. Spin coated E9 with one drop of undiluted Tantalumfilm. Some damage to resist observed, possibly from solvent? Lifted off, severe damage to film visible. Need thicker layer next time. Returned E9 to die tray. Exposed darkfield companion cube mask on E10 thorough camera tube with Mag-Lite for 15 minutes using 10x objective, developed. Spin coated E10 with one drop of undiluted Tantalumfilm at maximum speed. Coverage in low-lying areas was poor. Wondering if contamination on die after developing is responsible. Placed one drop of IPA onto die, blew dry. Spin coated with another drop of Tantalumfilm, using lower speed. Poorer lift-off profile observed. Lifted off in acetone. Decent results - film looks undamaaged, but some residue around desired areas. Baked E10 in air at 200C for 1 hour. Some cracking observed. Etched in 30% KOH at 95C for 5 mins. Hardmask appears to have broken off - thermal shock? Some traces of patterns still visible. Need to try less aggressive etch. -------------------------------------------------- June 20: Spin coated F1 with SP24 resist. Preparation: acetone rinse, blow dry. Soft baked at 70 C for 90 sec. Exposed darkfield companion cube mask at 10 objective through photo port for 15 minutes. Die slipped out of tweezers during developing and was slightly overdeveloped. Spin coated with one drop of Tantalumfilm at moderate speed. Tantalumfilm was allowed to soak too long, photoresist degraded. Aborted processing, returning to die tray. Forgot to take pictures before coating. -------------------------------------------------- June 22: Prepared several short pieces of 406 micron tungsten wire and 5 mL of 20% KOH solution. Electropolished one piece of wire for 5 minutes at 140 mA (2VDC) until wire broke. Looks very sharp, almost definitely submicron tip. Repeated for another probe. Duller (a micron or so?), possibly not immersed deep enough. -------------------------------------------------- June 23: Prepared solution of 4 ml distilled water : 500mg KOH. Etched three probes at 3VDC. Nice tips but not super sharp, 2um ish. Going to try building a more repeatable power supply in the future. -------------------------------------------------- June 25: Prepared several more specimens from <100> Si (doping unknown), placed in die tray at F4:G3. Spin coated dies F2:G3 with SP24 resist, soft baked 60 sec at 80C. Three dies had severe edge rings, stripped and returned to die tray (F2:F4). Remaining dies looked good, placed in gel tray in light-tight bag (F5:G3) for future work. No time to run any litho experiments tonight. -------------------------------------------------- June 27: Tried making probe tips again. Etched 120 sec at 3V, followed by 1.0V until snapping. First try was decent but no record. Second attempt looks to be 1.05 um diameter / ~500nm radius. Exposed die F6 for 15 mins using darkfield companion cube at 100x. Developed, hard baked 120 sec at 140C. As expected, some underexposed areas due to flashlight exposure but otherwise fine. Spin coated one drop of 30% Tantalumfilm in denatured alcohol at high speed. Coating was patchy as expected, brown. Applied a second coat, one layer at high speed, without baking. Coating was uneven but a bit thicker, blue. Applied a third coat, one layer at high speed, without baking. Blue to yellow. Lifted off resist in acetone, looks very good. Preheated oven to 200C while processing F9, stuck F6 in die tray in the meantime. Processed F9 in same manner as F6, stopped before hard bake, returned to die tray. Processed G2 in same manner as F6, stopped before hardmask deposition. Hot plate heated to 160C since then. Returned to die tray. Baked F6 in air at 200C for 60 mins. Looks good, some roughness but no visible cracking. Possible test dies to do later: TODO: after etch? TODO: before hardmask bake TODO: before lift-off TODO: before hard bake Samples to SEM image (in order of priority): Left hand probe tip, F6, G2, F9, E10, C9, C6, E5. -------------------------------------------------- June 28: Brought tray 5 up to campus, temporarily storing today's runs in tray 6 until done with SEM work on Thurs. Processed G3 in same manner as F6. Hardmask still has strange black particles in it, some chipping on edges. Baked for 1 hour at 200C. Processed F7 in same manner as F6 but used one drop of full-strength Tantalumfilm. Totally black surface, still no idea what it is. Baked one hour at 200C. Etched G3 for two 1 min periods in 30% KOH (no IPA) at 60C. Looks good so far but needs more time. Etched G3 another 2 mins nonstop. Hardmask appears to have degraded. Removed F7 from oven, inspected. No signs of thermal cracking. Etched F7 for 1 min in 30% KOH at ~80C. Hardmask started to degrade after first etch step, thermal shock? Stopped KOH etching, stripped hardmask in 3% HF in 60C water bath for 90 sec. Not stripped completly, left in bath for another 5 mins. Strange crystals visible. pH strip shows slight alkalinity (pH ~9) in rinse water, this may be the problem. Changed rinse water. Replaced acid in etch tube, stripped for 10 mins. Still not removed. Going to repeat experiment tomorrow with separate rinse for acid and base steps. -------------------------------------------------- Jul 5 and 11: Imaged several samples (F6, F7, G2, G3) and one probe tip under JEOL JSM-840 scanning electron microscope after sputtering in ~100A of Pt. Probe tip was bumpy but sharp, final point was roughly cylindrical and 200nm in diameter. Performed EDS analysis of contaminant on F6. Results were inconclusive - one particle of brass and one of organic dust were located, but the majority of contaminated surface showed nothing but silicon, tantalum chloride, and tantalum oxide. -------------------------------------------------- Jul 14: Inspected wafer test dies were taken from under light microscopy. Clearly visible particulate contamination. Current hypothesis is that careless handling of wafer during scribing allowed silicon dust to stick to surface. Created new Glade library lithography_tests/default_600dpi for test patterns optimized for 600DPI printing. Lambda is 42.333um on the mask or 1.058 um on the dies at 40x reduction. Initial design rules: * Minimum axially aligned trench = 5 lambda / 5.290 um * Minimum axially aligned space = 5 lambda / 5.290 um * Minimum axially aligned feature = 5 lambda / 5.290 um * Reticle size = 500 lambda / 529 um disk Created test pattern: 20x20 dots, 5 lambda across, 5 lambda spacing. Printed positive and negative versions of mask. Cleaned two dies by rubbing with cleanroom swab saturated in 70% IPA, then dripping IPA onto die and blowing dry. Particle counts decreased significantly, nearly eliminated. Ran both dies through slightly modified RCA clean: * Distilled water soak * SC1 (6 ml 3% H2O2 + 1 ml household ammonia @ 85C) for 10 mins * Distilled water soak for 1 min * 3% HF for 15 sec * Distilled water soak for 1 min * SC2 (6 ml 3% H2O2 + 1 ml conc HCl) for 10 min * Distilled water soak for 1 min * Blow dry with R-134A Spin coated both dies in SP24 resist, soft baked 1 min at 55C. Exposed 20um dots pattern on first die for 15 mins using maglite. Developed, all small features obliterated (developer too strong?) Spin coated with one drop of full strength Tantalumfilm, lifted off in acetone using swab. Some residue dried onto die, not sure if this will be enough to contaminate results. Exposed second 20um holes pattern on second die for 15 mins using maglite, developed. Looks slightly underexposed but many holes resolved. Spin coated with one drop of dilute Tantalumfilm, lifted off in beaker of acetone to avoid surface contaminants drying. Results look pretty good. Baked both dies in air at 200C for 1 hour. Slight cracking observed. Etched first die in 30% KOH at 85C for 2 min. Hardmask broke off. Returned to die tray, G4. Etched second die in 30% KOH at 85C for 30 sec. Not much etching observed, tossed in another 30 sec. Repeated once more. Stripped in 3% HF at 85C for 1 min. Hardmask not removed, stripped another 10 mins. Not completely stripped (but visibly thinned), out of time for tonight. Returned to die tray, G5. -------------------------------------------------- Jul 19: Prepared substrates for evaporation tests on Thursday: scribe, wipe with acetone-soaked swab, acetone rinse, IPA rinse, blow dry with R-134a. 6A3-6A4: <100> Si, SSP 6A5-6B7: glass microscope coverslip Prepared 50% dilution of SP24 resist in acetone. Exposed an older die with 20um dark-points mask, developed. Spin coated with 1 drop of dilute Tantalumfilm, lifted off in acetone. Pattern severely degraded, looks like it had dust under the mask. Returned to die tray, G6. Spin coated G7 and G8 (<100> Si) with diluted resist. Soft baked for 90 sec. Exposed comb drive test mask through 10x objective on G7 for 10 mins, developed. Beautiful results, except for the usual artifacts caused by use of a maglite instead of a uniform light source. Spin coated in one drop of full strength Tantalumfilm, dried, repeated. Lifted off in acetone. Way too much Tantalumfilm, coating didnt lift off fully. Returned to die tray, G7. Exposed comb drive test mask through 40x objective on G8 for 10 mins, developed. Focuser drifted during exposure, blurred beyond usability. Returned to die tray. -------------------------------------------------- Jul 20: Cleaved several tantalum oxide-coated dies out of original test wafer. Cleaned one die in acetone, spin coated in 50% diluted SP24 photoresist. Soft baked 90 sec at 75C. Exposed darkfield companion cube mask at 10x for 10 minutes, developed. Made centrifuge tube of BOE solution - 3% HF + household ammonia titrated to neutral pH. Etched die in BOE in 80C water bath for 60 sec. No visible etching. Returned to BOE bath for 3 mins. Some degradation of mask visible after rinse. Annealed at 90C for 90 sec. Returned to BOE bath for 5 mins. Resist severely degraded, no significant attack of hardmask. Returned to die tray, 5G9. Spin coated second die in 50% SP24, soft baked 90 sec. Exposed darkfield companion cube mask at 10x for 10 minutes. Developed, spin coated in full strength Tantalumfilm. Rough dark-colored pattern again, looks like photoresist is definitely the contaminant. Will test a deliberate mixture of the two tomorrow. Returned to die tray, 5G10. -------------------------------------------------- Jul 21: Coated several samples with evaporated copper (exact thickness unknown, around 200nm is current estimate): * Quarter of 2" <100> SSP wafer, bare * Quarter of 2" <100> SSP wafer with tantalum oxide thin film * Two <100> SSP dies, bare * 13 glass substrates (from microscope cover slip) Inspected glass sample under light microscope. Some slight defects, unsure of cause so far. Performed "Scotch tape test" on glass sample to test adhesion. Near-complete delamination observed. Etched glass sample in 3% HF in 70C water bath for 5 mins. Film did not degrade, but delaminated. Spin coated silicon sample in 50% SP24, soft baked 90 sec at 90C. Exposed comb drive wet etch mask at 10x for 10 mins, developed. Etched 1 min in SC2 at 80C. Photoresist degraded (overetch?). Stripped in acetone, pattern obliterated. Returned to die tray, 5H1. Spin coated silicon sample in 50% SP24, soft baked 90 sec at 90C. Exposed comb drive wet etch mask at 10x for 12 mins, developed. Wet etched in SC2 at room temperature for 60 sec. Not fully etched, put in for another 60. Etch appears to have penetrated sideways into Cu film, not sure of reason for this. Returned to die tray, 5H2. -------------------------------------------------- Jul 22: Etched Cu-coated glass sample in SC2 until film was removed. Less than 5 seconds to near-complete removal (some traces visible). Scribed Ta2O5 + Cu thin film coated wafer to release several dies, cleaned with acetone rinse + blow dry. Placed in die tray, 6C1 - 6C7. Spin coated one sample in 50% SP24 resist, soft baked 90 sec at 70 C. Exposed darkfield companion cube mask at 10x for 10 mins, developed. Wet etched 5 sec in SC2, copper completely removed from exposed areas. Placed in heated 3% HF, leaving PR intact (mechanical barrier to help hold Cu in place). Etched 5 mins. Copper separated from oxide layer during rinse, oxide not fully penetrated. Returned die to HF for 5 more mins. Mask is gone so isotropic etch will widen features, but it may be good enough for a PoC. Too long, all features obliterated. Going to repeat this experiment using 8 min initial etch. Returned to die tray, 5H3. Spin coated one sample in 50% SP24, soft baked 90 sec. Exposed darkfield companion cube mask at 10x for 10 mins, developed. Wet etched 5 sec in SC2, copper completely removed from exposed areas. Placed in heated 3% HF, etched 8 mins. Mask degraded but seems to have survived long enough to have a significant effect. If oxide layer is thinner this process should be very successful. Stripped remaining photoresist and copper in acetone followed by SC2. Inspected sample under optical microscope. Hardmask is definitely degraded from undercut of Cu, but there may be enough left for a shallow etch. Wet etched 2 mins in 30% KOH, rinsed in water. Dark precipitate visible on surface of etched areas, not sure what it is. Attempted to remove with SC2 at room temp for a few sec, no results. Attempted to remove by swabbing with IPA, no success. Attempted to remove with 60C SC2 for 10 mins, no luck. Stripped hardmask in heated 3% HF for 5 mins. Returned to die tray, 5H4. -------------------------------------------------- Jul 24: Spin coated Cu-coated glass substrate in 50% SP24, soft baked. Exposed negative twin-spiral mask at 10x for 10 mins, developed. Etched in SC2. Discovered after rinse that the wrong sample had been used - it was actually Ta2O5 + Cu coated Si. Going to cross section this die to measure typical layer thicknesses. Returned to die tray, 5H5. Spin coated Cu-coated glass substrate in 50% SP24, soft baked. Exposed Nyan Cat mask at 40x for 10 mins, developed. Exposed Nyan Cat mask on same die at 10x for 10 mins, developed. Etched in SC2. Overetched, possibly due to double exposure weakening resist. Returned to die tray, 5H6. -------------------------------------------------- Jul 30: Etched Cu-coated glass substrate in 30% KOH for 10 mins, increasing heat from 50C to 80C. Copper did not visibly degrade but delaminated from substrate. Looks like an adhesion layer of some sort will be necessary for future experiments. Created dilute SC2 solution: 8 ml 3% H2O2 and 0.5 ml conc. HCl, tested with Cu-coated Si sample. Too strong. Diluted solution further - 1 ml of SC2 solution to 4 ml distilled water. Complete etch of film in around 8 sec. -------------------------------------------------- Aug 06: Spin coated Cu-coated Si substrate in 50% SP24, soft baked. Exposed Nyan Cat mask for 10 mins with 10x objective, developed, hard baked. Created slow Cu etch based on SC2: 0.1 ml conc. HCl, 0.5 ml 3% H2O2, 5 ml distilled water. Projected etch rate: 350-400nm/min assuming linear variation with concentration. Etched die for 15 sec, stripped in acetone. Layer not fully penetrated. Re-coated same die, exposed, developed, baked. Etched die for 30 sec, stripped in acetone. Very good results. Returned to die tray, H7. -------------------------------------------------- Aug 11: Spin coated cu-coated Si substrate in 50% SP24, soft baked. Exposed ruler mask for 10 mins with 10x objective using fiber-optic illuminator and tissue-paper diffuser. Image was too dim, not adequately exposed. Repeated using maglite, developed. Wet etched in dilute SC2. Etched die for 8 mins in 80C 3% HF. As with previous samples, delamination of Cu and PR layers (as a unit) was observed upon placing sample in rinse water. HF was observed to have penetrated sample through etched holes in Cu. Cr adhesion layer is definitely going to be necessary but process appears sound otherwise. Returned to die tray, H8. -------------------------------------------------- Aug 15: Prepared coating solution: 0.2 ml Tantalumfilm in 1.8 ml denatured alcohol. Placed 2-inch 2SP <110> wafer on spin coater, swabbed with acetone, spin dried. First attempt at spin coating Tantalumfilm failed: coating beaded up for reasons unknown. Stripped in denatured alcohol followed by HF dip to remove native oxide and start clean. Baked in air at 200C for 10 mins to promote growth of new oxide layer. Repeated process except without acetone rinse. Same result. Stripped, soaked wafer in 3% H2O2 (room temp 15 mins, low heat on hot plate 10 mins). Beginning to suspect that my denatured alcohol is unsuitable for diluting Tantalumfilm. One of the additives destroys the proper surface tension. Re-coated using pure Tantalumfilm. Some pinholes (probably due to residue from previous experiments). Baked in air for 1 hour at 200C. Coated other side of wafer with pure Tantalumfilm. Poor coverage for reasons unknown. This can be the back side as some defects there are tolerable. Baked in air 1 hour at 200C. -------------------------------------------------- Aug 16: Evaporated ~10nm Cr + ~1000nm Cu over two 2-inch <110> wafers - both sides of 2SP wafer prepared yesterday and polished side of a blank 1SP wafer. -------------------------------------------------- Sep 13: Cleaved several dies out of a <110> wafer (SSP, 10nm Cr, 1000nm Cu) and spin coated with SP24 resist. Air dried, no soft bake. Exposed five dies with varying parameters using fiber optic illuminator at maximum brightness and min-space parallel-lines mask. I3: 10 mins, 10x objective. Severely overexposed. I4: 5 mins, 10x objective. Very good. I5: 5 mins, 40x objective. Overdeveloped. I6: 5 mins, 40x objective. Blurred. I7: 5 min, 10x objective. Very good. Etched I4 and I7 in full strength SC2, no discernable overetch. Planning to X-section one and top-down image the other on JSM-840 SEM in the near future. Ideally, a cross-section sample prep method can be found which does not attack photoresist so edge profiles can be observed. -------------------------------------------------- Sep 15: Performed two tests of double patterning (dies I8 and I9) at 10x reduction with 2:30 time per exposure. Half-exposed areas were removed so only fully unexposed areas were left, rather than full and half. Wet etched I4 and I9 in SC2 until copper was removed, plus an extra ~15 seconds to remove Cr. Wet etched both in KOH for 10-15 mins at ~80C in water bath. No etching of Si observed - Cr incompletely removed? -------------------------------------------------- Sep 16: Attempted to polish a piece of copper-clad FR4 and <111> Si (unpolished solar wafer fragment) using Ted Pella diamond paste. Polishing definitely worked however deep gouges were observed in the sample. Suspected cause is large abrasive particles not being completely removed before going to smaller sizes. -------------------------------------------------- Sep 18: Performed a test of double patterning (die 5I10) at 10x reduction. One minute per exposure. Severe line edge roughness, looks slightly underexposed. Wet etched in SC2 until copper was removed, returned to die tray. Most likely last test before SEM session. Dies to image: * I3 or I8: (cross section, need to SC2 before prep) empty disk with some traces of lines * I4: 20um lines in Cu:Cr over <110> Si, no resist, partial KOH etch not penetrating Si * I7: 20um lines in Cu:Cr over <110> Si, with resist. * I10: 20um lines in Cu:Cr over <110> Si, with resist, very rough sidewalls -------------------------------------------------- Sep 26: Began tests to determine how to remove Cr adhesion layer from trenches. Prepared several dies, <110> with Cu:Cr. Wet etched in SC2 for 5 mins at around 70C, rinsed. No visible surface film, copper was removed after only a few seconds. Subsequent KOH etch failed to attack the surface - Cr must still be there. Created new etch bath from 2 ml of conc. HCl. Placed die in at room temp, no attack of copper observed (as expected). Added a couple of drops of 3% H2O2 and stirred. Copper film dissolved rapidly. Left die in etch for several minutes to allow Cr to etch; then rinsed and etched in KOH. Die etched as expected - this looks like a good etch. Next step is to test if photoresist can mask it. Spin coated several <110> + Cu:Cr dies in 50% SP24. Exposed 50um line test pattern (4x) for 5 mins. Stepped sideways on die, exposed 20um lines (10x) for 5 mins. Etched in low-peroxide HCl:H2O2 for 60 sec. Copper was severely undercut. Etched in 30% KOH for 5 mins. Looks pretty good, seems that undercut Cu did not translate to damaged Cr. Stripped in SC2. Looks good except for some litho defects. Returned to die tray, J2. Exposed 20um lines for 4 mins at 10x, developed. Etched in low-peroxide HCl:H2O2 for 60 sec. Etched in 30% KOH for 30 mins. Cr was etched through in some spots (perhaps HCl etch was too long?) but overall a very good first die. Copper was attacked (though some traces were present in sporadic locations). This goes against data reported in several other sources indicating that KOH did not significantly attack copper - no explanation for this deviation yet. Possibly contamination in KOH or impure copper? Both were technical grade (drain cleaner and scrap AC power cord) and the KOH solution had been used several times before on different chips. Stripped last remaining Cu residue in SC2 (no attempt made to remove Cr hardmask residue) and photographed. Returned to die tray, J3. -------------------------------------------------- Oct 21: Not much work done recently due to academic obligations. Spin coated 2-inch <110> wafer in 50% SP24, soft baked on low heat. Exposed comb drive die separation mask by contact lithography (germicidal tube) for 5 minutes, developed. Very good results but some PR contamination on back side of wafer observed. Cleaned back side of wafer with acetone. Full clean should probably be done after top side Cr evaporation and lift-off before coating reverse. -------------------------------------------------- Oct 24: Evaporated ~1000nm Cr followed by ~100nm Cu over top side of wafer prepared on the 21st, flipped over and repeated for the back. Uneven Cr deposition on the bell jar of the evaporator was observed during the first evaporation - much higher near the top of the jar and very little near the samples. The top copper layer failed the "Scotch tape test". Reasons for the apparent failure of Cr deposition are unknown at this point. Lifted off hardmask layer in acetone with gentle rubbing. Copper peeled and tore, confirming poor adhesion. Etched wafer in KOH anyway to see what would happen, and test whether Cr was actually present. Copper dissolved almost immediately. Very slight masking was observed, but after a few minutes the etching was fairly uniform across the entire wafer. Experiment will need to be repeated.