Team:SUSTech Shenzhen/Notebook/Fabrication

Fabrication

Detailed Protocol

Detailed Protocol

Wash the glass mask holder by socking it in dilute ammonia water for over 1 hour, and refresh it with deionized water.

Wash the glass mask holder by socking it in dilute hydrochloric acid for over 1 hour, and refresh it with deionized water.

Wash the glass mask holder by socking it in positive photoresist remover for over 1 hour, and refresh it with deionized water.

Dry the glass mask holder in the drying oven.

Clean the mask film by wiping the two sides carefully on one direction with a clean paper socked in acetone.

Clean the mask for the second time film by wiping the two sides carefully on one direction with a clean paper socked in alcohol or isopropyl alcohol.

Fig. 4 Cleaning Photomask

Fix the mask film on to the mask holder with tape.

Fig. 5 Fixing Photomask

The tape can only touch the edges of the mask film in order to prevent contamination.

Pour some SU-8 2100 photoresist in a small bottle, keep it still in the refrigerator for at least a week(two weeks recommend) to remove the bobbles inside the photoresist.

Take the SU-8 photoresist out from the refrigerator, wait until the bottle hit room temperature, and carefully pour it on to a clean silicon wafer. The bottle should be held as close to the wafer as possible to prevent bobble from generating.

Fig. 6 Pouring Photoresist

Spin the wafer with photoresist on the spin coater with the following procedure.

Spin at 500 rpm for 10 seconds with acceleration time of 5 seconds.

Spin at 2000 rpm for 30 seconds with acceleration time of 5 seconds.

Spin at 500 rpm for 5 seconds with acceleration time of 5 seconds.

Stop with acceleration time of 5 seconds.

Fig. 7 Prepared to be Spin Coated

Fig. 8 Spin Coating

Bake the wafer on 65℃ hotplate for 5 minutes.

Fig. 9 Soft Bake at 65℃

Bake the wafer on 95℃ hotplate for 30 minutes.

Fig. 10 Soft Bake at 95℃

Keep the wafer still in room temperature for more than 1 hour and wait until the photoresist is dry enough.

Clean the backside of the wafer with a clean paper socked in SU-8 developer to remove excessive photoresist.

Fig. 11 Cleaning the Backside

Fix the wafer to the mask aligner.

Fig. 12 Fixing the Wafer

Place the mask holder on the wafer carefully.

Fig. 13 Placing the Photo Mask

Expose the wafer with the mask aligner with the exposure energy of 220 mJ/cm².

Bake the wafer on 65℃ hot plate for 5 minutes.

Fig. 14 Post Exposure Bake at 65℃

A visible pattern identical to the photomask will be seen in the film within 5 seconds after being placed on the hotplate.

Fig. 15 Pattern Seen During Post Exposure Bake

Bake the wafer on 95℃ hot plate for 12 minutes.

Keep the wafer still in room temperature for 15 minutes and wait until the photoresist is dry enough.

Pour fresh SU-8 developer into the container. Place the container on the shaking table and set the speed to 400rpm. Start the shaking table and wait for the speed to be stabilized.

Fig. 16 Pouring Developer

Put the wafer in the container and develop for 4 minutes.

Fig. 17 Developing

Spray and wash the developed image with fresh developer for approximately 10 seconds.

Fig. 18 Spraying Developer

Spray and wash the developed image with isopropyl alcohol for approximately 10 seconds.

Fig. 19 Spraying Isopropyl Alcohol

Air dry the wafer with nitrogen gun.

Bake the wafer on 150℃ hot plate for 20 minutes.

Check the developed image.

Fig. 20 Checking Developed Image

Fig. 21 Curing

Wait for the wafer to cool down.

Check the final image of the photoresist. The final image usually has a lot of defects at the edges of the channels. And due to the low transmittance of SU-8 photoresist to the low-wavelength light, the photoresist at the top side of the channel will absorb higher energy than the photoresist at the bottom, causing a trapezoidal cross section profile.

Fig. 22 Topside View of SU-8 Photoresist (5X)

Fig. 23 Topside View of SU-8 Photoresist (20X)

Fig. 24 Optical Transmittance of SU-8 Photoresist

Fig. 25 Cross Section Profile of SU-8 Photoresist under SEM

Mix about 30g PDMS base with about 3g curing agent (at the ratio of 10:1).

Wrap the wafer with tinfoil and pour the PDMS mix on to the wafer.

Put the wafer in the vacuum dryer to remove the bobbles inside.

Fig. 26 Removing Bobbles

Bake the wafer in the 80℃ drying oven for 3 hours.

Fig. 27 Baking PDMS

Take the wafer out and rip off the tinfoil.

Fig. 28 Baked PDMS

Carefully remove PDMS from the wafer and cut it into pieces on a piece of clean paper.

Fig. 29 Cutting PDMS

Fig. 30 PDMS Slices

Spray and wash the PDMS with alcohol.

Fig. 31 Spraying Alcohol

Spray and wash the PDMS with deionized water.

Fig. 32 Spraying Deionized Water

Air dry the wafer with nitrogen gun.

Fig. 33 Air Drying

Soak glass slides in 100g/L NaOH solution for 14~24 hours.

Fig. 34 Soaking Slides

Take the glass slides out, spray and wash them with deionized water.

Fig. 35 Spraying Deionized Water

Spray and wash the glass slides with alcohol.

Fig. 36 Spraying Alcohol

Spray and wash the glass slides with deionized water.

Fig. 37 Spraying Deionized Water

Air dry the wafer with nitrogen gun.

Fig. 38 Air Drying

Place the clean slides on a piece of tinfoil.

Fig. 39 Clean Slides

Dry the glass slides in the drying oven.

Fig. 40 Drying Glass Slides

Clean the glass slide in the ultra-violet ozone cleaner for 15 minutes.

Fig. 41 Cleaning in Ultra-Violet Ozone Cleaner

Take the slides out and wrap them with another piece of tinfoil.

Fig. 42 Wrapped Slides

Punch the holes for the tube on the PDMS.

Fig. 43 Punching Holes

Fig. 44 Punching Holes

Open the plasma cleaner and place the PDMS and the slide in the meddle. A piece of tinfoil should be placed under the PDMS.

Fig. 45 Glass Slide and PDMS in The Plasma Cleaner

Treat them with oxygen plasma for 1.5 minutes at 300W and the oxygen flow rate of 0.6mL/min.

Fig. 46 Plasma Cleaning

Stop the plasma cleaner and open the cover as soon as possible. Press the treated sides together and apply pressure in 5 seconds.

Fig. 47 Bonding

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