SU-8 2015 Processing

This page describe the adequate process for patterning a silicon wafer/sample with SU-8 2015 photoresist. The final thickness of the SU-8 layer will be between 10 and 40µm. The whole process can last 1-2 hours. Preparation and wafer/sample cleaning are necessary the day prior to resist processing.

Introduction

SU-8 2000 is a high contrast, epoxy based photoresist designed for micromachining and other microelectronic applications, where a thick, chemically and thermally stable image is desired. It is a negative type of resist: the exposed and subsequently thermally cross-linked portions of the film are rendered insoluble to liquid developers. SU-8 2000 has excellent imaging characteristics and is capable of producing very high aspect ratio structures.  SU-8 2000 has very high optical transmission above 360 nm, which makes it ideally suited for imaging near vertical sidewalls in very thick films.
SU-8 2000 is best suited for permanent applications where it is imaged, cured and left on the device.

It is quite difficult to remove from the substrate.

It is mainly use to prepare mold for PDMS casting to create microfluidic devices.

Equipment needed

Preliminaries

  • Make sure the cartridge has been filled with the appropriate resist at least 12h before using it
  • Check that the green air lines on the Site coater are plugged to this cartridge
  • Measure the lamp intensity with the SU-8 filter - report to lamp intensity check SOP for more details.

Process steps

Using Site Service Spin coater for 4 and 6in wafers

Step# Step Name Tool Recipe Comments
1 Clean Solvent WB Solvent Clean  A solvent clean is necessary to ensure optimal surface quality of the substrate prior to processing
2 Native oxide remove HF WB BOE or dilute HF etch SU8 adhesion is much stronger on fresh silicon. SU8 adhesion on oxides is problematic and requires a surface treatment.
3 Dehydration Oven 150°C - 30min Improves the adhesion by removing moisture from the surface.
4 Coat and softbake Site Service Spin coater SU8-2015.LN This will perform a coating and softbake @ 95°C. Change the speed and softbake time according to the wanted thickness. Go to spin curve section for more info.
5 Exposition EVG620 su8.rcp The exposure dosage will vary depending on the resist thickness. Report to process table for more details.
6 Post-exposure bake Site Service Spin coater SU-8-PEB.LN 95°C bake. time will vary depending on resist thickness. Check process table for more details.
7 Develop Litho WB 2 beakers Use two beakers labeled "SU8 ONLY". One for SU8 developer and one for IPA rinse. After PEB allow the wafer/sample to rest one minute to cool down before developing. Soak wafer/sample in developer and agitate every minute to help development. When time's up (see process table), rinse with IPA. If a white film is observed, develop more and rinse again until no white film is observable during IPa rinsing.
8 Spin dry Laurell B 1st step is @ 500rpm for more rinsing with IPA and 2nd step is @ 2500rpm for drying. Drying can also be done using a N2 gun.
9 Hardbake Hotplate 5min @ 150°C Hard bake the wafer/sample on the 2nd hotplate to "cure" the cracks formed during development and further harden the resist.

Process table

Thickness Speed Softbake @ 95°C Exposure Post-Exposure bake Development
10um      
20um      
30um      
40um      

Note that exposure dosage are given as a starting point and for specific pattern an exposition matrix should be done to determine the optimal parameter. As a rule of thumb, underexposure will lead to pattern liftoff and overexposure will lead to non vertical sidewall and feature size increase.

 More process tips can be found in the SU8-2000 datasheet.

Technical Data and References