SU-8 and polyimide in the STS

Ginel Hill ginel at
Wed Aug 17 11:22:56 PDT 2005

1.  Contact information:  Ginel Hill, coral login: ginel, 650-387-8208,
ghill at, PI for project: Prof. Beth Pruitt.

2.  Material:  We would like to fabricate and compare pressure-sensing
diaphragms made with two different materials: SU-8 and polyimide.  SU-8 is
an epoxidized bisphenol-A/formaldehyde novolac copolymer that is available
in two different formulations from Microchem.  The original SU-8 series
formulation uses gamma butyrolacetone as a solvent, while the newer SU-8
2000 series uses cyclopentanone as a solvent.

We are interested in using PI-2610, a polyimide manufactured by HD
microsystems in their LX series; SU-8 2, an original series Microchem
formulation; SU-8 2002, a 2000-series Microchem formulation; VM652, a
propylene glycol methyl ether sold as a polyimide adhesion promoter by HD
Microsystems;  and SU-8 developer from Microchem.

Both SU-8 and polyimide are currently allowed in the SNF. However, we
would like permission to use the materials in the process flow attached.

3.  SU-8 Manufacturer: Microchem, 1254 Chestnut Street, Newton MA 02464,
Polyimide manufacturer: HD Microsystems, Parlin Plant, Cheesecake Rd,
Parlin NJ 08859.  732-613-2278

4.  Reason for request:  We have previously fabricated and tested a
pressure-sensing device constructed from SU-8.  (Please see attached MEMS
paper.)  A 2 um SU-8 layer was used to form a diaphragm that deflects
under pressure, and a 50 um SU-8 layer set the cavity length of a
fabry-perot interferometer formed between the diaphragm and the end of a
fiber optic cable.  The interferometer measures cavity length, which is
affected by pressure-induced deflections of the diaphragm, as well as by
length changes in the 50 um cavity length layer from absorbtion or thermal
expansion.  While retaining a flexible polymer diaphragm in device to
maximize its sensitivity, the device could be improved by use of a
non-polymer material for the cavity length layer that does not swell from
water absorbtion.  Our proposed design incorporates a 50 um Silicon wafer
as the cavity length and fiber sleeve layers but retains a polymer

5.  Process flow:  See attached run sheet.  Note that the process would
EITHER use sheet 2A for SU-8 OR sheet 2B for polyimide, but not both.
The overall outline is:
1 - Etch alignment marks into a standard Silicon wafer
2 - Deposit an Aluminum release layer
  - Spin and pattern a polymer diaphragm layer of SU-8 OR polyimide
3 - Clean and grow Si02 for hard mask on a separate 50 um Si wafer
  - Bond 50 um wafer to handle wafer using thermocompression bonding
4 - Etch holes through 50 um wafer to see alignment marks on handle wafer
  - Etch 10 um Si in the 50 um wafer to form sleeve layer
5 - Etch cavity holes through 50 um wafer
  - Deposit metal reflector (Cr-Au) on polymer diaphram
6 - Insert fiber, glue, and release devices outside of snf

6.  Amount and Form:  Presumably, one to several 100 mL bottles of each
polymer in a solvent as formulated by the manufacturer.  It is possible we
might experiment with several different formulations.  Additionally, a
bottle of a polyimide adhesion promoter.

7. Storage: polyimide in the freezer in the back area of the clean room;
SU-8, and polyimide adhesion promoter in the solvent storage cabinet in
the clean room.

-------------- next part --------------
A non-text attachment was scrubbed...
Name: BP2rs_081505.xls
Type: application/octet-stream
Size: 95744 bytes
URL: <>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: BPpaper5.pdf
Type: application/pdf
Size: 462388 bytes
URL: <>

More information about the specmat mailing list