G'day,

A variable angle spectroscopic ellipsometer (VASE) may, even at that thickness,
give you pretty reliable data.  I doubt you want to buy one but there may well
be testing houses that will gather the data for you (Charles Evans and
Associates perhaps).

Cheers,
Matt

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of X Chen
Sent: Friday, August 13, 2004 4:12 PM
To: [email protected]
Subject: Spam:[mems-talk] refractive index measurement of thick films


Hello MEMS talkers,

Does anyone know a way to measure refractive index of thick films? I used
spectrophotometer to measure the VIS spectral transmission of 50 micron
SU-8 on Borofloat wafer. However, the transmittance modulation is just too
weak for reliable index fitting. With a large film thickness, light
coherence is lost due to finite bandwidth and surface vaiation. Reducing
film thickness to a few microns using SU-8 thinner will solve this problem
but I doubt the index will be different. I need to have a precise
dispersion curve (index vs. wavelength) for optical devices. The index
mentioned in publised papers varies greatly and is available only for a
few individual wavelengths. This index variation could be caused by
different processing conditions. Therefore, the index should ideally be
measured for my own process. But I would appreciate if someone can give me
a dispersion curve for SU-8 in VIS-NIR range.

Best regards,

Xianling Chen

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