Hello Chu,

SEMI standard SEMI P27-96 - PARAMETER CHECKLIST FOR RESIST THICKNESS
MEASUREMENT ON A SUBSTRATE refers to the ANSI standard ASTM F804 -
Standard Practice for Producing Spin Coating Resist Curves, 7.4
Thickness Measuring Instrument. Unfortunately this standard has been
withdrawn without replacement, so I do not know whether it contains
required information. You can contact globalcustomerservice@ihs.com to
obtain the copy.

To my experience, most common way of defining the resist coating
uniformity I met is (MAX - MIN)/(2*AVERAGE)*100% - this way you will get
coating uniformity in +/- XX% from average value (+/- before value is
important) or (MAX - MIN)/(AVERAGE)*100% where you of coarse do not use
+/- notation.

(MAX - MIN)/(2*MAX)*100% is also often used as well as (MAX -
MIN)/(MAX)*100%.

Using the StDev or 3*StDev is another approach, if you have enough data
for one wafer (>30) - nevertheless I would recommend to do the normality
test on the data before you use StDev - if your data do not follow the
normal distribution (and the distribution of resist thickness usually
does not) the meaning of the StDev will be different than to normal
distribution. 3*StDev will not represent 99,7% of you data etc.

Maybe the best to use is specification for SEMI MF1618-1104 - PRACTICE
FOR DETERMINATION OF UNIFORMITY OF THIN FILMS ON SILICON WAFERS

which defines parameter Standard Deviation Uniformity, SUP, in percent
like SUP(%) = standard dev./average.

Best regards,

Daniel Figura

EV Group
invent * innovate * implement
Process Technology Engineer - Phone: +43 7712 5311 0, Fax: +43 7712 53111500
E-Mail: D.Figura@EVGroup.com, Web: www.EVGroup.com

-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of GQ Chu
Sent: Mittwoch, 28. Januar 2009 18:32
To: General MEMS discussion
Subject: [mems-talk] PR Thickness Uniformity Calculation

Hello:

I need your help. What is the formula you use to calculate your PR thickness
uniformity across the wafer? Where is the reference or source for this, is
it ANSI standard calculation or SEMI standard calculation? Can you please
help me site the source? I'm having an argument with few people how to
calculate it. What is the industry standard and where can I find that source
to calcualte it.