Instructions for Stsetch Process Qualification
Purpose: to provide verification and trend of the DEEP program
including etch rates of silicon and photoresist, selectivity of those
materials, and within-a-wafer uniformity of etch.
of the test: to be completed after
major maintenance such as cleaning or gas line replacement or on a set schedule
to be determined or as needed based on user feedback.
of results: to be posted on the log
sheet located in the assigned book at the tool, posted in the equipment archive
for amtetcher on the SNF website and in a file or webpage available to users in
data or chart format.
- Use wafers with 3 or 7 um layer of SPR220
photoresist. The wafer should have
the resolution mask used in litho area.
- Measure photoresist thickness using one of the
Nanospecs. Be sure to use
reference wafer before testing to calibrate the tool. Take readings for the Center, Top,
Bottom, Right and Flat positions of the wafer. Readings should be taken about 20mm from the edge. Use Statistics feature to get mean
value. See Fig.1.
- Season the chamber for 10 minutes using the
DEEP. Be sure to check the program
parameters before starting.
- Etch the wafer for 10 minutes. Monitor gas flows, RF power and chamber
pressure during passivation and etch.
Record on Process Qualification Log Form.
- Measure photoresist thickness using the same
Nanospec. Be sure to use reference
wafer before testing to calibrate the tool. Take readings for the Center, Top, Bottom, Right and Flat
positions of the wafer. Use
Statistics feature to get mean value.
Readings should be taken about 20mm from the edge. Record in the Log.
- Subtract the mean values of the pre-etch measurements
from the post-etch measurements.
This gives you the amount of photoresist etched.
- Measure the depth of the etch using one of the
calibrated microscopes. Focus
first on the photoresist then, using a smooth motion, focus on the bottom
of the etch. Choose a larger feature and focus in a corner. This may be somewhat difficult as the
etch is not very deep and not too roughed up. Two tricks: 1) look for texture or 2) ‘crawl’ down the
sidewall to the bottom.
- Take readings in about the same 5 places as you took
readings for the photoresist. Once you get consistent readings in each
spot, record the measurement in the Log.
- Subtract the photoresist measurement from Step 6 from
the etch measurement to get the etch depth.
- Record results on the Monitor Log. Record results in
data file to get within-a-wafer uniformity.
- To get the total amount of photoresist etched,
subtract the average of the second reading from the average of the first
- To get the etch rate per minute divide the etch
measurements by 10.
- To get the selectivity of silicon to photoresist
divide the etch rate of Si by the etch rate of PR.
Figure 1: Reading placement. Note that the major flat is to the “left.”