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.

Frequency 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.

Documentation 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.

1. Use wafers with 3 or 7 um layer of SPR220 photoresist. The wafer should have the resolution mask used in litho area.
2. 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.
3. Season the chamber for 10 minutes using the DEEP. Be sure to check the program parameters before starting.
4. Etch the wafer for 10 minutes. Monitor gas flows, RF power and chamber pressure during passivation and etch. Record on Process Qualification Log Form.
5. 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.
6. Subtract the mean values of the pre-etch measurements from the post-etch measurements. This gives you the amount of photoresist etched.
7. 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.
8. 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.
9. Subtract the photoresist measurement from Step 6 from the etch measurement to get the etch depth.
10. 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 reading.
• 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.”