WCM   Wafer Charging Monitors, Inc.

Frequently Asked Questions

The first section of this page deals with Basic FAQ's about wafer charging, the problems it can cause, and how wafer charging monitors can help. If you are already familiar with these issues, you can skip this section and go directly to the more Advanced FAQ's.

Basic FAQ's

1.Q. What is "wafer charging"?
A. Buildup of electrical charge on the surface of a wafer during any given wafer processing step.

2.Q. What kinds of processes can cause wafer charging?
A. Ion implantation, plasma etching, ashing, plasma deposition, and spray rinsing.

3.Q. Can wafer charging damage wafers?
A. Definitely! And this damage can reduce wafer yield, product reliability, or both.

4.Q. What structures are vulnerable to charging damage?
A. Thin gate oxides, shallow junctions, EEPROM cells, and others.

5.Q. How can I find out if I have a wafer charging problem?
A. By using WCM's "CHARM®-2" wafer charging monitors and ChargeMap® software.

6.Q. What is the best way to identify which equipment is responsible for charging damage?
A. Run a CHARM®-2 wafer through each process tool. If charging is a problem, the offending tool will stand out like a "sore thumb"!

7.Q. Can I also use CHARM®-2 wafers to help qualify new processing tools for production?
A. Yes. This can be done by comparing CHARM®-2 results from a presently used tool that is known to be "good" (in terms of not causing wafer charging damage) and the CHARM®-2 results from the new tool. If CHARM®-2 results for the new tool are better than or equal to those for the presently-used tool, then wafers processed in the new tool will also be free of wafer charging damage.

8.Q. How do WCM's "CHARM®-2" wafer charging monitor wafers work?
A. They contain specialized EEPROM-based sensors that measure the amount of charging during the actual wafer processing step.

9.Q. Do I need to modify my equipment to use CHARM®-2 wafers?
A. No.

10.Q. How are the monitor wafers used?
A. They are put through the actual wafer processing step that is being investigated and then the specialized EEPROM-based sensors are measured to determine the amount of charging.

11.Q. How many CHARM®-2 wafers are needed per experimental split to accurately quantify wafer charging in process equipment?
A. One. And since CHARM®-2 wafers can be re-used many times, they are very cost-effective.

12.Q. How reproducible are CHARM®-2 results?
A. CHARM®-2 results are very reproducible, wafer-to-wafer and lot-to-lot, since CHARM®-2 wafers are calibrated before use.

13.Q. How reliable are these monitors at predicting damage to product wafers?
A. When the charging results are "good", charging damage is very unlikely.
When the charging results are "bad", damage is likely.
When the results are "borderline", further testing is needed to be safe.

14.Q. Do I have to write my own test software to measure the monitor wafers?
A. No. WCM provides CHARM®-2 monitor test software for most Agilent (HP) and Keithley parametric testers.

15.Q. Can I use CHARM®-2 wafers if I do not have access to a tester?
A. Yes. WCM can test the wafers for you and provide you with a report (complete with wafer maps and J-V plots) summarizing the results.

16.Q. Does WCM provide application assistance for CHARM®-2?
A. Yes. WCM provides both application assistance and assistance with analysis of data to all its clients.

17.Q. Who uses "wafer charging monitors"?
A. Process equipment makers, to check out new processes and hardware designs, and process engineers to qualify or improve wafer fabrication processes.

18.Q. What are CHARM®-2 wafers used for?
A. CHARM®-2 wafers are most commonly used for identifying bad equipment, for monitoring equipment stability, for improving equipment and processes, for qualifying equipment after maintenance, and for improving wafer through-put.

19.Q. Who can I call to get a reference on the usefulness of these monitors?
A. WCM can supply names and phone numbers of clients who have agreed to provide "non-proprietary" references.

Advanced FAQ's

Click on any of the following process areas to see advanced FAQ's that relate to that area.


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