by Debra Vogler, Senior Technical Editor, Solid State Technology
Buildup of chemical residues inside an ion implanter limits the tool’s overall utilization efficiency. James Dunn, Atmel Corp.’s equipment engineering section manager, described for WaferNEWS the results of the company’s evaluation of a new in situ chemical cleaning technology from ATMI that reduces such deposits and achieves greater predictability for source change-outs.
Deposit build-up is one cause of ion beam instability, which in turn adversely affects process integrity. Two major problems arise from ion beam instability. One problem is momentary drop-out in the beam current on the wafer being processed because of high-voltage arcing, which leads to undesired species being implanted into the process wafer for a certain period of time, according to Dunn. Such high-voltage glitches result in the nonuniformity of implants and particle contamination. Another kind of beam instability causes drifting of the beam current, which leads to dose errors. These process integrity problems lead to unpredictable change-out of the ion source.
While source lifetimes vary according to implanter type (i.e., medium-current vs. high-current) as well as application, according to Dunn, a typical medium current implanter application at Atmel might see a variation in source life between 200-500 hrs, when the actual filament life should be 500hrs.
During Atmel’s evaluation of ATMI’s AutoClean process — an in situ process that introduces a cleaning agent at regular intervals into the ion implanter — Dunn told WaferNEWS that 100% of the sources subject to the purge process have gone to the end of filament life (500hrs) — and even higher in some cases (see figure). During the evaluation, process qualifications and particle checks were done and the results indicated no harm was done to the wafers using the new cleaning technology.
According to Dunn, the fab’s population of medium current implanters has averaged 292 hours of source life, which translates to 27 source changes per tool per year. The two sources running AutoClean have averaged double that lifetime (588 hrs) with the third source still running stable with 501.28 hours, he said, and the company expects its annual source changes to drop to 13-14 per tool per year, “thereby reducing our costs for cleaning and consumable parts by 50%.” Dunn noted that the source changes average 5hrs to complete, involving the actual source change and also tool re-qualification, so fewer source changes with the new tools “translates to 65 hours of additional production time per tool per year, and a reduction of one-half the process qualifications, which frees up additional processing and metrology equipment in the fab.”
An additional benefit of using the new technology cited by ATMI is the ability to do species rotation, for example, being able to run a phosphorus process immediately after a boron process or vice versa. Having the ability to be flexible is becoming more important as fabs need to have shorter reaction times to respond to customer demand. — D.V.
IMAGE: Effect of in situ cleaning on ion source life. (Source: Atmel Corp.)