Plasma Descum: This procedure is used to remove thin residual layers of photoresist areas following photoresist development. These residual films are typically less than 1,000 Angstroms thick, but can interfere significantly in resolving the pattern during etching, especially if the pattern geometries are small (such as contact windows). A plasma descum can generally remove these residues in less than a minute.
The wafers or substrate is loaded into the reactor chamber, and a plasma is established by using oxygen. Some people add 4% CF4 if the resist is difficult to remove. A plasma is established for the appropriate time, usually about one minute and the system is vented to atmosphere. The wafers or sample is now ready for etching. Good uniformity is required for this process. The AutoGlow 200 is recommended for this application–a single wafer system that can accommodate up to a 200 mm wafer or square substrate and has both plasma or RIE configurations. A shower-head gas distribution option is suggested for improved uniformity.
Plasma descum process itself demands stringent control be maintained so as not to adversely affect the integrity of the photoresist layer or alter the pattern quality. Serious degradation in the uniformity of etching can result.
Yale University has several AutoGlow 200 systems that are used for plasma Descum. Here is their comment and link: The AutoGlow 200 is a basic plasma asher, enabled with O2 and Ar for substrate cleaning, descumming, and surface treatment. It can operate between 50 W and 300 W, typically at 300 mTorr. The two-level table design creates separate zones for high power film removal and low power cleaning. Note that the relationship between power and etch rate aren’t necessarily linear.
To see the Yale web site and their comments, click HERE.
To see a video of the AutoGlow 200 (bottom video) click HERE.