The present invention relates to methods and apparatus for cleaning a chemical vapor deposition (CVD) chamber.
During CVD processing, the reactant gases can create compositions which deposit upon the inside surfaces of the chamber. As these deposits build up, the residues can flake off and contaminate future processing steps. Such residue deposits can also adversely affect other processing conditions such as deposition uniformity, deposition rate, film strength and the like.
Accordingly, processing chambers are typically periodically cleaned to remove the residue material. Typically, the use of etching gases is used to clean the chamber after each process or after a few processes are run through the chamber. After longer periods of time, typically 1000-2000 wafers, the chamber is opened up and cleaned by hand using rinse water and clean wipes. Clearly, it is desirable to minimize the amount of cleaning time required in order to improve the throughput of wafers through the processing chamber.
The cleaning using the cleaning gases typically involves a plasma enhanced dry cleaning technique. These techniques require a separate process step which requires introducing the cleaning gases into the chamber, striking a plasma from the cleaning gases, and using the-plasma to remove contaminant residues. Typically, fluorine is used as a cleaning gas species. Descriptions of such a cleaning process may be found, for instance, in U.S. Pat. Nos. 4,960,488 and 5,124,958, assigned to Applied Materials, Inc.
A disadvantage of the dry cleaning operation is that it contributes to the degradation of the wafer support, such as a susceptor, which is typically made of aluminum. A susceptor typically has an anodized layer on its surface, which forms some protection. However, during a plasma cleaning process, the fluorine chemistry of a conventional cleaning process can penetrate an anodized layer and cause the formation of aluminum fluoride. This usually occurs at point defect sites in the anodized layer, which results in the formation of nodules, cracks, and delamination. This formation of aluminum fluoride or other compounds can cause uniformity and particle problems on process wafers subsequently placed on the wafer support.
One method for addressing the above degradation of a susceptor is to use a two step cleaning process, as set forth in U.S. Pat. No. 5,158,644, assigned to Applied Materials, Inc. In that two step process, the chamber is first cleaned in an extended state in which the susceptor is lowered to be well spaced from the gas discharge manifold, thus limiting the amount of plasma reaching the susceptor by decreasing the plasma due to the distance between the susceptor and the gas discharge head. With this configuration, the plasma will be somewhat redirected to the grounded walls of the chamber to effect cleaning there. In a second step, the susceptor is moved back up close to the gas discharge head for cleaning of the susceptor itself. The two step process reduces the amount of time the susceptor is exposed to a high intensity plasma.