In fabricating a semiconductor device, a process of depositing a film on a wafer is performed in a chamber. During the deposition process, the material to form the film are deposited on the inside walls of the chamber as well as on the wafer thereby forming an undesired film on the chamber walls. If a sufficient amount of the undesired film is deposited on the chamber walls, the particles of the undesired film may fall from the inside walls of the chamber onto the wafer, thereby causing defects in the wafer or in a device fabricated on the wafer. To obviate the possibility of falling particles from the undesired film causing defects, a cleaning process is periodically performed wherein clean gas supplied into the chamber to remove the undesired film in the chamber. The type of clean gas is selected based on the type and the thickness of the undesired film deposited in the chamber. The cleaning process is performed until the undesired film in the chamber is completely removed. The time spent attempting to remove an undesired film in a chamber is defined as clean time. The clean time is the most important factor in performing a cleaning process. If the clean time is too short, the undesired film in the chamber may not be completely removed. On the contrary, if the clean time is too long, the inside walls of the chamber may be damaged.
A conventional cleaning process is performed at a constant pressure in a chamber. The clean time is determined by using an endpoint detector. The endpoint detector detects the intensity of a specific wavelength of the cleaning gas. When the intensity of the wavelength detected by the endpoint detector is stabilized, the cleaning process is finished.
FIG. 1 is a graph illustrating wavelengths detected by an endpoint detector. Referring to FIG. 1, the end point of a cleaning process occurs when a concentration trend is stabilized.
Korean patent publication number 10-2001-0004243, which is assigned to Hynix Semiconductor Inc., describes a method for cleaning a plasma chamber of semiconductor device manufacturing equipment. The described method of cleaning a plasma chamber includes performing a polysilicon etch-back process within a plasma chamber, flowing mixed gas into the plasma chamber to form a plasma for chamber cleaning, and performing a plasma cleaning to remove a polymer from the inner wall of the plasma chamber. The plasma cleaning process is performed without unloading a run wafer and with the bottom bias power set at 1˜800 W, and by applying a top power at 1000˜3000 W.
This conventional cleaning technology determines the clean time by using an endpoint detector which detects the intensity of a specific wavelength for the cleaning gas. However, when residual products generated during the cleaning process influence the intensity of the wavelength or when the position of the endpoint detector is changed, the cleaning process may not be sufficiently performed.