The present invention relates to ceramic heater system which heats a substrate in treatments, such as CVD (Chemical Vapor Deposition) and plasma etching, and to a substrate processing apparatus having this heater system installed therein.
The general fabrication of semiconductor devices includes a step of performing a vacuum treatment, such as CVD or plasma etching, on a semiconductor wafer to be processed. In such a treatment, a heat treatment for heating a semiconductor wafer to a predetermined temperature is carried out. To execute such a heat treatment, a heater is buried in a substrate support member. A typical conventional heater of this type is a stainless heater.
Ceramic heaters that are hard to be corroded by halogen-base gases which are used in processing semiconductor wafers and have a high heat exchanging efficiency have been developed recently and are becoming popular. Such a ceramic heater has a heat generating wire of a high-melting-point metal buried in a heater base which is a dense ceramic sintered body of AlN or the like and on the top of which a semiconductor wafer is to be mounted.
A heat treatment which is executed at the time of performing CVD, plasma CVD or the like is demanded of an extremely high uniform heating performance while heating a semiconductor wafer to 500° C. or higher.
Further, it is required that semiconductor wafers should be resistant to plasma during plasma etching.
Because it is difficult to provide the desired uniform heating by a ceramic heater alone, which is buried in the heater base, various schemes are attempted to achieve the uniform heating. For example, the technique that is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 272834/1995 has a fluid passage with a fine cross-sectional area provided between a semiconductor-wafer mounting surface of a ceramic heater base and a buried heater. The temperature differences at individual positions of the ceramic heater base are therefore reduced by the convection of a fluid flowing in the fluid passage, thereby ensuring a uniform heating temperature on the mounting surface.
There are demands for further improvement of the throughput in the fabrication of semiconductor devices is demanded of and for a shorter down time at the time of maintenance of the substrate processing apparatus.
For example, a single wafer type CVD system regularly executes in-situ cleaning with a halogen-base gas and needs to lower the temperature of a ceramic heater to 150 to 500° C. from a film deposition temperature of 700° C. As the conventional cooling time is about 3 hours, a shorter cooling time is demanded. The interior of the chamber is exposed to the atmosphere for maintenance or the like. The interior of the chamber is cooled to near the room temperature to facilitate the maintenance. The cooling requires a long time. It is demanded that the cooling be achieved within a short time.
The aforementioned technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 272834/1995 can cool the heater base by the flow of the fluid at the time of maintaining the processing apparatus that uses the ceramic heater. This can shorten the down time in which the apparatus is stopped.
Generally speaking, to provide a sufficient cooling performance, the cross-sectional area of the fluid passage should be increased to permit the flow of a larger amount of fluid to carry the heat out. This technique has been developed to mainly ensure uniform heating and does not provide a sufficient cooling performance. Since the technique is intended to make the heating temperature on the mounting surface even, however, it is necessary to avoid deterioration of the heating efficiency. This is achieved by preventing the heat transmission from the heater to the mounting surface from becoming lower, and requires that the cross-sectional area of the fluid passage be made as small as possible.
Therefore, the more the heating efficiency is improved, the less the performance of the cooling means for the heater becomes sufficient. The conventional technique suffers a limitation to shortening the time of cooling the heater base and faces a difficulty in satisfying the demanded short cooling time.