In the process for forming a film by depositing silicon nitride (Si3N4), silicon oxide (SiOx) or polysilicon, etc. on a wafer in the method for manufacturing ICs, the batch type vertical hot wall low pressure CVD device is widely utilized and comprises a process tube including a processing chamber for forming film on multiple wafers while held in a boat; and a standby chamber formed directly below the process tube for allowing the boat to await loading into or unloading from the processing chamber; and a boat elevator for raising or lowering the boat for loading into or unloading from the processing chamber.
A CVD device of this type in the prior art is a batch type vertical hot wall low pressure CVD device (hereafter called a load-lock CVD device) of the load-lock system in which the standby chamber is formed by a vacuum container (referred to as a load-lock chamber) for withstanding a pressure below atmospheric pressure (for example, see Japanese patent No. 3239977).
The load-lock system separates the processing chamber and the loading/unloading chamber by using a separation valve such as a gate valve to prevent air from flowing into the processing chamber, and minimizing external disturbances from temperature and pressure to stabilize the process.
The load-lock chamber (vacuum container) forming the standby chamber in the load-lock CVD device is built from stainless steel or cast iron for structure possessing large mechanical strength to withstand a pressure below atmospheric pressure and so the load-lock chamber has the problem of a large weight.
Constructing the load-lock chamber in load-lock CVD devices from aluminum for a light weight and corrosion resistance is considered. However, the thermal conductivity of the aluminum (236 W/m·K at 0° C., 240 W/m·K at 100° C.) is large compared to the thermal conductivity of stainless steel (16.3 W/m·K at 0° C. to 100° C.). This method therefore possesses the problem that vacuum seal welding on material with a plate thickness of 20 millimeters or more is extremely difficult with the TIG (tungsten inert gas) welding method and MIG (metal inert gas) welding method.
Methods to construct a vacuum container of aluminum without welding include a manufacturing method for cutting out the container from a clump of aluminum or the aluminum diecast method. However, along with limits on the depth of the cutting direction and the size of the metal mold, when the cutting depth and size of the metal mold become too large, the material costs become excessive so utilizing these methods is not practical for manufacturing large capacity vacuum containers.
The present invention therefore has the object of providing a light-weight and low cost container that can be manufactured by welding, as well as a manufacturing method for a substrate processing device utilizing that container and a method for manufacturing semiconductor devices.