As film forming methods to form a film on a substrate, e.g., a semiconductor wafer (hereinafter, referred to as a “wafer”), there are known methods such as a chemical vapor deposition (CVD) method for depositing sediment by reacting reaction gases on a surface of the wafer and an atomic layer deposition (ALD) method or a multi-layer deposition method (MLD) for depositing sediment by sequentially providing a plurality of reaction gases, which are reactive to each other, to the wafer to thereby absorb the reaction gases and deposit sediment onto a surface of the wafer (hereinafter, generally referred to as a ALD method).
Some of the reaction gases, which are easy to penetrate into a gap between members among various reaction gases used in the CVD method or the ALD method, may penetrate into a gap between the wafer and a mounting table thereof. Such penetration causes a film forming even on a lateral side or a back side of the wafer. If the film forming is performed on these regions, particles may be generated due to the contact with a transfer arm for transferring the wafer, which may become a pollution source of the wafer.
For example in a conventional film forming method, there is a technology where an edge part of the wafer positioned on a mounting table is covered by using a circular shaped clamp ring to thereby limit an area on which the film forming process is performed. However, it may be difficult to prevent the film formation at a back side of the wafer just by contacting the clamp ring because the reaction gases are likely to penetrate into the gap between the members (referred to as penetrability). Thus, the conventional film forming method is not capable of preventing reaction gases with high penetrability from moving to the back of the wafer.