Patent ID: 8168270

Claim:
A film formation method for forming a silicon oxide film containing a low concentration of nitrogen on a target substrate by CVD, in a process container configured to be selectively supplied with a silicon source gas, an oxygen gas, and ammonia gas and equipped with an exciting mechanism configured to generate plasma by exciting the oxygen gas and the ammonia gas, the method performing a plurality of cycles to laminate thin films, each of the cycles alternately comprising, in the order: a first supply step of supplying the ammonia gas to the process container without supplying either of the silicon source gas and the oxygen gas to the process container, the first supply step including an excitation period of supplying the ammonia gas to the process container while generating plasma of the ammonia gas by excitation in the exciting mechanism; a first intermediate step of supplying an inactive gas to the process container and exhausting gas from the process container without supplying any of the silicon source gas, the oxygen gas, and the ammonia gas to the process container; a second supply step of supplying the silicon source gas to the process container without supplying either of the oxygen gas and the ammonia gas to the process container, thereby forming an adsorption layer containing Si on the target substrate; and a third supply step of supplying the oxygen gas to the process container without supplying either of the silicon source gas and the ammonia gas to the process container, the third supply step including an excitation period of supplying the oxygen gas to the process container while generating plasma of the oxygen gas by excitation in the exciting mechanism, thereby oxidizing the adsorption layer, wherein the method uses conditions within reference conditions to set the low concentration of nitrogen to be not more than 0.7 atomic %, the reference conditions being such that the silicon source gas is a gas containing no amino group, which is selected from the group consisting of dichlorosilane, monosilane, tetrachlorosilane, disilane, hexachlorodisilane, and tetraethoxysilane, the first supply step is performed at beginning of the plurality of cycles to treat an initial underlying layer of the target substrate with ammonia radicals to assist formation of the adsorption layer in the second supply step performed next, and the process container is set at a temperature of 400 to 600° C. therein during each of the cycles, and is set at a pressure of 40 to 100 Pa and at a pressure of 40 to 400 Pa therein during the first and third supply steps, respectively.