The present invention relates to a method for controlling chemical vapor deposition (CVD).
In general, the films grown utilizing a C V D have heretofore been conducted according to the following method.
A reacting gas A and a mixed gas B are introduced into a reactor, and a substrate on which a film is to be formed is heated in the reactor, whereby a film is formed on the surface of the substrate. The kinds of the reacting gas A and mixed gas B are changed depending on the material of the film to be formed. For example, when it is intended to deposit SiO.sub.2 films, O.sub.2 is used as the reacting gas A and a mixed gas of N.sub.2 and SiH.sub.4 is used as the mixed gas B. In case phosphorus is doped in the SiO.sub.2 film, PH.sub.3 is additionally admitted into the mixed gas B of N.sub.2 and SiH.sub.4. When it is intended to form Si.sub.3 N.sub.4 films, NH.sub.3 is used as the reacting gas A and a mixed gas of N.sub.2 and SiH.sub.4 is used as the mixed gas B. Also the substrate temperature is changed depending on the material of the film to be formed. For example, in the case of SiO.sub. 2 films, the substrate is heated at about 400.degree. C, and in the case of Si.sub.3 N.sub.4, the substrate is heated at about 900.degree. C. In order to obtain a homogeneous composition of the film and uniform film in the thickness, the substrate is placed on a susceptor and this susceptor is subjected to rotation and revolution. Further, at the film-forming step, the total gas pressure in the reactor is maintained at substantially one atmosphere.
For films deposited by this method, it is required that the composition should be homogeneous throughout the entire surfaces of the substrates; the thickness should be uniform and such defects as pin holes and flakes should not be formed.
However, films formed by the C V D are not always satisfactory in the foregoing points. One of the causes is the so-called fogging phenomenon, that is large particles of the film-forming substance fall on the substrate. This phenomenon is explained as follows:
In some combination of the reacting gas A and mixed gas B to be reacted with each other, the reaction between the reactants proceeds very promptly. Therefore, the moment reactants are introduced into the reactor, particles of the film-forming substance are formed. As the particles move in the reactor towards the substrate disposed below in the reactor, they grow and large particles come to fall on the substrate. When this fogging phenomenon takes place, these large particles are mingled with the film-forming substance to be deposited on the substrate, such as silicon wafer, and defects such as pin holes and flakes are caused on the resulting film.