1. Field of the Invention
This invention relates to a process for forming a metal oxide film by means of a CVD system using a complex of a .beta.-diketone compound and a group IV metal glycolate.
2. Description of the Related Art
Complexes of metals of the group IV such as titanium, lead and zirconium are of importance as a material for forming a metal oxide thin film by chemical vapor deposition (hereinafter referred to as a CVD material). In particular, complexes metals of the group IV with .beta.-diketone compounds are known to be highly useful because of their high vapor pressure and high oxidation reactivity.
However, the metal complex of dipivaloylmethane (a .beta.-diketone compound), which is a typical CVD material, is labile per se and ready to decompose on reacting with moisture or carbon dioxide in air or oligomerize to change its vaporization characteristics. Japanese Patent Application Laid-Open No. 132776/93 proposes adding a nucleophilic organic substance, such as tetrahydrofuran or a glyme, to these metal complexes. Further, Japanese Patent Application Laid-Open No. 98444/93 teaches addition of an o-phenanthroline derivative or a crown ether to the metal complex for obtaining more stable complexes. However, these proposed complex adducts release the added moiety when exposed to high temperatures and come to have instable vaporization characteristics. A metal complex having satisfactory performance properties as a CVD material in practice has not been obtained yet.
It has therefore been desired to develop a chelating compound which does not require a complex stabilizer such as the above-described nucleophilic organic substance.
Japanese Patent Application Laid-Open No. 271253/93 discloses an alcoholatotitanium complex composed of 2 moles of dipivaloylmethane and 2 moles of a monohydric alcohol. This complex has a low evaporating temperature and exhibits satisfactory volatility and oxidation reactivity. Further, the complex can be synthesized with high purity.
Where a complex metal oxide film is formed by CVD, the CVD material of the group IV metal is used as a mixture with other metal complexes, such as complexes of barium, strontium or zirconium. Therefore, it is desired for the metal complex compound to be similar to other CVD materials in vaporization characteristics and oxidation decomposability and to have low reactivity to the other CVD materials so as not to change its own vaporization characteristics when mixed with other CVD materials.
In this respect, because the above-mentioned alcoholatotitanium complex has reactive monovalent alkoxide groups, it has high reactivity with other metal complexes in CVD thin film formation. The reaction product, which may be produced, differs from each metal complex before the reaction in vaporization characteristics or oxidation decomposability, which has made it difficult to control the composition of the complex metal oxide film.
Besides, in controlling the vaporization characteristics it is not favorable to control the vaporizing temperature by increasing the molecular weight of the metal complex, because such means a decrease in content of the metal as an active component.