1.  Field of the Invention
The present invention relates to a semiconductor device manufacturing method and a substrate processing apparatus for depositing a ruthenium film or films on a substrate by using a raw material gas, which contains ruthenium, and an oxygen-containing gas, which contains oxygen. 
2.  Description of the Related Art
In the past, when a ruthenium film is deposited on a silicon wafer by a thermal CVD method by using a raw material gas containing ruthenium and an oxygen-containing gas containing oxygen, the oxygen-containing gas, which is the gas with a greater flow rate of supply, is supplied prior to or earlier than the ruthenium raw gas, which is the gas with a smaller flow rate of supply, as illustrated in FIG.  7. ( Line a represents a change in the amount of supply of the ruthenium raw gas, and line b represents a change in the amount of supply of the oxygen-containing gas.)  This is carried out so as to suppress pressure fluctuations at the time of deposition.  That is, the supply of the ruthenium raw gas is started to initiate deposition of ruthenium films after the amount of supply of the oxygen-containing gas becomes constant.  Then, after the deposition of the ruthenium films is completed, the supply of the oxygen-containing gas is stopped after the supply of the ruthenium raw gas is stopped. 
However, in such a gas supply method, the oxygen ratio, i.e., the volume ratio of the oxygen-containing gas to the ruthenium raw gas becomes greater before the start of deposition (before time t1) and after the end of deposition (after time t2), and hence oxygen becomes excessive so that ruthenium oxide can be easily formed, thus impairing homogeneity or uniformity in the film quality of the ruthenium films.  Also, the sheet resistance or the like of the ruthenium films becomes non-uniform, and the reproducibility of the surface morphology becomes poor, too. 
The present invention is intended to obviate the problems as referred to above, and has for its object to provide a semiconductor device manufacturing method and a substrate processing apparatus which is capable of depositing a ruthenium film with excellent homogeneity in the film quality and excellent reproducibility of the surface morphology. 
In order to achieve this object, according to the present invention, in a semiconductor device manufacturing method in which a ruthenium film is deposited on a substrate by using a raw material gas containing ruthenium and an oxygen-containing gas containing oxygen, an oxygen ratio before the start of deposition of the ruthenium film or after the end of deposition thereof is controlled to be smaller than an oxygen ratio at the time of deposition thereof.  Incidentally, note that the oxygen ratio referred to herein means a volume ratio of the oxygen-containing gas to the ruthenium raw gas. 
Moreover, in a semiconductor device manufacturing method in which a ruthenium film is deposited on a substrate by using a raw material gas containing ruthenium and an oxygen-containing gas containing oxygen, an oxygen ratio before the start of deposition of the ruthenium film or after the end of deposition thereof is controlled to be not greater than a value at which there takes place no deposition reaction. 
In these cases, the raw material gas may be supplied earlier than the oxygen-containing gas before the start of deposition of the ruthenium film. 
In addition, the amount of supply of the oxygen-containing gas before the start of deposition may be gradually increased when the raw material gas and the oxygen-containing gas are supplied at the same time before the start of deposition of the ruthenium film. 
Further, the amount of supply of the oxygen-containing gas before the start of deposition may be controlled to be smaller than the amount of supply of the oxygen-containing gas at the time of deposition, or the amount of supply of the oxygen-containing gas before the start of deposition may be controlled to be not greater than a value at which there takes place no deposition reaction. 
Furthermore, the supply of the oxygen-containing gas may be stopped earlier than the supply of the raw material gas after the end of deposition of the ruthenium film. 
Still further, the amount of supply of the oxygen-containing gas after the end of deposition may be gradually decreased when the supply of the raw material gas and the supply of the oxygen-containing gas are stopped at the same time after the end of deposition of the ruthenium film. 
Besides, when the supply of the raw material gas is stopped earlier than the supply of the oxygen-containing gas after the end of deposition of the ruthenium film, the amount of supply of the oxygen-containing gas after the end of deposition may be controlled to be smaller than the amount of supply of the oxygen-containing gas at the time of deposition, or the amount of supply of the oxygen-containing gas after the end of deposition may be controlled to be not greater than a value at which there takes place no deposition reaction. 
Additionally, a gas, which does not contribute to deposition reactions, may be introduced before the start of deposition of the ruthenium film or after the end of deposition thereof so as to hold substantially constant the pressures before the start of deposition, at the time of deposition and after the end of deposition. 
Moreover, the present invention may be characterized in that the raw material gas containing ruthenium comprises a gas evaporated from Ru(C2H5C5H4)2, and that the oxygen-containing gas containing oxygen comprises an O2 gas. 
Furthermore, the present invention provides a substrate processing apparatus in which a ruthenium film is deposited on a substrate in a reaction chamber by using a raw material gas containing ruthenium and an oxygen-containing gas containing oxygen, the apparatus being characterized by comprising: an oxygen-containing gas supply section for supplying the oxygen-containing gas to a reaction chamber; a raw material gas supply section for supplying the raw material gas to the reaction chamber; and a controller for controlling the oxygen-containing gas supply section and the raw material gas supply section in such a manner that an oxygen ratio before the start of deposition of the ruthenium film or after the end of deposition thereof is made smaller than an oxygen ratio at the time of deposition thereof.