Generally, various steps in a manufacturing process of a semiconductor integrated circuit, such as a forming a film step, an oxidation diffusion step, an etching step and others are repeated to be carried out on a surface of a semiconductor wafer which is an object body of the above-mentioned processes. A concave part such as a contact hole or through hole is formed during the manufacturing process of the semiconductor integrated circuit. There is a tendency that a metal tungsten film formed by a chemical vapor deposition method (CVD method) is mostly utilized to be embedded into the concave part. The metal tungsten film formed by the CVD method has a high covering ability, a robustness of the wire snapping, and a low specific resistance and is relatively easy to be formed.
It is general, as a method of forming a film of the metal tungsten, to supply a WF6 (tungsten hexafluoride) gas as an ingredient gas including a tungsten and a H2 (hydrogen) gas as a reduction gas, to reduce WF6 by H2 in a state of a temperature in a range between 400 and 450° C., and to form a film of the metal tungsten on a TiN (titanium nitride) film as a base film mainly.
The TiN film formed by a physical vapor deposition method (PVD method) or a CVD method is generally utilized as a base film because of the following reasons. Firstly, it is necessary to form a film of tungsten equally on a whole of a surface of the wafer. This is because metal tungsten formed by a H2 reduction method has different rates of forming a film on between a metal surface and an insulator surface. Secondly, the base film is necessary as a barrier preventing WF6 which is an ingredient of tungsten from encroaching a lower layer.
A conventional process of forming the metal tungsten will be described as follows.
During the process of forming a film of metal tungsten, if the film is attempted to be formed by the CVD method from the beginning of the process, it is hard to stick the film on the surface of the wafer and there is a tendency in that an incubation time becomes long. In order to prevent the above-described state, firstly a WF6 gas as an ingredient gas, a H2 gas as a reduction gas, a SiH4 (monosilane) gas, and the like are flown a small amount each, so that a nucleus making layer of tungsten which is a crystal seed is grown on the surface of the wafer. Next, the large amount of the above-mentioned ingredient gas or the reduction gas is flown, thereby the tungsten film is grown at high growth rate on the nucleus making layer as a seed. Thus, the tungsten film having designated thickness can be achieved.
FIG. 1 is a graph showing a relation between a process time and a film thickness in the above-mentioned film forming process. Following the pre-process, a nucleus making layer forming step is carried out. At a first part of the nucleus making layer forming step starts, the film does not stick for a period of time, namely for an incubation time T1. Also, at a first part of the a main tungsten film forming step starts following to the nucleus making layer forming step, a film does not stick for a period of time, namely for an incubation time T2. After the incubation time T2, the large amount of the tungsten film is formed.
Meanwhile, recently, it becomes more difficult to embed the metal film into a contact hole or a through hole such as a via-hole 2 as a result of that a semiconductor integrated circuit becomes minute and high integrated. As shown in FIG. 2, it is a main way to utilize a MOCVD-TiN (metal organic CVD-TiN) film 3, which is refined by a plasma step from a CVD film for which an organic Ti (titanium) source is utilized, as a base barrier film of the via-hole 2 used for particularly wiring in upper layers. It is not possible to obtain a sufficient covering ability of the base barrier film by the PVD method. A carbon is an impurity and stays inside of the film due to that an organic material is utilized as an ingredient of the CVD film. By the plasma step, it is possible to throw the carbon out after the film is formed, so that a purity and density of the film can be heighten.
The CVD-W film forming was carried out conventionally to the PVD-TiN film or the inorganic CVD-TiN film for which TiCl4 is utilized. As shown in FIG. 3, a tungsten film having a high quality can be formed on the base barrier film by such the CVD-W film forming, because an upper plane surface and a base part of a hole are refined sufficiently by reaching plasma thereon. However, as a fundamental nature with regard to the plasma, it is difficult for the plasma to reach the side wall of the hole. Hence, refining by the plasma may not be sufficient and it may be difficult to form a film of the tungsten thereon. Thereby, even if the film of the tungsten is formed, the tungsten film may have a low quality and the tungsten film may not be embedded into the hole sufficiently.