In response to large integration and development of high-speed semiconductor devices, wiring structure thereof is becoming finer; and, as a result, achieving a high-definition of a wiring pattern in a resist film and reducing electrical capacitance among wirings have become more important. Achieving such high-definition of wiring pattern requires a uniform thickness of the resist film. Further, a uniform thickness of an interlayer insulating film is required for an accurate etching process.
Widely used in forming the resist film or the interlayer insulating film is a spin coating technique where, e.g., a coated insulating film (referred to as SOD (spin on dielectric) film hereinafter) is formed by coating an organic material on a surface of an object to be processed by using a spin coater and a bake oven. In order to reduce the interwiring capacitance of the interlayer insulating film, various low-k film materials have been developed as SOD film materials. As one of the steps of film forming, heat curing is performed on the SOD film. And recently, an electron beam (EB) curing process is performed thereon by using an EB processor.
In case of forming the SOD film on an object to be processed (e.g., a wafer) by using the spin coater, a center portion of the wafer has a comparatively small thickness and the thickness of the wafer becomes greater toward an outward radial direction thereof, as illustrated in FIG. 9A. Conventionally, while the EB curing process is performed on the SOD film, each of electron beam tube emits a uniform output of electron beams to an entire surface of the wafer, as shown in FIG. 9B.
Although the irregularity of the film thickness in case of forming a thin film such as an interlayer insulating film on a wafer by using a plasma processing apparatus is not as great as that of using the spin coater, the irregularity nevertheless makes it difficult to achieve a uniform film thickness. Moreover, in case of forming the thin film by using a plasma processing apparatus, the thin film may suffer from an onset of electric charges from a plasma, causing various processing problems in subsequent processes. The charging problem may also occur during an etching process.
Therefore, there have been proposed various methods for removing electric charges from a thin film, e.g., a method of neutralizing positive ions on the thin film by irradiating electron beam (negative ions) onto a wafer (claim 1 to 3, paragraph [0007], and FIG. 2 of Japanese Patent Laid-Open Publication No. H9-181056); and a method for generating floating electric charges (including positive ions and electrons) from Ar gas or the like by using a neutralizing electric charge generator such as an ultraviolet lamp and then neutralizing electric charges on a surface of a thin film by using thus generated floating electric charges (claims 1 and 2, and paragraph [0022] of Japanese Patent Laid-Open Publication No. H7-14761). In addition, there is known a method for removing electric charges from a surface of a semiconductor substrate by irradiating ultraviolet to a charge accumulated region of the surface of semiconductor substrate (claims 1 and 4, paragraph [0008] of Japanese Patent Laid-Open Publication No. H5-243160).
However, in the conventional thin film forming process of a resist film or interlayer insulating film, which involves the SOD film coating process, the SOD film baking process and the curing process described above, there is a tremendous difficulty in achieving a uniform film thickness in every process. For example, in case of coating the SOD film by using a spin coater, the film thickness becomes nonuniform as shown in FIG. 9A and such nonuniformity can not be corrected even after a heat treatment using a bake oven and an EB curing process. Therefore, nonuniformity in the film thickness prevails even after the EB curing process as shown in FIG. 9C, making it difficult to obtain a uniform thickness. Moreover, if the film thickness is nonuniform, it becomes difficult to perform succeeding processes. For instance, when the interlayer insulating film is processed, such nonuniformity hampers an accurate etching of a desired pattern and deterioration of yield may result. Further, when the resist film is processed, it is difficult to achieve a highly detailed patterning required in an exposure process.
In case of employing the first prior art method, discussed above, for removing electric charges from a thin film formed on a wafer surface, only positive ions of the thin film can be removed by the electron beam (negative ions). In case of adopting the second prior art method using ultraviolet, it may be possible to remove electric charges from the surface of the thin film; however, electric charges generated by the ultraviolet cannot penetrate into the thin film, and, therefore, electric charges accumulated inside the thin film cannot be removed. The third prior art method is also saddled with the same problem since the ultraviolet may not be able to penetrate into the thin film.