1. Field of the Invention
The present invention relates to a method for forming a silicon-containing resist underlayer film by spin coating method.
2. Description of the Related Art
In LSIs, advanced integration and higher process speed have made growing demands for more micro pattern size. Lithography technology has achieved further fine patterning by introducing a shorter wavelength of a light source and a resist composition appropriately selected according thereto.
Even in case of finer patterning by using the same light source, finer patterning with a constant thickness of a photoresist film used (i.e. a smaller pattern width) can make an aspect ratio of a photoresist pattern after development higher, leading to pattern fall. To solve this technical problem, photoresist film thickness has been determined smaller in accordance with finer patterning, so that the aspect ratio of a photoresist pattern is set within a proper range.
A multilayer resist method is known to solve these problems. Specifically, this method is a method for interposing an underlayer film having an etching selectivity different from a resist upper layer film (a photoresist film) between the resist upper layer film and a substrate to be processed to pattern on the resist upper layer film, transferring the pattern on the underlayer film by dry etching with a upper resist pattern as a dry etching mask, and further transferring the pattern on the substrate to be processed by dry etching with the underlayer film as a dry etching mask.
A silicon-containing resist underlayer film composition, consisting of a resist underlayer film in a multilayer resist method, has been recently used as such, due to its excellent processing property, an easy film forming property, and an etching selectivity different from an upper layer resist (Patent Documents 1 and 2).
Meanwhile, the silicon-containing resist underlayer film composition is disadvantageous to polymer cleaning. In fact, once a polymer precipitates in a pipe of an apparatus for coating and forming a film, it is very hard to remove the polymer to clean therein by using a commonly-used thinner such as acetone, propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, and γ-butyrolactone, cyclohexanone, as opposed to an organic film composition containing no silicon such as a conventional photoresist.
This problem is derived from a silicon-containing polymer contained in a silicon-containing resist underlayer film composition, thereby causing a precipitate of the polymer to form an insoluble polymer substance (generally known as siloxane gel). The siloxane gel is so small that it can pass through a filter (diameter: approx. 20 nm) connected to a discharge pipe of an apparatus for coating and forming a silicon-containing film, and observed as a foreign object in a silicon-containing film formed on a substrate for manufacturing a semiconductor apparatus. Now that there are no effective methods for cleaning and removing the siloxane gel generated in a pipe, such methods are urgently required.