1.  Field of the Invention
The present invention relates to a silicon-containing resist underlayer film-forming composition and a patterning process using the same. 
2.  Description of the Related Art
In 1980s, a g-beam (436 nm) or an i-beam (365 nm) of a mercury lamp had been widely used as an exposure light in the resist patterning.  As a means for further miniaturization, shifting to a shorter wavelength of the exposure light was assumed to be effective, so that, in mass production process after the DRAM (Dynamic Random Access Memory) with a 64-Mega bit (processing dimension of 0.25 μl or less) in 1990s, a KrF excimer laser (248 nm), a shorter wavelength than the i-beam (365 nm), had been used in place of the i-beam as an exposure light source.  However, in production of DRAMs with integration of 256 M and 1 G or higher which require further miniaturized process technologies (processing dimension of 0.2 μm or less), a light source with further short wavelength is required, and thus, a photolithography using an ArF excimer laser (193 nm) has been investigated seriously since about a decade ago.  At first, the ArF lithography was planned to be applied to manufacturing of a device starting from a 180-nm node device, but the life of the KrF excimer lithography was prolonged to mass production of the 130-nm node device; and thus, a full-fledged application of the ArF lithography started from the 90-nm node.  Further, mass production of the 65-nm node device is now underway by combining thereof with a lens having an increased NA till 0.9.  Further shortening of wavelength of the exposure light is progressing in the next 45-nm node device; and for that, the F2-lithography with 157 nm wavelength became a candidate.  However, there are many problems with the F2 lithography: cost-up of a scanner due to use of a large quantities of expensive CaF2 single crystals for a projection lens; extremely poor sustainability of a soft pellicle, which leads to change of an optical system due to introduction of a hard pellicle; decrease in etching resistance of a resist film, and so forth.  Because of these problems, development of the F2 lithography was stopped, and the ArF immersion lithography was introduced. 
In the ArF immersion lithography, water having refractive index of 1.44 is introduced between a projection lens and a wafer by a partial fill method thereby enabling high speed scanning; and thus, mass production of the 45-nm node device is now underway by using a lens with a 1.3 NA class. 
For the 32-nm node lithography technology, a lithography with a vacuum ultraviolet beam (EUV) of 13.5 nm wavelength is a candidate.  Problems to be solved in the EUV lithography are a higher output power of the laser, a higher sensitivity of the resist film, a higher resolution, a lower line edge roughness (LER), a non-defective MoSi laminate mask, a lower aberration of the reflective mirror, and so forth; and thus, there are mounting problems to be solved. 
Development of the immersion lithography with a high refractive index, another candidate for the 32-nm node, was suspended, because transmittance of LUAG, a candidate for a high refractive index lens, is low, and refractive index of the liquid could not reach an aimed value of 1.8. 
As mentioned above, in the photo-exposure used as a general technology, resolution due to the wavelength of a light source is approaching to its inherent limit.  Therefore, in recent years, development by an organic solvent, with which a very fine hole pattern that could not been formed by a patterning process with a positive tone by a conventional alkaline development is formed by a patterning process with a negative tone by the organic solvent development, is receiving an attention again.  This is a patterning process with which a negative pattern is formed by the organic solvent development by using a positive resist composition having a high resolution.  Further, an investigation to obtain a doubled resolution by combining two developments of the alkaline development and the organic solvent development is now underway. 
As to the ArF resist composition used for the negative tone development by an organic solvent as mentioned above, a conventional positive ArF resist composition can be used; and a patterning process thereof is shown, for example, in Patent Documents 1 to 3. 
One method to transfer the negative tone pattern formed as mentioned above to a substrate is a multilayer resist method.  In this method, a resist underlayer film having different etching selectivity from a photoresist film (i.e., resist upperlayer film), for example, a silicon-containing resist underlayer film is intervened between the resist upperlayer film and the substrate to be processed whereby obtaining a pattern in the resist upperlayer film; and then, after the pattern is transferred to the silicon-containing resist underlayer film by dry etching by using the upperlayer resist pattern as a dry etching mask, the pattern is further transferred to the substrate to be processed by dry etching by using the silicon-containing resist underlayer film as a dry etching mask. 
Illustrative examples of the silicon-containing resist underlayer film used in the multilayer resist method as mentioned above include a silicon-containing inorganic film formed by CVD, such as a SiO2 film (for example, Patent Document 4 etc.)  and a SiON film (for example, Patent Document 5 etc.),  and those formed by a spin-coating method, such as a SOG film (spin-on-glass film) (for example, Patent Document 6 etc.)  and a crosslinking silsesquioxane film (for example, Patent Document 7 etc.).