Integrated circuits increase their degree of integration more and more, and it has become necessary to process ultrafine patterns made up of line widths of quarter micron or less in the fabrication of semiconductor substrates of very large scale integration (VLSI). As one of means to make ultrafine patterns, known is short-wavelength regime of an exposure light source used for pattern formation of resists.
For example, i-ray (365 nm) of a high pressure mercury lamp has been used to date for fabricating semiconductor devices with integration degrees up to 64 M bits. As positive type resists corresponding to this light source, compositions containing novolak resin and naphthoquinone diazide compound as a photosensitized material have been developed in large numbers, and sufficient outcomes have been obtained for processing the line widths up to about 0.3 μm. Also, Krf excimer laser light (248 nm) instead of i-ray has been employed as the exposure light source for fabricating semiconductor devices with the integration degrees of 256 M bits or more.
Furthermore, for the purpose of fabricating semiconductors with the integration degrees of 1 G bits or more, recently, the use of ArF excimer laser light (193 nm) which is the light source of shorter wavelength, and further the use of F2 excimer laser light (157 nm) for forming the patterns of 0.1 μm or less have been studied.
Components and compound structures of resist materials have been largely changed in conjunction with the short-wavelength regimes of the light source.
As a resist composition for the exposure by KrF excimer laser light, a so-called chemically amplified resist has been developed, which is the composition where a resin having a backbone of poly (hydroxystyrene) with less absorbance at 248 nm area and protected with an acid degradable group is used as a primary component and a compound (photoacid generator) which generates an acid by the radiation of far ultraviolet light is combined.
Also, as the resist composition for the exposure of ArF excimer laser light (193 nm), the chemically amplified resist has been developed, which uses an acid degradable resin where an alicyclic structure having no absorbance at 193 nm is introduced in a main chain or a side chain of polymer.
It has been found that absorbance at a 157 nm area is high even in the above alicyclic resin for F2 excimer laser light (157 nm) and thus it is insufficient to obtain the target patterns of 0.1 μm or less. On the contrary, it has been reported in Proc. SPIE., 3678:13, 1999 that the resin where fluorine atoms are introduced (perfluoro structure) has sufficient transparency at 157 nm. The structures of effective fluorine resins have been proposed in Proc. SPIE., 3999:330, ibid., 357, ibid., 365, 2000, and WO-00/17712, and the resist compositions containing fluorine-containing resins have been studied.
However, the resist compositions containing fluorine resins for the exposure of F2 excimer laser light have problems such as line edge roughness, development time dependence, weak dissolution contrast and large footing formation, and solution of these points has been desired.
The line edge roughness is referred to exhibiting a shape where edges of a line pattern of the resist and a substrate interface irregularly fluctuate in a vertical direction for the line direction, attributing to the resist property. When these patterns are observed from right above, the edges look convexo-concave (±approximately some nm to tens nm). Since this convexo-concave state is transferred to the substrate by an etching process, if unevenness is remarkable, electric property faults are caused and process yields are reduced.
Also, the development time dependence is referred to degrees of changes of pattern sizes due to variation of the development time. When the development time dependence is remarkable, size uniformity in a wafer surface is aggravated, and controllability of the process becomes difficult.
Also, footing formation means the condition where a sectional shape of the line pattern forms a footing shape in a ground substrate interface. When the level of the footing formation of the pattern shape are remarkable, it is problematic because controllability (management) of the pattern size in the etching process is aggravated.