Currently, in fabrication of a mass storage semiconductor integrated circuit, such as a 64 Mbit dynamic random access memory (DRAM) and a logic device or a system LSI with a 0.25 μm through 0.15 μm rule, a resist pattern is formed by using a chemically amplified resist material including a polyhydroxystyrene derivative and an acid generator as principal constituents with KrF excimer laser (wavelength: a 248 nm band) used as exposing light.
Moreover, for fabrication of a 256 Mbit DRAM, a 1 Gbit DRAM or a system LSI with a 0.15 μm through 0.13 μm rule, a pattern formation method using, as exposing light, ArF excimer laser (wavelength: a 193 nm band) lasing at a shorter wavelength than the KrF excimer laser is now under development.
The resist material including a polyhydroxystyrene derivative as a principal constituent has high absorbance against light of a wavelength of a 193 nm band because of an aromatic ring included therein. Therefore, exposing light of a wavelength of a 193 nm band cannot uniformly reach the bottom of a resist film, and hence, a pattern cannot be formed in a good shape. Accordingly, the resist material including a polyhydroxystyrene derivative as a principal constituent cannot be used when the ArF excimer laser is used.
Therefore, a chemically amplified resist material including, as a principal constituent, a polyacrylic acid derivative or a polycycloolefin derivative having no aromatic ring is used when the ArF excimer laser is used as the exposing light.
On the other hand, as exposing light for a pattern formation method capable of coping with high resolution, an electron beam (EB) and the like are being examined.
When the EB is used as the exposing light, however, the throughput is disadvantageously low, and hence, the EB is not suitable to mass production. Thus, the EB is not preferred as the exposing light.
Accordingly, in order to form a resist pattern finer than 0.10 μm, it is necessary to use exposing light of a wavelength shorter than that of the ArF excimer laser, such as Xe2 laser (wavelength: a 172 nm band), F2 laser (wavelength: a 157 nm band), Kr2 laser (wavelength: a 146 nm band), ArKr laser (wavelength: a 134 nm band), Ar2 laser (wavelength: a 126 nm band), soft X-rays (wavelength: a 13, 11 or 5 nm band) and hard X-rays (wavelength: not longer than a 1 nm band). In other words, a resist pattern is required to be formed by using exposing light of a wavelength not longer than a 180 nm band.
Therefore, the present inventors have formed resist patterns by conducting pattern exposure using a F2 laser beam (wavelength: a 157 nm band) on resist films formed from conventionally known chemically amplified resist materials respectively including a polyhydroxystyrene derivative represented by Chemical Formula 31, a polyacrylic acid derivative represented by Chemical Formula 32 and a polycycloolefin derivative represented by Chemical Formula 33.
Chemical Formula 31:

Chemical Formula 32:

Chemical Formula 33:

Now, a method for forming a resist pattern by using any of the aforementioned conventional chemically amplified resist materials and problems arising in the conventional method will be described with reference to FIGS. 2(a) through 2(d).
First, as shown in FIG. 2(a), the aforementioned chemically amplified resist material is applied on a semiconductor substrate 1 by spin coating and the resultant is heated, so as to form a resist film 2 with a thickness of 0.3 μm. Thereafter, as shown in FIG. 2(b), the resist film 2 is irradiated with a F2 laser beam 4 through a mask 3 for pattern exposure. Thus, an acid is generated from the acid generator in an exposed portion 2a of the resist film 2 while no acid is generated in an unexposed portion 2b of the resist film 2.
Next, as shown in FIG. 2(c), the semiconductor substrate 1 is heated with a hot plate 5 at a temperature of, for example, 100° C. for 60 seconds.
Then, the resist film 2 is developed with an alkaline developer, thereby forming a resist pattern 6 as shown in FIG. 2(d).
However, as shown in FIG. 2(d), the resist pattern 6 is formed in a defective pattern shape, and there remains much scum (residues) on the semiconductor substrate 1. Such problems occur not only in using the F2 laser beam as the exposing light but also in using any of the other light of a wavelength not longer than a 180 nm band.
Accordingly, a resist pattern cannot be practically formed by irradiating a resist film formed from any of the aforementioned chemically amplified resist materials with light of a wavelength not longer than a 180 nm band.