## RESIST COMPOSITION AND PATTERNING PROCESS USING THE SAME 

## BACKGROUND OF THE INVENTION 

The present invention relates to a resist composition and a patterning process, and more particularly to a resist com› position using a polymer compound suitable for a base resin of a chemically amplified resist composition. 

A finer pattern rule has been recently required for Large› Scale Integrated circuits (LSI) with higher integration and higher processing speed. Under such circumstances, photo› exposure, which has been currently used as a general tech› nique, is approaching to essential limit ofresolution accord› ing to the wavelength of a light source. As the exposure light used in resist patterning, g-line beam ( 436 nm) or i-line beam (365 nm) of mercury lamp had been widely used in 1980s. Shifting the exposure light to shorter wavelength was assumed to be effective in finer patterning. Thus, KrF excimer laser (248 nm), whose wavelength is shorter than i-line beam (365 nm), had been used in place of i-line beam as the exposure light source in the mass production process of Dynamic Random Access Memory (DRAM) with 64 MB (work size of 0.25 m or less) in 1990s and later ones. However, the production of DRAM with integration of 256 MB and 1 GB or higher, which requires still finer processing technologies (work size of 0.2 µm or less), needs a light source with still shorter wavelength, and thus a photolithog› raphy using ArF excimer laser (193 nm) has been investi› gated seriously over a decade. It was expected at first that the ArF lithography would be applied to the production of 180 nm-node devices. However, the KrF excimer lithography survives to the mass production of 130 nm-node devices, so that a full-fledged application of the ArF lithography starts from 90 nm-node. Furthermore, the mass production of 65 nm-node devices is now underway by combining the ArF lithography with a lens having an increased numerical aperture (NA) of 0.9. For next 45 nm-node devices, the wavelength of the exposure light has further shortened, and F $_{2 }$lithography with 157 nm wavelength comes up. However, there are many problems in the F 2 lithography: cost-up of a scanner due to use of a quantity of expensive CaF $_{2 }$ single crystals for a projection lens; extremely poor durability of a soft pellicle; change of an optical system caused by intro› ducing a hard pellicle; a decrease in etching resistance of a resist film, and so forth. For these problems, development of the F 2 lithography was suspended, and ArF immersion lithography was introduced. 

In the ArF immersion lithography, water having a refrac› tive index of 1.44 is put between a projection lens and a wafer by a partial fill method. This enables high speed scanning, and the mass production of the 45 nm-node devices is now underway by using a lens with a NA of 1.3. 

For 32 nm-node lithography, a lithography with an extreme ultraviolet ray (EUV) of 13.5 nm wavelength is considered to be a candidate. Unfortunately, the EUV lithog› raphy has problems such as needs for a higher output power of the laser, a higher sensitivity of the resist film, a higher resolution, a lower edge roughness (LER, LWR), a non› defect MoSi laminate mask, a lower aberration of the reflective mirror, and so forth. Thus, there are innumerable problems to be solved. 

## Field of the Invention 

## Description of the Related Art 

Development of an immersion lithography with high refractive index, which is another candidate for the 32 nm-node, was suspended because of low transmittance of LUAG, a candidate for a high refractive index lens, and an inability to obtain a target value of a liquid’s refractive index at 1.8. 

In recent years, a double patterning process, in which a first pattern is formed by first exposure and development, and then a pattern is formed exactly in the space of the first pattern by second exposure, draws attention. As the double patterning process, many processes are proposed. One example is a method that includes forming a photoresist pattern with a line-to-space ratio of 1 :3 by first exposure and development; processing an underlayer hard mask by dry etching; laying another hard mask thereon; forming a line pattern by subjecting the photoresist film to exposure and development at the space obtained by the first exposure; processing the hard mask by dry etching to form a line and space pattern having half pitch of the first pattern. Another example is a method that includes forming a photoresist pattern with a space-to-line ratio of 1 :3 by first exposure and development; processing an underlayer hard mask by dry etching; applying a photoresist film thereon; forming a second space pattern on a remaining portion of the hard mask by second exposure; and processing the hard mask by dry etching. In both methods, the hard mask is processed by dry etching twice. 

A hole pattern is more difficult to be made fine than the line pattern. When a positive resist film is combined with a hole pattern mask and then subjected to under-exposure to form fine holes by the conventional method, exposure mar› gin becomes extremely narrow. It is then proposed to form large holes and shrink the holes by thermal flow or RELACS™ method after development. Unfortunately, these methods cause a large difference between a pattern size after development and a pattern size after shrinking, and thus decrease a control accuracy with an increase in shrinkage. Moreover, the hole-shrinking methods fail to narrow the pitch although they can decrease the hole size. 

In addition, there is proposed a method that includes forming a line pattern in X-direction with a positive resist film by dipole light; curing the resist pattern; applying a resist composition thereon again; exposing a line pattern in Y-direction by dipole light to form a hole pattern from gaps of the grid-like line pattern (Non-Patent Document 1). The combination of X and Y lines by dipole light with high contrast enables the hole pattern to be formed with a wide margin. However, the combined line patterns are difficult to be etched with high dimensional precision. On the other hand, there is proposed a method in which a negative resist film combining a Levenson-type phase shift mask in X-di› rection and a Levenson-type phase shift mask in Y-direction is exposed to light to form a hole pattern (Non-Patent Document 2). However, the negative resist film has disad- vantage of lower resolution than the positive resist film because a limiting resolution of ultrafine hole of the cross› linkable negative resist film depends on a bridge margin. 

A hole pattern formed by twice exposure combining a line in X-direction and a line in Y-direction followed by conver- sion into a negative pattern can be obtained by using a line pattern light with high contrast. Thus, this pattern has finer holes with a narrower pitch than that obtained by the conventional method. 

Non-Patent Document 3 discloses the following three methods for forming a hole pattern by inversion: a method including forming a dot pattern by twice exposure of X and Y lines of a positive resist composition by double dipole, 

