US 10,005,868 B2  2  1  RESIST COMPOSITION AND PATTERNING  PROCESS USING THE SAME  BACKGROUND OF THE INVENTION  Field of the Invention  Description of the Related Art  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.  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,  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.  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 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 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.  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. 