US 9,360,753 B2  1  2  RESIST COMPOSITION AND PATTERNING  PROCESS  CROSS-REFERENCE TO RELATED  APPLICATION  TECHNICAL FIELD  BACKGROUND ART  This non-provisional application claims priority under 35  U.S.C. §119(a) on Patent Application No. 2011-161640 filed  in Japan on Jul. 25, 2011, the entire contents of which are  hereby incorporated by reference.  This invention relates to a resist composition, and more  particularly to a chemically amplified positive resist compo› sition adapted for the EB and EUV lithography processes;  and a patterning process using the same.  To meet the demand for higher integration density and  operating speed ofLSis, the effort to reduce the pattern rule is  in rapid progress. The wide-spreading flash memory market  and the demand for increased storage capacities drive forward  the miniaturization technology. As the advanced miniaturiza› tion technology, manufacturing of microelectronic devices at  the 65-nmnode by theArF lithography has been implemented  in a mass scale. Manufacturing of 45-nm node devices by the  next generationArF immersion lithography is approaching to  the verge of high-volume application. The candidates for the  next generation 32-nm node include ultra-high NA lens  immersion lithography using a liquid having a higher refrac› tive index than water in combination with a high refractive  index lens and a high refractive index resist film, EUV lithog› raphy of 13.5 nm wavelength, and double patterning version  of the ArF lithography, on which active research efforts have  been made.  The current technology is approaching to the processing  size which is reduced below 50 nm as minimum line width.  When the processing size is so reduced, the thickness of resist  film must be reduced below 100 nm, depending on the surface  material of the substrate to be processed, because of such  factors as the structural strength to maintain the pattern  against the surface tension of developer and the adhesion  strength to the substrate. On use of prior art chemically ampli› fied resist materials intended to form high-resolution resist  film, for example, based on a base resin having an acetal  protective group, no significant degradation of line edge  roughness (LER) does occur with a resist film having a thick› ness of 150 nm, but LER is substantially exacerbated when  the film thickness is reduced below 100 nm.  With respect to high-energy radiation of very short wave› length such as EB or x-ray, hydrocarbons and similar light  elements used in resist materials have little absorption. Then  polyhydroxystyrene base resist materials are under consider- ation. Resist materials for EB lithography are practically used  in the mask image writing application. Recently, the mask  manufacturing technology becomes of greater interest.  Reduction projection exposure systems or steppers have been  used since the time when the exposure light was g-line. While  their demagnification factor was $^{1}$/s, a factor of…  is now used  as a result of chip size enlargement and projection lens diam› eter increase.  It  becomes of concern that a dimensional error  of a mask has an impact on the dimensional variation of a  pattern on wafer.  It  is pointed out that as the pattern feature is  reduced, the value of a dimensional variation on the wafer  becomes greater than the value of a dimensional error of the  mask. This is evaluated by a mask error enhancement factor  (MEEF) which is a dimensional variation on wafer divided by  a dimensional error of mask. Patterns on the order of 45 nm  often show an MEEF in excess of 4. In a situation including a  demagnification factor of … and a MEEF of 4, the mask  manufacture needs an accuracy substantially equivalent to  that for equi-magnification masks.  The exposure system for mask manufacturing made a tran› sition from the laser beam exposure system to the EB expo- IO sure system to increase the accuracy of line width. Since a  further size reduction becomes possible by increasing the  accelerating voltage of the electron gun in the EB exposure  system, the accelerating voltage increased from 10 keV to 30  15  keV and reached 50 keV in the current mainstream system,  with a voltage of 100 ke V being under investigation.  As the accelerating voltage increases, a lowering of sensi› tivity of resist film becomes of concern. As the accelerating  voltage increases, the influence of forward scattering in a  resist film becomes so reduced that the contrast of electron  image writing energy is improved to ameliorate resolution  and dimensional control whereas electrons can pass straight› forward through the resist film so that the resist film lowers its  sensitivity. Since the mask exposure tool is designed for expo- sure by direct continuous writing, a lowering of sensitivity of  resist film leads to an undesirably reduced throughput. Due to  a need for higher sensitivity, chemically amplified resist com› positions are contemplated.  As the feature size is reduced, image blurs due to acid  diffusion become a problem (see Non-Patent Document 1).  To insure resolution for fine patterns with a size of 45 nm et  seq., not only an improvement in dissolution contrast is req› uisite, but control of acid diffusion is also important (see  Non-Patent Document 2). Since chemically amplified resist  compositions are designed such that sensitivity and contrast  are enhanced by acid diffusion, an attempt to minimize acid  diffusion by reducing the temperature and/or time of post› exposure bake (PEB) fails, resulting in drastic reductions of  sensitivity and contrast.  Addition of an acid generator capable of generating a bulky  acid is effective for suppressing acid diffusion.  It  is then  proposed to copolymerize a polymer with an acid generator in  the form of an onium salt having polymerizable olefin. Patent  Documents 1 to 3 disclose sulfonium salts having polymer- izable olefin capable of generating a sulfonic acid and similar  iodonium salts. Patent Document 1 discloses a polymer› bound sulfonium salt in which sulfonic acid is directly  attached to the backbone.  The EB writing of a resist film encounters a problem that  the point of writing is shifted by electrostatic charges on the  resist film.  It  is proposed to overlay the resist film with an  antistatic film to prevent the resist film from being charged.  Undesirably coating of the antistatic film adds to the cost of  the overall process.  It  was avoided to use metal-containing materials as the  photoresist material for the semiconductor lithography  because of a possible malfunction of semiconductor devices.  However, it is known in the application other than the semi› conductor, for example, as the resist material for forming  color filters for LCD ( see Patent Document 2), to use a metal› containing (meth)acrylate as a copolymerizable monomer.  The metal-containing (meth)acrylate is typically contem› plated as the antifouling paint for ships. Patent Document 3  shows many examples such as zinc acrylate, copper acrylate  and magnesium acrylate.  Patent Document 4 discloses EB resist and antistatic film  having alkali metal, alkaline earth metal and cesium salts 