Polymer, resist composition and patterning process

#This invention relates to (i) a polymer comprising specific recurring units, (ii) a resist composition comprising the polymer as a base resin, and (iii) a patterning process using the resist composition.

#While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, deep-ultraviolet lithography is thought to hold particular promise as the next generation in microfabrication technology. In particular, photolithography using a KrF or ArF excimer laser as the light source is strongly desired to reach the practical level as the micropatterning technique capable of achieving a feature size of 0.3 μm or less.

#For resist materials for use with a KrF excimer lasers, polyhydroxystyrene having a practical level of transparency and etching resistance is, in fact, a standard base resin. For resist materials for use with ArF excimer lasers, polyacrylic or polymethacrylic acid derivatives containing an adamantane structure in their side chain are often used as described in JP-A 9-73173 and JP-A 9-90637. Few of these polymers are regarded as exhibiting satisfactory performance.

#Synthesis Examples and Examples are given below by way of illustration and not by way of limitation. The abbreviation Mw is a weight average molecular weight as measured by GPC using a polystyrene standard, and SEM is scanning electron microscope.

#Polymers within the scope of the invention were synthesized by the following procedure.

#A mixture of 112.0 g of 3-oxo-2,7-dioxatricyclo-[4.2.1.04,8]nonan-9-yl methacrylate, 117.0 g of 2-methyl-2-adamantyl methacrylate, 1.40 g of 2-mercaptoethanol, and 763.3 g of tetrahydrofuran was heated at 60° C. To the solution was added 3.28 g of 2,2′-azobisisobutyronitrile. The solution was stirred for 15 hours while keeping at 60° C. The reaction solution was cooled to room temperature and dissolved in 500 ml of acetone, which with vigorous stirring, was added dropwise to 10 liters of isopropyl alcohol. The resulting solids were collected by filtration and dried in vacuum at 40° C. for 15 hours, obtaining a polymer in white powder solid form. The amount was 183.9 g and the yield was 80.3%. This is designated Polymer 1.