Absorptive layer for optical lithography

DETAILED DESCRIPTION OF THE INVENTION The compositions of this invention are useful in forming an absorptive layer in a multilayer resist recording medium.
An absorptive coating formed from the subject compositions is useful as a base layer having a photoresist layer thereover or as a thin intermediate layer between a base or planarizing layer and a photoresist layer.
The particular advantage of absorptive layers formed from the subject compositions is not realized when they underlie a hardmask layer since the hardmask layer would substantially prevent the dye in conventional absorptive coatings from being absorbed into the overlying photoresist compositions.
The resin component of the subject compositions is poly(methylmethacrylate) (PMMA) having a molecular weight of from about 100,000 to 1,000,000, suitably about 345,000, or a copolymer of methylmethacrylate (MMA) and methacrylic acid (MA) wherein the weight ratio of MMA to MA is from about 85/15 to 99/1, suitably about 91.
5/8.
5.
The molecular weight of the copolymer is from about 100,000 to 1,000,000, suitably about 300,000.
The dye component of the subject compositions must possess all of a list of critical properties.
First, the dye must have a window of high absorption at the specific wavelengths used to irradiate the resist layer.
Generally, this means that the dye should have high absorbance in the range 350 nm to 450 nm and be essentially transparent in the range 500 nm to 600 nm.
The dye must be compatible with the materials which the subject layer contacts both in the substrate and in adjacent layers.
Further, the dye must be able to withstand temperatures necessary for the processing of the remainder of the medium, i.
e.
it must be stable up to a temperature of at least about 200.
degree.
C.
, preferably up to about 300.
degree.
C.
It is particularly important that the dyes utilized in the subject compositions be substantially insoluble in the solvents conventionally utilized to form the positive photoresist top layer in a multilayer resist recording medium