US 5,239,015 A · Process for making low optical density polymers and copolymers for photoresists and optical applications

Abstract

The present invention pertains to a process for the preparation of polymers comprising poly(4-hydroxystyrene) or substituted poly(4-hydroxystyrene) or both. The polymers have low optical density (absorbance) over a wavelength range from about 240 to about 260 nm, as well as low optical density over the near UV and visible spectrum (310 to 800 nm). Such polymers are produced by polymerizing 4-acetoxystyrene and/or substituted 4-acetoxystyrene monomers, with or without other comonomers, and subsequently performing transesterification. In the most preferred embodiment of the present invention, the polymers are produced using at least one alcohol as a reaction medium, a chain transfer agent and a transesterification reactant, providing an unusually economic process. These polymers are particularly useful as photoresist components for use in combination with deep UV, X-ray, and E-Beam imaging systems. To obtain polymers having low optical density over the 240 to 260 nm radiation wavelength range, it is necessary to use an initiator which does not comprise a substantially absorbant structure over the 240 to 260 nm range or to use an initiator concentration of less than about 3 mole % of the monomer(s), to obtain a polymerization conversion of the initial polymerization monomers of at least about 90% by weight, or to remove residual monomer(s) from the reaction medium prior to transesterification, and to obtain a transesterification conversion of the polymerized monomers of at least 85% by weight. It is also necessary to avoid the use of transesterification catalyst which can cause the formation of chemical structures which can absorb over the 240 to 260 nm radiation wavelength range.

Claims53

Dependent claims

A process for preparation of polymers having low optical density at 240-260 nm, comprising poly(4-hydroxystyrene) or substituted poly(4-hydroxystyrene) or both, said process comprising the steps of:

a) reacting a mixture comprising 4-acetoxystyrene monomer or substituted 4-acetoxystyrene monomer or both and an initiator, wherein said initiator and its decomposition products alone or as polymer capping groups do not substantially absorb radiation over wavelengths ranging from about 240 to about 260 nm, or wherein said initiator is present at a concentration of less than about 3 mole % of said monomer, in a reaction medium comprising at least one organic solvent, to produce a polymer comprising poly(4-acetoxystyrene) or substituted poly(4-acetoxystyrene) or both, whereby, either as a result of monomer conversion, or due to removal of residual monomer, 10 wt % or less residual monomer, based on the weight of polymer produced, is present in the reaction mixture used during a subsequent transesterification reaction step;
and
b) subsequently transesterifying said poly(4-acetoxystyrene) to poly(4-hydroxystyrene) or transesterifying said substituted poly(4-acetoxystyrene) to substituted poly(4-hydroxystyrene) or transesterifying both, in a transesterification reaction medium comprising at least one equivalent of alcohol per equivalent of non-transesterified poly(4-acetoxystyrene) or substituted poly(4-acetoxystyrene), using approximately 5-2000 ppm of an acid catalyst to achieve said transesterification, wherein at least 85% by weight conversion of said poly(4-acetoxystyrene) to said poly(4-hydroxystyrene) or conversion of said substituted poly(4-acetoxystyrene) to said substituted poly(4-hydroxystyrene) or at least 85% by weight transesterification of both is obtained.

A process for preparation of polymers having low optical density at 240-260 nm, comprising poly(4-hydroxystyrene) or substituted poly(4-hydroxystyrene) or both, said process comprising the steps of:

a) reacting a mixture comprising 4-acetoxystyrene monomer or substituted 4-acetoxystyrene monomer or both and a comonomer having at least one vinyl group present, wherein said comonomer does not substantially absorb radiation over wavelengths ranging from about 240 to about 260 nm;
and an initiator, wherein said initiator and its decomposition products alone or as capping groups do not substantially absorb radiation over wavelengths ranging from about 240 to about 260 nm, or wherein said initiator is present at a concentration of less than about 3 mole % of said monomer;
in a reaction medium comprising at least one organic solvent, to produce a copolymer of poly(4-acetoxystyrene) or said substituted poly(4-acetoxystyrene) with said comonomer, whereby, either as a result of monomer conversion or due to removal of residual monomer, 10 wt % or less residual monomer, based on the weight of polymer produced, is present in the reaction mixture during a subsequent, transesterification reaction step;
and
b) subsequently transesterifying said poly(4-acetoxystyrene) to poly(4-hydroxystyrene) or transesterifying said substituted poly(4-hydroxystyrene) to to substituted poly(4-hydroxystyrene) or transesterifying both to a conversion of at least 85% by weight, in a transesterification reaction medium comprising at least one equivalent of alcohol per equivalent of non-transesterified copolymer, using approximately 5-2000 ppm of an acid catalyst to achieve said transesterification.

2 more elements

Dependencies are inferred from the claim text.

Process for making low optical density polymers and copolymers for photoresists and optical applications

Life of this patent

Process for making low optical density polymers and copolymers for photoresists and optical applications

Life of this patent

Abstract

Claims53