Novolak resin for positive photoresist

摘要

A novolak resin for a positive photoresist is provided herein, which resin is produced by the addition condensation reaction of a phenol with formaldehyde. This novolak resin has improved heat resistant and sensitivity properties and the thickness retention of the novolak resins are very high. The novolak resins are characterized in that the area ratio of the gel permeation chromatographic pattern (GPC) as measured by the use of a UV(254 nm) detector, is as follows: a range wherein the molecular weight, calculated as polystyrene, is from 150 to less than 500, not including a phenol and the unreacted monomer, is from 8 to 35%, hereinafter referred to as an A region, the range wherein the molecular weight calculated as polystyrene is from 500 to less than 5000 is from 0 to 30%, hereinafter referred to as a B region, and the range wherein the molecular weight calculated as polystyrene exceeds 5000 is from 35 to 92%, hereinafter referred to as the C region, and wherein the ratio of the B region to the A region is 2.50 or less.