1. Field of the Invention
This invention relates to ionizing radiation sensitive materials which are useful as electron beam resists and information recording media.
2. Description of the Prior Art
Unsaturated ester derivatives of a 1:1 copolymer of octadecyl vinyl ether-maleic anhydride exhibit electron sensitivity of about 10.sup.-7 to about 5.times.10.sup.-7 coulomb/cm.sup.2, but since the contrast of these materials is generally less than about 1.2 they do not have the ability to record submicron images. When exposed to electrons with energies below about 30 keV, other derivatives, namely the hydroxyethylpyrrolidone (HEP) esters of the same copolymer, have a sensitivity of only about 10.sup.-4 coulomb/cm.sup.2 to electron radiation.
The literature indicates that a mixture of electron sensitive polymers with widely differing sensitivities would be expected to have sensitivity intermediate between the values of the components of the mixture and to exhibit a greatly inferior contrast--and hence resolving power--to either of the constituents. I find that this is not the case with mixtures of the aforementioned hydroxyethyl pyrrolidone derivative with the mixtures of the products of reaction of the unsaturated ester derivatives. Even more significantly, it has been found that the contrast of such resists improves appreciably, which feature provides a resolution capability of less than 0.5 micrometer. This increased contrast is achieved herein with resists made by mixing the products of reaction of an alkylvinyl ether-maleic anhydride copolymer with a hydroxyalkyl acrylate such as hydroxyethyl acrylate, hydroxyethyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropylmethacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate or allyl or propargyl alcohol or pentaerythritol triacrylate and the products of reaction of an N-hydroxyalkyl amide or an N-aminoalkyl amide and an alkylvinyl ether-maleic copolymer anhydride to form the novel half-ester copolymer.