This invention relates to a radiation sensitive resin composition for microlens. Particularly, it relates to a positive type radiation sensitive resin composition suitable to the preparation of microlens using radiations such as ultraviolet ray, far ultraviolet ray, X-ray, electron beam, molecular beam, .gamma.-ray, synchrotron radiation, proton beam and the like. More particularly, it relates to a positive type radiation sensitive resin composition for microlens suitable to the preparation of a lens array composed of fine optical lenses arranged regularly.
Microlenses having a lens diameter of about 5-20 .mu.m or microlens array composed of microlenses arranged regularly are applied to an image-forming optical system of on-chip color filter such as facsimile, electron copying machine, charged coupled device and the like.
Among the above-mentioned microlenses (microlens arrays), refractive index distributed cylindrical lens prepared by an ion-exchange method and convex microlenses prepared from photosensitive glass have been put to practical use.
However, the microlenses which are now practically used have such problems that the production cost therefor is high because the processes for producing them are all complicated and that it is impossible to unify the microlenses with other parts in the course of producing the lenses because of limitations due to production processes. For example, such problems are present that distributed refractive index type flat microlenses prepared by an ion-exchange method are required to be subjected to surface polishing, and convex microlenses prepared from photosensitive glass cannot be molded into other forms than the predetermined form. Hence, there has recently been tried a method comprising forming a lens pattern by melting a positive type photoresist which is used in semiconductor integrated circuit production. The resist pattern was heated to make it round shape for utilizing a microlens or for transferring that shape to a under layer by dry etching to obtain desired curvature radius.
When microlenses are, however, prepared by the above-mentioned methods, such problems are caused that the heat resistance, solvent resistance, transparency and adhesion to substrate of the lens are unsatisfactory though the sensitivity, resolution and refractive index are satisfactory. Moreover, when microlenses are prepared according to the method mentioned hereinafter, there are such problems that the process for preparing the microlenes is complicated and the properties of the surfaces of microlenses are changed by dry-etching.