Photomask used by photolithography and a process of producing same

Claim 1

A photomask comprising: a transparent substrate; a transparent electroconductive layer formed substantially on the entire surface of the substrate; and a pattern of a transparent layer, wherein the photomask does not include a light shielding layer, and wherein the transparent layer has a thickness t defined by the following formula, t=(2i-1)λ/[2(n-1)] where t is a thickness of the transparent layer, n is a refractive index of the transparent layer, i is an integer and λ is a wavelength of an incident light to the photomask, thereby providing a phase difference of π or π multiplied by an odd number between the light transmitting the transparent substrate and the light transmitting the transparent layer; interfering with said two lights to reduce the intensity of the incident light; and forming resist patterns in the doubled number of that of the transparent layer pattern, said resist patterns having a width equal to the resolution limit R defined by the following formula, R=K.sub.1 λ/NA where K 1 is an optical constant of the photomask, λ is a wavelength of incident light and NA is a numerical aperture of the optical system.