Technique of exposing a resist using electron beams having different accelerating voltages, and method of manufacturing a photomask using the technique

A method of manufacturing a photomask, comprising steps of:

• producing several test electron beam resists;
• designing a test pattern to be reproduced on each of the test electron beam resists;
• exposing each of the test electron beam resists to a first electron beam having an accelerating voltage so low and at such a dosage that the electron beam resist absorbs an amount of energy less than the threshold energy of the resist, the threshold energy being that necessary to cause the electron beam resist to develop when subjected to a developing process designated for use in developing the resist;
• and
• exposing each of the test electron beam resists to a second electron beam having an accelerating voltage greater than that of the first electron beam to which the test electron beam resist is exposed and at a dosage sufficient to cause the resist to absorb an amount of energy which, when added to the energy absorbed by the resist as the result of its exposure to the first electron beam, exceeds the threshold energy of the resist required for the resist to develop when subjected to said developing process;
• wherein at least one of the steps of exposing each of the test electron beam resists to an electron beam comprises irradiating the electron beam resist in said test pattern, and the intensity of at least one of the first and second electron beams to which the test electron beam resists are exposed is varied among the steps of exposing the test electron beam resists such that the sum of the dosages to which the test electron beam resists are exposed during said exposing varies from resist to resist;
• subsequently developing the test electron beam resists using said developing process to thereby form test electron beam resist patterns;
• generating data representative of characteristics of the test electron beam resist patterns;
• based on the data, selecting appropriate dosages of first and second electron beams, respectively, from among those used to form the test electron beam resist patterns;
• forming at least one of a phase shift film and an opaque layer on a transparent substrate;
• coating said at least one of the phase shift film and the opaque layer with an electron beam resist;
• exposing the coating of electron beam resist to the dosages of the first and second electron beams selected as a result of the analysis of the test electron beam resist patterns;
• developing the exposed coating of electron beam resist, to thereby form an electron beam resist pattern;
• and
• subsequently etching said at least one of the phase shift film and the opaque layer, using the electron beam resist pattern, formed thereon, as an etching mask.