be discussed in this specification the present invention is based upon the principle that when the entire area of the resist film on the wafer is subjected to a exposure to be referred to as 34 the first exposure 34 prior to the exposure to be referred to as 34 the second exposure 34 for imaging a pattern on the resist film the intensity of the electron beam for the second exposure becomes the intensity required for complete exposure minus the intensity used for the first exposure for instance when the first exposure is made with the intensity of 0 8 u00d7 10 4 coulomb cm 2 the second exposure is made with the intensity of 5 u00d7 10 5 coulomb cm 2 which is equal to 1 3 u00d7 10 4 0 8 u00d7 10 4 coulomb cm 2 when the resist film is exposed in two stages as described above the following effects may be attained 1 the apparent sensitivity of the resist film may be considerably increased when a pattern is imaged that is when the resist film is subjected to the first exposure with the intensity of 0 8 u00d7 10 4 coulomb cm 2 the apparent sensitivity becomes 5 0 u00d7 10 5 coulomb cm 2 when a pattern is imaged that is as compared with the one step exposure wherein the resist film is not subjected to the first exposure the apparent sensitivity is increased by 2 6 times when a decrease in the thickness of the resist film at an unexposed area in the second exposure after development is permitted the intensity of the first exposure may be further increased so that the apparent sensitivity may be further increased accordingly.