This invention relates to the method for repairing a pattern film on a substrate such as a photomask for IC., a semiconductor etc., which is carried out using a focused ion beam.
In a typical conventional method, as shown in FIG. 2a and 2b a mask is disposed in an organic compound vapor 2, and a region 3 including a defect portion of a pattern film 4 which is to be corrected is irradiated with a scanning focused ion beam to form a pattern film 6.
In this case, irradiating with the focused scanning ion beam is repeated a predetermined number of times in order to form a pattern film having predetermined thickness.
However, if, during the focused ion beam scanning, the focused ion beam is drifted at a rate of X .mu.m/hr due to some cause such as a change in an ion source, an electric circuit for allowing the focused ion beam to scan, or a stage for moving a mask secured thereto, a correcting pattern film 7 having an edge finished with a low degree of precision may be formed as shown in FIG. 2, disadvantageously. This gives rise to a serious problem in the case of correcting a transparent defect of the photomask which takes much time to be corrected, that is, which has a relatively large area.