Method of manufacturing photo masks

A pattern formation method, comprising:

• acquiring circuit pattern data;
• dividing patterns in the circuit pattern data into multiple areas having different pattern density ranges;
• and
• generating dummy pattern data such that dummy patterns surround each of the multiple areas to generate drawing data,
• wherein the dummy patterns included in the dummy pattern data not printable as a pattern when a resist layer formed on a substrate is exposed with an electron beam by an electron beam lithography apparatus and is developed, and
• the dummy pattern data are generated such that a variation of pattern density of an entire area is smaller than 10%.

A pattern formation method comprising:

• acquiring circuit pattern data;
• calculating a pattern density from the circuit pattern data;
• generating dummy pattern data for areas having pattern density less than a threshold density;
• generating drawing data from the circuit pattern data and the dummy pattern data;
• drawing, by using an electron beam from an electron beam lithography apparatus, patterns according to the drawing data on a resist layer formed on a substrate;
• and
• developing the drawn resist layer using a developing solution,
• wherein dummy patterns included in the dummy pattern data are not printed as a pattern when the resist layer is exposed with the electron beam and is developed.