Semiconductor device manufacturing method and pattern forming method

A semiconductor device manufacturing method includes forming a first film on a substrate having a first region and a second region. A second film is formed on the first film. Guide grooves are formed by removing portions of the second film and exposing the first film. A self-assembly material is coated on the exposed first film and heated to cause a phase separation into a first and a second phase section. The self-assembly material is irradiated. A mask pattern including at least a portion of the first phase section is formed by removing the second phase section. The mask pattern has a first dimension in the first region and a second dimension in the second region that is different from the first dimension. The first film is etched after the mask pattern is formed.