本发明的目的之一在于提供一种利用DC溅射法形成氧化镓膜的成膜方法。本发明的目的之一还在于提供一种半导体设备的制造方法，在该半导体设备中将氧化镓膜用作晶体管的闸极绝缘层等的绝缘层。使用含有氧化镓(也写为GaOX)的氧化物靶材并且借由DC溅射法或脉冲DC溅射方式形成绝缘膜。氧化物靶材含有GaOX，其中X小于1.5，最好为0.01以上且0.5以下，更佳为0.1以上且0.2以下。该氧化物靶材具有导电性，并且在氧气体气围或氧气体和如氩等的稀有气体的混合气围下进行溅射。

An object is to provide a deposition method in which a gallium oxide film is formed by a DC sputtering method. Another object is to provide a method for manufacturing a semiconductor device using a gallium oxide film as an insulating layer such as a gate insulating layer of a transistor. An insulating film is formed by a DC sputtering method or a pulsed DC sputtering method, using an oxide target including gallium oxide (also referred to as GaOX). The oxide target includes GaOX, and X is less than 1.5, preferably more than or equal to 0.01 and less than or equal to 0.5, further preferably more than or equal to 0.1 and less than or equal to 0.2. The oxide target has conductivity, and sputtering is performed in an oxygen gas atmosphere or a mixed atmosphere of an oxygen gas and a rare gas such as argon.