A method of forming a high aspect ratio metal plate pattern and a circuit board by multi-stage etching with a metal mask is disclosed. A resist (12) is coated on one of two surfaces of a copper plate (10) and patterned to form a resist pattern. A tin plating layer (14) is formed using this resist pattern, and with this tin plating layer as a mask, the copper plate is selectively half etched. By coating, exposing and developing the positive resist (18), the side etched portion under the tin plating layer is protected by the positive resist. With the tin plating layer and the protective resist layer as a mask, the half etching is executed again. This process is repeated until the resist and the tin plating layer used as a mask are finally removed to produce a metal pattern (20).