Microroughness, which accompanies the miniaturization of device dimensions, is essential to the reliability of the device. The atomic force microscope (AFM) is available as a Si microroughness evaluation apparatus but most models cannot measure large size wafers in an environment with a lot of disturbance, such as a clean room. The AFM used for the measurement is a lever scan type in which a small scale optical lever defection detector and cantilever are installed at the top of a tube piezoscanner, and is linked to an optical microscope. It can accurately position within 4 mum on up to an 8 in. sample. The performance of this system includes a lateral resolution of approximately 5 angstrom and a Z direction resolution of about 0.5 angstrom. The CZ P-type (100) size 4 in. wafer used in the measurement is oxidized after three types of washing, and the relationship between the roughness of the bare wafer and the roughness of the oxidized wafer is measured.