Method of processing synthetic quartz glass substrate for semiconductor

A method of processing a synthetic quartz glass substrate, comprising putting a polishing part of a rotary small-sized processing tool having a rotational axis set in a direction inclined relative to a normal to the substrate surface in contact with a surface of the synthetic quartz glass substrate in a contact area of 1 to 500 mm2, and scanningly moving the polishing part and substrate surface relatively while rotating the polishing part so as to polish the substrate surface, wherein

• the processing tool is put into reciprocating motion in a fixed direction on the substrate surface, and is advanced at a predetermined pitch in a direction perpendicular to the direction of the reciprocating motion on a plane parallel to the substrate surface, as the polishing proceeds, and wherein the reciprocating motion is performed in parallel to the direction of a projected line obtained by projecting the rotational axis of the processing tool onto the substrate.