Processing method of large-specification photomask substrate

The invention relates to a processing method, in particular to a processing method of a large-specification photomask substrate. According to the processing method, a quartz mask plate semi-finished product is prepared through cutting, detecting and polishing. According to the processing method of the large-size photomask substrate, the tension, the movement speed, the cutting speed and the spraying liquid flow are determined through experiments, the flatness of a quartz plate blank can be controlled to be 130-290 microns during cutting, the flatness of the quartz plate blank can be reduced to be within 50 microns during grinding, and the processing difficulty that a semi-finished product is processed to be within 20 microns in a semi-finished product stage is effectively reduced. The problem that in an existing machining method, flatness control is poor in the blank stage machining process, and consequently the semi-finished product stage machining difficulty is large is solved. 本发明涉及一种加工方法，具体涉及一种大规格光掩模基板的加工