PURPOSE: To improve a yield in the cutting of an artificial diamond coat and enable cost reduction by bonding preliminarily a separation protection plate to said coat of two-layer structure with an adhesive, and cutting said coat and plate concurrently.

CONSTITUTION: An artificial diamond coat is generated and adhered to a silicon mono-crystal of about 600μm thickness and about three inches diameter on a microwave CVD method. A white plate glass is bonded thereto with an adhesive of wax. Cooling water is jetted to the white plate glass and the diamond coat and the glass are concurrently cut with a diamond disc. And acetone flushing is applied to remove said glass and adhesive, thereby separating a substrate from the coat. According to the aforesaid process, there occurs no separation of the coat from the substrate or no micro cutting thereof due to the collision energy of cooling water, thereby improving a yield and reducing the cost of a product.