Manufacturing method of shallow trench isolation

A manufacturing method of shallow trench isolation, comprising:

• (a) depositing pad oxide / silicon-nitride on a substrate as a hard mask for etching;
• (b) begin to deposit a high extinction coefficient silicon oxy-nitride (SiON) layer on the silicon nitride (Si3N4) layer to a desired thickness, then changing the flow rate of silane and N2O gradually to decrease the extinction coefficient to 0.3, and then keeping the flow rate of silane and N2O, continue to deposit said low extinction coefficient silicon oxy-nitride (SiON) to a desired thickness;
• (c) exposing by using a STI mask and developing to form an etching mask of said STI;
• (d) etching said silicon oxy-nitride (SiON), silicon nitride, pad oxide and said substrate to form a shallow trench;
• (e) growing an oxide layer on the side wall and the bottom of said shallow trench to remove damage and decrease leakage;
• (f) depositing an oxide layer on said shallow trench and said silicon nitride to fill said shallow trench;
• (g) planarizing by chemical mechanical polishing (CMP).