Methods for manufacturing a diffuser plate for a PECVD chamber are provided. The methods provide for applying a compliant abrasive medium to round the sharp edges at corners of the output holes on a contoured downstream side of a gas diffuser plate. By rounding the edges of the output holes reduces the flaking of deposited materials on the downstream side of the gas diffuser plate and reduces the amount of undesirable particles generated during the PECVD deposition process.