Dual-tank etch method for oxide thickness control

A method of controlling thickness of a pad oxide layer comprising:

• providing a plurality of substrates each having a pad oxide layer underlying a nitride layer;
• providing a nitride strip chemical saturated with oxide;
• providing an oxide etchant separate from said nitride strip chemical;
• stripping to remove said nitride layer from said underlying pad oxide layer by immersing said substrates in said nitride strip chemical;
• removing said substrates from said nitride strip chemical;
• etching said pad oxide layer to a target thickness by immersing said substrates in said oxide etchant for a processing time, said pad oxide layer etched following removal of said silicon nitride layer;
• measuring a post-etch thickness of said pad oxide layer on each of said substrates;
• comparing said post-etch thickness to said target thickness;
• and
• prolonging said processing time of remaining successive ones of said substrates in said substrate lot when said post-etch thickness is greater than said target thickness.

A method of preventing surface defects induced by silicon oxide precipitates on a substrate in a processing tank, comprising the steps of:

• providing a substrate having a pad oxide layer and a silicon nitride layer on and overlying said pad oxide layer;
• providing a nitride strip chemical saturated with oxide in a first processing tank;
• providing an oxide etchant in a second processing tank;
• stripping to remove said nitride layer from said underlying pad oxide layer by immersing said substrates in said nitride strip chemical;
• removing said substrate from said first processing tank;
• and
• etching said pad oxide layer to a target thickness by immersing said substrate in said oxide etchant for a processing time, said pad oxide layer etched following removal of said silicon nitride layer.