Method for forming a split gate device

A method for forming a semiconductor device, the method comprising:

• forming a dielectric layer over a substrate;
• forming a select gate layer over the dielectric layer;
• using a first etch chemistry etching the select gate layer at a first etch rate to form a sidewall of a select gate;
• using a second etch chemistry different from the first etch chemistry, selectively etching the dielectric layer;
• and
• etching the substrate at a second etch rate lower than the first etch rate to form a recess in the substrate adjacent to the sidewall of the select gate, wherein the step of etching the substrate at the second etch rate includes using an oxidizing agent.

A method for forming a semiconductor device, the method comprising:

• forming a dielectric layer over a substrate;
• forming a select gate layer over the dielectric layer;
• etching the select gate layer at a first etch rate to form a first portion of a sidewall of a select gate, wherein the step of etching the select gate layer at the first etch rate includes using an oxidizing agent to oxidize at least a top portion of the substrate underlying the dielectric layer to form an oxide layer below the dielectric layer;
• etching the select gate layer at a second etch rate lower than the first etch rate to form a second portion of the sidewall of the select gate, wherein the step of etching the select gate layer at the second etch rate includes removing only a top portion of the dielectric layer;
• using a wet etch removing the oxide layer and any remaining portion of the dielectric layer to expose a portion of the substrate;
• forming a charge storage layer overlying exposed portion of the substrate and the sidewall of the select gate;
• forming a control gate layer overlying the charge storage layer;
• and
• forming a control gate by patterning the control gate layer and the charge storage layer.