Automated method for monitoring and controlling the orthophosphoric acid etch rate of silicon nitride insulator layers

摘要

A method for continuously monitoring and controlling the etch rates within integrated circuits of silicon nitride insulator layers and silicon nitride insulator structures in aqueous ortho-phosphoric acid (H3PO4) solutions. To practice the method of the present invention, there is first provided an etch bath chamber containing therein an aqueous ortho-phosphoric acid (H3PO4) solution. There is provided continuously from the etch bath chamber to a hydrometer cell a sample stream of the aqueous ortho-phosphoric acid (H3PO4) solution. The sample stream of the aqueous ortho-phosphoric acid (H3PO4) solution is analyzed continuously within the hydrometer cell to provide a continuous specific gravity analysis of the sample stream of the aqueous ortho-phosphoric acid (H3PO4) solution. Finally, the continuous specific gravity analysis of the sample stream of the aqueous ortho-phosphoric acid (H3PO4) solution is employed to add intermittently to the aqueous ortho-phosphoric acid (H3PO4) solution a quantity of water sufficient to maintain a first water content of the aqueous ortho-phosphoric acid (H3PO4) solution within the etch bath chamber at a value greater than about 5 weight percent. Optionally, the continuous specific gravity analysis of the sample stream of the aqueous ortho-phosphoric acid (H3PO4) solution may also be simultaneously employed to add intermittently to the aqueous ortho-phosphoric acid (H3PO4) solution a quantity of heat sufficient to maintain a second water content of the aqueous ortho-phosphoric acid (H3PO4) solution within the etch bath at a value less than about 20 weight percent. The present invention also discloses the hydrometer cell and an automated etch bath chamber which are employed in practicing the method of the present invention.