Method for depositing silicon nitride using low temperatures

摘要

A method for depositing silicon nitride on a semiconductor wafer uses plasma enhanced chemical vapor deposition at very low temperatures. The temperature in a silicon nitride deposition chamber is set to be about 170 DEG C. or less. Silane gas (SiH4) flows into the silicon nitride deposition chamber with a flow rate in a range of from about 300 sccm (standard cubic cm per minute) to about 500 sccm. Nitrogen gas (N2) flows into the silicon nitride deposition chamber with a flow rate in a range of from about 500 sccm to about 2000 sccm. Ammonia gas (NH3) flows into the silicon nitride deposition chamber with a flow rate in a range of from about 1.0 slm to about 2.2 slm. A high frequency RF signal is applied on a showerhead within the deposition chamber. A low frequency RF signal is applied on a heating block for holding the semiconductor wafer. A predetermined volume for the silicon nitride deposition chamber is used such that pressure within the silicon nitride deposition chamber is in a range of from about 1.0 torr to about 2.4 torr. The semiconductor wafer is placed inside the silicon nitride deposition chamber for a soak time period of about 30 seconds or greater before the high frequency RF signal is applied on the showerhead in the deposition chamber and the low frequency RF signal is applied on the heating block. When the semiconductor wafer reaches the deposition temperature, the high frequency RF signal and the low frequency RF signal are applied for deposition of the silicon nitride layer onto the semiconductor wafer. By using low temperatures during the deposition of the silicon nitride layer, the structural integrity of any structure already on the semiconductor wafer is advantageously preserved.