High etch rate method for plasma etching silicon nitride

Abstract

This invention is directed to a method for rapid plasma etching of materials which are difficult to etch at a high rate. The method is particularly useful in plasma etching silicon nitride layers more than five microns thick. The method includes the use of a plasma source gas that includes an etchant gas and a sputtering gas. Two separate power sources are used in the etching process and the power to each power source as well as the ratio between the flow rates of the etchant gas and sputtering gas can be advantageously adjusted to obtain etch rates of silicon nitride greater than two microns per minute. Additionally, an embodiment of the method of the invention provides a two etch step process which combines a high etch rate process with a low etch rate process to achieve high throughput while minimizing the likelihood of damage to underlying layers. The first etch step of the two-step method provides a high etch rate of about two microns per minute to remove substantially all of a layer to be etched. In the second step, a low etch rate process having an etch rate below about two microns per minute is used to remove any residual material not removed by the first etch step.