Method and apparatus for plasma etching

摘要

This invention is directed to a method for plasma etching difficult to etch materials at a high etch rate. The method is particularly useful in plasma etching silicon nitride layers more than five microns thick. The method includes a plasma formed by energy provided from two separate power sources and a gaseous mixture that includes only an etchant gas and a sputtering gas. The power levels from the separate power sources and the ratio between the flow rates of the etchant gas and a 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 the. In the second step, a low etch rate process having an etch rate below about two microns per minute is used remove any residual material not removed by the first etch step.