Quantification Of Laser Interference Fringes As Applied To Plasma Etch Endpoint Detection

As integrated circuit feature sizes have continued to decrease, plasma etching has become the method of choice for achieving the resolution and process control required for device fabrication. To maintain tight control, the precise detection of etch endpoint is very important. A variety of endpoint detection schemes are available. These include the optical emission spectroscopy, mass spectroscopy, monitoring of chamber pressure and dc bias, and laser interferometry. This paper deals with the application of laser inteferometry for endpoint detection in plasma or dry etching, which is the removal of a film in a plasma or low pressure gaseous discharge. Etching consists of the following steps. The exposed film, i.e. not covered by resist, is removed by chemical and/or physical processes which are determined by the type of etch. In plasma etching, the etching is done by ions and highly reactive chemical species called free radicals. There are many different types of dry etch methods. In this case, the process was RIE, reactive ion etching, where chemical and physical effects interact to produce the etch.