Plasma process control with optical emission spectroscopy

摘要

Plasma processes for etching and desmear of electronic componentsand printed wiring boards (PWB) are difficult to predict and control.Non-uniformity of most plasma processes and sensitivity to environmentalchanges make it difficult to maintain process stability from day to day.To assure plasma process performance, weight loss coupons or post-plasmadestructive testing must be used. The problem with these techniques isthat they are not real-time methods and do not allow for immediatediagnosis and process correction. These tests often require scrappingsome fraction of a batch to insure the integrity of the rest. Sincethese tests verify a successful cycle with post-plasma diagnostics, poortest results often determine that a batch is substandard and theresulting parts unusable. These tests are a costly part of the overallfabrication cost. A more efficient method of testing would allow forconstant monitoring of plasma conditions and process control. Processanomalies should be detected and corrected before the parts beingtreated are damaged. Real time monitoring would allow for instantaneouscorrections. Multiple site monitoring would allow for process mappingwithin one system or simultaneous monitoring of multiple systems.Optical emission spectroscopy conducted external to the plasma apparatuswould allow for this sort of multifunctional analysis without perturbingthe glow discharge. In this paper, optical emission spectroscopy fornon-intrusive, in situ process control is explored along withapplications of this technique towards process control, failure analysisand endpoint determination