Spectroscopic ellipsometry (SE) based real-time control of CF4 /O2 plasma etching of silicon nitride

Real time feedback controllers for the electron cyclotron resonance CF₄/O₂ plasma etching of plasma enhanced chemical vapor deposited silicon nitride thin films are designed and tested. Variations in etch rate resulting from factors such as etch chamber wall seasoning which are inherent to plasma etching necessitate the use of feedback control to achieve precise and reliable etching of ultrathin films. In this paper, a non-adaptive and an adaptive controller are proposed for this task. The controllers are implemented and tested both in simulation studies and in the laboratory on the actual etching chamber. The results of these tests are reported and discussed