Plasma diagnostics for semiconductor processing

Abstract

Frequency-modulated infrared diode laser absorption spectroscopy (IRLAS) and full-spectrum CCD-based optical emission spectroscopy (OES) are two powerful new tools for plasma diagnostics. This presentation focuses on the use of these diagnostics in plasma etch processing used for semiconductor manufacturing. In particular, IRLAS is finding extensive use in measuring absolute concentrations of gas phase radicals formed in the oxide etch process performed with fluorocarbon high-density plasma discharges. Knowledge of the absolute concentrations of reactant and product species formed in trace amounts during etching of oxide substrates is important for predicting the behavior of this complex plasma-surface interaction. These measurements are a critical element in a program for plasma etch model development, and are intended for validating computer simulation models of this complex process. Full-spectrum OES on the other hand is a more mature technology that is finding application in day-to-day semiconductor fab plasma processing operations like end-point and fault detection. With the development of CCD sensors and micromachined diffraction gratings, it has been possible to build miniaturized spectrometers mounted on computer boards that allow rapid acquisition of the complete UV-visible optical emission spectrum of the plasma. Chemometric multivariate statistical analysis of this full-spectrum database in real time is made possible by integrating the spectrometer with a fast portable computer. In combination, these techniques have been shown to provide superior sensitivity for detecting process end-point in real-time and information for process fault detection.