Laser diagnostic techniques for reactive ion etching: Plasma understanding to process control

Abstract

Reactive ion etching is the current process of choice for production of high-speed integrated circuits; yet the development and use of this technology has evolved largely through empirical efforts. Beam/surface studies have proven instrumental in examining fundamental issues in etching; however, extension of these results to process plasmas requires considerable extrapolation. Laser diagnostic measurements may be used as a bridge between UHV measurements and the process plasma, a role which is possible due to the high specificity and sensitivity of these techniques. Spatially resolved laser studies provide three-dimensional in situ measurement of concentration gradients for reactive etchants and ions in the plasma. Key plasma etchants such as O and Cl may be studied using two-photon excitation processes. Finally, the emerging use of lasers for process control applications is discussed and compared with conventional approaches, such as optical emission end-point detection.