Real-time plasma etch control by means of physical plasma parameters with SEERS

Abstract

The plasma monitoring system HERCULES utilizes the Self Excited Electron Plasma Resonance Spectroscopy (SEERS) technique. It takes into account the non-linearity of the space charge sheath at the rf electrode, which provides harmonics with the modulated sheath width and high frequency oscillations in the bulk plasma. By using a general discharge model, SEERS provides volume averaged values of electron collision rate, electron density, and bulk power. It thus provides a very efficient real time data compression. The rf sensor head at the chamber wall is on ground potential and does not influence plasma-or process conditions. The sensor measures rf currents only, hence, there is no impact of polymer or other insulating layers on the measured signals. HERCULES is the first process control tool providing real-time accessibility to plasma parameters -based on an electrical measurement principle -for rf plasmas under industrial conditions. The efficient data handling being ready for use in production includes an internal process data bank and offers two ways to control the process: I .) independent of the etch tool, and 2.) using a data coupling utility providing fast and easy access to wafer and lot data. Here, the second possibility was used based on a chamber log-sheet for lot and single wafer control. The major benefit ofthis choice is that data can be analysed by lot and product using standard software. The SEERS tool demonstrated a high sensitivity and significant correlation of measured signals to variations of fundamental process parameters. It was found to be well suited to control stability of process equipment and to support process optimisation and development. Important suppliers, e.g. Applied Materials and Lam Research, have supported the assessment and are interested in applying this process control tool.

Correlation of III/V semiconductor etch results with physical parameters of high-density reactive plasmas excited by electron cyclotron resonance

“…Therefore, in the short introductory preparative section, this parameter is presented for several conditions. Over the past two decades, the influence of the walls and the electrode on plasma parameters has become a subject of intense research [20,21], not at least associated with issues such as the 'first wafer effect' (different etch rate after reactor cleaning) [22] and 'arcing' (flashes at the walls due to coating) [23], which are due to contamination of the walls [24,25] and their subsequent different yields of secondary electrons that are generated by ion impingement. Hence, the strongest influence on this experiment is expected to occur by changing the transport platens, which carry the substrates and are placed on the 'hot' electrode.…”