A comparison of etching conditions in the GEC reference cell to a commercial reactive ion etcher.

Abstract

The increased use of rf glow discharges in microelectronics fabrication has resulted in the need for greater comprehension and control of plasmas. One of the most important factors affecting plasma behavior is the geometry of the discharge chamber, as minor alterations in design result in large variations in plasma parameters and, hence, in the etching results. In industry, apparently identical commercial etchers can behave differently. Because of the number of different systems used, it is difficult to compare data from machines of differing properties. As semiconductor manufacturers move toward automating each fabrication step, there is a need for a more complete understanding of not only the discharges but also the behavior of the tools themselves. Only after gaining this understanding will it be possible to truly attain real-time control of a process step and to ensure that the multitude of machines on the factory floor will deliver identical results. Because of the number of different systems used for experiments in the past, it was difficult to compare data from machines of differing properties. For this reason, a standardized discharge chamber was designed so that models and measurements at different locations could be directly compared. This chamber, referred to as the GEC Reference Cell, was used for the work presented in this thesis. The electrical characteristics of the cell were investigated and compared to similar cells at other locations. In addition to the electrical characterization studies, the uniformity of the discharge present in the reference cell during operations was monitored by spatially resolved optical emission spectroscopy (SR-OES). The uniformity of the discharge had a direct affect on the uniformity of the etch performed in the cell. The operation of the GEC Reference cell during the etching of polysilicon was compared to that of a commercial reactive ion etcher, the SEMI Group RIE. It was possible to determine a regime where both systems behave similarly by monitoring the relative fluorine concentrations, etch rates and bias voltages in the two systems. To attain this similarity, it was necessary to alter the plate spacing on the SEMI Group RIE to match that of the reference cell as well as to adjust the input power in order to create similar power densities in the two systems. This was a very important result in that it showed the GEC reference cell could mimic commercial cells, which are much more difficult to study. Finally, FCONC, a simple, batch reactor, chemical equation solver, is presented. FCONC quickly determines species concentrations in an etching tool in real time. FCONC's results are compared to the actinometry data to both verify the code and to determine the fluorine concentration in the GEC reference cell as power and pressure are varied. The results of FCONC follow the data trends of the actinometry results and are close in magnitude.