Afterglow Thermal Oxidation of Silicon Carbide
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Afterglow Thermal Oxidation of Silicon Carbide Andrew M. Hoff, Arti Tibrewala, and Stephen E. Saddow Department of Electrical Engineering, University of South Florida, Tampa, FL. 33620, U.S.A. ABSTRACT We report, for the first time, the growth of thermal oxides on silicon carbide at temperatures below 900 °C using a novel afterglow thermal reactor. Flowing afterglows of microwave plasmas have been used for decades to study fundamental chemical reactions and in recent years they are employed as rich atomic oxygen sources for one of the principal techniques of polymeric photoresist removal in IC plants around the globe. The advantage of afterglow generation of a high flux of reactive species is that microwave plasmas may be excited inside clean quartz tubing and further the plasma potential of such discharges is less than 10 electron volts, which is far below the sputtering threshold of most materials, lowering the chance of contamination. In our case, we have integrated an afterglow source with a vacuum furnace system. The substrates to be oxidized are placed in the hot zone of the furnace where they are exposed to the flowing afterglow at a pressure near 1 Torr. The afterglow chemistry generated from pure oxygen traveling through the source includes O2, atomic oxygen, and excited states of O2. All ions and electrons generated by the plasma source are confined to the microwave cavity limits and photons are excluded by trapping techniques. The wafers in the furnace are exposed to a rich chemistry of afterglow species that were generated by non-thermal means. The furnace temperature alone controls the chemical reaction between the afterglow species and the substrates. We present the results of oxide growth on 4H and 6H silicon carbide substrates over a range of temperature. An example result is over 200Å of film grown at 800 °C in 2 hours. Atmospheric processing in O2 at 1050 °C would require 14 hours to grow a similar thickness on SiC. Possible mechanisms and oxide properties will also be discussed. INTRODUCTION The thermal oxidation of silicon carbide is routinely achieved at temperatures higher than 950 °C over two to four hours of process in either a dry O2 or in a steam oxidative environment at atmospheric pressure [1-4]. A silicon oxide, SiO2, thin film ranging in thickness from 200 Å to 400 Å is obtained given such process conditions. In this work we demonstrate the growth of oxide films on various polytype and doping types of SiC and on p-type (100) oriented silicon from 20 Å to near 300 Å thick, grown in an oxidant flux generated by a remote plasma or afterglow source, at temperatures ranging from 400 °C to 800 °C, times from 30 to 120 minutes, and total system pressure near 1 Torr. These results suggest a higher rate of interface reaction between SiC and afterglow species than is observed with typical atmospheric processes. In addition comparable oxide films are grown in the afterglow process for (100) oriented silicon substrates as well as for 4H and 6H n- and p-type silicon carbide substrates. The m
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