Plasma Oxidation/Anodization of Silicon Films for Photovoltaic and Flat Panel Display Applications

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Research on electronic devices fabricated in thin films of amorphous silicon (a-Si) or polycrystalline silicon (p-Si) has recently gained momentum due to a variety of new applications for these devices. For example, the efficiency of experimental solar cells produced using a-Si films currently exceeds 12%. These efficiencies make such devices attractive for the realization of large area, low cost photovoltaic energy conversion systems. Another example is a-Si and p-Si thin film transistors (TFTs) which have made possible the fabrication of full color, flat panel displays. Such displays can be used in laptop computers and in future high definition TV. In addition to flat panel displays, TFTs fabricated in a- Si or p-Si can be used as switching elements in other large area electronic systems such as lenseless contact-type image sensors and position sensitive detectors. All of these devices (flat panel displays, image sensors and position sensitive detectors) are fabricated on low cost glass substrates; therefore the manufacturing temperatures must be kept below 600 C to avoid glass distortion. In the case of hydrogenated a-Si devices, the process temperatures should be below 450 C to avoid deterioration of the electronic properties of the a-Si. Oxidation of single crystal silicon (c-Si) has been used in the successful development and manufacture of integrated circuits. The importance of silicon oxidation is that thermal oxidation of silicon results in the growth of a high quality insulator and passivation layer with an interface to silicon that has relatively few surface traps which alter device properties and affect device stability. Oxidation temperatures used in the production of silicon integrated circuits is in the range of 800 to 1100 C. An alternative method will be tested in this research, the plasma oxidation or anodization process, in which the grown film is exposed to reactive ions, electron, atomic oxygen, and ultra violet (UV) photons during oxidation. This exposure leads to enhancement of the oxidation rates at low temperatures. Electron cyclotron resonance (ECR) plasmas will be used to oxidize or anodize a-Si and p-Si films. The oxidation kinetics of these processes will be studied as functions of the substrate temperature and plasma process conditions. Electronic devices will be fabricated and their characteristics correlated with growth conditions. This technology could impact the manufacture of low cost, high reliability, flat panel displays and solar cells.***//