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Conventional polycrystalline silicon thin-film transistor (TFr) fabrication processes rely on an etching process to isolate individual transistors. The subsequent growth of a gate insulator film by thermal oxidation of the islands produces a dielectric film which is significantly thinner along the edges of the island. As a result, the completed transistor exhibits significantly reduced gate breakdown characteristics, as well as other adverse effects related to the higher electric fields along the edges of the transistor channel. This paper discusses an alternative TFF fabrication process which employs a local oxidation process in order to eliminate these adverse effects. Breakdown voltages for 60 nm thick gate insulators on 20 ~tm long p-channel TI~rs are increased from 37.5 to 60 V. This represents a breakdown field of 1.1 • 10 v V/cm. Transistors with 5 ~m channel lengths, which cannot be reliably fabricated using the conventional process, also exhibit breakdown fields of 1.1 • 10 v V/cm using this oxide isolation proccss.

As-deposited polycrystalline silicon and argon ion laser recrystallized silicon thin film transistors (TFT's) have been fabricated on Corning Code 1729 glass substrates. This novel aluminosilicate glass has an expansion coefficient matched to that of silicon and a chemical durability comparable to that of fused silica. N-channel enhancement mode transistors were made using conventional IC device fabrication procedures (including thermal oxidation to form the gate insulator) modified to have a maximum processing temperature of 800 C. The- polycrystalline silicon TFT's exhibit leakage currents of less than 2x10-11 A/ μm; of channel width and good stability and reproducibility. Transistors made in the recrystallized silicon show field effect electron mobilities as high as 270 cm2/V s, approximately 15 times the mobility of comparable devices made in as-deposited polycrystalline silicon. The recrystallized silicon devices also exhibit lower threshold voltages and lower leakage currents than do the comparable polycrystalline silicon devices. Major advantages of this TFT technology include the use of a novel, potentially low cost glass substrate and the simultaneous processing of both polycrystalline and recrystallized silicon devices on the same substrate material. This approach represents a new avenue for the incorporation of active devices into a variety of applications including integrated active matrix displays.

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