Polycrystalline Si thin-film transistors using thermally crystallized low-pressure chemical vapor deposition a-Si films for the channel layer and P-doped microcrystalline Si films for the source and drain layers

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Abstract
We have fabricated thin‐film transistors with a field‐effect mobility of 17 cm2 /V s using thermally crystallized low‐pressure chemical vapor deposition (LPCVD) a‐Si films for the channel layer and P‐doped microcrystalline Si films deposited by plasma CVD for the source and drain layers. The maximum processing temperature equals 630 °C. The characteristics of these films have been investigated as well. It is found that the grain size of the thermally crystallized LPCVD a‐Si films increases and a {111} preferential orientation of the films becomes more pronounced as the film thickness increases. The average grain size amounts 440 nm on the long axis and 200 nm on the short axis for a film thickness of 460 nm. The conductivity of P‐doped microcrystalline Si films deposited by plasma CVD at 270 °C is closely dependent on the deposition rate of the films and the grain size of the underlying channel polycrystalline Si films. By decreasing the deposition rate and using crystallized LPCVD a‐Si films for the underlying channel layer, highly conductive P‐doped microcrystalline Si films are realized.