Application of Thermal Plasma Jet Irradiation to Crystallization and Gate Insulator Improvement for High-Performance Thin-Film Transistor Fabrication

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Large grains with a maximum length of ${\sim}60$ μm were grown by high speed scanning (${\sim}4000$ mm/s) of a molten region in amorphous silicon (a-Si) films formed by micro-thermal-plasma-jet (μ-TPJ) irradiation. By reducing the TPJ nozzle diameter and increasing the spacing between anode and cathode, the power density transferred to a-Si film surface increased to as high as 53 kW/cm2, which enabled melting and lateral solidification in the microsecond time domain. The a-Si transformed to crystalline through solid-phase crystallization, followed by melting and recrystallization induced by the movement of the molten region with the maximum size of ${\sim}483$ μm in width and ${\sim}990$ μm in length. The laterally crystallized Si films show anisotropic large grains and a high crystalline volume fraction of ${\sim}100$% and preferential surface orientation of (111) plane. Thin-film transistors (TFTs) fabricated by solid-phase-crystallized microcrystalline Si (μc-Si) show a small field effect mobility ($\mu_{\text{FE}}$) of ${\sim}2$ cm2 V-1 s-1 with small variation less than 1%, while the high-speed lateral-crystallization (HSLC) Si film shows a very high $\mu_{\text{FE}}$ of 350 cm2 V-1 s-1. We improved the bulk bond network of the low-temperature-deposited gate SiO2 films by TPJ-induced millisecond annealing. By combining TPJ annealing and postmetallization annealing (PMA), a high-quality SiO2/Si interface with a density of interface states ($D_{\text{it}}$) of $3.0 \times 10^{10}$ cm-2 eV-1 is obtained. In addition, we found that the improvement in the bulk bond network of SiO2 is quite effective to improve the stress immunity of μc-Si TFTs. TFTs fabricated with TPJ-annealed gate SiO2 films show much smaller on-current degradation and threshold voltage shift after DC bias stress compared with untreated TFTs. Not only the threshold voltage ($V_{\text{th}}$) shift under high-gate-field stress condition, but also on-current degradation under drain avalanche hot carrier (DAHC) generation condition are markedly suppressed. This improvement is attributed to the reduction of Si--OH bonds and relaxation of the bulk chemical bond network of SiO2 induced by TPJ annealing.
2011-03-25

Application of Thermal Plasma Jet Irradiation to Crystallization and Gate Insulator Improvement for High-Performance Thin-Film Transistor Fabrication

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