Al2O3 Gate Dielectric on GaAs by Atomic Layer Deposition System
|關鍵字:||砷化鎵;原子層沉積;GaAs;Atomic Layer Deposition|
GaAs offers the advantages of high electron mobility, rich band gap engineering, low power consumption and high breakdown fields and thus is expected to outperform Si in the specific metal-oxide-semiconductor (MOS) applications. With wet-chemical cleaning of GaAs wafers, it is necessary to effectively suppress the formation of native oxide before dielectric deposition. From XPS spectra, we found that HCl solution could better eliminate native oxide with decreasing concentration, but with a limit of around 10%. Less than 10%, the situation became worse. Moreover, as we used the mixture solution of HCl and H2O2, the substrates would be oxidized and cleaning effect decreased. We also found that (NH4)2S passivation was effective in suppression of native oxide formation. In this thesis, we grew Al2O3 by atomic layer deposition system (ALD). For low leakage current, the growth temperature was set at 300oC. Prior to dielectric deposition, we employed additional interfacial passivation layers (IPLs) in order to deposit excellent Al2O3 film. Si capping and (NH4)2S passivation were the two most commonly used IPLs techniques. We found that these two methods were effective in eliminating native oxide and in turn very helpful in achieving high-quality Al2O3 film deposition. In particular, we found that dipping in 2% (NH4)2S solution for 30s was the optimized treatment condition. After depositing Al2O3, we conducted post deposition annealing (PDA) to further improve the deposited film. We observed that the C-V curves of the samples became sharper and their hysteresis decreased significantly with PDA at 600oC concomitant with larger leakage current, especially in N2 atmosphere. We believe it is due to the fact that N2 annealing would cause more As layer incorporated into the dielectric than O2, which is likely to form the leakage current path. Finally, the reliability of MOS capacitors has been characterized and discussed. It was observed that (NH4)2S treatment was effective in preventing rapid Jg increase during stressing. Considering not only Jg, hysteresis but also Dit, O2 PDA with sulfide treatment was the best treatment condition.
|Appears in Collections:||Thesis|
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