氧化后退火技术对SiO2/4H-SiC界面态密度的影响

采用等离子体增强化学气相沉积(PECVD)低温处理和高温快速退火的技术,研究了退火条件对SiO2/4H-SiC界面态密度的影响.在n型4H-SiC外延片上高温干氧氧化50 nm厚的SiO2层并经N2原位退火,随后在PECVD炉中对样品进行350℃退火气氛为PH3,N2O,H2和N2的后退火处理,之后进行高温快速退火,最后制备Al电极4H-SiC MOS电容.I-V和C-V测试结果表明,各样品的氧化层击穿场强均大于9 MV/cm,PH3处理可以降低界面有效负电荷和近界面氧化层陷阱电荷,但PH3处理样品的界面态密度比N2O处理的结果要高.经N2O氛围PECVD后退火样品在距离导带0.2和0.4 eV处的界面态密度分别约为1.7× 1012和4×1011eV-1·cm-2,有望用于SiC MOSFET器件的栅氧处理.

Effects of Post-Oxidation Annealing Technique on SiO2/4H-SiC Interface State Density

The effects of annealing conditions on the SiO2/4H-SiC interface state density were investigated by plasma enhanced chemical vapor deposition (PECVD) low temperature treatment and high temperature rapid annealing technique.The SiO2 layer with the thickness of 50 nm was grown on the n-type 4H-SiC epitaxial wafer by dry oxidation at high temperature.After in-situ N2 annealing,the samples were post-annealed in a PECVD furnace with different combinations of PH3,N2O,H2 and N2 annealing atmosphere at 350 ℃.Finally,the 4H-SiC MOS capacitor with Al electrodes was fabricated after high temperature rapid annealing.The I-V and C-V test results show that the breakdown field strengths of the oxide layer of the samples are greater than 9 MV/cm,and PH3 treatment can reduce the interface effective negative charge and the near-interface oxide layer trap charge.However,the interface state density of the PH3 treated sample was higher than that of the N2O treated sample.The interface state densities of N2O post-oxidation annealed samples by PECVD are about 1.7× 1012 and 4×1011 eV-1 · cm-2 at 0.2 and 0.4 eV from the conduction band,respectively,which is promising for gate oxide processing of 4H-SiC MOSFET devices.