氢气体积流量对n型4H-SiC同质外延生长的影响

Effect of Hydrogen Volume Flow on Homoepitaxial Growth of n-Type 4H-SiC

在商业化偏4°导电型4H碳化硅(SiC)衬底上采用化学气相沉积(CVD)的方法进行n型4H-SiC同质外延层生长,研究反应过程中氢气(H2)对外延生长的影响,并使用表面缺陷测试仪、汞探针和红外膜厚仪等设备对外延层进行分析和表征。结果表明,氢气体积流量由基础值80增加到120 L/min,生长速率呈先增加后降低的趋势,生长速率的增加值最大为2μm/h,但缺陷呈先减少后增加的趋势。在高温CVD外延过程中,生长速率阶段性变化的原因:一是生长速率由气相质量转移系数和表面化学反应速率共同决定;二是氢气体积流量过大时,大量的析出氢难以及时离开生长表面,不利于反应物的有效分解和再沉积过程。综上所述,采用100 L/min氢气体积流量的生长工艺可在较高生长速率下制备高质量、厚度均匀性0.91%和载流子浓度均匀性1.81%的SiC外延片。

n-type 4H-SiC homoepitaxial layers were grown on the commercial 4°off-axis conductive 4H-SiC substrates using the chemical vapor deposition(CVD)method.The effect of hydrogen(H2)on the epitaxial growth during the reaction was investigated.The epitaxial layers were analyzed and characterized by using the surface defect tester,mercury-probe and the infrared film thickness measuring apparatus.The results show that the growth rate increases first and then decreases when the volume flow of H2 increases from the basic value 80 L/min to 120 L/min.The maximum increase value of the growth rate is 2μm/h,and the defects show a trend of first decreasing and then increasing.In the high temperature CVD epitaxial process,the reasons for the periodic changes of the growth rate can be attributed to the following aspects:the growth rate is determined by the gas phase mass transfer coefficient and surface chemical reaction rate;moreover,when the volume flow of H2 is too large,a large amount of precipitated hydrogen can hardly leave the growth surface in time,which is not conducive to the effective decomposition and redeposition of reactants.In conclusion,with the H2 volume flow of 100 L/min,the high quality SiC epitaxial wafer with a thickness uniformity of 0.91%and a carrier concentration uniformity of 1.81%can be prepared at high growth rate.