Suppressing Al memory effect on CVD growth of 4H-SiC epilayers by adding hydrogen chloride gas

Abstract

The Al memory effect during the growth of Al-doped 4H-SiC by the hot-wall chemical vapor phase epitaxy method was investigated. To suppress unintentional incorporation of Al impurities during succeeding growth, a technique was developed by employing HCl-assisted “site-competition” growth. Three methods of introducing HCl, namely, HCl flushing before growth, HCl addition during growth, and the combination of the two preceding methods, have been performed and the Al suppression effects corresponding to the input C/Si ratio were studied separately. It is found that lowering the C/Si ratio reduces Al incorporation for all methods of introducing HCl and using the combination of HCl flushing and HCl addition is highly effective. Optimizing growth rate, temperature, and pressure can further improve Al suppression efficiency; thus, a highly abrupt change in Al distribution between Al-doped and undoped epilayers with Al concentration differences of more than five orders of magnitude was obtained, e.g., a steep change from 1020 to 1014 cm−3.

Precise Control of Al Incorporation during CVD Growth of SiC Epilayers by Using Hydrogen Chloride

“…Several solutions limiting the influence of this uncontrolled Al contamination were proposed: reactor baking between runs, site-competition growth with high Si/C ratio or adding hydrogen chloride (HCl) gas to the process. The latter solution, proposed by Ji et al, was particularly efficient to reduce Al residual and achieve abrupt p+/NID interface [3], however the mechanism was not explained.…”

An empirical growth window concerning the input ratio of HCl/SiH4gases in filling 4H-SiC trench by CVD

“…13) To reduce the risk of void formation, nonmasked quasiselective epitaxial growth (quasi-SEG), 15) has been proposed, in which hydrogen chloride (HCl) gas is introduced to the CVD process as it enables strong etching. 16,17) Results show that the existence of HCl effectively suppresses growth around the mesa and completely fills a 5-µm-deep trench with an aspect ratio of up to 5. 15) Nevertheless, at a higher pressure, the same amount of HCl induces the defective growth of an etched mesa, i.e., trench-shape deformation of reduced depth as a result of overetching on the mesa.…”

Filling 4H-SiC trench towards selective epitaxial growth by adding HCl to CVD process

“…[21][22][23][24] For this reason, in this work, the authors propose the addition of HCl during the CVD process to enhance the etching reaction, and, therefore, to achieve and maintain similar rates for the deposition and etching reactions, thus reducing the net growth rate outside trenches to near zero. That is to say, we developed a novel 4H-SiC trench-filling technique by realizing nonmasked, quasi-selective epitaxial growth.…”

“…In the case of SiC, although HCl has proven to be an effective etchant that can yield a higher etching rate than pure H 2 , the popular masks that are utilized in Si trench filling with HCl (silicon nitride and oxide) are incompatible with the standard CVD process of SiC. [21][22][23][24] For this reason, in this work, the authors propose the addition of HCl during the CVD process to enhance the etching reaction, and, therefore, to achieve and maintain similar rates for the deposition and etching reactions, thus reducing the net growth rate outside trenches to near zero. That is to say, we developed a novel 4H-SiC trench-filling technique by realizing nonmasked, quasi-selective epitaxial growth.…”