Influence of growth pressure on filling 4H-SiC trenches by CVD method

Abstract

To construct a superjunction structure consisting of p/n columns, narrow stripe-shaped trenches (∼1.5 µm wide and ∼4.7 µm deep) preformed on an n+ 4H-SiC substrate were filled by the hot-wall CVD method using a conventional gas reaction system, SiH4:C3H8:H2. The influences of growth pressure on the coverage distribution of epilayers and the corresponding filling efficiency (the thickness ratio of epilayers on trench bottom and mesa top) were investigated. Two benefits of increasing the growth pressure from 10 to 38 kPa were found: one is the reduced growth around the mesa surface, which lessens the risk of void formation; the other is a high filling rate as well as an improved filling efficiency up to ∼7. By supplying source gases at high flow rates, a void-free trench filling with a filling rate of ∼1.3 µm/h was successfully achieved at 38 kPa.

Effects of ion implantation process on defect distribution in SiC SJ-MOSFET

“…In SiC SJ-MOSFETs, several fabrication methods, such as multi-epitaxial growth 7,8) and trench-filling epitaxial growth, can be employed. [9][10][11] Among the fabrication methods, trench-filling epitaxial growth is not sufficiently easy for practical processes involved the mass production of devices. Specifically, it is difficult to form void-free trenches and fill them with defect-free epitaxial growth.…”

“…Specifically, it is difficult to form void-free trenches and fill them with defect-free epitaxial growth. [9][10][11] Conversely, multi-epitaxial growth enables the fabrication of SJ-MOSFETs with deep p-n columns via repeated ion implantation and epitaxial growth. 7,8) However, in this fabrication process, defect generation, via the ion implantation process, is unavoidable, and the defects will impact the performance of the device performance.…”

Strong impact of slight trench direction misalignment from $[11\bar{2}0]$ on deep trench filling epitaxy for SiC super-junction devices

“…As an alternative, a trench-filling epitaxy technique is expected to be used in higher voltage applications. A trench-filling process for SiC has been developed, [14][15][16][17][18][19][20][21][22][23][24] and we previously reported 7-µm-deep trench-filling by chemical vapor deposition using SiH 4 =C 3 H 8 =H 2 precursor gases, 18) but the reproducibility of the trench-filling growth process 18) was poor. Subsequently, addition of HCl etchant gas to the gas mixture in a 5-µm-deep trench-filling process was found to produce significantly higher growth stability.…”

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

“…[2][3][4] Therefore, epitaxial growth by refilling an epilayer into the SiC trench is thought to be highly practicable, 5,6) and some preliminary studies have been implemented with chemical vapor deposition (CVD) in a conventional gas system: SiH 4 :C 3 H 8 :H 2 . [6][7][8][9][10][11][12] The use of a high temperature (1650 °C), 6,7) a relatively high pressure of up to 38 kPa, 13) and a reduced flow rate of the H 2 carrier gas has been found helpful for increasing the filling rate (R G ). These techniques applied together produce R G ∼1.5 µm=h for 5-µm-deep trenches.…”

“…However, in the CVD trench-filling process, the defective growth of voids usually occurs when using high source flow rates, i.e., the trench closes prior to complete filling owing to mesa overgrowth. 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.…”