<i>In Situ</i> Boron and Aluminum Doping and Their Memory Effects in 4H-SiC Homoepitaxial Layers Grown by Hot-Wall LPCVD

Abstract

The in-situ p-type doping of 4H-SiC grown on off-oriented (0001) 4H-SiC substrates was performed with trimethylaluminum (TMA) and/or diborane (B2H6) as the dopants. The incorporations of Al and B atoms and their memory effects and the electrical properties of p-type 4H-SiC epilayers were characterized by secondary ion mass spectroscopy (SIMS) and Hall effect measurements, respectively. Both Al- and B-doped 4H-SiC epilayers were p-type conduction. It was shown that the profiles of the incorporated boron and aluminum concentration were in agreement with the designed TMA and B2H6 flow rate diagrams. The maximum hole concentration for the Al doped 4H-SiC was 3.52×1020 cm-3 with Hall mobility of about 1 cm2/Vs and resistivity of 1.6~2.2×10-2 Wcm. The heavily boron-doped 4H-SiC samples were also obtained with B2H6 gas flow rate of 5 sccm, yielding values of 0.328 Wcm for resistivity, 5.3×1018 cm-3 for hole carrier concentration, and 7 cm2/Vs for hole mobility. The doping efficiency of Al in SiC is larger than that of B. The memory effects of Al and B were investigated in undoped 4H-SiC by using SIMS measurement after a few run of doped 4H-SiC growth. It was clearly shown that the memory effect of Al is stronger than that of B. It is suggested that p-type 4H-SiC growth should be carried out in a separate reactor, especially for Al doping, in order to avoid the join contamination on the subsequent n-type growth. 4H-SiC PiN diodes were fabricated by using heavily B doped epilayers. Preliminary results of PiN diodes with blocking voltage of 300 V and forward voltage drop of 3.0 V were obtained.

Acceptor incorporation in SiC epilayers grown at high growth rate with chloride-based CVD

“…Previous report on the memory effect of aluminum and boron doping in the chloride-based process at 2000 1C found a lowest achievable Al and B doping of 1 Â10 15 cm À3 and 2 Â 10 16 cm À3 , respectively, after growth of thick heavily p-type-doped epilayers [21]. Recent report on boron-and aluminum-doped layers grown in low pressure CVD (40 Torr) found a longer memory effect for aluminum than for boron [27]. It has previously been suggested that HCl-etch of the susceptor after growth reduces the memory effect of both aluminum and boron [12], however in [21] it is stated that the chlorine present in the process does not reduce the aluminum and boron content in unintentionally doped layers to the level before the growth of heavily doped layers.…”

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

“…Much research effort has been made to suppress the Al memory effect. [7][8][9][10][11] We have studied the suppression methods using site-competition growth and achieved a reduction factor (the ratio of Al concentration N Al in the undoped epilayer to that in the p + layer) of about 1/17,000, e.g., N Al from 9 © 10 19 to 6 © 10 15 cm ¹3 or from 1.7 © 10 20 to 1.0 © 10 16 cm ¹3 . 7) On the other hand, La Via et al reported that the growth using trichlorosilane can decrease the Al impurity level to 10 14 cm ¹3 after a p + epilayer growth with N Al ³ 1 © 10 18 cm ¹3 , but it is a concern that there may be an upper limit of Al doping level of approximately 10 18 cm ¹3 .…”

Suppression of Al Memory-Effect on Growing 4H-SiC Epilayers by Hot-Wall Chemical Vapor Deposition

“…Up to now, only seldom works have been reported about Al memory-effect in CVD growth of SiC. 3,[5][6][7] One conclusive solution has been made that the growth should be carried out in separate reactors for n/p layers. 6) It is inapplicable in consideration of possible Al contaminations to n-reactor.…”

“…3,[5][6][7] One conclusive solution has been made that the growth should be carried out in separate reactors for n/p layers. 6) It is inapplicable in consideration of possible Al contaminations to n-reactor. Besides, a previous report demonstrates that the device by a continual growth shows superior performance than that grown by an interrupted growth.…”