Active dopant profiling and Ohmic contacts behavior in degenerate n-type implanted silicon carbide

Abstract

This Letter reports on the active dopant profiling and Ohmic contact behavior in degenerate P-implanted silicon carbide (4H-SiC) layers. Hall measurements showed a nearly temperature-independent electron density, corresponding to an electrical activation of about 80% of the total implanted dose. Using the Hall result as calibration, the depth resolved active P-profile was extracted by scanning capacitance microscopy (SCM). Such information on the active P-profile permitted to elucidate the current injection mechanism at the interface of annealed Ni Ohmic contacts with the degenerate n-type 4H-SiC layer. Modeling the temperature dependence of the specific contact resistance with the thermionic field emission mechanism allowed extracting a doping concentration of 8.5 × 1019 cm−3 below the metal/4H-SiC interface, in excellent agreement with the value independently obtained by the SCM depth profiling. The demonstrated active dopant profiling methodology can have important implications in the 4H-SiC device technology.

Selective Doping in Silicon Carbide Power Devices

“…In this context, we have recently elucidated the active dopant profiling and the Ohmic contact behavior in highly P-doped (~1 × 10 20 cm −3 ) 4H-SiC implanted layers, by combining the integral carrier density measurement determined by Hall effect and scanning capacitance microscopy (SCM) carrier depth profiles [ 100 ]. In particular, Al-doped (~1 × 10 17 cm −3 ) p-type 4H-SiC layers were implanted at 400 °C with P + -ions at multiple energies (30–200 keV) and doses (in the range 7.5 × 10 13 –5 × 10 14 cm −2 ), in order to obtain a peak concentration in the order of 10 20 cm −3 .…”

“…Achieving a high electrical activation is a key technological aspect for the fabrication of low-resistance Ohmic contacts on the n-type implanted 4H-SiC, e.g., in the source/drain regions of a MOSFET. In particular, nickel silicide Ohmic contacts fabricated on this n-type implanted layer by deposition of 100 nm Ni film and annealing at 950 °C exhibited a specific contact resistance, ρ c = 5.4 × 10 −6 Ωcm 2 [ 100 ]. In this context, the knowledge of the depth distribution of the electrically active dopant in the implanted region, as that reported in Figure 12 , and its value at the interface with the metal contact (e.g., a nickel silicide layer), is important to optimize the properties of Ohmic contacts and, ultimately, to minimize the specific on-resistance of the devices.…”

“…The dashed line represents the total implanted dose as determined by SIMS. Adapted with permission from [ 100 ]. Copyright 2020 © AIP Publishing.…”

“…(Right scale, black circles) Chemical P-concentration profile obtained by SIMS. Reprinted with permission from [ 100 ]. Copyright 2020 © AIP Publishing.…”

High-Resolution Two-Dimensional Imaging of the 4H-SiC MOSFET Channel by Scanning Capacitance Microscopy

“…As an example, the lateral straggling of implanted Al in 4H-SiC has been observed to depend on the crystallographic orientation [ 8 ] and can result in asymmetric p-type doping profiles. Furthermore, for the degenerate phosphorous-implanted 4H-SiC, an electrical activation of n-type dopant in the order of 80% has been evaluated after annealing at typical temperatures of 1675 °C [ 9 ], whereas ~39% activation has been reported for high concentration Al implants (required for ohmic contact formation on the p-type body) under the same annealing conditions [ 10 ]. Clearly, the incomplete dopant activation in 4H-SiC introduces a degree of uncertainness for the device design.…”