Effect of BCl3 in chlorine-based plasma on etching 4H-SiC for photoconductive semiconductor switch applications

Abstract

Inductively coupled plasma reactive ion etching (ICP-RIE) of n-type SiC epitaxial layers grown on ð000 1Þ 4H-SiC semi-insulating substrates has been investigated using chlorine-based plasma. The etch rate and postetching surface morphology have been studied as functions of the plasma composition, ICP power, RIE power, and process pressure. The authors found that the surface smoothness of the epitaxial layer was increased by introducing BCl 3 into Cl 2 /Ar plasma. An optimized process has been developed yielding etch rates of $220 nm/min and very smooth surfaces with root mean square roughness of $0.3 nm. The spatial-frequency dependence of the one dimensional power spectral density was interpreted using the surface height function h(x) including a low-frequency range, which exhibits saturation and a high-frequency range, which exhibits scaling properties. Through this etching process, the effects of subcontact doping on 4H-SiC photoconductive semiconductor switch (PCSS) performance were investigated. A PCSS was fabricated using this etching process with a 1 lm heavily doped (1.6 Â 10 18 cm À3 n-type) epitaxial layer beneath the device contacts and compared with a PCSS fabricated with a subcontact doped layer created through laser enhanced diffusion ($50 nm depth, 2.0 Â 10 18 cm À3 n-type). The PCSS with the epitaxial layer demonstrated on average a 30% reduction in minimum on-state resistance, and eliminated cracking of the bulk material when switching currents 38 A.

A Review: Inductively Coupled Plasma Reactive Ion Etching of Silicon Carbide

“…The RF power affecting the plasma flux is called the inductive power ( P ICP ), and the RF power to accelerate the plasma ions, and generate the polarization voltage of the etched material is called RF bias power ( P RIE ). The power delivered from both sources influences the etching rate [ 22 , 28 , 33 ]. Theoretical considerations [ 34 ] showed that regardless of the type of etched material and used working gases, the etching rate in the ICP method is directly related to the self-polarization voltage induced by RF power.…”

“…Obtaining the profiles with different wall inclination angles is also possible by the selection of the appropriate composition of the plasma used in the etching process [ 22 , 29 ]. Sung et al [ 23 ] carried out a detailed analysis of the influence of various plasmas (as gas mixtures) on the obtained profiles, for which it was possible to obtain almost vertical walls, with an inclination angle of 87°.…”

“…The micromasking effect may also occur when the etching process takes place under elevated pressure in the reactor chamber. Ekinci et al [ 22 ] investigated the effect of process pressure on the etching rate and the morphology of 4H-SiC surface after etching in Cl 2 + Ar + BCl 3 plasma. The authors noticed that as the pressure in chamber increased, the etching rate decreased.…”

“…The plasma etching can be one of the stages in the process of heterostructures fabrication, such as SiC/SiO 2 , SiC/Si and SiC/glass, by direct adhesive bonding and annealing at T ≤ 200 °C, for potential electronic, optical, mechanical and biomedical applications [ 13 ]. ICP-RIE serves also to obtain: MESA structures of TLM layout in the production of ohmic contacts for SiC [ 14 , 15 ], MOS structures (metal-oxide-semiconductor structures) [ 16 , 17 ], MOSFETs (metal-oxide-semiconductor field effect transistors) [ 8 , 18 ], SiC nanostructures [ 4 , 19 , 20 , 21 ] and photoconductive semiconductor switches (PCSs) [ 22 ].…”

High Power Lateral Silicon Carbide Photoconductive Semiconductor Switches and Investigation of Degradation Mechanisms

“…Prior to electron beam irradiation of the samples used in version 3, the doped epitaxial layer was blanket etched to a thickness of 1 µm, after which the doped epitaxial layer remaining between what would become the anode and cathode contacts was completely removed. The etching process used is described in detail in [49]. The region between what would become the anode and cathode contacts was then irradiated with an electron beam with the same parameters as versions 1 and 2; a brass shadow mask was used to prevent irradiation of the anode and cathode regions [50].…”