Optimization of a Concentrated Chloride-Based CVD Process for 4H–SiC Epilayers

Abstract

Concentrated homoepitaxial growths of 4H-SiC was performed using a chloride-based chemical vapor deposition ͑CVD͒ process on different off-angle substrates ͑on-axis, 4 and 8°off-axis toward the ͓1120͔ direction͒. A suitable combination of gas flow and process pressure is needed to produce the gas speed that yields an optimum cracking of the precursors and a uniform gas distribution for deposition over large areas. The use of low pressure and the addition of chlorinated precursors bring the added benefit of achieving higher growth rates. A systematic study of the gas speed's effect on the growth rate, uniformity, and morphology on the 4H-SiC epitaxial layers was performed. Growth rates in excess of 50 m/h were achieved on 50 mm diameter wafers with excellent thickness uniformity ͑below 2% /mean without rotation of the substrate͒ and smooth morphology using only 1/10 of the typical gas carrier flow and process pressure demonstrating the feasibility of a concentrated chloride-based CVD process for 4H-SiC. Thermodynamic calculations showed that the improved thickness uniformity could be due to a more uniform gas phase composition of the silicon intermediates. The concentration of the SiCl 2 intermediate increases by a factor of 8 at a reduced carrier flow, while all the other hydrogenated silicon intermediates decrease.

Silicon Chemistry in Fluorinated Chemical Vapor Deposition of Silicon Carbide

“…This decrease is similar to what has been observed for chlorinated SiC CVD. 22,23 After the growth rate increase, at the same position as the growth rate reaches its maximum, the growth also becomes epitaxial. This transition to epitaxial growth is such abrupt that the position for it is easily recognized.…”

Chloride-Based CVD Growth of Silicon Carbide for Electronic Applications

“…37 Surprisingly, when using a low pressure (15 mbar) process, no silicon droplet related defects were formed on the epitaxial layer at such low Cl/Si ratio, indicating that the chlorine content was high enough to prevent silicon aggregation. 46 Low temperature homoepitaxial growth has been demonstrated by chloride-based CVD processes, as further described below. Using the approach of adding HCl to the standard precursors, 4H-SiC was homoepitaxially grown with a growth rate of 7.5 μm/h at 1300 °C.…”

“…A lower amount of chlorine may be used, but electrical characterization indicated a degradation of material quality. Report on epitaxial growth at a reduced carrier flow and process pressure indicates that these conditions may require lower chlorine inputs due to the increased desorption of silicon species at lower pressure. The increased desorption combined with the etching of silicon atoms by the chlorine significantly increases the C/Si ratio at the surface.…”

Epitaxial growth of SiC with chlorinated precursors on different off-angle substrates

“…When the growth was done in concentrated growth condition, i.e. one order of magnitude lowered carrier flow and process pressure, it was clear that both in situ etching conditions and the C/Si ratio had to be more Silicon-rich compared to when using lower off-angle substrates [14]. In the case of growth at a very low temperature of 1300 1C, the optimal conditions used for 81 off-axis substrates were found to be too carbon-rich for 41 off-axis substrates (surface covered with triangular defects), and for almost on-axis 4H-SiC (growth of 3C-SiC) [15].…”