AVS 53rd International Symposium
    Electronic Materials and Processing Tuesday Sessions
       Session EM-TuA

Paper EM-TuA9
Optimized RIE Process for High Performance SiC BJTs

Tuesday, November 14, 2006, 4:40 pm, Room 2003

Session: Materials for Power Electronics
Presenter: A.B. Goulakov, Microsemi Inc.
Authors: A.B. Goulakov, Microsemi Inc.
F. Zhao, Microsemi Inc.
I. Peres-Wurfl, Microsemi Inc.
B. Van Zeghbroueck, Colorado University
J. Torvik, Microsemi Inc.
Correspondent: Click to Email
SiC high-power RF devices are slated to replace Si devices to enhance the system performance and to reduce overall cost. Because of mechanical stability and the lack of dopant diffusion in SiC at normal temperatures, a common SiC RF BJT fabrication process includes homoepitaxial growth of differently doped layers followed by several dry etching steps. In this paper we will focus on two critical etch processes and two inch SiC wafer fabrication. The first process is a deep (> 5 micron) etch for electrical isolation between BJT fingers. The second process is a shallow (< 0.3 micron) precise etch down to the base layer. Due to thin 100 -150 nm base layer in the vertical n-p-n structure, a non uniform RIE process is a "yield killer". In this paper, we present details on a novel etching process for SiC RF BJTs fabrication process by combining optimized RIE etch, conductivity measurements, and oxidation. RIE etch parameters were optimized resulting in smooth etched surfaces and sufficient etch depth uniformity of < 8% for shallow etch, and < 2% for deep etch across two inch SiC wafers. Our etching process provides a precision (± 10nm) emitter etch to the emitter-base junction, even when the actual epitaxial layer thicknesses are different than expected. This method was also used to measure the emitter layer thickness and resistivity uniformity across different wafers and lots, and data will be presented. Furthermore, precise etching of the emitter epitaxial layer results in improved RF performance of the BJT by optimizing the base sheet resistance. Using this RIE process, we successfully fabricated several lots of 50W UHF SiC BJTs with a dc probe yield > 90%.