Helium plasma enhanced chemical vapor deposited oxides and nitrides: Process mechanisms and applications in advanced device structures

Abstract

New plasma-enhanced chemical vapor deposition (PECVD) dielectric processes enable deposition of films of much higher quality than previously possible by PECVD. The use of He-diluted PECVD processes (He-PECVD) for depositing near-thermal quality Si02 and high-quality Si3 N4 films is described. Excellent Si-SiQ2 interfacial properties are achieved in this process by a dilute, low-rate, low-power plasma oxidation step prior to the deposition. The use of He-PECVD dielectrics in advanced bipolar and CMOS structures is described. In bipolar technology, high-performance SiGe heterostructures with extremely narrow base profiles have been fabricated using low processing temperatures in order to prevent diffusive broadening of the base dopant distribution and to avoid relaxation of the SiGe strained layer. When used in combination with a low-temperature emitter process, He-PECVD dielectrics make possible a completely low-temperature process, resulting in final base widths as low as 40 nm. In CMOS technology, successful fabrication of field-effect transistors (FET's) with ultrathin (4.0-7, 0 nm) He-PECVD gate oxides is described, with particular attention paid to producing a high quality (low Dit) Si-Si02 interface. Device characteristics with He-PECVD dielectric are comparable to those with thermal oxide, except that slightly lower transconductance is obtained in the He-PECVD oxide devices. © 1991, American Vacuum Society. All rights reserved.