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DEPENDENCE OF PECVD SILICON OXYNITRIDE PROPERTIES ON DEPOSITION PARAMETERS Aubrey L. Helms, Jr.* and Robert M. Havrilla°° *AT&T Bell Laboratories - Engineering Research Center, PO Box 900, Princeton, NJ 08540 Microelectronics, 2525 N. 12th St., Reading, PA 19604

"*AT&T

ABSTRACT The properties of Plasma Enhanced Chemical Vapor Deposited (PECVD) silicon oxynitride thin films were determined for a variety of deposition conditions. The films were characterized with respect to stress, refractive index, deposition rate, hydrogen content, dielectric constant, and uniformity. The films were deposited in an Electrotech ND6200 parallel plate reactor using a silane - ammonia - nitrous oxide process gas chemistry. Deposition parameters which were investigated include process gas flow rate, power, and total pressure. The possible application of these films as both inter-layer and final passivation layers for use on GaAs ICs will be discussed.

INTRODUCTION The deposition of high quality dielectric films at low temperatures is critical to the realization of GaAs ICs. The common use of Au-Ni-Ge ohmic contacts limits the processing temperatures of GaAs ICs to -300 *C. This has driven the development of deposition techniques for dielectric materials to those based on plasma enhanced chemical vapor deposition (PECVD) processes. Traditionally, Si 3N 4 has been the material of choice because of its passivation properties, mechanical strength, barrier properties, and process compatibility [1-31. One of the disadvantages of Si 3 N 4 is its high dielectric constant which contributes to parasitic line capacitances that limit the device speed. The lower dielectric constant of Si0 2 makes this material appealing, however, the long term reliability of devices encapsulated in SiO 2 is not as good as those passivated with Si 3 N 4 [4]. Recently, there has been much work on the development of silicon oxynitride (SiON) films [5-7]. The hopes are that these films will exhibit the best properties of both Si 3 N 4 and SiO 2 , namely the passivation and mechanical properties of Si 3 N 4 and the low dielectric constant and low stress of Si0 2 . The properties of these films are very sensitive to the composition and deposition parameters. The implementation of such a material into the manufacture of GaAs ICs requires that the properties of the thin films be well understood as a function of process parameters.

EXPERIMENTAL The films were deposited in an Electrotech ET 6200ND plasma enhanced chemical vapor deposition (PECVD) system. This unit is a cassette-to-cassette system capable of handling as many as 14 wafers (3" diameter) in each deposition run. The reactor is a parallel plate design which operates at a plasma frequency of 380 kHz. The power, pressure, temperature, and process gas flows are microprocessor controlled. The process gases were SiH 4 , N2 0, NH 3 , and a carrier gas of N 2 . In each deposition, a 3" Si monitor wafer was included to determine the stress of the film. It has been our experience that Si wafers tend to distort in a unif