In Situ Measurements of Hydrogen Flux, Surface Coverage, Incorporation and Desorption During Magnetron Sputter-Depositio
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IN SITU MEASUREMENTS OF HYDROGEN FLUX, SURFACE COVERAGE, INCORPORATION AND DESORPTION DURING MAGNETRON SPUTTER-DEPOSITION OF A-SI:H. J. R. ABELSON, N. MALEY, J. R. DOYLE, G. F. FENG, M. FITZNER, M. KATIYAR, L. MANDRELL, A. M. MYERS, A. NURUDDIN, D. N. RUZIC, AND S. YANG Coordinated Science Laboratory and the Materials Science Department, University of Illinois, Urbana IL 61801 ABSTRACT High quality a-Si:H films are deposited by d.c. magnetron reactive sputtering of a Si target in an (Ar + H 2 ) plasma. This paper reports the first comprehensive understanding of the growth process. The incident flux, surface H coverage, H2 release, and bulk H incorporation are determined using four in situ, real time techniques: double modulation mass spectroscopy, isotope replacement experiments, reflection absorption infra-red spectroscopy, and spectroscopic ellipsometry. In addition, the sputtered particle transport is simulated using Monte-Carlo techniques. For conditions which produce electronic quality a-Si:H, the total H flux arriving at the surface varies between 0.5 - 2 times the depositing Si flux; approximately half of this flux appears to reflect from the surface without interaction. The growth surface has excess H varying between 0.5 - 2 x 10 15/cm 2 , and this surface H coverage is uniquely related to the bulk H incorporation. INTRODUCTION Hydrogen plays a key role in determining the structure, optical, and electronic properties of a-Si:H films. For example, bonded H is an alloying element which raises the optical band gap of a-Si from -1.5 - 1.9 eV [1]. The H content also appears to be associated with the rate at which metastable defects form [2]. Our goal is to understand the microscopic details of the H incorporation process during film growth. We deposit a-Si:H films by d.c. magnetron reactive sputtering of a Si target in an (Ar + H2) plasma. This process produces high quality a-Si:H, and offers two advantages for fundamental understanding. First, the H flux is controlled by the H 2 partial pressure injected in the discharge; thus, kinetic processes can be studied across a wide range. Second, the total gas pressure is low (1 - 2 mTorr), which minimizes gas phase collisions and chemistry. This greatly simplifies analysis of the process. The identity and energy of the deposition species in reactive sputtering has been discussed in previous reviews, based in part on direct measurements and in part on physical inference [3, 4]. The present work provides the first comprehensive picture of the growth fluxes in a magnetron system. These are measured by in situ double modulation mass spectroscopy and particle transport simulations, under conditions which produce electronic quality a-Si:H. Unlike previous studies, the identity, flux, and energy of neutral species are directly measured. The identity, flux, and energy of ions and silane radicals are also measured in the same system. In addition, we determine the release rate of H2 from the growing surface using an isotope replacement technique. The arriving flux interacts wit
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