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ENHANCED DIFFUSION AND FORMATION OF DEFECTS DURING THERMAL OXIDATION* J. NARAYAN, J. FLETCHER, B. R. APPLETON AND W. H. CHRISTIE1 Solid State Division, Oak Ridge National Laboratory, Oak Ridge,

TN

37830

ABSTRACT

Enhanced diffusion of dopants and the formation of defects during thermal oxidation of silicon has been investigated using electron microscopy, Rutherford backscattering, and secondary ion mass spectrometry techniques. Enhanced diffusion of boron was clearly demonstrated in laser annealed specimens in which secondary defects were not present. In the presence of secondary defects, such as precipitates, enhanced diffusion of boron was not observed. The absence of enhanced diffusion during thermal oxidation was also observed for arsenic in silicon. The mechanisms associated with thermal-oxidation enhanced diffusion are discussed briefly.

INTRODUCTION Thermal oxidation to form a passivating oxide layer constitutes a very important step in device manufacturing processes [1]. During thermal oxidation stacking faults are generated, which are often connected to the oxide layer [1,2]. Oxidation enhanced diffusion (OED) has been reported for boron but there is controversy with respect to OED of arsenic in silicon [1]. The purpose of this paper is to show that secondary defects often play an important role in determining the enhancement of diffusion. While OED is observed for boron in the absence of secondary defects, it is not observed for arsenic in silicon. These results and observed changes in microstructures due to oxidation are critically evaluated in view of the following mechanisms: (1) undersaturation of vacancies created by oxidation, (2) the generation of self interstitials, and (3) generation of dopant interstitials which may create self interstitials. EXPERIMENTAL Silicon (2-6 fl-cm) specimens with and orientations were 15 16 2 7 implanted with 1iB+ (35 key, doses 2.0 x 10 and 1.0 x 10 cm- ), 5As+ 15 2 16 4 x 10 1.0 dose keV, (80 28Si+ ), and cm10 1.0 x and 101 x 1.0 (100 keV, 2 cm- ) ions. Some of these specimens were laser annealed with single ruby laser 2 pulses (X = 0.694 Um, Energy density E = 1.5-2.0 J cmand pulse duration 9 T = 15-20 x 10s) with a laser beam diameter of about 2 cm. In order to determine the role of defects in thermal oxidation, the defect-free laser annealed specimens, and the ion implanted specimens containing dislocation loops, were thermally oxidized under wet steam at 900*C. Companion specimens 0 were treated in dry nitrogen at 900 C and these results were compared with those obtained under steam oxidation. Steam oxidation was accomplished by evaporating extremely pure water and passing it through the furnace tube. Defect microstructures were investigated using plan-view and x-section electron microscopy. The dopant distributions and the lattice location of dopants were monitored using Rutherford ion backscattering and channeling, and dopant "Research sponsored by the Division of Materials Sciences, U.S. Department of Energy under contract W-7405-eng-26 with Union Car