Oxygen Bubble Formation and Transformation During High-Dose Oxygen Implantation and Annealing of Silicon
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OXYGEN BUBBLE FORMATION AND TRANSFORMATION DURING HIGH-DOSE OXYGEN IMPLANTATION AND ANNEALING OF SILICON S.J. Krause, S. Seraphin*, B.L. Chen, B. Cordts**, and P. Roitman*** Chemical, Bio and Materials Engineering Dept., Arizona State University, Tempe, AZ 85287 * Materials Science and Engineering Dept., University of Arizona, Tucson, AZ 85721 ** Ibis Technology Corporation, Danvers, MA 01923 *** National Institute of Standards and Technology, Gaithersberg, MD 20899
ABSTRACT The formation of bubbles during high dose implantation of oxygen into silicon, and the subsequent transformation of the bubbles during annealing, were studied with transmission electron microscopy (TEM). There was a threshold for bubble formation at a minimum dose of 0.3 x 1018 oxygen/cm 2 and a lower temperature of 550°C. As dose increased the bubbles grew larger and the bubble trails lengthened. However, increasing beam current by a factor of 10 or increasing temperature to 700"C did not affect bubble formation. Bubble evolution during intermediate temperature annealing was also studied using TEM techniques. For 2 hour anneals between 1000 and 1100*C the oxygen bubbles transform into SiO 2 particles by first forming a "shell" of SiO 2 , which then facets, grows inward, and finally completely transforms the bubble into an oxide particle. At temperatures greater than 1I00*C the oxide particles dissolve by outdiffusion of the oxygen to the wafer surface. INTRODUCTION Silicon-on-insulator (SO) material fabricated by high dose oxygen implantation (SIMOX) is a material increasingly used for higher speed and radiation hard circuits. During implantation a variety of structural changes occur, including the formation of defects, bubbles, precipitates, and the buried oxide layer. The topic of bubble formation and evolution has received only limited study [1-3]. Sjoreen et al. [1] first reported the presence of spherical, randomly distributed precipitates near the top surface of the silicon layer. El-Ghor et al. [2] further examined these precipitates and proposed that they were cavities filled with oxygen. Maszara [3] confirmed the presence of spheroids filled with oxygen in the silicon top surface region in the 1mA cm- 2 as-implanted samples. The bubbles were aligned in individual columns whose orientation matched the direction of the implantation. In this work, transmission electron microscopy (TEM) techniques were used to investigate the effect of implantation conditions on the bubble formation and the effect of subsequent annealing conditions on the evolution of bubbles. EXPERIMENTAL Si (100) wafers were implanted at 200 keV to doses from 0.3 x 1018 to 2.0 x 101s cm- 2 , at current densities of 1 to 10 mA cm- 2, and temperatures from 525 to 700"C. Samples for annealing studies were implanted at 600"C, 200 keV with a 1 mA cm-2 beam current density, to a dose of 1.8 x 1018 cm- 2. They were annealed under an argon atmosphere for 2 hours at 50"C temperature intervals from 800"C to 1200"C. Cross-section samples were studied in bright field imaging in a
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