Effects of Lamp Pulses on the Oxygen - Precipitation - Gettering of Cr in Czochralski Grown Si
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EFFECTS OF LAMP PULSES ON THE OXYGEN - PRECIPITATION - GETTERING OF Cr IN CZOCHRALSKI GROWN Si. N-E. CHABANE-SARI, S. KRIEGER-KADDOUR, C. VINANTE, D. BARBIER. Laboratoire de Physique de la Mati~re, URA-CNRS 0358, Institut National des Sciences Appliqudes de Lyon, 20 Avenue Albert Einstein, F 69621, Villeurbanne Cedex, France.
ABSTRACT Experiments on the intrinsic gettering of Cr in p-type Czochralski-grown Si including lamp pulse annealings have been carried out. Transmission Electron Microscopy observations of both oxide and metallic precipitates on cross-sectional specimens, as well as quantitative results about the electrically active metal depth-profiles, using Deep Level Transient Spectroscopy measurements, are presented. We have observed that a lamp pulse (1200 °C/5 s) applied prior to a three-step gettering cycle produced a strong retardation of the oxygen precipitation, and consequently an inhibition of the Cr bulk precipitation during the nucleation step. Besides, it was observed that the Cr-precipitates formed in the bulk during the oxygen nucleation step were highly unstable upon a post-gettering 2-4 s lamp pulse at 1000 "C, whereas the same lamp pulse did not produce a significant re-dissolution of Cr-precipitates formed during the oxide precipitate growth step. The reversibility of the intrinsic gettering of Cr upon a post-gettering lamp pulse thus critically depends on the oxide precipitate growth rate during the gettering process. INTRODUCTION Metallic impurities which are present in Czochralski-grown (CZ) Si substrates are usually removed from the active region of devices by a gettering treatment. The principle of gettering is based on the drawing of the metals away from the front surface of Si wafers through their precipitation on the back surface (extrinsic gettering) or in the bulk (intrinsic gettering). However as the diameter and consequently the thickness of Si wafers are progressively increased in device technology, intrinsic gettering which uses the as-grown oxygen content of CZ wafers (about 1018 cm-f)-, becomes more and more attractive for moderately fast diffusers (Ti, Cr, Mn, Fe). The treatment is commonly achieved by a three-step thermal cycle (high-low-high temperature annealing sequence: H-L-H) [1,2,3]. During the first step, the interstitial oxygen out-diffuses from the surface region of Si wafers, so that a so-called denuded zone is formed over a few tens of microns, wherein the interstitial oxygen concentration drops down near the solid solubility. According to the classical interpretation of intrinsic gettering, the second and third annealing steps lead to the nucleation and growth of O-precipitates acting as gettering sites for the metals, in the bulk of the wafer [2,3,4]. According to the model proposed by Gilles et al. [2,3,5], the intrinsic gettering efficiency is based on the difference between the precipitation kinetics of metallic impurities in the denuded zone and in the bulk near the O-precipitates (oxygen precipitation-gettering). Up to now, two types of O-precipitates
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