The Effect of Carbon on the Precipitation of Oxygen in Czochralski Silicon
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and Tan, eds.
387
Defects in Semiconductors
THE EFFECT OF CARBON ON THE PRECIPITATION OF OXYGEN CZOCHRALSKI SILICON
R. F. PINIZZOTTO AND H. F. SCHAAKE Central Research Laboratories, Texas Instruments Inc.,
IN
Dallas, TX 75265
ABSTRACT
Researchers in both the U. S. and Japan have reported that carbon impurities can significantly alter the precipitation of oxygen in CZ silicon. We have employed FTIR, x-ray topography and TEM to study this phenomenon in sili3 3 or 1.3 x 1017 C cm- . A con containing < 2 x 1016 C cmsingle step anneal of 16 hours at 1000°C will cause oxygen precipitation to occur in the high carbon material, while a 32 hour pre-anneal at 600%C is necessary for precipitation in the low carbon material. If a single anneal of 120 hours at 750%C is used, light precipitation occurs in both types of material. A pre-anneal of 15 minutes at 0 1000 C followed by 120 hours at 750'C reduces precipitation in the high carbon material only slightly, but completely eliminates precipitation in the low carbon material. It can be concluded that carbon causes heterogeneous nucleation of oxygen precipitation in CZ silicon and it is proposed that it does so by lowering the interfacial energy of the precipitates. INTRODUCTION The precipitation of oxygen in Czochralski silicon has recently become a very important research topic for materials scientists working in the semiconductor industry. Oxygen precipitation has been shown to be an effective intrinsic gettering mechanism which can reduce the deleterious effects of heavy metal contamination during integrated circuit processing. Several companies have published process modifications that were specifically designed to promote oxygen precipitation during semiconductor device fabrication. Transmission electron misroscopy (TEM) studies of oxygen precipitation in CZ silicon have identified over 20 unique microdefect morphologies. These include many familiar structures such as stacking faults and prismatic dislocation loops, and some highly unusual ones such as (100) platelets and small precipitate clusters. At the present time there is no comprehensive model capable of explaining why so many types of defects occur or how material processing affects the microstructure. There is yet to be agreement on the nucleation mechanism responsible for precipitate formation or on the growth kinetics. Several workers have suggested that carbon plays an important role in the process by promoting heterogeneous nucleation which enhances the rate of precipitation [1,2,3]. Many of the results are not based on one-to-one comparisons of material with high and low carbon concentrations and are speculative in nature. Even worse, many of the reports do not supply the details of the type of material used, whether or not it received a resistivity stabilization anneal after crystal growth, or the anneal ambient used in the experiments. The goals of this study are to examine the effect of carbon concentration on both the morphology of the oxygen precipitates and on their nucleation
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