Oxygen Precipitation Nonuniformity for Thermal History Around 723K During CZ Crystal Growth
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OXYGEN PRECIPITATION NONUNIFORMITY FOR THERMAL HISTORY AROUND 723K DURING CZ CRYSTAL GROWTH
I. FUSEGAWA and H. YAMAGISHI Isobe R&D Center, Shin-Etsu Handotai Co., Annaka, Gunma, 379-01, Japan
Ltd.,
Isobe 2-13-1
ABSTRACT We investigated phenomena of oxygen precipitation nonuniformity along crystal growth axis due to different thermal histories during CZ crystal growth. The oxygen precipitation process employed in this paper was two-step thermal treatments consisting of the first annealing in nitrogen ambient at 1073K for 4 hrs and the second annealing in dry oxygen ambient at 1273K for 16 hrs. The amount of the oxygen precipitation at the shoulder of a silicon single crystal was higher than the one at the tail end. We found this nonuniform distribution profile was due to the thermal history around 723K during crystal growth. Such an nonuniformity could be improved remarkably by adding a preannealing in dry oxygen ambient at 723K for 2 hrs before the two-step thermal treatment. INTRODUCTION It is very important to control the amount of oxygen precipitation in silicon wafers to utilize for an intrinsic gettering effect [1,2] in a LSI fabrication process. On the other hand, it is well known that the oxygen precipitation of silicon wafers strongly depends on the thermal history in CZ crystal growth process [3,4], but we couldn't success to control the oxygen precipitation because the influence of the thermal history was not eliminated from crystals. Especially, we had to grow short crystals and to take out quickly from the CZ furnace because of the requirement of satisfying the resistivity specifications. Then, they were rapidly cooled from high temperature to room temperature, and the nuclei of oxygen precipitation may be generated in various temperature ranges. In this paper we investigated the influence of thermal history on the oxygen precipitation by a two-step thermal treatment. We studied the most effective temperature range for the nuclei generation against such treatment and how to improve nonuniform distribution profile by some preannealing process. EXPERIMENTAL Several oriented CZ silicon single crystals of 15 cm diameter were grown from quartz crucibles of 46 cm diameter. We grew two kinds of single crystals, with short body length of 60 cm or with long body length of 110 cm, in order to get different thermal histories. Phosphorus was doped and their resistivities were approximately 6-10 ohm cm. Silicon wafers of 2 mm thickness were made by slicing those crystals and etched with HF/HNO 3 mixed acid solution for 2 min. The substitutional carbon concentrations were measured using FTIR and those values Mat. Res. Soc. Symp. Proc. Vol. 262. 01992 Materials Research Society
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Table 1. Summary of thermal treatment conditions temperature / time (ambient) 1073K/4hrs(N ) + 1273K/16hrs(0 2 ) 1273K/16hrs( 6 2 ) 1553K/lhr(O2 )+(X)/2hrs(O )+1073K/4hrs(N )+1273K/16hrs(0 2 ) where (X) is 573K to 1273K at intervals of 50K
NO [A] [B] [C] [D] [E]
923K/0.5hr(N ) 723K/2hrs(O 2 ý+1073K/4hrs(N 2 )+1273K/16hrs(0 2)
were
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