Characteristics of Oxygen Precipitation in Silicon Wafers Preannealed at 723K
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CHARACTERISTICS OF OXYGEN PRECIPITATION IN SILICON WAFERS PREANNEALED AT 723K
I. FUSEGAWA, E.IINO, T.HIROHATA, and H. YAMAGISHI Isobe R&D Center, Shin-Etsu Handotai Co., Ltd., Annaka, Gunma, 379-01, Japan
Isobe 2-13-1
ABSTRACT We investigated phenomena of oxygen precipitation in silicon single crystals by two kinds of thermal treatment, supposing a CMOS fabrication process. The one consisted of the first annealing at 1123K for 4 hrs and the second annealing at 1423K for 16 hrs. The other one consisted of the annealing at 1273K for 4 hrs and the second annealing at 1423K for 13 hrs. In the results, a single-step preannealing at 723K for 2 hrs was effective for the oxygen precipitation by the former process and nonuniform distribution profiles along crystal growth axis were well improved, however, insufficiently improved against the latter process. We considered a two-step preannealing process consisting of the first annealing at 723K for 2 hrs and the second annealing at 923K for 2 hrs. This new process was effective for the oxygen precipitation by the latter process. Especially, we could obtain uniform distribution profiles of oxygen precipitation along a crystal growth axis. INTRODUCTION A thermal treatment at high temperature such as 1423K is employed for a CMOS fabrication process. It is very important but very difficult to control the amount of oxygen precipitation against such a CMOS process. Because the amount of oxygen precipitation after a CMOS process is very low and is nonuniformly distributed along the growth axis. Especially, it is well known that the thermal history during CZ crystal growth strongly affects on the oxygen precipitation along its growth axis [1,2]. We have already reported that a thermal history around 723K during crystal growth was a predominant factor for the fluctuation of the oxygen precipitation by a two-step thermal treatment consisting of the first annealing in nitrogen ambient at 1073K for 4 hrs and the second one in dry oxygen ambient at 1273K for 16 hrs [3]. In this paper, we investigated the effect of such a thermal history on oxygen precipitation after the CMOS simulation processes. Then we tried to obtain a uniform oxygen precipitation profile along a growth axis by adding some preannealing treatments before the CMOS simulation processes. EXPERIMENTAL Several oriented CZ silicon single crystals of 15 cm diameter were grown in a body length of about 70 cm. Boron was doped and their resistivities were approximately 6-10 ohm cm. For an evaluation of the characteristics of oxygen precipitation, silicon wafers of 2 mm thickness were sliced from these crystals in an interval of 35 cm length from the Mat. Res. Soc. Symp. Proc. Vol. 262. @1992 Materials Research Society
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Table 1 : Summary of thermal treatment conditions NO. temperature / time (ambient) [A] 1423K/16hrs(O2 ) [B] l123K/4hrs(O ) + 1423K/16hrs(0 2 ) [C] 1273K/4hrs(O) + 1423K/13hrs(0 2 ) [D] (X)K/4hrs(O 2) + 1423K/16hrs(0 2 ) where (X)=873K - 1073K (intervals at 50K) [E] [F] [G] [H]
723K/2hrs(O 2 ) + [B] 723K/2h
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