Studies of Oxygen Thermal Donor Formation Under Stress*
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STUDIES OF OXYGEN THERMAL DONOR FORMATION UNDER STRESS
PAUL W. WANG and JAMES W. CORBETT Institute for the Study of Defects in Solids Physics Department, SUNY/Albany Albany, NY 12222 USA
ABSTRACT Oxygen thermal donor formation under stress and following various pre-heat treatments was investigated by resistivity measurements. Thermal donor formation at 450'C, with and without bending stress, is monitored in p-type Cz-silicon following various heat-treatments. As has been shown by others, the thermal donor formation rate depends upon the pre-treatment of the samples. We find that the rate also depends on the stress, being faster, or slower, on the tensile side than on the compressed side depending on the pre-treatment. I.
INTRODICTION
There are typically ca. 1018 oxygen/cm3 dissolved in Cz-silicon from quartz crucible during the growth process. These oxygen atoms, which occupy interstitial sites [1], are electrically neutral and highly supersaturated during device processing. Oxygen atoms precipitate (homogeneously or heterogeneously [2]) during thermal processing, which can have negative effects such as the formation of 4501C (old) thermal donors [3] and 650*C (new) donors [4], or positive effects such as the formation of bulk defects, i.e., dislocation loops and stacking faults [5], which acting as gettering sites for metallic impurities and native point defects [6]. Silicon wafers are subjected to mechanical, thermal and film-edge-induce stress during device manufacturing, i.e., polishing, oxidation, ion implantation,
annealing,
and diffusion etc.[7,8].
In this paper we study the
influence of stress and pre-treatment on the oxygen thermal donor formation. II.
EXPERIMENTAL
All the samples used in this study are boron-doped, Cz-grown, 18 oxygen atoms/cm3 and oriented, ca. 10 2-cm, silicon which contains 1.4x10 15 3 less than 2.5x01 carbon atoms/cm . In order to study the pre-heat-treatment effects we divided the samples into three groups: (1) as-provided samples, (2) 1200°C, 20h., dry nitrogen ambient pre-heated samples, and (3) 9000C, 2h., dry nitrogen ambient pre-heated samples. Samples were cut, polished, and cleaned after pre-treatment. Then samples were bent by a quartz jig, as shown in Fig. 1, during various 450*C annealing periods in dry nitrogen ambient. One end of the sample is fixed by a 1.8 cm#x 18 cm long quartz rod with a 0.1 cm x 0.5 cm x 1.8 cm slot, which rod is supported by a quartz boat. The other end of the sample is pressed down by a 40 gram, 1.8 cmox 3.5 cm quartz rod with the same slot. The long dimensions of the samples are 80 off the direction and the stress due to the weight of short quartz rod is parallel with the long side of the sample. (An orientation dependence study is being done separately). The dimensions of all sample are 1.2 cm wide, 2.5 cm long, and ca. 0.05 cm thick. After bending and 450WC heat treatment, the samples were washed in dilute hydrofluoric acid to eliminate the surface oxide. The oxygen thermal donor concentration was monitored by measuring the resistivity
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