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SCANNING EECTRON BEAM ANNEALING OF OXYGEN DONORS IN CZOCHRALSKI SILICON C J POLLARD, J D SPEIGHT British Telecom Research Labs, Martlesham Heath, Suffolk, England K G BARRACLOUGH Royal Signals and Radar Establishment, St Andrews Road, Great Malvern, Worcestershire, England

ABSTRACT The destruction of the oxygen donor complex in

Czochralski silicon has been studied using scanning electron beam annealing in the range 5500C to 1050 C for 5s to 1000s. A two stage annealing schedule ensured a rapid rise to the target temperature and overscanning provided a uniform, non-distorting heating field. Four point probe and spreading resistance measurements showed a very rapid donor destruction rate above 6500 C; between 550 C and 650°C the lower donor destruction rate allowed a study of the annealing behaviour.

INTRODUCTION The presence of oxygen in silicon has a significant effect on its mechanical and electrical properties during i.c. processing. Such effects are seen in Czochralski silicon (Cz-Si) wafers ygich coytain interstitial oxygen at supersaturated levels up to approx 10 at cm- , as a result of the incorporation of oxygen during Cz-Si crystal pulling when the molten silicon reacts with the silica crucible. Whereas oxygen impurities may enhance the yield and performance of devices fabricated in Cz-Si wafers by pinning slip dislocations (1) and gettering impurities away from the active device regions (2), a disadvantage of oxygen in silicon is the formation of donors at elevated temperatures. The rate of the oxygen donor formation is a maximum at 450 0 C, and is dependent on the fourth power of the oxygen concentration (3). The exact nature of the oxygen donor (sometimes referred to as the thermal donor) is not known. From the formation kinetics, Kaiser et al (4) proposed a model based on SiO4 complexes built up by successive unimolecular steps. Infra-red spectroscopy (5), photoluminescence (6,7) and EPR (8) data indicate that the donor is a composite of vlgious degect species. Since oxygen donor concentrations as high as 10 at cm can be formed during the cooling of high oxygen Czochralski silicon, it is important that they are destroyed at the wafer manufacturing stage, and not reformed during subsequent processing. Thermal donor destruction is normally accomplished by annealing at temperatures above 500 OC followed by rapid cooling through 45 0 °C to room temperature (9). This paper describes a preliminary investigation of the annealing of oxygen donors in Cz-Si in the temperature range 550 C to 1050 C using a scanning electron beam annealing system which provides rapid, clean and accurately controlled whole-wafer heating conditions.

Mat.

Res.

Soc.

Symp. Proc.

Vol.

13 (1983)

Published by Elsevier Science Publishing

Co.,

Inc.

414

EXPERIMENTAL Two batches of 50mm diameter p-type (boron doped) polished Cz-Si wafers have been examined. Batch A wafers were prepared from seed- an• tail-end sections of a in a low pressure puller. dislocation free crystal grown at 1.5 mm mmn The target resistivity was 25 - 35 o