The effects of heat treatment on dislocation-free oxygen-containing silicon crystals

Abstract

A dislocation-free silicon crystal grown by the Czochralski technique has been heat treated over a wide temperature-time range to explore the basic silicon-oxygen relationship. The processes occurring were followed by carrier-concentration changes and infrared measurements over the range 1.2–25 μ. The infrared absorption changes occurring below 900 °C were found to follow an Arrhenius plot with an activation energy of 0.5±0.03 eV. This value is compared with the results found for other processes occurring on the surface or in bulk silicon and is seen to be low. The changes occurring above 900 °C are in agreement with the generally accepted theory that all the oxygen initially present in the crystal returns to its bound interstitial position. The carrier-concentration changes measured were at variance with currently accepted theories in several respects, particularly at 650 °C, an important temperature since all silicon producers use it to stabilize resistivity for measurement control prior to the thermal cycling experienced during device manufacture. Several experiments are described where slices were thermally cycled to study some of the ’’equilibrium’’ carrier-concentration situations believed to hold. Finally, a general discussion is given of the overall situation concerning the behavior of the various silicon-oxygen complexes believed to exist at the various temperatures. Some speculation is presented as to the interactions of the various Si-O complexes, but it is found that all the results cannot be fully explained on the basis of purely silicon-oxygen interactions and that other effects, particularly those due to carbon, must be taken into consideration.