Relaxation-Induced Geitering of Metal Impurities in Silicon: Microscopic Properties of Effective Gettering Sites
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RELAXATION-INDUCED GEITERING OF METAL IMPURITIES IN SILICON: MICROSCOPIC PROPERTIES OF EFFECTIVE GEITERING SITES MSeibt IV.Physikalisches Institut der Universiti't G6ttingen, Bunsenstr. 13-15, 3400 G6ttingen, Federal Republic of Germany, present adress: AT&T Bell Laboratories, Crawfords Corner Road, Holmdel, NJ-07733
ABSTRACT Some gettering processes like internal gettering or backside damage gettering base on heterogeneous precipitation of metal impurities at defects in pre-determined parts of silicon wafers during cooling from high temperatures. We consider microscopic properties of effective heterogeneous nucleation sites for cobalt, nickel and copper impurities from the fundamental point of view of silicide precipitate formation. We follow the basic concept that such gettering sites are defects which allow fast precipitation, i.e. which remove kinetic limitations known from homogeneous precipitation of these impurities at small supersaturation. For Co and Ni it follows that distorted lattice sites in the core of dislocations may establish high incorporation rates of interstitial atoms into silicide particles, whereas for Cu sinks for silicon selfinterstitials are suitable gettering sites. INTRODUCTION The presence of metal impurities in active device areas either as isolated point defects or as precipitates is known to cause a variety of device failures [1]. As a consequence, different gettering processes are incorporated into fabrication of silicon devices. The majority of gettering techniques base on heterogeneous precipitation of impurities at defects in pre- determined parts of wafers duringcooling from high temperatures. For this reason, these techniques have been termed relaxation- induced getteiing [2] or precipitation getteting [3]. As an example, internal gettering in Czochralski silicon exploits heterogeneous precipitation of impurities at SiO - particles, extrinsic stacking faults and/or prismatic dislocation loops which fornr as a result of oxygen precipitation. All these defects have been made responsible for the removal of impurities during internal gettering depending on the impurity under study, experimental conditions and methods applied [4-9]. Clearly, the ability of defects to serve as gettering sites not only depends on their microscopic properties but also on their density and location in the wafer. Since these parameters cannot be controlled independently under usual conditions it is difficult to learn about the microstructure of gettering sites from measurements of the "efficiency" of gettering procedures. As an alternative approach, this paper relates fundamental aspects of metal silicide precipitate formation to the question of microscopic properties of defects suitable for relaxation-induced gettering. The homogeneous precipitation of cobalt, nickel and copper impurities in silicon proceeds via the formation of metastable intermediate configurations when high cooling rates are applied [2,10]. Under such conditions extremely large chemical driving forces for precipitation are operative
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