Gettering and Gettering Stability of Metals at Oxide Particles in Silicon
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GETrERING AND GETTERING STABILITY OF METALS AT OXIDE PARTICLES IN SILICON
R. FALSTER*, Z. LACZIK**, BOOKER*", A.R. BHATTI** AND P. TOROK"t *MEMC, SpA, Viale Gherzi 31,G.R. 28100 Novara, Italy **Department of Materials, Oxford University, Parks Road, Oxford OX1 3PH, UK
ABSTRACT Several aspects of metal gettering at internal oxide particle sites in Cz Si have been studied by 'haze tests', scanning infra-red microscopy (SIRM) and transmission electron microscopy (TEM). Haze tests indicated that complete gettering of Cu, Ni, Co and Pd can occur even when the amount of oxygen precipitated is below the detectable limit. TEM showed that the gettering of Cu, Pd and Ni proceeds by one of three different self-perpetuating mechanisms involving oxide particles and associated dislocations, the particular mechanism depending on the oxide particle size and the metal type. Haze tests and SIRM showed that for Cu and Ni there were minimum oxide particle number densities for effective gettering, and also maximum oxide particle number densities above which the additional oxide particles played no role in the gettering. These number densities depended on the metal type and specimen cooling rate. For all of these gettering behaviours, mechanisms are suggested to explain the results. The SIRM was also used to investigate for Cu and Ni the thermal stability of the gettering sites and the precipitated metals. The results showed that during repeated heat treatments the gettering occurs by a dynamic process. INTRODUCTION Internal gettering (IG) is often required to control the effects of metallic contamination commonly occurring in the complex environment of integrated circuit (IC) manufacturing. For IG a wide range of oxide precipitate particles and associated defect distributions are possible. Factors such as particle size and number density and the presence of bulk stacking faults depend on many variables including initial oxygen and carbon concentration, the exact details of thermal treatments, etc. It is important that the roles played by such factors on the gettering mechanisms, limitations and stability of an IG system are understood. In a preliminary study [1] which used a modified 'haze test' [2] to investigate the gettering of transition metals by a wide variety of oxygen related defects formed during various stages of a simulated CMOS process, it was shown that the threshold in precipitated oxygen for effective gettering was surprisingly low and well defined. In fact, effective gettering of all the metals studied (Cu, Ni, Co and Pd) was observed even before the precipitation of oxygen could be reliably detected by the standard techniques of Fourier transform infrared spectroscopy (FTIR) or cross-sectional Secco etching. In addition to this, no evidence was found to support the view [3] that bulk stacking faults are required for effective gettering. TEM investigations were subsequently performed on material from that study to examine the gettering mechanisms for Ni, Cu and Pd at large and small oxide particles [4]. Further haze t
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