A New Technique for Monitoring Metallic Contamination During Aqueous Semiconductor Wafer Processing

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9634058 Suni As device and interconnect sizes continuously shrink, the microelectronics industry faces a number of serious technological challenges. One important challenge is to decrease the level of metallic contamination on wafer surfaces during processing. This is evidenced both by the tolerance limit of 1010 metal atoms/crn2 during fabrication of 16-MB dynamic random access memory(DRAM) and by the ability of metallic contaminants to short-circuit ultrathin((40() gate oxides . The level of contamination on the wafer surface is determined to a large extent by the tradeoff between deposition and dissolution of trace metallic impurities in aqueous chemical process solutions. This tradeoff involves a number of fundamental physical and chemical processes, including surface electroless reaction, bulk diffusion and convection. The potential sources, deposition mechanism(s) and transport of contaminants are still poorly understood despite their critical importance. Study of these problems has been hampered by analytical difficulties in measuring the level of surface contamination. We propose to develop a new in situ technique for indirect monitoring of metal contaminant deposition and dissolution in aqueous chemical process solutions. This employs spatially resolved absorption spectroscopy to detect concentration gradients in the boundary layer near the wafer surface with sensitivity limits in the ppb range. We will employ this technique to monitor the rate of Cu(( deposition from a buffered oxide etchant(BOE) and to monitor the rate of Cu dissolution in a standard chemical process solution SC-1. The experimental measurements will be complemented by computer modeling of metal contaminant deposition and dissolution during aqueous wafer processing using realistic process geometries. The proposed model will include diffusion, convection and electroless surface processes using time-dependent, three-dimensional finite difference solution of the governing momentum and mass transport equation s. Experimental determination of the rates of surface electroless processes and bulk transport are essential to correctly predict rates of metal contaminant deposition and dissolution. Besides potential applications as an in situ sensor, the experimental technique can be employed in a variety of studies of the fundamental physical and chemical processes occurring during metal contaminant deposition and dissolution. By illuminating the surface with ultraviolet light and controlling the surface electrochemically, the potential at which deposition is initiated can be measured. This will allow determination of the applicability of the Nernst equation to the prediction of metal contaminant deposition by electroless processes. ***