AVS 45th International Symposium
    Electronic Materials and Processing Division Wednesday Sessions
       Session EM-WeM

Paper EM-WeM3
Dissolution of Cu and Au into Aqueous Semiconductor Processing Solutions

Wednesday, November 4, 1998, 9:00 am, Room 316

Session: Fundamentals of Si Cleaning and CMP
Presenter: I. Suni, Clarkson University
Authors: I. Suni, Clarkson University
D. Chopra, Clarkson University
A.A. Busnaina, Clarkson University
Correspondent: Click to Email
Dissolution of Cu into 50:10:1 H@sub 2@O:H@sub 2@O@sub 2@:NH@sub 4@OH from p-type Si wafers was studied by total reflection x-ray fluorescence spectroscopy (TXRF). Starting from an initial surface coverage of approximately 1.2x10@sup 13@ atoms/cm@sup 2@, Cu dissolution was seen to be first order in Cu surface coverage, although slight deviations from this behavior are seen at longer times. The rate constant for this dissolution process was about 2.7x10@sup -2@ sec@sup -1@. Prior literature results indicate that Au dissolution into acidic solutions is also 1st order when dissolution is slow, but deviates from 1st order when dissolution is rapid. One possible explanation for these phenomena is that metal dissolution is a reversible reaction which slows down as the concentration of metal ions in solution increases and diffusion is slow. This explanation is consistent with recent results published by Sony Corp. The dissolution process in a wafer cleaning tank was modeled using experimentally determined constants through finite difference solution of the convective diffusion equation by the ADI method, including a 1st-order surface reaction as a boundary condition. The results demonstrate the transition between rate-limitation by surface reaction and rate-limitation by product diffusion as the dissolution rate is increased. This can be done by raising the temperature, increasing the solution strength, or using a more active oxidizing agent. The possibility is demonstrated of large removal gradients on the wafer surface arising from the coupling of convection, diffusion, dissolution and redeposition.