Silicon Cleaning Methods Compared at Metal Concentrations Below 1E10 atoms/cm2

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AbstractAn alkaline aqueous silicon wafer cleaner has been developed which reduces trace metal contamination levels on “p-type” unpatterned silicon wafers to below 1E10 atoms/cm2 without acidic cleaning. This patented technology uses a specially formulated buffering system consisting of an oxidation resistant chelating agent and salt of a weak acid. The aqueous cleaner maintains a stable pH of about 9.5 over a wide range of dilutions, temperatures, hydrogen peroxide concentrations and bath aging times. A single-step bath, megasonic bath or spray clean with this formulation leaves the chemical oxide on the silicon wafer surface free of particles, atomically smooth, free of organics and lower in trace metal contamination levels than similar surfaces cleaned with conventional formulations.An analytical method was developed which allows the reliable detection of trace metals on silicon wafer surfaces down to 1E8 atoms/cm2 for aluminum, calcium, copper, iron, nickel, sodium and zinc. The procedure uses an ICP-MS with a concentric nebulizer and a desolvator. The acids used were ultrapure to keep the blanks to a very minimum and analyses were run in a class 10 clean room. The trace metals on the wafer were extracted using known amounts of ultrapure acids and were directly aspirated using a special arrangement with the concentric nebulizer. The J.T. Baker cleaner was compared to and outperformed the conventional RCA-1&2 clean and dilute RCA-1&2 chemistries using ultrapure ammonium hydroxide, hydrochloric acid and hydrogen peroxide.