Efficient method for monitoring gate oxide damage related to plasma etch chamber processing history
 It has been observed that, when a commercial plasma etcher is used for multiple etching tasks involving a variety of products, the amount of plasma damage incurred depends upon the chamber history of the etching tool. Thus, etching a gate sidewall spacer on a damage sensitive product, for example, in a MOSFET product with very thin gate oxide, may result in significant degradation of the gate oxide if the plasma etching tool had been used to etch vias on another type product in the preceding job. A method for monitoring and recording the chamber history and ascertaining the status of a plasma etching tool with regard to the tendency of said tool to introduce plasma damage in thin gate and tunnel oxide layers is disclosed. The method includes an a oxide damage monitor wafer which contains arrays of simple test devices. The monitor wafers can be partially formed and banked for later use. The test devices comprise a polysilicon plate partially covering a gate oxide. A conformal oxide is formed over the structure and the wafer is subjected to a spacer etch in the plasma etching tool being appraised. Dielectric breakdown the thin oxide is measured and the data is compared to a chamber history of the etcher. Those etching procedures which adversely affect the chamber are identified. Once a chamber history is established, the etcher can be expeditiously scheduled and the incidence of jobs lost to oxide damage greatly reduced. 
Taiwan Semiconductor Manufacturing Ltd.
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Chi-Hung Dean-E Sheng-Liang Chia-Der
Liao Lin Pan Chang