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A plasma etcher has been developed for the mask industry to achieve uniform and tight dimension linewidth control. It also achieves a very low material loss of PBS in the descum process. This paper describes the problems encountered in designing such a system and the methods used to overcome the difficulties. The BMP reactive ion etcher has especially been developed for mask making and is used in two fields: the dry etching of masks with rather vertical resist structures (novalak, PM, PMMA). the linewidth adjustment of bevelled PBS structures by a sophisticated descum process prior to wet etching. The etch chemistry is comparable to the silicide etching in the silicon wafer technology, the difference in the mask processing is caused by the frequent changing substrate sizes and mainly by the different thicknesses of the isolating masks. In addition, the PBS descum process requires extreme low power densities, whereas the plasma etch process of the chrome requires high power densities to enable the single substrate etching within reasonable times (1-2 minutes). Instead of the usual II-filter coupling, direct coupling of the generator is used to enable these requirements. The power is controlled via several fixed amplitudes (constant self bias voltage within each amplitude level) and fine regulation via duty cycle, thus ensuring the ignition voltage for the low power process as well. The endpoint recognition uses direct metering of the transmission of the plasma radiation through the mask. The transmission curve indicates different compositions of the antireflection layer and the chromium layer as well as inhibition effects on the top and on the interfaces, thus additionally serving as a tool to characterize the material. The chrome oxide of transparent masks and molybdenum silicide layers etch faster than chrome, without inhibition at the beginning and they exhibit a linear etch behavior. The linewidth uniformity of the dry etch process is within 500 A (3 sigma). The material loss of the PBS descum process is +/- 1 nm (using an F.T.M. across 7" square resist blanks). System and process data are developed according to semi control standards (SECS) and enable full system control, the remote data storage and the integration of the system into fully automated mask fabrication.
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