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12 February 1997 Plasma etching of Cr photomasks: optimization of process conditions and CD control
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As device design rules continue to shrink, on-mask Cr structures must experience a corresponding reduction in size. Although 0.25 micrometer design rules require only 1 micrometer Cr features, the use of OPC structures, which may be needed to minimize line foreshortening and corner rounding, necessitate features to be etched into the Cr which are significantly smaller than this. This need, coupled with the demand for reduced CD bias and improved CD uniformities, requires the use of an alternate chrome etch technology. Plasma etching of Cr can be highly anisotropic, greatly reducing the etch undercut which is responsible for the CD bias typically associated with wet etching. Reactive ion etching (RIE) can provide significant enhancements in the capability of replicating micron and sub-micron features, but the Cr etch rate non-uniformity which is typical of this technique can translate into a CD non-uniformity. This is due in part to the relatively high pressure of operation (50 - 100 mTorr) which is necessary to reduce the self generated dc voltage and which, in turn, minimizes the photo resist etch rate. Recently, high density plasma sources, such as inductively coupled plasma (ICP), have become available which have the ability to operate both at low pressures and high plasma density while maintaining a low and controllable dc voltage. The low pressure operation significantly improves the etch rate uniformity and consequently the CD uniformity. By coupling this ICP plasma source with a non-contact backside photomask handling system and a true multi-station 'cluster tool.' In this study a design of experiment (DOE) is used to investigate the parameter space associated with the dry etching of Cr using an ICP source. The responses of Cr etch rate, selectivity to photo resist, CD uniformity and mean CD to target are studied, and from this an optimized parameter space is defined. Within this space the effect of overetch, dc voltage and pattern loading on the CD uniformity are also investigated. The role played by the photo resist profile in determining the Cr etch profile is also studied, and preliminary measurements are made to understand the effect of the above parameters on the mask CD bias.
© (1997) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Chris Constantine, David J. Johnson, Russell J. Westerman, Thomas P. Coleman, Thomas B. Faure, and Leonard F. Dubuque "Plasma etching of Cr photomasks: optimization of process conditions and CD control", Proc. SPIE 3236, 17th Annual BACUS Symposium on Photomask Technology and Management, (12 February 1997);


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