This paper summarized a collection of work and experimentation on detecting, classifying and reducing post developer defects. Various experiments demonstrate the effects of substrate priming, pH shock at rinse, resist hydrophobicity, rinse methods and developer surfactants in reducing post develop defects.
The mechanisms of the formation of microgroove and protuberance defects in novolac/diazonaphthoquinone resists were studied and found to be influenced by the resist composition, the degree of substrate silylation, and the developer composition. Low molecular chains in the novolac polymer and high PAC contents promote the formation of microgrooves and protuberances. A mechanism is proposed wherein short polymer chains migrate toward the substrate interface and PAC migrates away from the substrate during post-bake; this migration enhances the dissolution rate near the substrate, leading to an undercut. The possibility that the migration of developer along the resist/substrate interface occurs through percolative diffusion is explored. Developer-induced hydrolysis of trimethylsilyl groups from the silylated substrate is shown to be a contributory mechanism in the formation of microgrooves. Adding select surfactants to the developer is shown to reduce the rate of substrate desilylation and inhibit microgroove formation.
The behavior of the focus-exposure window for a half micron process was analyzed across a range of resist thicknesses. The range examined was selected to encompass a minima through maxima region of the I-line swing curve. This analysis is shown for an I-line resist; the undyed version contrasted to the dyed. The process tube characterization method calculates the common corridor exposure latitude for the two resist data sets. The common corridor for a given resist system defines that area in the focus-exposure plane that meets a single process specification for all the resist thicknesses in the selected swing curve range. In this study the undyed resist demonstrates a superior process window at a given resist thickness but is found to be inferior to the dyed resist as determined by the process tube characterization method.
A real I-line process case study of a dense array submicron pattern is analyzed using a 3-D simulator tool, instead of the traditional `experimental trials' approach. The array consists of 2-D mask geometry with strong edge distortions at pattern XY corners. The lithography process' most common variations are considered: exposure energy and resist/nitride/oxide thin film thicknesses. Relative edge-to-center linewidth variations are the responses in a quadratic statistical experiment designed for the process window volume determination. Once the process window is built the targets for the process parameters are set and their variations within the window are monitored to desensitize the 2-D mask array edge-to-center distortions. Analysis of the process window volume allows answers to lithography process questions.
A new concept, the 'Application Specific Microscopy', is proposed here for today's complex lithography patterns containing 3D halfmicron information. The concept is based on the fact that a consistent 2D metrology process is no longer sufficient to characterize samples with 3D information. The Z information becomes necessary for the correlation between metrology measurement results to the sample XYZ topography. Also a complete Z information helps both metrology and lithography engineers to trace process variations. the Z information is in fact the FOCUS parameter. It becomes the most critical parameter in the XY halfmicron metrology process, similar to optical halfmicron lithography process. The Z information is acquired when the sample is scanned in Z. A Z-scan capability with nanometer resolution was used here to acquire the necessary Z information, an information that was then used to determine metrology system Depth Response Function. The Depth Response Function was used to monitor focus and to manipulate the metrology system for optimum performance on a particular sample.
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