The shrinking of contact opening is inevitable, as the technology progresses. The most obvious shrink strategies, wavelength reduction and phase-shifting masks (PSM) offer the most significant improvements to meet these demands, but at a hefty price. By using focus latitude exposure technique (FLEX) it is possible to print down contact hole with reasonable processing latitude using 248nm wavelength lithography and binary mask. A few parameters were varied to obtain suitable condition. Several feature sizes were printed and measured to get the proper combination of the print bias and focal distances with acceptable process margin. Verification on production wafer is needed for different pitch of feature sizes and fine-tuning on the focal distance for optimum results.
This research characterizes line edge roughness (LER), determines which resist has lowest LER for all process variations, and investigates the effect of chromophore bulkiness on LER. Three KrF photoresists with different chromophore bulkiness were evaluated. The characteristics evaluated were depth of focus (DOF), profile and resolution, LER, exposure latitude, iso-dense bias and CD linearity. Different feature sizes were tested from 100nm to 190nm. From the results, it is seen that resist Pt has the lowest average LER for all process conditions and variations with a 3 sigma value of 10.074. This is followed by resist P5 and P6 with a 3 sigma LER value of 12.562 and 15.468. It is concluded that high chromophore bulkiness results in high UV activation. This is seen from the LER for resist P6 that is the highest out of all the photoresist. Reducing the chromophore bulkiness will reduce LER until it reaches a saturation point where reduction will not result in any lower LER. Reducing the chromophore bulkiness further beyond the saturation point will in fact increase the LER.
Overlay requirement is one of the biggest obstacles in achieving a very small feature. With the continued growth of small feature size, overlay requirement becomes tighter. Such a tight requirement requires a very high performance in alignment. Alignment performance is greatly dependent on alignment signal quality. Variation in metal deposition thickness, polishing time, and mark depth may deteriorate the alignment signals quality. In this paper, different types of alignment mark was used to evaluate the alignment performance in various process environment. Based from the findings, two grating alignment mark gives the worst alignment performance, which clearly indicates the unsuitability to use in production environment.
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