Contact Hole Printing in Binary Mask by FLEX Technique

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 248 nm 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.