Design and application of the interlayer van der Pauw resistor alignment bridge

The interlayer van der Pauw (VDP) resistor alignment bridge combines the sheet resistor and registration-sensitive bridge into one unified structure. As a result of symmetry, it does not require the width corrections resulting from image exposure and etch variations typical of linear resistor structures. It uses minimum area and pad count and provides orthogonal registration measurements. Bridges designed for 1.5- mu m feature size with body dimensions of 18 and 21 mu m and a tap length to width ratio of 0.5 show a sensitivity of 34-38 mV/ mu m at 10 mA. Registration errors of 0.2 mu m have been measured with an error of less than 10%. A good statistical correlation has been obtained between drawn and measured registration offsets. The correlation between the VDP bridge and the optical vernier is within +or-2% using a vernier spacing of 0.125 mu m. These results clearly indicate that the VDP bridge has the potential to provide accurate measurements of photo mask registration with the precision required for very large scale integration (VLSI) processing. The application of the VDP resistor bridge for interlayer registration using standard production procedures is described. Measurement precision and accuracy are discussed along with some fundamental bridge-design considerations.<
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