Measurement of contact resistance distribution using a 4k contacts array

A new test structure suitable for measuring a contact resistance distribution has been developed. It includes the following two components: (1) a 256 row, 16 column (=4096) four-terminal cross-contact array; and (2) peripheral circuits, which consist of an eight-stage CMOS binary counter and 256 bit CMOS decoders. It was found that contact resistance can be fitted by a Gaussian distribution more than three standard deviations of the mean value. The relationships between the contact size and the standard deviation of the contact resistance has been discussed for two types of contacts: Al/TiN/TiSi₂-n+Si and WSi₂/poly-n+Si. This test structure can simultaneously measure the series resistance of a two-terminal contact chain and the individual contact resistance. Comparing these results, it was found that the increase of the series resistance of the contact chain is due to the appearance of the contact that is outside of the Gaussian distribution