Infrared differential interference contrast microscopy for 3D interconnect overlay metrology.

One of the main challenges for 3D interconnect metrology of bonded wafers is measuring through opaque silicon wafers using conventional optical microscopy. We demonstrate here the use infrared microscopy, enhanced by implementing the differential interference contrast (DIC) technique, to measure the wafer bonding overlay. A pair of two dimensional symmetric overlay marks were processed at both the front and back sides of thinned wafers to evaluate the bonding overlay. A self-developed analysis algorithm and theoretical fitting model was used to map the overlay error between the bonded wafers and the interconnect structures. The measurement accuracy was found to be better than 1.0 micron.

Scatterometry-based metrology with feature region signatures matching.

Scatterometry takes advantage of the sensitivity exhibited by optical diffraction from periodic structures, and hence is an efficient technique for lithographic process monitoring. A feature region measurement algorithm has been developed to extract accurately and quickly the relevant constitutive parameters from diffraction data. It is a method for efficiently determining grating structure by seeking the reflectance at some angles contains more information about the structure of the surface relief profile than the reflectance at other angles in a library data match process. The number of measurements and size of signature matching library will be reduced in a great percentage by performing the feature region algorithm.