Through-focus scanning optical microscopy (TSOM) transforms conventional optical microscopes into truly 3D metrology tools for nanoscale- to- microscale dimensional analysis with nanometer-scale sensitivity. Although not a resolution enhancement method, TSOM has been demonstrated to provide lateral and vertical measurement sensitivity of less than a nanometer, comparable to the dimensional measurement sensitivity of other critical dimension (CD) metrology tools. The technique captures much richer data at many z-heights (i.e., through focus positions). Additionally, TSOM appears to decouple the measurement of profile dimensional changes at the nanoscale, such as small perturbations in sidewall angle and height, with little or no ambiguity, and may be able to analyze target dimensions ranging from as small as 10 nm up to many micrometers with similar nanometer-scale sensitivity. The exceptional z-height resolution of the technique, as well as very fast measurement time, is particularly important for high volume manufacturing. For example, TSOM has been demonstrated to show sensitivity to nanometer-scale changes in height. These two attributes make TSOM particulary attractive for 3D-stacked IC measurements of TSV reveal structures, and possibly C4 bumps and microbumps. In this work, we apply TSOM to through-silicon via copper (TSV) reveal height measurements in the 3-5 micrometer height and 5 micrometer diameter range, as well as simulate TSOM measurements on TSV features. Simulation results, combined with optical profilometry, are used to correlate TSOM image features among classes of variation in TSV height, diameter, and sidewall angle (SWA). In addition, inter-die and intra-die TSVs are compared to illustrate that greater magnitude variation occurs in inter-die TSV dimensions. Finally, TSOM can be used to compare rotationally isotropic TSV reveal structures with rotationally anisotropic structures.
Proceedings Title: Metrology Inspection and Process Control
Conference Dates: February 24-28, 2013
Conference Location: San Jose, CA
Conference Title: SPIE Advanced Lithography
Pub Type: Conferences
TSV, TSOM, through-focus scanning optical microscope, Cu reveal