Quantitative Model-Based Photoelastic Characterization of Wafer-Bonding Stresses: a Tool for Industry and Education

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Intellectual Merit: In this project a modeling framework will be developed to complement a newly developed technique for interface characterization in direct-bonded silicon wafers. The infrared grey field polariscope (IR-GFP) photoelastic measurement technique is a powerful method that offers faster throughput and finer spatial resolution than other techniques for investigating stress sources at direct-bond interfaces. The method can make qualitative comparisons of stress intensities due to various types of defects, but it measures only a through-thickness average of stress in the wafers. The new modeling method will make the characterization technique more quantitative by incorporating the mechanics of adhesion in direct wafer bonding through an atomistic consideration of surface adhesion forces. Surface contact elements will be developed to mimic the atomistic interactions between the two surfaces, and several important geometries will then be studied both computationally and experimentally for validation. Broader Impact: The quantitative model-based characterization approach will allow for full-field stress tensor measurements with high accuracy, resolution, and speed. This will make a major contribution to the industrial inspection of wafer-bonded interfaces for silicon-on-insulator (SOI) device processing. The method will also be developed for use as a lab module in the Undergraduate Materials Testing Instructional Laboratory at UIUC. By including this model-based experimental technique as a characterization methods taught in the materials lab, a new generation of undergraduate students will be exposed to a high-tech approach relevant to the semiconductor industry, they will investigate contact mechanics in small scale systems, and they will learn about fundamentals of photoelasticity.