Reducing stress effects on multi-project-wafer reticles


Collaborating with MOSIS by using GOTmuch and GOTfiller, XYALIS has set up a new methodology to MPW yield and control CPI. The result has been presented in a paper during the SPIE Advanced Lithography online conference, California, USA, 22-26 february 2021.

We propose a new method applied on Multi-Project Wafer (MPW) reticles to reduce thermal-mechanical stress.

Wafer bumping processes generate residual thermal-mechanical stress, causing crack and delamination across wide regions on a wafer. In this paper, we show the work achieving optimized metal layer densities and density gradients across the reticle to minimize the stress effects. We propose a new MPW chip placement flow that places chips on an MPW reticle meeting the minimum density gradients as the placement criterion. The flow also performs inter-die dummy metal fills to optimize densities with regard to each chip density. We show intentional crack-stop dummy metal rings the flow generates surrounding a chip. The dummy rings further reduce the propagation of stress cracks. We show the results of optimized density gradients and crack-stop rings across the chips on an MPW reticle.



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