Monday, July 11, 2022

3D Wafer Stacking: Review paper in IEEE TED June 2022 Issue

In IEEE Trans. Electr. Dev. June 2022 issue, in a paper titled "A Review of 3-Dimensional Wafer Level Stacked Backside Illuminated CMOS Image Sensor Process Technologies," Wuu et al. write:

Over the past 10 years, 3-dimensional (3-D) wafer-level stacked backside Illuminated (BSI) CMOS image sensors (CISs) have undergone rapid progress in development and performance and are now in mass production. This review paper covers the key processes and technology components of 3-D integrated BSI devices, as well as results from early devices fabricated and tested in 2007 and 2008. This article is divided into three main sections. Section II covers wafer-level bonding technology. Section III covers the key wafer fabrication process modules for BSI 3-D waferlevel stacking. Section IV presents the device results.

This paper has quite a long list of acronyms. Here is a quick reference:
BDTI = backside deep trench isolation
BSI = backside illumination
BEOL = back end of line
HB = hybrid bonding
TSV = through silicon via
HAST = highly accelerated (temperature and humidity) stress test
SOI = silicon on insulator
BOX = buried oxide

Section II goes over wafer level direct bonding methods.

Section III discusses important aspects of stacked design development for BSI (wafer thinning, hybrid bonding, backside deep trench isolation, pyramid structure to improve quantum efficiency, use of high-k dielectric film to deal with crystal defects, and pixel performance analyses).

Section IV shows some results of early stacked designs.

Full article:

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