Mobility change of MOSFETs in a chip-stacked multichip package

Akihiro Ikeda, Kiyoshi Hamaguchi, Hiroshi Ogi, Kazuya Iwasaki, Reiji Hattori, Yukinori Kuroki

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

We studied the mobility change of MOSFETs in a chip-stacked multichip package. A 6-inch wafer that had the back ground to 50 μm thickness was diced into chips and a chip was cemented to a glass epoxy substrate with a nonconductive paste (NCP), and in addition, a second chip was bonded on the first chip in a flip chip arrangement. The interchip connection was made by thermocompression bonding of Au/Ni bumps formed on the upper and lower chips. The MOSFETs on the first chip had not shown changes in mobility before stacking the second chip, but after stacking the chip, the mobility of the pMOSFETs increased and the mobility of the nMOSFETs decreased. Before chip stacking, the first chip had been slightly convex, but after stacking it was deformed to a greatly concave shape. It is considered that the glass epoxy substrate or the NCP had undergone a plastic deformation during the thermocompression bonding of the chip and that the strain from this deformation remained after the thermocompression bonding process. As a consequence, bending compressive stress occurred in the first chip in the [110] direction, and it is considered that the mobility of the MOSFET changed due to the piezoresistive effect.

Original languageEnglish
Pages (from-to)1-8
Number of pages8
JournalElectronics and Communications in Japan, Part II: Electronics (English translation of Denshi Tsushin Gakkai Ronbunshi)
Volume89
Issue number7
DOIs
Publication statusPublished - Jul 1 2006

All Science Journal Classification (ASJC) codes

  • Electrical and Electronic Engineering

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