Impact of Cu contamination on memory retention characteristics in thinned DRAM chip for 3-D integration

Kangwook Lee, Takaharu Tani, Hideki Naganuma, Yuki Ohara, Takafumi Fukushima, Tetsu Tanaka, Mitsumasa Koyanagi

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)

Abstract

The influence of Cu diffusion at the backside surface of a thinned dynamic random access memory (DRAM) chip for 3-D integration on memory retention characteristics was electrically evaluated. A DRAM test chip was bonded to a Si interposer at 300°C for 2 min and thinned down to 30-μm thickness. The DRAM cell characteristics, which show 50% failure at 200 μs, were not degraded from the packaged sample (prethinning) even after chip bonding, chip thinning, and no-Cu postannealing for 30 min at 300°C. Meanwhile, the DRAM cell array shows 50% failure at 70 μs after an intentional Cu diffusion from the backside surface for 30 min at 300°C. It means that Cu atoms at the back surface reach the Si-SiO 2 interface of the front surface in active areas and cause functional failures such as increasing carrier recombination rate, consequently shortening retention time. However, the NMOS transistor characteristics show no significant change even after Cu diffusion. The on-current performance characterized by majority carriers is not an effective criterion to characterize sensitively the Cu contamination effect.

Original languageEnglish
Article number6238299
Pages (from-to)1297-1299
Number of pages3
JournalIEEE Electron Device Letters
Volume33
Issue number9
DOIs
Publication statusPublished - 2012

Keywords

  • 3-D LSI
  • Capacitance-time (C-t)
  • Cu diffusion
  • dynamic random access memory (DRAM)
  • retention time

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Electrical and Electronic Engineering

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