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High-Density Full-CMOS SRAM Cell Technology with a Deep Sub-Micron Spacing between nMOS and pMOSFET
Fumitomo MATSUOKA Kazunari ISHIMARU Hiroshi GOJOHBORI Hidetoshi KOIKE Yukari UNNO Manabu SAI Toshiyuki KONDO Ryuji ICHIKAWA Masakazu KAKUMU
IEICE TRANSACTIONS on Electronics
Publication Date: 1994/08/25
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on High Speed and High Density Multi Functional LSI Memories)
Category: General Technology
full-CMOS SRAM cell, shallow trench isolation, dual gate CMOS,
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A full CMOS cell technology for high density SRAMs has been developed. A 0.4 µm n+/p+ spacing has been achieved by a shallow trench isolation with a retrograde and a shallow well design. Dual gate 0.35 µm n- and p-channel MOSFETs were used for the high density full CMOS SRAM cell. The side-wall inversion problem to which MOSFETs are subject due to the trench isolation structure has been controlled by combining taper angled trench etching and a rounded trench edge shape. A dual gate 0.4 µm nMOS/pMOS spacing has also been accomplished with no lateral gate dopant diffusion by an enlarged grain size tungsten polycide gate structure. These techniques can resolve the bottleneck problem of full CMOS SRAM cell size reduction, and realize a competitive cell size against conventional polysilicon resistor load SRAM cell (E/R type cell) or thin-film-transistor load SRAM cell (TFT type cell) structures. A test chip of a 256 k bit full CMOS SRAM was fabricated to verify the process integration of the shallow trench isolation with the retrograde shallow well design and the dual gate CMOS structure. It has been recognized that the above techniques are possible solutions for deep sub-micron high density full CMOS SRAM cell structure.