Characterization of Vth fluctuation in 0.15-um n-MOSFETs for gigabit DRAM cell transistors

Toshihiko Miyashita; Hiroshi Suzuki; Manabu Kojima; Yasuo Nara; Nobuo Sasaki

doi:10.1117/12.284589

27 August 1997 Characterization of V_th fluctuation in 0.15-μm n-MOSFETs for gigabit DRAM cell transistors

Toshihiko Miyashita, Hiroshi Suzuki, Manabu Kojima, Yasuo Nara, Nobuo Sasaki

Proceedings Volume 3212, Microelectronic Device Technology; (1997) https://doi.org/10.1117/12.284589
Event: Microelectronic Manufacturing, 1997, Austin, TX, United States

Abstract

This paper presents a study of threshold voltage (V_th) fluctuation in n-MOSFETs having both gate lengths (L_g) and widths (W) as small as 0.15 micrometer for giga-bit DRAM cell transistors. The effects of varying L_g, W, and the gate oxide thickness (T_ox) and fluctuation in the concentration of channel impurities (N_a) were studied in detail. We fabricated and evaluated n-MOSFETs having various sizes of L_g and W. The V_th and the V_th fluctuation of these devices, when L_g/W equals 0.14/0.15 micrometer and the channel implantation condition was B⁺, 10 keV, and 9E12 cm^-2, were 0.33 V and 47 mV, respectively. A short- channel effect and a slight inverse narrow-width effect were also observed. By determining the origin of the V_th fluctuation, we found that the short- and narrow-channel effect (combined with variations in device dimensions) had only a minor effect on V_th fluctuations at higher channel impurity concentrations, and that the channel impurity fluctuation had the biggest influence. This channel impurity fluctuation cannot be explained simply by the statistical dopant fluctuation. We presume that anomalous impurity diffusion, such as transient enhanced diffusion (TED), during the gate oxidation process may be the dominant factor.

Citation Download Citation

Toshihiko Miyashita, Hiroshi Suzuki, Manabu Kojima, Yasuo Nara, and Nobuo Sasaki "Characterization of V_th fluctuation in 0.15-μm n-MOSFETs for gigabit DRAM cell transistors", Proc. SPIE 3212, Microelectronic Device Technology, (27 August 1997); https://doi.org/10.1117/12.284589

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