Research Papers

Evaluation of Stress Effects on Electrical Characteristics of N-Type MOSFETs: Variations of DC Characteristics During the Resin-Molding Process

[+] Author and Article Information
Masaaki Koganemaru

Mechanics and Electronics Research Institute, Fukuoka Industrial Technology Center, 3-6-1 Norimatsu, Yahatanishi-ku, Kitakyushu 807-0831, Japan

Toru Ikeda, Noriyuki Miyazaki

Department of Mechanical Engineering and Science, Graduate School of Engineering, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501, Japan

Hajime Tomokage

Department of Electronics Engineering and Computer Science, Fukuoka University, 8-19-1 Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan

J. Electron. Packag 132(1), 011003 (Mar 04, 2010) (8 pages) doi:10.1115/1.4000718 History: Received April 06, 2009; Revised September 26, 2009; Published March 04, 2010; Online March 04, 2010

Stress-induced changes in the electrical characteristics of a semiconductor device become a major concern in the production of semiconductor packages because the electrical characteristics are adversely affected by packaging (residual) stresses. The objective of our project is to evaluate the effects of stress on semiconductor devices. In this study, the shift of the DC characteristics of nMOSFETs during the resin-molding process was investigated experimentally. After a silicon chip including the n-type metal oxide semiconductor field effect transistors (nMOSFETs) was encapsulated in a quad flat package, the drain current variations and the transconductance shifts were measured. The drain current decreased during the resin-molding process while no significant shift in threshold voltage was observed. The experimental results were estimated adequately from the residual stress predicted by numerical and experimental analyses and from the stress-sensitivity of the nMOSFETs measured by the four-point bending method. Also, we tested the validity of an electron-mobility model that included the effect of stress. The electron-mobility model takes into account the variation in the relative occupancy of the electrons in each conduction-band energy valley. It was found that the effect of biaxial stress on the variation in electron-mobility can be qualitatively evaluated by the electron-mobility model but are quantitatively different from the experimental results. Several needed improvements to the electron-mobility model are proposed in this article.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

Schematic cross section of nMOSFET specimens

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Figure 2

Four-point bending specimens for measuring the stress sensitivities of nMOSFETs: (a) schematic configuration of nMOSFETs in the specimens and (b) enlarged surface image of nMOSFET specimens (W/L=24/24)

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Figure 3

System for measuring the stress-sensitivity of nMOSFETs: (a) schematic illustration of the system and (b) schematic diagram of four-point bending fixture

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Figure 4

Drain current shifts induced by four-point bending loading (W/L=24/0.8, longitudinal)

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Figure 5

Transconductance (Gm) variations induced by four-point bending loading (W/L=24/0.8)

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Figure 6

Schematic configuration of silicon chip

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Figure 7

QFP specimens: (a) schematic diagrams of specimens and (b) image of specimens

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Figure 8

Location of nMOSFETs and piezoresistive gauges on a silicon chip

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Figure 9

Evaluated results of residual stress on silicon chips: (a) resin A molding and (b) resin B molding

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Figure 10

Experimental results of drain current variation induced by resin-molding: (a) W/L=24/24, resin A; (b) W/L=24/24, resin B; (c) W/L=24/0.8, resin A; and (d) W/L=24/0.8, resin B

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Figure 11

Experimental results and estimated results of Gm change (ΔGm/Gm)

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Figure 12

Schematic illustrations of many-valley energy surfaces of a silicon conduction-band in k- (wave number) space

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Figure 13

(001) silicon MOS conduction-band energy in an inversion layer (18): (a) conduction-band valleys, unstrained state; (b) sub-band energies, unstrained state; (c) conduction-band valleys, biaxial compressive stress; and (d) sub-band energies, biaxial compressive stress

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Figure 14

Comparison of the effect of residual stress on the electron-mobility change rate among experiments, electron-mobility model and piezoresistive effect model (W/L=24/24)




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