^{1}, Toshinori Numata

^{1,a)}, Toshikazu Nishida

^{1}, Rusty Harris

^{2}and Scott E. Thompson

^{1,b)}

### Abstract

Uniaxial four-point wafer bending stress-altered gate tunneling currents are measured for germanium (Ge)/silicon (Si) channel metal-oxide-semiconductor field-effect transistors (MOSFETs) with gate dielectrics and poly Si electrodes. Carrier separation is used to measure electron and hole currents. The strain-altered hole tunneling current from the -type inversion layer of Ge is measured to be times larger than that for the Si channel MOSFET, since the larger strain-induced valence band-edge splitting in Ge results in more hole repopulation into a subband with a smaller out-of-plane effective mass and a lower tunneling barrier height. The strain-altered electron tunneling current from the metal gate is measured and shown to change due to strain altering the metal work function as quantified by flatband voltage shift measurements of Si MOS capacitors with TaN electrodes.

The authors would like to thank the Applied Materials Foundation, Cypress Semiconductor, IBM, Intel Foundation, Semiconductor Research Corporation (SRC), U.S. Air Force Office of Scientific Research (USAFOSR), and the National Science Foundation (NSF) under Grant No. ECS-0524316 for funding this research.

I. INTRODUCTION

II. EXPERIMENTAL SETUP

III. RESULTS AND DISCUSSION

A. Stress-altered hole tunneling currents of Ge and Si -MOSFETs

B. Stress-altered electron tunneling current from metal gate

IV. CONCLUSION

### Key Topics

- Tunneling
- 43.0
- Germanium
- 34.0
- Electric measurements
- 17.0
- Elemental semiconductors
- 10.0
- Dielectrics
- 9.0

## Figures

Schematic illustration of carrier separation measurement of -MOSFET and four-point wafer bending. The gate tunneling current can be separated into electrons and holes tunneling from gate and substrate, respectively (Ref. 39).

Schematic illustration of carrier separation measurement of -MOSFET and four-point wafer bending. The gate tunneling current can be separated into electrons and holes tunneling from gate and substrate, respectively (Ref. 39).

(a) Source/drain and substrate tunneling current as a function of gate voltage for Ge -MOSFET. (b) and as a function of for Si -MOSFET.

(a) Source/drain and substrate tunneling current as a function of gate voltage for Ge -MOSFET. (b) and as a function of for Si -MOSFET.

Relative change in of Si and Ge -MOSFET as a function of stress. Symbols and lines are measured data and modeling, respectively. The magnitude of hole tunneling current change in Ge is approximately 4 times larger than that in Si.

Relative change in of Si and Ge -MOSFET as a function of stress. Symbols and lines are measured data and modeling, respectively. The magnitude of hole tunneling current change in Ge is approximately 4 times larger than that in Si.

(a) A schematic band diagram for the hole gate tunneling current in a -MOSFET on a (100) wafer. (b) and subbands shift under stress results in hole repopulation into subband, which has lower tunneling barrier height and smaller out-of-plane effective mass. (c) Strain-altered out-of-plane effective mass for each subband is listed.

(a) A schematic band diagram for the hole gate tunneling current in a -MOSFET on a (100) wafer. (b) and subbands shift under stress results in hole repopulation into subband, which has lower tunneling barrier height and smaller out-of-plane effective mass. (c) Strain-altered out-of-plane effective mass for each subband is listed.

Valence band-edge splitting of Ge and Si under tensile stress along [110] (not including confinement). Ge has larger valence band-edge splitting than Si.

Valence band-edge splitting of Ge and Si under tensile stress along [110] (not including confinement). Ge has larger valence band-edge splitting than Si.

Charge density vs applied stress for the top , bottom , and third subbands at an inversion charge density of for (a) Ge and (b) Si, respectively. Strain-altered out-of-plane effective mass of each subband is denoted (e.g., 0.12 ). Note, due to larger valence band-edge splitting of Ge, hole repopulation in Ge is more than in Si.

Charge density vs applied stress for the top , bottom , and third subbands at an inversion charge density of for (a) Ge and (b) Si, respectively. Strain-altered out-of-plane effective mass of each subband is denoted (e.g., 0.12 ). Note, due to larger valence band-edge splitting of Ge, hole repopulation in Ge is more than in Si.

Relative change in of Ge -MOSFET as a function of stress at gate bias of . Due to decreased work function of TiN gate, electron gate tunneling current from TiN gate increases up to with 100 MPa of stress. The inset shows the decreased tunneling barrier height via strain by the decreased work function of TiN gate.

Relative change in of Ge -MOSFET as a function of stress at gate bias of . Due to decreased work function of TiN gate, electron gate tunneling current from TiN gate increases up to with 100 MPa of stress. The inset shows the decreased tunneling barrier height via strain by the decreased work function of TiN gate.

(a) curve of MOS capacitor, measured at 100 kHz. is extracted from (Ref. 40). (b) shift as a function of tensile and compressive stress. decreases /increases with tension/compression.

(a) curve of MOS capacitor, measured at 100 kHz. is extracted from (Ref. 40). (b) shift as a function of tensile and compressive stress. decreases /increases with tension/compression.

Work-function shifts of TaN, bulk Al, and bulk Cu as a function of stress (Ref. 33). Work functions of three different metal increase/decrease with compressive/tensile stress. Line is the linear fit of extracted data.

Work-function shifts of TaN, bulk Al, and bulk Cu as a function of stress (Ref. 33). Work functions of three different metal increase/decrease with compressive/tensile stress. Line is the linear fit of extracted data.

Relative changes in gate tunneling current of MOS capacitor with TaN gate as a function of stress. Symbols and lines are measured data and modeling, respectively.

Relative changes in gate tunneling current of MOS capacitor with TaN gate as a function of stress. Symbols and lines are measured data and modeling, respectively.

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