1. Strained Silicon MOSFET
R Jie-Ying Wei
Department of Electrical Engineering and
Graduate Institute of Electronics Engineering
National Taiwan University, Taipei, Taiwan, R.O.C.

2. Cubic Lattice at Equilibrium

4. Lattice constant for a Si1-xGex alloy as a function of x

5. Critical thickness of Si1-xGex layers as a function of Ge fraction

6. The size change of each valley in a constant energy surface diagram indicates a shift up(smaller) or down(larger) in energy

7. LH：light hole band HH：heavy hole band SO：spin-orbit band

8. Sub-bands in an MOS inversion layer
Sub-bands in an MOS inversion layer. Additional energy separation reduces inter-valley scattering

9. Band Alignment

10. Surface Channel MOSFET Structure

11. Extraction
Mobility
Band Offsets

12. Mobility

13. Split C-V measurement configuration

14. Measured split C-V capacitance from a surface strained-Si n-MOSFET grown on a relaxed-Si0.7Ge0.3
VT :the intersection of the CGC and CGB curves

15. Gate-channel capacitance curve CGC

16. Gate-bulk capacitance curve CGB

17. When VGS < V FB , holes begin to accumulate at the Si/SiGe interface, confined by the valence band offset. The hole confinement causes the observed plateau at C’OX in CGB curve.

18. Effective mobility of surface-channel, strained-Si n-MOSFET at room temperature (Na=2E16)

19. Peak mobility enhancement ratio at room temperature as a function of apparent Ge fractions in the buffer layer

20. Transconductance for W. L = 5
Transconductance for W*L = 5*10 µm strained-Si n-MOSFETs Performance saturation with Ge fractions x > 0.2

21. Extraction
Mobility
Band Offsets

22. Full C-V characteristics of a surface strained-Si n-MOSFET (on relaxed Si0.7Ge0.3) compared to a CZ Si control

23. Some parameters
Qf : match the flatband voltages between the measured data and the theoretical curves
ΔEC = ΔVT since the thickness of the Si channel(10nm) is less than the Debye length of the material(20nm)
ΔEV : the difference between Va and V’a is not straight-forward, so simulation of the theoretical curve is required

24. Threshold voltage shift (ΔVT ) as a function of Ge fraction x

25. Two major assumptions in band offset extraction using SEDAN simulation
All material properties, other than the bandgap, in strained-Si and relaxed SiGe are identical to bulk Si.
The results may be affected by
1. the material dielectric constant
2. the electron affinity
3. the density-of-state (DOS) effective mass
Data of Braunstein, at al. is accurate for the bandgap of relaxed SiGe.

26. The results were identical, except for a shift in the flatband voltage

27. Strained-Si band parameters and channel thickness extracted from C-V measurments

30. Bandgap of strained-Si grown on a relaxed SiGe buffer layer

31. IEDM 2002 Strained Silicon MOSFET Technology
Low Field Mobility Characteristics of Sub-100nm Unstrained and Strained Si MOSFETs

32. Strained Silicon MOSFET Technology Schematic illustration a surface-channel strained-Si n-MOSFET

33. Effective mobility enhancement ratios

34. Mobility behavior in strained Si(20% Ge) and unstrained Si n-MOSFETs as a function of doping

35. Comparison of hole mobility enhancement ratios in strained Si p-MOSFETs as a function of vertical effective field, Eeff

36. Low field Mobility Characteristics of Sub-100nm Unstrained and Strained Si MOSFETs

38. The slopes of the lines were used to calculate mobility

39. Comparison of mobility extracted on long channel and short channel devices using the conventional and dR/dL method

40. Mobility enhancement factor as a function of temperature

41. Reference
Jeffrey John Welser “ The application of strained-silicon/relaxed-silicon germanium heterostructures to metal-oxide-semiconductor field-effect transistors”
Kern Rim “Application of silicon-based heterostructures to enhanced mobility metal-oxide-semiconductor field-effect transistors”
J.L. Hoyt, IEDM 2002
K. Rim, IEDM 2002