1. 金屬閘極與絕緣層上鍺 晶圓製程 Metal Gate and Ge on Insulator Process
指導教授：劉致為 博士
學生：李呈峻
臺灣大學電子工程學研究所

2. Outline
Introduction
The Electrical Characteristics of Tantalum Nitride Metal Gate
Ge-on-Insulator Substrates Formation by Wafer
Bonding and Layer Transfer
A Novel 850 nm, 1.3μm and 1.5μm GOI MOS
Photodetector for Optical Communication
Summary

3. Intern’l Technology Roadmap for Semiconductors-- ITRS

4. Why metal gate ? Problems in conventional poly silicon gate (poly-Si)
High gate resistance
High gate tunneling leakage current
Poly silicon gate depletion
Boron penetration into the channel region
Solution
Metal gate

5. Pure Metal Work Functions
The work-function with various pure metals.
The band gap of silicon that between the conduction band (Ec) and valence band (Ev) is 1.12eV at room temperature.

6. Why tantalum metal is suitable for semiconductor industry?
Advantages
Body-centered-cubic (BCC) crystal structure
High melting point(2996℃)
Low-resistance ohmic contact
Cubic, Body Centered
Cubic, Face Centered
For instance, Al, Pt and Cu

7. Outline
Introduction
The Electrical Characteristics of Tantalum Nitride Metal Gate
Ge-on-Insulator Substrates Formation by Wafer Bonding and Layer Transfer
A Novel 850nm, 1.3μm, and 1.5μm GOI MOS Photodetector for Optical Communication
Summary

8. Alloy Work Functions

9. Experiment Process Flow

10. C-V Curves of TaN with PMA 400℃
Before N2 Annealing
After N2 Annealing
After PMA 5minutes in 400℃, the interface traps of TaN gate device
are significantly reduced by heat treatment.

11. Calculation of Flat-Band Voltage
Cfb
Vfb
Cox , Vg, A as known
Vfb
Here LD was the Debye length defined

12. Flat-Band Voltages Versus Silicon Dioxide Thickness

13. Flat-Band Voltages Versus Nitrogen Flow Ratio
The VFB converge to a specific value (i.e V)
when the N2 flow rate is upto abut twenty.

14. Work Functions of Tantalum Nitride

15. The C-V Curves Dispersion After PMA 900℃ 20sec
After PMA 900C 20sec, the Cox of TaN gate devices continues
to decrease as nitrogen flow ratio.

16. The Value of Cox Dispersion After PMA 900℃ 20sec
If nitrogen gas flow ratio is higher than thirteen percents,
the Cox dispersion phenomenon is obviously.

17. The TaN Gate Analysis of Auger Microprobe
After PMA 400℃ 5min
After PMA 900℃ 20sec
With increasing nitrogen gas flow ratio, the thermal stability
decreased by tantalum diffusion into dielectric layer.

18. Outline
Introduction
The Electrical Characteristics of Tantalum Nitride Metal Gate
Ge-on-Insulator Substrates Formation by Wafer Bonding and Layer Transfer
A Novel 850nm, 1.3μm, and 1.5μm GOI MOS Photodetector for Optical Communication
Summary

19. Roadmap for GOI Process

20. Direct Wafer Bonding Megasonic acoustic cleaning SC1 cleaning
KOH cleaning
KOH:H20
DI water rinse
Hydrophilic surface (OH-)
SC1 cleaning
NH4OH:H2O2:H2O
Hydrophilic surface (OH-)
Pre-bonding
Alignment
Form a single bonding wave
High temperature treatment
6500C, O2, 30min
Strength the chemical bonds

21. GOI Wafer Formation Ge Si BPSG Wafer Bonding Without Smart-cut
The scanning electron microscopy (SEM) picture of a Ge wafer
bonds to another Si wafer capped with 600 nm BPSG. Ge
BPSG Si
Wafer Bonding Without Smart-cut

22. The hydrogen-induced exfoliation of Germanium
Formation of point defect in the lower concentration of hydrogen implant.
Rearrangement of the defect structure above 650℃.
H2 trap in the microvoids.
Development of these microvoids into cracks leading to complete layer transfer.
650℃

23. GOI Smart Cut Process Flow
Ion Implant (Hydrogen Dose 1E17)
Megasonic acoustic cleaning
Direct Wafer Bonding
KOH Cleaning
SC1 Cleaning
Pre-bonding
H Induced Layer Transfer
High temperature treatment
(650℃ 30min in Oxygen gas)
Surface Roughness Reduction
High temperature annealing
(825℃ 60min in hydrogen gas)

24. Ion Implantation Depth
The hydrogen implant depth in Ge vs. implant energy.
The longitudinal Straggle in Ge vs. implant energy.

25. TRIM Simulation
The concentration profile of hydrogen atoms is simulated by TRIM.
The hydrogen implant into germanium with 200KeV implant energy.

26. SEM of GOI After Smart Cut Process
The surface of GOI substrate is rough after smart cut process.
The thin germanium layer (i.e. 1.46μm) transfers upon BPSG. Ge Si
BPSG
rough

27. Microroughness Measurement After Smart-cut
No Annealing
With Annealing in F. G.
After GOI annealed in furnace 825℃ with
forming gas , GOI surface roughness
reduced to RMS~27nm.
GOI surface
Roughness-mean-square(RMS)~97nm.

28. Microroughness Measurement After Smart-cut
With Annealing in N2
With Annealing in H2
After GOI annealed in furnace 825 ℃
with N2 gas , GOI surface roughness
reduced to RMS~62nm.
After GOI annealed in RTP 825 ℃
with H2 gas , GOI surface roughness
reduced to RMS~43nm.

29. GOI Surface Roughness Reduction
Surface microroughness of Ge-on-insulator with different kind of gas,
for an hour annealing at 825℃ in furnace.

30. Outline
Introduction
The Electrical Characteristics of Tantalum Nitride Metal Gate
Ge-on-Insulator Substrates Formation by Wafer Bonding and Layer Transfer
A Novel 850 nm, 1.3μm and 1.5μm GOI MOS Photodetector for Optical Communication
Summary

31. Roadmap for GOI Photodetector

32. GOI Smart Cut at Low Temperature Splitting Annealing
Ion Implant (Hydrogen Dose 1E17)
Megasonic acoustic cleaning
Direct Wafer Bonding
KOH Cleaning
SC1 Cleaning
Pre-bonding
H Induced Layer Transfer
Low temperature splitting annealing
(150℃ 12hr in 10% Oxygen gas)

33. Low Temperature Splitting Annealing
After splitting, the microroughness of Ge-on-insulator substrate.
The cross-section SEM image of Ge-on-insulator substrate. Ge
800nm Si
SiO2
80nm
After low temperature splitting annealing
150℃ with N2 gas , GOI surface roughness
is around 6.6nm (r.m.s).
After splitting annealing, the germanium
layer thickness is 800nm.

34. Current Reduction by Metal Technique
Device Area = 3x10-4 (cm2)
Pt is good selection for Ge N(100).

35. GOI Photodetector Process Flow
Ion implant (hydrogen
dose=1E17).
Direct Wafer bonding.
H induced layer transfer.
(150℃ 12Hr in 10% Oxygen)
Liquid Phase Deposition.
Gate electrode fabrication.
(Pt gate and Al contact)

36. GOI Photodetector Formation
The cross-section TEM image of Ge-on-insulator PMOS devices. Ge
800nm
Thermal oxide 80nm Si Pt
LPD

37. Photocurrent Under 850nm Light Source
The dark and photocurrent of the GOI PMOS detector exposures
to 850nm lightwave with different light intensity.
Responsivity = 0.2 (A/W)
Bulk Ge MOS detector
Responsivity = 0.2 ~ 0.3 (A/W)
GOI PMOS Photodetector

38. Photocurrent under 1300 and 1550 nm light source
The dark and photocurrent of the GOI PMOS detector exposures
to 1300nm and 1550 nm lightwave with different light intensity.
Responsivity = 0.2 (A/W)
Responsivity = 0.06 (A/W)

39. Responsivity and Efficiency
The responsivity of GOI PMOS detector exposures to 850nm, 1.3μm, and 1.5μm
lightwave with different light intensity.
The quantum efficiency (η) of the GOI photodetectors versus power under different
lasers exposure.

40. Impulse Response Bulk Ge Detector
The Full-Width Half-Maximum (FWHM) is 722 ps for the typical Ge MOS detector
under 850nm pulse measurement.
After fast fourier transform (FFT), the -3 dB bandwidth can be obtained about
340 MHz.

41. Impulse Response GOI Detector
The Full-Width Half-Maximum (FWHM) is 543 ps for the typical Ge MOS detector
under 850nm pulse measurement.
After fast fourier transform (FFT), the -3 dB bandwidth can be obtained about
340 MHz.
The 60% enhancement is achieved with -3 dB bandwidth, comparing to bulk
Ge MOS detector.
Since some of diffusion current is eliminated in GOI MOS photodetectors,
the speed and bandwidth of the device increases.

42. Outline
Introduction
The Electrical Characteristics of Tantalum Nitride Metal Gate
Ge-on-Insulator Substrates Formation by Wafer Bonding and Layer Transfer
A Novel 850nm, 1.3μm, and 1.5μm GOI MOS Photodetector for Optical Communication
Summary

43. Summary Tantalum Nitride Metal Gate
In experiment, we obtained that the oxide charges are positive in TEOS and the flat-band voltages concentrated -0.42V at twenty percents nitrogen flow ratio.
With increasing nitrogen gas flow ratio, the thermal stability decreased by tantalum diffusion into dielectric layer.
If nitrogen gas flow ratio is higher than thirteen percents, the tantalum diffusion phenomenon is obviously.
Ge-on-Insulator substrates Formation
The GOI surface roughness is reduced by thermal rapid annealing with hydrogen gas in furnace.
The bonding condition of low temperature heat treatment is at 150℃ with 10% oxygen flow in furnace.

44. Summary GOI MOS Photodetector
The leakage current is decreased at inversion bias by platinum gate electrode.
The novel GOI PMOS photodetectors have high responsivity (0.3 A/W) and high quantum efficiency of 40% at 850nm (0.25mW).
The 60% enhancement is achieved with -3 dB bandwidth, comparing to bulk Ge MOS detector.

45. Future Work
The RF pattern can be designed to enhance the speed (3-dB bandwidth) of GOI MOS photodetectors.
The thickness of germanium layer on insulator can be designed for fabricating resonant-cavity-enhanced (RCE) photodetectors to increase the bandwidth-efficiency.