金屬閘極與絕緣層上鍺 晶圓製程 Metal Gate and Ge on Insulator Process

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. 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 Why 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. -0.42V) • 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 900℃ 20sec After PMA 400℃ 5min • 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 • KOH cleaning • KOH:H20 • DI water rinse • Hydrophilic surface (OH-) • SC1 cleaning • NH4OH:H2O2:H2O • DI water rinse • 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 Wafer Bonding Without Smart-cut Ge BPSG Si • The scanning electron microscopy (SEM) picture of a Ge wafer • bonds to another Si wafer capped with 600 nm BPSG.

22. 650℃ 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.

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 rough Ge BPSG Si • The surface of GOI substrate is rough after smart cut process. • The thin germanium layer (i.e. 1.46μm) transfers upon BPSG.

27. Microroughness Measurement After Smart-cut With Annealing in F. G. No Annealing 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. Ge 800nm 80nm SiO2 Si Low Temperature Splitting Annealing • After splitting, the microroughness of Ge-on-insulator substrate. • The cross-section SEM image of Ge-on-insulator substrate. 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. LPD Pt Ge 800nm Thermal oxide 80nm Si GOI Photodetector Formation • The cross-section TEM image of Ge-on-insulator PMOS devices.

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.