Strain-relaxation of SiGe Layers on Insulator

1. Strain-relaxation of SiGe Layers on Insulator 指導教授：劉致為 博士 學生：陳博文 台灣大學電子工程學研究所

2. Outline Introduction Direct Wafer Bonding Technology SiGe-on-Insulator formation by wafer bonding and layer transfer Buckled SiGe layers Summary

3. Introduction Ref：The International Technology Roadmap for Semiconductors (ITRS), 2001 edition

4. Motivation SGOI (Strained Si on SiGe-On-Insulator) =Strained Si+SOI. Combining the benefits of carrier mobility enhancement ofstrained Siand the advantages ofSOI.

5. Outline • Introduction • Direct Wafer Bonding Technology • SiGe-on-Insulator formation by wafer bonding and layer transfer • Buckled SiGe layers • Summary

6. ~200℃ >700℃ Stengl’s model for silicon wafer bonding • Hydrogen bonding • between adsorbed • water molecules. T=RT • (b) Water molecules form • cyclic tetramer and • increase bond strength • T=200℃ • (c) Water decomposition and • diffusion. Covalent bonds • forms. T≥700 ℃ ~ ~ ~ ~

7. Direct Wafer Bonding • Megasonic acoustic cleaning • SC1 cleaning • NH4OH:H2O2:H2O • DI water rinse • Hydrophilic surface (OH-) • Pre-bonding • Alignment • Form a single bonding wave • High temperature treatment • 8000C, O2, 30min • Strength the chemical bonds

8. Check by Breaking Wafer Method • Simple bonding check by breaking the wafers

9. TEM of Wafer Bonding Using Si with BPSG + bare Si wafer bonding No defect at interface

10. GOI Wafer Formation The GOI are formed by bonding BPSG/Si and Ge at 600°C . The measured Energy Dispersive Spectroscopy (EDS) from the interface layers.

11. IR viewing Camera Monitor IR lamp Infrared transmission system Light with wavelengths longer than 1.10μm (Si) can pass through silicon

12. Infrared image of a bonded Si/Si pair Bubbles with a diameter greater than 1 mm can be observed without IR microscopy.

13. Outline • Introduction • Direct Wafer Bonding Technology • SiGe-on-Insulator formation by wafer bonding and layer transfer • Buckled SiGe layers • Summary

14. SGOI Process Flow Ion implant. (hydrogen dose=5E16) Direct Wafer bonding. H induced layer transfer. Thin down.

15. 400℃ The schematic illustration of the hydrogen-induced exfoliation of silicon Formation of point defect in the lower concentration of hydrogen implant. Extensive disruption of the silicon lattice and 50~100A platelet formation. Rearrangement of the defect structure above 400 0C. H2 trap in the microvoids. Development of these microvoids into cracks leading to complete layer transfer.

16. Depth depends only on the implant energy with about 9nm / keV in silicon and silicon oxide. Ion implantation Depth

17. Wafer Bonding Without Smart-cut Wafer A (Host Wafer ) Si0.9Ge0.1 BPSG Bonding Interface 400 nm Wafer B (Handle Wafer )

18. 100nm Si0.9Ge0.1 layer and 500nm Si layer transfer upon BPSG. Si Si0.9Ge0.1 100nm Buried Oxide (BPSG) SGOI Wafer Formation

19. The surface is rough after smart cut process. rough 500 nm 100 nm SGOI Wafer Formation

20. Microroughness Measurement After Smartcut Roughness(r.m.s.)=7.34nm Roughness(r.m.s.)=6.17nm Host wafer Handle wafer

21. Interfaces microroughness (R.M.S.) increases with implantation energy of hydrogen ions Microroughness Measurement

22. Thermal Budget No lattice damage at 800oC, O2, 30min (Bonding and Smartcut recipe)

23. Si layer thin down (KOH etching) • Annealing Composed of three peaks: r-Si, s-Si, and Si in SiGe. Lorentz model is used. Peak shift to lower wave number with high temperature anneal.

25. Outline • Introduction • Direct Wafer Bonding Technology • SiGe-on-Insulator formation by wafer bonding and layer transfer • Buckled SiGe layers • Summary

26. Diagram of relaxation mechanisms

27. 10µm Buckled SiGe layers on SGOI compliant substrates Two-dimensional perpendicular to each other Oxidized for 300 sec at 960℃ with 1000 sccm oxygen flow Buckled SiGe Layers

28. Buckling can also be seen by optical microscopy.

29. Buckling seen by optical microscopy Buckling seen by AFM Surface roughness (r.m.s.) increase with oxidized time. Buckling seen by AFM for oxidation time > 30 sec. Buckling seen by optical microscopy for oxidation time > 60 sec.

30. Micro-Raman 514.5 nm (Ar+ laser) 4.5 mW power Micro-Raman Measurement Detectable Raman peak shift (~0.5 cm-1) after 30 sec oxidation

31. Edgy Effect w/o SiGe layer edgy Buckled SiGe layers Buckled SiGe layers directions near the patterned edgy are become along one-dimension, i.e.,normal to the edge

32. 5 sec 1 sec 10um 10um 10um 10um 10 sec 30 sec Buckling nucleus are randomly located at the initial oxidation The undulation was well-developed for the time exceeding 30 sec

33. TEM Analysis of Buckled SiGe Layers Sinusoidal undulations are clearly observed by TEM

34. The Undulation Morphology vs. Ge Fraction Surface roughness (r.m.s.) increase with oxidized time. The wavelength of the buckled SiGe layer increase with oxidized time.

35. Theoretical limits of buckling phenomenon Upper region (larger mesa) : w/i buckled SiGe layers Lower region (smaller mesa) : w/o buckled SiGe layers

36. as grown (Si0.9Ge0.1) oxidation 200×200 μm2 as grown (Si0.8Ge0.2) oxidation 150×150 μm2 Buckled SiGe layers formation on MESA after oxidation

37. as grown (Si0.8Ge0.2) oxidation 70×70 μm2 MESA size = 70×70 μm2 for Si0.8Ge0.2 elastic layer Nobuckled SiGe layers formation on MESA after oxidation

38. Experiment results are well consistent with theoretical buckled SiGe Layers limit

39. Outline • Introduction • Direct Wafer Bonding Technology • SiGe-on-Insulator formation by wafer bonding and layer transfer • Buckled SiGe layers • Summary

40. Summary Semiconductor films on insulator are successfully achieved by wet chemical activated bonding. Strain-relaxed compliant SGOI substrate has been fabricated by wafer bonding and hydrogen-induced layer transfer techniques. Strong buckling for exceeding 30 sec oxidation. Experiment results are well consistent with theoretical buckled SiGe layers limit.