SCIENCE AND TECHNOLOGY
OF SEMICONDUCTOR WAFER BONDING
Q.-Y. Tong* and U. Gösele
Max-Planck-Institute of Microstructure Physics, D-06120 Halle, Germany
And
School of Engineering, Duke University
Durham, NC 27708, USA
And
*Southeast University, Nanjing 210018, China
Preface
Chapter 1 Introduction
1.1. Short history of bonding materials
1.2. What is wafer direct bonding?
1.3. What is it good for (driving forces)?
1.4. How does it work?
1.5. Typical problems and solutions
Chapter 2 Basics of Interactions Between Flat Surfaces
2.1 Interaction forces between surfaces
2.1.1 Van der Waals interactions
2.1.2 Electrostatic (Coulombic) forces
2.1.3 Capillary forces
2.1.4 Very short-ranged forces
2.2 Bond strength and its measurement
2.2.1 Interface energy and surface energy
2.2.2 Surface energy measurement: crack-opening method
2.2.3 Bond strength measurement: fracture strength method
Chapter 3 Influence of Particles, Surface Steps and Cavities
3.1 Investigation methods for unbonded areas
3.1.1 Optical transmission
3.1.2 X-ray topography
3.1.3 Acoustic microscopy
3.1.4 Magic mirror method
3.1.5 Interface etching
3.1.6 Transmission electron microscopy
3.2 Bubble diameter as a function of particle size
3.3 Influence of surface flatness, steps and cavities
Chapter 4 Surface Preparation and Room Temperature Wafer
Bonding
4.1 Polishing of wafer surfaces
4.2 Wafer surface cleaning
4.2.1 Cleaning principle of hydrogen peroxide-based RCA solutions
4.2.2 Microroughening and modified RCA1 solution
4.2.3 Alternative cleaning technologies I: sulfuric- and HF-based solutions
4.2.4 Alternative cleaning technologies II: hydrogen plasma cleaning and thermal treatment in UHV
4.3 Activation of wafer surface
4.3.1 Hydrogen bonding
4.3.2 Wet chemical activation of Si or Si0
2 surface4.3.2.1 Wet chemical hydrophilization of Si0
2 surface4.3.2.2 Wet chemical electrophilization of Si surface
4.3.3 Surface activation by plasma treatment
4.3.3.1 Plasma activation via formation of surface bond defects
4.3.3.2 Plasma activation via removal of surface layers
4.3.4 Surface activation by UHV annealing
4.4 Room temperature bonding in a conventional cleanroom
4.4.1 Manual bonding
4.4.2 Bonding fixtures and machines
4.5 Room temperature bonding with micro-cleanroom setup
4.6 Initiation and propagation of bonding front
4.7 Interface of room temperature bonded Si pairs
4.7.1 Interface of room temperature bonded hydrophilic Si pairs
4.7.2 Interface of room temperature bonded hydrophobic Si pairs
4.8 Thick wafer bonding
4.9 Debonding
4.9.1 Physics background and modeling
4.9.2 One-wafer bent concept
4.9.3 Water-enhanced crack opening
Chapter 5 Thermal Treatment of Bonded Wafer Pairs
5.1 Bonding strength as a function of time
5.2 Bonding strength as a function of temperature
5.2.1 Bonding strength of hydrophilic Si/Si, Si/SiO2 and SiO2/SiO2 pairs
5.2.2 Bonding strength of hydrophobic Si/Si pairs
5.3 Low temperature wafer bonding
5.4 Temperature dependent interface bubbles
5.4.1 Causes of temperature-dependent interface bubbles
5.4.2 Prevention of temperature-dependent interface bubbles
5.4.3 A simple model of bubble formation
5.5 Structure development of thin interface oxide
5.5.1 Influence of rotational wafer misorientation
5.5.2 Influence of oxygen content in Si bonding wafers
Chapter 6 Thinning Procedures
6.1 Mechanical thinning
6.1.1 Chemical-mechanical polishing
6.1.2 Refinement by local thinning
6.1.3 Polish-stop approach
6.2 Silicon chemical etching
6.2.1 Aqueous alkaline etchants
6.2.2 Etch selectivity of aqueous alkaline
6.2.2.1 Silicon oxide
6.2.2.2. P++ silicon
6.2.2.3. Carbon-doped silicon
6.2.2.4. Germanium-doped silicon
6.2.2.5. Nitrogen-implanted silicon
6.2.3 Silicon anisotropic etching
6.2.4 Silicon isotropic etching
6.3 Layer transfer
6.3.1 Layer transfer by bonding and etch-back
6.3.1.1 B and B/Ge etch-stop
6.3.1.2 Carbon-implanted etch-stop
6.3.1.3 Oxygen-implanted etch-stop
6.3.1.4 SiC etch-stop for transfer of SiC layers
6.3.1.5 Porous silicon etch-release layer
6.3.2 Layer transfer by bonding and layer-splitting
6.3.3 Layer transfer by bonding and lateral etching
Chapter 7 Electrical Properties of Bonding Interfaces
7.1 Electrical properties of interfaces in bonded hydrophilic and hydrophobic Si/Si wafers
7.1.1 Charges in bonded Si/Si interface region
7.1.2 Boron contamination at bonding interfaces
7.1.3 Recombination centers at bonding interface
7.2 Electrical properties of Si/SiO2 and SiO2/SiO2 bonding interfaces
7.2.1 Charges in bonded Si/SiO2 interface region
7.2.2 Charges in bonded SiO2/SiO2 interface region
7.3 Electrical properties of bonded oxide
Chapter 8 Stresses in Bonded Wafers
8.1 Stresses caused by surface waviness
8.2 Stresses in bonded dissimilar materials
8.2.1 Basic analytic equations
8.2.2 Stresses in thin films
8.2.3 Stresses in bonded GaAs/Si structures
8.2.4 Stresses in bonded SOI and multilayered structures
8.3 Bonding of pre-stressed wafers
Chapter 9 Bonding of Dissimilar Materials
9.1 Bonding of wafers of dissimilar materials
9.1.1 GaAs/Si bonding
9.1.2 InP/Si bonding
9.1.3 Quartz crystal/Si bonding
9.1.4 Si/quartz glass bonding
9.1.5 Si/glass bonding
9.1.6 Si/sapphire bonding
9.2 Bonding layers for direct bonding of dissimilar materials
9.2.1 CVD silicon oxide
9.2.2 CVD polysilicon
9.2.3 CVD silicon nitride
9.2.4 CVD InP and other materials
Chapter 10 Bonding of Structured Wafers
10.1 Design considerations of patterned wafers
10.2 Bonding of wafers with cavities
10.3 Bonding of partially or fully processed wafers
Chapter 11 Mainstream Applications
11.1 Bonding applications in VLSI
11.1.1 Competing SOI technologies
11.1.2 Radiation-hard SOI devices
11.1.3 DRAMs
11.1.4 Low power, low voltage CMOS
11.1.5 Body contacts of SOI MOSFETs
11.2 Bonding applications in high voltage and power devices
11.2.1 Dielectric isolation
11.2.2 High voltage devices
11.2.3 High power devices
11.2.4 Smart power circuits
11.2.5 Buried metal structures
11.3 Bonding applications in micromechanics
11.3.1 Surface sacrificial layers
11.3.2 Pressure sensors and accelerometers
11.3.3 Microchannel and microvalve systems
Chapter 12 Emerging and Future Applications
12.1 Bonding applications in optoelectronics
12.1.1 Optoelectronic integrated circuits
12.1.2 Low threshold, long wavelength lasers
12.1.3 Quasi-phase-matched second-harmonic generation
12.1.4 Cleaved GaN facet mirrors on sapphire substrates
12.2 Bonding applications in electro-acoustics
12.3 Bonding applications in electro-magneto-optics
12.4 Surface protection of semiconductor wafers
12.5 New material combinations
12.3.1 Infrared window protection using Si on ZnS bonding
12.3.2 Buried C
60 layers12.6 Bonding interface as gettering layer
12.7 Research applications
12.7.1 Room temperature UHV bonding
12.7.2 Very abrupt pn junctions
12.7.3 Self-stressed semiconductor structures
12.7.4 Grain boundary generation
12.7.5 Investigation of surface contamination
12.7.6 Determination of surface topology and surface energy
12.7.7 Formation of uniformly spaced silicon wafers
12.7.8 Curved single crystal silicon x-ray analyzer
12.7.9 Double-gate SOI MOSFETs