U. Gösele and Q.-Y. Tong
Max-Planck-Institute of Microstructure Physics, D-06120 Halle, Germany and School of Engineering, Duke University Durham, NC 27708, USA
Tentative Table of Contents
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
2. Silicon surface
2.1. Surface morphology and chemical properties
2.2. Micromechanical properties
2.3. Thermaldynamic properties
2.4. Electrical properties
3. Basics of interactions between flat surfaces
3.1. Van-der-Waals interactions
3.2. Interface energies and their measurement
3.3. Flatness criterion for avoiding unbonded areas
4. Influence of particles, surface steps and cavities
4.1. Investigation methods for unbonded areas
4.1.1 transmission
4.1.2 X-ray topography
4.1.3 Acoustic microscopy
4.1.4 Magic mirror method
4.1.5 Interface etching
4.2.5 Transmission Electron Microscopy
4.2 Bubble diameter as a function of particle size
4.3 Influence of surface steps and cavities
4.4 Hydrophilic versus hydophobic wafer surfaces
5. Initiation of wafer bonding at room temperature
5.1 Basic conditions for room temperature(RT) bonding
5.2 Cleaning of wafer surfaces
5.3 Activation of wafer surfaces
5.4 Room temperature bonding in conventional cleanroom
5.4.1 Manual bonding
5.4.2 Bonding fixtures and machines
5.5 Room temperature bonding with micro-cleanroom setup
5.6 Initiation and propagation of bonding front
5.7 Thick wafer bonding
5.8 Debonding
6. Temperature treatment of bonded wafer pairs
6.1 Bonding strength as a function of time
6.2 Bonding strength as a function of temperature
6.3 Low temperature wafer bonding
6.4 Temperature-dependent interface bubbles
6.4.1 Phenomenology: IR-type and X-type bubbles
6.4.2 Cause of bubbles
6.4.3 Thermodynamics of bubble formation
6.4.4 Elimination of bubble formation
6.5 Structural development of thin interface oxides
6.5.1 Influence of rotational wafer misorientation
6.5.2 Influence of oxygen content (CZ versus FZ silicon wafers)
7.1 Mechanical thinning
7.1.1 Chemical-mechanical polishing
7.1.2 Refinement by local thinning
7.1.3 Polish-stop approach
7.2 Silicon chemical etching
7.2.1 Aqueous alkaline etchants
7.2.2 Etch selectivity of aqueous alkaline
7.2.2.1 Silicon oxide
7.2.2.2 p++ silicon
7.2.2.3 Carbon-doped silicon
7.2.2.4 Germanium-doped silicon
7.2.2.5 Nitrogen-implanted silicon
7.2.3 Silicon anisotropic etching
7.2.4 Silicon isotropic etching
7.3 Layer transfer
7.3.1 Layer transfer by bonding and etch-back
7.3.1.1 B and B/Ge etch-stop
7.3.1.2 Carbon-implanted etch-stop
7.3.1.3 Oxygen-implanted etch-stop
7.3.1.4 SiC etch-stop for transfer of SiC layer
7.3.1.5 Porous silicon etch-release layer
7.3.2 Layer transfer by bonding and layer-splitting
7.3.3 Layer transfer by bonding and lateral etching
8. Electrical properties of bonded interface
8.1 Electrical properties of bonded hydrophilic and hydrophobic Si/Si interface
8.1.1 Charges in bonded Si/Si interface region
8.1.2 Boron contamination at bonding interfaces
8.1.3 Current transport through bonded Si/Si unipolar and pn junctions
8.1.4 Recombination centers at bonded interface
8.1.5 Origins of interface traps
8.2 Electrical properties of bonded Si/SiO2 and SiO2/SiO2 interface
8.2.1 Charges in bonded Si/SiO2 interface region
8.2.2 Negative charges in bonded SiO2/SiO2 region
8.2.3 Leakage current of bonded oxide layer
8.2.4 Radiation-hardness of bonded Si/SiO2 structure
9. Basics of stress and strain in bi-layer structures
9.1 Origins of stress in bonded wafers
9.2 Thermal stress distribution in bonded materials and at bonded interface
9.3 Stress relief mechanisms
9.4 Stress reduction methods
10. Bonding of dissimilar materials
10.1 Bonding of wafers of dissimilar materials
10.1.1 GaAs/Si bonding
10.1.2 InP/Si bonding
10.1.3 Quartz crystal/Si bonding
10.1.4 Si/quartz glass bonding
10.1.5 Si/glass bonding
10.1.6 Si/sapphire bonding
10.2 Bonding layers for direct bonding of dissimilar materials
10.2.1 CVD silicon oxide
10.2.2 CVD polysilicon
10.2.3 CVD silicon nitride
10.2.4 CVD InP and other materials
11. Stresses in bonded wafers
11.1 Stresses caused by surface nonuniformity
11.2 Stress in bonded GaAs/Si structures
11.3 Deformation of bonded SOI pairs
11.4 Bonding of pre-stressed wafers
12. Bonding of structured wafers
12.1 Design considerations of patterned wafers
12.2 Bonding of wafers with cavities
12.2.1 Influence of hydrocarbon contamination
12.2.2 Bonding in different atmospheres
12.3 Bonding alignment for structured wafers
13. Mainstream applications
13.1 Bonding applications in VLSI
13.1.1 Competing technologies (SIMOX, ZMR and SOS)
13.1.2 Radiation-hard CMOS
13.1.3 DRAM s
13.1.4 Low power, low voltage CMOS
13.1.5 High temperature CMOS
13.1.6 Body contacts of SOI MOSFETs
13.2 Bonding applications in high voltage and power devices
13.2.1 Dielectric isolation
13.2.2 High voltage devices
13.2.3 High power devices
13.2.4 Buried metal structures
13.3 Bonding applications in micromechanics
13.3.1 Surface sacrificial layers
13.3.2 Microchannel systems
13.3.3 Microvalves and microinstrumentation
13.3.4 Pressure sensors and accelerometers
13.3.5 Electro-acoustic devices
13.4 Bonding application in optoelectronics
13.4.1 Integrated optical waveguides
13.4.2 Lasers and photodetectors
14. Emerging and future applications
14.1 Surface protection of semiconductor wafers
14.2 New material combinations
14.2.1 Infrared window protection using Si on ZnS bonding
14.2.2 Buried C60 layers
14.3 Bonding interface as gettering layer
14.4 X-ray masks
14.5 X-ray optics with curved membranes
14.6 Micro-vacuum-tubes
14.7 Thick wafer bonding for cooling application
14.8 Non-linear optics via multiple GaAs or ZnS bonding
14.9 3-D devices
14.10 SOI microwave MMIC
14.11 Research applications
14.11.1 Room-temperature UHV bonding
14.11.2 Grain boundary generation
14.11.3 Determination of interface energies
14.11.4 Electrical and mechanical properties and interactions of monolayers of polymers and biomolecules
14.11.5 Self-stressed semiconductor structures
14.11.6 Investigation of surface contamination
14.11.7 Investigation of surface topology
14.11.8 Investigation of helium quantum effect
15. New developments
includes anything in terms of essential information which appears after finishing the rest of the book and which would be difficult to incorporate.
Table of constants
list of mechanical, thermal and physical properties of commonly used materials for wafer bonding
list of commonly used constants