Polycrystalline Silicon for Integrated Circuits and Displays

Polycrystalline Silicon for Integrated Circuits and Displays, Second Edition presents much of the available knowledge about polysilicon. It represents an effort to interrelate the deposition, properties, and applications of polysilicon. By properly understanding the properties of polycrystalline silicon and their relation to the deposition conditions, polysilicon can be designed to ensure optimum device and integrated-circuit performance.
Polycrystalline silicon has played an important role in integrated-circuit technology for two decades. It was first used in self-aligned, silicon-gate, MOS ICs to reduce capacitance and improve circuit speed. In addition to this dominant use, polysilicon is now also included in virtually all modern bipolar ICs, where it improves the basic physics of device operation. The compatibility of polycrystalline silicon with subsequent high-temperature processing allows its efficient integration into advanced IC processes. This compatibility also permits polysilicon to be used early in the fabrication process for trench isolation and dynamic random-access-memory (DRAM) storage capacitors.
In addition to its integrated-circuit applications, polysilicon is becoming vital as the active layer in the channel of thin-film transistors in place of amorphous silicon. When polysilicon thin-film transistors are used in advanced active-matrix displays, the peripheral circuitry can be integrated into the same substrate as the pixel transistors. Recently, polysilicon has been used in the emerging field of microelectromechanical systems (MEMS), especially for microsensors and microactuators. In these devices, the mechanical properties, especially the stress in the polysilicon film, are critical to successful device fabrication.
Polycrystalline Silicon for Integrated Circuits and Displays, Second Edition is an invaluable reference for professionals and technicians workingwith polycrystalline silicon in the integrated circuit and display industries.

1. Deposition.- 1.1 Introduction.- 1.2 Thermodynamics and kinetics.- 1.3 The deposition process.- 1.4 Gas-phase and surface processes.- 1.4.1 Convection.- 1.4.2 The boundary layer.- 1.4.3 Diffusion through the boundary layer.- 1.4.4 Reaction.- 1.4.5 Steady state.- 1.5 Reactor geometries.- 1.5.1 Low-pressure, hot-wall reactor.- 1.5.2 Single-wafer, cold-wall reactor.- 1.5.3 Cold-wall batch reactor.- 1.6 Reaction.- 1.6.1 Decomposition of silane.- 1.6.2 Surface adsorption.- 1.6.3 Deposition rate.- 1.6.4 Rate-limiting surface process.- 1.7 Deposition from disilane.- 1.8 Deposition of doped films.- 1.8.1 n-type films.- 1.8.2 p-type films.- 1.8.3 Electrostatic models.- 1.9 Conformai deposition.- 1.10 Enhanced deposition techniques.- 1.11 Summary.- 2. Structure.- 2.1 Nucleation.- 2.1.1 Amorphous surfaces.- 2.1.2 Single-crystal surfaces.- 2.2 Surface diffusion and structure.- 2.3 Evaluation techniques.- 2.4 Grain structure.- 2.5 Grain orientation.- 2.5.1 Films formed by thermal CVD.- 2.5.2 Effect of plasma on structure.- 2.5.3 Evaporated and sputtered films.- 2.5.4 Other mechanisms controlling structure.- 2.6 Optical properties.- 2.6.1 Index of refraction.- 2.6.2 Absorption coefficient.- 2.6.3 Ultraviolet surface reflectance.- 2.6.4 Use of optical properties for film evaluation.- 2.7 Thermal conductivity.- 2.8 Mechanical properties.- 2.9 Oxygen contamination.- 2.10 Etching.- 2.11 Structural stability.- 2.11.1 Recrystallization mechanisms.- 2.11.2 Undoped or lightly doped polycrystalline films.- 2.11.3 Heavily doped polycrystalline films.- 2.11.4 Amorphous films.- 2.12 Hemispherical-grain (HSG) polysilicon.- 2.13 Epitaxial realignment.- 2.14 Summary.- 3. Dopant Diffusion and Segregation.- 3.1 Introduction.- 3.2 Diffusion mechanism.- 3.2.1 Diffusion along a grain boundary.- 3.2.2 Diffusion in polycrystalline material.- 3.3 Diffusion in polysilicon.- 3.3.1 Arsenic diffusion.- 3.3.2 Phosphorus diffusion.- 3.3.3 Antimony diffusion.- 3.3.4 Boron diffusion.- 3.3.5 Limits of applicability.- 3.3.6 Heavy doping.- 3.3.7 Nitrogen.- 3.3.8 Implant channeling.- 3.4 Diffusion from polysilicon.- 3.5 Interaction with metals.- 3.5.1 Aluminum.- 3.5.2 Other metals.- 3.5.3 Silicides.- 3.6 Dopant segregation at grain boundaries.- 3.6.1 Theory of segregation.- 3.6.2 Experimental data.- 3.7 Computer modeling of diffusion.- 3.8 Summary.- 4. Basic Definitions of The Fuzzy Sets Theory.- 4.1 Introduction.- 4.2 Oxide growth on polysilicon.- 4.2.1 Oxidation of undoped films.- 4.2.2 Oxidation of doped films.- 4.2.3 Effect of grain boundaries.- 4.2.4 Effect of device geometry.- 4.2.5 Oxide-thickness evaluation.- 4.3 Conduction through oxide on polysilicon.- 4.3.1 Interface features.- 4.3.2 Deposition conditions.- 4.3.3 Oxidation conditions.- 4.3.4 Dopant concentration and annealing.- 4.3.5 Carrier trapping.- 4.3.6 CVD dielectrics.- 4.4 Summary.- 5. Basic Definitions of The Fuzzy Sets Theory.- 5.1 Introduction.- 5.2 Undoped polysilicon.- 5.3 Amorphous silicon.- 5.4 Moderately doped polysilicon.- 5.4.1 Carrier trapping at grain boundaries.- 5.4.2 Carrier transport.- 5.4.3 Trap concentration and energy distribution.- 5.4.4 Thermionic-field emission.- 5.4.5 Grain-boundary barriers.- 5.4.6 Limitations of models.- 5.4.7 Segregation and trapping.- 5.4.8 Summary: Moderately doped polysilicon.- 5.5 Grain-boundary modification.- 5.5.1 Grain-boundary passivation.- 5.5.2 Recrystallization.- 5.6 Heavily doped polysilicon.- 5.6.1 Solid solubility.- 5.6.2 Method of doping.- 5.6.3 Stability.- 5.6.4 Mobility.- 5.6.5 Trends.- 5.7 Minority-carrier properties.- 5.7.1 Lifetime.- 5.7.2 Switching characteristics.- 5.8 Summary.- 6. Applications.- 6.1 Introduction.- 6.2 Silicon-gate MOS transistor.- 6.2.1 Complementary MOS.- 6.2.2 Threshold voltage.- 6.2.3 Silicon-gate process.- 6.2.4 Polysilicon interconnections.- 6.2.5 Gate-oxide reliability.- 6.2.6 Limitations.- 6.2.7 Process compatibility.- 6.2.8 New structures.- 6.3 Nonvolatile memories.- 6.4 Polysilicon resistors.- 6.5 Fusible links.- 6.6 Gettering.- 6.7 Polysilicon contacts.- 6.7.1 Reduction of junction spiking.- 6.7.2 Diffusion from polysilicon.- 6.8 Vertical npn bipolar transistors.- 6.8.1 Fabrication: Polysilicon contacts.- 6.8.2 Physics of the polysilicon-emitter transistor.- 6.9 Lateral pnp bipolar transistors.- 6.10 Device isolation.- 6.10.1 Dielectric isolation.- 6.10.2 Poly-buffered LOCOS.- 6.10.3 Trench isolation.- 6.11 Dynamic random-access memories.- 6.11.1 Trench capacitor.- 6.11.2 Stacked capacitor.- 6.12 Polysilicon diodes.- 6.13 Polysilicon thin-film transistors.- 6.13.1 Device physics.- 6.13.2 Methods of improving polysilicon for TFTs.- 6.13.3 TFTs for active-matrix, liquid-crystal displays.- 6.13.4 TFTs for static random-access memories.- 6.14 Microelectromechanical Systems.- 6.14.1 Integrated sensors.- 6.14.2 Polysilicon for MEMS.- 6.15 Summary.