Polycrystalline Silicon for Integrated Circuit Applications

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 reactors.- 1.5.2 Atmospheric-pressure, cold-wall 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 step.- 1.7 Deposition of doped films.- 1.7.1 n-type deposited films.- 1.7.2 p-type deposited films.- 1.7.3 Electrostatic model.- 1.8 Step coverage.- 1.9 Enhanced deposition techniques.- 1.10 Summary.- 2 Structure.- 2.1 Nucleation.- 2.1.1 Amorphous surfaces.- 2.1.2 Single-crystal surfaces.- 2.2 Surface diffusion and structure.- 2.2.1 Subsurface rearrangement.- 2.3 Evaluation techniques.- 2.4 Grain structure.- 2.5 Grain orientation.- 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 Etch rate.- 2.8 Stress.- 2.9 Thermal conductivity.- 2.10 Structural stability.- 2.10.1 Recrystallization mechanisms.- 2.10.2 Undoped or lightly doped films.- 2.10.3 Heavily doped films.- 2.10.4 Implant channeling.- 2.10.5 Amorphous films.- 2.11 Epitaxial realignment.- 2.12 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.- 3.4 Diffusion from polysilicon.- 3.5 Interaction with metals.- 3.5.1 Aluminum.- 3.5.2 Other metals and silicides.- 3.6 Dopant segregation at grain boundaries.- 3.6.1 Theory of segregation.- 3.6.2 Experimental data.- 3.7 Summary.- 4 Oxidation.- 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 Effects 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.- 4.4 Summary.- 5 Electrical Properties.- 5.1 Introduction.- 5.2 Undoped polysilicon.- 5.3 Moderately doped polysilicon.- 5.3.1 Carrier trapping at grain boundaries.- 5.3.2 Carrier transport.- 5.3.3 Trap concentration and energy distribution.- 5.3.4 Thermionic field emission.- 5.3.5 Grain-boundary barriers.- 5.3.6 Limitations of models.- 5.3.7 Segregation and trapping.- 5.3.8 Summary.- 5.4 Grain-boundary modification.- 5.5 Heavily doped polysilicon films.- 5.5.1 Solid solubility.- 5.5.2 Method of doping.- 5.5.3 Stability.- 5.5.4 Mobility.- 5.5.5 Future trends.- 5.6 Minority-carrier properties.- 5.6.1 Lifetime.- 5.6.2 Switching characteristics.- 5.7 Summary.- 6 Applications.- 6.1 Introduction.- 6.2 Silicon-gate technology.- 6.2.1 Threshold voltage.- 6.2.2 Polysilicon interconnections.- 6.2.3 Process compatibility.- 6.2.4 New structures.- 6.2.5 Gettering.- 6.2.6 Gate-oxide reliability.- 6.3 Nonvolatile memories.- 6.4 High-value resistors.- 6.5 Fusible links.- 6.6 Polysilicon contacts.- 6.6.1 Reduction of junction spiking.- 6.6.2 Diffusion from polysilicon.- 6.7 Bipolar integrated circuits.- 6.7.1 Vertical npn bipolar transistors.- 6.7.2 Lateral pnp bipolar transistors.- 6.8 Device isolation.- 6.8.1 Dielectric isolation.- 6.8.2 Epi-poly isolation.- 6.8.3 Trench isolation.- 6.8.4 Summary.- 6.9 Trench capacitors.- 6.10 Polysilicon diodes.- 6.11 Polysilicon transistors.- 6.12 Polysilicon sensors.- 6.13 Summary.