Low Pressure Chemical Vapor Deposition (LPCVD)

Low Pressure Chemical Vapor Deposition (LPCVD) can be used for a variety of materials such as polysilicon for gate contacts, very short interconnect lines and resistors in analog technologies; thick oxides used for isolation between metal interconnects; doped oxides useful for global planarization; nitrides and other dielectrics for isolation or capacitors (higher K materials for larger capacitance) and metals for seed layers for vias and interconnect lines (not typically used for the entire metal line due to slow deposition rate)

LPCVD for Si Technology

For polysilicon deposition Si containing compounds are reacted with the wafer at ~0.2 to 1 torr and ~575-650°C. Silane (SiH₄) is the most common silicon source and typically 100% silane or 20-30% silane with 80-70% inert gas is used as precursors. The temperature range is either limited by low deposition rate at low temperature end (insufficient thermal energy for the reaction) or by the formation of particles in the gas phase (gas spontaneously reacting before it reaches the wafer) and poor adhesion. On the upper temperature end deposition rate is limited by reaction rate (controlled by temperature and pressure) and arrival rate (controlled by gas pressure). Crystalline Structure is also controlled by temperature. Poly-Si can be doped using Diborane (B₂H₆), arsine (AsH₃) or phosphine (PH₃), diffusion or by implantation. Diffusion process results in lowest resistivity doping compared to high resistivity doping in implantation. The resistivity can vary from ~10^-3 to 10⁺⁵ -cm. Doped poly-Si makes good short interconnect lines.