Trap Rich Layer Physics for RF Silicon Substrates
Trap-rich polysilicon layers beneath buried oxide pin interface carriers to eliminate parasitic conduction and lower sub-6 GHz harmonic generation.
LPCVD Polysilicon Layer
Meaning
Crystalline thin film deposited on a substrate using the low pressure chemical vapor deposition method. Fabrication of the lpcvd polysilicon layer functions as a conductive or structural material in the production of integrated circuits and micro-electromechanical systems. This deposition technique ensures high uniformity and excellent step coverage across complex surface topologies.
It is the standard choice for creating gate electrodes in metal-oxide-semiconductor transistors.
Deposition Process
Thermal decomposition of silane gas at low pressure results in a highly controlled growth rate. A typical lpcvd polysilicon layer is formed at temperatures ranging from 600 to 650 degrees Celsius. This temperature range balances the need for crystalline structure with the requirement to avoid damaging underlying metal layers.
Controlling the pressure within the reaction chamber allows for the precise adjustment of the film thickness and grain size.
Doping Phase
Electrical conductivity is achieved by introducing impurities like phosphorus or boron into the film. The lpcvd polysilicon layer becomes a low-resistance path for signals after a high-temperature activation step.
Mechanical Fit
Structural integrity of the film is required for its use in sensing membranes and moving parts. Because the lpcvd polysilicon layer exhibits predictable mechanical properties, it is often used to build the oscillating structures in gyroscopes and accelerometers. Internal stress within the film must be carefully managed to prevent the warping or cracking of the delicate microstructures.
Final inspection involves measuring the sheet resistance and the surface roughness to ensure the layer meets the requirements of the device specification.