Piezoresistive Silicon Diaphragm Doping and Strain Gauge Adhesion Defect Modes
Optimal piezoresistive stability requires heavy surface boron doping above 2e19 cm-3 combined with plasma-activated silane coupling to prevent delamination.
Thermal Annealing
Material Restoration
A heat treatment process alters the physical, chemical, or electrical properties of a semiconductor wafer through controlled heating and cooling cycles. Through thermal annealing, the crystal lattice damage caused by ion implantation is repaired, and implanted dopants are driven into active substitutional sites. This high-temperature step is essential for restoring the carrier mobility and reducing the defect density of the semiconductor material.
Lattice Rearrangement
Wafers are heated in a furnace or rapid thermal processing chamber to temperatures typically ranging from six hundred to over one thousand degrees Celsius. This thermal energy allows displaced silicon atoms to migrate back to their original positions in the single-crystal lattice. The duration and temperature of the anneal are selected to balance lattice recovery against the unwanted diffusion of dopants.
High temperatures promote complete recrystallization but can also cause shallow junctions to deepen.
Defect Reduction
This process also reduces the mechanical stress in deposited metal and dielectric films by allowing atomic relaxation to occur. Reducing this stress prevents subsequent film cracking or delamination during chemical mechanical planarization or packaging. In-line metrology uses stress measurement tools to verify that the film stress has been reduced to acceptable levels.
Process Integration
Excessive thermal budgets can lead to dopant out-diffusion or the deformation of pre-existing fine features on the wafer surface. Consequently, the annealing process must be designed to fit within the overall thermal budget of the device.