Piezoresistive Gauge Factor Temperature Compensation via Degenerate Boron Implantation
Degenerate boron implantation above 8e19 cm-3 pins the Fermi level into the valence band, matching TCR to TCGF for passive constant-current bridge compensation.
Pre-Amorphization
Substrate Preparation
Modification of a crystalline substrate into an amorphous state precedes the introduction of dopants to prevent unwanted ion channeling during semiconductor manufacturing. The technique of pre-amorphization involves bombarding the silicon wafer with heavy ions, such as germanium or silicon, to destroy the periodic arrangement of atoms. This process ensures that subsequent dopant implants remain confined to the intended depth profile.
Channeling Control
Ions entering a perfect crystal lattice can travel deep into the structure by sliding through the open paths between rows of atoms. By creating a disordered layer at the surface, pre-amorphization forces these ions to collide with the substrate atoms immediately. This interaction produces a narrower and shallower junction than is possible in a crystalline material.
Lattice Transformation
Restoration of the crystal structure is required after the implantation is complete, usually through a process known as solid phase epitaxial regrowth where the wafer is heated to allow atoms to rearrange themselves using the underlying crystal as a template. This heat treatment is vital for electrical performance. If the amorphized layer is too deep, residual defects known as end-of-range damage may remain at the original amorphous-crystalline interface.
These defects can act as traps for electrical carriers or lead to increased leakage current in the finished device. Careful metrology using transmission electron microscopy verifies the depth and quality of the regrown layer.
Production Metric
Measurement of the amorphous layer thickness is performed using spectroscopic ellipsometry. This optical technique quantifies the change in the refractive index of the silicon.