Ion Implantation Profile Optimization for Thermal Drift Suppression in MEMS
Dual-implant boron-phosphorus profiles achieve zero-crossing TCR at 3.5e19 cm^-3, suppressing piezoresistive thermal drift to 12 ppm/K.
Dopant Channeling
Pathing Phenomenon
Penetration of ions into a crystalline lattice along specific crystallographic axes or planes occurs without substantial nuclear collisions. This effect, described as dopant channeling, happens when the incident ion beam aligns with the open spaces between atomic rows during the implantation process. It results in a deeper distribution of impurities than predicted by standard models.
Consistent junction depths across the production lot require precise control over the wafer orientation relative to the beam.
Implantation Control
Tilting the wafer by a specific angle minimizes the probability of ions entering the crystal channels. Rotation also helps.
Profile Distortion
Tail regions of the dopant distribution curve often show an elongated slope due to the channelling of a small fraction of the ion dose. This dopant channeling extends the metallurgical junction deeper into the substrate. It creates challenges for sub-micron devices where shallow junctions are required for electrostatic control.
Metrological Verification
Spreading resistance profiling and secondary ion mass spectrometry identify the extent of the channelling tail. These measurements compare the actual depth against a reference profile generated from a pre-amorphized silicon sample. When the channelling effect is present, the measured depth exceeds the calculated range for a random orientation.