Ion Implantation Profile Optimization in Piezoresistive Diaphragms
Implantation energy and post-anneal thermal budgets set piezoresistive sensitivity and offset stability in silicon pressure sensor diaphragms.
Projected Range
Implantation Depth
Ion trajectories in a solid target are distributed statistically about a mean penetration depth. Projected range is the average distance an ion travels along the direction of the incident beam before coming to rest. This parameter is used to locate the peak of the dopant concentration profile in a semiconductor substrate.
Simulation Methodology
Computer models calculate the cumulative energy losses from nuclear and electronic stopping interactions. During boron or phosphorus implantation, the projected range is determined by the starting kinetic energy of the ions and the atomic density of the target material. Slower ions or denser targets produce shallower distributions.
These calculations form the basis for establishing correct implant energies during process development.
Analytical Profiling
High-resolution secondary ion mass spectrometry measurements are used to determine the actual peak position in the wafer. If the measured projected range deviates from the process specification, the acceleration voltage of the implanter is adjusted. This physical measurement is verified across several points on the wafer to ensure spatial uniformity.
The calibration of the measurement tool is maintained against certified reference standards.
Process Limit
Non-crystalline targets can show significant variations in ion penetration due to channeling along crystal axes. Wafers are tilted during implantation to disrupt these direct pathways and maintain predictable profiles.