Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Principles of Ion Implant • Generation of ions – dopant gas containing desired species • BF3, B2H6, PH3, AsH3, AsF5 – plasma provides positive ions • (B11)+, BF2+, (P31)+, (P31)++ • Ion Extraction – Ions are extracted from the source due to a high electric field • Ion Selection – Magnetic field mass analyzer selects the appropriate ion (mass & charge) • Ion Acceleration – Further accelerate ions giving the ions their final kinetic energy. • Beam Scan / Disk Scan – Provides a uniform dose of ions over the wafer surface. • In-situ Dose Monitoring Microelectronic Engineering Rochester Institute of Technology K.D. Hirschman Silicon Processes: Ion Implantation 1 Implant Mechanics Microelectronic Engineering Rochester Institute of Technology K.D. Hirschman Silicon Processes: Ion Implantation 2 Plasma source and ion extraction Gas feed Nielsen-type gaseous source Plasma Chamber + ions mT level pressure To pump Vext variable extraction voltage (typically ~30KV ) Microelectronic Engineering K.D. Hirschman Rochester Institute of Technology Silicon Processes: Ion Implantation 3 Ion selection ( Analyzing Magnet) V : ion velocity KE = qVext = ½M v 2 B|v R X radius of curvature Resolving Aperture R-H-R B v F selected ions Heavier ions Magnetic Field F = q v xB = M v 2 / R Mass to charge ratio of the selected ions: Centripetal Force Microelectronic Engineering Rochester Institute of Technology The ions are extracted from the source and analyzed in a magnetic field. The Lorentz force makes the ions take a curved path with a radius of curvature that depends on the mass of each ionic species. By adjusting the magnetic field strength, only the selected ions will enter the accelerating column. M /q = R2 B2 / (2 Vext) K.D. Hirschman Silicon Processes: Ion Implantation 4 BF3 Gas Spectrum Microelectronic Engineering Rochester Institute of Technology K.D. Hirschman Silicon Processes: Ion Implantation 5 PH3 Gas Spectrum Microelectronic Engineering Rochester Institute of Technology K.D. Hirschman Silicon Processes: Ion Implantation 6 Ion Acceleration µΤ level pressure Resolving Aperture Final Kinetic Energy of the Ion = q ( Vext + Vacc ) E field Example: Vext = 30 KV Vacc = 70 KV Energy of the Ion = 100 KeV Vacc Ground Column length = 3 ‘ Microelectronic Engineering Rochester Institute of Technology K.D. Hirschman Silicon Processes: Ion Implantation 7 Projected Range (Rp) Rp of Boron, Phosphorous, Arsenic and Antimony in Silicon as a function of the ion energy Rp (µm) Rp depends on incident and target atomic masses (complex) Ion Energy (KeV) Microelectronic Engineering Rochester Institute of Technology K.D. Hirschman Silicon Processes: Ion Implantation 8 Beam Scanning Electostatic scanning (low/medium beam current implanters (I < 1mA) Vy Scan Patterns Si wafer Vertical Scan Vx Y X Horizontal Scan This type of implanter is suitable for low dose implants. The beam current is adjusted to result in t > 10 sec/wafer. With scan frequencies in the 100 Hz range, good implant uniformity is achieved with reasonable throughput. Microelectronic Engineering Rochester Institute of Technology K.D. Hirschman Silicon Processes: Ion Implantation 9 In-situ Dose Control End Station secondary electrons wafer ion beam back plate VFaraday cup ( - 100 V ) Vsuppression ( - 500 V ) I A DOSE MONITORING ∫ Ι dt = Q=A q φ Ground Microelectronic Engineering Rochester Institute of Technology K.D. Hirschman Silicon Processes: Ion Implantation 10 Mechanical Scanning Stationary Ion Beam Rotating Disc ( 1200 rpm ) Beam Area ~ 20 cm2 (diameter ~ 5cm) Si wafer Excellent wafer cooling needed. Substantial load/unload time. 15 - 25 wafers /disc. Excellent throughput for high dose implants. High current (~20mA) Scan speed adjustment to insure uniform dose Microelectronic Engineering Rochester Institute of Technology K.D. Hirschman Silicon Processes: Ion Implantation 11