The mass analyzer in an ion implanter uses a magnetic field to separate ions by mass-to-charge ratio, ensuring only the desired dopant species reaches the wafer. Principle: Charged particles in magnetic field follow circular paths. Radius depends on mass, charge, and velocity. Different masses follow different radii. Equation: r = (mv)/(qB), where m is mass, v is velocity, q is charge, B is magnetic field strength. Resolving slit: After magnetic deflection, a slit passes only ions with the correct radius (mass). All other species are blocked. Importance: Source produces multiple ion species. Without mass analysis, unwanted species would contaminate the implant (wrong dopant, wrong energy). Examples: From BF3 source: B+ (m=11), BF+ (m=30), BF2+ (m=49). Typically B+ or BF2+ selected depending on desired energy. Resolution: Must separate closely spaced masses. Mass resolution M/deltaM typically 20-60. Higher resolution for exotic species. Magnet: Electromagnet with precise field control. Sector angle typically 60-120 degrees. Doubly charged ions: B++ has same m/q as some contaminants. Mass analyzer distinguishes by m/q, not m alone. Must account for charge states. Calibration: Mass spectrum scanned periodically to verify correct species selection. Contamination: Non-selected species deposited inside analyzer chamber. Regular cleaning required.