Implant energy is the kinetic energy of accelerated ions, directly determining how deep they penetrate into the semiconductor substrate. Units: Expressed in keV (kilo-electron-volts) or MeV (mega-electron-volts). 1 keV = 1000 eV. Depth relationship: Higher energy = deeper penetration. Relationship is not linear - governed by ion stopping power in the target. Projected range (Rp): Average depth of implanted ions. For example, B+ at 10 keV in Si has Rp ~35nm; at 100 keV, Rp ~300nm. Straggle (deltaRp): Statistical spread of ion distribution around Rp. Also increases with energy. Ion mass effect: Heavier ions (As) penetrate less deeply than lighter ions (B) at the same energy. As+ at 100 keV: Rp ~60nm vs B+ ~300nm. Low energy applications: Sub-keV to 10 keV for ultra-shallow junctions in advanced CMOS (source/drain extensions). Medium energy: 10-200 keV for well implants, channel doping, threshold voltage adjustment. High energy: 200 keV to several MeV for deep retrograde wells, buried layers. Requires specialized high-energy implanters. Channeling: At certain crystal orientations, ions travel deeper along crystal channels. Energy and tilt/twist angles must account for this. Simulation: SRIM/TRIM Monte Carlo codes predict depth profiles for given ion, energy, and target material.