ion source

An ion source generates dopant ions from precursor gases for use in ion implantation systems. **Source types**: **Freeman source**: Hot cathode arc discharge. Versatile, widely used. **Bernas source**: Similar to Freeman but with different geometry. Common in high-current implanters. **Indirectly heated cathode (IHC)**: Longer cathode life, better stability. Modern standard. **Feed gases**: BF3 for boron (p-type), AsH3 for arsenic (n-type), PH3 for phosphorus (n-type), GeF4 for germanium (PAI), SiF4 for silicon. **Ionization**: Gas molecules introduced into arc chamber. Electrons from heated cathode ionize gas by electron impact. Plasma contains multiple ion species. **Extraction**: Positive ions extracted through slit by negative extraction electrode. High extraction voltage (10-40 kV) forms beam. **Ion species**: Source produces multiple species (e.g., BF3 gives B+, BF+, BF2+, F+). Mass analyzer selects desired species. **Plasma**: Dense plasma in source chamber. Arc current and gas flow control plasma density and ion output. **Source life**: Cathode and arc chamber components degrade over time. Source replacement every few hundred to thousand hours. **Beam current**: Source brightness determines maximum achievable beam current. Higher current = higher throughput for high-dose implants. **Cluster ions**: Some sources produce molecular or cluster ions for ultra-low-energy shallow implants.