Ion Implantation and Synthesis of Materials - Studium

15.2 Implanters Used in CMOS Processing 215implanters are often used to dope channels and adjust threshold voltage. Likewise,some processes employ retrograde wells with energies in the range of mediumcurrent systems. Finally, the dosimetry systems of HC implanters are perfectlycapable of controlling implants in the 10 12 –10 13 cm −2 range and are therefore usedto perform channel implants normally defined as medium current. With thetransition to 300 mm wafer size, sub-65 nm technology nodes, and ultra-thin bodydevice architectures, it is quite possible that a further blurring of the traditionalsegments will follow. Whatever implantation segment is required for devicefabrication, the processing constraints (such as across-wafer dose uniformity orcontamination) are exacting. These are shown in Table 15.1.All segments use the same basic set of primary dopant species. The dominantp-type dopant in use today is boron, usually delivered by the implanter in the formof B + or BF +2ions. These ions are typically generated from BF 3 (boron trifluoride)ion source feed gas. The dominant n-type dopants in use are phosphorous andarsenic, usually delivered in the form of P + and As + ions from PH 3 (phosphine)and AsH 3 (arsine) feed gases, respectively. Formerly, these species were deliveredfrom solid P and As heated in vaporizers built into the implantation sources. Forsome higher energy applications in both the medium current and high energysegments, multiply charged ions – including doubly and triply charged n-typedopants (P ++ , P +++ , As ++ ) and doubly charged p-type dopants (B ++ ) – are notuncommon. Other species that are important but typically used less frequentlyinclude indium and antimony from solid source materials InCl 3 (indiumtrichloride) and Sb 2 O 3 (antimony oxide), respectively. Nondopant speciesgermanium and silicon from GeF 4 (germanium tetrafluoride) and SiF 4 (silicontetrafluoride) are often used for preamorphization of the crystal lattice. In addition,nitrogen, oxygen, and fluorine are used for materials modification.15.2.1 Beamline ArchitecturesThere are elements of beamlines that are generally common among the threemajor types of implanters. All beamlines begin with an ion source and extractionoptics, responsible for injecting an appropriately shaped beam of ions into thesubsequentTable 15.1. Control and contamination requirements for production-grade ion implantersSpecificationTargetdose uniformity < 0.5%dose repeatability 0.5 – 1.0%energy integrity < 1.0%angular integrity < 1°metallic contamination< 1 x 10 10 cm −2particle contamination < 0.1 cm −2 for particles < 0.12 µm