Formation of CoSi 2 Wires by Maskless Implantation with the Focused Ion Beam
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Mat. Res. Soc. Symp. Proc. Vol. 320. @1994 Materials Research Society
energies between 20 and 50 keV. With a gallium beam a smallest beam spot size of about 100 nm and a current density of
L i
10 A /CM2 were reached. The beam scan field is 200 pm * 200 pmn. A digital scan
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processing
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In contrast to the usual applications
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xy-stage with laser interferometer control allow an accurate processing of wafers with a diameter up to 6 inch. of FIB systems with gallium ion sources like mask repair, circuit inspection, or micromachining the use for ion implantation requires a mass separator which rejects unwanted ion species. For that purpose an achromatic ExB; mass separation system with high mass resolution and small optical aberrations [8] was implemented into our ion optical column.
Figure 1. Schematic drawing of the FIB system IMSA-JOO. Two types of cobalt containing LAIS were developed and investigated to its suitability for FIB implantation. From the metallurgic point of view with respect 'to a relatively low operation temperature a neodymium-cobalt composition was chosen first [9]. The melting temperature in the eutectic point amounts to 566 'C at a cobalt concentration of 36 atomic percent. A problem of using neodymium is its high reactivity to oxygen. This oxidation during the transfer of the LAIS from the vacuum chamber, used for preparation, to the FIB system can be reduced by a protective cover of benzine and a minimized handling time. The mass spectrum of the Co-Nd ion source obtained after the ExB filter of the IMSA-100 column is shown in Fig. 2. The relatively high portion of doubly charged cobalt ions allows to use them for implantation and expands the energy range of the equipment. Comparable results were obtained with a Co-Ge LAIS. For substrate heating the standard wafer holder was reconstructed. An implemented pyrolytic carbon/boron nitride heat plate allows to implant at temperatures up to about 500 *C for two inch wafers.
EXPERIMENTAL The first experiment was done at room temperature (RT). Lines and square like structures were written into a Si substrate (p = 220 Qcm). The implantation doses were varied between 0.5 and 5 x 1017 cm-' using Co' and Co"~ ions with energies of 30 and 60 keV, respectively. The implanted samples were annealed in a two step mode (600 *C for
154
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Nd'
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Cod".
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ELECTRIC FIELD (kV/cm) Figure 2. Mass spectrum of the ions obtained from a Co-Nd LAIS. 60 min and 1000 'C for 30 min, furnace, N. atmosphere). Inthe as-implanted state as well as after the first annealing step electrical resistivity measurements were carried out. After complete annealing the samples were also analysed using SEM and EDX. The investigation of the substrate temperature dependence during Co' (30 keV) and
Co"~ (60 keV) implantations with doses of 1 x 10"~and 3 x
1017
ions
cm'
2
into Si
was done at s
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