Ion Beam Synthesis (IBS) with Focused Ion Beams (FIB)Cobalt implantation in silicon with stoichiometric doses and subsequent annealing form Cobalt disilicide films (A.E. White et al., Appl. Phys. Lett. 52(1987)95). CoSi2 shows metallic behaviour with low resistivity of about 15 µOhmcm and high thermal stability, and its fabrication is compatible with silicon technology. Crystalline CoSi2 has a cubic lattice with a mismatch to silicon of only
-1.2 %. It has been shown that ion beam synthesis allows the fabrication of epitaxial buried or surface CoSi2 layers on silicon. Submicron patterns can be directly produced by focused cobalt implantation. Ion beam synthesis with the Co FIB together with dynamic focus control of the beam can be applied for the formation of interconnects in three-dimensional devices. At present, Metal-semiconductor-metal photodiodes with CoSi2 electrodes are fabricated and investigated.
A new phenomenon using the FIB for IBS purposes is correlated with the 4 - 6 orders of magnitude higher current density of the FIB compared with conventional ion implanters. So it is possible to amorphize silicon at higher temperatures and long pixel dwell times which leads to disrupted CoSi2 layers. It was shown that the amount of damage creation and dynamic annealing during FIB implantation is mainly influenced by the pixel dwell time and the implantation temperature. The fabrication of closed CoSi2 layers by FIB IBS is only successful using propper chosen parameters.
|The figure shows the resistivity of CoSi2 lines produced by FIB cobalt implantation in (111) Si as a function of line width.
|FIB implanted CoSi2 interconnects between the top surface and the bottom of an etch.
|SEM micrograph of a fabricated MSM detector with a 40*80µm2 active area, 0.8µm finger width and 3.15µm spacing.