Ion beam synthesis of silicide layers for silicon bipolar applications

• Main Author: Spraggs, Russell Stuart
• Published: University of Surrey 1993
• Subjects: 530.41; Solid-state physics
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359870

This thesis reports a study of the microstructural and electrical characterization of high quality epitaxial CoSi2 layers fabricated by the relatively new technique of Ion Beam Synthesis (IBS). The effect of incorporating common device processing dopants such as phosphorus, arsenic, antimony, boron and indium into the ion beam synthesised CoSi2/Si structure is also studied. Using Rutherford Backscattering Spectrometry (RBS), Transmission Electron Microscopy (TEM) and four point probe resistivity measurements the crystallinity and resistivity of ion beam synthesised CoSi2 layers fabricated by implanting cobalt to doses in the range 0.7 - 7 x 1017 ions cm-2 at 200keV are examined. Substrates of (100), (111) and (110) orientation are used. The results show that the microstructure of the 'as implanted' sample is strongly dependent on the ion dose, the crystallinity and resistivity being sensitive to the cobalt:silicon ratio within the implanted region. The microstructure is also dependent on the orientation of the substrate. A detailed examination on the effect of annealing the cobalt implanted layer is also undertaken. Annealing at 600°C for 1 hour, 600°C/1 hour + 1000°C/30 minutes, sequential annealing in the range 200°C - 1000°C for 15 mins and rapid thermal annealing (RTA) in the range 700°C - 1100°C for 5-60 seconds are all used allowing a number of different processes to be studied in the implanted region. The layers with the highest crystalline quality form after the highest temperature anneals (≥ 1000°C). The lowest resistivities can, however, be obtained after annealing at lower temperatures. The current/voltage characteristics of IBS (100) n-type CoSi2/Si Schottky barrier diodes are investigated using mesa device structures prepared by wet chemical etching. Measurements are performed over the temperature range 100 K - 400 K. For temperatures (T) > 250K the barrier height of the IBS CoSi2/Si interface is found to be 0.64 +/- 0.01 eV. The ideality factor (≈ 1.05 for T > 250 K) is found to increase with decreasing temperature. C/V measurements at 293 K also reveal the same value for the barrier height. The redistribution of indium, antimony and arsenic implanted to doses ≥ 5 x 1015 ions cm-2 into 'as implanted' and annealed CoSi2layers is examined after sequential annealing in the range 200°C - 1000°C for 15 minutes. Segregation of the implanted dopant occurs towards the interfaces of the layer and also into the underlying silicon, demonstrating the use of the silicide as a diffusion source. After annealing at the higher temperatures the crystallinity of the CoSi2 layer is restored and there is in addition evidence to suggest that the defect density at the interface is reduced by the presence of the dopant. A detailed study of the electrical characteristics of dopant implanted IBS CoSi2/Si structures shows that the barrier height can be controlled by varying the dose, and subsequent annealing temperature. The conclusions in the latter part of the thesis point the way to further research on IBS CoSi2.