Titanium silicide and titanium nitride formation by titanium-ion implantation for MOS LSI applications
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A 70-nm-thick, 19-//J7 • cm TiSi2 layer is formed using a Ti-ion implantation technique. TiN/TiSi 2 double layers, whose surface morphology is superior to that obtained with conventional deposition and reaction techniques, can also be simultaneously formed by Ti-ion implantation into monocrystalline Si screened with the S13N4 film. Discrete /7«-junction diodes with a shallow TiSi2 layer and Ti-polycide-gate MOS capacitors are fabricated to determine the influences of Ti-ion implantation on electrical characteristics. The leakage current of the B-doped p+n junction and As/P-doped n+p junction with Ti-ion implanted silicide layer is low enough for device applications. Silicide formation on the gate polycrystalline-Si does not affect the breakdown electric field strength of a 20-nm-thick gate oxide. MOS capacitors showed normal C-V characteristics.
I. INTRODUCTION Many kinds of silicides have been studied for the purpose of reducing parasitic resistance in MOS devices.1"3 Recently, silicidation by transition metal-ion implantation has been suggested as an alternative to that done by conventional metal sputtering deposition and reaction.4 The ion implantation technique is considered to be superior to sputtering deposition because of the uniform reaction over the metal/Si interface. With ion implantation, moreover, it is possible to prevent contamination. This paper investigates the formation of TiSi2, which has the lowest resistivity among the silicides, using Tiion implantation. Recently, considerable research has focused on developing a barrier material beneath the metal to obtain thermally stable contact properties. Since TiN has attracted some attention in this area,5 a method of optimizing the simultaneous formation of TiSi2 and TiN films by Ti-ion implantation is also investigated. The influences of the silicidation process on electrical characteristics in pn junctions and Si-gate MOS capacitors are also evaluated. II. EXPERIMENTAL PROCEDURE The Ti-ion beam was extracted from a microwave ion source. A beam current of 1 or 2 mA reached wafers that were mounted on a spinning disk at the end station. Wafer temperature was kept below 200 °C by chilling the disk with running cold water. No procedure to protect against wafer charge-up was applied. Implantation into polycrystalline-Si or Si3N4 film and bulk Si was performed followed by annealing at temperatures ranging from 400 °C to 900 C C in Ar ambient for 30 min. Then, the sheet resistance of the films was measured 1238 http://journals.cambridge.org
J. Mater. Res., Vol. 6, No. 6, Jun 1991
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with a 4-point probe, and their composition and crystallinity were analyzed by Auger Electron Spectroscopy (AES), X-ray Photoelectron Spectroscopy (XPS), and X-Ray Diffraction (XRD). A TiSi2 layer was also formed by conventional metal sputter deposition and reaction for comparison with the Ti-ion implanted technique. Deposited Ti film thickness was 50 nm. Annealing for the reaction was carried out in two steps: first at 600 °C for 30 min and then at 800
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