Search

The formation of titanium disilicide (TiSi2) from Ti deposited using ionized metal plasma under different deposition conditions has been investigated. It is shown that deposition at elevated substrate temperature (450°C) enhances the formation of the low-resistivity C54 TiSi2, especially in patterned narrow lines. Grain-boundary footprint pictures obtained by atomic force microscopy indicate a larger grain-size distribution for the films deposited at higher substrate temperature. Deposition under substrate bias resulted in reduced contact resistivity. However, the use of substrate bias results in increased probability of bridging of silicide over the isolating spacers.

TiSi 2 was formed on amorphous, polycrystalline or single crystal silicon. Undoped samples are compared with specimens where the silicon had been doped with phosphorus or arsenic prior to titanium deposition. A non-destructive optical technique, total intergrated scattering (TIS) was used together with more conventional methods to evaluate the surface conditions after various treatments. These analyses were correlated with Rutherford backscattering spectrometry (RBS) to obtain more comprehensive information on the bulk morphologies. The dopant species play an important role for the morphology and stability of these structures. It is shown that TiSi 2 on undoped polysilicon is unstable at temperatures above 800°C and that an amorphous substrate offers potential advantages such as a smoother and more stable silicide.

The morphological instability of bilayers of NiSi, or CoSi 2 , on polysilicon has been investigated as a function of the thickness of the silicide, the presence of alloying additions and the initial oxidation of the silicide layer. The effect of Ir additions in enhancing the stability of the bilayers and the formation of NiSi 2 confirms the expectation that the morphological instabilities and the nucleation of NiSi 2 are dictated by surface energy effects (capillarity). Stresses may play a role in the initial step of the process which ultimately leads to a nearly complete inversion of the positions of the silicide and polysilicon layers. However, it is quite certain that the main driving force is the change in grain boundary energy of the polysilicon which starts with very small grains to begin with and ends up, at a different location, with much bigger grains.

The phase formation during rapid thermal annealing of a Ti/Mo bilayer sequentially deposited on Si substrates has been studied. The Mo layer varied from 0.5 to 2 nm and the Ti layer was always 60 nm thick. The presence of the Mo interposing layer enhances the formation of the C54 of TiSi2 by first forming a Mo‐bearing silicide phase of hexagonal structure. The desired C54 phase then nucleates and grows on top of this Mo‐bearing silicide phase at a temperature as low as 650 °C via Si diffusion through the growing silicide layers. This is about 100 °C lower than what is usually needed for the C49–C54 transformation. The significance of this finding is that the usual route for the formation of TiSi2, i.e., the C49 phase forms as a result of the Ti–Si interaction and the C54 phase forms as the product of phase transformation, is altered by the interposition of a thin refractory metal (here Mo) layer between Ti and Si.

Dual work function gate electrodes have been implemented in a 1- mu m CMOS process. Dopant atoms were implanted into tungsten silicide simultaneously with the source-drain implantations and subsequently diffused into the underlying polycrystalline silicon layer by rapid thermal annealing. Physical analyses showed that arsenic and boron could easily be incorporated in the polysilicon to concentrations greater than 10/sup 20/ cm/sup -3/. Capacitor and transistor measurements confirmed that n/sup +/ and p/sup +/ silicon could be obtained, with a difference of about 1 V between the respective flat-band voltages. By comparison with conventional n-type gate MOSFETs, it was verified that significantly improved subthreshold characteristics were obtained with p-type PMOS gate electrodes. >

The influence of high temperature processing steps on the integrity of a polycide metal-oxide-semiconductor system has been investigated. At temperatures exceeding 900°C the TiSi 2 /poly-Si (where poly-Si is polycrystalline silicon) system is not stable, and the dielectric strength of an underlaying gate oxide deteriorates. Degradation of the silicide-poly-Si interface was detected by backscattering spectrometry. Scanning and transmission electron microscopy revealed silicon precipitation and silicide film deformation.

An evaluation of the processing of zirconium nitride and the usefulness of this nitride as a diffusion barrier between aluminum and silicon has been carried out. Reactive sputtering from an elemental zirconium target in a mixture of Ar/N2 makes it possible to change the nitrogen content in the deposited film. The composition variation with N2 concentration will be presented. Films have been prepared using rf‐diode reactive sputtering. The as‐deposited film resistivity dependence on bias voltage has also been studied. Zirconium deposited on silicon forms a silicide at 550–600 °C. We have found by Rutherford backscattering spectroscopy analysis that during this silicide formation on arsenic implanted silicon substrates, the arsenic is piled up at the silicon/silicide interface. This effect favors the formation of a low resistance Ohmic contact. Since the barrier height between the silicide and silicon is expected to be 0.55 eV we want to point out that this contact may be useful for both n‐ and p‐type regio...