Glen L. Miles

Reduction of the C54–TiSi2 phase transformation temperature using refractory metal ion implantation

We report that the ion implantation of a small dose of Mo into a silicon substrate before the deposition of a thin film of Ti lowers the temperature required to form the commercially important low resistivity C54–TiSi2 phase by 100–150 °C. A lesser improvement is obtained with W implantation. In addition, a sharp reduction in the dependence of C54 formation on the geometrical size of the silicided structure is observed. The enhancement in C54 formation observed with the ion implantation of Mo is not explained by ion mixing of the Ti/Si interface or implant‐induced damage. Rather, it is attributed to an enhanced nucleation of C54–TiSi2 out of the precursor high resistance C49–TiSi2 phase.

Low temperature formation of C54–TiSi2 using titanium alloys

We demonstrate that the temperature at which the C49 TiSi2 phase transforms to the C54 TiSi2 phase can be lowered more than 100 °C by alloying Ti with small amounts of Mo, Ta, or Nb. Titanium alloy blanket films, containing from 1 to 20 at. % Mo, Ta, or Nb were deposited onto undoped polycrystalline Si substrates. The temperature at which the C49–C54 transformation occurs during annealing at constant ramp rate was determined by in situ sheet resistance and x-ray diffraction measurements. Tantalum and niobium additions reduce the transformation temperature without causing a large increase in resistivity of the resulting C54 TiSi2 phase, while Mo additions lead to a large increase in resistivity. Titanium tantalum alloys were also used to form C54 TiSi2 on isolated regions of arsenic doped Si(100) and polycrystalline Si having linewidths ranging from 0.13 to 0.56 μm. The C54 phase transformation temperature was lowered by over 100 °C for both the blanket and fine line samples. As the concentration of Mo, Ta...

TiSi2 phase transformation characteristics on narrow devices

Accurate prediction of TiSi2 transformation requires test structures with small silicided surface areas. To evaluate the area dependence of the C49 to C54 transformation, a new monitor was developed with minimal silicide surface area. Small area structures were found to exhibit a bimodal resistance distribution that was nearly insensitive to process transformation conditions. Starvation for C54 nucleation sites resulted in a high frequency of non-transformation even at high annealing temperatures. Transmission electron microscopy analysis showed that the Ti silicide in these structures is either C49 or C54 phase, with little or no mixed phases present. A cooperative C54 nucleation mechanism is proposed to explain this phenomena. The presence of small quantities of a molybdenum impurity such as molybdenum during silicide formation has been found to increase the availability of C54 forming nuclei by two orders to magnitude. The molybdenum acts as a catalyst and does not require interface mixing or the creation of an amorphous Si layer to enhance nucleation. The addition of molybdenum has been demonstrated to eliminate the bimodal resistance distribution.

Reduction of the C54-TiSi2 Phase Formation Temperature Using Metallic Impurities

The effects of small concentrations of metallic impurities have been studied in conjunction with the formation of titanium disilicide. We report that, by introducing small quantities of a refractory metal such as molybdenum or tungsten at or near the titanium/silicon interface, the temperature required to form the C54 phase TiSi 2 can be reduced by as much as 100°C. Furthermore, the resulting C54-TiSi 2 film exhibits small (∼ 0.2μm) grain size and improved thermal stability. This discovery has the potential to reduce the complexity and cost associated with forming low resistivity TiSi 2 on submicron structures and to significantly improve the titanium silicide process window for future sub-half-micron VLSI applications.

Precision Resistor Integration into a Submicron Silicided Complementary Metal Oxide Semiconductor Technology

This paper examines the process issues of integrating a precision resistor feature into an existing salicided complementary metal oxide semiconductor technology. The resistor features are created by selectively blocking salicide formation with a thin nitride layer that must be compatible with the existing device and salicide processes. The integrity of the blocking layer during the HF-based salicide preclean is of special concern. Methods to monitor and control the properties of the thin nitride blocking layer have been developed.