Bruno Deweerdt

Comparative study of Ni-silicide and Co-silicide for sub 0.25-mm technologies

In this work, the phase formation is compared for Ni- and Co-silicidation with and without Ti cap. In addition, the electrical performance of Ni-silicidation with and without Ti-cap is investigated and compared to the performance of a Co-silicidation process with a Ti cap that has the same Si consumption. The lateral confinement of the silicide in the active areas is also studied.

Thermal Stability of CoSi 2 on Submicron Polycrystalline Silicon Lines

The thermal stability of CoSi2 layers on undoped, B- and As-doped, submicron-sized polycrystalline Si lines has been investigated. It is found that the highest thermal stability is obtained for undoped poly-Si lines. The thermal stability of the silicide layers on As- or B-doped lines is largely improved if an additional Ge implant is performed prior to Co sputtering which amorphizes the complete Si layer which is consumed during silicidation.

A manufacturable process to improve thermal stability of 0.25-/spl mu/m cobalt silicided poly gate

A CoSi/sub 2/ salicidation process using a thin titanium capping layer is developed to improve the thermal stability of deep submicron CoSi/sub 2//poly stacks. 50 nm CoSi/sub 2/ was uniformly formed on 0.25-/spl mu/m wide poly lines. The electrical results show that the lines formed by a capping process using Ti can withstand higher thermal treatment (750/spl deg/ C for 30 min) without significant degradation. This work shows that the modified CoSi/sub 2/ process should be considered for 0.25-/spl mu/m CMOS applications. >

The Detrimental Effect of a Passivation on the Electromigration Lifetime of Narrow Al-Si-Cu Lines

2 mm long, 0.8 μm wide and 0.8 μ thick Al-Si-Cu lines, passivated with a 1.14 μ m thick PETEOS SiO 2 were found to have a lower electromigration lifetime compared to identical unpassivated lines. The high tensile stress in the passivated lines is assumed to accelerate electromigration failure. This is confirmed by the very low activation energy for electromigration failure in the passivated lines and by the multiple events of recovery during and after electromigration testing, suggesting failure sites are slit voids.

Investigation of an in-situ probe for phase transformations during RTP silicidation

In-situ emissivity measurements at a wavelength of 2.4 μα were used to monitor RTP Co silicidation on crystalline and polycrystalline silicon substrates. The influence of various parameters influencing the silicidation reaction was extensively studied. It is shown that particularly the phase transformation from CoSi to the final suicide phase, COSi 2 , strongly depends on parameters such as background doping level and type of substrate. This is illustrated for As-doped substrates. The method is extremely sensitive for the in-situ detection of the thermal degradation of thin COSi 2 films at high temperatures, which is demonstrated for 25 nm COSi 2 layers on highly As-doped c-Si substrates.

Ti/co bilayers in salicide technology - electrical evaluation

A detailed investigation of the applicability of TiCo bilayers for the salicide technology is presented. In the first place the silicide formation on poly-Si gate lines using TiCo bilayers has been studied. It is demonstrated that lateral silicide growth over the spacers can be avoided by making use of a two-step silicidation. In addition, the thermal stability of CoSi2 obtained on small poly-Si lines by two-step silicidation of a TiCo bilayer has been investigated and compared to the thermal stability of CoSi2 obtained by standard silicidation of a 20 nm Co film. The performance of TiCo silicidation with respect to bridging has been studied making use of a special yield monitor chip with dedicated bridging cells. Similar as for standard Co silicidation, close to 100% yield numbers are obtained for two-step TiCo silicidation. Finally, the contact resistance between the silicide and the p+ and n+ diffusion areas has been evaluated making use of four terminal cross-bridge Kelvin resistor structures. Contact resistivity values were calculated to be in the range of 5−6 × 10−7 Ω · cm2 for CoSi2p+ contacts and in the range of 1–2 × 10−7 Ω · cm2 for CoSi2n+ contacts.

Two-step anneals to avoid bridging during Co silicidation

Abstract A two-step rapid thermal process has successfully been applied for the simultaneous Co silicidation of source/drain and gate areas in MOS test structures while avoiding lateral creep or bridging. The method is based on the formation of CoSi on the active areas and poly-Si gate lines during the first RTP step, while keeping the thermal budget sufficiently low in order not to form this silicide phase on the spacers. Following a selective etch, a second RTP step leads to the formation of CoSi2. After sputtering of 20 nm Co on either undoped or doped wafers, RTP was done at 487°C for 30 s to form CoSi. A subsequent selective etch and a second RTP step heating the wafer up to 850°C, resulted in a sheet resistance of 3–6Ω/□ on both the active areas and poly-Si gate lines. A “non-bridging” yield, which is in all cases close to 100%, has been found, irrespective of the considered processing parameters.

On the formation of silicides on poly runners with topography by a two-step silicidation process

The formation of titanium and cobalt silicide on poly runners with topography is studied in this work. Poly runners with various topography heights and slopes were silicided by a two-step salicide process and inspected by SEM and electrical measurements. Even though the topography was more severe than in current PBLOCOS processes, no electrical defects in the continuity of the silicide were observed. Cross-section SEM reveals, however, that the metal coverage on the steps plays a major role in the continuity of the silicide formed.