Ternary amorphous metallic thin films as diffusion barriers for Cu metallization

A Pt/Ge/Au contact of the structure: /Pt(17nm)/Ge(25nm)/Au(43nm), overlaid with a Ta-Si-N barrier layer and a Au metallization layer has a contact resistivity, ρc, of 3.7×10−6 Ωcm2 after annealing at 450°C for 15 min. After aging at 450°C for 60 h, ρcslightly degrades to 5.5×10−6 Ωcm2 while the surface keeps smooth. When alloyed at 550°C for 15 min, ρc is 1.8×10−6 Ωcm2 and stays about the same value after annealing at 550°C for 1 h. Without the Ta-Si-N barrier and the Au overlayer, the Pt/Ge/Au contact alone is also ohmic after annealing at 450°C for 15 min but with a ρc of ~10−5 Ωcm2 while the surface morphology deteriorates significantly after aging at 450°C for 20 h. The thermal reactions of this Pt/Ge/Au contact on GaAs, with or without a Ta-Si-N barrier layer, are investigated by backscattering spectrometry, x-ray diffraction, and transmission electron microscopy in conjunction with energy dispersive analyses of x-rays. For all samples, the main reaction products after annealing at 450°C for 15 min are Au7Ga2, and PtGe:As, a PtGe phase that also contains arsenic. The product phases are randomly distributed within a laterally uniform reacted layer when the Pt/Ge/Au contact is covered by a Ta-Si-N layer. Without the Ta-Si-N barrier layer, a small arsenic loss and a Ga-rich phase (probably Ga-oxides) on the contact surface are observed after annealing at 450°C. In this case, the surface and contact-semiconductor interface are more faceted than with a Ta-Si-N barrier layer.

Stable Pt/Ge/Au ohmic contact to n-GaAs with a Ta-Si-N barrier

Depth profiling by backscattering spectrometry, x-ray photoelectron spectroscopy and diffractometry, scanning electron microscopy, and sheet resistance measurements were used to study the thermal stability of ternary Ti27Si20N53 films as diffusion barriers between a gold overlayer and substrates of aluminum nitride, silicon oxide, and β-silicon carbide when thin titanium films are added on either side of the barrier to enhance adhesion. It is shown that titanium and gold interdiffuse upon 30 min annealing in vacuum at 400 °C and above, which raises the sheet resistance of the gold layer by factors that increase with the amount of titanium present. For the same annealing ambient and duration, nitrogen begins to diffuse at 600 °C from the Ti27Si20N53 layer into the titanium layer, releasing silicon. This silicon reacts eutectoidally with the gold, leading to breakup of the barrier.

Thermal stability of a Ti-Si-N diffusion barrier in contact with a Ti adhesion layer for Au metallization

Backscattering spectrometry, x-ray diffractometry, and scanning electron microscopy have been used to study the reaction of a thin Pt film with an epilayer of [110] GaN on [110] sapphire upon annealing at 450, 550, 650, 750, and 800 degrees C for 30 min. A Ga concentration of 2 at. % is detected by MeV He-4(++) backscattering spectrometry in the Pt layer at 550 degrees C. By x-ray diffraction, structural changes are observed already at 450 degrees C. At 650 OC, textured Ga2Pt appears as reaction product. The surface morphology exhibits instabilities by the formation of blisters at 650 degrees C and voids at 800 degrees C.

/pdf/thermal-reaction-of-pt-film-with-110-gan-epilayer-59t2osq3qr.pdf

Thermal reaction of Pt film with 〈110〉 GaN epilayer

Contacts are the limiting factor in the performance of electronic devices operated at high temperatures. To fulfil the advanced requirements for contacts in that application, the most effective metallization scheme, at present, is one which is functionally divided into intermediate layers. A diffusion barrier is introduced between the interconnecting metal and the semiconductor to minimize interactions between the two. The best results are obtained with chemically inert ternary amorphous alloys that lack extended defects and grain boundaries. The contacting layer determines the electrical characteristics of the contact. Its design is complicated by the complex multielemental nature of its chemical interaction with high-temperature compound semiconductors. The concept and implementation of diffusion barriers and contacting layers are discussed with an emphasis on contacting layers to SiC.

High-temperature contact metallization to semiconductors

Ohmic behaviour of Au/WSiN/(Au,Ge,Ni)-n-GaAs systems

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Ohmic behaviour of Au/WSiN/(Au,Ge,Ni)-n-GaAs systems