A gold-free, fully Cu-metallized InGaP/GaAs heterojunction bipolar transistor using platinum as the diffusion barrier has been successfully fabricated. The HBT uses Pd/Ge and Pt/Ti/Pt/Cu for n-type and p þ -type ohmic contacts, respectively, and Ti/Pt/Cu for interconnect metals with platinum as the diffusion barrier. The Ti/Pt/Cu structure was stable during annealing up to 350 C judging from the X-ray diffraction (XRD) data and sheet resistance. A current-accelerated stress test was conducted on the device with a current density J C ¼ 140 kA/cm 2 for 24 h, and the current gain showed no degradation. The devices were also thermally annealed at 250 C for 24 h and showed little change. We have successfully demonstrated that an Au-free, fully Cu-metallized HBT can be realized using Pt as the diffusion barrier and Pd/Ge and Pt/Ti/Pt/Cu as the ohmic contacts.
An alloyed Pd∕Ge∕Cu Ohmic contact to n-type GaAs is reported for the first time. The Pd∕Ge∕Cu Ohmic contact exhibited a very low specific contact resistance of 5.73×10−7Ωcm2 at a low annealing temperature of 250°C. This result is comparable to the reported Pd∕Ge and Au∕Ge∕Ni Ohmic contact systems to n-type GaAs with doping concentrations about 1×1018cm−3. The Ohmic contact formation mechanisms and microstructure evolution were investigated using secondary ion mass spectrometry, x-ray diffraction, transmission electron microscopy, and energy dispersive spectrometer. The Ohmic contact behavior was related to the formation of Cu3Ge and PdGaxAsy compounds after annealing.
A gold-free, fully Cu-metallized InP heterojunction bipolar transistor using non-alloyed Ti/Pt/Cu and Pt/Ti/Pt/Cu ohmic contacts and platinum diffusion barrier has been successfully fabricated. The InGaAs/Ti/Pt/Cu ohmic structure was stable after annealing up to 350°C as judged from the Auger depth profiles. A current-accelerated stress test was conducted on the device with a current density J
C=80 kA/cm2 for 24 h, and the current gain showed no degradation after the current stress. The devices were also thermally annealed at 200°C for 3 h and showed almost no change in the electrical parameters after the heat treatment. The results show that the Au-free, fully Cu-metallized InP heterojunction bipolar transistor (HBT) can be realized using non-alloyed ohmic contacts and Pt diffusion barrier.
A low contact resistance Pd/Ge/Cu ohmic contact to n-type GaAs is successfully developed. The Pd/Ge/Cu ohmic contact exhibits a very low contact resistivity of 5.73 x 10-7 Ω-cm2 at a low annealing temperature (250 {degree sign}C). This result is comparable to the reported Pd/Ge and Au/Ge/Ni ohmic contact systems to n- type GaAs with doping concentrations about 1x1018 cm-3. The ohmic contact formation mechanisms and microstructure reactions were investigated using x-ray diffraction (XRD), secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM).
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