Long-term reliability of Pt and Mo diffusion barriers in Ti–Pt–Au and Ti–Mo–Au metallization systems for GaAs digital integrated circuits

Abstract

Reliability of Ti–Pt–Au and Ti–Mo–Au systems has been investigated for GaAs integrated circuit first-level metallizations on semi-insulating GaAs substrates and second-level metallizations on interlayer SiO2 films using Auger depth profile analysis, residual resistance examination and temperature storage step-stress testing. Auger analysis and residual resistance examination showed significant reaction between first-level Ti–Pt–Au and GaAs substrates during metallization processes, while Ti–Mo–Au system with the electron-beam evaporated Mo film showed higher thermal stability because the Mo film acted as a good diffusion barrier between GaAs and Au. The second-level Ti–Pt–Au on SiO2 was found to be free from the reaction with GaAs substrates, and its degradation was ascribed to interdiffusion of composite metals. The resistance increase in step-stress testing for the second Ti–Pt–Au was analyzed on the basis of a new diffusion-controlled model, and long-term reliability was estimated. A mean time to failure value of 3×105 h at 150 °C was obtained for a failure defined as 10% increase in resistance. Much higher reliability was estimated for Ti–Mo–Au, because the resistance continued to decrease as long as 3000 h at 250 °C. The decrease in resistance clearly indicates defect annealing with reduced defect scattering in Au layers. This also shows that foreign metal diffusion into Au, acting as impurity scattering centers, is perfectly eliminated by Mo diffusion barriers.

Long-term reliability of Ti–Pt–Au metallization system for Schottky contact and first-level metallization on SiC MESFET

“…3). Meanwhile, as reported by several authors [6,7], Pt acts as a barrier to the diffusion of Au into the Ti as confirmed by the analysis (Fig. 5(b)).…”

Comparison of Au-In Transient Liquid Phase Bonding Designs for SiC Power Semiconductor Device Packaging

“…Each TLP stack contains material diffusion barrier layers to contain the gold and indium materials through processing and over its lifetime. Each of the Au-In TLP bonds are sandwiched within a stack of barrier layers of tungsten for adhesion, titanium as the primary diffusion barrier, and platinum to prevent undesirable Au-Ti intermetallics [8], [9]. These barrier layers also ensure the ratio of indium to gold remains constant.…”

Optimization of the base electrode for InGaAs/InP DHBT structures with a buried emitter-base junction

“…These particular metals were chosen, since they are commonly used for ohmic contacts in III-V materials. [2][3][4][5][6] Pt and Ti tend to have a fairly smooth diffusion profile when annealed at our maximum processing temperature of 300°C. [2][3][4] Although Pd and Au have rougher diffusion profiles, some work has indicated that if they are thin enough, they may also be used.…”

“…[2][3][4][5][6] Pt and Ti tend to have a fairly smooth diffusion profile when annealed at our maximum processing temperature of 300°C. [2][3][4] Although Pd and Au have rougher diffusion profiles, some work has indicated that if they are thin enough, they may also be used. 5 Furthermore, Pt is an excellent diffusion barrier to Au at our processing temperature of 300°C, provided it is thick enough to avoid pinholes or other defects, so Au can be used as the top metal for all of the subsequent interconnects.…”