Howard M. Day

Transient radiation study of GaAs metal semiconductor field effect transistors implanted in Cr‐doped and undoped substrates

Flash x‐ray measurements have been made on GaAs metal semiconductor field effect transistor structures fabricated in both Cr‐doped and undoped semi‐insulating substrate material in order to characterize the levels responsible for long term transients in these devices. Prominent electron and hole traps with activation energies in the 0.76–0.90‐eV range have been identified. The main electron trap, which is present in both Cr‐doped and undoped substrates, appears to be primarily responsible for the observed transient response. However, traps related to Cr‐doping also contribute to the transient behavior.

Silicide formation and interdiffusion effects in Si-Ta, SiO2-Ta AND Si-PtSi-Ta thin film structures

The formation of TaSi2 in the Si-PtSi-Ta and Si-Ta systems has been studied using Auger spectroscopy, x-ray diffraction and electron diffraction techniques. The reaction of tantalum with PtSi was observed by Sinha, et al.l to take place with high temperature (800°-900°c) annealing of thin film systems consisting of Si-PtSi-Ta-W1. In the present investigation, it is shown that tantalum reacts with PtSi at approximately 600°C to form a mixture of Ta5Si3 and TaSi2 and predominantly TaSi2 at 785°C. Platinum is displaced at the refractory metal (Ta)-PtSi interface, whereupon the more stable refractory metal-silicide is formed. The displaced platinum reacts further with the excess silicon which diffuses from the Si-PtSi interface. The Si-PtSi-Ta reaction is similar to the Si-PtSi-W reaction. However, unlike tungsten which migrates very little in the Si-PtSi-W system, tantalum appears to interdiffuse with the PtSi at temperatures as low as 600°C. In the case of the Si-Ta couple, TaSi2 forms at approximately 750°C as determined by transmission electron microscopy (TEM) measurements. The kinetics of TaSi2 formation at the Si-Ta interface are compared to that which takes place at the PtSi-Ta interface to determine the influence of the PtSi layer. Silicide formation was not observed in SiO2-Ta specimens. after anneals up to 800°c. At 750°C Ta2O5 formed as observed by electron diffraction.

Low‐temperature interdiffusion between aluminum thin films and GaAs

Al‐GaAs interdiffusion at temperatures between 250 and 450 °C has been studied using Auger electron spectroscopy. Ga has been observed to migrate through 2000‐A Al films at 250 °C and 24 h vacuum anneal. Schottky barrier height φB increases approximately 0.10 eV as a result of annealing at 250 °C. However, φB remains constant between 250 and 450 °C.

Structure and thermal stability of sputtered Au--Ta films

The structure and thermal stability of bimetallic Au‐Ta films has been studied by x‐ray diffraction, electrical resistivity, and by microscopy. Annealing above 450 °C forms a TaAu compound. The growth of the TaAu layer at the Au–Ta interface follows a parabolic rate law. A low‐temperature depletion of gold at tantalum grain boundaries occurs below 350 °C with an activation energy of 0.41 eV. Grain growth occurs with an activation energy of 0.50–0.55 eV for gold and 0.40–0.50 eV for tantalum. Thermal stresses of the order of 1.0×109 dyn/cm2 exist in the sputtered films.

Trap distribution in gold-refractory/GaAs Schottky barriers

Abstract Interfacial and bulk traps are shown to be introduced in GaAs Schottky barriers as a result of metal deposition. Majority carrier and minority carrier traps are correlated with degradation in field effect transistor properties. The interface traps are present in both the sputtered and electron beam evaporated layers.

Epitaxial growth of Al/GaAlAs films on (100) GaAs by hot vacuum deposition

Epitaxial growth of (100) GaAlAs and Al was achieved on (100) n‐GaAs substrates using vacuum deposition in an ultrahigh vacuum system. In situ Auger electron analysis, microspot Auger electrospectroscopy, LEED, and reflection electron diffraction was used to characterize the films. Regions of GaAlAs and Al were identified. Electrical measurements indicated the presence of a stable Schottky barrier with a barrier height of 0.76 eV.

A stabilized tantalum diffusion barrier for the gold metallization system

A stabilized tantalum-gold thin film system on quartz substrates has been investigated as a metallization system for microwave power transistors. The stabilized tantalum was used as the barrier metal in order to minimize interdiffusion and eutectic formation between the gold and silicon. In order to stabilize the tantalum against rapid diffusion of gold at tantalum grain boundaries, a 200–300Å film of platinum was deposited between 1000Å layers of tantalum. The resulting structure was then overlaid with 3000Å of sputtered gold. The present investigation has shown that the Au/Ta-Pt metallization is (1) metallurgically stable with no significant degradation of resistivity below 500°C, (2) resists electrochemical corrosion and (3) is readily processed with existing technology.

Annealing kinetics of sputtered gold‐tungsten and gold‐molybdenum films

The annealing kinetics of sputtered Au–W and Au–Mo films have been investigated as a function of temperature up to 500°C. The electrical resistivity of the gold layer after deposition was measured to be 1.25 times the bulk resistivity. The excess resistivity was attributed to structural defects such as vacancies, interstitials, twins, dislocations, and impurities which were quenched in during deposition. Particle size changes in Au–W and Au–Mo occur in two stages, with an activation energy for gold of 0.4 eV below 200°C and 0.7 eV above 200°C. The activation energy for the refractory layer particle growth was 1.8 eV up to 500°C. The kinetics of dislocation (Nd) annealing at 500°C was determined to follow an equation of the form Q(Nd) = − A(Nd)m, with m = 3. Annealing the films up to 500°C resulted in a decrease of internal stress in gold from 2.5 × 109 dyn/cm2. The observed results are discussed in terms of microstructural changes and the dependence of internal stress on film thickness.

Scanning Micro-Spot Auger Spectroscopy Study of Interdiffusion and Eutectic Formation in W-Pt-W-Au Thin Films

Reactions in rf sputtered W-Pt-W-A,u films on oxidized and unoxidized Si substrates have been analyzed using a micro-spot scanning Auger spectroscopy and microscopy technique. The analysis shows that the W-Pt-W-Au films on Si substrates have undergone three annealing stages resulting in gold-silicon eutectic formation and migration. Stage I (450°C, 12 hours) was characterized by the formation of Si rich globular regions on the Au film. During Stag,,, II (450°C, 24 hours) the entire unreacted gold film was consumed. Finally, during Stage III (550°C, 24 hourS) gold and the liquid phase eutectic migrated toward the metal-Si interface. For W-Pt-W-Au on oxidized Si substrates, the diffusion barrier of W-Pt-W was observed to be effective up to 550°C tot 24 hours.

Characterization of Sputtered Gold-Tungsten and Gold-Molybdenum Metallizations for Microwave Power Transistors

The stability and hence reliability of sputtered gold-tungsten and gold-molybdenum films has been determined as a function of anneal temperature up to 650°c. Isothermal and isochronal resistivity experiments have yielded an activation energy for particle growth in 3000 A gold films of 0.4 eV below 200oc and 0.7 eV about 200oc. The activation energy for the refractory layer was calculated to be 1.8 eV from particle size measurements. Annealing the films up to 500oc for 24 h resulted in a decrease of internal stress in gold from 2.5 x 109 dyn/cm2 to 0.2 x 109 dyn/cm2. Similar decreases in internal stress were observed for tungsten and molybdenum. The observed results are discussed in terms of microstructural changes.