Interfacial reactions of Co and Si/Co films on GaAs have been investigated using X-ray diffraction(XRD), Auger electron spectroscopy(AES), cross-sectional transmission electron microscopy(XTEM), microdiffraction, and energy dispersive spectroscopy(EDS). Cobalt starts to react with GaAs at 380°C by formation of ternary phase, most probably Co2GaAs. At 420°C, CoGa nucleates at the Co and Co2GaAs interface and grows with Co2GaAs. At higher temperature, Co2GaAs disappears and CoGa/GaAs layer structures are formed. Annealing of the layer-deposited Si/Co films at 380°C results in the formation of Co2GaAs. At 420°C, the entire layer of Co is consumed, while Co2Si transforms to CoSi, and binary phases, CoGa and CoAs, are formed on top of the ternary phase beneath the CoSi layer. In the subsequent reaction, CoSi grows at the expense of the decompositions of CoGa and CoAs at 460°C. At 600°C, ternary phase is decomposed, and CoSi forms interface with GaAs. This finding can be understood from the calculated Si-Co-Ga-As quaternary phase diagram.

WNX thin films were deposited at room temperature on (100) n-type GaAs substrates by rf reactive sputtering of a high purity W target in Ar/N2 gas mixtures. Deposition parameters such as the rf power, the ratio of gas flows, and the total pressure can be optimized for the preparation of uniform and low resistivity WNX thin films. The W:N ratio in the as-deposited WNX films was determined using Auger spectroscopy and the morphology was examined by scanning electron microscopy (SEM).

The WNx/GaAs samples were subjected to rapid thermal annealing in an N2 atmosphere at temperatures between 400°C and 800°C. The thermal stability of these structures was examined using electrical measurements and Auger profiling . The results are correlated with the properties of as-deposited films and the influence of various processing parameters will be discussed.

We report on the use of AuGeNi/W and AuZn/W metallizations and their further processing by rapid thermal nitridation. Nitrided tungsten serves as a cap suppressing the sublimation of As. To study the effect of annealing conditions on the properties of the W cap, comparative experiments involving conventional annealing in H2, and RTA in N2 or O2 flow, have been performed. TEM, XRD, RBS, and SIMS have been employed to investigate contact microstructures. The obtained results prove the superiority of the contacts with nitrided W cap over conventional insulating cap. No W-N phase is observed in nitrided W layers, which is consistent with the model of a "stuffed" barrier by Nicolet.

The electrical properties of Pd/Zn/Pd/Au based ohmic contacts to p-type In0 47Ga0 53As/ InP with an interposed superlattice of 50Å In047Gao 53As/ 50 Å InP have been investigated. In this study, several configurations of the Pd/Zn/Pd/Au metallization were fabricated with varying thicknesses of the Zn and interfacial Pd layers in the range 0 to 400 Å. The lowest values of specific contact resistance, ρc, were 1.2 x 10-5 Ω cm2 as-deposited and 7.5 x 106 Ω cm2 for samples annealed at 500 °C. In the as-deposited structures, ρc was reduced by an increase in thickness of both the Zn and Pd layers to 300 Å. For annealed samples, a critical thickness of the Zn ≥ 50 Å and Pd ≥ 100 Å layers was required in order to significantly reduce the magnitude of ρc. These results are consistent with a model of Pd/Zn contacts based on Zn doping of the interface. Studies of thermal stability of the contacts at 400 °C and 500 °C have shown that the Zn/Pd/Au and Pd/Zn/Pd/Au configurations were significanty lower in ρc at extended ageing times than the Pd/Au contacts.

The electrical properties of a Au/Cr/(Au)/Zn/Au (50/25/(50)/100/2 nm) multilayer metallization to n- and p-type InP have been investigated. The results consistently show that it is possible to modulate the effective Schottky barrier height of the metal-semiconductor contact over a large range of values extending from ∼0 eV for contacts to p-type InP to values close to the bandgap of the InP (∼1.3 eV) for contacts to n-type InP. The limiting factor in the developement of the highest quality metal-semiconductor diodes to n-type InP with very high Schottky barrier heights is found to be diffusion of Au elements at high annealing temperatures above 500°C, as determined from I-V, C-V and DLTS plots.

The metallurgical and electrical behavior of Au/Zn contacting metallization onp-type InP was investigated as a function of the Zn content in the metallization. It was found that ohmic behavior can be achieved with Zn concentrations as small as 0.05 atomic percent Zn. For Zn concentrations between 0.1 and 36 at.%, the contact resistivity ρc was found to be independent of the Zn content For low Zn concentrations the realization of ohmic behavior was found to require the growth of the compound Au2P3 at the metal-InP interface. The magnitude of ρc is shown to be very sensitive to the growth rate of the interfacial Au2P3 layer. The possibility of exploiting this sensitivity to provide low resistance contacts while avoiding the semiconductor structural damage that is normally attendant to contact formation is discussed.

Pd and Ni contacts on various p-InP substrates which were grown by liquid-encapsulation Czochralski (LEC) and metal organic chemical vapor deposition (MOCVD) were investigated. Pd contacts on the substrates supplied by one manufacturer were found to be ohmic contacts with a minimum contact resistivity of ∼ 5xl0-5Ω-cm2 for annealing temperature between 420°C and 500°C. However, ohmic behavior was not observed for Pd contacts on other substrates. Hall measurement and double-crystal x-ray diffractometer were used to evaluate the substrates. It was speculated that existence of intrinsic defects in p-InP grown by LEC method may be responsible for the observed ohmic behavior. This defect-assisted tunneling mechanism is potentially usefully for making ohmic contacts on other compound semiconductors.

Schottky contacts to n type InP and GaAs have been made by deposition on substrates cooled to low temperature (LT=77K) in a vacuum close to 10-7 Torr.The Schottky barrier height, ФB, was found to be as high as 0.96eV with Pd/InP and 0.95eV for Au/GaAs. This indicated a significant increase in ФB compared with the room temperature (RT=300K) deposition. For diodes fabricated at room temperature, the reverse saturation current density, JO, decreased sharply with decrease in measuring temperature. For the RT InP diodes, the conduction mechanism was controlled by thermionic emission (TE). For the LT InP diodes, the value of JO was about six orders smaller than for the RT diode at the same temperature. As testing temperature decreased, the barrier height was increased from 0.96 to 1.15eV, with a temperature coefficient of -3.2 x 10-4 eV/K. The forward transport mechanism was controlled by thermionic field emission (TFE). For the GaAs diodes, thermionic emission (TE) dominated in the current transport at room temperature for both RT and LT diodes. At low testing temperature, RT diodes exhibited an excess current component at low forward bias.

Non-alloyed ohmic contacts using Ti/Pt/Au and Ni/Ge/Au on InGaAs/GaAs layers grown by Molecular Beam Epitaxy (MBE) have been investigated. The n-type InGaAs film has a doping concentration higher than 1X1019 cm-3. Specific contact resistance below 2X10-7 Ωcm2 could be easily achieved with Ti/Pt/Au. Due to the layer intermixing and outdiffusion of In and Ga, the specific contact resistance and sheet resistance increase after thermal treatment. When Ni/Ge/Au is used as the contact metal, the outdiffusion of In and Ga atoms is more severe than that of Ti/Pt/Au. After annealing at 450°C for two minutes, the Au4In formed and the characteristics of the contact became worse. All the phenomena illustrated above have been observed and investigated by Transmission Line Model, X-ray diffraction, Auger Electron Spectroscopy and Secondary Ion Mass Spectrum. As far as the thermal stability is concerned, it is convinced that Ti/Pt/Au is the best one of these two non-alloyed ohmic contact studied.

Nickel is widely used in electrical contacts to InP, especially in NiAuGe ohmic contact to n-type InP. Several researchers have even suggested that the reaction of Ni with InP plays an important role in the ohmic nature of Ni-based contacts. However, numerous discrepancies are found in the literature concerning the Ni/InP reaction. In this study, an examination of the phase equilibria in the Ni-In-P system aids in an interpretation of bulk and thick film diffusion couples, and many of the apparent discrepancies in the literature are clarified. Finally, minor variations in the processing of the contacts (changes in the annealing gas and substrate cleaning procedure) are found in this study to have a less important role in altering the Ni/InP reactions than previous researchers have suggested.

The high thermal conductivity of diamond (four times that of copper) and its low dielectric constant (less than alumina or aluminum nitride) makes it a desirable material for electronic substrates. The advent of CVD methods for depositing diamond in large areas at reasonable cost has spurred numerous applications for metallized CVDD. This paper describes several processes developed to provide reliable and stable metallization on CVDD including bond coats, diffusion barriers, vias, and solder die attach. Transition metals were found to provide well-adhered bond coats through carbide formation at the metal/CVDD interface. XPS depth profiles and conductivity measurements of three metallization systems: Ti/Pt/Au, WTi/Au, and Nb/Au after various heat treatments show WTi/Au to be the most stable system. Via filling was accomplished by LPCVD-W and electrolytic Cu for high and low aspect ratio holes respectively. The low thermal expansion coefficient of CVDD, -1.5 ppm/°C, presents a major challenge for reliable die attach of GaAs (5.85 ppm/°C). A novel concept for a compliant interface on CVDD which can overcome this problem will be presented.

The effect of heat treatments between 400°C and 500°C on electrical contacts of In, Ga, Pb, and AU to n- or p-GaAs, and Ni to n-GaAs have been studied using current-voltage (I-V), Auger electron spectroscopy and scanning electron microscopy. Ohmic contacts were formed between In and GaAs upon heating due to formation of an InGaAs surface layer with low interfacial transport barriers. The contacts between Ga or Pb and n- and p-GaAs remained rectifying due to a lack of interfacial reaction. Films of Au reacted with both n-and p-type GaAs resulting in rectangular "pits". This led to ohmic contacts only on n-type substrates due to segregation of the Si dopants to the surface of the decomposed GaAs "pits". Dopant segregation did not occur when Au reacted with p-GaAs or Ni reacted with n-GaAs, thus these contacts remained rectifying at lower doping densities (4 x 1017 cm-3).

Extremely low contact resistance of non-alloyed Ti/Pt/Au metallization on n-type InN is demonstrated. The contacts were annealed at different temperatures up to 420 °C to investigate their thermal stability. A low contact resistivity of 1.8 x 10-7 ohm-cm2 was measured at room temperature using the transmission line method. This was due to the extremely high doping level (5 x 1020 cm-3) in the InN. After 300 °C annealing, the contact resistivity increased to 2.4 x 10-7 ohm-cm2- For 360 °C annealing, the contact morphology showed some degradation, but the contact resistivity was almost the same as at 300 °C. There was serious degradation of the contacts after 420 °C annealing. The morphology became very rough, and the contact and sheet resistances increased by factors of 3-5 times. This degradation is believed due to the decomposition of the InN film. The contact resistivities between n-type epitaxial GaAs and InN were also investigated, and showed values around 10-4 ohm-cm2.

Selective chemical vapor deposition (CVD) of conductive, adherent copper films was achieved on single-crystal and polycrystalline diamond substrates modified with a ligating aminosilane and a Pd-based catalyst. Only isolated copper particles deposited on hydrogenated or aminosilane-coated diamond substrates without Pd. The Pd catalyst enhanced selectivity by a factor of 103 to 104. Copper CVD was performed in a cold-walled chamber at 446-456 K and 8x10-3 Pa using hexafluoroacetylacetonate-Cu-trimethylvinylsilane in H2 (1:1). Surfaces were characterized with x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Patterned Cu features were formed by exposing the aminosilane films to patterned ultraviolet (193 nm) radiation prior to Pd-catalyst addition and Cu CVD.

Effects of Pt and W2N/W bottom electrodes on dielectric properties of 1000 Å thick BaTiO3 thin film capacitors are studied. The tetragonality of BaTiO3 on W2N/W electrode is better than that of BaTiO3 on Pt electrode and leakage current of W2N/W/BaTiO3/Au capacitor is four orders of magnitude less than that of Pt/BaTiO3/Au capacitor. The excellent properties of W2N/W/BaTiO3/Au capacitor is ascribed to both of the tetragonal structure of WO3 formed at the interface of W/BaTiO3 and the diffusion barrier property of W2N preventing the interfacial reaction among bottom electrodes, BaTiO3, and Si.

Titanium monoxide films were deposited on silicon by reactive ion beam sputtering from a Ti target. The film composition was measured in situ by Auger electron spectrometry. It was observed that oxygen content in the deposit does not depend on the substrate temperature, up to 600 °C. Synthesized TiO films had a cubic structure with a lattice parameter of 4.17 Å, which confirmed that the O/Ti concentration ratio in the films was very close to the expected value. The films were found to be conductive, with a resistivity value equal to 170 μΩ cm. They had a yellowish metallic appearence and a very smooth surface. Sequences of annealings at increasing temperatures were performed under ultra-high-vacuum. No AES signal from silicon was observed up to a temperature of 700 °C.

A new method of epitaxial growth of CoSi2 film on Si substrate by ternary solid state interaction is investigated. XRD, RBS and TEM show that single-crystalline CoSi2 can be formed on both Si (111) and (100) substrates by using Co/Ti/Si or TiN/Co/Ti/Si multilayer. The evolution of multilayer structure and its resistivity is studied and epitaxy mechanism is discussed. Experimental results indicate strong affinity between Co and Si. During the ternary interaction the epitaxial CoSi2 can be grown directly on Si and its growth may behave as a diffusion controlled process. The thickness of Ti layer and the annealing procedure have important effect on CoSi2 epitaxial growth.

Silicides are used widely in microelectronic fabrication, yet there are very little data available regarding their optical constants at most wavelengths, and specifically at those of interest to G-line and I-line lithography. We have studied extensively the optical properties of Ti, Co, as metal films and as silicide films formed at various temperatures, and of CVD (chemical vapour deposition) W. Using spectroscopic ellipsometry at two angles of incidence, we have calculated the complex index of refraction N = (n, k) of these films every 10nm at 68 wavelengths between 230 and 900nm. These data are necessary to model accurately the reflectivity of wafers to study the effects of various thermal and surface treatments on silicide growth and to set exposure times for lithography. They also allow the use of reflectivity vs X as a non-contact method to map film thicknesses across wafers within the patterned devices themselves.

The shrinkage in type II end-of-range dislocation loops was used to determine the relative flux of vacancies from the silicidation of titanium on silicon (100) wafers. A low temperature anneal (700°C 20 min.) in a forming gas ambient formed the initial silicide (approximately 750 Å thick), and several higher temperature anneals with the silicide intact and etched off followed to study the diffusion of the vacancies. The concentration of vacancies captured by the loops after a 900°C 60 minute post silicidation anneal was approximately 7.8 x 1013 /cm2 while the concentration after a 700°C 60 minute post silicidation anneal was only 9 x 1012 /cm2. Removal of the silicide prior to the high temperature post silicidation anneals resulted in fewer vacancies captured by the loops.

We have fabricated buried cobaltdisilicide schottky contacts in silicon using wafer bonding with a patterned metal layer. The schottky contacts show good rectifying behaviour with ideality factors of 1.02-1.09 and low reverse leakage currents.