Maurice Heathcote Norcott

Properties of SiO2/Si/GaAs structures formed by solid phase epitaxy of amorphous Si on GaAs

We have achieved solid phase epitaxy of thin amorphous Si layers on GaAs using in situ plasma processing and subsequent annealing. High‐resolution transmission electron microscopy of the SiO2/Si/GaAs structure shows that a Si layer ≂20 A thick epitaxially crystallizes on GaAs after annealing at ≂570 °C in N2. Metal‐oxide‐semiconductor capacitors fabricated on these structures confirm the high quality of these interfaces. By comparing a high‐ frequency (100 kHz) capacitance‐voltage curve with a quasi‐static one, interface state densities as low as 4×1012 eV−1/cm−2 were measured on both n‐ and p‐type GaAs.

A novel elastomeric connector for packaging interconnections, testing and burn-in applications

Elasticon connectors have been developed for a wide variety of interconnection and test applications which include module-to-board, board-to-board interconnections; high density module, board and LCD testings; as well as chip/wafer testing and burn-in to produce Known-Good-Die. Depending on the applications, the Elasticon connectors can be fabricated into two basic types, the single-sided (integrated to a substrate) and the double-sided (interposer) structure. The single-sided structure, the Integrated Probe, is designed and fabricated for test and burn-in applications. The density, compliance, thickness, pattern and size of both the one- and two-sided structures can be easily tailored to meet the requirements of each specific application. The fabrication processes involve wire bonding, laser and polymer casting and curing. The electrical, mechanical and thermal properties of the connector have been fully characterized. To achieve high compliance with low contact force, a proprietary elastomeric material has been formulated to achieve not only high compliance but high thermal stability. The conductive element uses highly conductive, corrosion free, and oxidation resistant noble metals and their alloys. The reliability and durability of the elastomeric connector have been evaluated with mechanical cycling, thermal cycling, stress relaxation, outgassing, and temperature and humidity rest. The thermal stability of the connector, including both the polymer and the conductive element, has been measured to exceed the burn-in temperatures, which range from 125 to 180/spl deg/C.

Thermally stable ohmic contacts to n‐type GaAs. VII. Addition of Ge or Si to NiInW ohmic contacts

The effects of Si or Ge addition to NiInW ohmic contacts on their electrical behavior were studied, where the samples were prepared by evaporating Ni(Si) or Ni(Ge) pellets with In and W and annealed by a rapid thermal annealing method. An addition of Si affected the contact resistances of NiInW contacts: the resistances decreased with increasing the Si concentrations in the Ni(Si) pellets and the lowest value of ∼0.1 Ω mm was obtained in the contact prepared with the Ni‐5 at. % Si pellets after annealing at temperatures around 800 °C. The contact resistances did not deteriorate during isothermal annealing at 400 °C for more than 100 h, far exceeding process requirements for self‐aligned GaAs metal‐semiconductor field‐effect‐transistor devices. In addition, the contacts were compatible with TiAlCu interconnects which have been widely used in the current Si process. Furthermore, the addition of Si to the NiInW contacts eliminated an annealing step for activation of implanted dopants and low resistance (∼0.2 Ω mm) contacts were fabricated for the first time by a ‘‘one‐step’’ anneal. In contrast, an addition of Ge to the NiInW contacts did not significantly reduce the contact resistances.

Thermally stable ohmic contacts to n‐type GaAs. VI. InW contact metal

The electrical properties and thermal stability of In/W Ohmic contacts in n‐type GaAs were studied by analyzing interfacial microstructure using cross‐sectional transmission electron microscopy and measuring the contact resistances by transmission line method. Indium layers with various thicknesses were deposited directly on GaAs substrates, which were kept at room or liquid‐nitrogen temperature. The lower contact resistances (Rc) were obtained when the contacts were prepared at liquid‐nitrogen temperature. These low Rc values were due to formation of large‐areal InxGa1−xAs phases on the GaAs substrate after annealing at temperatures higher than 600 °C. The In layer thicknesses of the In/W contacts prepared at liquid‐nitrogen temperature strongly affected the contact resistances as well as the thermal stability after contact formation. The optimum In layer thickness which provided the best electrical properties and thermal stability was determined to be 3 nm. The In(3 nm)/W contacts yielded Rc values less...

Outdiffusion of Be during rapid thermal annealing of high‐dose Be‐implanted GaAs

The outdiffusion of Be implanted into GaAs has been found to be identical after capless or capped (Si3N4 or SiO2 ) rapid thermal annealing (RTA) at 900–1000 °C and to depend on the Be dose and its proximity to the surface. The outdiffusion is more pronounced when the Be implant is shallow ( 1×1015 cm−2 ). It is demonstrated that the Be outdiffusion is driven by the presence of a highly damaged surface layer. Auger results suggest the formation of a BeOx compound at the surface of a high‐dose (1×1016 cm−2 ) Be‐implanted sample that underwent capless RTA at 1000 °C/1 s. It appears that BeOx formation occurs when the outdiffused Be interacts with the native Ga/As oxides during annealing. All the Be remaining in the GaAs after a >900 °C/2 s RTA is electrically active.

Low Au content thermally stable NiGe(Au)W ohmic contacts to n-type GaAs

Thermally stable low‐resistance ohmic contacts to n‐type GaAs incorporating a very thin layer of Au in conjunction with a layered Ni/Ge/W structure are reported. A minimum contact resistance of 0.16 Ω mm was obtained for contacts annealed at ∼650 °C. The contact resistance was ∼0.3 Ω mn after thermal stressing at 400 °C for 20 h. Cross‐sectional transmission electron microscopy reveals a uniformly reacted layer only ∼34 nm deep, making these contacts significantly shallower and more homogeneous than eutectic‐based AuGeNi contacts. X‐ray diffraction shows the presence of NiGe, β‐AuGa, and W phases in the reacted contacts. The volume fraction of the low melting point β‐AuGa phase is considerably reduced from that reported for eutectic‐based AuGeNi contacts. This, along with the presence of the high melting point NiGe compound, explains in part the improved thermal stability and morphology of the low Au content ohmic contacts.

Thermally stable ohmic contacts to p‐type GaAs. IX. NiInW and NiIn(Mn)W contact metals

Thermally stable, low‐resistance p‐type ohmic contacts have been developed by depositing NiInW metals on GaAs substrates in which Be and F were coimplanted. The contacts provided resistances of about 1.4 Ω mm after annealing at temperatures in the range of 300–800 °C for short times. The electrical properties did not deteriorate after annealing at 400 °C for more than 100 h, which far exceeds the requirements for current GaAs device fabrication. The present study demonstrated for the first time that thermally stable, low‐resistance ohmic contacts to both n‐ and p‐type GaAs can be fabricated using the same metallurgy. In addition, NiInW ohmic contacts were prepared by simultaneous (one‐step) annealing for ion‐implant activation and contact formation, which simplifies significantly the device fabrication process. A factor‐of‐2 reduction of the contact resistances was achieved by slight etching of the GaAs surface prior to the contact metal deposition so that the metal/GaAs interface contacted the peak posit...

WNx Schottky diodes on plasma treated GaAs

The influence of the GaAs surface condition on the properties and thermal stability of WNx Schottky diodes on GaAs has been studied by performing in situ H2 and N2 plasma treatments just before the WNx sputter deposition. The WNx/GaAs contacts have been investigated by x‐ray photoelectron spectroscopy, Rutherford backscattering, nuclear reaction analysis, secondary ion‐mass spectroscopy, x‐ray diffraction, and transmission electron microscope and correlated to electrical current‐voltage and capacitance‐voltage measurements. A strong correlation was found between the diode properties and the surface conditions, both for the as‐deposited samples and for samples annealed in the range 700–850 °C. Poor rectifying properties were obtained for the plasma‐cleaned diodes due to the cumulative effects of plasma cleaning and sputter deposition. After annealing, improved characteristics were generally found. The highest Schottky barrier height values φI‐V=0.76 V, which were found for the H2 plasma treated diodes anne...

Thermally stable ohmic contacts to n‐type GaAs. VIII. Sputter‐deposited InAs contacts

The electrical properties and microstructure of InAs ohmic contacts to n‐type GaAs, prepared by sputter‐depositing a single target, were studied by measuring the contact resistance (Rc) by the transmission line method and analyzing the interfacial structure by x‐ray diffraction and cross‐sectional transmission electron microscopy. Current‐voltage measurement of an as‐deposited InAs/W contact showed Schottky behavior, where the W layer was used as a cap layer. The InAs layer had an amorphous structure and a uniform oxide layer was observed at the InAs/GaAs interface. Even after annealing at 800 °C, ohmic behavior was not obtained in this contact because the intervening oxide layer prevented the InAs and GaAs interaction. By adding Ni to the InAs/W contacts (where Ni was deposited by an evaporation method), the interaction between the InAs and the GaAs was enhanced. Nickel interacted with As in the InAs layer and formed NiAs phases after annealing at temperature above 600 °C. The excess In in the InAs layer...

Effect of F co‐implant during annealing of Be‐implanted GaAs

F+ co‐implantation at different doses and energies was performed into GaAs already implanted with Be+ at high dose (1015 cm−2) and low energy (20 keV), in order to reduce the beryllium diffusion during post‐implant annealing. The redistribution behavior of Be and associated electrical effects were studied by secondary‐ion mass spectrometry, transmission electron microscopy (TEM), Hall effect measurements, and current‐voltage profiling. Be outdiffusion was reduced by co‐implantation of F; more than 80% of the implanted Be was retained during rapid thermal annealing up to 850 °C. The dose and energy of the F implant strongly influenced Be electrical activation efficiency. High activation, up to 48.5%, was obtained when F was co‐implanted at high dose (1015 cm−2) and low energy (10 keV). Hole profiles shown reduced electrical activation in the region where F and Be profiles overlapped and TEM studies indicated the formation of {111} coherent plates, possibly BeF2 precipitates, in the same region. The reducti...