Dean Malta

Diamond devices and electrical properties

Abstract Diamond offers tremendous potential for electronic applications such as field effect transistors. An investigation of the electrical properties of boron-doped homoepitaxial diamond films and the metal-oxide-diamond gate structure was performed. Additionally, field effect transistors were fabricated and characterized. Improvements in the diamond deposition process produced boron-doped homoepitaxial diamond films where the room temperature Hall mobility exceeded 1000 cm 2 V −1 s −1 . Analysis of the temperature-dependent carrier concentration indicated that the compensation was 15 cm −3 . The gate structure for metal-silicon dioxide-boron-doped diamond field effect transistors was evaluated by current-voltage and capacitance voltage measurements. Good correlation of the uncompensated acceptor concentration, determined by capacitance-voltage measurements, and the boron concentration, determined by secondary ion mass spectroscopy, was attained. Preliminary measurements suggested that the density of interface states for this structure was ≈ 10 12 cm −2 eV −1 . Field effect transistors exhibited saturation and pinch-off at temperatures as high as 773 K. The highest normalized transconductance measured was 1.3 mS mm −1 . The field effect transistors were combined into analogue and digital circuits that operated at 523 K and 673 K, respectively.

Comparison of the electrical properties of simultaneously deposited homoepitaxial and polycrystalline diamond films

The electrical transport properties of simultaneously deposited, B‐doped homoepitaxial and polycrystalline diamond thin films have been evaluated by Hall‐effect and resistivity measurements over a temperature range of 80–600 K. The same films were later characterized by scanning electron microscopy, secondary‐ion‐mass spectroscopy, and an oxidation defect etch. The study involved four sets of chemical‐vapor‐deposited diamond films with individual B concentrations ranging from 1.5×1017 to 1.5×1020 cm−3. In each of the four cases the mobility of the polycrystalline film was lower than that of the homoepitaxial film by 1–2 orders of magnitude over the entire temperature range. Polycrystalline films also incorporated 2–4 times more B, had 3–5 times higher compensation ratios, and displayed activation energies that were 0.05–0.09 eV lower than in the homoepitaxial films. Hopping conduction was observed in both types of films at low temperatures, but was enhanced in polycrystalline films as evident by higher tr...

Hall effect measurements on boron‐doped, highly oriented diamond films grown on silicon via microwave plasma chemical vapor deposition

A highly oriented, (100) textured diamond film was grown on a Si substrate, followed by the deposition of an epitaxial boron‐doped layer for electrical characterization. Temperature‐dependent Hall effect measurements were performed between 180 and 440 K. The 165 cm2/V⋅s hole mobility measured at room temperature is approximately five times greater than the highest reported mobilities for polycrystalline diamond. The relative improvement in the electronic quality of diamond films grown on Si, due to the reduction of misorientation and grain boundary angles, has been demonstrated. X‐ray diffraction pole measurements were performed on the (100) oriented film in order to quantify the degree of misorientation.

Epitaxial nucleation, growth and characterization of highly oriented, (100)-textured diamond films on silicon

Abstract Growth of highly oriented, (100)-textured diamond films has been achieved through a multistep growth process which included biasenhanced nucleation and textured growth. The grain misorientation was analyzed by polar X-ray diffraction, electron diffraction and analysis of the dislocation spacing at a small-angle grain boundary. The electronic properties of simultaneously deposited, randomly oriented polycrystalline; highly oriented, (100) textured, and single-crystal homoepitaxial diamond films were compared to assess the role of grain boundaries. Calculations suggest that the highly oriented, (100)-textured film possessed a lower density of interfacial traps by about 50% compared with randomly oriented polycrystalline diamond film. This reduction in interfacial traps in the highly oriented, (100)-textured film could account for the mobility improvement by a factor of 3 over the mobility of the polycrystalline film. The homoepitaxial film possessed a mobility three times that of the highly oriented, (100)-textured film, and it appeared that additional reductions in trap density should provide additional opportunities for improved mobility in highly oriented, (100)-textured films.

High density vertical interconnects for 3-D integration of silicon integrated circuits

This paper describes a technology platform being developed for three-dimensional (3-D) integration of thin stacked silicon integrated circuits (ICs). 3-D integration technology promises to dramatically enhance on-chip signal processing capabilities of a variety of sensor and actuator array devices hybridized with silicon read-out electronics. Currently, advanced 3-D integrated infrared focal plane array detectors are being developed within the DARPA vertically integrated sensor arrays (VISA) program. Here, we describe the 3-D integration process flow and demonstrations developed in the VISA program

Evaluation of ohmic contacts formed by B+ implantation and Ti-Au metallization on diamond

Low‐resistance ohmic contacts have been fabricated on a naturally occurring B‐doped diamond crystal and on polycrystalline diamond films by B ion implantation and subsequent Ti/Au bilayer metallization. A high B concentration was obtained at the surface by ion implantation, a post‐implant anneal, and a subsequent chemical removal of the graphite layer. A bilayer metallization of Ti followed by Au, annealed at 850 °C, yielded specific contact resistance (ρc) values of the order of 10−5 Ω cm2 for chemical vapor deposition grown polycrystalline films and the natural IIb crystal. The ρc values from transmission line model measurements on three different contact configurations, namely, standard rectangular pads, rectangular pads on diamond mesas, and three‐ring circular structures have been compared. These contacts were stable to a measurement temperature of ∼400 °C and no degradation due to temperature cycling was observed. Chemical analysis by x‐ray photoelectron spectroscopy (XPS) in conjunction with Ar+ sp...

Comparison of electronic transport in boron‐doped homoepitaxial, polycrystalline, and natural single‐crystal diamond

Hall‐effect and resistivity measurements were performed on simultaneously deposited B‐doped homoepitaxial and polycrystalline diamond films, as well as a (100)‐oriented type‐IIb natural diamond crystal, over a temperature range of 140–600 K. At 298 K, the respective Hall mobilities for the homoepitaxial and polycrystalline films were 519 and 33 cm2/V s, while the active carrier concentrations were both approximately 2×1014 cm−3. For the natural diamond, a Hall mobility of 564 cm2/V s and a carrier concentration of 2×1013 cm−3 were measured at room temperature. A comparison of the transport behavior of the three specimens indicates that the electronic properties of diamond grown by chemical vapor deposition are potentially of equal or greater quality than natural diamond and that the transport properties of polycrystalline films are severely degraded by the effects of grain boundaries.

Integrated process for defect-free copper plating and chemical-mechanical polishing of through-silicon vias for 3D interconnects

The fabrication of through-silicon vias (TSVs) is a major component in the development of three-dimensional (3D) integration technology and advanced 3D packaging approaches. The large diameter and length of TSVs, as compared to traditional interconnects, create some unique process challenges. Via plating and chemical-mechanical polishing (CMP) processes used in standard copper interconnect technology are generally not suitable for TSV fabrication. Therefore, efforts are being made to develop such processes specifically for TSV technology. This paper will describe the development of a void-free Cu electroplating process for TSV filling, along with CMP processing to remove the overburden layer and expose the Cu-filled vias for subsequent metallization. The focus of the paper will be the integration of the TSV plating and CMP processes, with discussion regarding observed integration challenges and their solutions. First, a Cu electroplating process was developed for defect-free, bottom-up filling of silicon vias from 20–200µm in diameter and 150–375µm deep, with aspect ratios from 1:1 to 8:1. Next, CMP tests were conducted using Cu-filled silicon vias of 50µm diameter and 150µm depth, designed for use in a MEMS wafer-level packaging application. These tests indicated that plating nonuniformity and Cu mound defects over filled vias caused significant CMP process issues. The plating process was then modified to eliminate these problems in the Cu films, resulting in improved CMP uniformity and reduced polishing time.

High Density 3-D Integration Technology for Massively Parallel Signal Processing in Advanced Infrared Focal Plane Array Sensors

The paper describes a platform technology for three-dimensional (3-D) integration of multiple layers of silicon integrated circuits. The technology promises to dramatically enhance on-chip signal processing capabilities of a variety of sensor and actuator devices hybridized with Si electronics. Among these applications are high performance infrared focal plane array detectors

Electrical characterization of semiconducting diamond thin films and single crystals

Naturally occurring semiconducting single crystal (type IIb) diamonds and boron doped polycrystalline thin films were characterized by differential capacitance-voltage and Hall effect measurements, as well as secondary ion mass spectroscopy (SIMS). Results for natural diamonds indicated that the average compensation for a type IIb diamond was >17%. Mobilities for the natural crystals varied between 130 and 564 cm2/V·s at room temperature. The uncompensated dopant concentration obtained by C-V measurements (2.8 ± 0.1 × 1016 cm−3) was consistent with the atomic B concentration measured by SIMS performed on similar samples (3.0 ± 1.5 x 1016 cm−3). Measurement of barrier heights for three different metals (platinum, gold, and aluminum) found essentially the same value of 2.3 ± 0.1 eV in each case, indicating that the Fermi level was pinned at the diamond surface. Polycrystalline semiconducting diamond thin films demonstrated a complex carrier concentration behavior as a function of dopant density. This behavior may be understood in terms of a grain boundary model previously developed for polycrystalline silicon, or by considering a combination of compensation and impurity band conduction effects. The highest mobility measured for a polycrystalline sample was 10 cm2/V·s, indicating that electrical transport in the polycrystalline material was significantly degraded relative to the single crystal samples.