Diamond Wafers Research Articles

Potential and Challenges of Diamond Wafer Toward Power Electronics

To achieve a 50% worldwide reduction of CO2by the middle of this century, development of energy saving power device technology using wide bandgap materials is urgently needed. Diamond is receiving increasing attention as a next generation material for wide bandgap semiconductors owing to its extreme characteristics. Research studies investigating large wafers, low resistivity, and low dislocation have accelerated. This study targets the use of wafers for power electronics applications, and the required machining technologies for diamond, including wafer shaping, slicing, and surface finishing, are introduced.

Damage-free highly efficient polishing of single-crystal diamond wafer by plasma-assisted polishing

Single-crystal diamond (SCD) is considered to be an ideal material for next-generation power devices. Plasma-assisted polishing (PAP) without using an abrasive was applied to polish SCD fabricated by chemical vapor deposition. Argon-based plasma containing water vapour was used in the PAP to modify the surface of polishing plate and SCD (100), and SCD was polished under a polishing pressure ranging from 10 to 52.6kPa. Raman spectroscopy measurement showed that there was no residual stress on the polished SCD surface, and a polishing rate of 2.1μm/h and a surface roughness of 0.13nm Sq were obtained.

Development and Test of a Diamond-Based Fast Neutron Detector for 200 °C Operation

Recent improvements in the production of artificial single-crystal diamonds have made it possible to produce commercial radiation detectors. However, the availability of diamond detectors for high-temperature and high-shock applications is limited. We have developed a compact solid-state diamond detector for high-temperature applications which require compact size, stable performance, and extreme ruggedness. It is used as a fast neutron detector for monitoring the output of a pulsed neutron generator in oil well-logging tools. The sensor consists of a high-purity monocrystalline diamond wafer with metallized electrodes on both faces. One of the metallized surfaces is mounted on a metallic plate resting on a ceramic substrate. The metallized diamond assembly is mounted in a TO-257 metal housing, which has pins connected to the two electrodes on the two faces of the diamond. The detector package, consisting of the diamond sensor and the electronics assembly, has been qualified for operation in the harsh downhole environment of oil fields. This includes high temperature and repeated shocks and vibration. Units have been tested for up to 150 h at 200 °C with no degradation in signal or count rate accuracy. The count rate accuracy with a simple detection threshold regulation scheme can reach ±1% over the range from 25 °C to 200 °C. However, this detector has applications beyond well logging, wherever there is a need for a compact, reliable detector for fast neutrons in an environment where ruggedness, exposure to high temperature, compactness, and radiation hardness are essential.

Coaxial CVD diamond detector for neutron diagnostics at ShenGuang III laser facility.

A coaxial, high performance diamond detector has been developed for neutron diagnostics of inertial confinement fusion at ShenGuangIII laser facility. A Φ10 mm × 1 mm "optical grade" chemical-vapor deposition diamond wafer is assembled in coaxial-designing housing, and the signal is linked to a SubMiniature A connector by the cathode cone. The coaxial diamond detector performs excellently for neutron measurement with the full width at half maximum of response time to be 444 ps for a 50 Ω measurement system. The average sensitivity is 0.677 μV ns/n for 14 MeV (DT fusion) neutrons at an electric field of 1000 V/mm, and the linear dynamic range is beyond three orders of magnitude. The ion temperature results fluctuate widely from the neutron time-of-flight scintillator detector results because of the short flight length. These characteristics of small size, large linear dynamic range, and insensitive to x-ray make the diamond detector suitable to measure the neutron yield, ion temperature, and neutron emission time.

Partitioning very hard semiconductor sapphire wafers into monolithic integrated circuits using laser controlled thermal cleavage

The works on the partitioning of very hard semiconductor sapphire wafers with a diameter of 52 mm and thickness of 90 μm into monolithic integrated circuits (MICs) have been carried out using lasercontrolled thermal cleavage (LCT). The studies have been carried out and the works on cutting polycrystalline diamond wafers have been performed, as a result of which a method to partition the wafers into crystals, i.e., the laser plasmochemical method of cutting, is proposed, the basic advantage of which is the absence of the material bursting out from the cutting region and its deposition onto already formed device structures.

Characterization of the Diamond Wire Sawing Process for Monocrystalline Silicon by Raman Spectroscopy and SIREX Polarimetry

A detailed approach to evaluate the sub-surface damage of diamond wire-sawn monocrystalline silicon wafers relating to the sawing process is presented. Residual stresses, the presence of amorphous silicon and microcracks are considered and related to diamond wire velocity and cutting ability. In particular, the degree of amorphization of the wafer surface is analyzed, as it may affect the etching performance (texturing) during solar cell manufacture. Raman spectroscopy and Scanning Infrared Stress Explorer (SIREX) measurements are used independently as non-destructive, contactless optical characterization methods to provide stress imaging with high spatial resolution. Raman mappings show that amorphous silicon layers can occur inhomogeneously across the surface of diamond wire-sawn wafers. The Raman and SIREX results reveal a connection between a higher fraction of the amorphous phase, a more inhomogeneous stress distribution and a lower peak maximum of the stress difference on wafers, depending on both the wire wear and the wire velocity. SIREX line scans of the in-plane difference of the principal stress components ∆σ taken across the sawing grooves show significant differences in magnitude and periodicity. Furthermore, the results are compared with the microcrack depth from the same investigation areas. The possibility to optimize the diamond wire sawing processes by analyzing the sub-surface stress of the wafers is offered by complementary use of both Raman and SIREX measurements.

Ion bombardment induced buried lateral growth: the key mechanism for the synthesis of single crystal diamond wafers

A detailed mechanism for heteroepitaxial diamond nucleation under ion bombardment in a microwave plasma enhanced chemical vapour deposition setup on the single crystal surface of iridium is presented. The novel mechanism of Ion Bombardment Induced Buried Lateral Growth (IBI-BLG) is based on the ion bombardment induced formation and lateral spread of epitaxial diamond within a ~1 nm thick carbon layer. Starting from one single primary nucleation event the buried epitaxial island can expand laterally over distances of several microns. During this epitaxial lateral growth typically thousands of isolated secondary nuclei are generated continuously. The unique process is so far only observed on iridium surfaces. It is shown that a diamond single crystal with a diameter of ~90 mm and a weight of 155 carat can be grown from such a carbon film which initially consisted of 2 · 1013 individual grains.

Growth of 4″ diameter polycrystalline diamond wafers with high thermal conductivity by 915 MHz microwave plasma chemical vapor deposition

Polycrystalline diamond (PCD) films 100 mm in diameter are grown by 915 MHz microwave plasma chemical vapor deposition (MPCVD) at different process parameters, and their thermal conductivity (TC) is evaluated by a laser flash technique (LFT) in the temperature range of 230–380 K. The phase purity and quality of the films are assessed by micro-Raman spectroscopy based on the diamond Raman peak width and the amorphous carbon (a-C) presence in the spectra. Decreasing and increasing dependencies for TC with temperature are found for high and low quality samples, respectively. TC, as high as 1950 ± 230 W m−1 K−1 at room temperature, is measured for the most perfect material. A linear correlation between the TC at room temperature and the fraction of the diamond component in the Raman spectrum for the films is established.

Design and fabrication of high-performance diamond triple-gate field-effect transistors.

The lack of large-area single-crystal diamond wafers has led us to downscale diamond electronic devices. Here, we design and fabricate a hydrogenated diamond (H-diamond) triple-gate metal-oxide-semiconductor field-effect transistor (MOSFET) to extend device downscaling and increase device output current. The device’s electrical properties are compared with those of planar-type MOSFETs, which are fabricated simultaneously on the same substrate. The triple-gate MOSFET’s output current (174.2 mA mm−1) is much higher than that of the planar-type device (45.2 mA mm−1), and the on/off ratio and subthreshold swing are more than 108 and as low as 110 mV dec−1, respectively. The fabrication of these H-diamond triple-gate MOSFETs will drive diamond electronic device development forward towards practical applications.

Heatsink diamond nanostructures for microwave semiconductor electronics

A basic technique for manufacturing and processing polycrystalline diamond as a promising material for heatsinks of high-power microwave semiconductor devices is proposed. The fabrication of polycrystalline diamond wafers by chemical vapor deposition is investigated. The choice of a method for fragmenting polycrystalline diamond wafers is considered and a new technique for low-pressure laser/plasma chemical cutting of wafers in a gaseous medium is proposed which consists of growing polycrystalline diamond on preshaped silicon substrates and subsequent silicon etching.

Single crystal diamond wafers for high power electronics

According to international energy proposal, about 25% of the total CO2 reduction should come from “end use efficiency”. Hence, low loss power devices are an important technology for the 21st century. Diamond-based devices have the potential, but this would require fast development in order to contribute to the CO2 reduction plan early in this century. Here, we present a clear target for the R&D of diamond wafer. According to the expected applications of diamond devices with a vertical structure, the required target properties for first stage diamond wafers are; a killer defect density less than 0.1cm−2, resistivity less than 0.005Ωcm and a size of 4in. For the final commercialization stage, targets of zero killer defects, resistivity of 0.001Ωcm and a size of 6in. are proposed. The challenges and proposal solutions are reviewed for each technology.

Dielectric properties of single crystalline diamond wafers with large area at microwave wavelengths

In this paper, we present first measurements, carried out at microwave wavelengths, aiming to characterize the dielectric properties of large size single crystalline diamond (SCD) wafers. While the sizes of the SCD wafers are still not sufficient for practical use, we obtained good optical property results. The sample with both sides polished shows a dielectric loss tangent tanδ as low as or possibly lower than a polycrystalline diamond sample with high quality. Results show the importance of surface treatment, especially on the boundaries of the composed SCD chips even without any graphitic component in the diamond wafers.

Failure Mechanisms of CVD Diamond Wafers and Thin Films During Polishing

This article investigates the failure mechanisms of CVD diamond wafers and thin films during a fast dynamic friction polishing process. To explore the evolution of temperature and stress fields, a comprehensive finite element analysis was systematically carried out, with the aid of experimental examination. It was found that the discontinuity and sharp change of the stresses across the film-substrate interface causes debonding failure of a CVD diamond thin film specimen. In the case of a CVD diamond wafer, however, the high surface tensile stress and bulk bending is responsible for the cracking. It was concluded that specimen cracking is sensitive to the polishing pressure, and that the polishing window for the CVD thin films is smaller. Polishing time is a critical factor, because a longer time corresponds to a higher thermal stress. This article points out that using the combination of a smaller polishing load and a greater sliding speed is a good option in selecting polishing parameters. To minimize cracking, a stepwise polishing process can be used. With the proper parameters obtained in this study, very smooth, high-quality surfaces of CVD diamond wafers and thin films can be produced in a short polishing duration of minutes.

単結晶ダイヤモンドウェーハ作製における要素技術の現状と課題

単結晶ダイヤモンドウェーハ作製における要素技術の現状と課題

Lateral scan profiles of the recombination parameters correlated with distribution of grown-in impurities in HPHT diamond

Abstract The profiling of the microwave probed photoconductivity transients and of the time resolved photoluminescence spectra has simultaneously been performed on the synthetic diamond wafer samples in order to clarify correlation of the distribution of the grown-in defects and carrier radiative and non-radiative recombination channels. The wafer samples were sliced from the diamond single crystals, synthesized by the high pressure and high temperature (HPHT) technology using the Ni–Fe liquid solvent/catalyst system. To estimate the microscopic characteristics of the grown-in defects, the EPR spectroscopy has been carried out. The changes of carrier lifetime, ascribed to the radiative and non-radiative recombination, have been resolved. The correlation between the parameters extracted from the absorption spectra and recombination characteristics has been obtained. The prevailing grown-in point defects, associated with neutral and charged nitrogen impurity complexes as well as the pairs of nitrogen atoms on neighbouring sites, and the nickel precipitates have been unveiled.

A 2-in. mosaic wafer made of a single-crystal diamond

We synthesized a mosaic diamond wafer 2 in. in size (40 × 60 mm2), which consisted of 24 single-crystal diamond (SCD) plates 10 × 10 mm2 in area, by using microwave plasma chemical vapor deposition. Even by using a cloning technique, cracking frequently occurred and the non-uniformity was remarkable for wafers that were larger than 1 in. in size. This has not been observed in smaller samples before. Appropriate crystallographic directions could avoid the cracking and is one of the predominant factors in fabricating large area SCD wafers. Comparison with numerical simulations highlighted the importance of uniformity of the substrate temperature distribution on the uniformity of the growth.

Effect of arc characteristics on the properties of large size diamond wafer prepared by DC arc plasma jet CVD

Diamond wafer with 100mm in diameter and 1mm in thickness was prepared by DC arc plasma jet CVD. The area arc distribution above the surface space of substrate, consisting of arc center, arc main and arc edge, directly determined the quality and homogeneity of diamond wafer. As the distance to the central area increased, the crystal size of diamond increased firstly and then decreased. Meanwhile, “dark feature” texture quantity of polished diamond film corresponding to arc main was lower than that corresponding to arc center and arc edge. XRD results showed the ratio of I(220)/I(111) of diamond films increased from edge to center gradually. The intrinsic stress of diamond film corresponding to arc main was greater than the other two areas according to the Raman spectrum, and the highest transmittance in the 10.6 micron wavelength was obtained in the area corresponding to arc main by Fourier infrared. The difference of fracture strength in three areas was less than 20MPa, which reveals the arc characteristics have less effect on fracture strength.

Quality evaluation of diamond wire-sawn gallium-doped silicon wafers

Most of the world's solar cells in photovoltaic industry are currently fabricated using crystalline silicon. Czochralski-grown silicon crystals are more expensive than multicrystalline silicon crystals. The future of solar-grade Czochralski-grown silicon crystals crucially depends on whether it is usable for the mass-production of high-efficiency solar cells or not. It is generally believed that the main obstacle for making solar-grade Czochralski-grown silicon crystals a perfect high-efficiency solar cell material is presently light-induced degradation problem. In this work, the substitution of boron with gallium in p-type silicon single crystal is studied as an alternative to reduce the extent of lifetime degradation. The diamond-wire sawing technology is employed to slice the silicon ingot. In this paper, the quality of the diamond wire-sawn gallium-doped silicon wafers is studied from the chemical, electrical and structural points of view. It is found that the characteristic of gallium-doped silicon wafers including texturing behavior and surface metallic impurities are same as that of conventional boron-doped Czochralski crystals.

Surface morphology and bond characterization of nanocrystalline diamonds grown on tungsten carbide via hot filament chemical vapor deposition

Nanocrystalline diamonds (NCDs) were deposited on chemically prepared tungsten carbide substrates via hot filament chemical vapor deposition. The surface morphology of the NCDs was examined using field emission scanning electron microscopy. The NCDs formed a ballas morphology evenly across the tungsten carbide surface. Overetching affected the diamond deposition by causing the ballas to form aggregations. Cross-sectional fragmentation using a diamond wafering blade caused the nanocrystalline diamond to fragment at overetched boundaries, and delamination only occurred 30–50µm off the edge and revealed that the thickness of the diamond film was 6µm. Grazing XRD is an effective method to identify diamonds even at the nanoscale. The crystallite size was calculated to be 18.4nm by modeling. Cross-sectional TEM analysis indicated that the diamond grain size was approximately 10–30nm near the interface. Amorphous carbon, an embedded diamond and voids were also observed. TEM also revealed that the tungsten carbide surface undulates. The nanocrystalline diamonds nucleated and grew on the tungsten carbide (100) planes in the 〈111〉 direction, forming (111) planes, as observed from HRTEM, d-spacing measurements, SAD and FFT analyses for a FIB-prepared sample.

Polishing of CVD Diamond Wafers and Films

This paper investigates the applicability of the dynamic friction polishing (DFP) technique to process the chemical vapour deposition (CVD) diamond surfaces. Two types of CVD diamond specimens were studied. A stepwise polishing process was introduced to minimise the cracking in CVD thin films. The investigation focused on the polished surface quality in relation to the polishing conditions and material remove rates. It was found that by selecting proper polishing parameters, surfaces of quality finish with a roughness of less than 70 nm Ra could be obtained in 15 minutes when the specimens were CVD diamond wafers with an initial roughness of 17 μm. The polishing time could be reduced to only 2.5 minutes in the case of diamond thin film specimens of initial roughness of 1.6 μm.