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We report on the growth and power performance of GaN/AlGaN/GaN high electron mobility transistors (HEMTs) grown by plasma-assisted molecular beam epitaxy (MBE) on semi-insulating SiC substrates. We detail the MBE growth conditions that consistently produce high mobility two-dimensional electron gases (2DEGs) with room temperature mobility of ~1400 cm²/Vs at a sheet density of 1.2 × 10¹³ cm⁻². Transistors fabricated from these layers have demonstrated power densities in excess of 8 W/mm at 2 GHz, 6 W/mm at 7 GHz, and 3 W/mm at 25 GHz. All power data is achieved without the use of a SiN surface passivation layer. Central to the achievement of high power operation is the reduction of RF dispersion. Our growth studies have focused on the suppression of RF dispersion and maximizing RF output power. Pulsed I–V and gate lag measurements are used to quantify the amount of dispersion in different heterostructure designs. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

High-frequency gratings with rectangular-groove profiles are used to generate high-efficiency beam splitters and beam deflectors. The effects of the grating design parameters, i.e., period, groove depth, duty cycle, number of phase levels, and polarization state (TE and TM) of the incoming signal, are considered. The case of the binary beam splitter grating is analyzed by using rigorous electromagnetic grating analysis. Fabrication techniques are presented in which three different lithographic techniques are considered (optical contact, deep-UV stepper reduction, and electron-beam direct write). Experimental results of 97% efficiency for the beam splitter grating and up to 80% for the beam deflector grating are reported.

We tested the ability of normal-incidence, multilayer-coated x-ray optics to produce diffraction-limited images. The imaging performance at 14 nm of a spherical mirror substrate coated with a single metal layer was compared with that of the same substrate coated with a Mo–Si multilayer. A knife-edge test was used to quantify the image aberrations. The knife-edge data were fitted with a model based on Fresnel diffraction theory. We found that the multilayer coating introduced a measurable but small figure error into the optic; the change in figure was less than λ/16 peak to valley. We conclude that a properly deposited multilayer coating will not degrade the imaging performance of an optical system designed to operate at the diffraction limit.

A molybdenum/silicon multilayer-coated 1:1 ring-field optic with a numerical aperture of 0.0835 is used to carry out soft-x-ray projection imaging with undulator radiation at 12.9 nm. An ideal optic of this type should be able to image 0.1-μm features with a contrast exceeding 90% at this wavelength. The useful resolution of our ring-field optic is experimentally found to be approximately 0.2 μm, probably because of the presence of substrate figuring errors.

Soft-x-ray projection imaging is demonstrated by the use of 14-nm radiation from a laser plasma source and a single-surface multilayer-coated ellipsoidal condenser. Aberrations in the condenser and the Schwarzschild imaging objective are characterized and correlated with imaging performance. A new Schwarzschild housing, designed for improved alignment stability, is described.

Using 14-nm wavelength illumination, we have imaged 0.1-μm-wide lines and spaces in single-layer thin films of the highy sensitive, negative, chemically amplified resist AZ PN114 by using both a Schwarzschild 20× camera and an Offner ring field 1× optical system. For soft-x-ray projection lithography the approximate 0.2-μm absorption length in resists at 14-nm wavelength necessitates a multilayer resist system. To explore further the requirements of the imaging layer of such a system, we have transferred patterns, exposed by a high-resolution electron beam in a 60-nm-thick layer of AZ PN114, into the underlying layers of a trilevel structure. Significant pattern edge noise and resist granularity were found. It remains to be determined whether the observed noise is dominated by statistical fluctuations in dose or by resist chemistry. We also investigated pinhole densities in these films and found them to increase from 0.2 cm^−2 for 380-mm-thick films to 15 cm^−2 for 50-nm-thick films.

We describe a variety of technologies for patterning transmissive and reflective soft x-ray projection lithography masks containing features as small as 0.1 μm. The transmission masks fabricated for use at 13 nm are of one type, a Ge-absorbing layer patterned on a boron-doped Si membrane. Reflective masks were patterned by various methods that included absorbing layers formed on top of multilayer reflectors, multilayer-reflector-coating removal by reactive ion etching, and ion damage of multilayer regions by ion implantation. For the first time, we believe, a process for absorber repair that does not significantly damage the reflectance of the multilayer coating on the reflection mask is demonstrated.

In the metalorganic chemical vapor deposition of GaAs there is increasing interest in replacing arsine with a less toxic arsenic source. However, GaAs films grown with metalorganic arsenic reactants usually contain significantly higher levels of carbon than films grown with arsine. Using 50% isotopically enriched13C trimethylarsenic (TMAs), we report the first direct evidence that the methyl groups from TMAs are a major source of the carbon observed in the GaAs films. The measured13C concentration in these films was 5 x 1016cm.3Conversely, incorporation of13C was not detected when 99%13C-enriched methane was added to the source gases during growth of GaAs with arsine in place of the13C-TMAs.

We report the construction and test of an x-ray phase zone plate with 0.1-μm imaging resolution and >14% diffraction efficiency. The zone plate served as the focusing optic in a scanning microscope that operated in the water window, 2.5 nm < λ < 4.5 nm, and therefore is optimally suited for imaging wet biological specimens. We enhanced the efficiency of the zone plate by using germanium for the absorbing zones, so that some of the incident radiation is transmitted with the correct phase shift to interfere constructively at the focal spot. The zone plate was supported on a relatively transparent membrane, giving the microscope a high absolute throughput.

Projection imaging of 0.1-μm lines and spaces is demonstrated with a Mo/Si multilayer coated Schwarzschild objective and 14-nm illumination from a laser plasma source. This structure has been etched into a silicon wafer by using a trilevel resist and reactive ion etching. Low-contrast modulation at 0.05-μm lines and spaces is observed in polymethylmethacrylate.

We demonstrate nearly diffraction-limited printing of 0.2-μm features, using soft x rays of approximately 36-nm wavelength. An open-stencil transmission mask with minimum features of 4 μm was imaged by a twentyfold-reduction Schwarzschild-type objective onto silicon wafers coated with various e-beam resists. Implications for soft-x-ray projection lithography are discussed.

Resist features as small as 200 A˚ and gold lines as narrow as 400 A˚ separated by 800‐A˚ center to center have been fabricated on thick silicon. substrates. A two‐layer electron‐sensitive resist structure is employed consisting of an upper layer of polymethyl‐methacrylate and a lower layer of a copolymer of methacrylic acid and methyl methacrylate. Use of the more electron‐sensitive lower layer results in an undercut which provides clean lift‐off of the evaporated gold. Degradation in the pattern resolution by electrons backscattered from the substrate is minimized by the presence of the lower resist layer. This method provides the finest resolution lift‐off patterns reported.

Presents the outlook of nanotechnology industry executives for the industry. Lack of control on the placement of individual elements of carbon nanotubes according to Ilesanmi Adesida of the University of Illinois in Urbana-Champaign; Use of single-wall nanotubes for devices as mechanical switches according to National Science Foundation director Ahmed Busnaina; Integration of microelectromechanical systems with integrated circuits to current applications according to D. M. Tennant of Lucent Technologies.