J. Goodberlet

Femtosecond passively mode-locked Ti:Al(2)O(3) laser with a nonlinear external cavity.

Ultrashort pulses are generated in a Ti:Al(2)O(3) laser by using a coupled nonlinear external cavity. The external cavity uses self-phase modulation in an optical fiber to achieve passive mode locking without the need for synchronous pumping or acousto-optic modulation. A stable train of chirped 1.4-psec pulses is generated. After dispersive compensation, pulses as short as 200 fsec are obtained.

Patterning Sub-50 nm features with near-field embedded-amplitude masks

Sub-50 nm lines, holes, and posts have been patterned photolithographically using near-field embedded-amplitude masks and an exposing wavelength of 220 nm generated by an arc-lamp source. Interference in the optical near field is utilized to produce the fine patterns. In some cases, the feature sizes on the mask are more than six times larger than the size of the smallest features patterned on the substrate. Numerical simulations support the experimental results.

Optical waveguides with apodized sidewall gratings via spatial-phase-locked electron-beam lithography

We describe a technique to fabricate Bragg gratings in the sides of optical waveguides using a single lithographic step. This technique is particularly suited to the apodized gratings required for add/drop filters in dense-wavelength-division multiplexing. Apodization minimizes cross talk between channels and improves the filter response. Silicon-on-insulator rib waveguides with both uniform and apodized gratings were fabricated using direct-write spatial-phase-locked electron-beam lithography (SPLEBL). This approach combines SPLEBL’s pattern-placement accuracy with the flexibility of direct-write device prototyping. The resulting grating-based devices exhibited substantially reduced side-lobe levels.

Patterning 100 nm features using deep-ultraviolet contact photolithography

The extension of contact photolithography to pattern features at the 100 nm level, and below, is described. Isolated lines, nested L’s, and gratings with 100 nm linewidths are patterned using a conformable embedded-amplitude mask, a trilayer resist stack on the substrate, and a deep-ultraviolet radiation source having a wavelength of λ∼220 nm. A broad exposure latitude of ±21% for a linewidth control of ±10% is measured. Preliminary calculations indicate a practical resolution limit for the lithographic process. The patterning process is reliable and repeatable.

Starting dynamics of additive-pulse mode locking in the Ti:Al 2 O 3 laser

The starting dynamics of the additive-pulse mode-locked Ti:AI(2)O(3) laser are investigated. Mode locking develops from mode beating with pulse formation times of several hundred microseconds. A simple model based on additivepulse mode-locking theory is developed that describes self-starting and pulse evolution.

Performance of the Raith 150 electron-beam lithography system

The performance of a Raith 150 electron-beam lithography system is reported. The system’s resolution, stability, intrafield distortion, stitching, and overlay performance are evaluated. Patterning at low- and high-acceleration voltages is compared. The system was used to pattern sub-20 nm features, and the largest intrafield distortion for a 100 μm field was measured to be 15 nm. Pattern-placement accuracy below 35 nm, mean plus twice the standard deviation, was demonstrated.

Amplification in Ni-like Nb at 204.2 Å pumped by a table-top laser

We identified for the first time the 3d94d1S − 3d94p1P line in Ni-like Nb at 204.2 Å that was predicted to show gain. When pumped with a train of pulses containing less than 1 J per pulse, significant emission was recorded at 204.2 Å following the second and the third pulses. We measured the small signal gain coefficient per Joule of incident laser energy to be 1.49±0.42 cm−1 J−1 for this laser transition, which is higher by several orders of magnitude than that reported for other collisional laser systems in this wavelength range.

Two-dimensional spatial-phase-locked electron-beam lithography via sparse sampling

We report a new mode of spatial-phase-locked electron-beam lithography based on alignment of each e-beam deflection field to a fiducial grid on the substrate. Before exposing the pattern in a given field, the fiducial grid is sparsely sampled with the electron beam at a subexposure dose. These samples form a two-dimensional moire pattern that is analyzed to calculate field shift, scale, rotation, nonorthogonality, and trapezoidal distortion. Experimental verification of the approach was carried out with a scintillating fiducial grid quenched by interference lithography. Despite a poor signal-to-noise ratio, we achieved sub-beamstep field-stitching and pattern-placement accuracy.

Spatial-phase-locked electron-beam lithography with a delay-locked loop

A delay-locked loop is used in a one-dimensional demonstration of the global-fiducial-grid mode of spatial-phase-locked electron-beam lithography. A pattern-placement precision of σ∼5 nm is demonstrated under nonideal conditions. Results compare well with numerical simulations.

Scintillating global-fiducial grid for electron-beam lithography

An organic scintillator has been developed for use in electron-beam lithography. The scintillator can be deposited in a thin film ( 2) optical signal. It is expected that the signal from this type of grid will improve the pattern-placement precision to within 1 nm when used in conjunction with spatial-phase-locked electron-beam lithography.