J. M. Carter

Large‐area achromatic interferometric lithography for 100 nm period gratings and grids

Achromatic interferometric lithography is the preferred approach for producing large‐area, spatially coherent 100 nm period gratings and grids. We report on improvements to processes which have enabled exposure areas of ≊10 cm2. In addition, we report on the fabrication of 100 nm period free‐standing gold gratings.

Achromatic interferometric lithography for 100‐nm‐period gratings and grids

For the fabrication of periodic structures with spatial periods of 100 nm or less, achromatic interferometric lithography is preferred over other lithographic techniques. We report on processes we have developed, using achromatic interferometric lithography, to fabricate large‐area coherent gratings and grids with spatial periods of 100 nm.

Fabrication of 200 nm period nanomagnet arrays using interference lithography and a negative resist

Magnetic information storage density has increased at the rate of 60% per year for the past seven years. There is wide agreement that continuation of this trend beyond the physical limits of the continuous thin-film media currently used will likely require a transition to discrete, lithographically defined magnetic pillars. Interference lithography (IL) appears to be the most cost-effective means of producing two-dimensional arrays of such pillars. IL can rapidly expose large areas with relatively simple equipment, without the need for a mask, and with fine control of the ratio of pillar diameter to period. We show that negative-tone imaging yields three times the contrast of positive-tone imaging for the generation of holes in photoresist, suitable for subsequent deposition or electroplating of magnetic material. We use a negative i-line, chemically-amplified resist (OHKA THMR-iN PS1) to form 200 nm period arrays of magnetic dots in Co and Ni. Such arrays, with a variety of well controlled diameters, are...

High‐quality GaAs on sawtooth‐patterned Si substrates

We report a novel technique for growing GaAs on Si substrates with a low density of threading dislocations. The process involves patterning a 200 nm period sawtooth grating on (100) Si using a combination of holographic lithography and wet chemical etching. The GaAs layers grown by metalorganic chemical vapor deposition on such substrates exhibit a dramatic reduction in the density of threading misfit dislocations, even when the grown layers are thin. Twins and stacking faults are also reduced dramatically by either in situ thermal‐cycle growth or ex situ rapid thermal annealing.

Ridge-waveguide sidewall-grating distributed feedback structures fabricated by x-ray lithography

A novel distributed feedback structure has been developed in which the grating is patterned onto the sidewalls of a ridge waveguide. Such a laser structure results in simplified processing in that the grating fabrication is independent of both the materials growth and the guide formation. The ridge waveguide is first formed by wet‐chemical etching. Then, a poly(methylmethacrylate) grating (Λ=230 nm) is patterned onto this ridge waveguide using x‐ray lithography. A Ti/Al etch mask is lifted‐off to serve as a mask for subsequent reactive‐ion etching. Gratings with long‐range spatial‐phase coherence and negligible distortion, characteristics which are necessary for accurate control of the wavelength and bandwidth, are obtained using a holographically generated x‐ray mask.

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.

Large‐area, free‐standing gratings for atom interferometry produced using holographic lithography

Interferometers based on matter waves promise orders‐of‐magnitude improvements in metrology over laser‐based systems by virtue of the fact that the de Broglie wavelengths of atoms are about 104 times shorter. To date, the required matched set of four aligned gratings for such atom interferometers has been made using electron beam lithography and, as a result, such gratings suffer from a lack of spatial‐phase coherence. We report on processes we have developed for fabricating free‐standing gratings over large areas using conventional holographic lithography and achromatic holographic lithography to achieve spatial periods of 200 and 100 nm, respectively (i.e., nominal linewidths of 100 and 50 nm, respectively).

Sub‐100‐nm x‐ray mask technology using focused‐ion‐beam lithography

In the past, nearly all x‐ray nanolithography (i.e., sub‐100‐nm linewidths) employed the CK x‐ray line at 4.5 nm. This, in turn, necessitated near‐zero gaps (to avoid diffraction) and carbonaceous masks (e.g., polyimide, which is subject to distortion). In order to use x‐ray replication in the fabrication of multilevel devices and circuits that cover large areas (∼a few cm2) and have feature sizes well below 100 nm, we have turned to the CuL line at 1.3 nm. Masks consist of 1–1.5 μm thick Si or Si3N4 membranes and Au absorber patterns, 200 nm thick, which provide 10 db contrast. Focused‐ion‐beam‐lithography (FIBL) with Be++ ions at 280 keV was used to produce quantum‐effect‐device patterns with minimum linewidths of ∼50 nm. These were replicated using the CuL line, indicating that photoelectrons are not a serious problem. The FIBL process [exposure of 300 nm‐thick polymethylmethacrylate (PMMA), followed by Au electroplating] is high yield and much simpler than a trilevel electron‐beam‐lithography process ...

Spatial‐phase‐locked electron‐beam lithography and x‐ray lithography for fabricating first‐order gratings on rib waveguides

The two basic structural elements of the integrated resonant channel‐dropping filter are the rib waveguides and the first‐order Bragg gratings. Spatial‐phase‐locked electron‐beam lithography is used to write the Bragg grating patterns with a coherence better than λ0/150, and x‐ray nanolithography is used to transfer the gratings onto optically patterned rib waveguides. These technologies are successfully combined to demonstrate a process by which channel‐dropping filters and related devices can be fabricated.

X-ray masks with large-area 100mm-period gratings for quantum-effect device applications

Abstract We report the fabrication and replication of x-ray masks with large-area (∼50 mm 2 ) 100nm-period gratings. Achromatic holographic lithography was used to generate 100nm-period surface gratings in PMMA resist. Subsequent dry processing formed high-aspect-ratio grating lines down to the base of the resist. The x-ray absorber was defined by either: (i) reactive-ion etching low-stress sputter-deposited tungsten, using the resist lines as an etch mask, or (ii) electroplating gold using the resist lines as a mold. The absorber patterns were fabricated on silicon substrates coated with 1 μm-thick polyimide as the membrane material. X-ray masks were formed by etching away the silicon substrate, leaving the x-ray absorber pattern supported by the polyimide membrane. Results of x-ray exposures of PMMA, using the C K line ( λ =4.5 nm ), are presented.