David C. Shaver

Effects of excimer laser irradiation on the transmission, index of refraction, and density of ultraviolet grade fused silica

Radiation‐induced changes in high‐purity fused silica during prolonged irradiation with a pulsed laser at 193 nm have been studied. Radiolytically induced UV absorption bands, an increase in index of refraction, and stress birefringence are observed. The formation mechanisms are analyzed in terms of radiolytic atomic rearrangement of a‐SiO2 initiated by two‐photon absorption. The quantum efficiency for the formation of E’ point defects per pair of absorbed 193 nm photons has been determined to be ∼7.5×10−4; matrix compaction, as high as a few parts in 10−5, is identified as the source of the birefringence and index change. It has been further observed that E’ centers can be photobleached.

Megapixel CMOS image sensor fabricated in three-dimensional integrated circuit technology

A 1024/spl times/1024 integrated image sensor with 8 /spl mu/m pixels, is developed with 3D fabrication in 150 mm wafer technology. Each pixel contains a 2 /spl mu/m/spl times/2 /spl mu/m/spl times/7.5 /spl mu/m 3D via to connect a deep depletion, 100% fill-factor photodiode layer to a fully depleted SOI CMOS readout circuit layer. Pixel operability exceeds 99.9%, and the detector has a dark current of <3 nA/cm/sup 2/ and pixel responsivity of /spl sim/9 /spl mu/V/e at room temperature.

Alignment of liquid crystals using submicrometer periodicity gratings

Spatial‐period (320‐nm) square‐wave gratings fabricated on amorphous SiO2 substrates were used to produce uniform alignment of the director in nematic and smectic liquid‐crystal layers. This demonstrates that molecular alignment can be achieved using surface structures fabricated by a planar process. A novel method of producing twisted‐nematic liquid‐crystal displays using surface gratings is described.

InGaAsP/InP avalanche photodiodes for photon counting at 1.06 μm

Geiger-mode (photon-counting) operation at 1.06 μm has been demonstrated with InGaAsP/InP avalanche photodiodes operated at room temperature. A photon detection efficiency of 33% was measured on uncoated detectors, representing an internal avalanche probability of 60%. Under identical bias conditions a dark count rate as low as 1.7 MHz was measured at 290 K, consistent with a primary dark current of <0.3 pA. Dark count rates drop by approximately 50–200× by cooling the detectors to 210 K (−63 °C).

X-ray zone plates fabricated using electron-beam and x-ray lithography

Fresnel zone plate patterns, free of spherical aberration, with diameters of up to 0.63 mm and linewidths as small as 1000 A were fabricated on polyimide membrane x‐ray masks using scanning electron beam lithography. Distortion of the electron beam scan raster was reduced to ?2500 A over a 2×2 mm field by applying deflection corrections, while viewing the distortion using a Moire method. CK x‐ray lithography was used to replicate the zone plate pattern in thick PMMA over a 100 A thick plating base on a glass substrate. Zones plates in 1.3 μm thick gold were fabricated by plating, and made free‐standing by removal of the plating base and the supporting glass substrate. Zone plates were tested as imaging elements with visible light and soft x‐rays.

Surface relief structures with linewidths below 2000 Å

We describe techniques for producing high‐aspect‐ratio vertical‐walled relief gratings of 1600 A linewidth with smooth line edges in SiO2 and Si substrates. Soft x‐ray lithography (13.3–44.7 A) is first used to expose such structures in PMMA. Liftoff of chromium and reactive sputter etching in CHF3 gas are then used to transfer the structure into the SiO2.

Silylation processes for 193-nm excimer laser lithography

A silylation process for novolac-based resins was developed which results in positive-tone imaging. This process is based on 193nminduced crosslinking followed by a low temperature silylation step. Novolac resin without diazoquinone additives may also be used as positive-tone resists. Typical conditions were exposure to dimethylsilyldimethylainine vapor at 10 Torr for 1 minute at 100 °C. This incorporates silicon in the upperniost 100 to 1000 nn of the film, depending on the resist. Etch selectivities in a 10 rnTorr oxygen reactive ion etching plasma with a bias voltage of -200 V were typically 30:1. Resolution below 0.3 m has been demonstrated with this technique.

Silylation of focused ion beam exposed resists

Silylation processes for lithography involve the selective incorporation of silicon into a polymeric resist, which can then be patterned using an oxygen reactive ion etching plasma. These processes, like other multilayer approaches, have been developed primarily for optical lithography to minimize substrate reflectivity and allow higher resolution. We have extended this technique to exposure with focused beams of Be, Si, Ga, and Au ions with energies between 49 and 240 keV. Conventional focused ion beam exposure of resists relies upon solvent development and requires ion penetration through the entire resist thickness. With a silylation process, however, higher mass or lower energy ions may be used, and the resist thickness is decoupled from the exposure requirements. Resolution of features smaller than 100 nm has been demonstrated.

Small-field stepper for 193-nm lithography process development

A stepper operating at the 193-nm wavelength has been constructed for use in the development of resist processes. The stepper lens has a 4-mm field diameter and a 0.33 NA. The stepper uses an unnarrowed ArF excimer laser as the light source, and uses diffractive lenslet arrays to transform the low divergence excimer beam into a suitable pupil fill. The stepper is routinely used for resist studies and has been used to pattern lines and spaces as small as 0.15 ?m.

Visible-Wavelength Laser Photodeposition of Cobalt Interconnects

Cobalt interconnects were deposited with a cw visiblewavelength laser from gaseous Co 2 (CO) 8 . The deposited material was high-purity Co, and its electrical resistivity was as low as 13 μΩ-cm (twice that of bulk resistivity). The deposition is initiated by photochemical decomposition of Co 2 (CO) 8 , and therefore process parameters (pressure, power, writing speed) are insensitive to the optical and thermal properties of the substrate.