K. D. Cummings

Micromachining of integrated optical structures

Three‐dimensional features have been milled into optical materials by scanning a submicron focused gallium ion beam. Different shapes are obtained using computer controlled beam placement and dwell time during sputtering. We have used this technique to create micron‐sized facets and reflectors in the active areas of semiconductor lasers. Light output and quantum efficiency measurements indicate that these features are of sufficient quality to fabricate monolithic integrated optical devices. Some of the applications currently being investigated are laser‐detector pairs, coupled cavity lasers, lasers with integral lenses, distributed feedback lasers, confocal cavities, and laser cavity length tuning.

Decomposition of palladium acetate films with a microfocused ion beam

Submicron Pd features have been fabricated on Si and SiO2 substrates by microfocused Ga+ ion beam exposure of spin‐on palladium acetate, [Pd(O2CCH3)2]3, films. Electrical conductivity measurements were made on the exposed features as a function of ion dose for nominal linewidths of 1 and 10 μm. The sheet conductivity in the two cases is comparable and increases dramatically in the exposure dose range between 2×1014 and 5×1014 ions/cm2. The conductivity of the exposed lines is further increased after heating in a hydrogen furnace. Potential applications of this process include mask repair and integrated circuit modification.

Using focused ion beam damage patterns to photoelectrochemically etch features in III‐V materials

A method of patterning n‐type GaAs, InP, InGaAs, and InGaAsP by photoelectrochemical (PEC) etching in conjunction with a submicron focused ion beam (FIB) at low dose is described. The ion beam is used to produce damage in a desired pattern in the material. Subsequent PEC etching of the material reveals the ion induced features in relief. The procedure is highly sensitive, requiring a dose of only 5×109 ions/cm2 for the differential etch to become apparent. The sensitivity allows rapid pattern generation in our FIB system.

Cross coupled cavity semiconductor laser

A novel monolithic coupling scheme in which three or four active waveguides interact interferometrically to form a multicavity semiconductor laser is demonstrated. The coupling between perpendicular waveguides is obtained by an integrated beamsplitter. Frequency selection, tunability, and single mode operation are demonstrated.

Micron Features In III-V Materials By Photoelectrochemical Etching Of Focused Ion Beam Induced Damage Patterns

A method of patterning n-type GaAs, InP, InGaAs and InGaAsP by photoelectrochemical (PEC) etching in conjunction with a submicron focused gallium ion beam (FIB) at low dose is de-scribed. The ion beam is used to produce damage in a desired pattern on the material. Subsequent PEC etching of the material reveals the ion induc5d featurs in relief. The procedure is highly sensitive, requiring a dose of only 5x109 ions/cm2 (about 1 ion every 1500Å) for the differential etch to become apparent. The sensitivity allows rapid pattern generation in our FIB system.

Interaction of hydrogen and thermal donor defects in silicon

We have studied the interaction of hydrogen with thermal donors in silicon using transient capacitance and current spectroscopy. We find that a large degree of thermal donor passivation (a factor of 40) can be achieved by hydrogen plasma exposure at 120 °C. The residual electrical activity is shown to arise from perturbed E(0.07) and E(0.15) donor states. Annealing at 200 °C almost completely reactivates the low concentration of thermal donors present in these samples. A model involving different incorporation sites for hydrogen is proposed to explain the results.

Using a neural network to proximity correct patterns written with a Cambridge electron beam microfabricator 10.5 lithography system

This letter describes our initial results of using a theoretical determination of the proximity function and an adaptively trained neural network to proximity correct patterns written on a Cambridge electron beam lithography system. The methods described are complete and may be applied to any electron beam exposure system that can modify the dose during exposure. The patterns produced in resist show the effects of proximity correction versus noncorrected patterns.

Photon and Ion Beam-Induced Chemistry of Palladium Acetate Films

Electrically conducting palladium features have been produced by laser and ion beam irradiation of thin palladium acetate films. The photothermal reaction induced by scanned continuous wave Ar + laser irradiation leads to metal lines that may exhibit periodic structure. This results from repeated propagation of “explosive” reaction fronts generated by coupling of the heat from the absorbed laser radiation with the heat of the decomposition reaction of the film. In contrast, 2 MeV He + ion irradiation produces smooth metallic-looking features that contain up to 20% of the original carbon and 5% of the original oxygen content of the film. Films irradiated with 2 MeV Ne + ions contain slightly lower amounts of carbon and oxygen residues, but fully exposed thick films (0.90 μm) appear black rather than metallic silver. In addition to having significantly higher purity, the laser-written features have lower resistivities than the ion beam-irradiated features. Infrared spectroscopy of the ion beam-irradiated films as a function of dose indicates a progressive loss in intensity of the characteristics acetate (COO - ) vibrations. This occurs at doses lower than those associated with major C and O loss from the films. Partially ion-exposed films continue to decompose to metallic-looking material over a period of weeks after irradiation. Metallic palladium particles apparently catalyze this process.

Ion beam damage-induced masking for photoelectrochemical etching of III-V semiconductors

Ion implantation damage has been used as a mask for patterning III‐V semiconductors by photoelectrochemical etching. The damage inhibits etching and the optical absorption of the semiconductor prevents light from penetrating through the damaged layer. Patterns of ion implantation damage have been produced on the surface of InP, InGaAs, and InGaAsP by implantation of 50 and 150‐keV Be+ ions through a photoresist mask and with a focused beam of 20‐keV Ga+ ions. Subsequent photoelectrochemical etching produces surface relief features corresponding to the damage pattern. The effect of the electrolyte and the spectral composition of the light on the resolution are described. Micron size features have been delineated and the technique may be preferable to alternate masking methods (metallization or projection) in certain applications.

Neural network proximity effect corrections for electron beam lithography

The use of a neural network to compute corrections for images written by electron beams to eliminate the proximity effects caused by electron scattering is described. Optical local changes in the incident beam dose, found iteratively, require a prohibitively long time to compute for realistic pattern sizes. A neural network was trained to perform equivalent corrections, resulting in a significant decrease in computation time. Hardware implementations of the networks for this application, using both analog and digital electronic networks, were examined. Although the analog hardware was potentially faster, the digital network has the advantage of being much more flexible. Both networks had an acceptably small error of 0.5% compared to the results of the iterative computation. The neural network correctly generalized the solution of the problem to include patterns not contained in its training set. The experimental verification of the approach is described.<<ETX>>