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The formation of high-resistivity (>107Ω/⧠) regions in GaAs-AlGaAs heterojunction bipolar transistor (HBT) structures by oxygen and hydrogen ion implantation has been investigated as a function of ion dose and subsequent annealing temperature (400–700 °C). Isolation leakage currents as low as 8 μA mm−1 at 6 V can be achieved between 100-μm-wide ohmic contacts separated by a 16 μm spacing. The isolation of these 1.8-μm-thick heterojunctions requires up to six different energy oxygen implants (40–400 keV) and three different energy proton implants (100–200 keV) with doses in the mid 1012 cm−2 range for O+ and 5×1014 cm−2 for H+ ions. Similar results can be achieved by substituting a MeV energy oxygen implant for the proton implants. The optimum post-implant annealing temperature depends on the ion dose but is in the range 500–600 °C. The evolution of the sheet resistance of the implanted GaAs-AlGaAs material with annealing is consistent with a reduction in tunneling probabilities of trapped carriers between deep level states for temperatures up to ∼600 °C, followed by significant annealing of these deep levels. Small geometry (2×9 μm2) HBTs exhibiting current gain of 44 and cutoff frequency fT as high as 45 GHz are demonstrated using implant isolation.

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Articles you may be interested inFabrication of high resolution x-ray masks using diamond membrane for second generation x-ray lithographyThe viscosity of the gas in the proximity gap between x-ray mask and silicon wafer causes damping of any membrane motion. As x ray is extended to future integrated circuit generations, this effect becomes increasingly significant, because the gap must be rapidly scaled down to permit resolution of finer lithographic features. Damping is much greater at a reduced gap. Damping can be beneficial in reducing unwanted fluctuations in the gap due to vibration, convection, or ambient sound. The longer settling time following gap adjustment, however, can be detrimental to the throughput of x-ray steppers. This article introduces simple hydrodynamic models, formulas, and numerical algorithms to calculate membrane response to adjustments in gap setting. It applies the analysis to a variety of mask formats, including advanced "pedestal" design. Time constants of several seconds are shown to result from gap setting < 10 /-lm, which may be needed for 0.12 /-lm proximity x-ray lithography.

The Advanced Metrology Advisory Group (AMAG) comprised of representatives from International SEMATECH consortium member companies and the National Institute of Standards and Technology have joined to develop a new unified specification for an advanced scanning electron microscope critical dimension measurement instrument (CD-SEM). (Ailgair, et al., 1998) This paper describes the results of an effort to benchmark six CD-SEM instruments according to this specification.The consensus among the AMAG metrologists was that many critical areas of performance of CD-SEMs required improvement. Following this assessment this specification for benchmarking was developed. The advanced CD-SEM specification addresses several critical areas for improvement, each with its own a separate section. The critical areas covered are: precision, accuracy, charging and contamination, performance matching, pattern recognition and stage navigation accuracy, throughput, and instrumentation outputs. Each section of the specification contains a concise definition of the respective performance parameter, and wherever appropriate refers to ISO definitions. The test methodology is described, complete with the relevant statistical analysis. Many parameters (including precision, matching, and magnification accuracy) are numerically specified to be consistent with the International Technology Roadmap for Semiconductors (ITRS, 1999). Other parameters, such as charging and linewidth accuracy, are targeted with guidelines for improvement. The test wafers developed for determining the level of compliance with the specification are also discussed.The AMAG circulated this report among the metrology instrument suppliers and conferred with them. Certain components of the specification have already been adopted by some of the manufacturers in their newer metrology instruments. International SEMATECH fabricated the AMAG test wafers described herein. Measurements on six state-of-the-art metrology instruments using the AMAG test wafers have been carried out and the results were processed according to this specification. A review of the results is presented in this paper.