KEYWORDS: Semiconducting wafers, Metals, Backscatter, Electron beam lithography, Copper, Lithography, Electron beam direct write lithography, Monte Carlo methods, Critical dimension metrology, Tungsten
Direct write electron-beam (e-beam) lithography, which has the maskless patterning capability and the quick turnaround for new device designs and design changes, has been applied to making the engineering samples for the development of the System on Chip products (SoC). Using the e-beam lithography to the multilevel interconnect metal was known to be evaluate in view of cost and throughput. In the case of the high-energy e-beam lithography, however, the backscattered electron from the metal caused a significant proximity effect.
Authors evaluated the e-beam proximity effect using the accelerating voltage 50keV on some multi-level interconnect metal structures which consist in tungsten wiring, or Cu wiring. It was found that the backscattering range and the ratio of the backscattering energy to the incident energy depend on the thickness of metal, but also on the distance from the resist to the metal.
Therefore authors propose a new method of evaluating e-beam lithography property, concept of "EB-tree". That indicates the wafer backscatter property that has heavy metal wiring using e-beam lithography. EB-tree shows the relations of wafer backscatter range and heavy metal thickness, ratio of the backscattering energy and heavy metal thickness. EB-tree could show wafer property cause of lower levels layout, understructure metal wiring, that must be taken into account when e-beam lithography.
In the application of the high-energy electron-beam (e-beam) lithogrpahy to the multi-level interconnect metal; the backscattered electron from the heavy metal previously patterned in lower levels on the substrate causes a significant proximity effect. We estimated the "inter-level" proximity effect in the e-beam exposure with the accelerating voltage of 50kV on some multi-level interconnect metal structures which consist in aluminum wiring and tungsten plugs. It was found that the backscattering range and the backscattering energy ratio to the incident energy depend not only on the density and thickness of metal but also on the distance between the resist and the heavy metal plugs. In this paper, a novel proximity effect correction algorithm is proposed, where the exposing patterns are divided into some classes according to the metal structure, the total backscattering energy deposited in the resist is expressed by the sum of the backscattering energy from each structural class, and the exposrue dose is modulated by the function of the total backscattering energy.
A high-speed wind tunnel, made by using a Ludwieg tube, has been successfully developed for a highly repetitive discharge-pumped excimer laser. This apparatus allows the gas flow of velocity approximately 204 m/s, pressure approximately 293 kPa, temperature approximately 254 K, and duration time approximately 48 ms. The rate constant for the recombination process of Xe+ + Cl- + Ne yields XeClX + Ne is found to increase to a maximum of 4.2 X 10-6 cm3/s at 180 K in a gas pressure of 294.2 kPa. The kinetic simulation of XeCl excimer laser using such a rate constant indicates the enhancement of the laser output in the lower gas temperatures.
The breakdown characteristics of a short-distance discharge gap in an atmosphere by TEA- CO2 laser have been studied to control the lightning artificially. It is efficient to enhance the probability of electrical breakdown induced if the focal point is set behind the discharge gap axis or near the negative high-voltage electrode. The length of the optical-breakdown plasma channel is elongated by using the micro-particles diffused in an atmosphere. Using 3 micrometers -diam. aluminum particles, the optical-breakdown threshold is lowered to 15 MW/cm2 compared to 0.5 GW/cm2 in the absence of the micro-particles.
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