Resist debris formation and proximity exposure effect in electron beam lithography
04 Apr 2000-Journal of Vacuum Science & Technology B (American Vacuum Society)-Vol. 18, Iss: 2, pp 873-876
TL;DR: In this article, the formation of unsupported resist microfragments called resist debris (RD) over the exposed pattern areas in EBL is found to predict proximity exposure (PE) effects.
Abstract: Deliberate formation of unsupported resist microfragments called resist debris (RD) over the exposed pattern areas in electron beam lithography (EBL) is found to predict proximity exposure (PE) effects. Some simulation results and corresponding experimental results on RD formation discussed in the article show that both intra- and interpattern PE effects can be observed and explained from the nature of RD distribution. This gives a different kind of tool to tackle the problem of PE effect in EBL.
Citations
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TL;DR: The phenomenon of resist debris (RD) formation is shown to be a useful method for proximity exposure (PE) effect analysis in electron beam lithography as discussed by the authors, and some unique features associated with the method have direct relevance with the electron beam exposure parameters assumed in the simulation work.
Abstract: The phenomenon of resist debris (RD) formation is shown to be a useful method for proximity exposure (PE) effect analysis in electron beam lithography. Some simulation results and corresponding experimental results discussed in this article on RD formation over the electron beam exposed pattern areas before and after PE effect correction reveal certain unique features associated with the method. These unique features of the method have direct relevance with the electron beam exposure parameters assumed in the simulation work, their implementation during the experiments, pattern shape-spacing fidelity, and also the correction scheme used for the PE effect correction.
References
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TL;DR: In this article, a simple technique for the computation of the proximity effect in electron-beam lithography is presented, which gives results of the exposure intensity received at any given point in a pattern area using a reciprocity principle.
Abstract: A simple technique for the computation of the proximity effect in electron‐beam lithography is presented. The calculations give results of the exposure intensity received at any given point in a pattern area using a reciprocity principle. Good agreement between the computed results and experimental data was achieved.
459 citations
TL;DR: In this article, three corrections techniques are discussed: shape-dimension adjustment, region compensation, and self-consistent technique to compensate for proximity effects in regions between shapes, which leads to computational complexities and impracticalities.
Abstract: Electron lithography at micrometer dimensions suffers from a seemingly fatal problem due to proximity effects. Three corrections techniques are discussed. The self‐consistent technique computes the incident electron exposure such that identical average specific fragmentation occurs in each written shape of the pattern. A unique solution, that depends only on the form and on the magnitude of proximity function, is obtained. The unaddressed‐region compensation technique attempts to compensate for proximity effects in regions between shapes; this, however, leads to computational complexities and impracticalities. The shape‐dimension adjustment technique attempts to compute dimension of exposed shapes such that the shapes developed in the resist will have the designed dimension. A set of nonlinear (and impractical) equations are obtained in this case. The implementation of these techniques and the experimental results obtained therefrom are the subject of the two succeeding papers.
146 citations
TL;DR: In this article, a mathematical model for the exposure of electron-sensitive resists where an electron beam is incident normal to a substrate coated with a thin layer of resist is presented, and the resulting contours predict the undercutting effect experimentally observed for the 5-20-keV beam energies studied.
Abstract: We present a mathematical model for the exposure of electron-sensitive resists where an electron beam is incident normal to a substrate coated with a thin layer of resist. We include both the scattering of the incident electrons as they penetrate the resist and the electrons backscattered from within the resist and from the substrate. The calculations yield contours of equal absorbed energy density, and these are interpreted as the contours which bound the resist after development. The absorbed energy density is found as the sum, for all electrons, of the product of the energy absorbed per unit length of trajectory and the flux density of electrons at the point in question. We first calculate the absorbed energy density for an electron beam of vanishingly small cross section (an incident delta function) and then convolve that result with a beam of Gaussian current-density distribution to obtain the reSult for a single beam location. For poly(methyl methacrylate) resist, we study the achievable dot resolution, as a function of the incident charge, for various incident energies-and substrates. Since our main interest is in computer-controlled resist exposures in which patterns are generated as a succession of dots, we calculate the absorbed energy density contours for a line generated in that manner. Detailed comparison is made with the experimental results of Wolf et al., by fitting a single point on one contour at one beam energy to account for the unknown developer sensitivity. The resulting contours predict the undercutting effect experimentally observed for the 5-20-keV beam energies studied. The developed shape and linewidth are found to be nonlinear functions of the incident charge per unit length. Experimental data for the linewidth at 20 keV are presented and compared with theory.
69 citations
TL;DR: In this paper, a series of experiments of scanning electron beam exposure of PMMA films on silicon, copper, and gold substrates is described, and compared with the calculations of Monte Carlo and analytic models of energy dissipation per unit volume.
Abstract: A series of experiments of scanning electron beam exposure of PMMA films on silicon, copper, and gold substrates is described, and compared with the calculations of Monte Carlo and analytic models of energy dissipation per unit volume. Film thickness was varied from 1000 to 10 000 A, accelerating voltage from 10 to 20 kV, and linear charge density from 1×10−9 to 1×10−5 C/cm. Good agreement was obtained in the comparison with the predictions of Monte Carlo calculations, whereas some discrepancies were observed in the comparison with the analytic models. The assumption inherent in the theoretical approaches that PMMA acts like a linear recording medium, in the sense that exposure is additive, is experimentally evaluated by means of an Abel inversion. The assumption that developed profiles represent surfaces of equal energy dissipation was examined by means of a computer simulation of the development process.
49 citations
TL;DR: In this article, a computer-controlled scanning electron microscope (CCSEM) was used to expose polymethyl methacrylate (PMM) in a resist form for microelectronic device fabrication and in bulk form to determine energy dissipation profiles.
Abstract: In modern microelectronics, complicated structures with very small dimensions must be fabricated on active-device materials. This task has been traditionally accomplished by photolithographic techniques, but electron-beam exposure of resist materials has recently been explored [1]-[3]. Submicron electron devices have been fabricated in several laboratories, often featuring a flying-spot scanner to generate the pattern being exposed [4]-[7]. Paper tape drives have been used for repetitive patterns [8], and computer control of the electron beam has been reported also [1], [9]. The electron resist that has shown the highest resolution to date appears to be poly-(methyl methacrylate) (PMM). We have used this material in a resist form for microelectronic device fabrication, and in bulk form to determine energy dissipation profiles. The exposure is performed with a computer-controlled scanning electron microscope (CCSEM). In this paper, we describe the electron beam system briefly, discuss the processes involved in resist exposure and development, describe our exposure procedures using the CCSEM, and show results of fabricated devices and energy dissipation studies.
33 citations