The reflection of back-scattered electrons (BSE) at the objective lens of an electron beam writer leads to a diffuse resist
exposure which extends over several millimetres. The deposed energy of this unintentional exposure is much lower than
the direct one. However, if the area of the direct electron beam exposure is large enough the accumulated energy is no
longer negligible and may cause significant CD variations. Therefore, it is of crucial importance to study possible ways
of reducing this dose contribution to a minimum and in order to perform a correct proximity correction targeting to
determine its radial distribution.
In this work a model of a 50kV E-Beam writer was developed, consisting of a resist-coated silicon wafer and an opposing low-reflection disk mounted at the pole piece of the objective lens. In order to improve the low-reflection disk, different material compositions as well as an optimized surface topography of the disk are modelled.
KEYWORDS: Vestigial sideband modulation, Electron beam direct write lithography, Electron beam lithography, Beam shaping, Scanning electron microscopy, Standards development, Lithography, Prototyping, Semiconducting wafers, Electron beams
The ever more demanding requirements in the semiconductor manufacturing sector together with the increasing mask making costs and cycle times call for new lithographic solutions. Electron beam lithography has shown its superior performance and flexibility in advanced patterning applications. It enables already today process and technology developments ahead of the ITRS roadmap, which addresses currently the 32nm and 22nm node or even below. Thus electron beam direct write (EBDW) can avoid the high costs and delay times related to the advanced masks required for critical layers.
On the other side EBDW faces the concerns regarding its throughput, which bases upon the inherited sequential exposure method. A solution to improve the throughput performance offers the implementation of the cell projection method as already materialized in the Vistec SB3055 tool. In addition to the variable shape beam technology, which can project regular structures (rectangles, slants and triangles) only, cell projection is able to image complex structures. Thus, structures that would have required a multiple of regular shots are now projected in one single shot. Thanks to this approach not only the shot count is noticeably reduced, but also the overall throughput is increased. First experimental and simulation results show an improvement of a factor of about 3X. Nevertheless, the final throughput gain strongly depends on the pattern and data structure itself.
Combining high resolution variable shape beam technology with the cell projection feature allows advanced R&D and small volume and prototyping applications to be performed with one system. The Vistec SB3055 features the high resolution capability of variable shape beam lithography and incorporates the advantages of the cell projection technology. Owing to this new option we are able to improve the throughput for standard design features while maintaining the required high accuracy of our exposure system. Beside this, the combination of cell projection and standard shape beam technology still offers a high degree of flexibility as the key advantage of EBDW.
On the Vistec SB3055 system we have performed different resolution tests serving as comparison between cell projection and standard shape beam. In this paper we will present the resolution capability obtained with cell projection on test structures as well as the general accuracy achieved for real patterns.
KEYWORDS: Sensors, Signal to noise ratio, Monte Carlo methods, Signal detection, Lithography, Etching, Scattering, Electron beams, Direct write lithography, Vestigial sideband modulation
In this work, we investigated possible geometry optimizations of backscattered electron (BSE) detectors in order to significantly improve the signal to noise ratio (SNR) of shallow Si-topographic marks. To achieve this, Monte Carlo simulations of the BSE angular distribution as well as of the BSE exit position were performed. A comparison of some theoretical calculations with the respective experimental results allowed us to qualify the theoretical results. Based on these results, we are able to present an optimized BSE detector design featuring a significant improvement of the measured SNR.
KEYWORDS: Optical alignment, Monte Carlo methods, Sensors, Silicon, Signal to noise ratio, Signal detection, Semiconducting wafers, Vestigial sideband modulation, Electron beam direct write lithography, Lithography
New types of alignment marks to be applied in electron beam direct write (EBDW) have been studied theoretically and
experimentally.
The dependence of signal contrast and signal form on such mark properties like step height, mark pitch and stack
material has been investigated in detail using Monte Carlo simulations.
The different alignment marks were etched in Si to different depths and the respective alignment repeatability was determined
with a Vistec SB3050 DW lithography tool. Finally, for the most promising mark, test exposures were performed
and the overlay determined.
In semiconductor industry time to market is one of the key success factors. Therefore fast prototyping and low-volume production will become extremely important for developing process technologies that are well ahead of the current technological level. Electron Beam Lithography has been launched for industrial use as a direct write technology for these types of applications. However, limited throughput rates and high tool complexity have been seen as the major concerns restricting the industrial use of this technology. Nowadays this begins to change. Variable Shaped Beam (VSB) writers have been established in Electron Beam Direct Write (EBDW) on Si or GaAs. In the paper semiconductor industry requirements to EBDW will be outlined. Behind this background the Vistec SB3050 lithography system will be reviewed. The achieved resolution enhancement of the VSB system down to the 22nm node exposure capability will be discussed in detail; application examples will be given. Combining EBDW in a Mix and Match technology with optical lithography is one way to utilize the high flexibility advantage of this technology and to overcome existing throughput concerns. However, to some extend a common Single Electron Beam Technology (SBT) will always be limited in throughput. Therefore Vistec's approach of a system that is based on the massive parallelisation of beams (MBT), which was initially pursued in a European Project, will also be discussed.
An easy way to pattern 65nm CD target, when optical lithography technology is not available, is to use an Electron Beam Direct Write tool (EBDW), which is well known for its high resolution patterning potentials, with the drawback of a very low throughput. Emerging techniques of electron projection lithography also propose the same patterning capability with enhanced throughput. One of the most crucial issues, when dealing with integration, is the overlay capability of the systems. This paper exposes the studies made on the overlay capability issue of the LEICA EBDW installed in STMicroelectronics (STM) production plant in Crolles (France) and proves our tool is ready to support the 65nm node technology development.
Electron beam (e-beam) lithography is one of the potential candidates for defining fine patterns smaller than 100 nm. To increase throughput, variably shaped beams with vector scan and cell projection techniques have been proposed on the e- beam system. In order to achieve high pattern fidelity in the e-beam lithography special care must be taken with respect to effects, that could result from shot-to-shot, subfield-to- subfield, and stripe boundaries. The key considerations on the pattern fidelity are dimension control and edge roughness. In this paper, methods to enhance pattern fidelity are proposed and discussed. A Leica's WEPRINT 200 system (Leica Microsystems Lithography GmbH), which exerts exposure while continuously moving the stage technique to increase throughput, is used for evaluating the effectiveness of these methods. For the dimension uniformity, the important task is to master shot butting, subfield and stripe stitching and counteract the proximity effects. By employing beam sizing for proximity effect correction and double-pass exposure to suppress stitching error, the dimension variation is largely eliminated. Several factors including accelerating voltage, beam size, proximity effect, beam blur due to Coulomb interaction, and process controllability are found to affect the CD accuracy. To improve the CD accuracy, pattern-bias compensation and proximity effect correction methods are employed in 0.1 micrometer range and below. Good results on dimension accuracy are obtained by properly considering the intra- and inter-proximity effects. Finally, the performance comparison between these methods is discussed.
It is now widely accepted that variable shaped beam ( VSB ) writers have some
significant advantages compared to the gaussian principle systems, especially
when throughput is considered. The ZBA variable shaped beam system
introduced in this paper is the most advanced mask generator from Jenoptik
Germany. We have utilized the VSB electron optical concept from the very
beginning of designing e-beam systems of the ZBA-series more than 20 years
ago. The unique combination of this longstanding experience, more than 120
systems were constructed and comissioned, with some very recent developments
in the software and operation logistics of the system, allow the ZBA31H
maskwriter system to provide the complete performance that is required to
satisfy the demands of the 1 G-DRAM generation masks.
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