In electron beam writing on EUV mask, it has been reported that CD linearity does not show simple signatures as
observed with conventional COG (Cr on Glass) masks because they are caused by scattered electrons form EUV mask
itself which comprises stacked heavy metals and thick multi-layers. To resolve this issue, Mask Process Correction
(MPC) will be ideally applicable. Every pattern is reshaped in MPC. Therefore, the number of shots would not increase
and writing time will be kept within reasonable range. In this paper, MPC is extended to modeling for correction of CD
linearity errors on EUV mask. And its effectiveness is verified with simulations and experiments through actual writing
In order to support complex optical masks today and EUV masks in the near future, it is critical to correct mask
patterning errors with a magnitude of up to 20nm over a range of 2000nm at mask scale caused by short range mask
process proximity effects. A new mask process correction technology, MPC+, has been developed to achieve the target
requirements for the next generation node. In this paper, the accuracy and throughput performance of MPC+ technology
is evaluated using the most advanced mask writing tool, the EBM-70001), and high quality mask metrology .
The accuracy of MPC+ is achieved by using a new comprehensive mask model. The results of through-pitch and
through-linewidth linearity curves and error statistics for multiple pattern layouts (including both 1D and 2D patterns)
are demonstrated and show post-correction accuracy of 2.34nm 3σ for through-pitch/through-linewidth linearity.
Implementing faster mask model simulation and more efficient correction recipes; full mask area (100cm2) processing
run time is less than 7 hours for 32nm half-pitch technology node.
From these results, it can be concluded that MPC+ with its higher precision and speed is a practical technology for the
32nm node and future technology generations, including EUV, when used with advance mask writing processes like the
In order to comply with the demanding technology requirements for 45 nm half pitch (HP) node (32 nm technology
node), Nuflare Technology Inc. (NFT) has developed Electron-beam mask writing equipment, EBM-6000, with
increased current density (70A/cm2), while its other primary features basically remain unchanged, namely 50 kV
acceleration voltage, Variable Shaped Beam (VSB)/vector scan, like its predecessors [1-5]. In addition, new
functionalities and capabilities such as astigmatism correction in subfield, optimized variable stage speed control,
electron gun with multiple cathodes (Turret electron gun), and optimized data handling system have been
employed to improve writing accuracy, throughput, and up-time. VSB-12 is the standard input data format for
EBM-6000, and as optional features to be selected by users, direct input function for VSB-11 and CREF-flatpoly
are offered as well.
In this paper, the new features and capabilities of EBM-6000 together with supporting technologies are reported to
solidly prove the viability of EBM-6000 for 45 nm HP node.
EBM-5000 equipped with the new feature of high current density (50A/cm2) has been developed for 45 nm technology node (half pitch (hp) 65 nm). EBM-5000 adopts 50 kV variable shaped electron beam (VSB)/vector scan architecture and continuous motion stage, following the steps of preceding EBM series. In addition to the high current density, new technologies such as high resolution electron optics, finer increment for beam position and exposure time control, and new data format "VSB-12" to handle large data volume have been introduced on EBM-5000. These new technologies address two conflicting issues: improvement of throughput and better accuracy. This paper will report the key challenging technologies, certain results of EBM-5000 operation and findings obtained through our development efforts that can be applied to future generation tools. The fundamental local CD uniformity (LCDU) limit is also discussed.
Mask data preparation (MDP) is a complicated process because many kinds of EB data files and jobdeck data files are used in mask manufacturers and EB data files continue to become bigger. Therefore we have developed unified mask data formats for Variable-Shaped-Beam (VSB) EB writers with efficient data compaction. The unified mask data formats are composed of a pattern data format for EB writers named "NEO" and a layout format named "MALY". We released NEO and MALY on April 2003. To evaluate NEO and MALY, we have made a prototype system of MDP such as a converter from design data to NEO/MALY and converters from NEO/MALY to each EB data. We have evaluated about functions and performance of the MDP flow using real design data in device manufacturers. As a result, some improvements in NEO and MALY were achieved and we have revised the specification of NEO and MALY as the final version. We have confirmed that NEO and MALY can be used for a set of unified mask data formats among VSB EB writers and can reduce complexity of mask data handling in mask manufacturers. They will be put to practical use in MDP flow.
Mask data preparation is a complicated process because many kinds of pattern files and jobdeck files flow into mask manufacturers. This situation has a significant impact on data preparation operations especially in mask manufacturers. In this paper, we propose a solution to this problem: use of unified mask data formats for EB writers and a model of data preparation flow from a device manufacturer to an EB writer. The unified formats consist of pattern data format named "NEO", and mask layout format named "MALY".
NEO is a stream format which retains upper compatibility to GDSII and has higher compression rate than GDSII. NEO is intended to be a general input format of Variable-Shaped-Beam (VSB) mask writers in principle, not particularly designed for any specific equipment or software. Data conversion process between mask writers being taken into account, NEO requires some constraints for VSB mask writers, such as removal of overlapping figures. Due to many differences in jobdeck syntax and functions among mask writers, it is a complicated task to edit or modify a jobdeck, and convert it into another format. MALY is a text-based format whose purpose is to standardize mask layout information among mask writers. This unification of mask layout information optimized for EB writers is expected to reduce workload of mask data preparation significantly. Besides the information described in MALY, some other information specific to the target EB writer, such as drawing parameters, has to be prepared separately. This paper illustrates a model of data flow and benefits of using these unified formats. The format and the data flow are effective in reducing data handling cost, providing flexible data handling solution. Applying the handling flow using NEO and MALY would result in reducing the load on mask manufacturers. Moreover, device manufacturers would be freed from the need to specify the mask writer to be used when ordering masks to mask manufacturers.
Mask data preparation (MDP) systems are becoming more and more complicated due to increasing demand for higher resolution, and more commonly adopted technique of optical proximity correction (OPC). Conventionally, as a standard format to describe mask patterns, GDSII has been widely used in the EDA field as well as in the mask production field. These days, however, GDSII is revealing its disadvantage in terms of efficiency in data compaction. On the other hand, mask pattern data in a variety of formats, including GDSII, are flowing into mask manufacturers, and this is making their process extremely complicated.
In this paper, we propose a unified format, tentatively named "GDSII-NEO." GDSII-NEO is designed to retain GDSII upper compatibility in consideration of the utilization of existing GDSII data and to have several times higher compression rate than GDSII. GDSII-NEO can be seen as a multi-purpose format used widely in the EDA and mask field. An intended use, among others, of this format is to describe the pattern data fed into Electron Beam (EB) mask writers.
Toshiba and Toshiba Machine have developed an advanced electron beam writing system EX-11 for next-generation mask fabrication. EX-11 is a 50 kV variable-shaped beam lithography system for manufacturing 4x masks for 0.15 - 0.18 micrometer technology generation. Many breakthroughs were studied and applied to EX-11 to meet future mask-fabrication requirements, such as critical dimension and positioning accuracy. We have verified the accuracy required for 0.15 - 0.18 micrometer generation.
We have developed a new method of preparing pattern data to increase throughput of an EB writing system. The main idea is to expand cells smaller than a threshold size to the corresponding upper level cells during hierarchical shape data operations, which leads to reduction of the number of subfields and shots in our EB writing system. The cell expansions, however, could cause increase in the data volume and data conversion time as a result of destroying the hierarchy of CAD data. Therefore, we have introduced an additional rule, that is, not to expand cell arrays which have more elements than a threshold number. The new data conversion processor, which adopts the above-mentioned cell expansion algorithm, has been applied to a 64Mbit and a 256Mbit DRAM. The new module was applied to three layers, that is, the trench layer, the gate poly layer and metal layer of each DRAM. As a result, we found that the number of subfields and the number of shots were reduced by about 60% and 35%, respectively, for the average of 6 layers. Resulting throughput was evaluated as 1.8 times for the average of 6 layers. Performance change in the conversion processor has been examined in terms of data volume and data conversion time, and is discussed in the paper.
The critical dimension uniformity required in the fabrication of photomasks for 1 gigabit DRAMs will be more stringent that 20 nm in terms of 3 sigma. High-voltage variable-shaped e-beam (VSB) writing is advantageous because of its high resolution, linewidth stability, and throughput performance. However, stitching errors in VSB writing have been a critical problem in the fabrication of advanced photomasks. In this paper, an improved method to calibrate the size of a VSB shot and reduce shot stitching errors is proposed. The accuracy of the calibration method depends on that of the linewidth measurement system, and shot-size calibration with an accuracy of +/- 10 nm can be achieved using existing measurement systems. The positioning accuracy of VSB shots was enhanced by a multiple pass exposure scheme. With these procedures applied to a 50 kV VSB system, the linewidth variation of a photomask in a local area such as a square region of 200 micrometers X 200 micrometers was reduced to less than 20 nm.