UV NIL shows excellent resolution capability with remarkable low line edge roughness, and has been attracting
pioneers in the industry who were searching for the finest patterns.
We have been focused on the resolution improvement in NIL template making with a 100keV acceleration voltage
spot beam EB writer process, and have established a template making process to meet the requirements of the pioneers.
Usually such templates needed just a small field (several hundred microns square or so).
Now, for several semiconductor devices, the UV NIL is considered not only as a patterning solution for R&D
purpose but eventually as a potential candidate for production, and instead of a small field, a full chip field mask is
required. Although the 100kV EB writers have excellent resolution capability, they are adopting spot beams (SB) to
generate the pattern and have a fatally low throughput if we need full chip writing.
In this paper, we are focusing on the 50keV variable shaped beam (VSB) EB writers, which are used in current 4X
photomask manufacturing. The 50keV VSB writers can generate full chip pattern in a reasonable time, and by choosing
the right patterning material and process, we achieved resolution down to 28nm.
UV NIL shows excellent resolution capability with remarkable low line edge roughness, and has been attracting pioneers in the industry who were searching for the finest patterns.
We have been focused on the resolution improvement in mask making, and with a 100kV acceleration voltage EB writer process, we have achieved down to 18nm resolution, and have established a mask making process to meet the requirements of the pioneers. Usually such masks needed just a small field (several hundred microns square or so).
Now, UV NIL exploration seems to have reached the step of feasibility study for mass production. Here, instead of a small field, a full chip field mask is required, though the resolution demand is not as tough as for the extremely advanced usage. The 100kV EB writers are adopting spot beams to generate the pattern and have a fatally low throughput if we need full chip writing.
In this work, we focused on the 50keV variable shaped beam (VSB) EB writers, which are used in current 4X photomask manufacturing. The 50kV VSB writers can generate full chip pattern in a reasonable time, and by choosing the right patterning material and process, we could achieve resolution down to 32nm. Our initial results of 32nm class NIL masks with full chip field size will be shown and resolution improvement plan to further technology nodes will be discussed.
Over the last 5 years, Japanese consortium, Semiconductor Leading Edge Technologies Inc. (Selete), lead the way in developing unified mask data format. Specification of the format was released as OASIS.VSB and registered to SEMI standard, P44. It is expected that using OASIS.VSB would reduce TAT and improve efficient usage of data infrastructure. OASIS.VSB has advantages for mask data preparation since OASIS.VSB is based on OASIS<sup>TM</sup> (SEMI P39) and OASIS compliant software is already commercially available. Although fundamental evaluation of OASIS.VSB have been made by Selete on technical feasibility with VSB mask writers, its performance and advantage of data handling improvement is still controversial. We have been evaluating OASIS.VSB in order to estimate the impact of data handling improvement at mask manufacturer. Figure 1 shows that OASIS.VSB has good compression ratio compared to certain VSB mask data format. Although compression ratio partly depends on data and conversion software, OASIS.VSB is about 0.7 times as small as VSB data format on weighted basis average. Furthermore, we have confirmed by simulation that OASIS.VSB can hardly affect shot count and writing time.
Unification of mask data format by OASIS.VSB can realize flexible mask data preparation (MDP) and reduce a cost of data storage. To achieve further TAT reduction, it is necessary to apply OASIS.VSB to not only mask writing data but other mask making processes such as die to database inspection and mask rule check (MRC).
As patterns on photomasks are getting more complex due to RET technologies, mask rule check (MRC) has become an essential process before manufacturing photomasks. Design rule check (DRC) tools in the EDA field can be applied for MRC. However, photomask data has unique characteristics different from IC design, which causes many problems when handling photomask data in the same way as the design data.
In this paper, we introduce a novel MRC tool, SmartMRC, which has been developed by SII NanoTechnology in order to solve these problems and show the experimental results performed by DNP. We have achieved high performance of data processing by optimizing the software engine to make the best use of mask data's characteristics. The experimental results show that only a little difference has been seen in calculation time for reversed pattern data compared to non-reversed data. Furthermore, the MRC tool can deal with various types of photomask data and Jobdec in the same transparent way by reading them directly without any intermediate data conversion, which helps to reduce the overhead time. Lastly it has been proven that result OASIS files are several times smaller than GDS files.
We have developed a unified mask data format named “OASIS.VSB” for Variable-Shaped-Beam (VSB) EB writers. OASIS.VSB is the mask data format based on OASIS released as a successive format to GDSII by SEMI. We have defined restrictions on OASIS for VSB EB writers to input OASIS.VSB data directly to VSB EB writers just like the native EB data. We confirmed there was no large problem in OASIS.VSB as the unified mask data format through the evaluation results. The latest version of OASIS.VSB specification has been disclosed to the public in 2005.
OASIS (Open Artwork System Interchange Standard) is the new stream format to replace conventional GDSII and has become a SEMI standard 2003. Also, some EDA software tools already support OASIS. OASIS can apply not only layout design field but also photomask industory. OASIS is effective to reduce data volume even if it is a fractured data, therefore it is expected to solve file size explosion problem.
From mask manufacturer's perspective, it is also necessary to consider mask layout information. In present, there are various kinds of layout information and jobdeck formats. These circumstances require complicated data handling and preparation process at the mask manufacturers. Computerized automatic process needs to be more utilized to eradicate mistakes and miscommunications at the planning department. SEMI standard P10 (Specification of Data Structures for Photomask Orders) is one of the solutions. P10 is basically intended to communicate about mask order data which include layout information.
This paper reports the result of evaluation of mask data preparation unified with two SEMI standards: P39 (OASIS) and P10. We have developed a reticle pattern viewer (HOTSCOPE) which can view photomask data with combined OASIS with P10. Figure 1 shows connection between mask data formats, which include OASIS and P10 format with our reticle pattern viewer. HOTSCOPE provides reviewing mask data as a photomask image. It will interface between device manufacturers and mask manufacturers.
We have developed a unified mask data format named “OASIS.NEO<sup>1</sup>” for Variable-Shaped-Beam (VSB) EB writers as enhancement of unified mask data format named “NEO<sup>2</sup>”. OASIS.NEO is a pattern data format based on OASIS<sup>TM3</sup> released as GDSII replacement by SEMI. We have developed OASIS.NEO for practical use of unified mask data formats in mask data preparation (MDP) flow. For practical use, it is necessary to input OASIS.NEO data directly to VSB EB writers just like the native EB data. So we have defined restrictions on OASIS for VSB EB writers referring the restrictions in NEO based on GDSII named “GDSII.NEO<sup>4</sup>”. In this paper we proposed the specification of OASIS.NEO.
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 EB data files and jobdeck data files are used in mask manufacturers and EB data files continue to become bigger. Therefore we have started to develop new mask data format with efficient data compaction and unification among Variable-Shaped-Beam (VSB) EB mask writers. We have proposed the unified mask pattern data format for EB writers named "NEO"<sup>1</sup> in the 22nd annual BACUS symposium. We have proposed the unified mask layout format named "MALY" 2 and the high-compression data processing system3 for NEO in Photomask Japan 2003, too. Then we have decided to develop an enhanced mask data preparation system using NEO<sup>4</sup> and MALY<sup>5</sup>. This system has common MDP functions not to be related to each EB writer. That would be effective in reducing mask data handling cost. In this paper we introduce the abstract of NEO and MALY and new mask data preparation system using NEO and MALY.
Recently as the node size gets smaller into deep sub-micron, both chip designers and mask manufacturers have faced great problems as follows: (1) Explosion of the data size; (2) Further data complexity due to OPC or PSM; (3) Increasing numbers of data formats. Since these problems directly lead to the increase of the mask costs, we have thought that they need to be overcome from the viewpoint of data processing as well. Selete have made a proposal of a next generation EB handling format, called 'NEO', in order to cope with these issues. The greatest feature of NEO is its compaction capability of the data description and it is expected that the chip data size could be reduced far smaller than in any other existing EB formats. We have been working on the NEO project in cooperation with Selete and developed a new system 'GDS2NEO', which converts the conventional layout data described in GDSII to the NEO-formatted data. We also investigated the compaction efficiency of NEO with several sets of actual layout data using GDS2NEO. As the result, we have proved that NEO has an excellent efficiency of data compaction and GDS2NEO has achieved a satisfactory performance of data conversion. In this paper we present the concept of NEO format, the data processing flow and the basic algorithm of GDS2NEO, the experimental results and the future plans.
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.
It depends for the writing time of variable shaped electron-beam (VSB) writing system on the number of writing shots. For shortening of writing time, it is most effective to reduce the number of shots. However, Resolution Enhancement Technologies (RET), such as OPC and PSM, make the VSB shot number increase explosively, in addition to reduction of LSI pattern size, and worsens the writing throughput. This is a serious problem for VSB mask writer, and the improvement of a writing throughput is required. In order to solve this problem, we inquired towards diversifying beam shape only from a rectangle.
First, we investigated about the curtailment effect of the number of shots by trapezoid aperture adoption. Some latest VSB writer has adopted a triangle shaped aperture to compose the slanting figure in the LSI pattern efficiently. We investigated the efficiency of forming the slanting figure with trapezoid or parallelogram apertures compared with initial triangle aperture shot number. As the result of that, shown in Fig.1, we obtained the result that the shots number was reduced into 50% or more compared with initial triangle shots number. And, we examined a possibility of uniting and applying the character projection (CP) technique, which is adopted as EB direct writing (DW), to mask writing. Since pattern size is, for example, 4 times larger in the case of mask writing compared with the case of EBDW, the area that can extract a common CP pattern out from LSI patterns at mask writing is smaller than EBDW. Then, we extracted CP aperture pattern from cell library data for logic LSI. We obtained the result, shown in Fig.2, that the shot number that was used CP aperture was reduced into about 35% compared with initial VSB shots number. However, the arrangement number of aperture has restriction, and if the arrangement number decreases, the curtailment rate of the shots number will fall. These two techniques are fundamentally effective in curtailment of writing shots number. Furthermore, we will discuss with the possibility of applying these techniques to mask writing and with some problems to solve for the application of these techniques.
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.