Koki Kuriyama

UV NIL template making and imprint evaluation

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 100keV acceleration voltage spot beam EB writer process, we have achieved down to 16nm 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). At the same time, UV NIL exploration has reached the step of feasibility study for mass production, and full chip field masks have been required, though the resolution demand is not as tough as for the extremely advanced usage mentioned above. The 100kV EB writers are adopting spot beams to generate the pattern and have a fatally low throughput if we need full chip writing. So for full chip masks, we have started the adoption of 50keV variable shaped beam (VSB) EB writers, which are used in current 4X photomask manufacturing In this paper, we will show latest results both with the 100kV spot beam writer and the 50keV VSB EB writers. With the 100kV spot beam writer, we achieved 16nm resolution, but found that to achieve further improvement, an innovation in pattern generation method or material would be inevitable. With the 50kV VSB writers, we could 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. Eventually, NIL is coming closer to production stage. We will also start the discussion about the infrastructures necessary for NIL mask manufacturing in this paper.

Shot number analysis at 65-nm node mask writing using VSB writer

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.

UV NIL mask making and imprint evaluation

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.

Advanced mask rule check (MRC) tool

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 datas 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.

Evaluation of OASIS.VSB (SEMI P44) for practical use

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 OASISTM (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).

The unified mask data format based on OASIS for VSB EB writers

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.

Evaluation of mask data preparation with OASIS and P10

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 manufacturers 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.

Enhancement of unified mask data formats for EB writers

We have developed a unified mask data format named “OASIS.NEO1” for Variable-Shaped-Beam (VSB) EB writers as enhancement of unified mask data format named “NEO2”. OASIS.NEO is a pattern data format based on OASISTM3 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.NEO4”. In this paper we proposed the specification of OASIS.NEO.