Junji Hirumi

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.

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.

Extending OASIS for the unification of mask data representation

The diversification of mask making equipment in modern mask manufacturing has led to a large variety of different mask writing and inspection formats. Dispositioning the equipment and managing the data flow has turned into a challenging task. The data volumes of individual files used in the manufacture of modern integrated circuits have become unmanageable using established data format specifications. Several trends explain this: size, content and complexity of the designs are growing; the application of RET increases the vertex counts; complex data preparation flows post tape-out result in a large number of intermediate representations of the data. In addition assembly steps are introduced prior to mask making for leveling critical parameters. Despite the continuous effort to improve the performance of the individual tools that handle the data, is has become apparent that enhancements to the entire flow are necessary to gain efficiency. One concept suggested is the unification of the mask data representation: establishing a common format that can be accepted by all tools. This facilitates a streamlining of data prep flows to eliminate processing overhead and repeated execution of similar functions. OASIS, the new stream format developed under the sponsorship of SEMI, has the necessary features to full-fill the role of a common format in mask manufacturing. The paper describes the implementation of OASIS as a common intermediate format in the mask data preparation flow as well as its usage with additional restrictions as a common Variable-Shaped-Beam mask writer format. The benefits are illustrated with experimental results. Different implementation scenarios are discussed.

The study of high-speed electron beam deflection technology for VSB writers

The shortening of electron beam settling time is important for the shortening of writing time of variable-shaped beam (VSB) writers. The settling time is the time until the electron beam is deflected to a desired position, and is settled. In the case of electrostatic deflector, the electron beam is deflected in proportion to the voltage to which the amount of deflections is supplied. The Digital-Analog converter and Amplifier (DAC/Amp) circuit supplies voltage required for deflector and, in order to shorten a settling time; it is necessary to accelerate operation of a DAC/Amp circuit. Especially, the amplifier operation speed should be accelerated. The performances required of amplifier are high-speed operation and high-voltage operation. The key technology for high speed and high voltage operation of amplifier is the development of high speed, high voltage operation transistor. Although these two performances are the relation of a trade-off, the transistor that has attained our required performances dose not exists. For this reason, we started from joint development of the transistor, which had attained the required performances. Furthermore, we developed the trial peace amplifier using the developed transistor and evaluated. In addition to these results, we will also report the result of the throughput evaluation using the pattern for supposing the 65nm node device pattern.

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.