Photomask lithography for the 22nm technology node and beyond requires new approaches in equipment as well as
mask design. Multi Shaped Beam technology (MSB) for photomask patterning using a matrix of small beamlets instead
of just one shaped beam, is a very effective and evolutionary enhancement of the well established Variable Shaped Beam
(VSB) technique. Its technical feasibility has been successfully demonstrated [2]. One advantage of MSB is the
productivity gain over VSB with decreasing critical dimensions (CDs) and increasing levels of optical proximity
correction (OPC) or for inverse lithography technology (ILT) and source mask optimization (SMO) solutions. This
makes MSB an attractive alternative to VSB for photomask lithography at future technology nodes.
The present paper describes in detail the working principles and advantages of MSB over VSB for photomask
applications. MSB integrates the electron optical column, x/y stage and data path into an operational electron beam
lithography system. Multi e-beam mask writer specific requirements concerning the computational lithography and their
implementation are outlined here. Data preparation of aggressive OPC layouts, shot count reductions over VSB, data
path architecture, write time simulation and several aspects of the exposure process sequence are also discussed.
Analysis results of both the MSB processing and the write time of full 32nm and 22nm node critical layer mask layouts
are presented as an example.
CD control requirements for advanced node masks are in the low single digit nanometer range. CD control for Variable
Shaped Beam (VSB) lithography that is used to manufacture these masks is dependent on the post-fracture figure layout.
Shot linearity, shot size repeatability, and shot placement repeatability can affect CD control differently based on the
figure layout. The potential CD error contribution from poorly optimized fracture strategies thus can be a significant
contributor to the total CD error.
In this paper we present a set of fracture quality metrics based on the impact on mask CD control and methods using
EDA software to grade fracture strategies based on these fracture quality metrics. We also discuss applications of this
metric for fracture tool design and the implementation of different fracture strategies into mask manufacturing including
examinations of the predictability of fracturing results. Finally, we will discuss the usage of existing information about
the design (such as design intent) in conjunction with the proposed quality metrics to judge different fracture strategies.
Mask data file sizes are increasing as we move from technology generation to generation. The historical 30% linear
shrink every 2-3 years that has been called Moore's Law, has driven a doubling of the transistor budget and hence feature
count. The transition from steppers to step-and-scan tools has increased the area of the mask that needs to be patterned.
At the 130nm node and below, Optical Proximity Correction (OPC) has become prevalent, and the edge fragmentation
required to implement OPC leads to an increase in the number of polygons required to define the layout. Furthermore,
Resolution Enhancement Techniques (RETs) such as Sub-Resolution Assist Features (SRAFs) or tri-tone Phase Shift
Masks (PSM) require additional features to be defined on the mask which do not resolve on the wafer, further increasing
masks volumes. In this paper we review historical data on mask file sizes for microprocessor, DRAM and Flash memory
designs. We consider the consequences of this increase in file size on Mask Data Prep (MDP) activities, both within the
Integrated Device Manufacturer (IDM) and Mask Shop, namely: computer resources, storage and networks (for file
transfer). The impact of larger file sizes on mask writing times is also reviewed. Finally we consider, based on the trends
that have been observed over the last 5 technology nodes, what will be required to maintain reasonable MDP and mask
manufacturing cycle times.
CD requirements for advanced photomasks are getting very demanding for the 100 nm-node and below; the ITRS roadmap requires CD uniformities below 10 nm for the most critical layers. To reach this goal, statistical as well as systematic CD contributions must be minimized. Here, we focus on the reduction of systematic CD variations across the masks that may be caused by process effects, e.g. dry etch loading.
CD requirements for advanced photomasks are getting very demanding for the 100 nm-node and below; the ITRS roadmap requires CD uniformities below 10 nm for the most critical layers. To reach this goal, statistical as well as systematic CD contributions must be minimized. Here, we focus on the reduction of systematic CD variations across the masks that may be caused by process effects, e.g. dry etch loading. We address this topic by compensating such effects via design data correction analogous to proximity correction. Dry etch loading is modeled by gaussian convolution of pattern densities. Data correction is done geometrically by edge shifting. As the effect amplitude has an order of magnitude of 10 nm this can only be done on e-beam writers with small address grids to reduce big CD steps in the design data. We present modeling and correction results for special mask patterns with very strong pattern density variations showing that the compensation method is able to reduce CD uniformity by 50-70% depending on pattern details. The data correction itself is done with a new module developed especially to compensate long-range effects and fits nicely into the common data flow environment.
Within the past decades data file sizes and the related computing power for mask data preparation grew linearly following Moore’s law. However, within the last two years the balance between rising data complexity and computing equipment became unstable due to the massive introduction of OPC and the broad rollout of complex variable shaped beam (VSB) data formats. The disturbance of the former linear coherence led to exploding data conversion times (exceeding 100 hours for a single layer) accompanied by heavily escalating data volumes. A very promising way out of that dilemma is the recently announced introduction of distributed job processing within the mask data processing flow. This way was initially introduced to fracture flat jobs. Building on our first promising results last year we now implemented a fully automated design flow with an integrated Linux based cluster for distributed processing. The cluster solution is built in an automated environment in coexistence with our conventional SUN servers. We implemented a highly reliable DP flow on a large scale base which became as stable as our former Solaris SUN system. In the meanwhile we reached a job first time success rate exceeding 99%. After reaching a very stable state we recently started to extend our flat processing conversion steps by investigating hierarchical distributed processing in CATS version 23. We also report on benchmark results comparing new promising hardware configurations to further improve the cluster performance.
Raster scan pattern generators have been used in the photomask industry for many years. Methods and software tools for data preparation for these pattern generators are well established and have been integrated into design flows with a high degree of automation. But the growing requirements for pattern fidelity have lead to the introduction of 50 kV variable shaped beam pattern generators. Due to their different writing strategy these tools use proprietary data formats and in turn require an optimized data preparation. As a result the existing design flow has to be adopted to account for these requirements. Due to the fact that cycle times have grown severely over the last years the automation of this adopted design flow will not only enhance the design flow quality by avoiding errors during manual operations but will also help to reduce turn-around times. We developed and implemented an automated design flow for a variable shaped beam pattern generator which had to fulfill two conflicting requirements: Well established automated tools originally developed for raster scan pattern generators had to be retained with only slight modifications to avoid the (re)implementation and the concurrent usage of two systems while on the other hand data generation especially during fracturing had to be optimized for a variable shaped beam pattern generator.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.