For nearly all relevant applications of e-beam lithography the resolution and pattern quality requirements are
approaching or exceeding the limits of the available process. On one hand, for shrinking feature dimensions, the e-beam
proximity effect and process effects such as photo acid diffusion limit the pattern contrast and process window. On the
other hand, e-beam process related parasitic effects such as shot noise, fogging, developer loading, heating, charging, and
inhomogeneous bake introduce some significant errors. Even though e-beam tool and process tool suppliers continue to
implement new or improve current strategies to avoid or correct these effects, the amount of residual errors requires
some reasonable e-beam process window, in particular for high end applications.
For some patterns the undersize-overdose approach (SIZE) improves the pattern fidelity and process window. However,
for patterns with high fill factors this approach increases the overall deposited electron dose, which due to the increased
backscattering diminishes or even eliminates the advantages. The geometrically induced dose correction (GIDC) method
overcomes this issue by combining the SIZE concept with a short range framing technique, which reduces the deposited
dose in large filled pattern areas.
This paper provides a comparison of the standard, SIZE, and GIDC correction approaches for 1D test patterns as well as
production patterns. For a broad comparison, patterns were printed onto negative and positive chemically amplified
resists and on wafer and mask substrates using a Vistec SB352HR variable shape e-beam writer. Both wafers were also
The outcome of the study is that the SIZE and GIDC approaches often outperform the standard proximity effect
correction. For dense patterns, GIDC still provides a better pattern quality and process window, while the SIZE approach
suffers from the increased overall deposited electron dose and clearly falls behind GIDC in terms of process window.
Further it was shown that the lowering of the dose in inner areas due to GIDC does not impact the etch resistance.
The semiconductor industry and mask shops spend great efforts in order to keep pace with the requirements on pattern
fidelity of the ITRS lithography roadmap. Even for e-beam lithography - often referred to as technology with
"unlimited" resolution - the challenges increase with shrinking feature sizes in combination with applicable resist
processes. The pattern fidelity, specifically CD control, is crucial for the application of e-beam lithography.
One aspect in CD control is the intrinsic proximity effect of the electron beam. This together with other contributions
like influences from resist process or beam generation which are summarized altogether under the term process
proximity effect have to be corrected. An accurate e-beam process proximity effect correction is therefore a key
component of e-beam lithography.
Some process proximity effect correction algorithms provide not only accurate correction for the process proximity
effect induced pattern deformation but also optimize pattern contrast by adjusting geometry and dose simultaneously.
However, the quality of the process proximity effect correction is limited by the calibration accuracy of the used model,
i.e., the accuracy of the utilized process proximity function (PPF).
In a previous paper [R. Galler et al, "PPF - Explorer: Pointwise Proximity Function calibration using a new radialsymmetric
calibration structure", BACUS 2011] the PPF-explorer - a new experimental method for pointwise process
proximity function calibration - was introduced and some first promising calibration results were shown.
This paper presents the progress of the PPFexplorer proximity function calibration. This progress, among others,
comprises automatic generation of calibration patterns, including pre-correction with respect to a rough forecast of the
process proximity function to be calibrated. This pre-correction approach significantly reduces the number of necessary
calibration structures and the number of measurement sites, without sacrificing calibration accuracy. On the contrary, the
pre-correction has positive impact on the calibration quality, since it allows unifying the pattern contrast at the
measurement sites, which reduces the SEM measurement induced error.
We present the results of a PPFexplorer calibration with special focus on minimizing the number of measurement sites.
The results show that the PPFexplorer method can help to improve the proximity effect model calibration with
Lithographic patterning encounters growing challenges to meet the requirements of current and future semiconductor
technology nodes. Even e-beam lithography is challenged due to the physical characteristic of the whole transfer process
including the e-beam blur, electron scattering, and resist effects. These effects cause an unavoidable blurring of the
exposed shapes and are often described as process proximity effect. Besides the correction of this process proximity
effect pattern contrast and process window for the lithography step have to be regarded. There are promising approaches
for contrast enhancing proximity effect correction concepts. To enable a stable patterning great efforts have to be put into
decreasing the errors of all involved technologies.
The blurring resulting from the transfer process is usually described by a so-called process proximity function (PPF) and
mostly approximated by a superposition of two or more Gaussian functions. All algorithms for proximity effect
correction use that PPF to perform their correction. Thus, an accurate determination of that PPF contributes to reducing
the error budget of the proximity effect correction scheme. Several methods for PPF calibration were introduced in the
past. Some are based on modelling the transfer process and performing Monte Carlo simulations. Another common
approach is to design and expose calibration patterns, measure the resulting CDs, and obtain the process proximity
function as the result of a simulation based parameter fitting to a model function such as a sum of Gaussian functions. In
order to respect the increased accuracy requirements an even more accurate description of the PPF is expected.
This paper describes the newly developed PPF-explorer method for the calibration of a pointwise proximity function as a
complementary technique, which is based on the exposure and evaluation of new calibration layouts. Following the
common assumption that a process proximity function is radial-symmetric, we developed radial-symmetric calibration
For current and future semiconductor technology nodes with critical dimensions of 32 nm or below, the e-beam
lithography is faced with increasing challenges to achieve a reasonable patterning of structures, especially if a process
with a chemically amplified resist is used. The reasons for these limitations are the physical properties of the transfer
process used to print a structure onto the resist-coated substrate, which inherently contains an unavoidable blurring of the
deposited e-beam energy around the desired shape. This blurring is usually described by a so called process proximity
function (PPF) and mostly approximated by a superposition of two or more Gaussian functions. The PPF includes the e-beam
blur, electron forward scattering and resist effects (often described altogether by the so called alpha parameter of
the PPF [K. Keil et al, "Resolution and total blur: Correlation and focus-dependencies in e-beam lithography," J. Vac.
Sci. Technol. B 27, 2722 (2009)]) as well as the backscattering effect (often described by the so called beta parameter of
the PPF). When the desired critical dimensions of structures are near or below the alpha parameter of the PPF, depending
on their environment it may be just impossible to print the structures because of the vanishing image contrast. The PPF
model confirms this well-known behavior but also shows ways and limits for improvements.
This paper provides real pattern lithography results - comparing classical and GIDC correction - for exposures done on a
Vistec SB3050DW shaped e-beam writer. A performance comparison of the GIDC method and the classical dose
correction in terms of data preparation and writing time is presented.
The e-beam lithography is faced with increasing challenges to achieve a satisfying patterning of structures with critical dimensions of
about 32 nm or below. The reason for this issue is the unavoidable blurring of the deposited e-beam energy due to beam blur, electron
scattering (forward and backward), and resist effects. The distribution of the finally deposited dose differs from the dose weighted
geometry of the printed layout. In general, the finally deposited dose is described as convolution of the layout with a process specific
proximity function being a model for the unavoidable blurring. This process proximity function (PPF) is often approximated by a
superposition of two or more Gaussian functions. Thus, the electron forward scattering and resist effects, being most critical to the
pattern fidelity, are often described altogether by the so called alpha-parameter of the PPF. Due to these physical reasons, when the
desired critical dimension of a structure is near or below the alpha-parameter of the PPF, it may be just impossible to print the
structure because of the vanishing image contrast due to the blurring.
It was shown by means of the simulation feature of the ePLACE data prep package that in this situation a modification of both the
geometry and the dose assignment of the shapes will significantly increase the contrast of the deposited energy and thus, even preserve
the printability of critical structures. This geometrically induced dose correction (GIDC) method is implemented in the ePLACE
package. The simulation results for test structures are now validated by exposures of test patterns and its results clearly establish the
practical advantage of the new method.
In this paper we will publish the results of the related exposures - done on Vistec SB3050 series shaped e-beam writers -
demonstrating the practical importance of the GIDC method for layouts with critical dimensions of 32 nm and below.
All patterning technologies, including e-beam writing, encounter growing challenges to meet the requirements of current
and future semiconductor technology nodes. For e-beam writing the electron proximity effect is one of the most
prominent influencing factors and its optimal correction is a key for achieving sufficient pattern fidelity. Leading
correction algorithms like PROXECCO® currently use a dose modulation strategy for correcting the electron proximity
effect. For obtaining minimum feature sizes of below 50 nm and for most demanding patterns like dense line geometries
additional correction strategies seem to be necessary to meet the pattern fidelity requirements of the semiconductor
industry. The dense line geometries are so sensitive to suboptimal correction because of the achievable contrast in that
case, which is minimal. The result is a small process window and an increased line width roughness (LWR). One of the
possible modifications of the correction strategy is a combination of dose correction and a variation of the pattern shape.
For the scope of this paper we will investigate the potential gains (contrast enhancement) and losses (increase in data
prep and writing time) resulting from the so called "geometrically induced dose correction" method available in the
current version of PROXECCO® integrated in the ePLACE® software package. ePLACE means eBeam Direct Write
and Mask Data Preparation Layout Console and offers the ability to process layout data as well as a state-of-the-art
visualization and exposure simulation capabilities. In this paper we show that especially the simulation capability can be
used to reduce experimental work significantly.
The "geometrically induced dose correction" method is in fact a shape size biasing operation followed by a special dose
correction to meet the intended shape edges. By theoretical considerations and by applying the ePLACE® automatic
simulation & measurement feature to a huge number of measurement areas we investigate the influence of the
geometrically induced dose correction on exposure contrast and CD uniformity for test and real patterns. We also discuss
how the geometrically induced dose correction influences the data prep time and finally the e-beam writing time.
At the EMLC 2009 in Dresden the data preparation package ePLACE was already presented. This package has been
used for quite different applications covering mask write, direct write and special applications. In this paper we will
disclose results achieved when using the ePLACE package for processing of layout data of immediate interest. During
the evaluation phase of the new solution we could benefit from broad experience we collected over many years with the
fracture performance of the MGS software, which is one core element of today's ePLACE package.
A key interest of this paper is the investigation of the scalability of computing solutions as a cost-effective approach
when processing huge data volumes with the new solution. This is reflected against current state-of-the-art data processing
tasks being part of both mask write and direct write applications.
Furthermore, we evaluated visualization and simulation possibilities of the ePLACE package with respect to its use with
latest layouts in various applications.
The improved performance of the data preparation package including its adaptation to new e-beam lithography options,
as, for instance, the incorporation of the cell projection capability or the newly developed Multi Shaped Beam (MSB)
technology, will be also discussed.
As an example the matching of the data path with a Vistec SB3055 will be outlined. Processing of Design For E-Beam
(DFEB) data (including cell contents) and their conversion to real exposure data is reported. The advantages of the
parallel use of standard shaped beam und cell projection technologies are highlighted focussing on latest writing time
yields achieved when applying the CP feature.
Proc. SPIE. 7470, 25th European Mask and Lithography Conference
KEYWORDS: Lithography, Electron beam lithography, Electron beams, Magnesium, Visualization, Computer simulations, Data processing, Photomasks, Algorithm development, Electron beam direct write lithography
As chip design becomes more and more complex and alternative lithography technologies like EBDW get broader usage, the challenges increase with respect to all parts of the entire process. For exposure data preparation, we want to introduce a novel solution that offers new approaches to a user-friendly GUI, to exposure simulation, project definition and control, combined with proven kernels for data post-processing, fracturing and Proximity Effect Correction. This new solution has been implemented to run in an efficient 64 bit parallel computing environment and is called ePlace (eBeam Direct Write and Mask Data Preparation Layout Console). ePlace has the ability to process layout data of (in principle) unlimited size, given in various formats (GDSII, OASIS, DXF, CIF and others) and distributed over multiple files and hierarchies. Data post-processing capabilities include common Boolean functions (AND, OR, XOR, and Negation) as well as sizing, scaling, translation, rotation and overlap removal. Processed data can be fractured and formatted for e-beam writers (e.g. Vistec Shaped Beam (SB) tools). For Proximity Effect Correction both dose variations and newly developed geometry correction (EPC) algorithms are available and a simulation engine provides fast and precise results for exposure pattern predictions. In addition to the standard shape exposure, ePlace supports the latest Cell Projection (CP) feature of current Vistec's SB series as well as the upcoming Vistec Multi-Beam-Tool.