As feature size continuously decreasing new techniques to improve quality of wafer are developed. Hence a lot of new
problems in semiconductor industry arise. Strict control of quality of wafer during production process is very important
as many factors can influence on it, but the main contribution gives scanner error and mask. Thus at least impact of mask
should be reduced.
In this work we apply rigorous model to predict impact of microstructures to pattern fidelity on wafer. Such
microstructures are commonly generated in quartz layer to control transmittance distribution on photomask. It is shown
that effect from microstructures is not only changing of mask transmittance but also distortion of the pattern fidelity on
wafer. Rigorous modeling gives us possibility to calculate aerial image and CD on wafer in case of presence of microstructures
in the quartz. We vary optical parameters, such as refractive indexes, number, size and location of these
elements in order to reduce the distortion of pattern fidelity on wafer.
Our result allows prediction of the impact of microstructures in photomask on wafer pattern fidelity instead of doing set
of experiments. Moreover, the best conditions for experiment are found and discussed.
EUV lithography is one of the most developing and promising lithography techniques. Recently many papers are
focused on defect control of EUV mask multilayer blank, but development of profile metrology is also very important.
2D scatterometry becomes insufficient in conditions of further shrinking of feature size and complication of mask
patterns. To overcome these limitations 3D scatterometry should be used.
In this paper we study the precision of 3D scatterometry measurements of two-dimensional EUV mask features with
variety of geometrical shapes. As in reflectometry of EUV mask we can use only one or a few wavelengths, we have to
take into account intensities of many reflected orders to extract profile precisely. We calculate the library of diffraction
efficiencies for periodic circular, elliptical, and rectangular shaped with rounded corners features using 3D RCWA
method. Then we find the amplitudes of reflected diffraction orders from feature with random arbitrary shape, compare
them with each set of data in the library, and extract the most appropriate shape. After that we analyze whether the
extracted shape is really close to initial arbitrary shape or not.
In some cases extracted shape is not the closest one to the real. It is demonstrated that non-zero value of azimuth angle
of incident light influence on precision of feature shape determination and lead to deterioration of results. Using of
polarized light helps to improve precision of results, but unlike 2D scatterometry the optimal polarization can not be
determined unambiguously. According to received data we provide recommendations for optimal 3D EUV
scatterometry measurements and determine the necessary steps of varying of geometrical parameters for library features.
Control of critical dimension (CD) of 65nm and beyond nodes is the hot issue now. As feature size reduces it becomes
difficult to measure CD precisely. A lot of factors can influence on accuracy of measurement. Scatterometry method is
applicable for both production and development purpose, and can be used for in-situ or ex-situ control.
In this work we study influence of CD non-uniformity and sidewall angle as well as influence of parameters of
measurement system on precision of result. TE, TM and unpolarized light with different angle of incidence on grating
structure is considered to find the best conditions for CD measurements of 65 and 45nm nodes. Rigorous coupled-wave
analysis (RCWA) is used for theoretical spectra calculation and least square method for results extraction. Reflected
spectrum from structures containing non-uniform or uniform CDs with variation of sidewall angle is compared with the
set of theoretical spectra, and CD value with layer thickness is extracted in the same way as in the real experiment. It is
shown that CD non-uniformity and sidewall angle can be estimated through comparison of results obtained with different
polarization state of light. Best choice of polarization, angle of light incidence, range of wavelength for spectrum
measurement and parameters of library for spectrum analysis are obtained in order to provide precise and fast
scatterometry measurement for 65 and 45nm nodes mask structures.
Decreasing of node size significantly increases requirement to overlay precision. Complex structure of target demands
using of compound structures of overlay mark, which usually contain features with acute sidewall angles, coated by
several layers.
In this paper the possibility and limitations of image-based overlay with compound structures with overlay mark and
coating layers are analyzed in detail. Dependence of overlay signal shape on overlay offset is considered. Structures with
asymmetric sidewall angle, non-uniform thicknesses of layers and curved shape of layer borders are examined. Influence
of thickness variation, difference between left and right sidewall angles of asymmetric shape and curvature of layer
borders are investigated. For the simulation of such complex structures of overlay marks, our in-house simulator based
on rigorous coupled-wave analysis (RCWA) module is used. Maximum allowed values of these parameters are studied
in order to determine the limitations of image-based overlay.
Results of this consideration can be used for improvement of overlay precision and elaboration of optimal overlay
strategy in conditions of node shrinking in the semiconductor industry.
As the on-wafer transistor sizes shrink, and gate nodes reduce below 90 nm, it is becoming very important to precisely
measure and control the critical dimension (CD) on the mask. Phase shift technology for masks is essential for
decreasing of the feature size, therefore CD and profile metrology on the phase shifting materials becomes critical.
Scatterometry provides fast and nondestructive method of profile and CD measurements.
In this paper the conditions of determining of profile and CD measurement are analyzed. In the real experiment scattered
spectrum from structure with unknown profile is measured. Before experiment the library of spectra is generated. Spectra
in the library correspond to structures with various parameters (such us thickness, CD, sidewall angle, etc.). For
calculation of this library rigorous coupled-wave analysis (RCWA) was used. This method allows us to get precise
solution of Maxwell equations and find directly amplitude of zero diffraction order which is measured in the experiment.
To determine the possibility of measurement of sidewall angle various spectra with different sidewall angle value were
calculated. Calculated spectrum is changed by adding or deduction of random value. The randomly changed spectrum is
compared with spectra in the library in order to find spectrum with best fit. Therefore sidewall angle and CD can be
determined. Precision, possibility and maximum allowed error in the spectra measurements is obtained. Moreover,
influence of polarization of incident light on precision of extracted results was found.
Downscaling of microchip production technology continually increases requirements to precision of process control, and demands improvement of critical dimension (CD) measurement and control tools. In this paper we discuss the application of in situ method of critical dimension measurement for improvement of photomask development process. For this purpose scatterometry and fitting methods are applied to the CD end point detector system (CD EPD). The CD EPD system is different from the commonly used EPD system, which mainly detects the thickness of remaining resist. Measurement can be performed directly during development process, thus there is an advantage of measurement time decreasing in comparison with the ex situ method. In situ method allows one to control development precisely, and gives possibility to meet the requirements of process control. For the application of scatterometry to the CD measurement, diffraction analysis is carried out by using of rigorous coupled wave analysis (RCWA). We calculate the library of reflected spectra with various CD and heights of the pattern. These spectra are used for fitting with an experimentally measured one to get the CD and height. To increase precision and speed of measurements interpolation of spectra and various fitting methods are used.
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