Within this work an alternative approach to precision surface profilometry based on a low-coherence interferometer is presented. Special emphasis is placed on the characterization of edge effects, which influence the measurement result on sharp edges and steep slopes. In contrast to other works, this examination focuses on the comparison of very broadband light sources such as a supercontinuum white-light source (SC; 380 - 1100 nm) and a laser-driven plasma light source (LDP; 200 - 1100 nm) and their influence on the formation of these effects. The interferometer is equipped with one of these broadband light sources and a defined dispersion over a given spectral range. The spectral width of the light sources in combination with the dispersive element defines the possible measurement range and resolution. Instead of detecting the signals only in a one-dimensional manner, an imaging spectrometer on the basis of a high resolution CMOS-camera is set-up. Through the introduction of a defined dispersion, a controlled phase variation in the spectral domain is created. This phase variation is dependent on the optical path difference between both arms and can therefore be used as a measure for the height of a structure which is present in one arm.
The results of measurements on a 100 nm height standard with both selected light sources have been compared. Under consideration of the coherence length of both light sources of 1.58 μm for the SC source and 1.81 m for the LDP source differences could be recorded. Especially at sharp edges, the LDP light source could record height changes with slopes twice as steep as the SC source. Furthermore, it became obvious, that measurements with the SC source tend to show edge effects like batwings due to diffraction. Additional effects on the measured roughness and the flatness of the profile were investigated and discussed.
Manufacturing of precise structures in MEMS, semiconductors, optics and other fields requires high standards in manufacturing and quality control. Appropriate surface topography measurement technologies should therefore deliver nm accuracy in the axial dimension under typical industrial conditions. This work shows the characterization of a dispersion-encoded low-coherence interferometer for the purpose of fast and robust surface topography measurements. The key component of the interferometer is an element with known dispersion. This dispersive element delivers a controlled phase variation in relation to the surface height variation which can be detected in the spectral domain. A laboratory setup equipped with a broadband light source (200 - 1100 nm) was established. Experiments have been carried out on a silicon-based standard with height steps of 100 nm under different thermal conditions such as 293.15 K and 303.15 K. Additionally, the stability of the setup was studied over periods of 5 hours (with constant temperature) and 15 hours (with linear increasing temperature). The analyzed data showed that a height measurement of 97:99 +/- 4:9nm for 293.15 K and of 101:43 +/- 3:3nm for 303.15 K was possible. The time-resolved measurements revealed that the developed setup is highly stable against small thermal fluctuations and shows a linear behaviour under increasing thermal load. Calibration data for the mathmatical corrections under different thermal conditions was obtained.
Within this work a scan-free, low-coherence interferometry approach for surface profilometry with nm-precision is presented. The basic setup consist of a Michelson-type interferometer which is powered by a super-continuum light-source (Δλ= 400-1700 nm). The introduction of an element with known dispersion delivers a controlled phase variation which can be detected in the spectral domain and used to reconstruct height differences on a sample. In order to enable scan-free measurements, the interference signal is spectrally decomposed with a grating and imaged onto a two-dimensional detector. One dimension of this detector records spectral, and therefore height information, while the other dimension stores the spatial position of the corresponding height values.
In experiments on a height standard, it could be shown that the setup is capable of recording multiple height steps of 101 nm over a range of 500 m with an accuracy of about 11.5 nm. Further experiments on conductive paths of a micro-electro-mechanical systems (MEMS) pressure sensor demonstrated that the approach is also suitable to precisely characterize nanometer-sized structures on production-relevant components. The main advantage of the proposed measurement approach is the possibility to collect precise height information over a line on a surface without the need for scanning. This feature makes it interesting for a production-accompanying metrology.
This work introduces a modified low-coherence interferometry approach for nanometer surface-prolometry. The key component of the interferometer is an element with known dispersion which defines the measurement range as well as the resolution. This dispersive element delivers a controlled phase variation which can be detected in the spectral domain and used to reconstruct height differences on a sample. In the chosen setup, both axial resolution and measurement range are tunable by the choice of the dispersive element. The basic working principle was demonstrated by a laboratory setup equipped with a supercontinuum light source ( Δλ= 400-1700 nm). Initial experiments were carried out to characterize steps of 101 nm on a silicon height standard. The results showed that the system delivers an accuracy of about 11.8 nm. These measurements also served as a calibration for the second set of measurements. The second experiment consisted of the measurement of the bevel of a silicon wafer. The modified low-coherence interferometer could be utilized to reproduce the slope on the edge within the previously estimated accuracy. The main advantage of the proposed measurement approach is the possibility to collect data without the need for mechanically moving parts.
The measurement of a wavefront is a powerful tool for characterizing optical systems. The most commonly used wavefront measurement technique is the method of local-light aberrometry. The conventional version of this kind of measurement principle is the Hartmann-Shack wavefront sensor. This method returns the result of the matrix of spatially-resolved gradients of the wavefront. However, the last and crucial step of the wavefront analysis is the reconstruction of the wavefront from the measured data packets. The issues of the measurement preparation and design are interesting in the same volume. The work presented here describes the comparison between a Fourier-Iteration algorithm and the Zernike approximation method for the wavefront reconstruction in relation to the measurement design. In the context of this work, the term "design of the measurement" refers to the issue of the number and relative positions of the measurement points. In this work, the behavior of the wavefront reconstruction method using Monte-Carlo simulations was analyzed. The optimum point distribution was found and a validation parameter to describe the impact of measurement errors on the analysis results was determined. Based on this parameter, a Monte-Carlo based simulation to make the design of the experiment with the highest accuracy was realized. The technique of white noise injection was implemented in the reconstruction routine and the propagation of errors was analyzed. The presented comparison technique was applied to determine the optimum measurement positions over the beam's surface.
The work presented here describes the analysis of problems of the realization of alternative wavefront measurement methods for lithography exposure machines. The measurement method that is introduced is a redesign of a conventional Shack-Hartmann wavefront sensor and was based on the usage of a single pinhole and the lithography machine itself. Such a redesign is useful because it increases the degrees of freedom. Therefore, there is more freedom to analyze the problems of designing and planning measurements. A group of hardware prototypes under laboratory conditions with the required angular and lateral resolution were realized. For the approximation of the measurement results, numerical simulations are implemented using the Monte-Carlo method in order to statistically design the experiments themselves.
In this paper an alternative approach to surface profilometry based on a combined time-spectral domain white-light interferometer is shown. Within the setup a reference interferometer arm contains of a fixed mirror and a material with known dispersion while the object arm is aligned to a sample e.g. a wafer surface. Under the usage of a translation stage different height profiles in the nm - regime are emulated and measured accordingly with the interferometer. The signal analysis and calculation of interesting parameters is performed by a fitting algorithm. This algorithm is based on theoretical considerations on a dispersion affected interferometer which are also shown in the work. The experimental configuration allows a measurement range of 12 μm while a theoretical average resolution of 28 nm is possible. In the results it is observable that the measurement of height changes on a surface with an RMS error of 18 nm at the maximum is possible. In conclusion sources of error and further improvement possibilities are discussed.
We have been utilizing rigorous simulation software in order to predict the alignment mark signal quality and mark contrast variation induced by processes changes reliably. We have run simulations in order to understand which parameters influence alignment mark quality most and to determine the important parameters that can be manipulated in order to improve it. Simulation of alignment signals (also referred to as waveforms) has been done for resist marks and etched marks, coated and uncoated, as well as in presence of increasing topography complexity. To validate simulation analysis, mark signal collection for different processes (and/or variations of those) and products has been carried out; cross sections have also been generated.
In order to fulfill the demands of further shrinkage of our mature 90nm logic litho technologies under the constraints of
costs and available toolsets in a 200mm fab environment, a project called "Push to the Limits" was started. The aim ís
to extend the lifetime and capabilities of existing dry 193nm litho toolsets with medium to low numerical aperture,
coupled with the availability of materials and processes which were known to help up CD miniaturization and to shrink
the 90nm logic litho process as far as possible. To achieve this, various options were explored and evaluated, e.g.
optimization of illumination conditions, evaluation of new materials, usage of advanced RET techniques (OPC, LfD,
DfM and ILT) and resolution enhancement by chemical shrink (RELACS®). In this project we demonstrate how we were
able to extend our existing 90nm technology capability, down close to 65nm node litho requirements on most critical
layers. We present overall result in most critical layer generally and specifically on most difficult layer of contact.
Typical contact litho target at 100nm region was enabled, while realization of 90nm ADI target is possible with addition
of new process materials.
Taking the challenge of Moore's Law production of lCs crosses the lOOnm borderline for gate lengths. The feature size and the ultra large scale integration are not yet limited by physics but by the performance of the manufacturing systems. The capability of i.e. e-beam mask writers is determined to an increasing extent by environmental influences. Achieving high-level productivity measuring and analysis of these disturbances, and thereby the quality of the site, is taking on ever more significance. Taking the advantage of the monitoring data, future pattern fidelity requirements can be obtained by implementing both passive and active cancelling methods where needed. Although semiconductor production takes place in well controlled cleanrooms, data of several variables are not acquired permanently. In this paper we present within the framework of a new 50kV mask writer installation the benefit of an environmental monitoring system that is capable of observing magnetic field fluctuations and feedback its measurement results to an active magnetic cancellation. Additionally floor vibration data are acquired by this tool.
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