Wafer examination and critical dimension estimation using scattered light
01 Aug 1992-Vol. 1661, pp 323-332
TL;DR: In this article, the authors applied optical scatter techniques to improve several aspects of microelectronic manufacturing, such as surface planarization over a VLSI structure and line edge roughness of diffraction gratings.
Abstract: We have applied optical scatter techniques to improve several aspects of microelectronic manufacturing. One technique involves characterizing light scattered from two dimensional device structures, such as those from VLSI circuitry etched on a wafer, using a frosted dome which is imaged by a CCD camera. Previously, limited dynamic range available from affordable digital imaging systems has prevented the study of two dimensional scatter patterns. We have demonstrated a simple technique to increase the dynamic range by combining multiple images taken at different intensities. After the images have been acquired, image processing techniques are used to find and catalog the diffraction orders. Techniques such as inverse least squares, principal component analysis, and neural networks are then used to evaluate the dependence of the light scatter on a particular wafer characteristic under examination. Characterization of surface planarization over a VLSI structure and measurement of line edge roughness of diffraction gratings are presented as examples.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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Patent•
21 Sep 2001TL;DR: In this article, a rigorous model is used to calculate intensity or ellipsometric signatures of the diffracting structure of a semiconductor wafer, which is then matched with the signatures in the database to determine the grating shape parameters of the structure.
Abstract: Before the diffraction from a diffracting structure on a semiconductor wafer is measured, where necessary, the film thickness and index of refraction of the films underneath the structure are first measured using spectroscopic reflectometry or spectroscopic ellipsometry. A rigorous model is then used to calculate intensity or ellipsometric signatures of the diffracting structure. The diffracting structure is then measured using a spectroscopic scatterometer using polarized and broadband radiation to obtain an intensity or ellipsometric signature of the diffracting structure. Such signature is then matched with the signatures in the database to determine the grating shape parameters of the structure.
212 citations
Patent•
20 Sep 2001
TL;DR: In this article, an overlay target for spectroscopic measurement includes at least two diffraction gratings, one grating overlying the other, in order to improve resolution of the presence as well as the direction of any mis-registration.
Abstract: An overlay target for spectroscopic measurement includes at least two diffraction gratings, one grating overlying the other. The diffraction gratings may include an asymmetry relative to each other in order to improve resolution of the presence as well as the direction of any mis-registration. For example, the asymmetry between the two diffraction gratings may be a phase offset, a difference in pitch, line width, etc. The overlay target may be spectroscopically measuring, for example, using an optical model and a best fit analysis. Moreover, the overlay target may be optimized by modeling the overlay target and adjusting the variable parameters and calculating the sensitivity of the overlay target to changes in variable parameters.
74 citations
Patent•
04 Apr 2002
TL;DR: In this paper, the alignment target includes two locations, at least one of which has a designed in offset, and the radiation that interacts with the measurement locations is compared, where the difference between the patterns is extremely sensitive to any alignment error.
Abstract: An alignment target includes periodic patterns on two elements. The alignment target includes two locations, at least one of which has a designed in offset. In one embodiment, both measurement locations have a designed in offset of the same magnitude but opposite directions. For example, two separate overlay patterns that are mirror images of each other may be used. Alternatively, the magnitudes and/or directions may vary between the measurement locations. The radiation that interacts with the measurement locations is compared. The calculated difference is extremely sensitive to any alignment error. If the difference between the patterns is approximately zero, the elements are properly aligned. When an alignment error is introduced, however, calculated difference can be used to determine the error. In one embodiment, the alignment target is modeled to determine the alignment error. In another embodiment, additional overlay patterns with additional reference offsets are used to determine the alignment error.
58 citations
Patent•
07 Mar 2005
TL;DR: In this paper, the alignment target includes two locations, at least one of which has a designed in offset, and the radiation that interacts with the measurement locations is compared, where the difference between the patterns is extremely sensitive to any alignment error.
Abstract: An alignment target includes periodic patterns on two elements. The alignment target includes two locations, at least one of which has a designed in offset. In one embodiment, both measurement locations have a designed in offset of the same magnitude but opposite directions. For example, two separate overlay patterns that are mirror images of each other may be used. Alternatively, the magnitudes and/or directions may vary between the measurement locations. The radiation that interacts with the measurement locations is compared. The calculated difference is extremely sensitive to any alignment error. If the difference between the patterns is approximately zero, the elements are properly aligned. When an alignment error is introduced, however, calculated difference can be used to determine the error. In one embodiment, the alignment target is modeled to determine the alignment error. In another embodiment, additional overlay patterns with additional reference offsets are used to determine the alignment error.
31 citations
Patent•
30 Sep 2002
TL;DR: In this paper, an alignment target includes periodic patterns on two elements and the periodic patterns are aligned when the two elements are properly aligned by measuring the two periodic patterns with an incident beam having a single polarization state and detecting the intensity of the resulting polarized light.
Abstract: An alignment target includes periodic patterns on two elements. The periodic patterns are aligned when the two elements are properly aligned. By measuring the two periodic patterns with an incident beam having a single polarization state and detecting the intensity of the resulting polarized light, it can be determined if the two elements are aligned. The same polarization state may be detected as is incident or different polarization states may be used. A reference measurement location may be used that includes a third periodic pattern on the first element and a fourth periodic pattern on the second element, which have a designed in offset, i.e., an offset when there is an offset of a known magnitude when the first and second element are properly aligned. The reference measurement location is similarly measured with a single polarization state.
31 citations
References
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TL;DR: In this paper, the authors compared the performance of four multivariate calibration methods for spectral analyses by using extensive Monte Carlo simulations and found that the frequency-limited ILS method was never the best method, although in the presence of relatively large concentration errors it sometimes yields comparable analysis precision to the full spectrum methods for the major spectral component.
Abstract: The quantitative prediction abilities of four multivariate calibration methods for spectral analyses are compared by using extensive Monte Carlo simulations. The calibration methods compared include inverse least-squares (ILS), classical least-squares (CLS), partial least-squares (PLS), and principal component regression (PCR) methods. ILS is a frequency-limited method while the latter three are capable of full-spectrum calibration. The simulations were performed assuming Beer's law holds and that spectral measurement errors and concentration errors associated with the reference method are normally distributed. Eight different factors that could affect the relative performance of the calibration methods were varied in a two-level, eight-factor experimental design in order to evaluate their effect on the prediction abilities of the four methods. It is found that each of the three full-spectrum methods has its range of superior performance. The frequency-limited ILS method was never the best method, although in the presence of relatively large concentration errors it sometimes yields comparable analysis precision to the full-spectrum methods for the major spectral component. The importance of each factor in the absolute and relative performances of the four methods is compared.
485 citations
"Wafer examination and critical dime..." refers background or methods in this paper
...A scatterometer is an instrument for measuring the angular distribution of light scattered from a surface [1-4]....
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...Procedures to interpret the scattered light measurement, or scattergram, are developed using statistical techniques such as inverse least squares ( ILS ) principal component analysis ( PCA ) [4], and neural nets [5] These procedures all require a training set, which is a number of well characterized samples which have one or more properties which are to be analyzed....
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01 Jul 1991
TL;DR: In this paper, a relationship is demonstrated between the intensity of light diffracted from a latent image consisting of a periodic pattern in the undeveloped photoresist and the amount of energy absorbed by the resist material (the exposure dose).
Abstract: As the microelectronics industry strives to achieve smaller device design geometries, control of linewidth, or critical dimension (CD), becomes increasingly important. Currently, CD uniformity is controlled by exposing large numbers of samples for a fixed exposure time which is determined in advance by calibration techniques. This type of control does not accommodate variations in optical properties of the wafers that may occur during manufacturing. In this work, a relationship is demonstrated between the intensity of light diffracted from a latent image consisting of a periodic pattern in the undeveloped photoresist and the amount of energy absorbed by the resist material (the exposure dose). This relationship is used to simulate exposure dose control of photoresist on surfaces which have different optical properties chosen to represent surfaces typical of those found in operating process lines. Samples include a variety of photoresist materials and substrates with a wide variety of optical properties. The optical properties of the substrates were deliberately varied to determine the effect of these properties on CD (in the presence and absence of an exposure monitor) during lithography. It was observed that linewidth uniformity of the developed photoresist can be greatly improved when the intensity of diffracted light from the latent image is used to control the exposure dose. Diffraction from the latent image grating structures was modeled using rigorous coupled wave analysis. The modeling is used to predict the diffraction from a latent image as a function of the substrate optical properties and the parameters of the latent image (i.e., linewidth, sidewall angle). Good agreement is obtained between theoretical and experimental observations. Conversely, the inverse problem is solved in which the parameters of the diffracting structure (the latent image) are determined from a measurement of the diffracted power. Therefore, the diffracted power can be monitored for the purpose of determining when the latent image will produce the proper CD upon development.
23 citations
"Wafer examination and critical dime..." refers background or methods in this paper
...A scatterometer is an instrument for measuring the angular distribution of light scattered from a surface [1-4]....
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...The technique is nondestructive, noncontact, rapid, and easily implemented [1-3]....
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