N K Technology Ltd

Nanometrics Inc.

Nsh Technology, Inc.

Guoguang Li

Abdul Rahim Forouhi

Shuqiang Chen

Dale A Harrison

Phillip Walsh

Weilu Hang Xu

Marc T Aho

Hongwei Zhu

Rajeshwar Chhibber

Mehdi Balooch

Roger R Lowe-Webb

Weidong Yang

John D Heaton

Homan Amin

Erik Nackerud

A method and apparatus for convolving spectroscopic data with certain phase information for practicing phase-compensated sensitivity-enhanced spectroscopy (PCSES). PCSES uses a beam of radiation in a polarization state PSfrom a source emitting at a plurality of wavelengths, and places in the beam a compensator capable of altering polarization state PSby applying a delimited phase shift &#x394; between two orthogonal polarization axes of the radiation to restrict a finely-vibrating spectrum. A sample disposed in the beam after the compensator generates a response beam by reflection, transmission or even both. A polarization state PSof the response beam is passed to a detector to determine a spectrum of the response beam. A first spectrum is collected when polarization states PS, PSand the compensator are in a first polarization-altering configuration and a second spectrum is collected when polarization states PS, PSand the compensator are in a second polarization-altering configuration. A phase-compensated spectrum is then derived from just the first and second spectra thereby allowing the user to undertake optical characterization, including the measurement of film thickness t and complex indices of refraction n, k of the sample with as few as just two polarization-altering configurations.

Method and apparatus for phase-compensated sensitivity-enhanced spectroscopy (PCSES)

The refractive index, extinction coefficient, size and density of fluid suspended particles are simultaneously determined by combined transmittance and scattering measurements. The scattering measurements are preferably angle selective to obtain additional information about the scattered light. A charge-coupled device is employed for its high sensitivity to low light intensity in measurement of scattered light in combination with a photodiode array employed for its high signal to noise ratio, which is beneficial in transmittance measurement. The scattered light may be measured in an angle selective fashion by use of a motorized aperture that is concentrically positioned with respect to the impinging beam axis and moveable along the impinging beam axis. An ellipsoidal mirror collects the scattered light that passes through the motorized aperture and focuses the scattered light towards the charge-coupled device.

Combined transmittance and angle selective scattering measurement of fluid suspended particles for simultaneous determination of refractive index, extinction coefficient, particle size and particle density

Apparatus and method for examining a sample with a broadband radiation while preserving a small spot and low wave front distortion. The apparatus has a broadband source for generating the broadband radiation and a first reflective optics that employ toroidal mirrors that are barrel or donut-shaped and may be placed in a crossed or parallel arrangement for producing a broadband test beam that is guided to the sample such that it is incident on it at a small spot. A sampling aperture is provided for filtering a certain center portion from the broadband test beam. A second reflective optics is provided for shaping a reflected response beam from the broadband radiation that is reflected from the spot. The response beam is delivered by second reflective optics to a detector for examination. The apparatus and method can be applied to improve wave front distortion in reflectance measurements and for performing transmittance measurements with chromatic distortion compensation. The method and apparatus further provide for efficient monitoring of the broadband test beam.

Broadband optical metrology with reduced wave front distortion, chromatic dispersion compensation and monitoring

Improved optical characterization is provided by organizing the optical modeling calculations such that incident radiation parameters (e.g., wavelength) are varied in the outermost loop of any modeling run. By completing calculations for all combinations of structure parameters at one wavelength before moving to the next wavelength, calculation efficiency can be greatly improved. In particular, with this approach it is not necessary to cache (or re-compute) intermediate results pertaining to different wavelengths, in contrast to conventional approaches. Further improvements in efficiency can be obtained by organizing reflectance calculations such that for any layer L, stored intermediate results pertaining to layers below Lcan be used to calculate optical response as parameters for Land layers above Lare varied. Similarly, transmittance calculations can be organized such that for any layer L, stored intermediate results pertaining to layers above Lcan be used to calculate optical response as parameters for Land layers below Lare varied.

Implementation of rigorous coupled wave analysis having improved efficiency for characterization

Methods and apparatus for optical characterization based on symmetry-reduced 2-D RCWA calculations are provided. The invention is applicable to gratings having a grating reflection symmetry plane. A sample can be illuminated at normal incidence or at a non-zero angle of incidence such that the plane of incidence is parallel to or identical with the symmetry plane. The diffracted field components are either symmetric or anti-symmetric with respect to the grating symmetry plane. This symmetry is exploited to provide a symmetry-reduced 2-D RCWA having reduced matrix dimension (by about a factor of two) that is mathematically equivalent to a conventional 2-D RCWA. For normal incidence on a grating having two reflection symmetry planes, a symmetry-reduced 2-D RCWA having reduced matrix dimension (by about a factor of four) is provided. This normal incidence RCWA can be used to approximately characterize a sample illuminated at non-normal incidence. Approximation accuracy can be improved by modifying either the grating depth or the grating refractive index.

Efficient characterization of symmetrically illuminated symmetric 2-D gratings

Improved computation of Fourier coefficients for modeling of 2-D grating diffraction is provided. Let f(x,y) be defined in a region &#x3a9;. Typically, f(x,y) is piecewise constant (since it is a grating permittivity or inverse permittivity) and takes on various constant values in several domains in &#x3a9;. Let D be one of these domains, having a general shape. According to the invention, D is approximated as a set of trapezoids, and f(x,y) is taken to have a constant value within each of the trapezoids. Since the Fourier coefficient of a constant defined on a trapezoidal region can be analytically evaluated, an analytic approximation to the Fourier coefficient of f(x,y) on D is provided by summing the contributions from each trapezoid.

Efficient calculation of grating matrix elements for 2-D diffraction

An apparatus and method for examining features of a planar, disk-shaped samples on a stage that holdings the sample and has an X-drive, a Y-drive and a &#x3b8;-drive for rotating the stage about a center of rotation defined in the stage coordinates. The sample is placed on the stage such that the center of the sample is substantially aligned with the center of rotation and a measurement assembly is located above the sample to examine the features optically. A scheduling module coordinates the X-drive, the Y-drive and the &#x3b8;-drive with the measurement assembly such that the sample is examined in an even number n of angular sectors defined by a sector angle &#x398; that is the same for each sector. Specifically, the sector angle &#x398; is defined in terms of n as follows: where n=4and m is an integer, such that a multiple of sector angle &#x398; always includes angles 90&#xb0; and 180&#xb0;.

Apparatus and method for examining a disk-shaped sample on an X-Y-theta stage

A system and a method for optical characterization of a symmetric grating illuminated at off-normal incident angle are provided, where the plane of incidence is parallel to the grating lines. In this case corresponding positive and negative diffraction orders have the same intensity and phase. Several approaches for exploiting this symmetry are given. The first approach is a symmetric rigorous coupled wave analysis (SRCWA) adapted to the symmetric case, which accounts for N positive and N negative diffraction orders with M=N+1 space harmonics, without approximation. Various approximation methods are also given. Approximate versions of the RCWA (or SRCWA) can be developed by neglecting polarization coupling for small angles of incidence. A normal incident angle calculation can be used to approximate a situation with a small angle of incidence. Refinements to this approximation include revision of grating depth or refractive indices to improve accuracy. Methods other than the RCWA can also be symmetry simplified according to the invention.

System and method for efficient characterization of diffracting structures with incident plane parallel to grating lines

An apparatus and method for examining features of a sample with a broadband beam of light obtained from a long-wavelength source that may include two distinct emitters that emit a long-wavelength radiation and a short-wavelength source that emits a short-wavelength radiation. A passage is positioned between the sources and a reflective beam combining optics is provided for shaping the long-wavelength radiation to enter the short-wavelength source via the passage and also for shaping the short-wavelength radiation that exits through the passage and propagates toward the long-wavelength source. The reflective beam combining optics shape the short-wavelength radiation such that it re-enters the short-wavelength source via the passage and is combined with the long-wavelength radiation into the broadband beam that exits the short-wavelength source. A beam steering optics projects the broadband beam to a spot on the sample, and a scattered broadband radiation from the spot is intercepted and shaped to a broadband signal beam, which is passed through a sampling pinhole that passes a test portion of it on to a detector for optical examination; the test portion that is passed can correspond to a center portion of the spot.

System and method for high intensity small spot optical metrology

A system and method for optical offset measurement is provided. An offset between two grating layers in a compound grating is measured by illuminating the gratings with light having a plane of incidence that is neither parallel with nor perpendicular to the grating lines. This non-symmetrical optical illumination allows determination of the sign and magnitude of the offset. Two measurements are performed at azimuthal angles separated by 180&#xb0;, and a difference of these measurements is calculated. Measurement of this difference allows determination of the offset (e.g., with a calibration curve). Alternatively, two compound gratings having a predetermined non-zero offset difference can be employed. This arrangement permits determination of the offsets without the need for a calibration curve (or for additional compound gratings), based on a linear approximation.

System and method for measuring overlay alignment using diffraction gratings

An apparatus and method for determining a physical parameter of features on a substrate by illuminating the substrate with an incident light covering an incident wavelength range &#x394;&#x3bb;, e.g., from 190 nm to 1000 nm, where the substrate is at least semi-transparent. A response light received from the substrate and the feature is measured to obtain a response spectrum of the response light. Further, a complex-valued response due to the feature and the substrate is computed and both the response spectrum and the complex-valued response are used in determining the physical parameter. A direct approximate phase measurement is provided when the response light is transmitted light.

Phase shift measurement using transmittance spectra

Optical characterization of lateral features of a pattern is provided. A plane-wave optical response is calculated for each feature. At least one of these plane-wave responses is calculated from an effective optical property (e.g., a waveguide modal refractive index). Such effective optical properties depend on feature geometry and on intrinsic material optical properties. The plane-wave responses for each feature are combined to generate a modeled pattern response. By fitting the modeled pattern response to a corresponding measured pattern response, estimates for pattern feature parameters are obtained. The use of an effective optical property improves model accuracy, especially for features having a size on the order of a wavelength or less, without significantly increasing computation time.

Optical determination of pattern feature parameters using a scalar model having effective optical properties

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.

Method and apparatus for using an alignment target with designed in offset

An apparatus and method for determining a physical parameter of features on a substrate by illuminating the substrate with an incident light covering an incident wavelength range &#x394;&#x3bb;, e.g., from 190 nm to 1000 nm, where the substrate is at least semi-transparent. A response light received from the substrate and the feature is measured to obtain a response spectrum of the response light. Further, a complex-valued response due to the feature and the substrate is computed and both the response spectrum and the complex-valued response are used in determining the physical parameter. The response light is reflected light, transmitted light or a combination of the two. The complex-valued response typically includes a complex reflectance amplitude, a complex transmittance amplitude or both. The apparatus and method take into account the effects of vertical and lateral coherence length and are well suited for examining adjacent features.

Method and apparatus for examining features on semi-transparent and transparent substrates

A differential interferometer is used to measure the step height between a reference region and at least one point in a measurement region using the relative phase difference as well as the measured reflectance from at least the point in the measurement region. The measured reflectance can be derived from the information provided by the differential interferometer. The measured reflectance from the reference region can also be used to provide a step height measured, where, e.g., the reference region has a changing thickness. Where the measurement region includes a composite material, e.g., copper and silicon dioxide, the step height between the reference region and the measurement region may be determined by including the area fraction or the height difference of the materials in the composite material in the final determination of the step height.

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Fremont, CA, United States of America

Guoguang Li