Abstract: An ellipsometer, and a method of ellipsometry, for analyzing a sample using a broad range of wavelengths, includes a light source for generating a beam of polychromatic light having a range of wavelengths of light for interacting with the sample. A polarizer polarizes the light beam before the light beam interacts with the sample. A rotating compensator induces phase retardations of a polarization state of the light beam wherein the range of wavelengths and the compensator are selected such that at least a first phase retardation value is induced that is within a primary range of effective retardations of substantially 135° to 225°, and at least a second phase retardation value is induced that is outside of the primary range. An analyzer interacts with the light beam after the light beam interacts with the sample. A detector measures the intensity of light after interacting with the analyzer as a function of compensator angle and of wavelength, preferably at all wavelengths simultaneously.
Abstract: A broadband ellipsometer is disclosed with an all-refractive optical system for focusing a probe beam on a sample. The ellipsometer includes a broadband light source emitting wavelengths in the UV and visible regions of the spectrum. The change in polarization state of the light reflected from the sample is arranged to evaluate characteristics of a sample. The probe beam is focused onto the sample using a composite lens system formed from materials transmissive in the UV and visible wavelengths and arranged to minimize chromatic aberrations. The spot size on the sample is preferably less than 3 mm and the aberration is such that the focal shift over the range of wavelengths is less than five percent of the mean focal length of the system.
Abstract: A method and apparatus are disclosed for evaluating relatively small periodic structures formed on semiconductor samples. In this approach, a light source generates a probe beam which is directed to the sample. In one preferred embodiment, an incoherent light source is used. A lens is used to focus the probe beam on the sample in a manner so that rays within the probe beam create a spread of angles of incidence. The size of the probe beam spot on the sample is larger than the spacing between the features of the periodic structure so some of the light is scattered from the structure. A detector is provided for monitoring the reflected and scattered light. The detector includes multiple detector elements arranged so that multiple output signals are generated simultaneously and correspond to multiple angles of incidence. The output signals are supplied to a processor which analyzes the signals according to a scattering model which permits evaluation of the geometry of the periodic structure.
Abstract: Alignment accuracy between two or more patterned layers is measured using a metrology target comprising substantially overlapping diffraction gratings formed in a test area of the layers being tested. An optical instrument illuminates all or part of the target area and measures the optical response. The instrument can measure transmission, reflectance, and/or ellipsometric parameters as a function of wavelength, polar angle of incidence, azimuthal angle of incidence, and/or polarization of the illumination and detected light. Overlay error or offset between those layers containing the test gratings is determined by a processor programmed to calculate an optical response for a set of parameters that include overlay error, using a model that accounts for diffraction by the gratings and interaction of the gratings with each others' diffracted field. The model parameters might also take account of manufactured asymmetries.
February 12, 2002
Date of Patent:
November 16, 2004
Abdurrahman Sezginer, Kenneth C. Johnson, Fred E. Stanke
Abstract: A purge system for an optical metrology tool is disclosed. The metrology tool includes an optics plate for supporting the measurement optics. A movable stage supports a wafer below the optics plate. Inert purge gas is injected between the lower surface of the optics plate and the upper surface of the wafer. The gas flow functions to stabilize and homogenize the ambient in the measurement region. The gas flow also serves to clear the measurement area of absorbing species which is particular useful for measurements using vacuum ultraviolet light.
Abstract: A method is disclosed for evaluating isolated and aperiodic structure on a semiconductor sample. A probe beam from a coherent laser source is focused onto the structure in a manner to create a spread of angles incidence. The reflected light is monitored with an array detector. The intensity or polarization state of the reflected beam as a function of radial position within the beam is measured. Each measurement includes both specularly reflected light as well as light that has been scattered from the aperiodic structure into that detection position. The resulting output is evaluated using an aperiodic analysis to determine the geometry of the structure.
Abstract: A method of measuring at least one parameter associated with a portion of a sample having formed thereon one or more structures with at least two zones each having an associated zone reflectance property. The method includes the steps of illuminating the zones with broadband light, and measuring at least one reflectance property of light reflected from the at least two zones. The measurement includes a substantial portion of non-specularly scattered light, thereby increasing the quality of the measurement. The method further includes the step of fitting a parameterized model to the measured reflectance property. The parameterized model mixes the zone reflectance properties of the zones to account for partially coherent light interactions between the two zones.
Abstract: The subject invention relates to a method of mitigating the effects of spurious background signals in spectroscopic measurement systems. The design of a broadband imagining spectrometer is disclosed that enables direct measurement of the spurious optical background intensity during spectroscopic measurements of a sample. The background is measured on a two dimensional surface coincident with the spectrometer exit plane. The background contribution is used to correct the measurements improving the accuracy of the spectroscopic intensity measurement.
Abstract: An ellipsometric apparatus provides two impinging focused probe beams directed to reflect off the sample along two mutually distinct and preferably substantially perpendicular directions. A rotating stage rotates sections of the wafer into the travel area defined by two linear axes of two perpendicularly oriented linear stages. As a result, an entire wafer is accessed for measurement with the linear stages having a travel range of only half the wafer diameter. The reduced linear travel results in a small travel envelope occupied by the wafer and consequently in a small footprint of the apparatus. The use of two perpendicularly directed probe beams permits measurement of periodic structures along a preferred direction while permitting the use of a reduced motion stage.
Abstract: A combination metrology tool is disclosed for analyzing samples, and in particular semiconductor samples. The device includes a first measurement module for determining electrical characteristics of the sample. In general, such a measurement module will monitor voltage or capacitance characteristics to derive information such as carrier lifetimes, diffusion lengths and surface doping. The device also includes a second measurement module for determining compositional characteristics such as layer thickness, index of refraction and extinction coefficient. The second measurement module will include a light source for generating a probe beam which interacts with the sample. A detection system is provided for monitoring either the change in magnitude or polarization state of the probe beam. The output signals from both measurement modules are combined by a processor to more accurately evaluate the sample.
Abstract: A system is disclosed for evaluating nitrogen levels in thin gate dielectric layers formed on semiconductor samples. In one embodiment, a tool is disclosed which includes both a narrow band ellipsometer and a broadband spectrometer for measuring the sample. The narrowband ellipsometer provides very accurate information about the thickness of the thin film layer while the broadband spectrometer contains information about the nitrogen levels. In another aspect of the subject invention, a thermal and/or plasma wave detection system is used to provide information about the nitrogen levels and nitration processes.
Abstract: One aspect of the present invention relates to a system and method for mitigating errors in SE data in order to determine changes in a polarization state of a source beam after interaction with a specimen. The system includes a light source for directing a source beam to a focusing optical element, a polarization system comprising a diffractive optical element or a wire grid polarizer, located between the focusing optical element and the specimen such that the source beam is polarized after being reflected from the focusing optical element. The polarized source beam is transmitted to the specimen. Changes in polarization state of the beam created by interaction with the sample are monitored to characterize the sample.
Abstract: An optical measuring device generates a plurality of measured optical data from inspection of a thin film stack. The measured optical data group naturally into several domains. In turn the thin film parameters associated with the data fall into two categories: local and global. Local “genes” represent parameters that are associated with only one domain, while global genes represent parameters that are associated with multiple domains. A processor evolves models for the data associated with each domain, which models are compared to the measured data, and a “best fit” solution is provided as the result. Each model of theoretical data is represented by an underlying “genotype” which is an ordered set of the genes. For each domain a “population” of genotypes is evolved through the use of a genetic algorithm. The global genes are allowed to “migrate” among multiple domains during the evolution process.
Abstract: A narrow band ellipsometer is used to monitor and control the formation of thin layers in an multilayer, thin film interference filter. Optical interference filters used for DWDM application have a large number of thin layers deposited on a substrate. The thickness of the layers must be precisely controlled. An ellipsometer is used to monitor the deposition process and control the layer formation in situ, on a real time basis.
Abstract: A system for characterizing periodic structures on a real time basis is disclosed. A multi-parameter measurement module generates output signals as a function of wavelength or angle of incidence. The output signals are supplied to a parallel processor, which creates an initial theoretical model and calculates the theoretical optical response. The calculated optical response is compared to measured values. Based on the comparison, the model configuration is modified to be closer to the actual measured structure. Thereafter, the complexity of the model is iteratively increased, by dividing the model into layers each having an associated width and height. The model is fit to the data in an iterative manner until a best fit model is obtained which is similar in structure to the periodic structure.
Abstract: An optical measurement system for evaluating a sample has a azimuthally rotatable measurement head. A motor-driven rotating mechanism is coupled to the measurement head to allow the optics to rotate with respect to the sample. In particular, a preferred embodiment is a polarimetric scatterometer (FIG. 1) for measuring optical properties of a periodic structure on a wafer sample (12). This scatterometer has optics (30) directing a polarized illumination beam at non-normal incidence onto the periodic structure. In addition to a polarizer (8), the illumination path can also be provided with an E-O modulator for modulating the polarization. The measurement head optics also collect light reflected from the periodic structure and feed that light to a spectrometer (17) for measurement. A polarization beamsplitter (18) is provided in the collection path so that both S and P polarization from the sample can be separately measured.
March 29, 2002
Date of Patent:
August 17, 2004
Adam E. Norton, Abdurrahman Sezginer, Fred E. Stanke
Abstract: An optical measurement system is disclosed for evaluating samples with multi-layer thin film stacks. The optical measurement system includes a reference ellipsometer and one or more non-contact optical measurement devices. The reference ellipsometer is used to calibrate the other optical measurement devices. Once calibration is completed, the system can be used to analyze multi-layer thin film stacks. In particular, the reference ellipsometer provides a measurement which can be used to determine the total optical thickness of the stack. Using that information coupled with the measurements made by the other optical measurement devices, more accurate information about individual layers can be obtained.
Abstract: A stage system is disclosed for supporting and positioning a semiconductor wafer for inspection in an optical metrology device. A chuck for supporting a wafer is mounted to the stage system. The stage system can move the chuck along two linear orthogonal axes. A rotational stage is also provided for rotating the chuck. A mechanism is provided for adjusting the vertical position of a chuck to allow for focusing of the probe beam of the metrology device. The vertical adjustment mechanism is designed so that it does impede the rotational positioning of the chuck.
Abstract: A detector assembly is introduced that provides shielding of irradiation vulnerable regions of an X-ray detector against directly impinging and scattered X-rays. A shielding unit has a primary aperture to shape an X-ray beam reflected from a test area of a work piece such that the shaped beam directly impinges an X-ray sensing area of the detector. A secondary aperture shields off X-rays scattering off along the edges of the primary aperture. In the preferred embodiment, the shielding unit is a monolithic structure. An area between primary and secondary aperture is laterally recessed to prevent a portion of scattered X-rays from being deflected onto the sensing area.
Abstract: A database interpolation method is used to rapidly calculate a predicted optical response characteristic of a diffractive microstructure as part of a real-time optical measurement process. The interpolated optical response is a continuous and (in a preferred embodiment) smooth function of measurement parameters, and it matches the theoretically-calculated optical response at the database-stored interpolation points.