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Apparatuses and methods for enhanced critical dimension scatterometryApparatuses and methods for enhanced critical dimension scatterometry description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060285111, Apparatuses and methods for enhanced critical dimension scatterometry. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation-in-part of U.S. patent application Ser. No. 11/361,670, entitled "Apparatus and Method for Enhanced Critical Dimension Scatterometry," filed on Feb. 24, 2006, which claims the benefit of U.S. Provisional Patent Application No. 60/656,712, filed Feb. 25, 2005, both of which are incorporated by reference herein. TECHNICAL FIELD [0002] The present invention is related to apparatuses and methods for evaluating microstructures on a workpiece, such as a semiconductor wafer, by obtaining a representation of the distribution of radiation returning from the workpiece through a large range of angles of incidence. BACKGROUND [0003] Semiconductor devices and other microelectronic devices are typically manufactured on a workpiece having a large number of individual dies (e.g., chips). Each wafer undergoes several different procedures to construct the switches, capacitors, conductive interconnects, and other components of a device. For example, a workpiece can be processed using lithography, implanting, etching, deposition, planarization, annealing, and other procedures that are repeated to construct a high density of features. One aspect of manufacturing microelectronic devices is evaluating the workpieces to ensure that the microstructures are within the desired specifications. [0004] Scatterometry is one technique for evaluating several parameters of microstructures. With respect to semiconductor devices, scatterometry is used to evaluate film thickness, line spacing, trench depth, trench width, and other aspects of microstructures. Many semiconductor wafers, for example, include gratings in the scribe lanes between the individual dies to provide a periodic structure that can be evaluated using existing scatterometry equipment. One existing scatterometry process includes illuminating such periodic structures on a workpiece and obtaining a representation of the scattered radiation returning from the periodic structure. The representation of return radiation is then analyzed to estimate one or more parameters of the microstructure. Several different scatterometers and methods have been developed for evaluating different aspects of microstructures and/or films on different types of substrates. [0005] Eldim Corporation of France manufactures devices that measure the photometric and calorimetric characteristics of substrates used in flat panel displays and other products. The Eldim devices use an Optical Fourier Transform (OFT) instrument having an illumination source, a beam splitter aligned with the illumination source, and a first lens between the beam splitter and the sample. The first lens focuses the light from the beam splitter to a spot size on the wafer throughout a large range of angles of incidence (e.g., .PHI.=0.degree. to 360.degree. and .THETA.=0.degree. to 88.degree.). The light reflects from the sample, and the first lens also focuses the reflected light in another plane. The system further includes an optical relay system to receive the reflected light and a sensor array to image the reflected light. International Publication No. WO 2005/026707 and U.S. Pat. Nos. 6,804,001; 6,556,284; 5,880,845; and 5,703,686 disclose various generations of scatterometers. The scatterometers set forth in these patents are useful for assessing the photometric and calorimetric properties of flat panel displays, but they may have several drawbacks for assessing parameters of extremely small microstructures on microelectronic workpieces. [0006] One challenge of using scatterometry to evaluate very small microstructures is obtaining a useful representation of the radiation returning from such microstructures. For example, the scatterometers used to analyze flat panel displays may have relatively large spot sizes that are not useful to measure the properties of a 20-40 .mu.m grating because such large spot sizes generate reflections from the surrounding areas that result in excessive noise. Moreover, existing scatterometers that assess the films and surface conditions of flat panel displays typically use relatively long wavelengths of light (e.g., 532 nm). In contrast to flat panel displays, many microstructures on semiconductor wafers have line widths smaller than 70 nm. As a result, the relatively long wavelengths used to assess flat panel displays may not be capable of assessing very small microstructures on many microelectronic devices. Therefore, devices designed for assessing flat panel displays may not be well-suited for assessing gratings or other microstructures having much smaller dimensions on microelectronic workpieces. [0007] Another challenge of assessing microstructures using scatterometry is processing the data in the representation of the return radiation. Many scatterometers calculate simulated or modeled representations of the return radiation and then use an optimization regression to optimize the fit between the simulated representations and an actual reflectance signal. Such optimization regressions require a significant amount of processing time using high-power computers because the actual reflectance signals for measurements through a large range of incidence angles contain a significant amount of data that is affected by a large number of variables. The computational time, for example, can require several minutes such that the substrates are typically evaluated offline instead of being evaluated in-situ within a process tool. Moreover, the simulated representations are typically based on data from the zeroth-order diffraction, because the vector of the reflected beam is exactly opposite the angle of incidence, and also because the reflected (zeroth-order) radiation is typically the most intense. Higher order simulations may also be used to solve the inverse problem, either with or without the complementary zeroth-order. The diffracted orders may take different paths through the optical system, necessitating different calibration coefficients for each potential optical path. As a result, it is sometimes useful to decouple the zeroth-order return radiation from the higher orders, and to decouple the higher orders from each other. BRIEF DESCRIPTION OF THE DRAWINGS [0008] FIG. 1 is a schematic illustration of a scatterometer in accordance with one embodiment of the invention. [0009] FIG. 2A is a schematic view illustrating an optical system for use in a scatterometer in accordance with an embodiment of the invention. [0010] FIG. 2B is a schematic view of a cube-type polarizing beam splitter for use in a scatterometer in accordance with an embodiment of the invention. [0011] FIG. 2C is a schematic view of a CMOS imager for use in a scatterometer in accordance with an embodiment of the invention. [0012] FIG. 3 is a schematic top plan view of the mask illustrated in FIG. 2A. [0013] FIG. 4 illustrates one embodiment of the convergent beam formed by the optical system illustrated in FIG. 2A. [0014] FIG. 5 is a schematic diagram illustrating a convergent beam in accordance with one embodiment of the invention. [0015] FIG. 6 is a schematic illustration of an embodiment of the navigation system and the auto-focus system for use in the scatterometer. [0016] FIG. 7 is a schematic illustration of a simulated radiation distribution based on the mask illustrated in FIG. 3. [0017] FIG. 8 illustrates one embodiment for ascertaining the feature parameters of a microstructure in accordance with the invention. [0018] FIG. 9 is a schematic top plan view of a mask in accordance with another embodiment of the invention. [0019] FIG. 10 is a schematic top plan view of a mask in accordance with another embodiment of the invention. [0020] FIG. 11 is a schematic top plan view of a mask in accordance with another embodiment of the invention. Continue reading about Apparatuses and methods for enhanced critical dimension scatterometry... 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