Patent Document

BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to the area of thin film analysis. In particular, the present invention relates to a method and apparatus for combining multiple thin film analysis capabilities into a single instrument.  
           [0003]    2. Discussion of Related Art  
           [0004]    As the dimensions of semiconductor devices continue to shrink, accurate and efficient characterization of the components forming those devices becomes more critical. Typically, the manufacturing process for modern semiconductor devices includes the formation of a number of layers or “thin films”, such as oxide, nitride, and metal layers. To ensure proper performance of the finished semiconductor devices, the thickness and composition of each film formed during the manufacturing process must be tightly controlled. In the realm of thin film analysis, three basic techniques have evolved to measure film thickness and composition.  
           [0005]    Grazing-Incidence X-ray Reflectometry  
           [0006]    Grazing-incidence x-ray reflectometry (GXR), which is sometimes referred to as x-ray reflectometry (XRR), measures the interference patterns created by reflection of x-rays off a thin film. FIG. 1 shows a conventional x-ray reflectometry system  100 , as described in U.S. Pat. No. 5,619,548, issued Apr. 8, 1997 to Koppel. X-ray reflectometry system  100  comprises a microfocus x-ray tube  110 , an x-ray reflector  120 , and a detector  130 . X-ray reflectometry system  100  is configured to analyze a test sample  140  that includes a thin film layer  142  formed on a substrate  141 .  
           [0007]    Microfocus x-ray tube  110  directs a source x-ray beam  150  at x-ray reflector  120 . Source x-ray beam  150  typically comprises a bundle of diverging x-rays that can have a variety of different wavelengths. X-ray reflector  120  reflects and focuses the diverging x-rays of x-ray beam  150  into a converging x-ray beam  160 . Typically, x-ray reflector  120  is a singly- or doubly-curved monochromatizing crystal that ensures that only x-rays of a particular wavelength are included in converging x-ray beam  160 , which is directed at thin film layer  142 .  
           [0008]    Converging x-ray beam  160  is then reflected by thin film layer  141  as an output x-ray beam  170  onto detector  130 . X-ray beam  170  forms an interference pattern on the surface of detector  130  due to constructive and destructive interference of x-ray reflections at the top and bottom surfaces of thin film layer  142 . Detector  130  is a position-sensitive detector that measures the varying intensity of this interference pattern. The resulting reflectivity curve of intensity versus position can then be used to calculate the thickness of thin film layer  142 , as described in U.S. Pat. No. 5,619,548.  
           [0009]    GXR is best suited for measuring thickness and electron density for films in the range of 10A-2000A thick. It is well matched to the barrier/seed film stacks used in BEOL (back end of line) copper interconnects. However, GXR cannot measure thicker ECP (electrochemical plated) copper films having thicknesses greater than 1 um. Furthermore, GXR is not very good at measuring the composition of thin films—for example the composition of a barrier film such as TaN or TiSiN.  
           [0010]    Electron Microprobe Analysis  
           [0011]    To analyze the composition of a thin film layer, a technique known as electron microprobe (EMP) analysis is often used. EMP analysis involves the use of an electron beam (e-beam) to generate characteristic x-rays from a thin film layer. FIG. 2 shows a conventional EMP system  200  comprising an e-beam generator  210  and an x-ray detector  230 . EMP system  200  is configured to analyze a test sample  240  that includes a thin film layer  242  formed on a substrate  241 .  
           [0012]    To perform an EMP analysis, e-beam generator  210  directs an e-beam  250  at thin film layer  242 . The high-energy electrons in e-beam  250  cause characteristic x-rays  290  to be emitted by thin film layer  242 . The properties of characteristic x-rays  290  are then measured by x-ray detector  230  to determine the composition of thin film layer  242 .  
           [0013]    Generally, x-ray detector  230  comprises either an energy-dispersive x-ray spectrometer (EDX or EDS) or a wavelength-dispersive x-ray spectrometer (WDX or WDS). In an EDX detector, the energies of the characteristic x-rays are used to determine the composition of the thin film.  
           [0014]    [0014]FIG. 4 a  shows a conventional EDX detector  230   a  that includes a detector crystal  231  and a pulse analyzer  232 . Each of characteristic x-rays  290  incident on detector crystal  231  deposits an amount of charge proportional to the energy of that particular x-ray. These charge pulses are then measured by pulse analyzer  232 . Because different elements generate x-rays having different energies, the charge pulse magnitudes read by pulse analyzer  232  can be used to determine the intensity of the characteristic x-rays, which in turn can be used to determine thin film composition and thickness.  
           [0015]    While an EDX detector provides a relatively simple means for determining the composition of a thin film layer, x-rays having closely spaced wavelengths (i.e., energies) can be difficult to distinguish. For example, an ECP copper film may be formed over a tantalum nitride barrier film. The characteristic copper x-rays (Cu-K, indicating x-rays resulting from the ionization of the K shells of the copper atoms) and the characteristic tantalum x-rays (Ta-L, indicating x-rays resulting from the ionization of the L shells of the tantalum atoms) are only separated by 100 eV, and therefore cannot be resolved by an EDX detector, which typically has a resolution limit of greater than 150 eV. Furthermore, an EDX detector cannot detect low energy x-rays, such as those emitted by the nitrogen (N-K x-rays; i.e., x-rays resulting from the ionization of the K shells of the nitrogen atoms) in a barrier film.  
           [0016]    In contrast, WDX detectors have a much lower resolution limit of roughly 10-20 eV, and can therefore provide much more accurate measurements than an EDX detector. The low resolution limit of a WDX detector would enable Cu-K and Ta-L x-rays to be distinguished, and also enables the detection of low-energy N-K x-rays. In a WDX detector, x-rays having specific wavelengths are detected to improve the resolution of the measurement process.  
           [0017]    [0017]FIG. 4 b  shows a conventional WDX detector  230   b  that includes an x-ray reflector  238  and a proportional counter  239 . Incoming characteristic x-rays  290  are incident on x-ray reflector  238 . X-ray reflector  238  is a monochromator, and disperses the incoming characteristic x-rays  290  according to Bragg&#39;s Law. X-ray reflector  238  is configured such that only those characteristic x-rays  290  having a specific wavelength are directed onto proportional counter  239 . The specific wavelength is selected to be the characteristic wavelength of x-rays emitted by a particular element. Therefore, the output of proportional counter  239  can then be correlated to the concentration of the particular element in the thin film layer. Often, multiple WDX detectors are used simultaneously, with each of the multiple WDX detectors being configured to respond to a different element.  
           [0018]    Whether an EDX or WDX detector is used, EMP analysis can be performed relatively quickly due to the intense characteristic x-rays produced by the thin film in response to the e-beam. Also, by varying the energy of the e-beam, an EMP system can “depth profile” a stack of thin film layers, allowing composition measurements to be taken at various positions thoughout the film stack. However, as film thickness in the test sample increases, the electrons in the e-beam must be raised to higher and higher energies to properly penetrate the film. For example, to penetrate 1-2 um thick ECP (electro-chemical plated) copper films, electrons with at least 50 keV energy must be used. Such high-energy electrons are difficult to produce and can damage the test sample. In addition, higher power e-beam generators increase the cost of an EMP system while decreasing overall system reliability. This is in addition to the inherent complexity introduced by vacuum environment required to generate the e-beam.  
           [0019]    X-Ray Fluorescence  
           [0020]    Therefore, for analysis of “thicker” thin films, a technique known as x-ray fluorescence (XRF) is often used. In place of the e-beam used in EMP analysis, XRF analysis uses a source x-ray beam to cause emission of characteristic x-rays from a thin film. The source x-rays can penetrate the film(s) in the test sample much more easily than the electrons used in EMP analysis. For example, the molybdenum x-rays (Mo-K) commonly used in XRF systems can penetrate as much as 20 um of copper, and are therefore much more efficient than an e-beam at measuring thick copper films. FIG. 3 shows a conventional XRF system  300  that includes a microfocus x-ray tube  310 , an x-ray reflector  320 , and a detector  330 . X-ray fluorescence system  300  is configured to analyze a test sample  340  that includes a thin film layer  342  formed on a substrate  341 .  
           [0021]    Microfocus x-ray tube  310  directs a bundle of diverging x-rays  350  at x-ray reflector  320 . X-ray reflector  320  reflects and focuses the diverging x-rays of x-ray beam  350  into a converging x-ray beam  360 , directed at thin film layer  342 . The x-rays of x-ray beam  360  cause characteristic x-rays  390  to be emitted by thin film layer  342 . The properties of characteristic x-rays  390  are then measured by x-ray detector  330  to determine the composition of thin film layer  342 , in a manner substantially similar to that used with respect to EMP system  200  shown in FIG. 2. Detector  330  can comprise either an EDX or WDX detector, as described previously with respect to FIGS. 4 a  and  4   b , respectively.  
           [0022]    Because x-rays can penetrate a material much more easily than electrons can penetrate the same material, XRF systems are generally better suited to analyze thicker films than are EMP systems. Also, a vacuum chamber is not required for the generation of the source x-rays, which simplifies the design and operation of an XRF system. However, because the source x-rays are not absorbed by the film material as well as electrons would be, and because the source x-ray beam is not as intense as an electron beam can be, the resulting characteristic x-rays in an XRF system are weaker than the characteristic x-rays in an EMP system, making measurements on those characteristic x-rays significantly slower. Also, test samples having multiple thin film layers can be problematic since the source x-rays cannot be readily “tuned” to penetrate to a specific depth  
           [0023]    Thus, it is clear that no single one of the aforementioned analysis techniques is ideal for all situations. However, having a different set of tools for each set of circumstances can be cumbersome and expensive. This problem can be mitigated somewhat by building multi-technique functionality into a single system. For example, Jordan Valley has produced a tool, the JVX-5000, that combines GXR and XRF capabilities. As noted previously, GXR analysis can be used to measure films less than 2000 A thick, while XRF analysis is better suited for thicker films (such as ECP copper layers). However, the Jordan Valley tool incorporates an EDX detector to measure the characteristic x-rays generated during the XRF process, thereby significantly restricting the capabilities of the Jordan Valley tool. As described previously with respect to FIG. 4 a , the low resolution of an EDX detector limits its use to materials that generate x-rays having substantially different wavelengths.  
           [0024]    Accordingly, it is desirable to provide a tool that includes multi-technique capabilities to overcome limitations associated with individual analysis techniques, while reducing instrument cost, part-count, and increasing analytical efficiency.  
         SUMMARY  
         [0025]    The present invention provides a system and method for incorporating multiple film analysis techniques in a single instrument. This multi-technique capability can enable a user to perform a larger variety of analyses without purchasing multiple tools. Furthermore, combining the components required for the various analytical techniques in a single tool can lead to design and/or usage efficiencies that can reduce costs and increase throughput relative to separate single-technique tools.  
           [0026]    According to an embodiment of the present invention, a film analysis system includes both EMP and XRF analysis capabilities. EMP capability is provided by an e-beam generator for directing an e-beam at a sample coating (i.e., a film or films to be analyzed) and an x-ray detector(s) for measuring characteristic x-rays generated by the sample coating in response to the source e-beam. The x-ray detector(s) can be either an EDX detector(s), a WDX detector(s), or a combination of both types. XRF capability is provided by a microfocus x-ray tube and an x-ray beam focusing system for focusing a source x-ray beam from the microfocus x-ray tube onto the sample coating to generate characteristic x-rays via x-ray fluorescence. These characteristic x-rays can be measured by the same x-ray detector(s) used in the EMP analysis, thereby reducing part count and cost of the film analysis system. Furthermore, the film analysis system beneficially enables rapid EMP analysis for thinner films, while providing the capability for performing XRF analysis for thicker films.  
           [0027]    According to another embodiment of the present invention, a film analysis system includes both GXR and XRF analysis capabilities. GXR capability is provided by a microfocus x-ray tube, a x-ray beam focusing system for focusing the source x-ray beam from the microfocus x-ray tube onto a sample coating (i.e., a film or films to be analyzed), and a position-sensitive detector for measuring the interference pattern generated by the reflected x-rays from the sample coating. The film analysis system also includes a WDX x-ray detector(s) that can perform XRF analysis on the characteristic x-rays emitted by the sample coating in response the portion of the source x-ray beam that is absorbed, rather than reflected, by the sample coating. Because a separate microfocus x-ray tube and x-ray beam focusing system are not required for the XRF analysis, part count and cost of the film analysis system is reduced. Alternatively, a separate microfocus x-ray tube and x-ray beam focusing system for XRF analysis could be included so that operational settings could be optimized for both the GXR and XRF analyses. In either case, combining the two techniques in a single tool advantageously enables accurate GXR thickness measurement coupled with accurate XRF composition measurement. In addition, the film analysis system beneficially enables the GXR and XRF analyses to be performed simultaneously or in rapid succession with each other, thereby improving analysis throughput. Furthermore, by using a WDX detector(s), the resolution of the XRF analysis is significantly enhanced over conventional tools using an EDX detector(s).  
           [0028]    According to another embodiment of the present invention, a film analysis system includes both GXR and EMP analysis capabilities. GXR capability is provided by a microfocus x-ray tube, a x-ray beam focusing system for focusing the source x-ray beam from the microfocus x-ray tube onto a sample coating (i.e., a film or films to be analyzed), and a position-sensitive detector for measuring the interference pattern generated by the reflected x-rays from the sample coating. EMP capability is provided by an e-beam generator for directing an e-beam at the sample coating, and an x-ray detector(s) for measuring characteristic x-rays generated by the sample coating in response to the source e-beam. The x-ray detector(s) can be either an EDX detector(s), a WDX detector(s), or a combination of both types. By combining the two techniques in a single tool, accurate GXR thickness measurement can be coupled with accurate XRF composition measurement. In addition, the film analysis system beneficially enables the GXR and EMP analyses to be performed simultaneously or in rapid succession, thereby improving analysis throughput.  
           [0029]    According to another embodiment of the present invention, a film analysis system includes GXR, XRF, and EMP analysis capabilities. GXR capability is provided by a microfocus x-ray tube, a x-ray beam focusing system for focusing the source x-ray beam from the microfocus x-ray tube onto a sample coating (i.e., a film or films to be analyzed), and a position-sensitive detector for measuring the interference pattern generated by the reflected x-rays from the sample coating. EMP capability is provided by an e-beam generator for directing an e-beam at the sample coating, and an x-ray detector(s) for measuring characteristic x-rays generated by the sample coating in response to the source e-beam. The x-ray detector(s) can be either an EDX or WDX detector(s). To minimize component count, XRF capability can be provided by properly selecting and configuring the microfocus x-ray tube, so that a portion of the source x-ray beam is absorbed by the sample coating. The characteristic x-rays emitted by the sample coating in response to the absorbed source x-rays can then be measured by the x-ray detector(s) (used also in for EMP analysis).  
           [0030]    Alternatively, to optimize XRF and GXR performance, a second microfocus x-ray tube can be included to generate the source x-ray beam for XRF analyses. In any case, combining all three techniques in a single tool provides maximum flexibility in film analysis, and allows for component count reduction and/or throughput enhancement, as described with respect to the aforementioned embodiments.  
           [0031]    The present invention will be more fully understood in view of the following description and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]    [0032]FIG. 1 shows a conventional grazing incidence x-ray reflectometry (GXR) system.  
         [0033]    [0033]FIG. 2 shows a conventional electron microprobe analysis (EMP) system.  
         [0034]    [0034]FIG. 3 shows a conventional x-ray fluorescence (XRF) system.  
         [0035]    [0035]FIG. 4 a  shows a conventional energy-dispersive x-ray spectrometer (ESX).  
         [0036]    [0036]FIG. 4 b  shows a conventional wavelength-dispersive x-ray spectrometer (WDX).  
         [0037]    [0037]FIG. 5 shows a film analysis system combining XRF and EMP, in accordance with an embodiment of the present invention.  
         [0038]    [0038]FIG. 6 shows a film analysis system combining GXR and XRF using WDX, in accordance with an embodiment of the present invention.  
         [0039]    [0039]FIG. 7 shows a film analysis system combining GXR and EMP, in accordance with an embodiment of the present invention.  
         [0040]    [0040]FIG. 8 shows a film analysis system combining GXR, EMP, and XRF, in accordance with an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0041]    By combining the capability to perform multiple analysis techniques in a single instrument, the present invention advantageously improves overall tool expenses and/or improves analysis throughput.  
         [0042]    Electron Microprobe Analysis and X-Ray Fluorescence  
         [0043]    An embodiment of the present invention provides a film analysis system that advantageously combines the rapid measurement capabilities of EMP for thinner films with the thicker film measurement capabilities of XRF. In accordance with an embodiment of the present invention, FIG. 5 shows a film analysis system  500  that comprises a microfocus x-ray tube  512 , an x-ray beam focusing system  520 , an e-beam generator  511 , and an x-ray detector  531 . Film analysis system is configured to analyze a test sample  540  that includes a sample coating  541  formed on a substrate  542 . Note that substrate  542  can comprise any material on which a coating can be formed, including silicon, gallium arsenide, and metal. Note also that sample coating  541  can comprise any material or materials that can be analyzed using EMP and/or XRF, including oxides, nitrides, copper, titanium, and tantalum, among others. Sample coating  541  can also comprise multiple layers or thin films, such as a copper layer formed over a titanium nitride or tantalum nitride layer.  
         [0044]    To perform an EMP analysis, e-beam generator  511  directs an e-beam  580  at sample coating  541 . The high-energy electrons in e-beam  580  cause characteristic x-rays  590  to be emitted by sample coating  541 . Characteristic x-rays  590  are then measured by x-ray detector  531  to determine the composition and thickness of sample coating  541 . According to an embodiment of the present invention, x-ray detector  531  can comprise an EDX detector, as described with respect to FIG. 4 a . According to another embodiment of the present invention, x-ray detector  531  can comprise a WDX detector, as described with respect to FIG.  4   b , which would improve measurement resolution. Also, film analysis system  500  can comprise multiple x-ray detectors, as indicated by optional x-ray detector  532 . While only a single additional x-ray detector ( 532 ) is depicted for clarity, film analysis system  500  could comprise any number of x-ray detectors. Multiple WDX detectors would enable simultaneous measurement of characteristic x-rays having different wavelengths (i.e., characteristic x-rays from different elements in sample coating  541 ).  
         [0045]    To perform an XRF operation, microfocus x-ray tube  512  directs an x-ray beam  550  at x-ray beam focusing system  520 . X-ray beam focusing system  520  focuses the diverging x-rays of x-ray beam  550  into a converging x-ray beam  560 , directed at sample coating  541  of test sample  540 . According to an embodiment of the present invention, x-ray beam focusing system  520  can comprise an x-ray reflector  521  that redirects and focuses x-ray beam  550  into x-ray beam  560 . X-ray reflector  521  could be a singly- or doubly-curved crystal, and could also be a monochromator to ensure that only x-rays of a particular wavelength are included in x-ray beam  560 . However, note that x-ray reflector  521  is depicted for explanatory purposes only, as x-ray beam focusing system  520  can comprise any system for focusing x-ray beam  550  onto sample coating  541 . For example, according to another embodiment of the present invention, x-ray beam focusing system  520  can comprise a polycapillary array, in which multiple tubular waveguides direct the incoming x-rays in x-ray beam  550  to a localized spot on sample coating  541 .  
         [0046]    The x-rays in x-ray beam  560  cause characteristic x-rays  590  to be emitted by sample coating  541 . X-ray detector  531  then measures characteristic x-rays  590  to determine the composition and thickness of sample coating  541 , in a manner similar to that described with respect to the EMP analysis. If film analysis system  500  includes additional x-ray detectors such as x-ray detector  532 , measurements using those additional detectors could be taken at the same time. Because the XRF operation can use at least some of the same x-ray detector(s) as the EMP operation, the cost and complexity of film analysis system  500  is reduced.  
         [0047]    The inclusion of both e-beam generator  511  and microfocus x-ray tube  512  greatly increases the flexibility of film analysis system  500  over conventional single-technique tools. For example, a semiconductor manufacturing process might include first process step comprising the formation of a copper (Cu) seed/tantalum nitride (TaN) barrier film stack on a silicon X wafer, followed by a second process step comprising electro-plating a thick copper layer over the Cu—TaN seed/barrier film stack. After the first process step, film analysis system  500  could be used to perform an EMP analysis on the thin films making if up the Cu—TaN seed/barrier stack. Then after the second process step, film analysis system  500  could be used to perform an XRF analysis on the thick ECP copper layer.  
         [0048]    According to an embodiment of the present invention, e-beam generator  511  could be a variable-power device capable of producing an e-beam  580  having a 5 keV-35 keV energy level, while microfocus x-ray tube  512  could be configured to generate molybdenum x-rays (Mo-K). During the EMP analysis, the Cu-K, Ta-L, and N-K characteristic x-ray intensities could be measured at e-beam energies of 10 keV, 15 keV, and 25 keV to determine the copper seed film and tantalum nitride barrier film thicknesses, along with the tantalum-to-nitrogen ratio in the TaN barrier film. Note that simultaneously measuring all three types of x-rays would require three different x-ray detectors. Note further that, as mentioned previously, WDX detectors would have to be used to differentiate the Cu-K and Ta-L x-rays, as well as detect the softer N-K x-rays. Then during the XRF analysis, the Cu-K and Ta-L x-rays generated in response to the Mo-K x-rays from microfocus x-ray tube  512  could be measured to determine the total thickness of the ECP copper layer and the copper seed film. Note that a similar analytical procedure could be applied to a sample coating that included a titanium nitride barrier film instead of tantalum nitride  
         [0049]    Grazing Incidence X-Ray Reflectometry and X-Ray Fluorescence  
         [0050]    In accordance with an embodiment of the present invention, FIG. 6 shows a film analysis system  600  that advantageously combines the precision thin film thickness measurement capabilities of GXR with the high-resolution composition measurement capabilities of XRF using WDX detectors. Film analysis system  600  comprises a microfocus x-ray tube  612 , an x-ray beam focusing system  620 , a WDX x-ray detector  631 , and a position-sensitive detector  633 . Film analysis system  600  is configured to analyze a test sample  640  that includes a sample C coating  641  formed on a substrate  642 . As noted previously, substrate  642  can comprise any material on which a film can be formed, while sample coating  641  can comprise a single or multiple films of various compositions.  
         [0051]    To perform a GXR analysis, microfocus x-ray tube  612  directs a source x-ray beam  650  at x-ray beam focusing system  620 , which reflects and focuses the diverging x-rays of x-ray beam  650  into a converging x-ray beam  660  directed at sample coating  641 . According to an embodiment of the present invention, x-ray beam focusing system  620  can comprise an x-ray reflector  621  that redirects x-ray beam  650  into converging x-ray beam  660 , focused on a spot on the surface of sample coating  641 . X-ray reflector  621  could be a singly- or doubly-curved crystal, and could also be a monochromator to ensure that only x-rays of a particular wavelength are included in x-ray beam  660 . However, note that x-ray reflector  621  is depicted for explanatory purposes only, as x-ray beam focusing system  620  can comprise any system for focusing x-ray beam  650  onto sample coating  641 . For example, x-ray beam focusing system  620  could comprise a polycapillary array.  
         [0052]    Converging x-ray beam  660  is then reflected by sample coating  641  as an x-ray beam  670  onto position-sensitive detector  633 . Position-sensitive detector  633  resolves the varying intensity of the interference pattern caused by constructive and destructive interference of x-ray reflections at the top and bottom surfaces of sample coating  641 . The resulting reflectivity curve of intensity versus position can then be used to calculate the thickness of sample coating  641 , as described previously with respect to FIG. 1.  
         [0053]    Film analysis system  600  can also perform an XRF analysis by making use of the fact that x-ray beam  660  is typically not totally reflected by sample coating  641 . During the GXR process, a portion of x-ray beam  660  is absorbed by sample coating  641 , rather than being reflected. Note that this proportion of absorbed x-rays can be adjusted by properly selecting and configuring microfocus x-ray tube  612  and x-ray focusing system  620 . The absorbed x-rays excite the atoms of sample coating  641 , causing them to generate characteristic x-rays  680 . Characteristic x-rays  680  can then be measured by x-ray detector  631  to determine the composition of sample coating  641 . Note that film analysis system  600  can comprise multiple WDX x-ray detectors, as indicated by optional WDX x-ray detector  632 . While only a single additional WDX x-ray detector ( 632 ) is depicted for clarity, film analysis system  600  could comprise any number of additional WDX x-ray detectors and/or an EDX detector. Multiple WDX detectors would enable simultaneous measurement of characteristic x-rays having different wavelengths (i.e., characteristic x-rays from different elements in sample coating  641 ).  
         [0054]    By combining GXR and XRF capabilities in film analysis system  600 , the thickness of sample coating  641  can be accurately measured using GXR while the composition of sample coating  641  can be accurately determined using XRF. Furthermore, the use of WDX x-ray detector(s)  631  (and  632 ) enables film analysis system  600  to measure low-energy characteristic x-rays (e.g., N-K x-rays) and closely spaced x-rays (e.g., Cu-K and Ta-L x-rays) that cannot be resolved by the ESX detectors used in conventional tools combining GXR and XRF. For example, sample coating  641  could comprise a copper seed film formed over a tantalum nitride barrier film. According to an embodiment of the present invention, microfocus x-ray tube  612  could be configured to generate high-energy molybdenum x-rays (Mo-K) used to perform a GXR analysis on the copper seed film. At the same time, the Mo-K x-rays would be inducing Cu-K, Ta-L, and N-K characteristic x-rays from the seed/barrier stack, allowing an XRF analysis to be performed on the tantalum nitride barrier film. Because microfocus x-ray tube  612  generates high-energy Mo-K x-rays, a thick ECP copper layer subsequently formed over the copper seed film could be measured by film analysis system  600  using XRF.  
         [0055]    According to another embodiment of the present invention, microfocus x-ray tube  612  could be configured to generate lower-energy tungsten x-rays (W-L), in which case simultaneous GXR and XRF analyses could be performed on the seed/barrier stack. A thick ECP copper film could no longer bereadily measured by such a system, and a smaller proportion of the low-energy W-L x-rays would be absorbed by sample coating  641 , resulting in a reduction in the strength of characteristic x-rays  680 . However, this reduced absorption also means a stronger reflected signal, thereby enhancing the GXR fidelity of film analysis system  600 . Note that according to another embodiment of the present invention, microfocus x-ray tube  612  could be configured to generate low-energy copper Cu-K x-rays to provide similar measurement capabilities.  
         [0056]    In accordance with another embodiment of the present invention, separate x-ray microfocus tubes could be incorporated into film analysis system  600 , as indicated by optional microfocus tube  613 . One microfocus x-ray tube could then provide the (lower-energy) x-rays for the GXR analysis, while the other could provide the (higher-energy) x-rays for the XRF analysis. For example, microfocus x-ray tube  613  could be configured to provide high-energy Mo-K x-rays for XRF, directing an x-ray beam  651  at an x-ray beam focusing system  622 , which focuses a reflected x-ray beam  661  onto sample coating  641 . As previously described with respect to x-ray beam focusing system  620 , x-ray beam focusing system  622  can comprise any type of beam-guiding system, including an x-ray reflector  623  as depicted, or a polycapillary array (not shown). The high-energy Mo-K x-rays can then cause sample coating  641  to emit strong characteristic x-rays  680 , optimizing the associated XRF analysis. Meanwhile, microfocus x-ray tube  612  could be configured to provide lower-energy W-L (or Cu-K) x-rays for the GXR analysis, maximizing the strength of the interference pattern provided at position-sensitive detector  633 .  
         [0057]    Grazing Incidence X-Ray Reflectometry and Electron Microprobe Analysis  
         [0058]    In accordance with an embodiment of the present invention, FIG. 7 shows a film analysis system  700  that combines GXR and EMP capabilities in a single tool, advantageously combining the precision thin film thickness measurement capabilities of GXR with the composition measurement capabilities of EMP. Film analysis system  700  comprises a microfocus x-ray tube  712 , an x-ray beam focusing system  720 , a position-sensitive detector  733 , an e-beam generator  711 , and an x-ray detector  731 . Film analysis system  700  is configured to analyze a test sample  740  that includes a sample coating  741  formed on a substrate  742 . As noted previously, substrate  742  can comprise any material on which a film can be formed, while sample coating  741  can comprise a single or multiple films of various compositions.  
         [0059]    To perform a GXR analysis, microfocus x-ray tube  712  directs a source x-ray beam  750  at x-ray beam focusing system  720 , which reflects and focuses the diverging x-rays of x-ray beam  750  into a converging x-ray beam  760  directed at sample coating  741 . According to an embodiment of the present invention, x-ray beam focusing system  720  can comprise an x-ray reflector  721  that redirects x-ray beam  750  into converging x-ray beam  760 , focused on a spot on the surface of sample coating  741 . X-ray reflector  721  could be a singly- or doubly-curved crystal, and could also be a monochromator to ensure that only x-rays of a particular wavelength are included in x-ray beam  760 . However, note that x-ray reflector  721  is depicted for explanatory purposes only, as x-ray beam focusing system  720  can comprise any system for focusing x-ray beam  750  onto sample coating  741 . For example, by configuring microfocus x-ray tube  712  with an additional non-focusing monochromator to produce an x-ray beam  750  made up of x-rays of a single wavelength, monochromatizing by x-ray beam focusing system  720  would not be required, and x-ray beam focusing system  720  could comprise a polycapillary array.  
         [0060]    Converging x-ray beam  760  is then reflected by sample coating  741  as an x-ray beam  770  onto position-sensitive detector  733 . Position-sensitive detector  733  resolves the varying intensity of the interference pattern caused by constructive and destructive interference of x-ray reflections at the top and bottom surfaces of sample coating  741 . The resulting reflectivity curve of intensity versus position can then be used to calculate the thickness of sample coating  741 , as described previously with respect to FIG. 1.  
         [0061]    To perform an EMP analysis, e-beam generator  711  directs an e-beam  780  at sample coating  741 . The high energy electrons in e-beam  780  cause characteristic x-rays  790  to be emitted by sample coating  741 . Characteristic x-rays  790  are then measured by x-ray detector  731  to determine the composition and thickness of sample coating  741 . According to an embodiment of the present invention, x-ray detector  731  can comprise an EDX detector, as described with respect to FIG. 4 a . According to another embodiment of the present invention, x-ray detector  731  can comprise a WDX detector, as described with respect to FIG. 4 b , which would improve measurement resolution. Also, film analysis system  700  can comprise multiple x-ray detectors, as indicated by optional x-ray detector  732 . While only a single additional x-ray detector ( 732 ) is depicted for clarity, film analysis system  700  could comprise any number of additional EDX and/or WDX x-ray detectors. Multiple WDX detectors would enable simultaneous measurement of characteristic x-rays having different wavelengths (i.e., characteristic x-rays from different elements in sample coating  741 ).  
         [0062]    By combining GXR and EMP capabilities in film analysis system  700 , the relative weaknesses of each technique can be compensated for by the other. As noted previously, GXR analysis typically does not provide good composition measurement, while EMP typically cannot accurately measure the thickness of a film. However, in film analysis system  700 , the thickness of sample coating  741  can be accurately measured using GXR while the composition of sample coating  741  can be accurately determined using EMP. Furthermore, both types of analysis can be performed simultaneously or in rapid succession with each other, significantly improving analysis throughput over conventional systems in which the GXR analysis would be performed in one tool, and the EMP analysis would have to be performed in a different tool, after completion of the GXR analysis.  
         [0063]    Grazing Incidence X-Ray Reflectometry, Electron Microprobe Analysis, and X-Ray Fluorescence  
         [0064]    In accordance with an embodiment of the present invention, FIG. 8 shows a film analysis system  800  that advantageously combines the precision film thickness measurement capabilities of GXR with the efficient thin film composition measurement capabilities of EMP and the thicker film composition measurement capabilities of XRF. Film analysis system  800  comprises a microfocus x-ray tube  812 , an x-ray beam focusing system  820 , an e-beam generator  811 , an x-ray detector  831 , and a position-sensitive detector  833 . Film analysis system  800  is configured to analyze a test sample  840  that includes a sample coating  841  formed on a substrate  842 . As noted previously, substrate  842  can comprise any material on which a film can be formed, while sample coating  841  can comprise a single or multiple films of various compositions.  
         [0065]    To perform a GXR analysis, microfocus x-ray tube  812  directs a source x-ray beam  850  at x-ray beam focusing system  820 , which reflects and focuses the diverging x-rays of x-ray beam  850  into a converging x-ray beam  860  directed at sample coating  841 . According to an embodiment of the present invention, x-ray beam focusing system  820  can comprise an x-ray reflector  821  that redirects x-ray beam  850  into converging x-ray beam  860 , focused on a spot on the surface of sample coating  841 . X-ray reflector  821  could be a singly- or doubly-curved crystal, and could also be a monochromator to ensure that only x-rays of a particular wavelength are included in x-ray beam  860 . However, note that x-ray reflector  821  is depicted for explanatory purposes only, as x-ray beam focusing system  820  can comprise any go system for focusing x-ray beam  850  onto sample coating  841 . For example, by configuring microfocus x-ray tube  812  with an additional monochromator to produce an x-ray beam  850  made up of x-rays of a single wavelength, monochromatizing by x-ray beam focusing system  820  would not be required, and x-ray beam focusing system  820  could comprise a polycapillary array.  
         [0066]    Converging x-ray beam  860  is then reflected by sample coating  841  as an x-ray beam  870  onto position-sensitive detector  833 . Position-sensitive detector  833  measures the varying intensity of the interference pattern caused by constructive and destructive interference of x-ray reflections at the top and bottom surfaces of sample coating  841 . The resulting reflectivity curve of intensity versus position can then be used to calculate the thickness of sample coating  841 , as described previously with respect to FIG. 1.  
         [0067]    As described previously with respect to FIG. 6, film analysis system  800  can also perform an XRF analysis by measuring characteristic x-rays  890  generated by those x-rays in x-ray beam  860  that are absorbed by sample coating  842 , rather than being reflected. Characteristic x-rays  890  can be measured by x-ray detector  831  to determine the composition of sample coating  841 . According to an embodiment of the present invention, x-ray detector  831  can comprise an EDX detector, as described with respect to FIG. 4 a . According to another embodiment of the present invention, x-ray detector  831  can comprise a WDX detector, as described with respect to FIG. 4 b , which would improve measurement resolution. Also, film analysis system  800  can comprise multiple x-ray detectors, as indicated by optional x-ray detector  832 . While only a single additional x-ray detector ( 832 ) is depicted for clarity, film analysis system  800  could comprise any number of x-ray detectors. For example, multiple WDX detectors would enable simultaneous measurement of characteristic x-rays having different wavelengths (i.e., characteristic x-rays from different elements in sample coating  841 ).  
         [0068]    In accordance with another embodiment of the present invention, a separate x-ray microfocus tube  813  could provide the excitation source for the XRF analysis. Microfocus x-ray tube  813  would then direct an x-ray beam  851  at an x-ray beam focusing system  822 , which would focus a reflected x-ray beam  861  onto sample coating  841 . As previously described with respect to x-ray beam focusing system  820 , x-ray beam focusing system  822  could comprise any type of beam-guiding system, including an x-ray reflector  823  as depicted, or a polycapillary array (not shown). X-ray detector(s)  831  (and  832 ) would then measure characteristic x-rays  890  generated by sample coating  841  in response to x-ray beam  861 .  
         [0069]    Regardless of whether or not film analysis system  800  includes a separate x-ray microfocus tube for XRF analysis, at least some of the same x-ray detector(s) used in the XRF operation can also be used to perform an EMP analysis, by measuring characteristic x-rays  890  generated in response to an e-beam  880  from e-beam generator  811 . As previously described with respect to FIG. 5, by sharing some of the same x-ray detectors for both XRF and EMP, the benefits of both analysis techniques can be provided with a minimum of cost and a minimum of equipment. By using the same microfocus x-ray tube  812  for GXR and XRF, the cost and complexity of film analysis system  800  is further reduced, even as the overall capabilities of film analysis system  800  are increased.  
         [0070]    Thus, a multi-technique film analysis system is described. Although the present invention has been described in connection with several embodiments, it is understood that this invention is not limited to the embodiments disclosed, but is capable of various modifications that would be apparent to one of ordinary skill in the art. Thus, the invention is limited only by the following claims.

Technology Category: g