Patent Number: 
Section: description

In accordance with a preferred embodiment of the present invention, FIG. 1 depicts a system 10 for the x-ray fluorescence analysis of a sample of interest. An x-ray source 20 emits a field of x-ray radiation 12 directed at a reflective optic 22. The reflective optic 22 may be used for collimating or monochromatizing the x-ray radiation 12. Alternatively, the system 10 may operate without the reflective optic 22. As shown, however, the field of x-ray radiation 12 impinges upon a sample of interest 24, such as a silicon wafer that needs to be analyzed to determine chemical impurities. Due to a known physical reaction between the field of x-ray radiation 12 and the sample 24, a field of fluorescent radiation 14 is emitted from the sample. The field of fluorescent radiation 14 contains information in the form of radiation emission lines about the type of atomic or molecular elements present in the sample 24. The field of fluorescent radiation 14 is selectively reflected from the multilayer structure 26 of the present invention, creating a reflected fluorescent radiation field 36. The reflected fluorescent radiation field 36 is subsequently received and analyzed by a detector 28 that is adapted to interpret qualitative and quantitative aspects of the reflected fluorescent radiation field 36. Radiation is selectively reflected from the multilayer structure 26 in accordance with Bragg""s equation, Equation 1 above, where a distance d is schematically referred to in FIG. 2 as reference numeral 18. As shown in FIG. 2, incident radiation 16 that impinges upon a surface at an angle xcex8 is reflected at intervals that correspond to the d-spacing 18. Constructive interference between a predetermined number of layers 18 creates a uniform field of reflected radiation 17. FIG. 3 depicts a multilayer structure 26 in accordance with a preferred embodiment of the present invention. The multilayer structure 26 generally includes a substrate 34, upon which a series of triadic layers 30 may be periodically formed. As shown, the substrate 34 is planar in nature. However, in alternative embodiments, the substrate 34 may be formed into a curved member. For example, the substrate 34 may be formed into an ellipsoid, a paraboloid, or a spheroid as necessary to accomplish a particular objective. A series of triadic layers 30 is periodically formed on the substrate 34 to create the multilayer structure 26 of the present invention. Each triadic layer 30 includes a triad of layers 32a, 32b, 32c, which are sequentially deposited upon the substrate 34 to create the necessary periodicity. The multilayer structure 26 is composed of between 1 and 100 triadic layers 30, or between 3 and 300 individual layers 32a, 32b, 32c. In a preferred embodiment, the multilayer structure 26 is composed of between 30 and 60 triadic layers 30, and each triadic layer 30 is between 5 and 60 nanometers in thickness. This thickness is otherwise referred to as the d-spacing of the multilayer structure 26. As noted, each triadic layer 30 is composed of a triad of layers 32a, 32b, 32c including a first layer 32a, a second layer 32b, and a third layer 32c. Preferably, the first layer 32a is composed of one member from a first group, where the first group includes lanthanum (La), lanthanum oxide (La2O3), or a lanthanum-based alloy. The second layer 32b is preferably composed of one member from a second group, where the second group includes carbon (C), boron (B), silicon (Si), boron carbide (B4C), or silicon carbide (SiC). The third layer 32c is preferably composed of one member from a third group, where the third group includes boron (B) or boron carbide (B4C). As depicted in FIG. 3, the second layer 32b is preferably disposed between the first layer 32a and the third layer 32c.  In a second preferred embodiment of the present invention, shown in FIG. 4, the base period 31 of the multilayer structure 26 includes at least one quartet of layers 36a, 36b, 36c, 36d. A series of quartic layers 31 is periodically formed on the substrate 34 to create the multilayer structure 26 of the present embodiment. Each quartic layer 31 includes a quartet of layers 36a, 36b, 36c, 36d which are sequentially deposited upon the substrate 34 to create the necessary periodicity. The multilayer structure 26 is composed of between 1 and 100 quartic layers 31, or between 4 and 400 individual layers 36a, 36b, 36c, 36d. In a preferred embodiment, the multilayer structure 26 is composed of between 30 and 60 quartic layers 31, and each quartic layer 30 is between 5 and 60 nanometers in thickness. This thickness is otherwise referred to as the d-spacing of the multilayer structure 26. As noted, each quartic layer 31 is composed of a quartet of layers 36a, 36b, 36c, 36d including a first layer 36a, a second layer 36b, a third layer 36c, and a fourth layer 36d. Preferably, the first layer 36a is composed of one member from a first group, where the first group includes lanthanum (La), lanthanum oxide (La2O3), or a lanthanum-based alloy. The second layer 36b is preferably composed of one member from a second group, where the second group includes carbon (C), boron (B), silicon (Si), boron carbide (B4C), or silicon carbide (SiC). The third layer 36c is preferably composed of one member from a third group, where the third group includes boron (B) or boron carbide (B4C). The fourth layer 36d is preferably composed of one member from a fourth group, where the fourth group includes carbon (C), boron (B), silicon (Si), boron carbide (B4C), or silicon carbide (SiC). In a preferred embodiment, the second layer 36b and the fourth layer 36d are chemically identical, although their respective geometrical characteristics will preferably be non-identical. As depicted in FIG. 4, the second layer 36b is preferably disposed between the first layer 36a and the third layer 36c, and the third layer 36c is preferably disposed between the second layer 36b and the fourth layer 36d.  It is a feature of the present invention that the multilayer structure 26 may be shaped or otherwise tailored to maximize the performance of the system 10. For example, the multilayer structure 26 shown in FIGS. 3 and 4 may be shaped into a conic section, such as an ellipsoid, paraboloid, or spheroid in order to regulate the magnitude of the angle of incidence xcex8 at different points on the surface of the multilayer structure 26. By shaping the surface of the multilayer structure 26, the field of fluorescent radiation 14 can be conditioned in a particular manner such that the reflected field of fluorescent radiation 36 is focused upon the detector 28 in a preferred fashion. Additionally, the d-spacing of the multilayer structure 26 shown in FIGS. 3 and 4, i.e. the thickness of the triadic layer 30 or the quartic layer 31, may be varied along the depth of the multilayer structure 26, or alternatively, along a lateral axis of the multilayer structure 26. The latter manipulations are known as depth graded d-spacing and laterally graded d-spacing, respectively. The present invention as described in its preferred embodiments thus improves the procedure of x-ray fluorescent spectroscopy by providing a durable multilayer structure with improved spectral resolution, in particular with respect to the fluorescent radiation of boron. In particular, the formation of the multilayer structure composed of triadic or quartic periods greatly increases the overall performance of an x-ray fluorescence spectroscopy system. Both the triadic and quartic periods increase the longevity of the multilayer optic by adding structural integrity to the system, as well as dramatically improved resistance to water. It should be apparent to those skilled in the art that the above-described embodiments are merely illustrative of but a few of the many possible specific embodiments of the present invention. Numerous and various other arrangements can be readily devised by those skilled in the art without departing from the spirit and scope of the invention as defined in the following claims.