X-ray or gamma ray systems or devices – Specific application – Diffraction – reflection – or scattering analysis
Reexamination Certificate
1999-07-30
2001-10-09
Font, Frank G. (Department: 2877)
X-ray or gamma ray systems or devices
Specific application
Diffraction, reflection, or scattering analysis
C378S070000, C378S073000, C378S079000, C378S044000, C378S045000
Reexamination Certificate
active
06301330
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to the field of semiconductor manufacturing, and more specifically to crystallographic texture measurement and analysis systems for polycrystalline materials on wafers.
2. Background of the Invention
The physical properties of single crystals, such as electric, elastic, and magnetic properties, are directionally dependent and usually represented by tensors of the second, fourth and sixth order, respectively. As a consequence, a polycrystalline material, which is an aggregate of single crystals (called grains or crystallites), has anisotropic properties. The degree of anisotropy of a macroscopic specimen depends on the orientation distribution of its crystallites, or texture, with respect to the sample fixed coordinate system.
As an example, most thin film metallization processes for semiconductor applications result in a preferred orientation of grains with respect to growth surface. The crystallographic texture of thin films and discrete structures used in integrated circuits greatly affects their reliability and performance, and may be controlled by tunable manufacturing processes. A discussion of the importance of texture and disclosure of texture control methods is found in the paper titled “Microstructure Control in Semiconductor Metallization”, J. M. E. Harper, K. P. Rodbell, J. Vac. Sci. Technology, 15 (4), 763-779, (1997).
The quantitative measure of texture can be described by the so-called Orientation Distribution Function (ODF) which permits one to describe texture in a rigorous mathematical way and to calculate the macroscopic properties from the corresponding single crystal properties. However, a direct method of ODF measurement has not been developed. The experimental determination of ODF is currently only performed by destructive and time-consuming measurements of orientation and volume of large numbers of individual grains, subsequent mathematical analysis of which then yields a unique ODF for the sample of interest.
X-ray diffraction is a well-known technique for measuring the physical properties of polycrystalline materials. See, for example, H. P. Klug, L. E. Alexander, “X-ray Diffraction Procedures”, Wiley & Sons, (1974). X-rays diffracted from the surface of a polycrystalline material provide direct information about the size, spacing, and orientation of crystallites that comprise the polycrystalline material. X-rays impinging on the material will scatter in all directions. Constructive interference of the scattering x-rays occurs only at particular angles that the scattering x-rays make with the incident x-ray beam, and is dependent on the crystalline spacing and orientation. This information is represented in the form of diffracted x-ray intensity versus the diffraction angle from incident beam. Constructive interference of scattered x-rays from the crystalline structure results in intensity maxima, also referred to as diffraction peaks. Each particular set of crystalline structures of a material will have an associated diffraction peak that occurs at a particular angle.
There exist numerous commercial x-ray diffraction instruments that measure the physical properties from which the texture of polycrystalline materials may be determined, including those produced by Philips Analytical X-ray, Bruker AXS, Rigaku International Corp., Scintag Inc., Bede Scientific Inc. and others. However, use of these systems for texture determination, while feasible, is nonetheless time-consuming, lacks sufficient resolution, and is limited to relatively small semiconductor wafers. Furthermore, these current systems contain inherent limitations that make their conversion to a rapid, high precision measurement tool for large uncut wafers (e.g., 200 millimeter diameter, and recently introduced 300 millimeter diameter) problematic. The speed of measurement, obtainable measurement resolution, and applicable wafer size remain as limitations of the state of the art in texture analysis of semiconductor wafers.
Using an area x-ray detector on an x-ray diffraction instrument increases the speed of texture analysis considerably, but area x-ray detectors are not currently used as efficiently as possible for texture analysis. This is primarily due to the fact that they employ traditional texture analysis protocols that do not efficiently use all of the diffraction information captured by the area detector. The resultant measurement time is still quite long. As a consequence, fewer samples are typically analyzed due to the excessive measurement times required.
Motion control systems have been built into x-ray diffraction systems for the mapping of texture over the surface of a large (e.g., 150 millimeter) wafer, but they too are not designed to make the most efficient use of diffraction information obtained from the area detector. Such motion control systems also tend to be complex and very expensive. Even if current x-ray diffraction systems utilizing area detectors were converted to map texture in larger wafers (by increasing the size of the texture mapping stages), they would be extremely inefficient, complex, costly, and slow. Efficient integration of a wafer motion system (for mapping texture over the entire wafer surface) with an area x-ray detector has not been achieved with the currently available instruments.
The current texture analysis methodologies additionally are not suitable for new generations of materials (such as polycrystalline and epitaxial films, or superconductors) that have sharp textures. The methods lack the required resolution, do not take advantage of the sample and crystal symmetry in order to expedite testing, and do not take advantage of modern computing capabilities. The current texture analysis methodologies do not make efficient use of all the diffraction data captured on an area x-ray detector. While texture analysis using current commercial x-ray systems is versatile, it is tedious, slow and requires a highly trained operator. The present systems are not practical for large sample throughput rates and automated operation, as would be required for commercial manufacturing operations.
Considering texture analysis and the state of the art in more specific detail, the Orientation Distribution Function (ODF), the quantitative measure of texture, can be described in G-space, where the orientation g of an individual crystallite with respect to the reference system of the sample is described by three independent parameters (usually angles) g={&agr;, &bgr;, &ggr;}. A schematic representation of G-space is shown in
FIG. 1. A
direct method of ODF measurement does not exist. The experimental determination of ODF, as mentioned hereinabove, is possible through destructive and time consuming measurements of orientation and volume of large numbers of individual grains, which yield a unique ODF (see K. Lucke, H. Perlwitz, and W. Pitsch, “Elekronenmikroskopische Bestimmung der Orientierungsferteilung der Kristallite in gevaltztem Kupfer,” Phys. Stat. Sol. 7 (1964), 733-746, and F. Wagner “Texture Determination by Individual Orientation Measurement,” in Experimental Techniques in Texture Analysis, ed. H. J. Bunge (DGM, Oberusel, 1986), 115-124).
The more practical and nondestructive experimental method is the direct measurement of a volume of crystallites with two of the three angular parameters fixed and the third parameter varied through all possible values. This is the so-called pole figure measurement. The ODF is subsequently calculated from several pole figures (pole figure inversion). The term “pole figure” is understood as the intensity distribution of a certain physical quantity in reference to the sample coordinate system. The pole figure measurement is most commonly obtained by diffraction (of x-rays, neutrons or electrons). The measured physical quantity in this case is the intensity of x-rays diffracted from a particular set of crystallographic planes. The central problem of quantitative texture analysis is the reproduction of the ODF from experim
Kozaczek Krzysztof J.
Kurtz David S.
Moran Paul R.
Font Frank G.
Fuierer Marianne
Hultquist Steven J.
Hypernex, Inc.
Rodriguez Armando
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