X-ray or gamma ray systems or devices – Specific application – Fluorescence
Reexamination Certificate
2000-04-18
2002-09-17
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Fluorescence
C378S082000
Reexamination Certificate
active
06453002
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to X-ray spectrometry, and specifically to methods and devices to detect and analyze X-ray microfluorescence.
BACKGROUND OF THE INVENTION
X-ray microfluorescence analysis is a non-destructive technique known in the art for determining the atomic composition and thickness of thin films. Typically, a focused X-ray beam is directed at a sample, and the X-ray fluorescence induced by the interaction of the X-rays with the sample is detected by a detector located near the sample. The composition and thickness of the irradiated sample are determined from the intensity and energy of the fluorescent X-ray photons.
In “Annular-Type Solid State Detector for a Scanning X-Ray Analytical Microscope,”
Review of Scientific Instruments
66(9) (September, 1995) pp. 4544-4546, which is incorporated herein by reference, Shimomura and Nakazawa describe an annular germanium detector located near an irradiated sample which transduces the energy resulting from X-ray fluorescence into a single channel of data.
U.S. Pat. No. 5,937,026, to Satoh, whose disclosure is incorporated herein by reference, describes a microfluorescent X-ray analyzer in which a capillary tube is used to deliver X-ray excitation to a small region of a sample. The capillary passes through a hole in the center of a flat plate solid-state X-ray detector, which is used to detect fluorescent X-rays emitted by the sample. The geometry of the capillary tube and the detector allows fluorescent X-rays from a small excitation region to be detected over a large solid angle.
U.S. Pat. No. 3,256,431, to Fraser, U.S. Pat. No. 3,581,087, to Brinkerhoff and U.S. Pat. No. 5,778,039, to Hossain, whose disclosures are incorporated herein by reference, describe systems for detection and analysis of X-ray fluorescence using multiple detectors. In all of these patents, a sample is excited by an X-ray source, and the multiple detectors are used to detect the X-ray fluorescence in different, respective energy domains. Typically, the energy domains are chosen to correspond to emission bands of different elements in the sample, so that comparative measurements can be made of the relative concentrations of two elements, for example.
U.S. Pat. No. 5,497,008, to Kumakhov, which is incorporated herein by reference, describes analytic instruments using a polycapillary X-ray optic, also known as a Kumakhov lens, for X-ray fluorescence analysis or spectroscopy. The instruments described use a single fluorescence detector.
SUMMARY OF THE INVENTION
It is an object of some aspects of the present invention to provide improved apparatus and methods for X-ray microfluorescence analysis.
It is a further object of some aspects of the present invention to provide apparatus and methods for detection and analysis of X-ray microfluorescence associated with very small geometrical features of a sample.
It is yet a further object of some aspects of the present invention to provide apparatus and methods for detection of faults occurring in production of semiconductor devices.
In preferred embodiments of the present invention, an X-ray microfluorescence analyzer comprises an X-ray source which irradiates a small spot on a sample, and a plurality of individual detectors arrayed around the spot, so as to capture X-ray photons emitted from the sample responsive to the X-ray illumination. Preferably, the detectors are arrayed in a generally symmetrical pattern about the spot. A processing unit receives signals from the detectors and processes them to compare the intensity of photon emission captured by the different detectors, and thus to detect variations in the intensity as a function of azimuth about the irradiation beam. These variations are indicative of directional inhomogeneity of the emission from the sample.
The detected azimuthal differences in the intensity of emission in a selected energy range are preferably used to determine properties of microscopic structures in the sample under test. Alternatively or additionally, the differences are monitored in order to accurately align the X-ray source and detectors with such structures. The method of the present invention, wherein multiple detectors are used simultaneously to measure emission in a common energy range at different azimuths, is substantively different from methods of X-ray fluorescence analysis known in the art. Such methods, as described in the Background of the Invention, are generally based on detection at only a single azimuth at any given time. When multiple detectors are used, their purpose is to measure emission in different, respective energy ranges, and directional inhomogeneity of emission is not considered.
In some preferred embodiments of the present invention, the analyzer is used to measure overlay errors between successive layers, such as metallization layers, created on a semiconductor wafer in the course of integrated circuit production. Preferably, a test zone is created on the wafer, in which a pattern in a lower layer, using a first element,is overlaid by a substantially identical pattern in an upper layer, using a second, different element. The first and second elements are typically metal elements, although other types of X-ray detectable elements may also be used. When the layers are in proper registration, the pattern in the upper layer substantially shields the element in the lower layer from X-rays and prevents X-ray photons from the first element from reaching the detectors. When there is a registration error, however, a portion of the pattern in the lower layer is exposed to X-rays, so that photons from the first element can reach the detectors. The processing unit analyzes the intensity and direction of emission of these X-ray photons in order to determine the degree and direction of misregistration between the upper and lower layers.
In other preferred embodiments of the present invention, the analyzer is used to determine the composition and thickness of bumps formed on a surface of the sample. Such bumps typically comprise metal bumps, which are formed on the upper surface of a semiconductor wafer, for example, and are then used as contact points between an integrated circuit made from the wafer and a suitable chip carrier (in place of wire bonding). The analyzer of the present invention is used to measure the size and thickness of these bumps, in order to verify that they will provide a suitable connection to the chip carrier. To perform the measurement accurately, however, it is necessary that the small spot that is excited by the X-ray source be accurately aligned with one of the bumps. Preferably, directional inhomogeneity of X-ray emission from the bumps is measured so as to provide an indication of misalignment between the spot and the bump, and thus to drive a translation stage so that the spot and the bump are precisely aligned. Alternatively or additionally, the processing unit averages the signals from the different detectors to compensate for any residual misalignment.
In still other preferred embodiments of the present invention, the sample comprises a crystalline substance, such as single-crystal silicon, which generates a diffraction pattern when irradiated by the X-ray source. The diffraction pattern has directional inhomogeneity, whose direction is determined by an orientation angle of the substance. This diffraction pattern can cause anomalies in measurement of X-ray fluorescence by the analyzer. The processing unit detects the inhomogeneous diffraction pattern by detecting differences in the signals that it receives from the different detectors. Most preferably, the signal differences are used to drive a rotation stage so as to align the sample, relative to the detectors, in a manner that minimizes the impact of the diffraction on the fluorescence measurement. Alternatively, the signal differences may be used to determine the crystal orientation.
There is therefore provided, in accordance with a preferred embodiment of the present invention, a method of X-ray analysis, including:
irradiating a spot o
Bar-On David
Mazor Isaac
Yokhin Boris
Hoffman Wasson & Gitler PC
Jordan Valley Applied Radiation Ltd.
Kao Chih-Cheng
Kim Robert H.
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