Method of generating X-ray diffraction data for integral detection of twin defects in super-hetero-epitaxial materials
Inventors
Park, Yeonjoon • Choi, Sang Hyouk • King, Glen C. • Elliott, James R.
Assignees
National Aeronautics and Space Administration NASA
Publication Number
US-7558371-B2
Publication Date
2009-07-07
Expiration Date
2028-10-20
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Abstract
A method provides X-ray diffraction data suitable for integral detection of a twin defect in a strained or lattice-matched epitaxial material made from components having crystal structures having symmetry belonging to different space groups. The material is mounted in an X-ray diffraction (XRD) system. In one embodiment, the XRD system's goniometer angle Ω is set equal to (θB−β) where θB is a Bragg angle for a designated crystal plane of the alloy that is disposed at a non-perpendicular orientation with respect to the {111) crystal plane, and β is the angle between the designated crystal plane and a {111} crystal plane of one of the epitaxial components. The XRD system's detector angle is set equal to (θB+β). The material can be rotated through an angle of azimuthal rotation φ about the axis aligned with the material. Using the detector, the intensity of the X-ray diffraction is recorded at least at the angle at which the twin defect occurs.
Core Innovation
The invention provides a method of generating X-ray diffraction data suitable for integral detection of twin defects in strained or lattice-matched epitaxial materials composed of components having crystal structures with different space group symmetries. Specifically, the method involves mounting the material in an X-ray diffraction system and setting the goniometer and detector angles based on calculated Bragg and inter-planar angles to detect diffraction from designated crystal planes not perpendicular to the {111} crystal plane. Rotating the sample azimuthally about the [111] vector allows detection of twin defect diffraction intensities.
The problem addressed arises because high-quality thick epitaxial layers, such as cubic semiconductor alloys grown on substrates with different crystal symmetries, often develop twin defects and other dislocations due to lattice mismatches and crystal structure differences. Existing twin defect detection using transmission electron microscopy is destructive and unsuitable for quality control during mass fabrication. Hence, there is a significant need for a non-destructive, integral detection method applicable during fabrication, particularly for super-hetero-epitaxial materials where one material is epitaxially grown on another with differing crystal structures.
The method applies to various super-hetero-epitaxial combinations including cubic on trigonal, trigonal on cubic, hexagonal on trigonal, and hexagonal on cubic crystal structures. By precisely setting the XRD system's goniometer and detector angles relative to the Bragg angle and the inter-planar angle between a designated crystal plane and the {111} plane, and rotating the sample azimuthally, the method enables detection of twin defect-related diffraction intensities non-destructively. This facilitates quality monitoring and defect concentration estimation during semiconductor alloy fabrication.
Claims Coverage
The patent includes three independent claims, each covering a method for generating X-ray diffraction data suitable for twin defect detection with different settings of goniometer and detector angles and sample positioning.
Non-destructive twin defect detection by X-ray diffraction with specific angle settings
A method for generating X-ray diffraction data in which a designated non-perpendicular crystal plane of a lattice-matched or strained epitaxial material is identified, the Bragg angle is calculated, and the material is mounted such that the [111] vector makes an angle χ equal to the inter-planar angle β between the {111} plane and the designated plane. The goniometer angle Ω is set to θB, and the detector angle is set to 2θB. X-ray diffraction is measured at least at one azimuthal rotation angle φ aligned with potential twin defect diffraction.
Twin defect detection method with goniometer angle set to Bragg angle plus inter-planar angle
A method where the epitaxial material is mounted with its [111] vector aligned with the XRD system reference orientation, the goniometer angle Ω is set equal to the Bragg angle θB plus β, the detector angle is set to θB minus β, and diffraction is measured across azimuthal rotations to detect twin defects.
Twin defect detection method with goniometer angle set to Bragg angle minus inter-planar angle
A method similar to the previous, where the epitaxial material's [111] vector is aligned with the XRD reference orientation, but the goniometer angle Ω is set to θB minus β and the detector angle is set to θB plus β, with X-ray diffraction data collected at azimuthal rotations including angles where twin defect diffraction occurs.
The independent claims cover methods that adjust the goniometer and detector angles relative to calculated Bragg and inter-planar angles and orient the sample's [111] vector in specified ways to enable non-destructive detection and characterization of twin defects in lattice-matched or strained epitaxial materials through X-ray diffraction data at azimuthal rotations.
Stated Advantages
Provides a powerful non-destructive data generation tool for estimating twin defects in super-hetero-epitaxial materials.
Suitable for both laboratory and manufacturing applications, enabling quality monitoring and quality control during mass production.
Enables defining and optimizing epitaxial growth parameters to minimize or eliminate twin defects via integration into growth equipment.
Potential for 100% evaluation of production wafers, providing reliable product quality data to customers.
Serves as a key tool in developing novel crystal alloy systems with unprecedented properties.
Documented Applications
Non-destructive quality control and monitoring of twin defects in rhombohedrally-grown, strained or lattice-matched cubic semiconductor alloys on trigonal substrates and other super-hetero-epitaxial materials.
Use in manufacturing semiconductor wafers to define and optimize growth parameters to reduce twin defects.
Integration into epitaxial growth processes for iterative growth parameter adjustments and mass production quality assurance.
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