X-ray diffraction wafer mapping method for rhombohedral super-hetero-epitaxy

Inventors

Park, Yeonjoon • Choi, Sang Hyouk • King, Glen C. • Elliott, James R. • Dimarcantonio, Albert L.

Assignees

National Aeronautics and Space Administration NASA

Abstract

A new X-ray diffraction (XRD) method is provided to acquire XY mapping of the distribution of single crystals, poly-crystals, and twin defects across an entire wafer of rhombohedral super-hetero-epitaxial semiconductor material. In one embodiment, the method is performed with a point or line X-ray source with an X-ray incidence angle approximating a normal angle close to 90°, and in which the beam mask is preferably replaced with a crossed slit. While the wafer moves in the X and Y direction, a narrowly defined X-ray source illuminates the sample and the diffracted X-ray beam is monitored by the detector at a predefined angle. Preferably, the untilted, asymmetric scans are of {440} peaks, for twin defect characterization.

Core Innovation

The invention provides a new nondestructive X-ray Diffraction (XRD) method to acquire XY mapping of the distribution of single crystals, poly-crystals, and twin defects across an entire wafer of rhombohedral super-hetero-epitaxial semiconductor material. The method uses a point or line X-ray source with an incident angle close to normal (approximately 90°), replacing the traditional beam mask with a crossed slit, and moves the wafer in X and Y directions while monitoring diffracted X-rays at predefined angles. The preferred configuration involves un-tilted, asymmetric scans of {440} peaks for twin defect characterization in cubic semiconductors such as group IV, III-V, and II-VI materials or their alloys.

The problem addressed is the lack of a nondestructive analytic method to characterize and map defects—specifically twin defects—across entire wafers of rhombohedral super-hetero-epitaxial materials. Traditional techniques like electron microscopy target only small regions, and prior integral XRD methods lacked spatial resolution for XY mapping. The issue is particularly significant because twin defects arise due to 60° rotations on the (111) plane in cubic materials grown on trigonal or hexagonal substrates, causing poly-type crystalline structures that affect epitaxial layer quality.

The method achieves high spatial resolution (from a few nanometers to a few millimeters) with uniform isotropic XY scanning, enabling precise identification of defect regions and single crystal regions across entire wafers. This capability aids in quality control and optimization of epitaxial layers used in device fabrication. The approach includes specific angular settings related to the detector, sample tilt, and goniometer to ensure valid XRD configurations, focusing on {440} peaks for optimal characterization of twins in cubic semiconductor materials grown on trigonal or hexagonal substrates.

Claims Coverage

The patent contains one independent claim describing a method for X-ray diffraction XY mapping of crystalline forms and defects over semiconductor wafers of rhombohedrally aligned materials, detailing specific settings and procedures. The inventive features focus on the method's configuration and scanning steps.

The inventive features combine precise angular configurations with spatial XY scanning of a wafer using a narrowly defined X-ray source and phi-scanning to spatially map and characterize twin defects and crystal distributions in rhombohedrally aligned semiconductor materials.

Stated Advantages

Documented Applications