Sub-micron resolution CT for failure analysis and process development

Abstract

Many modern industrial processes and research applications place increasingly higher demands on x-ray computed tomography (CT) imaging resolution and sensitivity for low-contrast specimens with a low atomic number. The three approaches to increasing imaging resolution are (1) reduction in the x-ray spot size, (2) use of higher resolution detectors or (3) employment of x-ray optical elements. Systems that pursue one or more of these approaches are available and under continued development. The Xradia MicroXCT TM projection-type microscope described in this paper has been optimized for high-resolution x-ray CT by employing a high-resolution detector paired with a microfocus x-ray source. Large working distances in this CT system enable full tomographic data collection at micrometre resolution of large samples, such as flip-chip packages. X-ray CT instruments using x-ray optical elements for condenser optics and imaging objective lenses are a new development capable of reaching sub-50 nm resolution. These instruments find various applications, including die-level imaging in the semiconductor industry as well as the process development for fuel cells, which we describe here as one application. Sub-micron resolution CT instruments without x-ray optical elements have a large application base already; however, new instruments optimized for soft materials and low-contrast specimens, such as the Xradia nanoXCT TM , offer completely new capabilities and open new applications. New developments in the area of phase contrast imaging enable unprecedented image contrast for specimens with very low absorption, which for research applications enables for the first time the imaging of many specimens in their natural state (e.g., arteries to examine calcification). Zernike phase contrast for sub-50 nm x-ray CT even enables the imaging of single cell or thin tissue slices for biological or medical applications.

Accurate Resolution Measurement for X‐Ray Micro‐CT Systems

“…The nanoXCT system utilizes a Cu x-ray source, a reflective capillary optic to focus 8-keV Cu Ka x-rays onto the sample, and a Fresnel zone plate to form the image. The resolution of the microscope is determined by the outermost zone width of the zone plate, and resolutions below 40 nm can be achieved [6]. The focused x-rays are absorbed by a scintillator and converted to visible light-a microscope objective focuses this light onto the CCD.…”

“…The micro-CT employs projection-based x-ray imaging. The detection of x-rays utilizes a scintillator and a visible light objective, allowing resolution below 1 µm [6].…”

Sub-micron X-ray Computed Tomography for Non-Destructive 3D Visualization and Analysis

“…In the most common technique, x-rays project through the sample onto the detector in a cone-beam geometry, typically limiting resolution to the size of the x-ray source. Highresolution imaging is thus achieved by placing the sample very close to the source, which may restrict sample size for tomography to a very small volume [1]. By increasing the resolution of the detection system, however, source-to-sample distances may be relaxed while still achieving resolution of ~1 µm.…”

“…By increasing the resolution of the detection system, however, source-to-sample distances may be relaxed while still achieving resolution of ~1 µm. Source instabilities are much less influential in this scheme, permitting fast, high-resolution 3D tomography utlizing a larger spot size [1][2].…”

“…By pairing x-ray optical elements with a high-resolution detector, theoretical imaging resolution becomes a function only of the optical elements in use and not the x-ray source [1][2][3]. Such a geometry employs a high-efficiency reflective capillary x-ray condenser lens matched to a Fresnel zone plate objective, similar in design to a transmission light or electron microscope [4,[7][8].…”