Micro- and Nano Computed Tomography

Micro Computed Tomography (µCT) designs scans with a measured spatial resolution (BSR, MTF or LSF) between 2 µm and 50 µm. Many µCT scanners are operated at Fraunhofer EZRT for materials characterization and/or for CT metrology. They all include micro-focal anodes, typically with variable high voltage and spot size. Scan times range between 1 min and 2 h are typical. Geometric magnification is adjusted continuously between 50x and 2x. Flatpanel detectors (FPDs) with pixel sizes between 50 µm and 200 µm are routinely used; some scanners comprise CCD detectors with even smaller pixels (e.g. 9 µm or 24 µm).

Sub-Micrometer Computed Tomography (subµ CT) designs scans with a measured spatial resolution between 0.3 µm and 3 µm. Fraunhofer EZRT operates a detector-based subµ CT scanner: The Click-CT prototype employs a microscope X-ray detector, which resolves 0.5 µm details while using a standard micro-focal anode. Typical scan times range between 3 h and 12 h.

Nano Computed Tomography (nanoCT) is capable of resolving details below 300 nm size. Fraunhofer EZRT employs the XRM-II prototype, as well as the ntCT. The latter realizes a focal spot size down to 150 nm at 60 kV (i.e. geometric magnification up to 1000x), whereas the former integrates nanoCT with 50 nm resolving power at 30 kV inside a scanning electron microscope (SEM). Geometric magnification is variable for both systems. The XRM-II comprises a variety of target sizes and materials (Cu, W, Ag, Mo) which can be changed quickly. Typical scan times are 3 h for the ntCT and 12 h for the XRM-II.

© Fraunhofer IIS
Siemens Star Test Chart. Smallest features of 150 nm lines and spaces

Scanner Classes

Because of the strongly different parameters and X-ray components, different scanners are developed to meet different needs.

Typical parameters for the three high-resolution CT scanner classes:

Scanner /Parameter

µCT

Subµ CT

NanoCT

Max. High Voltage /kV

90 – 300

60 – 160

30

Emission Power /W

1 – 1200

0.06 – 0.4

<0.01

Max. object size /mm

250

2 – 5

0.06

Min. detail res. /µm

2 – 50

0.3 – 3

0.03 – 0.3

Geom. Magnification

2 – 50

25 – 250 (except for detector-based subµ)

250 – 10000

Scan times /h

0.01 – 3

3 – 12

8 – 16

 

© Fraunhofer IIS
Fig. Object size vs. detail resolution for the different scanner classes.