Clark-MXR Inc. now offers 3D Tomography characterization of opaque materials via serial sectioning as a fee-for-service. In addition to providing a more than tenfold improvement in throughput, femtosecond laser based serial sectioning provides unique capabilities that are unmatched by other more traditional mechanical or focused ion beam (FIB) techniques.
By way of background, serial sectioning is a technique used to characterize the structure and composition of opaque materials in 3-dimensions (3D). The surface of a material is imaged using a diagnostic technique such as photography or spectroscopy. That layer is then removed to some predetermined depth and the exposed surface again imaged. This process is repeated, usually hundreds of times, until a data set of 2D images is obtained that can then be assembled to provide a 3D profile of the material. The process is sometimes referred to as 3D tomography. It is about the only way to obtain information about the composition and structure of opaque materials.
There are several competitive techniques used to section materials. They are focused Ion Beam Milling (FIB) followed by scanning electron microscopy, mechanical systems (etching and/or polishing) and atomic probe systems. In comparison to these other techniques a femtosecond laser to section materials has the following advantages:
1.) The ability to section any material even materials as hard as diamond and as soft as polymer. The competitive mechanical techniques are limited to materials that can be etched or polished.
2.) The ability to expose successive layers while minimizing the physical and/or chemical properties of the native structure. The thickness of the layer accessible via mechanical techniques is limited to a few tenths of microns.
3.) The ability to precisely control the amount of material ablated, thereby achieving feature size and resolution on the scale of tens of nanometers (see Destructive Tomographic Techniques graph below).
4.) The ability to section materials at a rate that is five orders of magnitude higher than other high resolution ablative tools such as focused ion beam tools (FIB).
5.) The ability to perform layer-by-layer in situ analysis of exposed layers using linear and nonlinear spectroscopic techniques such as Rayleigh scattering and photoacoustic imaging for structural analysis, laser induced breakdown spectroscopy (LIBS) for elemental analysis, coherent antistokes Raman spectroscopy (CARS) and/or surface-specific vibrational sum frequency generation spectroscopy (Vib-SFG) for molecular species identification, or pump-probe spectroscopies such as transient absorption to study material dynamics, all of which are within the capabilities of the Clark-MXR Model ShapeShifter™ Nonlinear Spectrometer.
6.) fs serial sectioning can do all this without staining the sample since photons do not embed in the material (as do the gallium ions of the FIB or the grit used in mechanical polishing) without needing a vacuum since these processes can be done in a normal atmospheric pressure.
7.) Automatic image registration.
The attached serial sectioning poster illustrates the power of using a Clark-MXR Model UMW-2110 Micromachining Workstation to create a 3D image of an EEPROM IC chip. Each 2D layer was exposed by machining a 0.2 micron thick layer of material followed by photographic imaging. The dimensions of each 2D layer was 300 microns X 500 microns X 0.2 microns thick, and 200 layers were machined and imaged in slightly less than 200 minutes. Only 5 of the 200 layers that show substantial changes in the structure of the EEPROM are shown in the poster. It would have taken over 1.7 days for an FIB system to obtain the same size data set that we obtained with the Model UMW-2110 in slightly over 3 hours! In conclusion, our Model UMW Ultrafast Micromachining can not only micromachine materials, with only minor modification it can also do 3D characterization of materials at rates that far exceed what can be achieved with the other tools on the market today. We also offer sectioning services in our Job Shop facility for those customers who have only an occasional need to build up a 3D image of materials.