Paper AS+SS-WeA3
FIB-TOF Tomography Characterization of Organic Structures

Wednesday, October 21, 2015, 3:00 pm, Room 212D

1. Introduction

There are practical limitations to the use of ion beam sputtering for probing the sample chemistry beyond the surface region which include preferential sputtering and accumulated sputter beam damage. Both effects result in a distortion or complete loss of the true 3D chemical distribution as a function of depth

An alternative approach to achieve 3D chemical imaging of complex matrix chemistries is to utilize in situ FIB milling and sectioning in conjunction with TOF-SIMS chemical imaging, or 3D FIB-TOF tomography [1]. This can minimize or eliminate artifacts caused by sputter depth profiling such as differential sputtering and accumulated ion beam damage.

However, even with FIB polishing there remains some FIB beam-induced chemical or molecular damage that may or may not limit the detection of characteristic molecular signals. For certain specimens, it is an advantage to follow FIB polishing with cluster ion polishing to recover the characteristic molecular signals.

2. Method

The 3D chemical characterization of pure organic and metal-organic mixed composition structures was achieved utilizing 3D FIB-TOF tomography on a PHI TRIFT nanoTOF II (Physical Electronics, USA) imaging mass spectrometer. The spectrometer’s large angular acceptance and depth-of-field maintain high mass resolution and high mass scale linearity even in this challenging geometry. This provides the highly desirable ability to perform artifact-free chemical imaging of high aspect ratio features.

3. Results

The present study investigated samples from two classes of materials: one metal-organic mixed matrix composition and one mixed organic phase comprised of two polymer moieties. Since there was no preferential sputtering, an immediate result of the FIB-TOF imaging was the accurate determination of the depth scale. We have collected characteristic molecular information from each sample for the purposes of 2D and 3D imaging. Cluster ion beam polishing (e.g. C₆₀⁺ or Ar_2,500⁺) was necessary to remove the FIB beam-induced damage, and the new instrument configuration allows cluster ion polishing to be accomplished with ease. We will highlight certain aspects of the studies for presentation.

4. References

[1] A. Wucher, G.L. Fisher and C.M. Mahoney, Three-Dimensional Imaging with Cluster Ion Beams (p. 207-246) in Cluster Secondary Ion Mass Spectrometry: Principles and Applications, C.M. Mahoney (Ed.), Wiley & Sons, N.J. (2013).