Microspectroscopy
IR+Raman data provide both complementary and confir- matory capabilities for identification of unknown materials, with better accuracy and confidence. A new capability recently added to the mIRage system
is simultaneous collection of O-PTIR and Raman spectra of the same sample location with the same submicrometer spa- tial resolution (Figure 10) [9,23]. Tis is possible by use of a Raman-grade laser to measure the O-PTIR response. In the IR+Raman configuration, the Raman-shiſted light is simul- taneously diverted to a spectrograph, thus providing simul- taneous, same spot, same spatial resolution O-PTIR and Raman spectra. Tis new capability aids in the identification of organic and inorganic materials using both techniques. Raman is also used to examine coatings, stress/strain rela- tionships, and various applications in electronics and other industrial fields. Figure 11 shows an example of the complementary and
confirmatory O-PTIR and Raman spectral information that can be collected in reflection mode from a contamination particle that is ∼10 μm long and 2 μm wide. Te O-PTIR and Raman spectra were simultaneously collected from the same spot and at the same spatial resolution. Although collected in reflection mode, the O-PTIR spectrum is comparable with data taken from pure samples in transmission mode. When the spectra were digitally searched against KnowItAll IR and Raman databases, it was determined that this particular con- taminant is likely a polyether material. Te contaminates identified in these measurements
Figure 6: Comparison of the O-PTIR spectra of three polymers: poly(styrene) (PS); poly(ethyleneterephthalate) (PET); and poly(methylmethacrylate) (PMMA) with thin film-transmission spectra of these materials found in the KnowItAll™ IR spectral database (Wiley). The matches are excellent, even though the O-PTIR spectra were obtained in a reflection-like measurement on much thicker samples. If using FT-IR in transmission mode, it would be impossible to obtain unsaturated spectra from these samples because they would be optically too thick.
Figure 9 shows an example of the improved spatial reso-
lution achievable with O-PTIR as compared to conventional diffraction-limited FT-IR measurements. Te arrow indicates a particle (approximately 5 μm) that was identified via a library match of its O-PTIR spectrum to a KnowItAll™ IR library spectrum of polyetherimide. Collection of combined O-PTIR and Raman micros-
copy data. The complementarity of IR and Raman is well known and is often why analytical laboratories have sep- arate IR and Raman microscopes. However, to take full advantage of the complementarity the challenge is that for samples or regions of interest that are only a few microns in size, moving from an IR to Raman microscopes, or vice- versa, presents sample location and registration difficul- ties. An additional advantage of simultaneous IR+Raman is that it is also confirmatory. Unknown IR spectra can be searched against databases, and to confirm this search, simultaneously collected Raman spectra can be searched against Raman databases, or vice versa. As such, submicron
2020 May •
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include a small subset of the measurements Seagate has mea- sured using mIRage. Te contamination includes a variety of materials plus foreign particles that can be introduced during research and development and include polymers, lubricants, etc. For this evaluation the mIRage was able to achieve better than 90% chemical identification.
Additional Examples of O-PTIR Applications In February 2019 the Taiwan Semiconductor Manufac-
turing Company (TMSC) used a photoresist that included an abnormally treated element that created a foreign polymer in the photoresist resulting in an estimated loss of $550 million [24]. Systems that better identify contaminants quickly with minimal sample preparation and higher spatial resolutions while using typical training for optical microscope systems is needed to minimize these losses. Defect analysis is a major application area for O-PTIR spectroscopy. Failure analysis using conventional IR microspectroscopy has been signifi- cantly hampered by lack of spatial resolution, poor sample con- tact with the IRE in ATR measurements, and uninterpretable spectra in direct IR reflection mode. Figure 12 shows an ultrasonic welding application used
to make electrical connections for electronic devices. Raman microspectroscopy could have provided the spatial resolution required for such an analysis, but the dark color and strong fluorescence prevented effective chemical analysis of the weld defect with Raman microscopy. O-PTIR spectroscopy provides high spatial resolution even when the sample fluoresces. Te O-PTIR spectral features in the defective zone suggest there was an excess of flux, which is typically used to prevent the oxi- dation of the solder. In this case, the contamination effectively
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