TOF-SIMS：Time-of-Flight Secondary Ion Mass Spectrometry
Features
TOF-SIMS is a method for analysing the structure and composition of a sample surface. Due to its high sensitivity compared to other analytical devices, it is suitable for identifying organic contaminants on the outermost surface. By combining it with a sputter ion source, it is also possible to analyse the distribution in the depth direction.
- High sensitivity and selectivity
- Applicable to elements with atomic numbers 1-92 (H to U)
- Detection of molecular ions of organic substances
- Identification of organic and inorganic compounds
- Spatial distribution of identified substances by imaging function
- Import of contaminant location coordinates from inspection equipment
- Large range of particle sizes ( μm – cm)
- Qualitative analysis in depth direction
Features exclusive to MST
- Minimizing deterioration of sample due to oxygen and moisture by performing the entire process from sample opening to measurement under controlled atmosphere
- The entire process performed in a class 1000 clean room minimizing contamination by ambient substances
Application Examples
- Root cause analysis of discoloured parts (haze, stain) by composition analysis of surface contaminants
- Identification of organic and inorganic residues, adsorbents, and other contaminants with sizes ranging from several μm
- Analysis of the effect of surface treatment
- Distribution analysis of polymer film additive agents
- Analysis of thin-film composition in organic electroluminescent (EL) and photovoltaic (PV) devices
- Qualitative analysis of the structure of and impurities in metal thin films
- Qualitative evaluation of the binder state and Li decay in rechargeable batteries
- Distribution analysis of impurities and coating agents in powder surfaces
- Evaluation of drug permeability to skin and hair
Principle
Primary ions are accelerated and impinge on the sample at a flow and at an energy low enough to maintain the molecular state of the surface but high enough to generate secondary ions. Some molecules, however, dissociate and form fragment ions (see Fig. 2). Secondary ions are separated from the matrix by acceleration in an electric field and analysed with a time-of-flight mass spectrometer.
The dose of primary ions (Bi clusters) is controlled by the acceleration voltage and ion pulse width and frequency to be no more than 1012 ions cm-2. At such a low intensity, ionization occurs but the structural change of organic substances on the surface is negligible.
Secondary ions are separated by mass using the difference in their time of flight to reach the detector (see Fig. 3). The heavier the ion, the longer it takes to reach the detector. Since ions of opposite polarity are accelerated in opposite directions, they cannot be simultaneously measured. Therefore, the detector is unipolar (positive or negative).
Equipment configuration
Fig. 4 shows a schematic of the TOF-SIMS equipment with a Bi primary ion source and a reflectron-type mass spectrometer. The sputter ion source (including Ar gas cluster ion beam, GCIB) is used to selectively remove upper layers of the specimen in order to analyse the sample at various depths and locations.
Data examples
Fig. 5 shows the mass spectrum of a water mark on a Si wafer. Comparing it with the spectra of a standard sample allows qualitative evaluation of the watermark composition. If there is no standard sample, the presence or absence of substances of interest can be estimated by identifying the substance from the mass of the parent ion (ionized molecule).
By scanning primary ion beam and moving the sample stage, the spatial distribution of the secondary ions can be analysed within a small and large area at high and lower resolution, respectively. Fig. 6 shows an optical microscopy image of a three-dimensionally cultured sample of human skin for percutaneous (skin penetration) absorption evaluation of indomethacin.
Fig. 7 shows the spatial distribution and ionic strength and the associated concentration of each substance, each indicated by a different pseudo-color. By combining the pseudo-color images, it is possible to visualize the distribution of substances in a combined image.
Fig. 8 shows a depth profile analysis of a SiON film. While TOF-SIMS is often used for organic substances, depth profile analysis of inorganic substances such as SiON, is also possible.
Data delivery format
- Portable Document Format (PDF) file.
Specifications
Items for enquiries
- Purpose and content of measurement
- Sample information
・Number of samples, and availability of preliminary samples
・Sample structure, shape, layer structure, film thickness, patterned features, and expected substances
・Handling instructions
- Details on delivery
・Preferred due date for preliminary analysis report
・Due date for delivery of final report
・Priority in the case of a large number of samples
- Any other issues
Caution
- It is recommended to send the measurement surfaces together and wrap them in Al foil to avoid contamination from the ambient atmosphere
- For smaller samples, prepare preliminary samples
- For powder samples, prepare at least 3 glasses of spatula
- For insulating samples or samples with outgassing, prepare samples sized about 15×15×5 mm
- For samples that require refrigeration/freezing or atmospheric control, make an enquiry first
- For biological and chemical materials, inform us about handling precautions, approximate shelf life, and the method of sample return
- Signing a written consent may be necessary in the case of biological samples
［TOF-SIMS］飛行時間型二次イオン質量分析法の分析事例はこちらからご覧ください。