Depth resolution instrumentation

During testing a depth resolution of 50-80 micron and a lateral resolution of 20-40 micron was achieved. The spatial resolution was limited not mainly hy source or camera properties, but by the accuracy of compensation of the instrumental errors in the object movements and misalignments. According to this results a mote precision object rotation system and mote stable specimen holding can do further improvements in the space resolution of microlaminography. 

Depth resolution Minimum step Maximum step Lateral resolution Maximum sample size Instrument cost... 

In quadrupole-based SIMS instruments, mass separation is achieved by passing the secondary ions down a path surrounded by four rods excited with various AC and DC voltages. Different sets of AC and DC conditions are used to direct the flight path of the selected secondary ions into the detector. The primary advantage of this kind of spectrometer is the high speed at which they can switch from peak to peak and their ability to perform analysis of dielectric thin films and bulk insulators. The ability of the quadrupole to switch rapidly between mass peaks enables acquisition of depth profiles with more data points per depth, which improves depth resolution. Additionally, most quadrupole-based SIMS instruments are equipped with enhanced vacuum systems, reducing the detrimental contribution of residual atmospheric species to the mass spectrum. 

The choice of mass spectrometer for a particular analysis depends on the namre of the sample and the desired results. For low detection limits, high mass resolution, or stigmatic imaging, a magnetic sector-based instrument should be used. The analysis of dielectric materials (in many cases) or a need for ultrahigh depth resolution requires the use of a quadrupole instrument. 

The SNMS instrumentation that has been most extensively applied and evaluated has been of the electron-gas type, combining ion bombardment by a separate ion beam and by direct plasma-ion bombardment, coupled with postionization by a low-pressure RF plasma. The direct bombardment electron-gas SNMS (or SNMSd) adds a distinctly different capability to the arsenal of thin-film analytical techniques, providing not only matrbe-independent quantitation, but also the excellent depth resolution available from low-energy sputterii. It is from the application of SNMSd that most of the illustrations below are selected. Little is lost in this restriction, since applications of SNMS using the separate bombardment option have been very limited to date. 

In principle GD-MS is very well suited for analysis of layers, also, and all concepts developed for SNMS (Sect. 3.3) can be used to calculate the concentration-depth profile from the measured intensity-time profile by use of relative or absolute sensitivity factors [3.199]. So far, however, acceptance of this technique is hesitant compared with GD-OES. The main factors limiting wider acceptance are the greater cost of the instrument and the fact that no commercial ion source has yet been optimized for this purpose. The literature therefore contains only preliminary results from analysis of layers obtained with either modified sources of the commercial instrument [3.200, 3.201] or with homebuilt sources coupled to quadrupole [3.199], sector field [3.202], or time-of-flight instruments [3.203]. To summarize, the future success of GD-MS in this field of application strongly depends on the availability of commercial sources with adequate depth resolution comparable with that of GD-OES. 

State-of-the-art TOF-SIMS instruments feature surface sensitivities well below one ppm of a mono layer, mass resolutions well above 10,000, mass accuracies in the ppm range, and lateral and depth resolutions below 100 nm and 1 nm, respectively. They can be applied to a wide variety of materials, all kinds of sample geometries, and to both conductors and insulators without requiring any sample preparation or pretreatment. TOF-SIMS combines high lateral and depth resolution with the extreme sensitivity and variety of information supplied by mass spectrometry (all elements, isotopes, molecules). This combination makes TOF-SIMS a unique technique for surface and thin film analysis, supplying information which is inaccessible by any other surface analytical technique, for example EDX, AES, or XPS. 

Figure 37 High-depth-resolution profiling with a magnetic sector instrument using a 1-keV 00+ primary beam at 56° incidence with oxygen flooding. (From Ref. 126.)...

Electron cryomicroscopy, 2, 94-101, 401-2 field depth/resolution graph for, 100 instrument choices in, 97-101 theoretical consideration of, 94-101 three dimensional reconstruction and, 101 Electron density maps, 42 Electron microscopy resolution (EM resolution), 45-46... 

All direct depth profiling techniques used to study the surface segregation from binary polymer mixtures have a depth resolution [29] p limited to some 5-40 nm HWHM (half width at half maximum of the related Gaussian function). They cannot observe the real composition profile < )(z) (for the sake of comparison mimicked by mean field prediction (dashed line) in Fig. 16a) but rather its convolution (solid line in Fig. 16a) with an instrumental resolution function characterized by p. The total surface excess z however provides a good parameter, independent of resolution, as it has been concluded based on experimental data obtained using different direct techniques [170]. 

An example of such a plot is shown in Figure 3, where the increment between experimental data points is 35A, making this an extremely high resolution instrument. It is preferable to a conventional C-V profiler because it has no depth limitation and uses wafers without the need to fabricate devices. It is destructive, however, by leaving an approximately 1 mm diameter hole in the wafer. Spreading Resistance Profiling... 

Improved mathematical techniques for fusion and computer processing of the sensor data may, however, improve both the horizontal and the depth resolution attainable with these sensors if a rapid and convenient method of acquiring the sensor data can be developed. Ground-penetrating radar systems are limited in the depths to which they can "see " further, they tend to be somewhat delicate instruments that work best on smooth terrain, and they are not particularly well suited for use under rugged field conditions. Also, to date there is little evidence that airborne radars (or other sensors) can robustly detect buried ordnance under any but the most favorable conditions. 

Analysis performed directly on soil has continued to benefit from instrumental improvements, which now readily allow analysis at subparticle scale. Many of the techniques that provide a direct analysis also offer the potential for excellent spatial resolution with possibilities of even some depth resolution whilst also providing information on the chemical associations between individual minor components. 

In contrast, static SIMS measurements are performed with a number of incident ions (<10 ions/cm ) about one order of magnitude less than the number of atoms at the surface of the sample (one monolayer of Si contains 10 atoms/cm ). In this case, the damage to the sample surface is minimized and ions are mainly emitted from the first atomic layers, also promoting desorption of large fragments. However, count rates are low and information is restricted to relatively abundant species from the very superficial layers of the target. In both cases, instrumental parameters need to be selected according to the most critical factors in the analysis (e.g., lateral resolution, depth resolution, or sensitivity), and the optimal conditions represent a compromise between those different factors. 

Traditionally, SIMS uses energies of many kiloelec-tronvolts, although recently low or ultralow-energy SIMS makes use of primary ions with energy below 1 keV— more comparable to GD instruments. The requirement for lower SIMS primary beam energies is driven by the need for improved depth resolution, especially at the surface. Because the atomization and ionization steps are separated in GD-MS, it is possible to use lower projectile energies than are necessary for SIMS [47]. 

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