SIMS Instrument Designs

SIMS has experienced extensive growth and sophistication over the past few decades with its commercialization resulting in the availability of numerous stand-alone instruments (price tags range from several hundred thousand to several 

Owing to their relative simphcity and effectiveness, Quadrupole SIMS instruments found greatest commercial popularity throughout the 1970-1990s. Their market share has, however, dwindled as a result of the development in Time-of-Fhght-based SIMS instrumentation. That being said. Magnetic Sector-based SIMS instruments have remained the instrument of choice when sensitivity and detection limits are of utmost importance in the area of Dynamic SIMS. It should also be noted that there exists many niche areas where specific types of SIMS instrumentation excel. 

Primary advantages of these instrument types revolve around  

Fast peak switching times compared to Magnetic Sector instruments 

The primary disadvantages associated with this instrument-type concern  

---

Some spectra were recorded on a non-commercial SIMS instrument designed and built at EG G in Idaho Falls, ID. It has been described (13.141. Essentially, it is equipped with a primary source of SF6 neutrals and anions and a 0-2000 amu quadrupole mass analyzer. Qualitatively, the spectra obtained were identical to those of the commercial instrument, but the secondary ion yield was higher and charge neutralization was not required. 

The TOF SIMS instrument design is based on the flight time of the secondary ions. A pulsed primary beam impacts a sample surface and resulting pulses of secondary ions are accelerated by an electric field away from the sample and into the mass spectrometer analyzer. Ions with different mass/charge ratios will travel with... 

SIMS instrument designs based around FT-ICR have been able to replicate many of the advantages displayed by such mass filters when applied in mass spectrometry. As an example, mass resolution values of 385,000 have been demonstrated via the single ion method (see Section 5.1.1.1.1) albeit using the 50% definition (Smith et al. 2011). This was reported for molecular secondary ions produced via Cgo primary ion impact. Also demonstrated was the possibility of imaging the organic ions to unprecedented sensitivity and detection limits. This was carried out by synchronizing the pulsed Cgo beam raster with the FT-ICR mass filter detection electronics, i.e. the microprobe method (see Section 5.3.2.2). 

Not surprisingly, however, all of these capabilities are generally not achieved within a single SIMS Instrument. It Is necessary to examine critically the requirements at hand and choose those design features which lead to an Instrument best suited to the defined need. 

When designing a SIMS Instrument to give the best possible results for a given type of analysis one must know which components are necessary for the desired performance, and Indeed, what kind of performance Is required. Table I lists the three basic areas of SIMS analysis to be discussed here. Under each type of analysis are listed the most appropriate components and design features. 

It has been the purpose of this paper to provide an overview of the basic differences and similarities of the various types of Instruments which detect Ionized particles emitted from surfaces by energetic particle bombardment. Since the scope of secondary ion mass spectrometry Is so broad, It is not surprising that no one Instrument has been designed to perform optimally for all types of SIMS analyses. Design aspects of the primary beam, extraction optics, mass spectrometer, detection equipment and vacuum system must be considered to construct an Instrument best suited for a particular purpose. 

In 1949 Herzog and Viehbock reported a novel ion source for mass spec-trography (Fig. 4.2) [9]. This source provided separate accelerating fields for the primary and secondary ions and thus became the first modem instrument designed specifically for SIMS. The design included acceleration of the positive secondary ions from an equipotential surface through an electric field acting as an electron-optic lens. 

The second type of SIMS Instrument the direct Imaging type Is based on the design of Castaing and Slodzlan (IQ). In the direct Imaging Instrument an area 1 to 300 pm In diameter Is bombarded by the primary Ions. The secondary Ions are extracted by an electrostatic Immersion lens which maintains a point to... 

Both organic and Inorganic species can be Identified from SIMS mass spectra (12). One specialized commercial SIMS Instrument was designed to determine the molecular weight and structure of nonvolatile organic compounds (5fl). Although molecular SIMS has not been widely exploited for semiconductor process... 

In mass spectrometric studies, WT have been applied mainly in two areas including secondary ion mass spectrometry (SIMS) and instrumentation design. SIMS is a type of surface technique for trace analysis, determination of elemental composition, and the identity and concentrations of adsorbed species and elemental composition as a function of depth [46]. The application of wavelet denoising techniques to SIMS images has been studied by Grasserbauer et al. [47-50], and details about these studies are presented in another chapter of this book. 

The name, nanoSIMS 50, stands for a new-generation SIMS instrument. The unique feature of the instrument is that it combines high sensitivity with a high lateral resolution of 50 nm when operated with the Cs primary beam. This is achieved by using a specific design of ion optics where the primary and secondary ion optics are coaxial and the primary beam hits the sample surface at an angle of 90°. Compared to the old SIMS, the transmission of the new instrument for secondary ions is a factor of -20-30 better in typical measurement conditions. 

In this protocol, direct surface analyses using IT-SIMS will be described from the perspective of analyses that were conducted to measure chemical warfare agents and related compounds (precursors, degradation products, and surrogates) that were adsorbed on samples from exposed environments. During the course of the research that is described in this chapter, the basic instrumental design of the IT-SIMS was modified for the analysis of absorbed compounds, and so the utilization of the instrument for these purposes is also described. 

The IT-SIMS instruments were custom designed and fabricated in-house at the Idaho National Laboratory. All instruments were based on modifications of commercial gas chromatography/mass spectrometry (GC/ MS) instruments that were altered by removing the gas chromatography (GC) and inlet, and replacing it with a direct insertion probe, a modified conversion dynode and a Venetian blind electron multiplier, and a perrhenate primary ion gun. The primary ion gun and the direct insertion probe are located coaxial with the IT,... 

In most designs secondary neutral mass spectrometry (SNMS) instruments are to a large extent identical with SIMS instruments so there are usually hybrids that work... 

Instrument designs are defined by the type of mass filter used within the secondary ion column. Indeed, there are three types that have been heavily commercialized in the field of SIMS, with more available in the parent field of Mass Spectrometry. Those commercialized are based around ... 

As covered in Section 5.3.2.4.5, sample rotation (also referred to as Zalar rotation) during image depth profiling can minimize the latter. Alternatively, surface topography measurements carried out before and after image depth profiling can account for the latter two. Indeed, the effectiveness of this approach has been demonstrated via ex-situ Atomic Force Microscope (AFM) measurements (van der Heide 1998 Robinson et al. 2012). Based off of the success of this approach, lon-Tof has designed a hybrid APM/TOF-SIMS instrument. 

---