plasma analysis

Using Our Molecular Beam Mass Spectrometry

Unmatched Molecular beam mass spectrometry (MBMS)

In order to accurately characterize a plasma or other ‘high’ pressure reaction cell, you need to obtain a representative sample. Sampling the plasma as a molecular beam through rapid pressure reduction immediately after ions, radicals and neutrals leave the plasma, allows for an unadulterated snapshot of the plasma chemistry. With molecular beam sampling, you are looking directly at the chemical soup which comprises the plasma. This includes noise sources such as photons, electrons, metastable neutrals, and even particulates in addition to the ions, neutrals and radicals to be monitored.

A cross beam ionizer allows for the separation of the analyte signal, which is comprised of plasma ions and ions created in the ionizer from plasma molecules and neutrals, from these sources of noise. The use of a cross beam ionizer will also protect the quadrupole analyzer and detector from direct bombardment with the reactive species common to plasmas used in semiconductor applications. We have developed a novel two stage molecular beam sampling system centered around a new cross beam deflector ionizer, yielding a compact vacuum system with efficient pumping in both stages.

There are a wide variety of species present in a high-pressure source such as a plasma: metastable neutrals, radicals, positive ions, negative ions, electrons, photons, clusters and particulates. A plasma monitoring system must allow selective monitoring of these various species, without interference from the others. In order to obtain a representative sample, a molecular beam can be generated through rapid pressure reduction to a collision-free vacuum level. Ions present in the sampled gas need to be separated from the bulk gas flow, preferably using an energy filter for increased selectivity.

Our VERASPEC™ MOLECULAR BEAM & PLASMA ANALYSIS SYSTEM DELIVERS

Improved Signal-to-Noise: Photons, metastable neutrals, and energetic ions can cause noise if in line-of-sight with the detector.
Reduced Contamination: Condensables and particulates never see the off-axis mass filter and detector, and therefore cannot contaminate them.
Improved Pumping: With an Axial Molecular Beam Ionizer, most of the pumping load of a molecular beam must be pumped through limited conductance holes in the mass filter housing itself. With the Cross Beam Deflector Ionizer, there is virtually infinite pumping speed for the beam exiting the ionizer, limited only by the size of the pump.
Energy Filtering for Pre-formed Ions: The integral quadrupole deflector energy filter increases selectivity, allowing for differentiation of the source of the ions.

The Cross Beam Deflector Ionizer combines the high sensitivity ionization region of an Axial Molecular Beam Ionizer with a high transmission Quadrupole Deflector Energy Filter.
Ions generated external to the system are focused through the ion optics, using the molecular beam apertures and ionizing region as lenses, and are injected into a Quadrupole Deflector Energy Filter where they are deflected ninety degrees into a Quadrupole Mass Filter. Photons, metastables, particulates, and molecular beam gases pass through the Quadrupole Deflector to a pump or cold finger.
The Quadrupole Deflector is an energy filter. The potential difference between the pairs of rods determines the energy band pass, and the average of these potentials determines the center point of the band pass.

VeraSpec™ MB2