Radiant energy – Ionic separation or analysis – Ion beam pulsing means with detector synchronizing means
Patent
1998-05-04
1999-12-14
Westin, Edward P.
Radiant energy
Ionic separation or analysis
Ion beam pulsing means with detector synchronizing means
250281, 250399, H01J 37252, H01J 4940
Patent
active
060021284
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a sample analyzer for application in surface analysis, in particular comprising a source of a primary beam of charged particles and a time of flight mass spectrometer for analysing secondary charged particles from the sample surface.
Surface Analysis is dominated by instruments designed to perform x-ray photoelectron spectroscopy (XPS). A surface illuminated with x-radiation will release photoelectrons whose kinetic energy can be analyzed using an analysing means. Such an energy analysing means may take the form of a hemispherical energy analyzer. The kinetic energies of such photoelectrons emitted from elements present in the surface of the sample can be modified or shifted by the nature of the chemical bonding between adjacent elements. Interpretation of the kinetic energy spectra therefore yields information about the way elements are bound to one another and hence the chemical composition of the surface.
A complementary technique involves the release from the surface of intact molecules or parts thereof under the action of a beam of energetic ions or neutral particles. Where the secondary particles are charged they can be collected and mass analyzed by a mass spectrometer. This technique has become known as static secondary ion mass spectrometry (S-SIMS). The word static confirms that only the surface monolayer is interrogated. Static SIMS therefore has a natural limit on the total ion dose which may be employed before the surface monolayer is removed. This is recognised to be in the range of 10.sup.12 to 10.sup.13 ions or neutrals cm-2.
Recently, static SIMS has been transformed by performing the mass spectrometry by time of flight (TOF). Thus a complete mass spectrum may, in principle, be collected for every pulse of the primary beam ensuring that the maximum amount of data is collected.
Generally, XPS and Time of Flight SIMS are undertaken on separate instruments because it is difficult to configure both techniques on a single instrument. Therefore, the analysis laboratory must bear the costs of purchasing and running two instruments or forego one of the techniques.
Moreover, the configuration of a stand-alone TOF SIMS instrument is not straightforward. The main reason for this is that the extraction field for the TOF analyzer needs to be strong (.about.2,000-5,000 Volts/cm) to give a good collection efficiency and mass resolution and this requirement imposes a severe constraint on the relative positions of the TOF extraction system, the sample, the primary probe and the charge neutralising means.
FIG. 1 illustrates a conventional time of flight SIMS instrument. A sample 20 to be analyzed is mounted in a vacuum chamber 21. The vacuum chamber has a number of flanges 22-24 for mounting various elements for sample analysis. An ion gun is mounted to the flange 22 and emits a primary ion beam 25 which is focused by a primary focuser comprising 3 coaxial annular electrodes 26-28 and steered in a raster pattern onto the sample by a steering element 29. A secondary beam of ions 30 is collected from the sample and focused by a secondary focuser 31-33 into a time of flight mass spectrometer mounted to the flange 23. As can be seen in FIG. 1, other components can be attached to other flanges in the vacuum chamber, such as an electron gun fitted to flange 24, and a secondary electron detector and microscope/TV camera mounted to other flanges (not shown).
As is apparent from FIG. 1, the instrument is very congested. The chamber of an X-ray Photoelectron Spectroscopy (XPS) instrument is similarly congested, with many components competing for space around the sample. In general, an XPS instrument may have one spare flange, but not sufficient flanges or internal space to add in a conventional Time of Flight SIMS facility.
An example of a known Time of Flight SIMS is described in WO 91/03070.
In accordance with a first aspect of the present invention, there is provided a time-of-flight secondary ion mass spectrometer as specified in claim 1 hereinafter.
By providing focusing means th
Hill Rowland
Miles Paul William
Angeli Michael de
Ionoptika, Ltd.
Wells Nikita
Westin Edward P.
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