EP0708976A1 - Process for operating a time-of-flight secondary ion mass spectrometer - Google Patents
Process for operating a time-of-flight secondary ion mass spectrometerInfo
- Publication number
- EP0708976A1 EP0708976A1 EP95920015A EP95920015A EP0708976A1 EP 0708976 A1 EP0708976 A1 EP 0708976A1 EP 95920015 A EP95920015 A EP 95920015A EP 95920015 A EP95920015 A EP 95920015A EP 0708976 A1 EP0708976 A1 EP 0708976A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- mass
- time
- flight
- primary
- ions
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J49/00—Particle spectrometers or separator tubes
- H01J49/26—Mass spectrometers or separator tubes
- H01J49/34—Dynamic spectrometers
- H01J49/40—Time-of-flight spectrometers
Definitions
- the invention relates to a method for operating a time-of-flight secondary ion mass spectrometer for the analysis of mass spectra, in which several finely structured mass areas occur isolated at larger distances, with the following steps: a) a material sample surface is t at regular intervals t (cycle time ) bombarding successive primary ion pulses, b) the secondary ions of different masses m released from the primary ions from the material sample surface are accelerated to the same energy, c) the mass-dependent flight time t is measured via a path 1 and the mass is determined therefrom.
- the flight time t is proportional to the root of the mass (t proportional «/ in).
- the number of secondary ions which correspond to a specific mass m result in fine structure maxima in "nominal mass ranges" within a specified cycle time t at specific time intervals, the latter corresponding to an integer atomic or molecular weight of element or molecular ions.
- the amplitudes of the fine structure maxima allow a qualitative and quantitative analysis of the composition of the material sample surface.
- Time-of-flight secondary ion mass spectrometry also known as TOF-SIMS (time-of-flight secondary ion mass spectrometry)
- TOF-SIMS time-of-flight secondary ion mass spectrometry
- the sample surface is bombarded with a pulsed primary ion beam of pulse duration t. Secondary ions are detached from the sample surface by the primary ion beam. The extracted secondary ions are accelerated to the same energy E in an extraction field (a few KeV). Then they pass through a flight path 1, at the end of which they are detected by means of a time-resolving detector. The majority of the secondary ions are simply charged.
- the exact mass ra of a secondary ion can be determined from the flight time t thus determined with the same energy E.
- the secondary ions are registered within a time interval, called the cycle time tz, after the time at which the primary ion pulse strikes, with the following relationship (1):
- Mass range After this cycle time has elapsed, the next pri ion pulse can hit the sample.
- the measuring time is then typically about 100 to 1000 s.
- the different secondary ion species can be separated from one another by a sufficiently high mass resolution, ie they can be broken down into fine structure maxima and elements and compounds can thus be detected separately.
- the separation of such different species is an essential prerequisite for the detection of traces of compounds and elements.
- the mass resolution m / ⁇ m describes the mass difference ⁇ m with a mass m that can still be separated into two fine structure maxima. It hangs crucially depends on the primary ion pulse duration t. Further factors for the separation are the resolving power of the time-of-flight analyzer and the time resolution of the detector and registration electronics, which, however, are not the subject of the invention.
- the TOF-SIMS method is not only used to analyze the surface composition, but also allows the recording of lateral distributions of the various elements and connections with high spatial resolution in the sub- ⁇ m range.
- the primary ion beam is focused on a very small point and scanned over the sample with the aid of a deflection device.
- a mass spectrum is recorded and evaluated for each grid point.
- a distribution image (imaging TOF-SIMS) can then be generated from the results for a large number of raster points (typically e.g. 256 x 256).
- a depth distribution of the different species can be measured (depth profile) by sample removal using the primary ion beam or using an additional ion source and analysis at different erosion depths.
- the primary ion pulse duration required for a high mass resolution is only a few nanoseconds for a typical drift path 1 of approximately 2 m.
- the primary ion pulses are generated from the static beam of an ion source by a suitable beam pulsing method.
- the number of primary ions per pulse results from the static current of the ion source Ip and the pulse duration t:
- a shortening of the measuring time is only possible in the prior art by extending the primary pulse duration t with a corresponding loss of mast resolution, or by increasing the repetition rate with a corresponding restriction of the mass range detected (see Eq. 2).
- each primary ion pulse consists of a plurality of partial pulses, e) each partial pulse is so narrow that it allows the resolution of the finely structured mass areas, f) the distance t B of the partial pulses is greater than the width of the finely structured mass areas, g) the number n of partial pulses is selected such that is smaller than the distances between the finely structured mass ranges, ti) the n spectra belonging to the partial pulses of each finely structured mass range are added.
- tz in the time interval tz (see Eq. 2) the surface is not with a single short primary ion pulse, but within the cycle time t Z with a
- the distance between two partial pulses is greater than the time-of-flight difference of element and molecular ions of an integer nominal mass; in addition, the distance from the first to the last primary ion partial pulse is smaller than the time of flight difference between the nominal masses in the detected mass range.
- a device for carrying out the method is accordingly a time-of-flight secondary ion mass spectrometer, in which a material sample surface is bombarded with primary ions in a pulsed manner (primary ion pulses) and the primary ions detach secondary ions of different masses m from the material sample surface. The same energy E is applied to them after they have been extracted.
- the mass-dependent flight time t is measured via a path 1, the flight time t being proportional to the root of the mass and the number of secondary ions which correspond to a specific mass m within a defined cycle time t Z in specific
- Time intervals t result in fine structure maxima, the latter each corresponding approximately to an integer atomic or molecular weight of element or molecular ions.
- the amplitudes of the fine structure maxima allow a qualitative and quantitative analysis of the composition of the material sample surface.
- the device is characterized by a pulsed primary ion source, with which the material sample surface can be bombarded in the time interval t with a sequence of n essentially identical primary ions at a short time interval t B, the time interval t B of two primary ion pulses being greater than the time-of-flight difference between element and molecular ions one Nominal mass range and also the distance
- FIG. 1 shows a schematic arrangement of a time-of-flight mass spectrometer
- FIG. 3 shows a mass spectrum which was obtained in the operating method according to the invention.
- Fig. 1 shows the measuring principle of the TOF-SIMS method.
- a continuously operating ion source IQ is pulsed with the aid of a suitable beam pulser PS, which results in the primary ion pulses already mentioned.
- the pulsed primary ion beam which is filtered with a mass filter MF, is then focused and positioned on the sample P (target) using a focusing unit FK and a raster unit RS. All simply charged secondary ions generated by the primary ion beam are accelerated to the same energy E with the aid of a suction voltage U. Their runtime is then measured in a time-of-flight analyzer FZA with spatial and temporal focusing properties.
- a suitable time-resolving ion detector ID is used for the detection.
- the output pulses of the ion detector ID are processed by the registration electronics, consisting of a discriminator DS and a time-to-digital converter TDC in connection with a fast memory.
- FIGS. 2a and 2b A typical measurement result, which was recorded by the method according to the prior art, is shown in FIGS. 2a and 2b.
- a single primary ion pulse was used per cycle time t Z with a pulse duration of 1.3 ns.
- the triggered secondary ions are registered over the cycle time of 100 ⁇ s and all events are added over a total of 1695 ⁇ 10 7 cycles.
- the sample is a silicon wafer with an aluminum test structure. 2a shows the overview spectrum in the mass range (nominal masses) from 1 to 50 u.
- Fig. 2b shows in detail the fine structure of the maxima Mass range from 26.5 to 28.5 u of the spectrum according to Figure 2a.
- the separation of various atomic and molecular ions becomes clear with the help of the high mass resolution.
- Masses of the elements of the periodic table can be no further maxima between the maxima of the nominal masses 27 and 28, eg between CH "*" and Si "4" ).
- an operating mode which corresponds to the invention and which is expressed in FIGS. 3a and 3b.
- 12 partial pulses of the same pulse duration with a time interval of 25 ns were used with an unchanged one
- 3b shows the fine structure of the same mass spectrum in the mass range from 26.5 to 28.5 u.
- the 12-fold superimposition of the peak structure from FIG. 2b can be clearly seen by using the sequence of 12
- Partial pulses with a defined distance. By choosing the distance of 25 ns, a superposition of the maxima belonging to different primary ion pulses is avoided, so that an assignment of the peak series to a specific connection is possible. As in FIG. 2b, the maxima for AI "*" and C 2H3 are detected for the nominal mass 27 and the maxima for the nominal mass 28 for Si “1" , A1H * and C 2 H 4 "*” .
- the example shows that with the same measurement time the 12-fold secondary ion intensity can be registered without loss of mass resolution Accordingly, by adding the intensities of the respective secondary ion species, the same information as in Fig. 2a and 2b can be obtained in 1/12 of the measuring time, which means, for example, a shortening of the measuring time from 28 min to 2.3 min .
- the mode of operation corresponding to the invention also shortens the recording time for secondary ion images.
- an analysis as in FIG. 2 or FIG. 3 is carried out for each pixel (pixel) and then the distribution images of the different secondary ion species are constructed.
- FIG. 5 shows distribution images of the same sample with an operating mode according to the invention.
- a pulse sequence of 12 partial pulses per cycle at intervals of 25 ns was used. The events over 200 cycles were added and evaluated.
- the intensity and the dynamics in the secondary ion distribution images are significantly greater with the same measuring time and the same information content. So in Fig. 4 only 47 secondary ions AI "*" are registered in the brightest pixel, while in FIG. 5 a total of 411 secondary ions are contained in the brightest pixel.
- the other distributions of CH “*” , Si “1” and A1H “*” also show similar improvements in image quality with the same recording time. For the same image quality, there is a corresponding reduction in the image acquisition time by a factor of 12.
- the procedural use of a time pulse sequence instead of a single pulse can also be applied to analog methods, in particular to gas phase analysis using time-of-flight mass spectrometry.
- the ion generation takes place here with an electron pulse; the gas ions generated are accelerated and their masses determined by means of a time-of-flight measurement.
- a sequence of electron pulses is used instead of a single electron pulse, a shortening of the measurement time in high-resolution time-of-flight mass spectrometry can be achieved, as with the TOT-SIMS - utatis mutandis.
Landscapes
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
Abstract
Description
Claims
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE4416413 | 1994-05-10 | ||
DE4416413A DE4416413C2 (en) | 1994-05-10 | 1994-05-10 | Method of operating a time-of-flight secondary ion mass spectrometer |
PCT/EP1995/001767 WO1995031000A1 (en) | 1994-05-10 | 1995-05-10 | Process for operating a time-of-flight secondary ion mass spectrometer |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0708976A1 true EP0708976A1 (en) | 1996-05-01 |
EP0708976B1 EP0708976B1 (en) | 1997-11-12 |
Family
ID=6517732
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP95920015A Expired - Lifetime EP0708976B1 (en) | 1994-05-10 | 1995-05-10 | Process for operating a time-of-flight secondary ion mass spectrometer |
Country Status (5)
Country | Link |
---|---|
US (1) | US5633495A (en) |
EP (1) | EP0708976B1 (en) |
JP (1) | JP3358065B2 (en) |
DE (1) | DE4416413C2 (en) |
WO (1) | WO1995031000A1 (en) |
Families Citing this family (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5777326A (en) * | 1996-11-15 | 1998-07-07 | Sensor Corporation | Multi-anode time to digital converter |
US6117401A (en) * | 1998-08-04 | 2000-09-12 | Juvan; Christian | Physico-chemical conversion reactor system with a fluid-flow-field constrictor |
JP3658397B2 (en) * | 2002-06-28 | 2005-06-08 | キヤノン株式会社 | Device information acquisition method and information acquisition device by time-of-flight secondary ion mass spectrometry |
JP2004024203A (en) * | 2002-06-28 | 2004-01-29 | Canon Inc | Method for analysis of rna by time-of-flight secondary ion mass spectrometry |
DE10339346B8 (en) * | 2003-08-25 | 2006-04-13 | Ion-Tof Gmbh | Mass spectrometer and liquid metal ion source for such a mass spectrometer |
US8110814B2 (en) | 2003-10-16 | 2012-02-07 | Alis Corporation | Ion sources, systems and methods |
WO2007067296A2 (en) * | 2005-12-02 | 2007-06-14 | Alis Corporation | Ion sources, systems and methods |
US7728287B2 (en) * | 2007-03-01 | 2010-06-01 | Lawrence Livermore National Security, Llc | Imaging mass spectrometer with mass tags |
JP5848506B2 (en) * | 2010-03-11 | 2016-01-27 | キヤノン株式会社 | Image processing method |
JP5885474B2 (en) * | 2011-11-17 | 2016-03-15 | キヤノン株式会社 | Mass distribution analysis method and mass distribution analyzer |
Family Cites Families (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5396065A (en) * | 1993-12-21 | 1995-03-07 | Hewlett-Packard Company | Sequencing ion packets for ion time-of-flight mass spectrometry |
-
1994
- 1994-05-10 DE DE4416413A patent/DE4416413C2/en not_active Expired - Lifetime
-
1995
- 1995-05-10 WO PCT/EP1995/001767 patent/WO1995031000A1/en active IP Right Grant
- 1995-05-10 JP JP52869795A patent/JP3358065B2/en not_active Expired - Lifetime
- 1995-05-10 US US08/578,646 patent/US5633495A/en not_active Expired - Lifetime
- 1995-05-10 EP EP95920015A patent/EP0708976B1/en not_active Expired - Lifetime
Non-Patent Citations (1)
Title |
---|
See references of WO9531000A1 * |
Also Published As
Publication number | Publication date |
---|---|
JPH09500486A (en) | 1997-01-14 |
DE4416413C2 (en) | 1996-03-28 |
DE4416413A1 (en) | 1995-11-23 |
WO1995031000A1 (en) | 1995-11-16 |
EP0708976B1 (en) | 1997-11-12 |
US5633495A (en) | 1997-05-27 |
JP3358065B2 (en) | 2002-12-16 |
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