TIME-OF-FLIGHT MASS SPECTROMETRY OF SURFACES

• US 20090189072A1
• Filed: 01/26/2009
• Published: 07/30/2009
• Est. Priority Date: 01/25/2008
• Status: Active Grant

• Current Assignee: Ionwerks, Inc.
• Original Assignee: Ionwerks, Inc.
• Inventors: Schultz, J. Albert, Egan, Thomas F., Waters, Kelley L., Ulrich, Steven R.
• Granted Patent: US 8,101,909 B2
• Time in Patent Office: Days
• US Class Current: 250/287
• CPC Class Codes: G01N 23/203 Measuring back scattering
• CPC Class Codes: G01N 23/2206 Combination of two or more measurements, at least one measurement being that of secondary emission, e.g. combination of secondary electron [SE] measurement and back-scattered electron [BSE] measurement
• CPC Class Codes: G01N 23/2255 using incident ion beams, e.g. proton beams
• CPC Class Codes: H01J 49/40 Time-of-flight spectrometers H01J49/36 takes precedence

Abstract

The present invent provides a particle detector for counting and measuring the flight time of secondary electrons and scattered ions and neutrals and to correlate coincidences between these and backscattered ions/and neutrals while maintaining a continuous unpulsed microfocused primary ion beam for impinging a surface. Intensities of the primary particle scattering and secondary particle emissions are correlated with the position of impact of the focused beam onto a materials surface so that a spatially resolved surface elemental and electronic structural mapping is obtained by scanning the focused beam across the surface.

Claims

1. An method for analyzing a sample comprising:

generating a continuous micro-focused beam of primary ions;

directing the micro-focused beam of ions through an aperture in a position sensitive detector to a sample surface thereby creating a secondary species and backscattered primary species;

said position sensitive detector having a Multi-channel plate and a multi-anode array, wherein said secondary species is selected from the group consisting of electrons, photons, recoiled atoms, backscattered atoms backscattered ions and any combination thereof, and wherein said backscattered primary species have a backscattering angle between 90 to 180 degrees with respect to the primary ion beam incidence;

adjusting the micro-focused ion beam fluence such that about only one ion hits the sample surface within a 1 microsecond period;

accelerating the secondary from the sample to the detector by applying an electric field between the sample and the detector;

detecting the arrival time and angular trajectories of said backscattered primary species and said secondary species;

wherein the secondary species is selected from the group consisting of electrons and/or photons arriving in coincidence at the time-of-flight detector;

measuring a first timing signal from a first subset of secondary species selected from the group consisting of electrons, photons and any combination thereof and deriving this primary ion impact time by the known energies of the electrons or velocity of the photons and the geometry of the detector;

measuring a second timing signal wherein the signal is generated when a second subset of secondary species strikes the detector, wherein said second subset of secondary species is selected from the group consisting of recoiled atoms, backscattered atoms, backscattered ions and any combination thereof;

calculating the times of flight for the secondary species and the backscattering primary species using a linear time of flight analysis and the measured position of the secondary species impact.

2. The method of claim 1, further comprising applying a magnetic field to direct said flow of secondary species.

3. The method of claim 1, wherein the overall surface composition is measured with a technique selected from the group consisting of MSRI, XPS, AES or any combination thereof and compared to a backscattering spectra.

4. The method of claim 3, wherein the generated micro-focused ion beam is selected from the group consisting of Helium, Neon, Indium, Gold, Gold/Silicon clusters, Gold/Germanium Clusters and any combination thereof.

5. An method for analyzing a sample comprising

generating a continuous micro-focused beam of primary ions;

directing the micro-focused beam of ions through an aperture in a position sensitive detector to a sample surface thereby creating a secondary species and backscattered primary species;

said position sensitive detector having a Multi-channel plate and a multi-anode array, wherein said secondary species is selected from the group consisting of electrons, photons, recoiled atoms, backscattered atoms backscattered ions and any combination thereof, and wherein said backscattered primary species have a backscattering angle between 90 to 180 degrees with respect to the primary ion beam incidence;

adjusting the micro-focused ion beam fluence such that about only one ion hits the sample surface within a 1 microsecond period;

accelerating the secondary from the sample to the detector by applying an electric field between the sample and the detector;

intermittently firing a VUV laser across the surface in order to sample said secondary species;

detecting the arrival time and angular trajectories of said backscattered primary species and said secondary species;

wherein the secondary species is selected from the group consisting of electrons and/or photons arriving in coincidence at the time-of-flight detector;

measuring a first timing signal from a first subset of secondary species selected from the group consisting of electrons, photons and any combination thereof and deriving this primary ion impact time by the known energies of the electrons or velocity of the photons and the geometry of the detector;

measuring a second timing signal wherein the signal is generated when a second subset of secondary species strikes the detector, wherein said second subset of secondary species is selected from the group consisting of recoiled atoms, backscattered atoms, backscattered ions and any combination thereof;

calculating the times of flight for the secondary species and the backscattering primary species using a linear time of flight analysis and the measured position of the secondary species impact.

6. The method of claim 5, further comprising applying a magnetic field to direct said flow of secondary species.

7. The method of claim 5, wherein the overall surface composition is measured with a technique selected from the group consisting of MSRI, XPS, AES or any combination thereof and compared to a backscattering spectra.

8. The method of claim 6, wherein the generated micro-focused ion beam is selected from the group consisting of Helium, Neon, Indium, Gold, Gold/Silicon clusters, Gold/Germanium Clusters and any combination thereof.

9. An apparatus for counting and measuring the flight time of secondary species and correlating coincidences between the secondary species while maintaining a continuous unpulsed micro-focused beam of primary ions wherein the secondary species comprise electrons, photons, recoiled atoms, backscattered neutrals and backscattered ions, comprising:

a source for the generation of a flow of continuous micro-focused beam of primary ions;

a surface for holding a sample, said surface positioned such that said flow from said source is incident upon said sample;

a position sensitive detector having a Multi-channel plate, a multi-anode array, an aperture wherein said aperture is position such that said flow travels from said source through said position sensitive detector to said surface;

an electric field positioned between said detector and said surface; and

a time-to-digital converter.

10. The apparatus of claim 9, further comprising a VUV laser intermittently fired across said surface.

11. The apparatus of claim 10, further comprising a magnetic field to align secondary species upon leaving the surface

12. The apparatus of claim 10, further comprising an annular anode capable of detecting said secondary species in more than one region.

13. An apparatus for counting and measuring the flight time of secondary species and correlating coincidences between the secondary species while maintaining a continuous unpulsed micro-focused beam of primary ions wherein the secondary species comprise electrons, photons, recoiled atoms, backscattered neutrals and backscattered ions, comprising:

a source for the generation of a flow of continuous micro-focused beam of primary ions;

a surface for holding a sample, said surface positioned such that said flow from said source is incident upon said sample;

a position sensitive detector having a Multi-channel plate, a multi-anode array, an aperture wherein said aperture is position such that said flow travels from said source through said position sensitive detector to said surface;

an electric field positioned between said detector and said surface;

a time-to-digital converter;

a CMA type analyzer in which said micro-focused beam of primary ions and a co-axial backscatter detector are introduced co-axially through an axially symmetric curved energy analyzer wherein said energy analyzer is equipped with a position sensitive detector; and

a VUV laser intermittently fired across said surface.

14. The apparatus of claim 13, further comprising a magnetic field to align secondary species upon leaving the surface

15. The apparatus of claim 13, further comprising an annular anode capable of detecting the secondary species in more than one region.