Cluster analysis of unknowns in SEM-EDS dataset

• US 8,664,595 B2
• Filed: 06/28/2012
• Issued: 03/04/2014
• Est. Priority Date: 06/28/2012
• Status: Active Grant

• Current Assignee: FEI Company (Thermo Fisher Scientific Incorporated)
• Original Assignee: FEI Company (Thermo Fisher Scientific Incorporated)
• Inventors: Buhot, Michael, Phan, Van Hung, Owen, Michael James
• Primary Examiner(s): NGUYEN, KIET TUAN
• Application Number:
  US13/536,308
• Publication Number:
  US 20140001356A1
• Time in Patent Office: 614 Days
• Field of Search: 250/306, 250/307, 378/49
• US Class Current: 250/306
• CPC Class Codes: G01N 2223/616 earth materials
• CPC Class Codes: G01N 23/2252 Measuring emitted X-rays, e.g. electron probe microanalysis [EPMA]
• CPC Class Codes: G21K 7/00 Gamma- or X-ray microscopes
• CPC Class Codes: H01J 2237/24585 Other variables, e.g. energy, mass, velocity, time, temperature
• CPC Class Codes: H01J 2237/2807 X-rays

Abstract

The present invention discloses a method for determining the mineral content represented by the entire SEM-EDS dataset, including initially unknown data points. SEM-EDS data points are taken and compared to a set of known data points. Any data point that is not sufficiently similar to the known data point is classified as unknown and clustered with like unknown data points. After all data points are analyzed, any clusters of unknown data points with a sufficient number of data points are further analyzed to determine their characteristics. All clusters of unknown data points with an insufficient number of data points to allow further analysis are considered outliers and discarded.

Claims

1. A method for determining the mineral content of a sample, said method comprising:

directing an electron beam toward multiple point of unknown composition;

detecting x-rays emitted as a result of the electron beam impacting the sample to acquire an a-ray spectrum, and forming a data point;

classifying the data point from a sample by comparison to a set of known data points as a classified data point, wherein said classified data point is classified as a similar data point if the characteristics of the classified data point are similar to the characteristics of a known data point and alternatively the classified data point is classified as a dis-similar data point if the characteristics of the classified data point are not similar to that of a known data point;

placing the data point into a group wherein the characteristics of the data points within the group have characteristics similar to that of the classified data point;

repeating the previous steps until all data points are classified data points and are placed in groups with similar characteristics; and

analyzing the groups with dis-similar data points to for use in processing the mineral sample.

2. The method of claim 1, further comprising:

removing all groups of dis-similar data points except twenty groups with the most number of dis-similar data points before analyzing the groups with dis-similar data points to determine the mineral content of the groups with dis-similar data points.

3. The method of claim 1, further comprising removing all groups of dis-similar data points with five or less dis-similar data points before analyzing the groups with dis-similar data points to determine the mineral content of the groups with dis-similar data points.

4. The method of claim 1, further comprising removing all groups of dis-similar data points with twenty or less dis-similar data points before analyzing the groups with dis-similar data points to determine the mineral content of the groups with dis-similar data points.

5. The method of claim 1 wherein the groups with dis-similar data points are analyzed to determine the mineral content of the groups with dis-similar data points by conducting a quantitative energy dispersive x-ray spectroscopy to determine an elemental composition of the group of dis-similar data points.

6. The method of claim 5 wherein the set of known data points are altered based on the results of the energy dispersive x-ray spectroscopy analysis and the sample is processed again with the altered set of known data points.

7. The method of claim 1 wherein the groups with dis-similar data points are analyzed to determine the average atomic number of the groups with dis-similar data points by conducting a backscattered electron detector analysis.

8. The method of claim 7 wherein the set of known data points are altered based on the results of the back-scattered electron detector analysis and the sample is processed again with the altered set of known data points.

9. The method of claim 1 wherein each group of classified data points has an average value which is recalculated with the addition of each classified data point.

10. The method of claim 9 wherein the characteristic of each classified data point is within three percent of the average characteristic value of the group it is placed in.

11. The method of claim 9 wherein the characteristic of each classified data point is within one percent of the average characteristic value of the group it is placed in.

12. The method of claim 9 wherein the characteristic of each classified data point is within 0.01 percent of the average characteristic value of the group it is placed in.

13. The method of claim 1 wherein a newly classified data point is placed in a separate group if there are no previously classified data points with characteristics similar to the newly classified data points.

14. A scanning electron microscope x-ray spectroscopy device comprising:

a source of a charged particle beam or photon beam and means for directing the beam towards a mineral sample;

a detector for detecting emissions from the sample in response to the beam and for forming a data set comprising multiple data points;

a processor for controlling the scanning electron microscope; and

a computer readable data storage storing computer instruction to;

classify an x-ray spectroscopy data point taken from the sample by comparison to a set of known data points as a classified data point wherein said classified data point is classified as a similar data point if the characteristics of the classified data point are similar to the characteristics of a known data point and alternatively the classified data point is classified as a dis-similar data point if the characteristics of the classified data point are not similar to that of a known data point;

place the x-ray spectroscopy data point into a group wherein the characteristics of the data points within the group have characteristics similar to that of the classified data point;

repeat the previous steps until all x-ray spectroscopy data points are classified data points and are placed in groups with similar characteristics;

analyze the groups with dis-similar data points to for use in processing the mineral sample.