Scanning Electron Microscope

• US 20120256087A1
• Filed: 12/24/2010
• Published: 10/11/2012
• Est. Priority Date: 12/28/2009
• Status: Active Grant

• Current Assignee: Hitachi High-Technologies Corporation (Hitachi, Ltd.)
• Original Assignee: Hitachi High-Technologies Corporation (Hitachi, Ltd.)
• Inventors: Kanno, Seiichiro, Kitsunai, Hiroyuki, Matsushima, Masaru
• Granted Patent: US 8,653,459 B2
• Time in Patent Office: Days
• US Class Current: 250/310
• CPC Class Codes: H01J 2237/2007 Holding mechanisms
• CPC Class Codes: H01J 2237/28 Scanning microscopes
• CPC Class Codes: H01J 37/20 Means for supporting or positioning the objects or the material; Means for adjusting diaphragms or lenses associated with the support introducing the objects H01J37/18
• CPC Class Codes: H01L 21/6831 using electrostatic chucks

Abstract

There is provided a technique that is capable of attracting a sample without making the voltage applied to an electrostatic chuck unnecessarily large. Attraction experiments with respect to the electrostatic chuck are performed using a testing sample whose degree of warp and pattern of warp are known, and a critical application voltage at which the attraction state changes from “bad” to “good” is found. When measuring an inspection target sample, the flatness of the inspection target sample is measured, and the degree of warp and pattern of warp of the inspection target sample are detected. Based on the degree of warp and pattern of warp of the inspection target sample and on the known critical application voltage, the application voltage for the electrostatic chuck is set.

Claims

1. A method of setting an application voltage for an electrostatic chuck provided on a sample stage of a scanning electron microscope, the method comprising:

a testing sample mounting step of mounting on the electrostatic chuck a testing sample whose degree of warp and pattern of warp are known;

a step of detecting an attraction state of the testing sample with respect to the electrostatic chuck while increasing the application voltage for the electrostatic chuck;

an application voltage storage step of storing a critical application voltage at which the attraction state of the testing sample changed from “

bad”

to “

good”

;

an inspection target sample measuring step of measuring a flatness of an inspection target sample before the inspection target sample is transported into a processing chamber of the scanning electron microscope;

a step of detecting a degree of warp and pattern of warp of the inspection target sample from the flatness of the inspection target sample;

an application voltage setting step of setting the application voltage for the electrostatic chuck based on the degree of warp and pattern of warp of the inspection target sample and the critical application voltage stored in the application voltage storage step; and

an application voltage step in which the inspection target sample is transported into the processing chamber of the scanning electron microscope and mounted on the electrostatic chuck, and in which the application voltage that has been set in the application voltage setting step is applied.

2. The method of setting an application voltage for an electrostatic chuck according to claim 1, wherein

the application voltage setting step comprises an initial voltage setting step of setting an initial voltage to an application voltage immediately before the attraction state of the testing sample changes from “

bad”

to “

good”

, and

the application voltage step comprises;

a step of applying the initial voltage to the electrostatic chuck;

a step of detecting an attraction state of the inspection target sample with respect to the electrostatic chuck; and

an application voltage increasing step of increasing, in predetermined increments, the initial voltage until the attraction state of the inspection target sample changes from “

bad”

to “

good”

.

3. The method of setting an application voltage for an electrostatic chuck according to claim 2, wherein the predetermined increments in the application voltage increasing step are derived by dividing, into a plurality of equal parts, a unit of increase in the application voltage for the electrostatic chuck in the step of detecting the attraction state of the testing sample.

4. The method of setting an application voltage for an electrostatic chuck according to claim 2, wherein the predetermined increments in the application voltage increasing step are set based on a design tolerance for a thickness of a dielectric film on a surface of the electrostatic chuck.

5. The method of setting an application voltage for an electrostatic chuck according to claim 2, wherein, in the step of detecting the attraction state of the inspection target sample, the flatness of the inspection target sample is measured, and the attraction state of the inspection target sample is detected using the flatness.

6. The method of setting an application voltage for an electrostatic chuck according to claim 2, wherein, in the step of detecting the attraction state of the inspection target sample, the attraction state of the inspection target sample is detected using an optical microscope image or scanning electron microscope image of a surface of the inspection target sample.

7. The method of setting an application voltage for an electrostatic chuck according to claim 2, wherein it is determined that the attraction state of the inspection target sample has changed from “

bad”

to “

good”

when the flatness of the inspection target sample comes to fall within a predetermined reference value in the application voltage increasing step.

8. The method of setting an application voltage for an electrostatic chuck according to claim 1, wherein the testing sample mounting step, the step of detecting the attraction state of the testing sample, and the application voltage storage step are executed for each degree of warp and pattern of warp of the testing sample.

9. The method of setting an application voltage for an electrostatic chuck according to claim 1, wherein the inspection target sample measuring step is performed when the inspection target sample is in a load chamber connected to the processing chamber of the scanning electron microscope.

10. The method of setting an application voltage for an electrostatic chuck according to claim 1, wherein

the application voltage setting step comprises an initial voltage setting step of setting an optimal value for the application voltage to an application voltage immediately after the attraction state of the testing sample has changed from “

bad”

to “

good”

, and

the application voltage step applies the optimal value for the application voltage to the electrostatic chuck.

11. The method of setting an application voltage for an electrostatic chuck according to claim 1, further comprising a measurement target region determination step of determining whether or not a measurement target region is an edge of the inspection target sample, wherein

in the measurement target region determination step, if a measurement point is determined to be an edge of the inspection target sample, the application voltage for the electrostatic chuck is increased to a predetermined value.

12. A scanning electron microscope comprising:

a scanning coil that scans primary electrons from an electron source;

an objective lens that focuses, and irradiates a sample with, the primary electrons;

a secondary electron detector that detects secondary electrons from the sample;

an electrostatic chuck that holds the sample; and

a control device that controls an application voltage for the electrostatic chuck, wherein

on the control device and with respect to a testing sample whose degree of warp and pattern of warp are known, there is stored measurement data representing a relationship between the application voltage for the electrostatic chuck and an attraction state of the testing sample with respect to the electrostatic chuck, and

when an inspection target sample is mounted on the electrostatic chuck, the application voltage for the electrostatic chuck is set based on a degree of warp and pattern of warp of the inspection target sample and the measurement data stored on the control device.

13. The scanning electron microscope according to claim 12, wherein the application voltage for the electrostatic chuck when the inspection target sample is mounted is configured in such a manner that an initial voltage to be applied to the electrostatic chuck is set to an application voltage immediately before the attraction state of the testing sample changes from “

bad”

to “

good”

when the application voltage for the electrostatic chuck is increased, and the initial voltage is increased in predetermined increments until an attraction state of the inspection target sample changes from “

bad”

to “

good”

.

14. The scanning electron microscope according to claim 12, further comprising an attraction state detection device that detects an attraction state of the inspection target sample mounted on the electrostatic chuck.

15. The scanning electron microscope according to claim 14, wherein the attraction state detection device measures the attraction degree by measuring a flatness of the inspection target sample.

16. The scanning electron microscope according to claim 14, wherein the attraction state detection device comprises:

a height measuring device that measures a height of a surface of the inspection target sample; and

an image processing device that measures a flatness of the inspection target sample using an optical microscope image or scanning electron microscope image of the surface of the inspection target sample.

17. The scanning electron microscope according to claim 12, wherein, for the application voltage for the electrostatic chuck when the inspection target sample is mounted, an optimal value for the application voltage is set to an application voltage immediately after the attraction state of the testing sample changes from “

bad”

to “

good”

when the application voltage for the electrostatic chuck is increased.

18. A scanning electron microscope comprising:

a scanning coil that scans primary electrons from an electron source;

an objective lens that focuses, and irradiates a sample with, the primary electrons;

a secondary electron detector that detects secondary electrons from the sample;

an electrostatic chuck that holds the sample;

a control device that controls an application voltage for the electrostatic chuck; and

an attraction state detection device that detects an attraction state of the sample with respect to the electrostatic chuck, wherein

the electrostatic chuck is a bipolar electrostatic chuck comprising a main body, a circular internal electrode disposed within the main body, and a ring-shaped internal electrode disposed around the circular internal electrode,

the ring-shaped internal electrode has an outer diameter that is greater than an outer diameter of the sample attracted to the electrostatic chuck,

the application voltage for the electrostatic chuck is set to an optimal value capable of supporting the sample in a flat state if a position of a measurement point on an inspection target sample is located further inward than an edge of the sample, and the application voltage for the electrostatic chuck is set to a value greater than the minimum value if the position of the measurement point on the inspection target sample is at the edge of the sample.

19. The scanning electron microscope according to claim 18, wherein

on the control device and with respect to a testing sample whose degree of warp and pattern of warp are known, there is stored measurement data representing a relationship between the application voltage for the electrostatic chuck and an attraction state of the testing sample with respect to the electrostatic chuck, and

the optimal value for the application voltage is set based on a degree of warp and pattern of warp of the inspection target sample and the measurement data stored on the control device.

20. The scanning electron microscope according to claim 18, wherein the optimal value for the application voltage for the electrostatic chuck is obtained by increasing an initial voltage until the attraction state detected by the attraction state detection device becomes good.