Method of inspecting a sample with a charged particle beam device, and charged particle beam device

Patent metadata

Field	Value
Publication number	US-10345250-B2
Application number	US-201715782649-A
Country	US
Kind code	B2
Filing date	Oct 12, 2017
Priority date	Oct 12, 2017
Publication date	Jul 9, 2019
Grant date	Jul 9, 2019

Abstract

A method of inspecting a sample with a charged particle beam device is described. The method comprises arranging the sample on a stage, determining a first focusing strength of an objective lens adapted to focus a charged particle beam on a first surface region of the sample that is arranged at a first distance from the objective lens in a direction of an optical axis, calculating a difference between the first distance and a predetermined working distance based on the determined first focusing strength, adjusting a distance between the first surface region and the objective lens by the calculated difference, and inspecting the first surface region. According to a further aspect, a charged particle beam device configured to be operated according to the above method is described.

First claim

The invention claimed is:

1. A method of inspecting a sample with a charged particle beam device, comprising:
arranging the sample on a stage;
determining a first focusing strength of an objective lens adapted to focus a charged particle beam on a first surface region of the sample that is arranged at a first distance from the objective lens in a direction of an optical axis;
calculating a difference between the first distance and a predetermined working distance based on a measured focusing current at the determined first focusing strength;
adjusting a distance between the first surface region and the objective lens by the calculated difference; and
inspecting the first surface region.

2. The method of claim 1 , wherein the distance between the first surface region and the objective lens is adjusted by moving the stage by the calculated difference in the direction of the optical axis, wherein the stage is stationary while determining the first focusing strength and calculating the difference between the first distance and the predetermined working distance.

3. The method of claim 1 , wherein the first focusing strength of the objective lens is determined by an autofocusing process.

4. The method of claim 3 , wherein the autofocusing process comprises imaging the first surface region with varying focusing strengths of the objective lens and analyzing an image sharpness or an image contrast of obtained images.

5. The method of claim 1 , wherein the difference is calculated based on the measured focusing current at the determined first focusing strength and using a previously obtained table or function which relates focusing currents of the objective lens to respective focusing distances of the objective lens.

6. The method of claim 1 , wherein the distance between the first surface region and the objective lens is adjusted in an iterative process.

7. A method of inspecting a sample with a charged particle beam device, comprising:
arranging the sample on a stage;
determining a first focusing strength of an objective lens adapted to focus a charged particle beam on a first surface region of the sample that is arranged at a first distance from the objective lens in a direction of an optical axis;
calculating a difference between the first distance and a predetermined working distance based on the determined first focusing strength;
adjusting a distance between the first surface region and the objective lens by the calculated difference; and
inspecting the first surface region,
wherein after adjusting the distance between the first surface region and the objective lens by the calculated difference:
determining a second focusing strength of the objective lens adapted to focus the charged particle beam on the first surface region;
calculating whether a difference between the second focusing strength and a predetermined focusing strength is smaller than a predetermined threshold value, and continuing with the inspection of the first surface region, if the difference between the second focusing strength and the predetermined focusing strength is smaller than the predetermined threshold value.

8. The method of claim 7 , further comprising pre-specifying a measurement accuracy; and
determining the predetermined threshold value such that, in the case of a positive calculation result, the first surface region is arranged close enough to the predetermined working distance for being inspected with a measurement accuracy better than or equal to the pre-specified measurement accuracy.

9. The method of claim 1 , further comprising: previously calibrating the charged particle beam device by:
arranging a scan object with one or more known lateral dimensions at the predetermined working distance; and
determining a relation between a scan current of a scan deflector and at least one lateral dimension of the scan object.

10. The method of claim 1 , wherein the charged particle beam impinges on the sample with a landing energy of 5 keV or less.

11. The method of claim 1 , wherein a plurality of surface regions of the sample are subsequently inspected, the inspection of each of the plurality of surface regions comprising:
determining a respective focusing strength adapted to focus the charged particle beam on the respective surface region which is arranged at a respective distance from the objective lens;
calculating a difference between the respective distance and the predetermined working distance based on the respective focusing strength; and
adjusting a distance between the respective surface region and the objective lens by moving the stage by the calculated difference in the direction of the optical axis.

12. The method of claim 1 , wherein the first surface region and a second surface region of the sample laterally spaced-apart from the first surface region are located at different levels in the direction of the optical axis, the method comprising:
successively inspecting the first surface region and the second surface region at the predetermined working distance by providing a real-time control of a position of the stage along the optical axis.

13. The method of claim 1 , wherein the sample comprises a large-area substrate for display manufacturing having a surface area of 1 m 2 or more.

14. A charged particle beam device for inspecting a sample, comprising:
a stage for arranging a sample to be inspected;
an objective lens configured to focus a charged particle beam propagating along an optical axis on the sample;
a processing unit configured to determine a first focusing strength of the objective lens adapted to focus the charged particle beam on a first surface region of the sample that is arranged at a first distance from the objective lens in a direction of an optical axis;
a calculation unit configured to calculate a difference between the first distance and a predetermined working distance based on a measured focusing current at the determined first focusing strength; and
an adjusting unit configured to adjust a distance between the first surface region and the objective lens by the calculated difference.

15. The charged particle beam device of claim 14 , wherein the adjusting unit comprises a stage motion controller configured to move the stage in the direction of the optical axis.

16. The charged particle beam device of claim 14 , wherein the processing unit comprises an image acquisition and analyzing unit, particularly an autofocusing device.

17. The charged particle beam device of claim 14 , wherein the calculation unit comprises a memory, wherein a table or function which relates focusing strengths of the objective lens to respective focusing distances of the objective lens is stored in the memory.

18. The charged particle beam device of claim 14 , wherein the objective lens comprises a retarding field component configured to decelerate the charged particle beam to a landing energy of 5 keV or less.

19. The charged particle beam device of claim 14 , wherein the stage is configured for supporting a large-area substrate for display manufacturing having a size of 1 m 2 or more.

Assignees

• Applied Materials Inc

Inventors

• Mueller Bernhard G
• Virdi Kulpreet Singh
• Schüler Bernhard
• Trauner Robert
• Ledl Ludwig

Classifications

• G01N23/2251 Primary

  using incident electron beams, e.g. scanning electron microscopy [SEM] · CPC title

• H01J37/28

  with scanning beams {(H01J37/268, H01J37/292, H01J37/2955 take precedence)} · CPC title

• H01J2237/216

  Automatic focusing methods · CPC title

• H01J2237/04922

  electromagnetic · CPC title

• G01N2223/418

  electron microscope · CPC title