Sample height measurement using digital grating

• US 10,582,099 B2
• Filed: 05/07/2018
• Issued: 03/03/2020
• Est. Priority Date: 04/17/2018
• Status: Active Grant

• Current Assignee: Zhongke Jingyuan Electron Limited
• Original Assignee: Zhongke Jingyuan Electron Limited
• Inventors: Li, Shiguang, Guo, Jie
• Primary Examiner(s): Beck, Leron
• Application Number:
  US15/972,756
• Publication Number:
  US 20190320097A1
• Time in Patent Office: 666 Days
• Field of Search: 348135
• CPC Class Codes: G01B 11/0608 Height gauges
• CPC Class Codes: G01B 11/2513 with several lines being projected in more than one direction, e.g. grids, patterns
• CPC Class Codes: G01B 2210/42 with one or more detectors on a single side of the object to be measured and with a backing surface of support or reference on the other side
• CPC Class Codes: G01B 2210/48 for measurement of a wafer
• CPC Class Codes: G03F 9/7026 Focusing
• CPC Class Codes: G06T 7/521 from laser ranging, e.g. using interferometry; from the projection of structured light
• CPC Class Codes: H04N 23/54 Mounting of pick-up tubes, electronic image sensors, deviation or focusing coils
• CPC Class Codes: H04N 23/56 provided with illuminating means
• CPC Class Codes: H04N 23/60 Control of cameras or camera modules
• CPC Class Codes: H04N 23/67 Focus control based on electronic image sensor signals
• CPC Class Codes: H04N 25/71 Charge-coupled device [CCD] sensors; Charge-transfer registers specially adapted for CCD sensors
• CPC Class Codes: H04N 25/76 Addressed sensors, e.g. MOS or CMOS sensors

Abstract

A method, an apparatus, and a non-transitory computer-readable medium for measuring a height of a sample includes: receiving, by an optical sensor having pixels, an optical grating image of an illuminated optical grating reflected by a surface of the sample; determining, by a processor, a digital grating image by keeping values of first pixels of the optical grating image and resetting values of second pixels of the optical grating image; and determining the height based on a relationship between an integrated intensity of a portion of the digital grating image and the height.

Claims

1. A method for measuring a height of a sample, comprising:

receiving, by an optical sensor having pixels, an optical grating image of an illuminated optical grating reflected by a surface of the sample;

determining, by a processor, a digital grating image by keeping values of first pixels of the optical grating image and resetting values of second pixels of the optical grating image wherein keeping the values of the first pixels comprises multiplying the values of the first pixels with 1, and resetting the values of the second pixels comprises multiplying the values of the second pixels with 0; and

determining the height based on a relationship between an integrated intensity of a portion of the digital grating image and the height.

2. The method of claim 1, wherein the first pixels and second pixels form a digital grating having a first duty cycle and a first period, wherein the first pixels being grouped into first lines of pixels, and the second pixels being grouped into second lines of pixels, and wherein the second lines of pixels parallelly interleave the first lines of pixels.

3. The method of claim 2, further comprising:

adjusting alignment between the optical grating image and the digital grating by at least one of;

rotating at least one of the optical grating image and the digital grating, and adjusting a size of the optical grating image using an optical lens.

4. The method of claim 2, wherein the optical grating image have a second duty cycle and a second period, wherein

the second duty cycle is equal to the first duty cycle, and

the second period has a difference to the first period.

5. The method of claim 4, wherein the first and second duty cycles are 1:

1, and the difference is smaller than or equal to one half of the first period.

6. The method of claim 1, wherein determining the digital grating image comprises:

determining a first digital grating image by keeping the values of the first pixels and resetting the values of the second pixels; and

determining a second digital grating image by resetting the values of the first pixels and keeping the values of the second pixels.

7. The method of claim 6, wherein determining the height comprises:

determining an equal-intensity position on the optical sensor, wherein, at the equal-intensity position, an integrated intensity of a first portion of the first digital grating image is equal to an integrated intensity of a second portion of the second digital grating image;

determining a distance between the equal-intensity position and a reference position on the optical sensor, wherein the height is 0 when the equal-intensity position is the reference position; and

determining the height based on a linear relationship between the distance and the height.

8. The method of claim 7, wherein determining the equal-intensity position on the optical sensor comprises:

determining, at boundaries between the first and second pixels, first integrated intensities of the first digital grating image and second integrated intensities of the second digital grating image;

determining, at each of the boundaries, a differential integrated intensity based on a difference between the first and second integrated intensities at the same boundary; and

determining the equal-intensity position based on the differential integrated intensities.

9. An apparatus for measuring a height of a sample, comprising:

an optical sensor having pixels;

a processor; and

a memory coupled to the processor, the memory configured to store instructions which when executed by the processor become operational with the processor to;

receive, by the optical sensor, an optical grating image of an illuminated optical grating reflected by a surface of the sample;

determine a digital grating image by keeping values of first pixels of the optical grating image and resetting values of second pixels of the optical grating image, wherein keeping the values of the first pixels comprises multiplying the values of the first pixels with a first value, and resetting the values of the second pixels comprises multiplying the values of the second pixels with a second value; and

determine the height based on a relationship between an integrated intensity of a portion of the digital grating image and the height.

10. The apparatus of claim 9, wherein the optical sensor comprises one of a charge-coupled device (CCD) sensor and a complementary metal oxide semiconductor (CMOS) sensor.

11. The apparatus of claim 9, wherein

the first and second pixels form a digital grating having a first duty cycle and a first period, wherein the first pixels being grouped into first lines of pixels, and the second pixels being grouped into second lines of pixels, and wherein the second lines of pixels parallelly interleave the first lines of pixels;

and

the optical grating image has a second duty cycle and a second period, wherein the second duty cycle is equal to the first duty cycle, and the second period has a difference to the first period.

12. The apparatus of claim 9, wherein the memory further comprises instructions which when executed by the processor become operational with the processor to:

adjust alignment between the optical grating image and the digital grating by at least one of;

rotating at least one of the optical grating image and the digital grating, and adjusting a size of the optical grating image using an optical lens.

13. The apparatus of claim 9, wherein the first value is equal to 1, and wherein the second value is equal to 0.

14. The apparatus of claim 9, wherein the memory comprising the instructions operational with the processor to determine the digital grating image further comprises instructions which when executed by the processor become operational with the processor to:

determine a first digital grating image by keeping the values of the first pixels and resetting the values of the second pixels; and

determine a second digital grating image by resetting the values of the first pixels and keeping the values of the second pixels.

15. The apparatus of claim 14, wherein the memory comprising the instructions operational with the processor to determine the height further comprises instructions which when executed by the processor become operational with the processor to:

determine an equal-intensity position on the optical sensor, wherein, at the equal-intensity position, an integrated intensity of a first portion of the first digital grating image is equal to an integrated intensity of a second portion of the second digital grating image;

determine a distance between the equal-intensity position and a reference position on the optical sensor, wherein the height is 0 when the equal-intensity position is the reference position; and

determine the height based on a linear relationship between the distance and the height.

16. The apparatus of claim 15, wherein the memory comprising the instructions operational with the processor to determine the equal-intensity position on the optical sensor further comprises instructions which when executed by the processor become operational with the processor to:

determine, at boundaries between the first and second pixels, first integrated intensities of the first digital grating image and second integrated intensities of the second digital grating image;

determine, at each of the boundaries, a differential integrated intensity based on a difference between the first and second integrated intensities at the same boundary; and

determine the equal-intensity position based on the differential integrated intensities.

20. The apparatus of claim 9, wherein multiplying the values of the first pixels with a first value, and resetting the values of the second pixels comprises multiplying the values of the second pixels with a second value comprises modulating at least some of the first pixels or at least some of the second pixels with a phase.

17. A non-transitory computer-readable medium, comprising instructions for measuring a height of a sample which when executed by a processor become operational with the processor to:

receive, by an optical sensor having pixels, an optical grating image of an illuminated optical grating reflected by a surface of the sample;

determine a first digital grating image by keeping values of first pixels of the optical grating image and resetting values of second pixels of the optical grating image, and a second digital grating image by resetting the values of the first pixels and keeping the values of the second pixels, wherein keeping the values of the first pixels comprises multiplying the values of the first pixels with a first value, and resetting the values of the second pixels comprises multiplying the values of the second pixels with a second value; and

determine the height based on a relationship between the height and integrated intensities at portions of the first and second digital grating images.

18. The non-transitory computer-readable medium of claim 17, wherein the first value is 1, and wherein the second value is 0.

19. The non-transitory computer-readable medium of claim 17, wherein the instructions operational with the processor to determine the height further comprise instructions which when executed by the processor become operational with the processor to:

determine an equal-intensity position on the optical sensor, wherein, at the equal-intensity position, an integrated intensity of a first portion of the first digital grating image is equal to an integrated intensity of a second portion of the second digital grating image;

determine a distance between the equal-intensity position and a reference position on the optical sensor, wherein the height is 0 when the equal-intensity position is the reference position; and

determine the height based on a linear relationship between the distance and the height.