System and method for on-the-fly eccentricity recognition

• US 6,990,430 B2
• Filed: 12/18/2003
• Issued: 01/24/2006
• Est. Priority Date: 12/20/2002
• Status: Active Grant

• Current Assignee: Brooks Automation Ltd. (United Kingdom) (Azenta, Inc.)
• Original Assignee: Brooks Automation Incorporated (Azenta, Inc.)
• Inventors: Hosek, Martin
• Primary Examiner(s): Nghiem, Michael
• Assistant Examiner(s): Lau, Tung S.
• Application Number:
  US10/739,375
• Publication Number:
  US 20040167743A1
• Time in Patent Office: 768 Days
• Field of Search: 702/155, 335/20, 404/9, 414/783, 414/217, 414/800, 248/683, 700/275, 700/125, 700/218, 700/274, 700/121, 738/68, 356/73, 324/661, 451/9
• US Class Current: 702/155
• CPC Class Codes: G03F 7/7075 Handling workpieces outside exposure position, e.g. SMIF box
• CPC Class Codes: G03F 9/7003 Alignment type or strategy, e.g. leveling, global alignment
• CPC Class Codes: H01L 21/67265 of substrates stored in a container, a magazine, a carrier, a boat or the like
• CPC Class Codes: H01L 21/681 using optical controlling means
• CPC Class Codes: H01L 21/68707 the wafers being placed on a robot blade, or gripped by a gripper for conveyance

Abstract

A method of substrate eccentricity detection includes includes determining at least three positions on a perimeter of a first substrate, grouping the at least three perimeter positions to define one or more circles, estimating a location of a center of the first substrate as the location of a center of a predetermined circle approximated from the at least three perimeter positions, and determining an eccentricity vector as a difference between the estimated location and a reference position on a substrate transport mechanism on which the first substrate rests.

Claims

1. A method of substrate eccentricity detection comprising:

determining at least three positions on a perimeter of a first substrate as the first substrate is moving along a transfer path;

estimating a location of a center of the first substrate as the location of a center of a predetermined circle approximated from the at least three perimeter positions; and

determining an eccentricity vector as a difference between the estimated location and a reference position on a substrate transport mechanism on which the first substrate rests.

2. The method of claim 1, wherein determining at least three positions on a perimeter of the first substrate comprises:

capturing a position of the substrate transport mechanism upon detection of each of the at least three points on a perimeter of the first substrate;

utilizing a time delay to compensate the captured mechanism positions for detection delays; and

converting the mechanism positions to positions on the perimeter of the first substrate.

3. The method of claim 2, wherein the time delay is determined by:

placing a second substrate with a known radius on the reference position on the substrate transport apparatus;

moving the second substrate through a field of view of a plurality of sensors at a predetermined speed and detecting first positions and first velocities of the substrate transport apparatus when the sensors detect a leading and trailing edge of the second substrate;

moving the second substrate through the field of view of the plurality of sensors at a different predetermined speed and detecting second positions of the substrate transport apparatus when the sensors detect the leading and trailing edge of the second substrate;

calculating the locations of each of the sensors from the second positions and the known radius; and

reconstructing the motion of the substrate transport mechanism from the first positions to the second positions using the first velocities and the calculated sensor locations to determine the time delay between the sensors sensing the leading and trailing edges of the second substrate and detecting the first positions of the substrate transport apparatus.

4. The method of claim 3, wherein the time delay is determined by an automatic calibration routine.

5. The method of claim 1, wherein the predetermined circle is approximated by a best fit of the set of the at least three perimeter positions.

6. The method of claim 1, further comprising utilizing the eccentricity vector to correct a trajectory of the substrate transport mechanism.

7. The method of claim 1, further comprising utilizing the eccentricity vector to perform an additional substrate transport mechanism motion after a substrate placement.

8. The method of claim 1, further comprising:

grouping the at least three perimeter positions to define one or more circles; and

determining a corresponding radius of each of the one or more circles and detecting a deviation in the first substrate perimeter by determining if any of the corresponding radii exceeds a deviation threshold.

9. The method of claim 8, further comprising reporting an error condition upon detecting the deviation.

10. The method of claim 8, wherein the deviation threshold is determined by:

determining at least three positions on a perimeter of one or more eccentric substrates having a known radius and a predetermined eccentricity;

grouping the at least three perimeter positions to define one or more circles, each circle having a second radius; and

setting the deviation threshold to a maximum difference between each second radius and the known radius multiplied by a deviation safety factor.

11. The method of claim 10, wherein the deviation threshold is determined by an automatic calibration routine.

12. The method of claim 1, wherein determining at least three positions on a perimeter of the first substrate comprises:

displacing the first substrate along a path through a field of view of at least two sensors wherein the distance from the path to each of the sensors is asymmetric; and

detecting at least two points on a leading edge and at least two points on a trailing edge of the first substrate,

and wherein grouping the at least three perimeter positions to define one or more circles comprises grouping the at least two points on the leading edge and the at least two points on the trailing edge in trios to form at least four circles,

and wherein the method further comprises detecting a feature of the first substrate perimeter by determining if any first radius of the at least four circles exceeds a feature threshold.

13. The method of claim 12, wherein the set of the at least three perimeter positions comprises three points of the at least two points on the leading edge and the at least two points on the trailing edge that define a first radius that does not exceed the feature threshold.

14. The method of claim 12, wherein determining the feature threshold comprises:

determining at least two positions on a leading edge and at least two positions on a trailing edge of one or more feature substrates, each having a known radius and a predetermined feature;

grouping the at least two positions on a leading edge and at least two positions on a trailing edge in trios to define at least four circles, each circle having a third radius; and

setting the feature threshold to a maximum difference between each third radius and the known radius multiplied by a feature safety factor.

15. The method of claim 14, wherein the feature threshold is determined by an automatic calibration routine.

16. A method for determining the eccentricity of a first substrate comprising:

capturing a position of a mechanism upon detection of each of at least three points on a perimeter of the first substrate while the mechanism is transporting and moving the first substrate;

compensating the captured positions for detection delays;

converting the transport mechanism positions to positions on the perimeter of the first substrate;

estimating a location of a center of the substrate as the location of a center of a predetermined circle approximated from the perimeter positions; and

determining an eccentricity vector as a difference between the estimated location and a reference position on the substrate transport mechanism.

17. The method of claim 16, further comprising utilizing the eccentricity vector to correct a trajectory of the substrate transport mechanism.

18. The method of claim 16, further comprising utilizing the eccentricity vector to perform an additional substrate transport mechanism motion after a substrate placement.

19. The method of claim 16, further comprising:

grouping the perimeter positions into trios, each trio defining a circle;

calculating a first radius of each circle;

calculating a first difference between each first radius and a known nominal radius; and

validating the at least three perimeter positions by comparing each first difference with a threshold.

20. The method of claim 16, further comprising

determining at least three positions on a perimeter of one or more eccentric substrates having a known radius and a predetermined eccentricity;

grouping the at least three perimeter positions to define one or more circles, each circle having a second radius;

setting a deviation threshold to a maximum difference between each second radius and the known radius multiplied by a deviation safety factor; and

detecting a deviation in the substrate perimeter by determining if any first radius exceeds the deviation threshold.

21. The method of claim 16, further comprising:

determining at least two positions on a leading edge and at least two positions on a trailing edge of one or more feature substrates, each having a known radius and a predetermined feature;

grouping the at least two positions on a leading edge and at least two positions on a trailing edge in trios to define at least four circles, each circle having a third radius;

setting a feature threshold to a maximum difference between each third radius and the known radius multiplied by a feature safety factor; and

detecting a feature on the substrate perimeter by determining if any first radius exceeds the feature threshold.

22. A method for determining the eccentricity of a substrate comprising:

moving the substrate through a field of view of one or more sensors to detect at least three points on a perimeter of the substrate;

capturing a position of a mechanism upon detection of each of the at least three points while the mechanism is moving the first substrate;

compensating the captured positions for detection delays;

converting the transport mechanism positions to positions on the perimeter of the substrate;

grouping the perimeter positions into trios, each trio defining a circle;

estimating a location of a center of the substrate as the location of a center of a predetermined circle approximated from the perimeter positions; and

determining an eccentricity vector as a difference between the estimated location and a reference position on the substrate transport mechanism.

23. The method of claim 22, wherein displacing the substrate through a field of view of one or more sensors further comprises displacing the substrate in one step between at least a cassette and a load lock of a process chamber.

24. A system for substrate eccentricity detection comprising:

a substrate transport mechanism for transporting a first substrate along a path;

at least one sensor for sensing points on a perimeter of the first substrate as the first substrate is moving along the path; and

a controller connected to the substrate transport mechanism and to the at least one sensor, operable to;

determine at least three positions on the perimeter of the first substrate determined when the at least one sensor detects a perimeter of the first substrate;

estimate a location of a center of the first substrate as the location of a center of a theoretical circle which is approximated from a set of the at least three perimeter positions; and

determine an eccentricity vector as a difference between the estimated location and a reference position on the substrate transport mechanism.

25. The system of claim 24, wherein determining at least three positions on the perimeter of the first substrate comprises:

capturing a position of the substrate transport mechanism upon detection of each of the at least three points on a perimeter of the first substrate;

utilizing a time delay to compensate the captured mechanism positions for detection delays; and

converting the mechanism positions to positions on the perimeter of the first substrate.

26. The system of claim 25, wherein determining the time delay comprises:

placing a second substrate with a known radius on the reference position on the substrate transport apparatus;

moving the second substrate through the field of view of the plurality of sensors at a normal operational speed and detecting first positions and first velocities of the substrate transport apparatus when the sensors detect a leading and trailing edge of the second substrate;

moving the second substrate through the field of view of the plurality of sensors at a lower than normal operational speed and detecting second positions of the substrate transport apparatus when the sensors detect the leading and trailing edge of the second substrate;

calculating the locations of each of the sensors from the second positions and the known radius; and

reconstructing the motion of the substrate transport mechanism from the first positions to the second positions using the first velocities and the calculated sensor locations to determine the time delay between the sensors sensing the leading and trailing edges of the second substrate and detecting the first positions of the substrate transport apparatus.

27. The system of claim 26, wherein determining the time delay is performed by an automatic calibration routine.

28. The system of claim 24, wherein the controller approximates the center of the theoretical circle using a best fit of the set of the at least three perimeter positions.

29. The system of claim 24, wherein the controller utilizes the eccentricity vector to correct a trajectory of the substrate transport mechanism.

30. The system of claim 24, wherein the controller utilizes the eccentricity vector to perform an additional substrate transport mechanism motion after a substrate placement.

31. The system of claim 24, wherein the controller is further operable to detect a deviation in the first substrate perimeter by grouping the at least three perimeter positions to define one or more circles, each having a first radius, and determining if any first radius exceeds a deviation threshold.

32. The system of claim 31, wherein the controller is operable to report an error condition upon detecting the deviation.

33. The system of claim 31, wherein the controller is operable to determine the deviation threshold by:

determining at least three positions on a perimeter of one or more eccentric substrates having a known radius and a predetermined eccentricity;

grouping the at least three perimeter positions to define one or more circles, each circle having a second radius; and

setting the deviation threshold to a maximum difference between each second radius and the known radius multiplied by a deviation safety factor.

34. The system of claim 33, wherein the controller is operable to determine the deviation threshold by performing an automatic calibration routine.

35. The system of claim 33, wherein the controller is operable to determine at least three positions on a perimeter of the first substrate by:

causing the substrate transport apparatus to move the first substrate along a path through a field of view of at least two sensors wherein the distance from the path to each of the sensors is asymmetric; and

detecting at least two points on a leading edge and at least two points on a trailing edge of the first substrate,

and wherein the controller is operable to group the at least two points on the leading edge and the at least two points on the trailing edge in trios to form at least four circles, each having a first radius,

and wherein the controller is further operable to detect a feature of the first substrate perimeter by determining if any first radius of the at least four circles exceeds a feature threshold.

36. The system of claim 35, wherein the set of the at least three perimeter positions comprises three points of the at least two points on the leading edge and the at least two points on the trailing edge that define a first radius that does not exceed the feature threshold.

37. The system of claim 35, wherein the controller is operable to determine the feature threshold by:

determining at least two positions on a leading edge and at least two positions on a trailing edge of one or more feature substrates, each having a known radius and a predetermined feature;

grouping the at least two positions on a leading edge and at least two positions on a trailing edge in trios to define at least four circles, each circle having a third radius; and

setting the feature threshold to a maximum difference between each third radius and the known radius multiplied by a feature safety factor.

38. The system of claim 37, wherein the controller is operable to determine the feature threshold using an automatic calibration routine.

39. A system for substrate eccentricity detection comprising:

a substrate transport mechanism for moving a substrate along a path;

at least one sensor having, a centerline positioned eccentric to the path for sensing points on a perimeter of the substrate as the substrate is moving along the path; and

a controller connected to the substrate transport mechanism and to the at least one sensor, operable to;

determine at least three positions on a perimeter of the substrate when the at least one sensor detects the perimeter of the first substrate;

estimate a location of a center of the substrate as the location of a center of a theoretical circle with a radius equal to a nominal radius which is approximated by a set of the at least three perimeter positions; and

determine an eccentricity vector as a difference between the estimated location and a reference position on the substrate transport mechanism.