Pattern recognition alignment system

• US 5,621,813 A
• Filed: 11/14/1995
• Issued: 04/15/1997
• Est. Priority Date: 01/14/1993
• Status: Expired due to Fees

• Current Assignee: Ultratech Incorporated (Veeco Instruments Incorporated)
• Original Assignee: Ultratech Stepper, Inc. (Veeco Instruments Incorporated)
• Inventors: Brown, Robert L., Ward, Richard B., Pan, David S., Wanta, Mark S., Markle, David A., Jeong, Hwan J.
• Primary Examiner(s): Mancuso, Joseph
• Application Number:
  US08/558,613
• Time in Patent Office: 518 Days
• Field of Search: 382/141, 382/149, 382/151, 382/209, 382/218, 358/41, 358/43, 358/51, 256/401, 364/468, 250/204, 349/94, 349/95, 349/126, 349/129
• US Class Current: 382/151
• CPC Class Codes: G03F 7/70 Microphotolithographic exposure; Apparatus therefor photo-masks G03F1/00
• CPC Class Codes: G03F 9/70 for microlithography measuring printed patterns for monitoring overlay G03F7/70633 or focus G03F7/70641; projection system adjustment G03F7/70258; position control G03F7/70775
• CPC Class Codes: G06T 2207/30148 Semiconductor; IC; Wafer
• CPC Class Codes: G06T 2207/30204 Marker
• CPC Class Codes: G06T 7/33 using feature-based methods

Abstract

A substrate alignment and exposure system is disclosed The alignment is performed by capturing an image of the substrate with a pattern recognition system, determining the offset from the alignment and moving the substrate relative to the reticle to be in alignment. A first optical alignment system which captures an image of a position of the substrate off of the primary axis of the exposure optics is used to perform pre-alignment. A second optical alignment system captures an image of the reticle and the substrate through the lens of the exposure optics. The pattern recognition system recognizes the alignment keys on the reticle, alignment targets on the substrate, and computes their positions and displacement from alignment. The relative alignment can be direct or inferred. Any angular and translational misalignment is calculated. The pattern recognition system then moves the substrate to be in alignment with the reticle. In the present invention, any arbitrary feature on the reticle and substrate, including device features or specialized alignment keys and targets used by other exposure systems, can be recognized by the pattern recognition system and used for alignment.

Claims

1. An exposure and alignment system comprising:

an optical projection system disposed to expose a substrate with an exposure pattern from a reticle;

an optical alignment system disposed to form a first alignment image of a first region of said reticle defining a first key pattern therein and a superimposed image of a first portion of said substrate defining a first target pattern therein through said optical projection system;

a memory;

a pattern recognition system to recognize said first key and target patterns in said first alignment image, wherein said first key and target patterns to be recognized are arbitrary and user selectable, wherein said first key and target patterns are learned by said pattern recognition system and stored in said memory;

a computational subsystem coupled to said pattern recognition system to compute positions of said first key and target patterns and their positional difference to determine a deviation in position between said substrate and a reference position, in response to said position of said first key pattern.

2. The apparatus as described in claim 1, wherein said optical alignment system comprises a positional device coupled to said pattern recognition system to position said substrate approximately at a desired position relative to said first key pattern, in response to a command from said computational subsystem.

3. The apparatus as described in claim 2 wherein said substrate comprises fine alignment targets, and wherein said optical alignment system views at least a portion of said fine alignment targets, and wherein said positional device positions said substrate angularly and translationally such that said fine alignment targets on said substrate are within a first and second field of view of first and second objectives, respectively, of a fine alignment optical assembly.

4. The apparatus as described in claim 2 wherein said positioning is performed with a translational accuracy of ±

50 microns or better.

5. The apparatus as described in claim 1 wherein:

said optical alignment system further forms a second alignment image of a second region of said reticle defining a second key pattern therein and a superimposed image of a second portion of said substrate defining a second target pattern therein through said optical projection system

said pattern recognition system further recognizes said second key and target patterns in said second alignment image, wherein said second key and target patterns to be recognized are arbitrary and user selectable wherein said second key and target patterns are learned by said pattern recognition system and stored in said memory;

said computational subsystem further computes positions of said second key and target patterns and their positional differences to determine a deviation in position between said substrate and a reference position, in response to said position of said second key pattern; and

said system further comprises a positional device coupled to said pattern recognition system to position said substrate relative to said reticle based upon said positions and positional differences of said first and second key and target patterns in said first and second alignment images, respectively.

6. The apparatus as described in claim 5 wherein said positioning is performed with a translational accuracy such that said exposure pattern and said first substrate are aligned to an accuracy of ±

0.125 micron or better.

7. The apparatus as described in claim 5 further comprising a beamsplitter plate having a beamsplitter surface thereon, said beamsplitter surface reflecting a portion of alignment detection radiation from said first and said second regions of said reticle into said optical alignment system, said beamsplitter plate disposed over substantially all of an alignment field.

8. The apparatus as described in claim 5, further comprises a translational stage coupled to said pattern recognition system to move said substrate in a predetermined manner until said pattern recognition system finds said first and second target patterns.

9. The apparatus as described in claim 1, further comprising a translational stage couple to said pattern recognition system to move said substrate in a predetermined manner until said pattern recognition system finds said first target pattern.

10. The apparatus as described in claim 1 further comprising a beamsplitter plate having a beamsplitter surface thereon, said beamsplitter surface reflecting a portion of alignment detection radiation from said first region of said reticle into said optical alignment system, said beamsplitter plate disposed over substantially all of an alignment field.

12. The method as described in claim 6, wherein said key and target patterns are located on said reticle and substrate, respectfully, outside a useful pattern on said reticle and a region on said substrate to which said pattern is to be transferred.

11. A method of aligning a substrate to a reticle comprising the steps of:

learning first key and target patterns included on said reticle and substrate, respectively, and storing said first key and target patterns in a memory, wherein each of said first key and target patterns is arbitrary and user selectable;

forming a first alignment image of a first region of said substrate;

recognizing said first key and target patterns within said first alignment image

computing positions of said first key and target patterns and their positional difference;

determining a deviation in position between said substrate and a reference position, in response to said position of said first key pattern.

14. A method of aligning a substrate to a reticle as in claim 11 further comprising the steps of:

learning second key and target patterns included on said reticle and substrate respectively, and storing said second key and target patterns in said memory, wherein each of second key and target patterns are arbitrary and user selectable;

forming a second alignment image of a second region of said substrate;

recognizing said second key and target patterns within said second alignment image;

computing positions of said second key and target patterns and their positional difference; and

determining a deviation from an aligned position of said substrate relative to said reticle, in response to said position of said first key and target patterns and said position of said second key and target patterns.

15. The method as described in claim 14 further comprising the step of positioning said substrate relative to said reticle such that said substrate and said reticle are approximately in said aligned position.

16. The method as described in claim 15 wherein said positioning is performed with the translational accuracy such that said substrate is aligned to an exposure pattern of said reticle to an accuracy of ±

0.125 micron or better.

13. The method as described in step 4 wherein said substrate comprises fine alignment targets, wherein said first target pattern comprises at least a portion of said fine alignment targets, and wherein said step of positioning said substrate positions said substrate angularly and translationally such that said fine alignment targets on said substrate are within a first and second field of view of first and second objectives, respectively, of a fine alignment optical assembly.