Inspection tool for testing and adjusting a projection unit of a lithography system

Abstract

An inspection system and method are disclosed. The inspection system is configured to inspect a projection unit having multiple optical subsystems. The optical subsystems are configured to project an image during a lithography step. The inspection system provides self calibration by measuring both a test mask and the aerial image of the test mask with the same detector assembly. The inspection system is also capable of measuring multiple fields simultaneously using multiple detectors and 6 axis interferometry to accurately determine the position of each detector. Additionally, the inspection system is capable of measuring the distance between the test mask and the detector assembly with an indirect path around the projection unit which normally blocks the direct path.

1. An inspection system for performing optical tests associated with determining the imaging quality of a plurality of optical subsystems of an optical system, the optical tests being performed with a test mask having a plurality of measurable test patterns formed thereon, the inspection system comprising:
 a detector assembly capable of measuring the measurable test patterns of the test mask and the aerial image of the measurable test patterns as projected through the optical subsystems so as to determine the optical characteristics of each of the optical subsystems.  
 
   
   
     2. The system as recited in  claim 1  wherein the measured data associated with test patterns of the test mask is compared to the measured data associated with the image of the test patterns as projected through the optical subsystems to determine the optical characteristics of the optical subsystems. 
   
   
     3. The system as recited in  claim 2  wherein the measured data associated with test patterns of the test mask is calibrated out of the measured data associated with the image of the test patterns as projected through the optical subsystems to produce a resultant set of data that more closely matches the actual optical characteristics of the optical subsystems. 
   
   
     4. The system as recited in  claim 1  wherein the optical characteristics correspond to focus or distortion characteristics. 
   
   
     5. The system as recited in  claim 1  wherein the detector assembly includes a plurality of detector mechanisms for measuring the test patterns of the test mask and the images of the test patterns as projected through the optical subsystems. 
   
   
     6. The system as recited in  claim 5  wherein the number of detector mechanisms corresponds to the number of optical subsystems. 
   
   
     7. The system as recited in  claim 5  wherein the detector mechanisms are configured to simultaneously measure the optical characteristics of each of the optical subsystems. 
   
   
     8. The system as recited in  claim 5  wherein the detector mechanisms each have an imaging element configured to measure distortion characteristics and a confocal element configured to measure focus characteristics. 
   
   
     9. The system as recited in  claim 1  wherein the detector assembly is capable of moving during inspection so as to measure an array of test marks contained within each of the test patterns. 
   
   
     10. The system as recited in  claim 9  wherein the detector assembly includes a plurality of detector mechanisms that are ganged together so as to gather data at the same time during movements by the detector assembly. 
   
   
     11. The system as recited in  claim 9  further including a position location assembly configured to monitor the position of the detector assembly during movements thereof. 
   
   
     12. The system as recited in  claim 9  wherein the position location assembly includes a 6 axis interferometer system that continuously monitors the position of the detector assembly. 
   
   
     13. The system as recited in  claim 1  further including a mask assembly configured to hold the test mask during measurements and to move the test mask between a calibration position where the test patterns of the test mask are measured and a measurement position where the image of the test patterns are measured. 
   
   
     14. The system as recited in  claim 13  wherein the mask assembly comprises:
 a mask holder configured to hold the test mask; and  
 a mask stage configured to move the holder and thus the test mask when held thereon between the measurement and calibration positions.  
 
   
   
     15. The system as recited in  claim 13  further including a position location assembly configured to monitor the position of the mask assembly. 
   
   
     16. The system as recited in  claim 1  further including an illumination assembly configured to illuminate the test mask during measurement thereof. 
   
   
     17. The system as recited in  claim 16  wherein illumination assembly comprises:
 an illumination unit for generating and directing one or more beams through the test mask, the number of beams corresponds to the number of optical subsystems; and  
 an illumination stage for moving the illumination unit prior to measurements by the detector assembly.  
 
   
   
     18. The system as recited in  claim 1  wherein the detector assembly is capable of moving during measurements, and further including a mask assembly for moving the test mask to various test positions and a position location assembly for determining the position of the mask assembly and the position of the detector assembly relative to one or more reference points. 
   
   
     19. The system as recited in  claim 18  wherein the reference point is defined by the assemblies themselves, some fixed portion of the system or some component external to the system. 
   
   
     20. The system as recited in  claim 18  wherein the position location assembly includes a fixed reference frame configured to provide a reference point relative to the mask assembly and the detector assembly. 
   
   
     21. The system as recited in  claim 18  wherein the position locator assembly includes one or more first sensors for determining the position of the mask assembly and one or more second sensors for determining the position of the detector assembly. 
   
   
     22. The system as recited in  claim 19  wherein the first sensors are capacitance sensors and the second sensors are interferometer sensors. 
   
   
     23. The system as recited in  claim 1  wherein the optical system is a projection unit used in a lithography system, each of the subsystems being configured to collect and direct a corresponding light beam to the surface of a substrate. 
   
   
     24. The system as recited in  claim 1  further including a structural chassis and a support arrangement, the structural chassis being configured to support the support arrangement and the detector assembly, the support arrangement being configured to locate the projection unit relative to the detector system and an adjustment window, the adjustment window allowing adjustments to be made to the projection unit without removing the projection unit from the inspection system. 
   
   
     25. A detector assembly for use in a tool for inspecting optical systems having a plurality of optical subsystems, the detector assembly comprising:
 a plurality of detector mechanisms, each of the detector mechanisms corresponding to individual ones of the optical subsystems, the detector mechanisms being configured to simultaneously measure the optical characteristics of each of the optical subsystems.  
 
   
   
     26. The detector assembly as recited in  claim 25  further including a detector box attached to a detector stage, the detector box containing the plurality of detector mechanisms, the detector stage being configured to move the detector box so as to move the detector mechanisms in positions for measuring the optical characteristics of the optical subsystems. 
   
   
     27. The detector assembly as recited in  claim 25  wherein each of the detector mechanisms includes an objective lens and an optical testing system that is coupled to the objective lens. 
   
   
     28. The detector assembly as recited in  claim 27  wherein the optical testing system includes a confocal subsystem configured to measure the optical characteristics associated with focus. 
   
   
     29. The detector assembly as recited in  claim 27  wherein the optical testing system includes an imaging subsystem configured to measure optical characteristics associated with distortion or aberrations. 
   
   
     30. The detector assembly as recited in  claim 27  wherein the optical testing system includes a confocal subsystem and an imaging subsystem. 
   
   
     31. A position location assembly for use in a tool for inspecting optical systems having a plurality of optical subsystems, the assembly comprising:
 a detection system configured to continuously determine the position of a detector assembly relative to one or more reference points, the detection system including one or more first sensors that measure the distance between a fixed reference frame and the detector assembly, and one or more second sensors that measure the distance between a test mask and the detector assembly.  
 
   
   
     32. The position location assembly as recited in  claim 31  wherein the detection system is a 6 axis interferometer system configured to provide positional information in the x, y and z directions as well as the rotational θ x , θ y , θ z  directions. 
   
   
     33. The position location assembly as recited in  claim 32  wherein the one or more first sensors include a pair of x-axis interferometers and a y-axis interferometer, and wherein the one or more a second sensors include three z-axis interferometers, the pair of x-axis interferometers providing positional information in the x and θ z  directions, the y-axis interferometer providing positional information in the y direction, the z-axis interferometer providing positional information in the z, θ x  and θ y  directions. 
   
   
     34. The position location assembly as recited in  claim 33  wherein the pair of x-axis interferometers are spaced apart along a similar axis and positioned on the detector assembly across from the reference frame, the y-axis interferometer are positioned on the detector assembly across from the reference frame, the x-axis and y-axis interferometers interacting with a corresponding mirror positioned on the reference frame across from the corresponding interferometer. 
   
   
     35. The position location assembly as recited in  claim 33  wherein a pair of z-axis interferometers are spaced apart along a similar axis and positioned on the detector assembly across from the test mask, the pair of z-axis interferometers interacting with a pair of corresponding mirrors positioned proximate the test mask across from the corresponding interferometers, and wherein the other z-axis interferometer is positioned on the reference frame, the other z-axis interferometer interacting with corresponding mirrors positioned proximate the test mask and on the detector assembly. 
   
   
     36. The position location assembly as recited in  claim 31  further including a second detection system configured to determine the position of the test mask relative to one or more reference points, the detection system including one or more third sensors that measure the position of the test mask relative to the reference frame. 
   
   
     37. An inspection system, comprising:
 a test component configured to help determine the optical characteristics of an optical component;  
 an optical detection component configured to perform optical tests on an optical component, the detector component cooperating with the test component to determine the optical characteristics of the optical component, the optical component being disposed between the test component and the detector component while the tests are being performed;  
 a position detection component configured to measure the distance between the test component and the detector component with an indirect path around the optical component which blocks the direct path.  
 
   
   
     38. The inspection system as recited in  claim 37  wherein the position detection component includes an interferometer arrangement that produces a first beam that follows a first indirect path around the optical component to a first mirror and a second beam that follows a second indirect path around the optical component to a second mirror. 
   
   
     39. The inspection system as recited in  claim 37  wherein a differential change in the length of the indirect paths indicates a change in distance between the test component and the detector component. 
   
   
     40. The inspection system as recited in  claim 37  wherein the first and second indirect paths are proportional in length when the test component and the detector component are at first distance, and wherein the first and second indirect paths are not proportional in length when the test component and the detector component are at second distance. 
   
   
     41. The inspection system as recited in  claim 37  wherein the position detection component includes one or more bending mirrors to direct the beams around the optical component. 
   
   
     42. The inspection system as recited in  claim 37  wherein the first mirror is mounted on the test component, and wherein the second mirror is mounted on the detector component. 
   
   
     43. The inspection system as recited in  claim 37  wherein the interferometer arrangement includes one or more interferometers for producing the first and second beams. 
   
   
     44. The inspection system as recited in  claim 37  wherein the interferometer is disposed inside a frame, and wherein the first indirect path travels through a first portion of the frame and wherein the second indirect path travels through a second portion of the frame. 
   
   
     45. A method of self calibrating an inspection system, the inspection system being configured to inspect an optical component of a lithography system, the method comprising:
 providing a test mask having on or more test patterns;  
 measuring the test patterns with the inspection system;  
 measuring the images of the test patterns with the same inspection system, the images being formed by the optical component; and comparing the test patterns with the images.  
 
   
   
     46. The method as recited in  claim 45  wherein position measurements are performed so as to determine distortion characteristics of the optical components. 
   
   
     47. The method as recited in  claim 45  wherein focus measurements are performed so as to determine focus characteristics of the optical components. 
   
   
     48. The method as recited in  claim 45  wherein the optical characteristics of the optical component are determined during the comparison by calibrating out imperfections associated with the test mask and inspection system. 
   
   
     49. A method of inspecting optical projection units having multiple fields, the method comprising
 simulataneously measuring multiple fields with multiple detectors, each of the detectors corresponding to an individual field;  
 moving the multiple detectors to various measurement points within its corresponding individual field; and  
 determining the position of each detector with 6 axis interferometry.