SYSTEM AND METHOD FOR CREATING A FOCUS-EXPOSURE MODEL OF A LITHOGRAPHY PROCESS

• US 20070031745A1
• Filed: 08/02/2006
• Published: 02/08/2007
• Est. Priority Date: 08/08/2005
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: Brion Technologies Incorporated (ASML Holding NV)
• Inventors: Ye, Jun, Chen, Luoqi, Cao, Yu, Liu, Hua-Yu
• Granted Patent: US 7,747,978 B2
• Time in Patent Office: Days
• US Class Current: 430/30
• CPC Class Codes: G03F 7/705 Modelling or simulating from physical phenomena up to complete wafer processes or whole workflow in wafer productions
• CPC Class Codes: G03F 7/70516 Calibration of components of the microlithographic apparatus, e.g. light sources, addressable masks or detectors
• CPC Class Codes: G03F 7/70625 Dimensions, e.g. line width, critical dimension [CD], profile, sidewall angle or edge roughness
• CPC Class Codes: G03F 7/70641 Focus

Abstract

A system and a method for creating a focus-exposure model of a lithography process are disclosed. The system and the method utilize calibration data along multiple dimensions of parameter variations, in particular within an exposure-defocus process window space. The system and the method provide a unified set of model parameter values that result in better accuracy and robustness of simulations at nominal process conditions, as well as the ability to predict lithographic performance at any point continuously throughout a complete process window area without a need for recalibration at different settings. With a smaller number of measurements required than the prior-art multiple-model calibration, the focus-exposure model provides more predictive and more robust model parameter values that can be used at any location in the process window.

Claims

1. A method for creating a focus-exposure model of a lithography process, comprising:

selecting a model of a lithography process, the model including an optical model module, the model having a set of model parameters including focus, exposure, and a set of fitting parameters having variable values;

defining a process window for the lithography process in a focus-exposure space;

selecting a set of initial fitting parameter values for the model;

selecting a plurality of sampling locations within the process window, the plurality of sampling locations including nominal condition and being a subset of all possible process conditions within the process window;

generating simulated results of the lithography process at each of the plurality of sampling locations within the process window using the model with the set of initial fitting parameter values by simulating the lithography process with varying values of focus and exposure corresponding to the plurality of sampling locations within the process window while holding constant the initial fitting parameter values;

comparing the simulated results with actual results of the lithography process at each of the plurality of sampling locations within the process window to produce a total difference measure between the simulated results and the actual results at all of the plurality of sampling locations;

modifying the set of fitting parameter values and generating additional simulated results at each of the plurality of sampling locations within the process window to identify optimum fitting parameter values such that the total difference measure between the actual results and simulated results produced using the optimum fitting parameter values is minimized or is below a predetermined threshold; and

defining the focus-exposure model as the model including the optimum fitting parameter values, the focus-exposure model being capable of simulating the lithography process at any location within the entire process window.

2. The method of claim 1, wherein the focus-exposure model is used to simulate the lithography process at a single location within the process window.

3. The method of claim 1, wherein the focus-exposure model is used to simulate the lithography process at a location within the process window that is not one of the plurality of sampling locations by applying focus and exposure values corresponding to the location within the process window to the focus-exposure model in accordance with first principles without changing the optimum fitting parameter values.

4. The method of claim 1, wherein the set of model parameters further includes one or more first principle parameters in addition to focus and exposure.

5. The method of claim 4, wherein the one or more first principle parameters includes one or more of illumination source, numerical aperture, and optical aberrations.

6. The method of claim 1, wherein the model of the lithography process further includes a resist model module.

7. The method of claim 1, wherein the model of the lithography process further includes a mask model module.

8. The method of claim 1, wherein the plurality of sampling locations include only sampling locations at nominal exposure and varying values of focus.

9. The method of claim 1, wherein the plurality of sampling locations includes only nominal condition, a positive defocus condition at nominal exposure condition, and a negative defocus condition at nominal exposure condition.

10. The method of claim 1, further comprising:

selecting a set of test patterns for a test mask, wherein the set of test patterns covers a full range of proximity interactions that are characteristic of the lithography process;

printing the set of test patterns on a wafer to form a set of test structures; and

using the set of test structures to produce the actual results.

11. The method of claim 1, wherein the simulated results and the actual results are critical dimension measurements.

12. The method of claim 1, wherein the total difference measure is a root mean square difference.

13. A method for creating a focus-exposure model of a lithography process, comprising:

selecting a set of process conditions within a predetermined process window of a lithography process, the set of process conditions being a subset of all possible process conditions within the process window, each process condition being an exposure value and a defocus value;

selecting a model of the lithography process, the model including an optical model module, the model having a set of model parameters including focus, exposure, and a set of fitting parameters having variable values;

simulating the lithography process at each of the set of process conditions using the model to produce simulated results, wherein values of the focus and exposure parameters are varied to correspond to the set of process conditions and the fitting parameter values are held constant; and

calibrating the model by comparing the simulated results with actual results of the lithography process at all of the set of process conditions to produce a single focus-exposure model capable of simulating the lithography process at all possible process conditions within the predetermined process window.

14. The method of claim 13, wherein the focus-exposure model is used to simulate the lithography process at a process condition within the predetermined process window that is not one of the set of process conditions.

15. The method of claim 13, wherein the set of model parameters further includes one or more first principle parameters in addition to focus and exposure.

16. The method of claim 15, wherein the one or more first principle parameters includes one or more of illumination source, numerical aperture, and optical aberrations.

17. The method of claim 13, wherein the model of the lithography process further includes a resist model module.

18. The method of claim 13, wherein the model of the lithography process further includes a mask model module.

19. The method of claim 13, wherein the set of process conditions includes only process conditions at nominal exposure and varying values of focus.

20. The method of claim 13, wherein the set of process conditions includes only nominal condition, a positive defocus condition at nominal exposure condition, and a negative defocus condition at nominal exposure condition.

21. The method of claim 13, further comprising:

selecting a set of test patterns for a test mask, wherein the set of test patterns covers a full range of proximity interactions that are characteristic of the lithography process;

printing the set of test patterns on a wafer to form a set of test structures; and

using the set of test structures to produce the actual results.

22. The method of claim 13, wherein the simulated results and the actual results are critical dimension measurements.

23. A method for generating a focus-exposure model of a lithography process capable of simulating the lithography process over an entire process window, comprising:

obtaining measurements of a set of test structures printed on a wafer using the lithography process at each of a set of process conditions, the set of process conditions being a subset of all possible process conditions within a process window in an exposure-defocus space;

simulating the lithography process at each of the set of process conditions using a model of the lithography process to produce simulated results, the model including model parameters including focus, exposure, and a set of fitting parameters having variable values;

determining optimum values of the fitting parameters that produce simulated results that are a best fit with the measurements of the set of test structures at all of the set of process conditions; and

defining the focus-exposure model as the model having the optimum values of the fitting parameters.

24. The method of claim 23, wherein the focus-exposure model is used to simulate the lithography process at a process condition within the process window that is not one of the set of process conditions by applying focus and exposure values corresponding to the process condition within the process window to the focus-exposure model in accordance with first principles without changing the optimum values of the fitting parameters.

25. The method of claim 23, wherein the model parameters include one or more first principle parameters in addition to focus and exposure.

26. The method of claim 25, wherein the one or more first principle parameters includes one or more of illumination source, numerical aperture, and optical aberrations.

27. The method of claim 23, wherein the model of the lithography process includes a resist model module.

28. The method of claim 23, wherein the model of the lithography process includes a mask model module.

29. The method of claim 23, wherein the set of process conditions include only process conditions at nominal exposure and varying values of focus.

30. The method of claim 23, wherein the set of process conditions include only nominal condition, a positive defocus condition at nominal exposure condition, and a negative defocus condition at nominal exposure condition.

31. The method of claim 23, further comprising:

selecting a set of test patterns for a test mask, wherein the set of test patterns covers a full range of proximity interactions that are characteristic of the lithography process; and

printing the set of test patterns on the wafer to produce the set of test structures.

32. The method of claim 23, wherein the measurements of the set of test structures and the simulated results are critical dimension measurements.

33. A system for generating a single process window model for predicting the capability of a lithography process, comprising:

a storage area for storing information;

an input device;

an output device;

physical model information stored in the storage area; and

a model calibration module;

the storage area being in communication with the model calibration module such that selected physical model information can be accessed by the model calibration module;

the input device being in communication with the model calibration module such that process window definition information defining a process window can be made available to the model calibration module and such that discrete measurement information obtained from measurements of a wafer under different test conditions in the defined process window can be accessed by the model calibration module, and

the model calibration module is configured to generate a single process window model by using the process window definition information and the discrete measurement information to calibrate the selected physical model information such that the performance of a lithography process over the defined process window can be described with two continuously adjustable optical parameters,

wherein generating the single process window model includes comparing the discrete measurement information with simulated measurements, the simulated measurements produced by simulating the lithography process using the selected physical model information by varying the two continuously adjustable optical parameters while holding all other parameters in the physical model information constant.

34. The system of claim 33, wherein the two continuously adjustable optical parameters are focus and exposure.

35. The system of claim 34, wherein the simulated measurements are produced using values of the two continuously adjustable optical parameters only at nominal exposure and varying values of focus.

36. The system of claim 34, wherein the simulated measurements are produced using values of the two continuously adjustable optical parameters only at nominal condition, a positive defocus condition at nominal exposure condition, and a negative defocus condition at nominal exposure condition.

37. The system of claim 33, wherein the physical model information includes one or more of illumination source, numerical aperture, and optical aberrations.

38. The system of claim 33, wherein the physical model information includes resist model information.

39. The system of claim 33, wherein the physical model information includes mask model information.

40. A method for creating a model of a lithography process, comprising:

selecting a set of process conditions within a predetermined process window of a lithography process, the set of process conditions being a subset of all possible process conditions within the process window, each process condition being a value for at least one parameter;

selecting a model of the lithography process, the model having a set of model parameters including the at least one parameter of the process condition and a set of fitting parameters;

simulating the lithography process at each of the set of process conditions using the model to produce simulated results, wherein the value of the at least one parameter is varied to correspond to the set of process conditions while the fitting parameter values are held constant; and

calibrating the model by comparing the simulated results with actual results of the lithography process at all of the set of process conditions to produce a single model capable of simulating the lithography process at all possible process conditions within the predetermined process window.

41. The method of claim 40, wherein the at least one parameter is an optical parameter.

42. The method of claim 41, wherein the optical parameter is focus.

43. The method of claim 41, wherein the optical parameter is a numerical aperture of a lithography exposure tool.

44. The method of claim 40, wherein the at least one parameter is a resist parameter.

45. The method of claim 40, wherein the at least one parameter includes an optical parameter and a resist parameter.

46. A method for creating a single model of a lithography process for use at nominal condition, comprising:

selecting a set of process conditions within a predetermined process window of a lithography process, the set of process conditions being a subset of all possible process conditions within the predetermined process window, the set of process conditions including nominal condition, each process condition being a value for at least one parameter;

selecting a model of the lithography process having model parameters including the at least one parameter of the process condition and a set of fitting parameters;

simulating the lithography process at each of the set of process conditions using the model to produce simulated results, wherein the value of the at least one parameter is varied to correspond to the set of process conditions while the fitting parameter values are held constant; and

calibrating the model by minimizing a total difference measure between the simulated results and actual results of the lithography process at all of the set of process conditions to produce a single model,

wherein the single model is used to model the lithography process at the nominal condition.

47. The method of claim 46, wherein the at least one parameter is focus.

48. The method of claim 46, wherein the at least one parameter includes one or more of illumination source, numerical aperture, and optical aberrations.

49. The method of claim 46, further comprising:

selecting a set of test patterns for a test mask;

printing the set of test patterns on a wafer to form a set of test structures; and

using the set of test structures to produce the actual results.

50. The method of claim 46, wherein calibrating the model further comprises:

comparing the simulated results with actual results of the lithography process at all of the set of process conditions to produce the total difference measure between the simulated results and the actual results;

modifying values of the fitting parameters and generating additional simulated results at the set of process conditions to identify optimum fitting parameter values such that the total difference measure between the actual results and simulated results produced using the optimum fitting parameter values is minimized or is below a predetermined threshold; and

defining the single model as the model including the optimum fitting parameter values.

51. The method of claim 46, wherein the total difference measure is a root mean square difference.

52. The method of claim 46, wherein the set of process conditions includes only process conditions at nominal exposure and varying values of focus.

53. The method of claim 46, wherein the set of process conditions includes only nominal condition, a positive defocus condition at nominal exposure condition, and a negative defocus condition at nominal exposure condition.

54. A computer-readable medium storing instructions for causing a computer to create a focus-exposure model of a lithography process by performing:

storing a model of a lithography process, the model including an optical model module, the model having a set of model parameters including focus, exposure, and a set of fitting parameters having variable values;

storing a set of initial fitting parameter values for the model;

storing a plurality of sampling locations within a process window in a focus-exposure space, the plurality of sampling locations including nominal condition and being a subset of all possible process conditions within the process window;

generating simulated results of the lithography process at each of the plurality of sampling locations using the model with the set of initial fitting parameter values by simulating the lithography process with varying values of focus and exposure corresponding to the plurality of sampling locations while holding the initial fitting parameter values constant;

comparing the simulated results with actual results of the lithography process at each of the plurality of sampling locations to produce a total difference measure between the simulated results and the actual results at all of the plurality of sampling locations;

modifying the set of fitting parameter values and generating additional simulated results at each of the plurality of sampling locations such that the total difference measure between the actual results produced using the optimum fitting parameter values is minimized or is below a predetermined threshold; and

defining the focus-exposure model as the model including the optimum fitting parameter values, the focus-exposure model being capable of simulating the lithography process at any location within the process window.

55. The computer-readable medium of claim 54, wherein the set of model parameters further includes one or more first principle parameters in addition to focus and exposure.

56. The computer-readable medium of claim 55, wherein the one or more first principle parameters includes one or more of illumination source, numerical aperture, and optical aberrations.

57. The computer-readable medium of claim 54, wherein the model of the lithography process further includes a resist model module.

58. The computer-readable medium of claim 54, wherein the model of the lithography process further includes a mask model module.

59. The computer-readable medium of claim 54, wherein the plurality of sampling locations includes only sampling locations at nominal exposure and varying values of focus.

60. The computer-readable medium of claim 54, wherein the plurality of sampling locations includes only nominal condition, a positive defocus condition at nominal exposure condition, and a negative defocus condition at nominal exposure condition.

61. The computer-readable medium of claim 54, wherein the total difference measure is a root mean square difference.