METHOD AND SYSTEM FOR LITHOGRAPHY PROCESS-WINDOW-MAXIMIXING OPTICAL PROXIMITY CORRECTION

• US 20100162197A1
• Filed: 12/18/2009
• Published: 06/24/2010
• Est. Priority Date: 12/18/2008
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: Brion Technologies Incorporated (ASML Holding NV)
• Inventors: Feng, Hanying, Cao, Yu, YE, Jun
• Granted Patent: US 9,360,766 B2
• Time in Patent Office: Days
• US Class Current: 716/53
• CPC Class Codes: G03F 1/36 Masks having proximity correction features; Preparation thereof, e.g. optical proximity correction [OPC] design processes
• CPC Class Codes: G03F 7/70441 Optical proximity correction [OPC]
• 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: G06F 2119/18 Manufacturability analysis or optimisation for manufacturability
• CPC Class Codes: G06F 30/398 Design verification or optimisation, e.g. using design rule check [DRC], layout versus schematics [LVS] or finite element methods [FEM] optical proximity correction [OPC] design processes G03F1/36

Abstract

The present invention relates to an efficient OPC method of increasing imaging performance of a lithographic process utilized to image a target design having a plurality of features. The method includes the steps of determining a function for generating a simulated image, where the function accounts for process variations associated with the lithographic process; and optimizing target gray level for each evaluation point in each OPC iteration based on this function. In one given embodiment, the function is approximated as a polynomial function of focus and exposure, R(ε, f)=P₀+f²·P_b with a threshold of T+Vε for contours, where P₀ represents image intensity at nominal focus, f represents the defocus value relative to the nominal focus, ε represents the exposure change, V represents the scaling of exposure change, and parameter “P_b” represents second order derivative images. In another given embodiment, the analytical optimal gray level is given for best focus with the assumption that the probability distribution of focus and exposure variation is Gaussian.

Claims

1. A method for maximizing a process window of a photolithographic process comprising:

computing an analytical function of process condition parameters that approximates a resist image value across a process window for each of a plurality of evaluation points in the target pattern;

determining a target value of the resist image value at nominal condition for each evaluation point based on the analytical function, so that the process window is maximized; and

using the target value as an optimizing target for each evaluation point in an optical proximity correction iteration.

2. A method according to claim 1, wherein the process window comprises a range of a specific process parameter within which the resist critical dimension and therefore resist image value is contained in a pre-defined range.

3. A method according to claim 1, wherein the target resist image value at nominal condition is determined using numerical methods including a bisection method.

4. A method according to claim 1, wherein an analytical target resist image value is given for best focus.

5. A method according to claim 1, wherein the analytical function comprises a polynomial function.

6. A method according to claim 1, wherein the target value for each evaluation point is recomputed at each of a plurality of optical proximity correction iterations.

12. A computer program product comprising one or more computer-readable storage media having computer-executable instructions for causing a computer to perform the method of claim 1.

7. A method for maximizing lithographic process window for a target pattern, the method comprising:

determining an acceptable variation of resist image values around a fixed threshold for a plurality of evaluation points in the target pattern;

computing an optimal target value within the acceptable variation of resist image values for each evaluation point for a nominal process window condition, so that the process parameter variation range is maximal subject to the condition that the resist image value is kept within its acceptable variation;

performing an edge movement process in an iterative manner in an optical proximity correction process until an approximated resist image value at each evaluation point converges to the optimal target value.

8. A method according to claim 7, wherein the target level is dynamically set for each evaluation point in each iteration to maximize the process window.

13. A computer program product comprising one or more computer-readable storage media having computer-executable instructions for causing a computer to perform the method of claim 7.

9. A method for maximizing a process window associated with a lithography process for a target pattern, the method comprising:

determining an optimal target gray level of a resist image value for each of a plurality of evaluation points in the target pattern based on an analytical function so as to maximize the process window;

using the target gray level value as the optimization target for the resist image value for each evaluation point in an optical proximity correction iteration; and

determining the best edge movement amount of the optical proximity correction iteration so that the resulting resist image value equals to the target gray level.

14. A computer program product comprising one or more computer-readable storage media having computer-executable instructions for causing a computer to perform the method of claim 9.

10. A method for maximizing a process window associated with a lithographic process for a target pattern, the method comprising:

determining an optimal target gray level of a resist image value at a nominal process condition for each of a plurality of evaluation points in the target pattern based on an analytical function so as to maximize the process window for a given nominal condition;

performing an edge movement process in an iterative manner in an optical proximity correction process until an approximated resist image value at each evaluation point converges to the optimal target gray level value at the nominal process condition;

determining the optimal nominal condition for the resulting resist image from the optical proximity correction so as to maximize the process window; and

alternatively re-performing the determination of the optimal target gray level, the optical proximity correction, and the determination of the optimal nominal condition until convergence on an optimal target pattern.

15. A computer program product comprising one or more computer-readable storage media having computer-executable instructions for causing a computer to perform the method of claim 10.

11. A method for maximizing a range of acceptable values of at least one process condition parameter of a photolithographic process comprising:

using an analytical function of the at least one process condition parameter for approximating the value of a resist image characteristic across a plurality of values of the at least one process condition parameters for each of a plurality of evaluation points in the target pattern;

determining a target value of the resist image characteristic for each evaluation point based on the approximations corresponding to a range of maximum width; and

using the target value as an optimizing target for each evaluation point in an optical proximity correction iteration.

16. A computer program product comprising one or more computer-readable storage media having computer-executable instructions for causing a computer to perform the method of claim 11.