Method and system for lithography process-window-maximixing optical proximity correction

• US 9,360,766 B2
• Filed: 12/18/2009
• Issued: 06/07/2016
• Est. Priority Date: 12/18/2008
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Ye, Jun, Cao, Yu, Feng, Hanying
• Primary Examiner(s): THOMPSON, ANNETTE M
• Application Number:
  US12/642,436
• Publication Number:
  US 20100162197A1
• Time in Patent Office: 2,363 Days
• Field of Search: None
• US Class Current: 1/1
• 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, using a computer, 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 a target pattern;

determining a target value of the resist image value for each evaluation point based on the analytical function and a nominal condition comprising nominal values of one or more of the process condition parameters, wherein determining the target values for each evaluation point is performed such that the process window about the nominal values of the process condition parameters is maximized; and

performing optical proximity correction on the target pattern using the target value as an optimizing target for each evaluation point,

wherein determining the target value of the resist image value at nominal condition is by a bisection method.

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

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

4. The method according to claim 1, wherein computing the analytical function comprises computing a polynomial function.

5. The method according to claim 1, further comprising recomputing the target value for each evaluation point at each of a plurality of optical proximity correction iterations.

6. A method for maximizing a 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, using a computer, an optimal target value within the acceptable variation of resist image values for each evaluation point for a nominal process window condition, so that a process parameter variation range is maximal subject to a condition that a 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.

7. The method according to claim 6, further comprising dynamically setting the optimal target value for each evaluation point in each iteration to maximize the process window.

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

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

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

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

determining, using a computer, 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 an optimal target gray level value at the nominal process condition;

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

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

10. A non-transitory computer-readable storage medium having computer-executable instructions stored therein for causing a computer to perform a method 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 a target pattern;

determining a target value of the resist image value for each evaluation point based on the analytical function and a nominal condition comprising nominal values of one or more of the process condition parameters, wherein determining the target values for each evaluation point is performed such that the process window about the nominal values of the process condition parameters is maximized; and

performing optical proximity correction on the target pattern using the target value as an optimizing target for each evaluation point,

wherein determining the target value of the resist image value at nominal condition is by a bisection method.

11. A non-transitory computer-readable storage medium having computer-executable instructions stored therein for causing a computer to perform a 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 a process parameter variation range is maximal subject to a condition that a 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.

12. A non-transitory computer-readable storage medium having computer-executable instructions stored therein for causing a computer to perform a 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 a value associated with the optimal target gray level as an optimization target for the resist image value for each evaluation point when performing optical proximity correction process on the target pattern; and

determining a best edge movement amount of the optical proximity correction process so that a resulting resist image value equals to the value associated with the optimal target gray level.

13. A non-transitory computer-readable storage medium having computer-executable instructions stored therein for causing a computer to perform a 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 an optimal target gray level value at the nominal process condition;

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

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