METHOD AND APPARATUS FOR ENHANCING SIGNAL STRENGTH FOR IMPROVED GENERATION AND PLACEMENT OF MODEL-BASED SUB-RESOLUTION ASSIST FEATURES (MB-SRAF)

• US 20130311960A1
• Filed: 05/13/2013
• Published: 11/21/2013
• Est. Priority Date: 01/14/2010
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Tsai, Min-Chun, Chen, Been-Der, Lu, Yen-Wen
• Granted Patent: US 8,826,198 B2
• Time in Patent Office: Days
• US Class Current: 716/55
• CPC Class Codes: G03F 1/36 Masks having proximity correction features; Preparation thereof, e.g. optical proximity correction [OPC] design processes
• CPC Class Codes: G06F 30/00 Computer-aided design [CAD]

Abstract

Model-Based Sub-Resolution Assist Feature (SRAF) generation process and apparatus are disclosed, in which an SRAF guidance map (SGM) is iteratively optimized to finally output an optimized set of SRAFs as a result of enhanced signal strength obtained by iterations involving SRAF polygons and SGM image. SRAFs generated in a prior round of iteration are incorporated in a mask layout to generate a subsequent set of SRAFs. The iterative process is terminated when a set of SRAF accommodates a desired process window or when a predefined process window criterion is satisfied. Various cost functions, representing various lithographic responses, may be predefined for the optimization process.

Claims

1. A method for enhancing signal strength for placing sub-resolution assist features (“

SRAF”

) with respect to one or more target patterns in a mask layout, comprising;

generating an initial SRAF guidance map for the mask layout;

placing a first set of one or more SRAF in the mask layout according to the initial SRAF guidance map;

altering one or more of number, location and dimension of at least a portion of the first set of one or more SRAFs;

measuring improvement in signal strength in the initial SRAF guidance map; and

generating an updated SRAF guidance map with enhanced signal strength.

2. The method of claim 1, wherein the method further comprises:

placing a subsequent set of one or more SRAF in the mask layout according to the updated SRAF guidance map.

3. The method of claim 2, wherein the method further comprises:

repeating the steps of generating an updated SRAF guidance map and placing the subsequent set of one or more SRAF in an iterative process, until a predefined lithographic process window criterion is satisfied.

4. The method of claim 3, wherein the step of iteratively placing a subsequent set of one or more SRAF comprises:

replacing a prior set of one or more SRAF with a completely new subsequent set of one or more SRAF.

5. The method of claim 3, wherein the step of iteratively placing a subsequent set of one or more SRAF comprises:

retaining at least portions of a prior set of one or more SRAF; and

adjusting the prior set of one or more SRAF to obtain the subsequent set of one or more SRAF.

6. The method of claim 1, wherein the method further comprises:

applying optical proximity corrections (OPC) to original target patterns in the mask layout to generate a corrected mask layout.

7. The method of claim 3, wherein the iterative process comprises:

using a prior set of one or more SRAF and a prior corrected mask layout to generate an updated SRAF guidance map;

using the updated SRAF guidance map to generate a subsequent set of one or more SRAF;

applying OPC to the prior corrected mask layout to generate a subsequent corrected mask layout that includes the subsequent set of one or more SRAF; and

using the subsequent corrected mask layout to determine whether the predefined lithographic process window criterion is satisfied.

8. The method of claim 3, wherein the iterative process comprises:

using a prior set of one or more SRAF and original target patterns to generate an updated SRAF guidance map;

using the updated SRAF guidance map to generate a subsequent set of one or more SRAF;

generating a subsequent mask layout that includes the subsequent set of one or more SRAF; and

using the subsequent mask layout to determine whether the predefined lithographic process window criterion is satisfied.

9. The method of claim 1, further comprising generating SRAF placement rules using the SRAF guidance map.

10. The method of claim 1, wherein the mask layout includes a predefined mask bias.

11. The method of claim 3, wherein the process window comprises one or more of a focus window, and an exposure dose window.

12. The method of claim 3, wherein the iterative process is terminated when a predefined cost function representing a lithographic response reaches an optimum value that is associated with the predefined process window criterion.

13. The method of claim 12, wherein the predefined cost function represents an image log slope (ILS), an edge placement error, a mask error enhancement factor, or a combination thereof.