Method for improved lithographic patterning in a semiconductor fabrication process

• US 5,340,700 A
• Filed: 11/03/1993
• Issued: 08/23/1994
• Est. Priority Date: 04/06/1992
• Status: Expired due to Term

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: Microunity Systems Engineering Incorporated
• Inventors: Matthews, James A., Chen, Jang F.
• Primary Examiner(s): Kight, III, John
• Assistant Examiner(s): BOYKIN, TERRESSA M
• Application Number:
  US08/149,122
• Time in Patent Office: 293 Days
• Field of Search: 430/311, 430/312, 430/313, 430/319
• US Class Current: 430/312
• CPC Class Codes: G03F 7/2022 Multi-step exposure, e.g. hybrid; backside exposure; blanket exposure, e.g. for image reversal; edge exposure, e.g. for edge bead removal; corrective exposure
• CPC Class Codes: G03F 7/70466 Multiple exposures, e.g. combination of fine and coarse exposures, double patterning or multiple exposures for printing a single feature stitching G03F7/70475

Abstract

A method of printing a sub-resolution device feature having first and second edges spaced in close proximity to one another on a semiconductor substrate includes the steps of first depositing a radiation-sensitive material on the substrate, then providing a first mask image segment which corresponds to the first edge. The first mask image segment is then exposed with radiation using an imaging tool to produce a first pattern edge gradient. The first pattern edge gradient defines the first edge of the feature in the material.

A second mask image segment is then provided corresponding to the second feature edge. This second mask image segment is exposed to radiation to produce a second pattern edge gradient which defines the second edge of the feature. Once the radiation-sensitive material has been developed, the two-dimensional feature is reproduced on the substrate.

Claims

1. In a method for lithographically transferring a pattern from a mask into a radiation-sensitive material deposited over a semiconductor substrate utilizing an imaging tool, said pattern including a feature having first and second edges, each of said first and second edges having associated edge gradients, said first and second edges being spaced in close proximity to one another such that said associated edge gradients interact causing said feature to be distorted in said radiation-sensitive material, an improved method comprising the steps of:

a) providing a first rectilinear mask image segment, said first rectilinear mask image segment having a first set of mask edges, all opposing mask edges in said first set of mask edges being spaced a distance greater than the Rayleigh limit of said imaging tool and greater than the distance between said first and second edges, a single edge from said first set of mask edges corresponding to said first edge;

b) exposing said first rectilinear mask image segment with radiation using said imaging tool such that said single edge from said first set of mask edges produces a first pattern edge gradient defining said first edge of said two-dimensional feature in said material;

c) providing a second rectilinear mask image segment, said second rectilinear mask image segment having a second set of mask edges, all opposing mask edges in said second set of mask edges being spaced a distance greater than said Rayleigh limit of said imaging tool and greater than said distance between said first and second edges, a single edge from said second set of mask edges corresponding to said second edge;

d) exposing said second rectilinear mask image segment with radiation using said imaging tool such that said single edge from said second set of mask edges produces a second pattern edge gradient defining said second edge of said two-dimensional feature in said material, wherein said first and second edges are separated by distance which is less than or equal to the Rayleigh limit of said imaging tool and wherein said second pattern edge gradient and said first pattern edge gradient do not interact;

e) developing said radiation-sensitive material, thereby reproducing said feature on said substrate.

2. The method as defined in claim 1 wherein said first and second edges are substantially parallel to each other.

3. The method as defined in claim 1 wherein said first and second edges are orthogonal.

4. The method as defined in claim 3 wherein said feature comprises a device contact of an integrated circuit, and said first and second edges define a corner of said contact.

5. The method as defined in claim 1 wherein said first and second mask image segments comprise a single mask image having an area which is larger than said two-dimensional feature.

6. The method as defined in claim 1 wherein said first mask image segment is provided on a first mask and said second mask image segment is provided on a second mask.

7. The method as defined in claim 5 wherein said mask image is rectangular in shape, and said first mask image segment is substantially parallel to said second image segment.

8. The method as defined in claim 7 wherein step (d) comprises the step of offsetting said mask image relative to said substrate.

9. The method as defined in claim 2 wherein said material comprises a negative-acting photoresist layer.

10. The method as defined in either claim 5 or 6 wherein said first and second mask image segments each have associated therewith an additional sub-resolution edge segment, each of said additional segments being spaced a predetermined distance away from, and substantially parallel to, said associated mask image segment, said additional segments functioning to increase the slope of first and second patterned edge gradients to enhance said printing of said two-dimensional feature.

11. The method as defined in claim 10 wherein said predetermined distance is approximately 1.1 times the Rayleigh limit of said imaging tool.

12. In a process for fabricating semiconductor devices, including a method of lithographically printing a rectangular feature on a mask into a photoresist layer deposited over a semiconductor substrate utilizing an imaging tool, said rectangular feature having at least two opposing feature edges each having associated edge gradients, said at least two opposing feature edges being spaced such that said associated edge gradients interact causing said feature to be distorted in said photoresist layer, an improved method comprising the steps of:

decomposing said rectangular feature into a rectangular mask image having a pair of opposing mask edges of a length which is greater than or equal to the length of said opposing feature edges, said opposing mask edges being spaced apart a predetermined distance which is greater than the spacing between said opposing feature edges and greater than the Rayleigh limit of said imaging tool;

exposing a first one of said pair of opposing mask edges with radiation using said imaging tool to produce a first pattern edge gradient which defines a first one of said feature edges in said photoresist layer;

offsetting said rectangular mask image relative to said substrate;

exposing the second one of said pair of opposing mask edges with radiation using said imaging tool to produce a second pattern edge gradient defining the second one of said feature edges in said photoresist layer, wherein said spacing between said opposing feature edges is less than or equal to the Rayleigh limit of said imaging tool and wherein said second pattern edge gradient and said first pattern edge gradient do not interact.

13. The method as defined in claim 12 wherein said predetermined distance is greater than said Rayleigh limit.

14. The method as defined in claim 13 wherein said offsetting step offsets said mask image a distance approximately equal to said predetermined distance minus said spacing.

15. The method as defined in claim 13 wherein said rectangular feature is a square.

16. The method as defined in claim 13 wherein said decomposing step includes the step of calculating the length of said mask edges as having a minimum dimension, D, which is given by the equation

17. The method as defined in claim 12 wherein said pair of mask edges each have associated therewith an additional sub-resolution edge segment, each of said additional segments being spaced a certain distance away from, and substantially parallel to, said associated mask edge, said additional segments functioning to increase the slope of said first and second pattern edge gradients, thereby enhancing said printing of said rectangular feature.

18. The method ad defined in claim 17 wherein said certain distance is approximately 1.1 times said Rayleigh limit.

19. The method as defined in claim 14 wherein said photoresist comprises a negative-acting resist layer.

20. A process for fabricating an integrated circuit (IC) on a silicon substrate using a lithographic tool, an imaging decomposition algorithm for printing an array of square contacts having an edge dimension which is less than or equal to the Rayleigh limit of said lithographic tool comprising the steps of:

(a) calculating a minimum critical dimension (CD) for said printing process based on said edge dimension;

(b) forming a plurality of decomposed image squares, each of which corresponds to one of said contacts within said array, said image squares having a dimension which is greater than or equal to said minimum CD;

(c) calculating the minimum horizontal, vertical and diagonal pitches required between adjacent contacts within said array based upon a process of decomposing each of said contacts by sequentially exposing each edge of said image squares with radiation to produce the corresponding edge of said contacts on said substrate, said squares being offset relative to said substrate prior to each subsequent exposure in said sequence to align each of said image square edges to said corresponding edges of said contacts;

(d) identifying as belonging to a first set of contacts, which of said adjacent contacts in said array violates said pitches, said contacts which are not identified as belonging to said first set being included in a second set;

(e) forming a first decomposed image mask comprising the image squares corresponding to said second set of said contacts; and

(f) forming a second decomposed image mask comprising the image squares corresponding to said first set of said of contacts.

21. The algorithm as defined in claim 20 wherein said critical dimension is defined by the equation

22. The algorithm as defined in claim 21 wherein said minimum horizontal and vertical pitches are equal to said minimum critical dimension, and said minimum diagonal pitch is defined as M, where M is by the equation ##EQU2##