Monitoring of minimum features on a substrate

• US 5,629,772 A
• Filed: 12/20/1994
• Issued: 05/13/1997
• Est. Priority Date: 12/20/1994
• Status: Expired due to Term

• Current Assignee: GlobalFoundries, Inc.
• Original Assignee: International Business Machines Corporation
• Inventors: Ausschnitt, Christopher P.
• Primary Examiner(s): Pham, Hoa Q.
• Application Number:
  US08/359,797
• Time in Patent Office: 875 Days
• Field of Search: 356/372, 356/375, 356/123, 356/124, 356/125, 356/126, 356/127, 356/383, 356/384, 430/5
• US Class Current: 356/625
• CPC Class Codes: G01B 11/02 for measuring length, width or thickness G01B11/08 takes precedence
• CPC Class Codes: G03F 7/70633 Overlay, i.e. relative alignment between patterns printed by separate exposures in different layers, or in the same layer in multiple exposures or stitching

Abstract

A method of measuring bias of a minimum feature in a lithographic process uses creating an array of elements having a width and space corresponding to the minimum feature, and a length. The length change of the array element resulting from image shortening effect from a lithographic process is measured and the bias of the element in the width dimension is calculated. A test site having groups of array elements is described which facilitate automatic bias measurement of array lengths and separations and especially allows the use of non SEM metrology tools which is otherwise incapable of measuring the minimum feature width being monitored. Measurements by this method and test site used to control lithographic processing of substrates in manufacturing, routine monitoring of product substrates and lithographic tool and process for minimum bias, are disclosed.

Claims

1. A method of measuring lithographic process bias of a minimum feature formed in a lithographic process, using a measurement tool, comprising the steps of:

creating an array of elements on a substrate, each element in the array having a nominal length and a nominal width, and adjacent element having a nominal space therebetween, wherein the nominal width of each element and the nominal space between each adjacent element correspond to said minimum feature, the nominal length being larger than the minimum feature;

measuring length of said created elements in the array resulting from said lithographic process;

calculating change in length of said elements from nominal length; and

,

means for calculating lithographic process bias of the minimum feature (width, space) from said change in length of said elements in the array.

2. A method of claim 1 where in said measurement tool uses an optical measurement system.

3. A method of measuring lithographic process bias of a minimum feature formed in a lithographic process, using a measurement tool, comprising the steps of:

creating at least a pair of array of elements on a substrate, each element having a nominal length and a nominal width, and each adjacent element having a nominal space therebetween wherein the nominal width and the nominal space correspond to said minimum feature, said arrays of elements having an average nominal separation and an average nominal length;

measuring average length of said created elements in said arrays and average separation between said pair of created arrays resulting from said lithographic process;

calculating change in average length of elements and average separation from said average nominal length and average nominal separation respectively; and

,

means for calculating lithographic process bias of said minimum feature (width, space) from said change in average length of said elements and average separation between said pair of arrays.

4. A method of claim 3 wherein said measurement tool uses an optical measurement system.

5. A method of selecting a lithographic process from a plurality of lithographic processes for minimizing bias of a minimum feature created by use of said lithographic process, comprising the steps of:

creating an array of elements on a substrate, each element having a nominal length and a nominal width, and each adjacent element having a nominal space therebetween, wherein the nominal width of each element and the nominal space between adjacent elements correspond to said minimum feature, using a plurality of lithographic processes;

measuring length of said created elements in the array corresponding to said plurality of lithographic processes;

calculating change in length of said created elements from nominal length;

means for calculating bias of the minimum feature (width, space) from said change in length of said elements corresponding to said plurality of lithographic processes; and

,

selecting a lithographic process from said plurality of lithographic processes, corresponding to smallest calculated bias of said minimum feature.

6. A method of selecting a lithographic process from a plurality of lithography processes for minimizing bias of a minimum feature created by the use of said lithographic process, comprising the steps of:

creating at least a pair of array of elements on a substrate, each element having a nominal length and a nominal width, and each adjacent element having a nominal space therebetween wherein the nominal width and the nominal space correspond to said minimum feature, said arrays of elements having an average nominal length and average nominal separation, using a of different lithographic process conditions;

measuring average length of said created elements in the array and average separation between said pair of created arrays, corresponding to said plurality of lithographic processes;

calculating change in average length of elements and average separation between said pair of arrays from said average nominal length and average nominal separation respectively;

means for calculating bias of the minimum feature from said change in average length and average separation corresponding to said plurality of lithographic processes; and

,

selecting the lithographic process from said plurality of lithographic processes, corresponding to smallest calculated bias of said minimum feature.

7. A method of selecting hardware and software changes to an exposure tool, to achieve a preselected bias corresponding to a minimum feature size, comprising the steps of:

modifying the exposure tool using a plurality of hardware and software changes;

creating an array of elements on a substrate, each element having a nominal length and a nominal width, and adjacent elements having a nominal space therebetween, wherein the nominal width of each element and the space between adjacent elements corresponding to said minimum feature size, using said plurality of hardware and software changes;

measuring length of said elements in the array resulting from said plurality of hardware and software changes;

calculating change in length of said created elements from nominal length;

means for calculating bias of the minimum feature (width, space) corresponding to said plurality of hardware and software changes; and

,

selecting the hardware and software changes corresponding to said calculated bias of said minimum feature that is less than said preselected bias.

8. A method of measuring an etch process bias in forming a minimum feature, said etch process using a resist image from a lithographic process, said etch process bias determined by the difference between a combined bias of said minimum feature measured subsequent to said etch process, and a lithographic process bias measured prior to said etch process, comprising the steps of:

creating an array of elements on a substrate each element having a nominal length and a nominal width and adjacent elements having a nominal space therebetween, wherein the nominal width of each element and the nominal space between adjacent elements correspond to said minimum feature, using said lithographic process;

measuring length of said created elements in the array resulting from said lithographic process;

calculating change in length of said created elements from the nominal length;

means for calculating said lithographic process bias of the minimum feature (width, space) from said change in length of said elements in the array;

subjecting said substrate to an etch process;

remeasuring length of said etched elements in the array;

calculating the change in length of said etched elements from the nominal length;

means for calculating said combined process bias from said change in length of said elements in the array; and

,

determining said etch process bias from said combined process bias and said lithographic process bias.

9. A method of measuring an etch process bias in forming a minimum feature, said etch process using a resist image from a lithographic process, said etch process bias determined by the difference between a combined bias of said minimum feature measured subsequent to said etch process, and a lithographic process bias measured prior to said etch process, comprising the steps of:

creating at least a pair of array of elements on a substrate, using the lithographic process each element having a nominal length and nominal width, and adjacent elements having a nominal space therebetween wherein the nominal width and the nominal space correspond to said minimum feature, said arrays of elements having an average nominal length and average nominal separation;

measuring average length of said created elements in the array and average separation between said pair of created arrays, corresponding to said lithographic process;

calculating change in the average length of said elements and average separation between said pair of arrays from said average nominal length and average nominal separation respectively;

means for calculating said lithographic process bias of the minimum feature (width, space) from said change in average length and said change in average separation;

subjecting said substrate to an etch process;

remeasuring the average length of said etched elements in the array and average separation between said pair of created arrays;

calculating change in the average length of said elements in the array and average separation between said pair of arrays;

means for calculating the combined process bias from said change in average length of said elements in the array and change in average separation between said pair of arrays; and

,

determining said etch process bias from said combined process bias and said lithographic process bias.

10. A method of processing a substrate in a production environment, by use of a preselected bias of a minimum feature, comprising the steps of:

creating a test pattern on the substrate, said test pattern comprising at least two arrays, each array having a plurality of array elements, each element having a nominal width and a nominal space corresponding to the minimum feature, and each array having an average nominal length, and adjacent arrays having an average nominal separation therebetween;

measuring average length of said created array elements;

measuring average separation between said created adjacent arrays;

calculating change in average length and average separation from said average nominal length and average nominal separation;

means for calculating bias of said minimum feature (width, space) using said change in average length of said array elements and said change in separation between adjacent arrays;

comparing said calculated bias to said preselected bias; and

,

accepting said substrate for further processing if said calculated bias is less than said preselected bias.

11. A method of simultaneously determining lithographic process bias for a plurality of preselected feature sizes, comprising the steps of:

creating a test pattern with a plurality of arrays on a substrate, each of said arrays having a plurality of array elements having an unique nominal width and nominal spacing, corresponding to one of said preselected feature sizes, and a nominal length;

measuring length of said created elements in each of said arrays;

calculating change in length of array elements from the nominal length for each of said arrays; and

,

means for calculating bias for said preselected feature size (width,space) from the calculated change in length of elements from corresponding arrays.