Method and apparatus for the alignment of a substrate

• US 5,493,403 A
• Filed: 02/15/1995
• Issued: 02/20/1996
• Est. Priority Date: 07/05/1990
• Status: Expired due to Term

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Nishi, Kenji
• Primary Examiner(s): Rosenberger, Richard A.
• Assistant Examiner(s): HANTIS, KAREN
• Application Number:
  US08/390,285
• Time in Patent Office: 370 Days
• Field of Search: 356/399-401, 355/43, 355/53, 250/560-561, 250/548, 250/559.3
• US Class Current: 356/401
• CPC Class Codes: G03F 9/70 for microlithography measuring printed patterns for monitoring overlay G03F7/70633 or focus G03F7/70641; projection system adjustment G03F7/70258; position control G03F7/70775
• CPC Class Codes: G03F 9/7076 Mark details, e.g. phase grating mark, temporary mark
• CPC Class Codes: G03F 9/7092 Signal processing

Abstract

Method comprises a process for obtaining a photoelectric signal with a waveform have a pair of extremal values at respective positions corresponding to a pair of edge portions of an alignment mark by photoelectrically detecting the reflected light from the alignment mark on a substrate; a first determination process for determining the position of the alignment mark on the basis of a pair of slope portions existing inside the pair of extremal values of the photoelectric signal waveform; a second determination process for determining the position of the alignment mark on the basis of a pair of slope portions existing outside the pair of extremal values of the photoelectric signal waveform; a third determination process for determining the position of the alignment mark on the basis of both a pair of slope portions existing inside said pair of extremal values of the photoelectric signal waveform and a pair of slope portions existing outside; and a process for selecting any one of the first determination process, second determination process, or third determination process in accordance with the objective alignment accuracy of the substrate.

Claims

1. A method of aligning a substrate wherein an alignment mark formed on the substrate is irradiated with light and the position of the substrate is determined by detecting the position of the alignment mark with respect to a predetermined direction on the basis of light information from the alignment mark, said method comprising:

a process for obtaining a photoelectric signal having a waveform with a pair of extremal values corresponding to a pair of mark edge portions which define the width in said predetermined direction of said alignment mark, said photoelectric signal being obtained by detecting said light information from said alignment mark photoelectrically and said photoelectric signal changing its intensity in time-series with respect to said predetermined direction;

a first determination process for determining the position of said alignment mark on the basis of a pair of slope portions existing inside said pair of extremal values of said photoelectric signal waveform;

a second determination process for determining the position of said alignment mark on the basis of a pair of slope portions existing outside said pair of extremal values of said photoelectric signal waveform;

a third determination process for determining the position of said alignment mark on the basis of both a pair of slope portions existing inside said pair of extremal values of said photoelectric signal waveform and a pair of slope portions existing outside;

a process for selecting any one of said first determination process, second determination process, or third determination process in accordance with the objective alignment accuracy of said substrate; and

,

a process for moving said substrate relative to a predetermined reference position in accordance with the alignment mark position determined by the selected determination process.

2. A method of positioning a substrate on the basis of light information from an alignment mark on said substrate, comprising the steps of:

a) irradiating a portion of said substrate including said alignment mark with a light beam;

b) detecting photoelectrically light information generated by said alignment mark to form a photoelectric signal having a waveform with a pair of extremal values corresponding to a pair of mark edge portions which define the width in a predetermined scanning direction of said alignment mark;

c) selecting any one of signal information on the basis of a pair of slope portions existing inside said pair of extremal values of the waveform of said photoelectric signal, signal information on the basis of a pair of slope portions existing outside said pair of extremal values, and signal information on the basis of a plurality of slope portions including both the slope portions existing inside said pair of extremal values and the slope portions existing outside;

d) determining the position of said alignment mark on the basis of the selected signal information; and

,

e) moving the substrate relative to a predetermined reference position in accordance with the determined position of said alignment mark.

3. An apparatus for aligning a substrate, comprising:

an alignment mark provided on said substrate;

means for irradiating a portion of said substrate including said alignment mark with a light beam;

means for photoelectrically detecting light information generated by said alignment mark, said photoelectric detection means forming a photoelectric signal having a waveform with a pair of extremal values corresponding to a pair of mark edge portions which define the width in a predetermined scanning direction of said alignment mark;

means for selecting any one of signal information on the basis of a pair of slope portions existing inside said pair of extremal values of the waveform of said photoelectric signal, signal information on the basis of a pair of slope portions existing outside said pair of extremal values, and signal information on the basis of a plurality of slope portions including both the slope portions existing inside said pair of extremal values and the slope portions existing outside;

means for determining the position of said alignment mark on the basis of the selected signal information; and

,

means for moving the substrate relative to a predetermined reference position in accordance with the determined position of said alignment mark.

4. An apparatus for aligning a substrate provided with an alignment mark formed at a predetermined position thereon, the mark composed of a pattern which includes a plurality of mark elements aligned with a predetermined spacing in a predetermined detecting direction, the mark elements have predetermined width with respect to the detecting direction, the apparatus comprising:

(a) an illumination system for radiating a light beam onto said pattern;

(b) a photoelectric detecting device whose detecting area is of a constant length in said detecting direction, the device outputting, when said pattern falls within a part of the detecting area, a photoelectric signal with a waveform representing an optical profile of said pattern with respect to said detecting direction;

(c) slope extraction means for extracting up-slope portions and down-slope portions, which appear at positions corresponding to the edges of said mark elements defining said width, within the waveform of said photoelectric signal for each of said edges of the mark elements;

(d) means for obtaining first waveform positions which interiorly divide a shoulder level and an extreme value level of each slope portion with a predetermined ratio for each of said slope portions extracted by said slope extraction means;

(e) selection means for selecting at least one of a set of said first waveform positions obtained for two slope portions which is situated internally of a pair of said edges defining said width of said mark elements and a set of said first waveform positions obtained for two slope portions which is situated externally of said edges; and

(f) calculation means for calculating a center position of said pattern within said detecting area by averaging a plurality of said first waveform positions included in said at least one set of the first waveform positions selected by said selection means; and

,

(g) moving means for positioning the substrate in accordance with the calculated position of said pattern by said calculation means.

5. An apparatus according to claim 4 wherein said slope extraction means includes:

means for converting said waveform of said photoelectric signal into digital data through digital sampling and storing the data in a first memory;

a second memory for storing differential waveform data, which is obtained by differentiating said digital waveform data, in correspondence with said digital waveform data; and

means for extracting peak positions and bottom positions within said differential waveform data and selecting, based on levels of the peaks and bottoms, peak positions and bottom positions whose number correspond to the number of mark elements which constitute said pattern;

wherein said peak and bottom positions within the differential waveform data selected by the last-mentioned means correspond respectively to positions of said up-slope and down-slope portions in said digital waveform data in said first memory so as to extract each of said slope portions.

6. An apparatus according to claim 5 wherein said slope extraction means includes:

means for detecting a position in said digital waveform data of the photoelectric signal which corresponds to either one of the peak position or bottom position in said differential waveform data at a specified position within one slope portion;

means for adding the level of said slope portion at said specified position to a level of differential waveform data at said specified position and comparing the sum with a predetermined value;

wherein, when the sum is smaller than said predetermined value, said one slope portion is omitted.

7. An apparatus according to claim 4 wherein said calculation means includes:

a weighted averaging means which gives predetermined weights to each of two first waveform positions obtained for two slope portions situated internally of a pair of said edges defining said width of said mark elements and to each of two first waveform positions obtained for two slope portions situated externally of said edges and calculates a weighted average so as to obtain a center position of said pattern; and

an input means which changes said predetermined weight in accordance with a degree of asymmetry of cross sectional structure of the pair of edges of said mark elements.

8. An apparatus according to claim 4 wherein said photoelectric detecting device includes:

an objective optical system for magnifying an image of said pattern on the substrate so as to form an image on a predetermined image plane; and

an image pick up element disposed on said predetermined image plane and having an image pick-up surface corresponding to said detecting area;

wherein a numerical aperture, with respect to said objective optical system, of image forming light flux incident upon said image pick-up element through said objective optical system is about 0.2-0.3 and magnification from the substrate through the image pick-up element is about 30-50.

9. An apparatus for aligning a substrate provided with an alignment mark pattern formed at a predetermined position thereon, the mark pattern composed of one or a plurality of mark elements having a predetermined width with respect to a predetermined detecting direction, the apparatus having an objective optical system for radiating illumination light onto a local area on said substrate and receiving light reflected from the local area, the size of the local area being such that the local area can contain said mark pattern, and a photoelectric detecting device which outputs, when said mark pattern falls within a part of said local area, a photoelectric signal having a waveform representing an optical profile of said mark pattern, the apparatus comprising:

(a) means including a memory which performs digital sampling of level of said photoelectric signal so as to store digital waveform data corresponding to an optical profile of said mark pattern;

(b) a first means which detects a plurality of up-slope and down-slope portions, within said digital waveform data, whose contrast is above a predetermined value;

(c) a second means which detects, among the slope portions detected by said first means, a number of up-slope portion--down-slope portion pairs in which the up-slope portion and the down-slope portion are within a predetermined distance;

(d) a third means which, when said number of pairs corresponds to the number of all edges of said one or plurality of mark elements in said mark pattern, allows execution of position determination according to one of the following three position determination modes;

a first mode in which only two slope portions situated internally of a pair of edges which define the width of said mark element are used;

a second mode in which only two slope portions situated externally of a pair of edges which define the width of said mark element are used; and

a third mode in which four slope portions which appear for said pair of edges are used;

(e) a fourth means which, when said number of pairs is substantially different from the number of all edges of said one or plurality of mark elements, prohibits execution of said second and third position determination modes; and

,

a movable stage for moving said substrate in accordance with the position determined by said one of three position determination modes.

10. An apparatus for positioning a substrate held on a stage movable along a predetermined coordinate system, wherein the substrate is provided with a mark at a predetermined position on its surface, the mark being defined by at least two parallel linear edges, and wherein the apparatus positions the substrate with respect to a direction transverse to said linear edges, the apparatus comprising:

(a) a scanning image pick-up device which has a detection area positioned at a predetermined position within said coordinate system and which picks up, within said detection area, an image of a portion of the surface of said substrate including said mark, wherein, when the image pick-up device scans the image in the direction transverse to said linear edges of the mark, said image pick-up device generates an image signal which changes its level at least at positions of each of the linear edges;

(b) an interferometer measuring a coordinate position of said stage;

(c) means for designating a coordinate position of said substrate at which said mark appears within said detection area;

(d) first waveform processing means for processing a pair of the portions of a waveform of the image signal from said image pick-up device including an up-slope form corresponding to one of the two linear edges of said mark and a down-slope form corresponding to the other of the two linear edges of said mark so as to determine a center position of said mark within said detection area;

(e) second waveform processing means for processing portions of a waveform of the image signal from said image pick-up device including an up-slope--down-slope pair corresponding to one of the two edges of said mark and an up-slope - down-slope pair corresponding to the other of the two edges of said mark so as to determine a center position of said mark within said detection area; and

(f) control means for controlling movement of said stage based on said center position of said mark determined by either one of said first and second waveform processing means and a coordinate position measured by said interferometer.

11. An apparatus for positioning a substrate held on a stage movable along a predetermined coordinate system, wherein the substrate is provided with a mark which includes N mark elements at predetermined positions on its surface, N being a positive integer, the mark elements being arranged parallel to each other with a predetermined spacing and each of the mark elements being defined by two parallel linear edges, and wherein the apparatus positions the substrate with respect to a direction transverse to the linear edges, the apparatus comprising:

(a) a scanning image pick-up device which has a detection area positioned at a predetermined position within said coordinate system and which picks up, within said detection area, an image of a portion of the surface of said substrate including said mark, wherein, when the image pickup device scans the image of 2N linear edges of the mark, 2N being two times N, said image pick-up device generates an image signal which changes its level at least at positions of each of the 2N linear edges;

(b) means for designating a coordinate position of said substrate at which an image of said mark on the substrate appears within said detection area;

(c) first waveform processing means for processing N pairs of portions of a waveform of the image signal from said image pick-up device, where each pair includes an up-slope form corresponding to one of the linear edges of a mark element and a down-slope form corresponding to the other linear edge of the mark element, so as to determine a center position of said mark within said detection area;

(d) second waveform processing means for processing 2N up-slope--down-slope pair portions of a waveform of the image signal from said image pick-up device corresponding to each of the edges of said mark elements so as to determine a center position of said mark within said detection area;

(e) means for designating in advance which of said first waveform processing means or said second waveform processing means is to be used, in accordance with a waveform of said image signal; and

(f) control means for controlling movement of said stage based on said center position of said mark determined by the designated waveform processing means.

12. A method for detecting a position of a substrate comprising:

(a) irradiating a mark pattern on a mask composed of one or a plurality of mark elements having a predetermined width with respect to a predetermined detecting direction, with a light beam, and photoelectrically detecting light information from the mark pattern so as to obtain a photoelectric signal having a waveform representing an optical profile of the mark pattern with respect to the detecting direction;

(b) determining the position of the mark pattern according to one of the following three position determination modes;

a first mode in which two slope portions situated internally of a pair of edges which define the width of the mark element are used;

a second mode in which two slope portions situated externally of said pair of edges are used; and

a third mode in which four slope portions which appear for said pair of edges are used; and

(c) moving the substrate in accordance with the determined position.

13. An apparatus for detecting a position of a substrate comprising:

(a) a detection system which irradiates a mark pattern on a mask composed of one or a plurality of mark elements having a predetermined width with respect to a predetermined detecting direction, with a light beam, and which photoelectrically detects light information from the mark pattern so as to output a photoelectric signal having a waveform representing an optical profile of the mark pattern with respect to the detecting direction;

(b) a calculator which selects one of the following three position determination modes in accordance with a feature of the waveform of the photoelectric signal so as to determine the position of the mark pattern according to the selected mode;

a first mode in which two slope portions situated internally of a pair of edges which define the width of the mark element are used;

a second mode in which two slope portions situated externally of said pair of edges are used; and

a third mode in which four slope portions which appear for said pair of edges are used; and

(c) a drive system which moves the substrate in accordance with the determined position.

14. An apparatus for detecting a position of a substrate comprising:

(a) a detection system which irradiates a mark pattern on a mask composed of one or a plurality of mark elements having a predetermined width with respect to a predetermined detecting direction, with a light beam, and which photoelectrically detects light information from the mark pattern;

(b) a calculator which selects one of the following three position determination modes in accordance with a feature of a waveform of a photoelectric signal outputted from the detection system so as to determine the position of the mark pattern according to the selected mode;

a first mode in which two slope portions situated internally of a pair of edges which define the width of the mark element are used;

a second mode in which two slope portions situated externally of said pair of edges are used; and

a third mode in which four slope portions which appear for said pair of edges are used; and

(c) a drive system which moves the substrate in accordance with the determined position.

15. An apparatus for detecting a position of a substrate comprising:

(a) a detection system which irradiates a mark pattern on a mask composed of one or a plurality of mark elements having a predetermined width with respect to a predetermined detecting direction, with a light beam, and which photoelectrically detects light information from the mark pattern;

(b) a calculator which selects one of the following two position determination modes in accordance with a feature of a waveform of a photoelectric signal outputted from the detection system so as to determine the position of the mark pattern according to the selected mode;

a first mode in which two slope portions situated internally of a pair of edges which define the width of the mark element are used; and

a second mode in which two slope portions situated externally of said pair of edges are used; and

(c) a drive system which moves the substrate in accordance with the determined position.