EP0532927A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Automated photomask inspection apparatus
Assignee: KLA Corp
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Filing: 1992-08-20
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Granted: —
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Expires: 2012-08-20
Abstract
Abstract An automated photomask inspection apparatus including an XY state (12) for transporting a substrate (14) under test in a serpentine path in an XY plane, an optical system (16) comprising a laser (30), a transmission light detector (34), a reflected light detector (36), optical elements defining reference beam paths and illuminating beam paths between the laser, the substrate and the detectors and an acousto-optical beam scanner (40, 42) for reciprocatingly scanning the illuminating and reference beams relative to the substrate surface, and an electronic control, analysis and display system for controlling the operation of the stage and optical system and for interpreting and storing the signals output by the detectors. The apparatus can operate in a die-to-die comparison mode or a die-to-database mode.
Inventors
- 👤 Mark Joseph Whil
- 👤 Tao-Yi Fu
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-06 12:24
CPC Classifications
G; G01; G01N; G01N21/00; G01N21/84; G01N21/88; G01N21/95; G01N21/956; G01N21/95607; G01N21/17; G01N21/55; G01N2021/558; G01N21/8851; G01N2021/8854; G01N2021/8861; G01N2021/95615; G01N2021/95676; G01N2201/00; G01N2201/10; G01N2201/106
Claims Analysis
Total Claims: 41
Claim 1
Independent Claim
192 words
An optical inspection system for inspecting substrates such as photomasks and semiconductor wafers, comprising: stage means for carrying a substrate to be inspected along a predetermined path within an inspection plane; laser means for providing a pixel-illuminating beam of light; optical means defining a first optical axis intersecting said inspection plane and along which said beam of light is to be passed, said optical means being operative to focus said beam of light on a single pixel at a time on the substrate to be inspected; beam deflecting means disposed along said first optical axis and operative to deflect said beam of light in oscillatory fashion between opposite sides of said first optical axis and in directions substantially transverse to said predetermined path such that care areas of the inspected substrate are scanned in contiguous swaths; light detecting means for detecting changes in the intensity of said beam of light caused by the illuminated pixels of the inspected substrate and operative to develop scan signals corresponding thereto; electronic means for comparing said scan signals to corresponding reference signals whereby substantial differences therebetween may be used to identify defects in the inspected substrate.
Claim 2
Dependent Claim
38 words
An optical inspection system as recited in claim 1 wherein said stage means is constrained to move with no more than two degrees of freedom, and is driven by x-direction and y-direction inputs generated by said electronic means.
Claim 3
Dependent Claim
49 words
An optical inspection system as recited in claim 2 wherein said stage means is an X/Y air bearing stage driven by linear motors including stators and sliders separated by air bearing means, the stators being configured to preload the air bearings of each slider in at least two directions.
Claim 4
Dependent Claim
39 words
An optical inspection system as recited in claim 1 wherein said laser means is selected to have substantially the same wavelength as the light source which will later be used in association with the inspected substrate during wafer processing.
Claim 5
Dependent Claim
37 words
An optical inspection system as recited in claim 1 wherein said optical means includes means for rotating the direction of deflection of said beam of light so that it has a desired relationship to said predetermined path.
Claim 6
Dependent Claim
111 words
An optical inspection system as recited in claim 1 wherein said optical means also includes means defining a second optical axis along which said beam of light may be passed, and having a portion thereof in common with a portion of said first optical axis, the optical path lengths of said first and second optical axes being substantially equal so that the two axes experience substantially identical thermal variation, said second optical axis including a tilted mirror for reflecting the beam of light back along said second optical axis and onto said light detecting means for interferometric comparison with light reflected along said first optical axis from the substrate under test.
Claim 7
Dependent Claim
32 words
An optical inspection system as recited in claim 1 wherein said light-detecting means includes a first detector for detecting the intensity of light reflected from said substrate and generating first scan signals.
Claim 8
Dependent Claim
40 words
An optical inspection system as recited in claim 7 wherein said light detecting means further includes a second detector for detecting the intensity of light from said beam passing through the substrate under inspection and for generating second scan signals.
Claim 9
Dependent Claim
37 words
An optical inspection system as recited in claim 8 wherein said electronic means compares said first and second scan signals to first and second reference signals and determines both the existence and type of any defect encountered.
Claim 10
Dependent Claim
42 words
An optical inspection system as recited in claim 1 wherein said light detecting means includes a transmitted light detector for detecting the intensity of light from said beam of light passing through the substrate under inspection and for generating corresponding scan signals.
Claim 11
Dependent Claim
47 words
An optical inspection system as recited in claim 1 wherein said light detecting means includes means for monitoring the intensity of said beam of light and generating an output which may be used by said electronic means to provide beam intensity variation correction to said scan signals.
Claim 12
Dependent Claim
48 words
An optical inspection system as recited in claim 1 wherein said beam deflecting means includes an acousto-optic modulator for causing said beam of light to be deflected back and forth over a relatively small angle, said angle being the factor which determines the width of each scanning swath.
Claim 13
Dependent Claim
34 words
An optical inspection system as recited in claim 1 and further comprising database means containing ideal data corresponding to the substrate under inspection, said data being selectively read out to generate said reference signals.
Claim 14
Dependent Claim
37 words
An optical inspection system as recited in claim 1 and further comprising means for storing said scan signals, the stored signals being subsequently used to provide said reference signals to which presently scanned signals may be compared.
Claim 15
Dependent Claim
71 words
An optical inspection system as recited in claim 1 wherein said light detecting means includes a first detector for detecting light transmitted through the substrate being inspected and a second detector for simultaneously detecting light reflected from the substrate being inspected, said first and second detectors respectively generating first and second signals from which said electronic means can determine both the existence of a defect and the type of defect detected.
Claim 16
Dependent Claim
74 words
An optical inspection system as recited in claim 1 and further comprising means disposed along a second optical axis intersecting said first optical axis and operative to develop a beam of light for interfering with light reflected from the substrate under inspection such that the intensity of the interfering light detected by said light detecting means may be used by said electronic means to determine variations in the height of the inspected surface material.
Claim 17
Dependent Claim
78 words
An optical inspection system as recited in claim 1 and further comprising means defining an auto-focus optical axis intersecting said first optical axis and including means for introducing astigmatism in the beam reflected from the surface of the inspected substrate, and auto-focus detecting means for measuring the shape of the astigmatized beam and determining therefrom the degree of focus of the beam on the substrate, said auto-focus detecting means generating correction signals for input to said electronic means.
Claim 18
Dependent Claim
113 words
An optical inspection system as recited in claim 17 and further comprising means for splitting said auto-focus optical axis into first and second branches having oppositely polarized anamorphous elements which distort the shape of the light beam passed therethrough, and wherein said auto-focus detecting means includes a first image shape detector associated with said first branch and a second image shape detector associated with said second branch, the outputs of said image shape detectors being used by said electronic means to determine whether said beam of light is in focus at said inspection plane, and if not in focus to determine the degree and direction in which the beam is out of focus.
Claim 19
Dependent Claim
22 words
An optical inspection system as recited in claim 18 wherein said first and second image shape detectors are appropriately oriented quadrature detectors.
Claim 20
Dependent Claim
46 words
An optical inspection system as recited in claim 1 wherein said electronic means measures the magnitudes of said scan signals corresponding to predetermined grid points on the surface of the substrate under inspection and then uses such measurements to determine the surface dimensions of substrate features.
Claim 21
Dependent Claim
37 words
An optical inspection system as recited in claim 14 wherein said light-detecting means includes a first detector for detecting the intensity of light reflected from the substrate under inspection and for generating first scan signals commensurate therewith.
Claim 22
Dependent Claim
42 words
An optical inspection system as recited in claim 21 wherein said light detecting means further includes a second detector for detecting the intensity of light from said beam passing through the substrate under inspection and for generating second scan signals commensurate therewith.
Claim 23
Dependent Claim
38 words
An optical inspection system as recited in claim 22 wherein said electronic means compares said first and second scan signals to corresponding first and second reference signals and determines both the existence and type of any defect encountered.
Claim 24
Dependent Claim
47 words
An optical inspection system as recited in claim 23 wherein said light detecting means includes means for monitoring the intensity of said beam of light and generating an output which may be used by said electronic means to provide beam intensity variation correction to said scan signals.
Claim 25
Dependent Claim
78 words
An optical inspection system as recited in claim 24 and further comprising means defining an auto-focus optical axis intersecting said first optical axis and including means for introducing astigmatism in the beam reflected from the surface of the inspected substrate, and auto-focus detecting means for measuring the shape of the astigmatized beam and determining therefrom the degree of focus of the beam on the substrate, said auto-focus detecting means generating correction signals for input to said electronic means.
Claim 26
Dependent Claim
113 words
An optical inspection system as recited in claim 25 and further comprising means for splitting said auto-focus optical axis into first and second branches having oppositely polarized anamorphous elements which distort the shape of the light beam passed therethrough, and wherein said auto-focus detecting means includes a first image shape detector associated with said first branch and a second image shape detector associated with said second branch, the outputs of said image shape detectors being used by said electronic means to determine whether said beam of light is in focus at said inspection plane, and if not in focus to determine the degree and direction in which the beam is out of focus.
Claim 27
Dependent Claim
22 words
An optical inspection system as recited in claim 26 wherein said first and second image shape detectors are appropriately oriented quadrature detectors.
Claim 28
Dependent Claim
46 words
An optical inspection system as recited in claim 27 wherein said electronic means measures the magnitude of said scan signals corresponding to predetermined grid points on the surface of the substrate under inspection and then uses such measurements to determine the surface dimensions of substrate features.
Claim 29
Dependent Claim
49 words
An optical inspection system as recited in claim 28 wherein said stage means is an X/Y air bearing stage driven by linear motors including stators and sliders separated by air bearing means, the stators being configured to preload the air bearings of each slider in at least two directions.
Claim 30
Dependent Claim
41 words
An optical inspection system as recited in claim 29 wherein said optical means includes means which may be used to rotate the direction of deflection of said beam of light so that it has a desired relationship to said predetermined path.
Claim 31
Dependent Claim
34 words
An optical inspection system as recited in claim 13 wherein said light-detecting means includes a first detector for detecting the intensity of light reflected from said substrate and generating first scan signals commensurate therewith.
Claim 32
Dependent Claim
42 words
An optical inspection system as recited in claim 31 wherein said light detecting means further includes a second detector for detecting the intensity of light from said beam passing through the substrate under inspection and for generating second scan signals commensurate therewith.
Claim 33
Dependent Claim
37 words
An optical inspection system as recited in claim 32 wherein said electronic means compares said first and second scan signals to first and second reference signals and determines both the existence and type of any defect encountered.
Claim 34
Dependent Claim
78 words
An optical inspection system as recited in claim 33 and further comprising means defining an auto-focus optical axis intersecting said first optical axis and including means for introducing astigmatism in the beam reflected from the surface of the inspected substrate, and auto-focus detecting means for measuring the shape of the astigmatized beam and determining therefrom the degree of focus of the beam on the substrate, said auto-focus detecting means generating correction signals for input to said electronic means.
Claim 35
Dependent Claim
113 words
An optical inspection system as recited in claim 34 and further comprising means for splitting said auto-focus optical axis into first and second branches having oppositely polarized anamorphous elements which distort the shape of the light beam passed therethrough, and wherein said auto-focus detecting means includes a first image shape detector associated with said first branch and a second image shape detector associated with said second branch, the outputs of said image shape detectors being used by said electronic means to determine whether said beam of light is in focus at said inspection plane, and if not in focus to determine the degree and direction in which the beam is out of focus.
Claim 36
Dependent Claim
46 words
An optical inspection system as recited in claim 35 wherein said electronic means measures the magnitude of said scan signals corresponding to predetermined grid points on the surface of the substrate under inspection and then uses such measurements to determine the surface dimensions of substrate features.
Claim 37
Dependent Claim
49 words
An optical inspection system as recited in claim 36 wherein said stage means is an X/Y air bearing stage driven by linear motors including stators and sliders separated by air bearing means, the stators being configured to preload the air bearings of each slider in at least two directions.
Claim 38
Dependent Claim
114 words
An optical inspection system as recited in claim 1 wherein said light detecting means includes a transmission detector disposed along said first optical axis on the side of said inspection plane opposite the side including said laser means and operative to detect transmitted light passing through an inspected substrate, and wherein said optical means further includes means defining a second optical axis along which said beam of light may be passed, said second optical axis not intersecting said inspected substrate but having at least a portion thereof in common with said first optical axis and intersecting said transmission detector whereby interferometric comparison between said beam of light and said transmitted light may be conducted.
Claim 39
Dependent Claim
114 words
An optical inspection system as recited in claim 38 wherein said optical means also includes means defining a third optical axis along which said beam of light may be passed, and having a portion thereof in common with a portion of said first optical axis, the optical path lengths of said second and third optical axes being substantially equal so that the two axes experience substantially identical thermal variation, said third optical axis including a tilted mirror for spatially shifting and reflecting the spatially shifted beam of light back along said third optical axis and onto said reflection detector for interferometric comparison with light reflected along said first optical axis from the inspected substrate.
Claim 40
Dependent Claim
66 words
An optical inspection system as recited in claim 8 and further including circuit means responsive to said first and second scan signals and operative to develop gated signals for input to said electronic means to indicate defects in the inspected substrate as a function of the phase error between the light reflected from the surface of the substrate and the light passing through the inspected substrate.
Claim 41
Dependent Claim
65 words
An optical inspection system as recited in claim 40 wherein said circuit means includes: an analog phase detector for comparing said first scan signal to a reference signal to develop an analog signal proportional to the phase difference therebetween, means for converting said analog signal to a digital signal, and encoder means gated by said second scan signal and operative to generate said gated signals.
References Cited (Backward Citations)
No citation records indexed.
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