EP0502679A1
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Semiconductor integrated circuit fabrication utilizing latent imagery
Assignee: AT&T Inc
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Filing: 1992-03-02
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Granted: —
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Expires: 2012-03-02
Abstract
Abstract A method to achieve good stepper focus and exposure over an entire wafer for a particular mask level before the start of a product run is described. This method can also be used to produce a characterization of lens field curvature (i.e., a surface of optimum focus across the lens) and to characterize lens astigmatism, defocus sensitivity, relative resolution, and other characteristics, and to check the stepper for optical column tilt. The process prevents the complexities of resist development from affecting determination of focus. The process involves forming an array of latent images in a resist and examining the scattered light from the edges of the latent images. Analysis of the scattered light quickly provides information on correct exposure and focus together with lens characteristics over the printing field.
Inventors
- 👤 Thomas Evans Adams
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-10 02:26
CPC Classifications
G; G03; G03F; G03F7/00; G03F7/70; G03F7/70483; G03F7/7055; G03F7/70558; G03F7/70216; G03F7/70241; G03F7/70591; G03F7/706; G03F7/70605; G03F7/70616; G03F7/70641; G03F7/70653; G03F7/70675; G03F9/00; G03F9/70; G03F9/7003; G03F9/7023; G03F9/7026
Claims Analysis
Total Claims: 39
Claim 1
Independent Claim
87 words
A method of semiconductor integrated circuit fabrication comprising: providing a substrate having a resist; creating at least one latent image in said resist, each image having at least one predetermined lithographic parameter, and interrogating said latent image(s) by exposure to energy and measuring at least one characteristic of scattered energy; and characterised by selecting a desired said lithographic parameter value, chosen to create at least one desired latent image; and utilizing said desired lithographic parameter value to form at least one other latent image in said resist.
Claim 2
Dependent Claim
103 words
The method of claim 1, characterised in that the said one predetermined lithographic parameter of each image is achieved by forming each image at a different focus, or by forming each image at the same focus and a different respective exposure, in that each latent image is interrogated by measuring energy scattered from each image, either selecting a focus or a desired exposure value, said focus or exposure value chosen to create latent image(s) capable of producing a predetermined scattered energy; said other latent image(s) representing a semiconductor process level, said other latent image(s) being formed at said desired focus or exposure value.
Claim 3
Dependent Claim
29 words
The method of claim 1 or 2, in which the first mentioned latent image(s) is formed utilizing an exposure dose which is insufficient to produce a fully developed image.
Claim 4
Dependent Claim
53 words
The method of claim 1 or 2, in which said process of selecting a desired lithographic parameter includes determining a functional relationship between the said scattered energy and the said lithographic parameter; and determining a desired scattered energy from said model; and selecting said desired lithographic parameter to correspond to said desired energy.
Claim 5
Dependent Claim
22 words
The method of claim 1 or 2 in which said substrate includes a silicon wafer having partially fabricated integrated circuits formed thereon.
Claim 6
Dependent Claim
23 words
The method of claim 1 or 2, in which said latent images are formed within the boundaries of at least one integrated circuit.
Claim 7
Dependent Claim
34 words
The method of claim 1 or 2 in which the first latent images are formed in areas chosen from: regions which subsequently become streets overlying said substrate, and regions adjacent to the product array.
Claim 8
Dependent Claim
59 words
The process of claim 2, in which said process of selecting a desired focus includes determining a functional relationship between each of the energies scattered from each of said latent images and its respective focus; determining the maximal actual or interpolated scattered energy from said functional relationship; and selecting said desired focus to correspond to said maximal energy value.
Claim 9
Dependent Claim
76 words
The method of claim 2, in which said process of selecting a desired focus includes determining a functional relationship between each of the energies scattered from each of said latent images and its respective focus; determining the maximal signal or interpolated signal energy from said functional relationship; selecting a focus to correspond to said maximal energy value, and then selecting said desired focus to be a predetermined offset from said focus corresponding to said maximal energy.
Claim 10
Dependent Claim
22 words
The method of claim 2, in which said interrogation step is performed simultaneously with the step of creating said first latent images.
Claim 11
Dependent Claim
87 words
The method of claim 10, in which creation of said first latent images is accomplished by exposing said resist to an energy source, and further in which said interrogation step includes measuring energy originating from said energy source which is scattered from said latent image while said latent image is forming, the exposure dependence of the intensity of said scattered energy optionally being measured, and/or optionally including the step of selecting a desired exposure value chosen to create latent images capable of producing a predetermined scattered signal.
Claim 12
Dependent Claim
35 words
The method of claim 2, in which creation of the first mentioned latent images is accomplished by exposing said resist to an energy source chosen from x-rays, electrons, ions, neutral particle beams, and electromagnetic radiation.
Claim 13
Dependent Claim
60 words
The method of claim 10 in which the first mentioned latent images are formed by exposing said resist to a first energy source and further in which said interrogation step is performed by exposing said latent images to a second energy source and measuring the energy originating from said second energy source and scattered from each of said latent images.
Claim 14
Dependent Claim
70 words
A method of claim 1,2,6 or 7, characterised in that the at least one latent image is created in said resist by exposing said resist to a first energy source; the interrogation of the latent image is performed during its formation by measuring energy scattered from said latent image; and the exposure of said resist to said first energy source is terminated when said scattered energy reaches a predetermined value.
Claim 15
Dependent Claim
18 words
The method of claim 14 in which said latent image of interrogation encompasses substantially the entire printing field.
Claim 16
Dependent Claim
28 words
The process of claim 14 in which said interrogation process includes the measurement of light originating from said first energy source and subsequently scattered from said latent image.
Claim 17
Dependent Claim
42 words
The method of claim 14 in which said interrogation step includes exposure of said latent image during its formation to a second energy source and measurement of energy originally emanating from said second energy source and subsequently scattered from said latent image.
Claim 18
Independent Claim
75 words
A method of lithography tool adjustment comprising: providing a lens system; providing a substrate having a resist; creating a latent image in said resist; and characterised by interrogating said latent image to thereby determine a lens system parameter, and adjusting said lens system or lithography tool to improve said parameter, said lens system parameter optionally being chosen from the group consisting of astigmatism, defocus sensitivity, depth of focus, resolution, coma, spherical aberration, and field curvature.
Claim 19
Independent Claim
207 words
A method of lithography tool adjustment comprising: providing a lens system; forming a resist upon a substrate; creating a plurality of latent images, each of said latent images having an edge, which has first and second parts which are non-parallel, in said resist by exposing said resist to energy channeled through said lens system, and characterised by each of said latent images being formed at a respective predetermined focus offset of said lens system; and interrogating said first and second parts of each of said latent images, thereby obtaining the scattered energy from each of said latent image parts associated with its respective focus offset; determining the maximum scattered energy for said first parts and its respective first part focus offset; determining the maximum scattered energy for said second parts and its respective second part focus offset; determining the difference between said first part focus offset and said second part focus offset, said difference being associated with astigmatism; adjusting said lens system to reduce said difference, said adjusting step optionally including the movement of at least one element in said lens system, or the replacement of at least one element in said lens system, or the addition of one or more additional elements in said lens system.
Claim 20
Dependent Claim
130 words
The method of claim 19 in which a multiplicity of said pluralities of latent images are created in said resist, said multiplicity spanning at least a portion of the printing field of said lens system; and further including the step for each of said pluralities of latent images, determining the difference between said first part focus offset and second part focus offset, said difference being associated with the astigmatism of said pluralities; adjusting said lens system or said lithography tool to reduce at least some of said astigmatic difference, the adjusting step optionally including the movement of at least one element of said lens system, or the replacement of at least one element of said lens system, or the addition of one or more additional elements in said lens system.
Claim 21
Independent Claim
162 words
A method of lithography tool adjustment comprising: providing a lens system; forming a resist upon a substrate; creating first and second pluralities of latent images, said first plurality being characterised by first edges and said second plurality being characterised by second edges, said first and second edges being non-parallel; and characterised by each of said first plurality of images being formed at a first predetermined focus offset of said lens system and each of said second plurality of images being formed at a second predetermined focus offset of said lens system; interrogating said first and second pluralities of scattered images, thereby obtaining the scattered energy from each of said latent image associated with its respective focus offset; determining the maximum scattered energy for said first plurality and its respective first plurality focus offset; determining the difference between said first plurality focus offset and said second plurality focus offset, said difference being associated with astigmatism; adjusting said lens system to reduce said difference.
Claim 22
Independent Claim
81 words
A method of semiconductor integrated circuit fabrication comprising: providing at least two lithographic tools; using each of said lithographic tools to create a first plurality of latent images in a first resist; and characterised by interrogating said latent images to thereby measure a desired lithographic parameter characteristic of each lithographic tool; selecting a lithographic tool having a superior lithographic parameter; using said selected lithographic tool to form a second plurality of latent images in a second resist upon a product wafer.
Claim 23
Independent Claim
89 words
A method of semiconductor fabrication utilizing at least first and second lithographic tools comprising; providing at least one substrate having a resist; forming a first and second latent image, utilizing said first and second lithographic tools respectively; and characterized by interrogating said first and second latent images to determine a chosen lens characteristic from the group consisting of: spherical abberation, resolution, astigmatism, field curvature, column tilt, defocus sensitivity, and coma; determining which lithographic tool possesses the best of said chosen characteristic; utilizing said lithographic tool at predermined process levels.
Claim 24
Independent Claim
160 words
A method of latent image interrogation comprising: providing a resist with a latent image formed in a first region and no latent image formed in a second region; and characterised by illuminating said first region and said second region energy, said beam remaining fixed upon said first and second regions for a first period of time; measuring the energy scattered during said first period of time; illuminating said second region alone with a beam of energy, said beam remaining fixed upon said second region for a second period of time; measuring the energy scattered during said second period of time; determining a scattered signal strength by subtracting said energy scattered during said second period from said energy scattered during said first period, the first plurality of latent images optionally being formed utilizing an exposure dose which is insufficient to produce a fully developed image, and/or said resist optionally being positioned upon a substrate having partially fabricated integrated circuits formed thereon.
Claim 25
Independent Claim
157 words
A method of lithography tool adjustment comprising: providing a lens system; providing a substrate having a resist; forming a first plurality of latent images in said resist, each said latent image having an associated focus; and characterised by interrogating each said latent image to determine its scattered energy as a function of its respective focus; selecting a first optimum focus; blocking a first portion of said lens with an obstacle; forming a second plurality of latent images in said resist, utilizing said blocked lens, each of said latent images having an associated focus; interrogating each said second latent image to determine its scattered energy as a function of its respective focus; selecting a second optimum focus; determining the difference between said first and second optimum focus as a spherical aberration; adjusting said lens system to reduce said spherical abberation; a second portion of said lens optionally being blocked prior to forming said first plurality of latent images.
Claim 26
Independent Claim
103 words
A method comprising: providing a lithography tool having a lens system having: a printing field providing a substrate having a resist; and characterized by forming at least two pluralities of latent images in said resist, each said image having an associated focus, said pluralities of images substantially covering said printing field; interrogating each said latent image to determine its scattered energy as a function of its associated focus; determining the maximum scattered energy for each plurality by establishing the scattered energy as a function of focus; averaging the respective focuses associated with said maximum scattered energies, said average being associated with machine focus.
Claim 27
Dependent Claim
104 words
The method of claim 26 in which said latent images are created by exposing said resist to a first monochromatic light of a first frequency and a respective first machine focus is determined for said first monochromatic light, then another one or more pluralities of latent images are created by exposing said resist to a second monochromatic light of a second frequency and a respective second machine focus determined for said second monochromatic light, and further determining the difference between said first and second machine focus, said difference being associated with chromatic aberration and then adjusting said lens system to reduce said chromatic aberration.
Claim 28
Independent Claim
69 words
A method of lithography tool adjustment comprising: providing a lens system; providing a substrate having a resist; forming a plurality of latent images in said resist, each said image having an associated focus and exposure; and characterised by interrogating said latent images to determine the scattered energy associated with a respective focus, said scattered energy being associated with resolution; adjusting said lens system so that said resolution is increased.
Claim 29
Independent Claim
156 words
A method of lithography tool adjustment comprising: providing a lens system having a printing field; providing a substrate having a resist; and characterised by forming at least two sets of pluralities of latent images, each plurality having a set of lines parallel to a lens radius and a set of lines perpendicular to said lens radius in said resist, each said latent image having an associated focus; interrogating each said latent image to determine its scattered energy as a function of its respective focus; in each plurality of images, for each set of parallel latent images and each set of perpendicular latent images, determining the respective maximum scattered energy; determining the maximum amount of defocus required to make the scattered energy from each set of parallel latent images nearly equal to the scattered energy from each set of perpendicular latent images, said maximum amount being here termed coma; adjusting said lens system to reduce said coma.
Claim 30
Independent Claim
105 words
A method of lithography tool adjustment comprising: providing a multi-element lens system; providing a substrate having a resist; and characterized by forming a multiplicity of pluralities of latent images in said resist, said multiplicity spanning a substantial portion of the printing field of said lens system, each of said pluralities being associated with a location in the said printing field; interrogating each said plurality of latent images to determine a preferred focus associated with each plurality; said preferred focus being associated with locations in said printing field and defining a field curvature surface; adjusting said lens system to make said surface of preferred focus flatter.
Claim 31
Dependent Claim
77 words
The method of claim 30 wherein said lens system is exposed to incident energy starting at a first time and ending at a second time, and said field curvature surface is determined for both said first time and said second time, the temperature of said lens system optionally being permitted to rise from a first temperature to a second temperature, and a said field curvature surface being determined for both said first temperature and said second temperature.
Claim 32
Independent Claim
140 words
A method comprising: providing a substrate, having a resist, to a lithography tool; and characterised by forming a full field array having first elements of latent images in said resist; each first element of said full field array being a sub field array having second elements; each second element of said sub field array being a feature clump having third elements; each element of said feature clump being a feature group having fourth elements; each feature clump being characterised by at least one predetermined lithographic parameter; interrogating selected feature groups to measure scattered energy; displaying for each sub field array the scattered energy of each said feature group as a function of the associated lithographic parameter of its respective feature clump; adjusting said lithography tool so that the said scattered energies of selected feature groups tend towards a desired value.
Claim 33
Dependent Claim
60 words
The method of claim 32 further including the step of providing a wafer to said lithography tool and forming at least one integrated circuit upon said wafer, each of said feature groups optionally being characterised by a different linewidth, each said full field array optionally being a 7x7 array, and each said sub field array optionally being a 4x4 array.
Claim 34
Independent Claim
63 words
A method of semiconductor integrated circuit comprising: providing a substrate, having a resist, to a lithography tool having an optical column; forming a plurality of latent images in said resist; and characterised by interrogaring each said latent image thereby determining a field curvature surface; determining whether said field curvature surface exhibits an overall tilt; adjusting said optical colum to reduce said overall tilt.
Claim 35
Independent Claim
78 words
A method of lithography tool fabrication comprising: providing a lens system; providing a substrate having a resist; forming a plurality of latent images in said resist, each said latent image having an associated focus; and characterised by interrogating each said latent image to determine its scattered energy as a function of its respective focus; determining the defocus sensitivity as a curvature of the scattered energy as a function of focus; adjusting said lens to decrease said defocus sensitivity.
Claim 36
Dependent Claim
34 words
The method of claim 35 in which said interrogation is accomplished using a two-dimensionally addressable detector, the latter optionally being chosen from a mechanically movable detector, a CCD two-dimensional array, and a microchannel plate.
Claim 37
Independent Claim
63 words
A method of latent image interrogation comprising: forming at least one latent image in a resist, said latent image having at least a first dimension and a second dimension; and characterised by exposing said latent image to a static energy source, said source impinging upon said first dimension and not impinging upon said second dimension; measuring the energy scattered from said first dimension.
Claim 38
Dependent Claim
46 words
The method of claim 37 in which said latent image has a rectangular shape; said first dimension is the length of said rectangle, and said second dimension is the width of said rectangle, said energy source optionally being a beam of light having a rectangular shape.
Claim 39
Independent Claim
76 words
A method of semiconductor integrated circuit manufacture comprising: providing a substrate having a resist; creating a plurality of latent images in said resist; and characterised by interrogating said latent image to determine machine focus offset; measuring barometric pressure at a first time associating machine focus offset as a function of barometric pressure; at a second time, measuring barometric pressure and automatically adjusting machine focus offset according to said association between machine focus offset and barometric pressure.
References Cited (Backward Citations)
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