APPARATUS FOR AND A METHOD OF DETERMINING SURFACE CHARACTERISTICS
First Claim
1. Apparatus for determining information relating to a sample surface structure, the apparatus comprising:
- a light director operable to direct light along a sample path towards a region of a surface of a sample and along a reference path towards a reference surface such that light reflected by the region of the sample surface and light reflected by the reference surface interfere, the light director being capable of providing light having a point spread function with a spread at a sample surface greater than a pitch of surface structure elements providing a surface structure of the sample;
a mover operable to effect relative movement along a measurement scan path between a sample and the reference surface;
a sensing device operable to sense light representing interference fringes produced by a sample surface region during relative movement along the measurement scan path;
a controller operable to carry out a measurement operation by causing the mover to effect relative movement while the sensing device senses light intensity at intervals to provide a series of intensity values representing interference fringes produced by a sample surface region during the relative movement; and
a data processor operable to receive and process i) structure intensity data comprising a set of intensity values resulting from a measurement operation on a structure surface sample area using light with a point spread function having a spread at the sample surface greater than a pitch of surface structure elements providing the surface structure of the structure surface sample area, and ii) non-structure intensity data comprising a set of intensity values resulting from a measurement operation on a non-structure surface sample area not having the structure, the data processor comprising;
a frequency transform ratio determiner operable to determine a frequency transform ratio corresponding to a ratio between the structure and non-structure intensity data; and
a structure provider operable to relate the frequency transform ratio to a relationship involving a first structure measure representing a ratio between the width and pitch of the surface structure elements and a second structure measure representing the size of the surface structure elements in a direction transverse to the sample surface so as to enable determination of a value for at least one of said first and second structure measures.
1 Assignment
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Accused Products
Abstract
A coherence scanning interferometer (2) carries out: a coherence scanning measurement operation on a surface area (81) carrying a structure using a low numeric aperture objective so that the pitch of the surface structure elements (82) is much less that the spread of the point spread function at the surface (7) to obtain structure surface intensity data; and a coherence scanning measurement operation on a non-structure surface area (83), which may be part of the same sample or a different sample, to obtain non-structure surface intensity data. A frequency transform ratio determiner (105) determines a frequency transform ratio (the HCF function) related to the ratio between the structure surface intensity data and the non-structure surface intensity data. A structure provider (109) sets that frequency transform ratio equal to an expression which represents the electric field at the image plane of the coherence scanning interferometer in terms of surface structure element size (height or depth) and width-to-pitch ratio and derives the surface structure element size and width-to-pitch ratio using the frequency transform ratio. The structure provider (109) may also extract the surface structure element width, if the pitch is independently known.
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Citations
61 Claims
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1. Apparatus for determining information relating to a sample surface structure, the apparatus comprising:
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a light director operable to direct light along a sample path towards a region of a surface of a sample and along a reference path towards a reference surface such that light reflected by the region of the sample surface and light reflected by the reference surface interfere, the light director being capable of providing light having a point spread function with a spread at a sample surface greater than a pitch of surface structure elements providing a surface structure of the sample; a mover operable to effect relative movement along a measurement scan path between a sample and the reference surface; a sensing device operable to sense light representing interference fringes produced by a sample surface region during relative movement along the measurement scan path; a controller operable to carry out a measurement operation by causing the mover to effect relative movement while the sensing device senses light intensity at intervals to provide a series of intensity values representing interference fringes produced by a sample surface region during the relative movement; and a data processor operable to receive and process i) structure intensity data comprising a set of intensity values resulting from a measurement operation on a structure surface sample area using light with a point spread function having a spread at the sample surface greater than a pitch of surface structure elements providing the surface structure of the structure surface sample area, and ii) non-structure intensity data comprising a set of intensity values resulting from a measurement operation on a non-structure surface sample area not having the structure, the data processor comprising; a frequency transform ratio determiner operable to determine a frequency transform ratio corresponding to a ratio between the structure and non-structure intensity data; and a structure provider operable to relate the frequency transform ratio to a relationship involving a first structure measure representing a ratio between the width and pitch of the surface structure elements and a second structure measure representing the size of the surface structure elements in a direction transverse to the sample surface so as to enable determination of a value for at least one of said first and second structure measures. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 20, 21, 22, 23, 24, 25, 26, 27, 60)
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18. Apparatus for determining surface structure element characteristics, wherein the apparatus comprises a coherence scanning interferometer and a data processor, the data processor comprising a structure determiner operable:
to determine a frequency transform ratio relating to a ratio between; structure intensity data comprising a first series of intensity values resulting from a measurement operation by the coherence scanning interferometer on a surface structure sample area using a low numerical aperture objective such that the spread of light from a light source of the coherence scanning interferometer at the sample surface is greater than a pitch of surface structure elements of the surface structure sample area; and non-structure intensity data comprising a second series of intensity values resulting from a measurement operation on a second sample surface area not having the surface structure; to relate the frequency transform ratio to a relationship representing the amplitude and phase of the electric field at the image plane of an objective of the interferometer in terms of a first structure measure representing a ratio between the width and pitch of the surface structure elements and a second structure measure representing the size of the surface structure elements in a direction transverse to the sample surface; and to determine values for at least one of said first and second structure measures as a result of relating the frequency transform ratio to the relationship. - View Dependent Claims (19)
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28. A method of determining information relating to a sample surface structure, the method comprising the steps of:
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carrying out respective measurement operations on a structure surface sample area having a surface structure comprising surface structure elements having a pitch and a non-structure surface sample area not having the surface structure by, at least for the measurement operation on the structure surface sample area, using light having a point spread function with a spread at the sample surface greater than the pitch of the surface structure elements and by, in each measurement operation, directing the light along a sample path towards a region of the sample surface and along a reference path towards a reference surface such that light reflected by the region of the sample surface and light reflected by the reference surface interfere, and causing relative movement along a measurement scan path between the sample and the reference surface while a sensing device senses light intensity representing interference fringes produced by the sample surface region at intervals during the relative movement to provide structure intensity data comprising a series of intensity values resulting from a measurement operation on the structure surface sample area and non-structure intensity data comprising a series of intensity values resulting from a measurement operation on the non-structure surface sample area; determining a frequency transform ratio corresponding to a ratio between the structure and non-structure intensity data; and relating the frequency transform ratio to a relationship involving a first structure measure representing a ratio between the width and pitch of the surface structure elements and a second structure measure representing the size of the surface structure elements in a direction transverse to the sample surface to determine values for at least one of said first and second structure measures. - View Dependent Claims (55, 56, 58)
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29-54. -54. (canceled)
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57. (canceled)
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59. Apparatus for determining information relating to a sample surface structure, the apparatus comprising:
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light directing means for directing light along a sample path towards a region of a surface of a sample and along a reference path towards a reference surface such that light reflected by the region of the sample surface and light reflected by the reference surface interfere, the light directing means being operable to provide light having a point spread function with a spread at a sample surface greater than a pitch of surface structure elements providing a surface structure of the sample; moving means for effecting relative movement along a measurement scan path between a sample and the reference surface; sensing means for sensing light representing the interference fringes produced by a sample surface region during relative movement along the measurement scan path; control means for carrying out a measurement operation by causing the moving means to effect relative movement while the sensing means senses light intensity at intervals to provide a series of intensity values representing interference fringes produced by a sample surface region during the relative movement; and data processing means for receiving and processing i) structure intensity data comprising a set of intensity values resulting from a measurement operation on a structure surface sample area using light having a point spread function with a spread at the sample surface greater than a pitch of surface structure elements providing the surface structure of the structure surface sample area, and ii) non-structure intensity data comprising a set of intensity values resulting from a measurement operation on a non-structure surface sample area not having the structure, the data processing means comprising; frequency transform ratio determining means for determining a frequency transform ratio corresponding to a ratio between the structure and non-structure intensity data; and structure providing means for relating the frequency transform ratio to a relationship involving a first structure measure representing a ratio between the width and pitch of the surface structure elements and a second structure measure representing the size of the surface structure elements in a direction transverse to the sample surface to determine values for said first and second structure measures.
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61. (canceled)
Specification