A lithographic apparatus configured to project a patterned beam of radiation onto a target portion of a substrate is disclosed. The apparatus includes a first radiation dose detector and a second radiation dose detector, each detector comprising a secondary electron emission surface configured to receive a radiation flux and to emit secondary electrons due to the receipt of the radiation flux, the first radiation dose detector located upstream with respect to the second radiation dose detector viewed with respect to a direction of radiation transmission, and a meter, connected to each detector, to detect a current or voltage resulting from the secondary electron emission from the respective electron emission surface.

Lithographic apparatus, and device manufacturing method

A method for determining overlay between a first grating (110) and a second grating (120) on a substrate (100), the second grating (120) on top of the first grating(110), the second grating (120) having substantially identical pitch (P1) as the first grating (110), the second and first gratings forming a composite grating (110,120), the method including providing a first illumination beam (IB) for illuminating the composite grating (110,120) under an angle of incidence (β) along a first horizontal direction (D1) along the surface of the substrate, and measuring a first intensity (i+) of a first order diffracted beam (B+) from the composite grating (110,120); providing a second illumination beam for illuminating the composite grating (11θ!i2O) under the angle of incidence (-β) along a second horizontal direction (D2) along the surface of the substrate, wherein the second horizontal direction (D2) is opposite to the first horizontal direction (DI)1 and measuring a second intensity (i-) of a minus first order diffracted beam (B-) from the composite grating (110,120).

Diffraction Based Overlay Metrology Tool and Method

Disclosed is a method for determining an overlay error between at least two layers in a multiple layer sample. An imaging optical system is used to measure a plurality of measured optical signals from a plurality of periodic targets on the sample. The targets each have a first structure in a first layer and a second structure in a second layer. There are predefined offsets between the first and second structures. A scatterometry overlay technique is then used to analyze the measured optical signals of the periodic targets and the predefined offsets of the first and second structures of the periodic targets to thereby determine an overlay error between the first and second structures of the periodic targets.

Apparatus and methods for detecting overlay errors using scatterometry

Methods and systems for determining a critical dimension and overlay of a specimen

Alignment accuracy between two or more patterned layers is measured using a metrology target comprising substantially overlapping diffraction gratings formed in a test area of the layers being tested. An optical instrument illuminates all or part of the target area and measures the optical response. The instrument can measure transmission, reflectance, and/or ellipsometric parameters as a function of wavelength, polar angle of incidence, azimuthal angle of incidence, and/or polarization of the illumination and detected light. Overlay error or offset between those layers containing the test gratings is determined by a processor programmed to calculate an optical response for a set of parameters that include overlay error, using a model that accounts for diffraction by the gratings and interaction of the gratings with each others' diffracted field. The model parameters might also take account of manufactured asymmetries. The calculation may involve interpolation of pre-computed entries from a database accessible to the processor. The calculated and measured responses are iteratively compared and the model parameters changed to minimize the difference.

Overlay alignment metrology using diffraction gratings

A metrology apparatus for determining bias or overlay error in a substrate formed by a lithographic process includes an aperture between the objective lens and the image plane adapted to set the effective numerical aperture of the apparatus. The aperture is adjustable to vary the effective numerical aperture of the apparatus and the aperture may be non-circular, for example, rectangular, to individually vary the effective numerical aperture of the apparatus in horizontal and vertical directions. To determine bias or overlay error there is provided a target having an array of elements on a substrate, the array comprising a plurality of spaced, substantially parallel elements having a length and a width, the sum of the width of an element and the spacing of adjacent elements defining a pitch of the elements, edges of the elements being aligned along a line forming opposite array edges, the distance between array edges comprising the array width. The numerical aperture is adjusted such that the pitch of the elements is less than or approximately equal to the ratio of the wavelength of the light source to the numerical aperture value of the optical metrology tool in the direction of the array edges, and the edges of the array are resolved with the optical metrology tool and the width of the array are measured to determine bias or overlay error in the substrate. A camera may be adapted to create a digital image of a target and the components of the digital image in the direction of the pitch of the elements, normal to the length of the elements, may be suppressed to resolve the edges of the array and measure the width of the array. Preferably, the means for suppressing components of the digital image comprises a microprocessor adapted to perform a fast Fourier transform on the digital image to convert image intensity to a spatial frequency domain and a filter to suppress high spatial frequency components of the image in the direction of the pitch of the elements.

Optical metrology tool and method of using same

A process for determining critical dimension bias or overlay error in a substrate formed by a lithographic process initially provides an array of elements on a substrate, the array comprising a plurality of spaced, substantially parallel elements having a length and a width. The sum of the width of an element and the spacing of adjacent elements define a pitch of the elements. Edges of the elements are aligned along a line forming opposite array edges, with the distance between array edges comprising the array width. An optical metrology tool used for measurement of the array is adjustable for one or more of i) wavelength of the light source, ii) numerical aperture value or iii) partial coherence. The process includes selecting the pitch of the elements, the wavelength of the light source, the numerical aperture and the partial coherence such that the pitch of the elements is less than or about equal to the ratio of the wavelength of the light source to the numerical aperture value of the optical metrology tool in the direction of the array edges whereby individual elements are not resolved within the array. The edges of the array are resolved with the optical metrology tool and the width of the array is measured to determine bias or overlay error in the substrate. Where the pitch of the array differs in different directions, the optical metrology tool has a non-circular pupil and the numerical aperture value NA of the optical metrology tool in the direction of minimum array pitch is selected to be less than the numerical aperture value NA of the optical metrology tool in a direction of maximum array pitch, such that the array edges are resolved and individual elements are not resolved.

Method of optical metrology of unresolved pattern arrays

PROBLEM TO BE SOLVED: To provide a method and a target for optically judging dimension change (bias) of a pattern printed by lithography process and an overlay error. SOLUTION: An array consisting of a plurality of elements 115 with a length and a width arranged with intervals and substantially in parallel is provided on a base. The sum of the width of the element 115 and the interval to the adjacent element 115 determines the pitch of the elements 115. The edges of the elements 115 are aligned along a straight line and forms the array edge on both sides and the distance between the array edge constitutes the array width. The pitch of the elements 115 is chosen so as to be smaller than or nearly equal to the ratio of the opening digit value of an optical measuring apparatus in the array edge direction to the wave length of the light source. As the results, individual elements 115 are not analyzed in the array. The array edge is analyzed with the optical measuring apparatus and the array width is measured to judge the bias or overlay error on the base.

Timothy Allan Brunner

Papers

Optical metrology tool and method of using same

Method of optical metrology of unresolved pattern arrays

Optical measuring method for pattern array unavailable for image analysis