US-12618804-B2 - Methods and apparatus for acoustic metrology

US12618804B2US 12618804 B2US12618804 B2US 12618804B2US-12618804-B2

Abstract

A metrology apparatus for determining one or more parameters of a structure fabricated in or on a semiconductor substrate. The apparatus comprises a transducer array comprising a plurality of transducers positioned in a plane. The plurality of transducers comprises at least one transmitter transducer for emitting acoustic radiation in a frequency range from 1 GHz to 100 GHz towards the structure, and at least one receiver transducer for receiving acoustic radiation reflected and/or diffracted from the structure.

Inventors

Mustafa ümit ARABUL
Zili ZHOU
Willem Marie Julia Marcel Coene
Coen Adrianus Verschuren
Paul Louis Maria Joseph van Neer
Daniele Piras
Sandra BLAAK
Wouter Dick Koek
Robert Wilhelm Willekers

Assignees

ASML NETHERLANDS B.V.

Dates

Publication Date: 20260505
Application Date: 20211215
Priority Date: 20201222

Claims (19)

1 . A metrology apparatus for determining one or more parameters of a structure having a grating fabricated in or on a semiconductor substrate, the apparatus comprising: a transducer array comprising a plurality of transducers positioned in a plane, wherein the plurality of transducers comprise: at least one transmitter transducer configured to emit acoustic radiation in a frequency range from 1 GHz to 100 GHz towards the structure, and at least first and second receiver transducers configured to receive acoustic radiation reflected and/or diffracted from the structure, and a processor configured to: obtain, from the first and second receiver transducers, respective first and second signals indicative of an amplitude of the acoustic radiation received by the first and second transducers as a function of time, determine a time difference between the first and second signals, and use the time difference to determine the one or more parameters of the structure.
2 . The metrology apparatus of claim 1 , wherein the transducer array is disposed in or on a solid delay line element extending from the transducer array in the direction of the structure and includes a planar face configure to position adjacent to a corresponding planar face of the substrate or a structure fabricated on the substrate.
3 . The metrology apparatus of claim 1 , wherein the plurality of transducers are arranged along a common axis.
4 . The metrology apparatus of claim 1 , wherein the plurality of transducers comprises at least one receiver transducer on either side of the at least one transmitter transducer along the common axis.
5 . The metrology apparatus of claim 3 , wherein the at least one transmitter transducer comprises a plurality of transmitter transducers connected in parallel and arranged to be excited by a single signal.
6 . The metrology apparatus of claim 4 , the apparatus wherein the plurality of transmitter transducers is configured to be operated as a phased-array.
7 . The metrology apparatus of claim 5 , further comprising one or more switches configured to connect and/or disconnect one or more additional transducers of the plurality of transducers to the at least one transmitter transducer.
8 . The metrology apparatus of claim 1 , comprising one or more switches configured to switch one or more of the plurality of transducers from a transmitter transducer to a receiver transducer within a switching time of less than 50 ns.
9 . The metrology apparatus of claim 7 , further comprising a controller configured to control the one or more of the plurality of transducers to be a transmitter transducer or a receiver transducer.
10 . A metrology apparatus of claim 1 , wherein the one or more transmitter transducers is or are configured to emit the acoustic radiation in a pulse having a duration corresponding to a number of cycles of the acoustic radiation in a range from 1 to 1000 cycles.
11 . The metrology apparatus of claim 1 , wherein the transducer array has a pitch in a range from 250 nm to 10 μm.
12 . The metrology apparatus of claim 1 , further comprising a further transducer array comprising a plurality of further transducers coplanar with the transducer array, the plurality of further transducers comprising at least one further transmitter transducer for emitting acoustic radiation in a frequency range from 1 GHz to 100 GHz towards the structure, and at least one further receiver transducer for receiving acoustic radiation reflected and/or diffracted from the structure.
13 . The metrology apparatus of claim 1 , wherein the one or more parameters of the grating is a lateral offset of the grating with respect to the transducer array.
14 . The metrology apparatus of claim 13 , wherein the determining the time difference comprises one or more of: determining respective times at which each of the signals first crosses a particular amplitude; determining a respective one or more times at which each of the signals is zero; and determining a respective one or more times at which a gradient of each of the signals is zero.
15 . The metrology apparatus according to claim 14 , wherein the determining the time difference comprises: determining a cross correlation function of the signals; and determining the time difference based on a time for which the cross correlation function of the time-varying signals is maximal.
16 . The metrology apparatus of claim 1 , wherein: the structure comprises a further grating arranged, such that the grating is positioned between the further grating and the at least one transmitter transducer, the at least first and second receiver transducers are configured to receive acoustic radiation reflected and/or diffracted from the first and second gratings, and the grating has a first pitch and the further grating has a second pitch.
17 . The metrology apparatus of claim 1 , wherein: the structure comprises a further grating spaced apart from the grating along a direction parallel to a normal both gratings, and the grating has a first pitch and the further grating has a second pitch.
18 . The metrology apparatus of claim 16 , wherein the second pitch is different than the first pitch.
19 . The metrology apparatus of claim 17 , wherein the second pitch is different than the first pitch.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority of EP application 20216378.8 which was filed on Dec. 22, 2020 and which is incorporated herein in its entirety by reference. FIELD The present disclosure relates to metrology apparatus and methods usable, for example, in the manufacture of devices by lithographic techniques BACKGROUND A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern (also often referred to as “design layout” or “design”) at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., a wafer). The projected pattern may form part of a process to fabricate a structure onto the substrate. To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm and 13.5 nm. A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm. Low-k1 lithography may be used to process features with dimensions smaller than the classical resolution limit of a lithographic apparatus. In such process, the resolution formula may be expressed as CD=k1×λ/NA, where λ is the wavelength of radiation employed, NA is the numerical aperture of the projection optics in the lithographic apparatus, CD is the “critical dimension” (generally the smallest feature size printed, but in this case half-pitch) and k1 is an empirical resolution factor. In general, the smaller k1 the more difficult it becomes to reproduce the pattern on the substrate that resembles the shape and dimensions planned by a circuit designer in order to achieve particular electrical functionality and performance. To overcome these difficulties, sophisticated fine-tuning steps may be applied to the lithographic projection apparatus and/or design layout. These include, for example, but not limited to, optimization of NA, customized illumination schemes, use of phase shifting patterning devices, various optimization of the design layout such as optical proximity correction (OPC, sometimes also referred to as “optical and process correction”) in the design layout, or other methods generally defined as “resolution enhancement techniques” (RET). Alternatively, tight control loops for controlling a stability of the lithographic apparatus may be used to improve reproduction of the pattern at low k1. In lithographic processes, it is desirable to make frequent measurements of the structures created, e.g., for process control and verification. Various tools for making such measurements are known, including scanning electron microscopes, which are often used to measure critical dimension (CD), and specialized tools to measure overlay, the accuracy of alignment of two layers in a device. Markers such as gratings may be provided in or on the layers to assist with measuring one or more properties of the structure. Recently, various forms of scatterometers have been developed for use in the lithographic field. There are limitations in the performance of optical scatterometers. For example, for con-trolling the manufacture of semiconductor devices such as 3D XPoint non-volatile memory and 3D NAND, it is difficult or impossible to measure overlay through opaque mask layers that separate the overlaid upper pattern from the lower pattern. The opaque layers may be metal layers of several 10s of nm in thickness and carbon hardmasks of several μm in thickness. Metrology using optical scatterometers is challenging as the masks employed are barely transmissive for electromagnetic radiation, with the extreme case being metal masks, where electromagnetic radiation is absorbed and does not go through the metal mask at all. Scanning acoustic microscopes (SAMs) provide a way of measuring structures comprising opaque layers. One commercially available SAM system comprises a single element ultrasound transducer operating at an acoustic frequency of 1 GHz, which is scanned over a surface of the structure. An acoustic lens made of sapphire or quartz and having a concave curvature is used to focus acoustic radiation emitted by the transducer to a focus located a fixed distance away from the transducer. Water is provided between the acoustic lens and the structure to couple the acoustic radiation into the structure. Similar to optics, the resolution of an acoustic system increases with increasing frequency of the acoustic radiation and high acoustic frequencies are neede