Alignment Measurement System

Patent metadata

Field	Value
Publication number	US-2020142319-A1
Application number	US-201816619803-A
Country	US
Kind code	A1
Filing date	May 15, 2018
Priority date	Jun 7, 2017
Publication date	May 7, 2020
Grant date	—

Abstract

A method for determining a characteristic of a feature in an object, the feature being disposed below a surface of the object is disclosed. The surface of the object is irradiated with a pulsed pump radiation beam so as to produce an acoustic wave in the object. The surface of the object is then irradiated with a measurement radiation beam. A portion of the measurement radiation beam scattered from the surface is received and a characteristic of the feature in the object is determined from at least a portion of the measurement radiation beam scattered from the surface within a measurement time period. A temporal intensity distribution of the pulsed pump radiation beam is selected such that in the measurement time period a signal to background ratio is greater than a signal to background ratio achieved using a single pulse of the pulsed pump radiation beam. The signal to background ratio is a ratio of: (a) signals generated at the surface by reflections of acoustic waves from the feature to (b) background signals generated at the surface by reflections of acoustic waves which have not reflected from the feature.

First claim

1 .- 21 . (canceled)

22 . A method for determining a characteristic of a feature in an object, the feature being disposed below a surface of the object, the method comprising:
irradiating the surface of the object with a pulsed pump radiation beam so as to produce an acoustic wave in the object; irradiating the surface of the object with a measurement radiation beam; receiving at least a portion of the measurement radiation beam scattered from the surface; and determining a characteristic of the feature in the object from at least a portion of the measurement radiation beam scattered from the surface within a measurement time period; wherein a temporal intensity distribution of the pulsed pump radiation beam is selected such that in the measurement time period a signal to background ratio is greater than a signal to background ratio achieved using a single pulse of the pulsed pump radiation beam, the signal to background ratio being a ratio of: (a) signals generated at the surface by reflections of acoustic waves from the feature to (b) background signals generated at the surface by reflections of acoustic waves which have not reflected from the feature.

23 . The method of claim 22 , wherein the measurement time period corresponds to a time period during which a portion of an acoustic wave generated by an initial pulse of the pulsed pump radiation beam which is reflected from the feature and not from any other interfaces within the object arrives at the surface.

24 . The method of claim 22 , wherein the temporal intensity distribution of the pulsed pump radiation beam is such that in the measurement time period there is at least partial constructive interference between: (i) a reflected portion of the acoustic wave generated by a first pulse, the reflected portion of the acoustic wave generated by the first pulse having reflected from the feature; and (ii) a reflected portion of the acoustic wave generated by a second pulse, the reflected portion of the acoustic wave generated by the second pulse having also been reflected from the feature.

25 . The method of claim 22 , wherein the temporal intensity distribution of the pulsed pump radiation beam is such that in the measurement time period there is at least partial destructive interference between: (i) a reflected portion of the acoustic wave generated by a first pulse which is not incident on the feature; and (ii) a reflected portion of the acoustic wave generated by a second pulse which is not incident on the feature.

26 . The method of claim 22 , wherein the temporal intensity distribution of the pulsed pump radiation beam is selected such that the signal to background ratio in the measurement time period is generally maximized.

27 . An apparatus for determining a characteristic of a feature in an object, the feature being disposed below a surface of the object, the apparatus comprising:
a pump radiation source operable to irradiate the surface of the object with a pulsed pump radiation beam so as to produce an acoustic wave in the object; a measurement radiation source operable to irradiate the surface of the object with a measurement radiation beam; and a measurement system operable to receive at least a portion of the measurement radiation beam scattered from the surface and further operable to determine a characteristic of the feature in the object from at least a portion of the measurement radiation beam scattered from the surface within a measurement time period; wherein the pump radiation source is arranged such that a temporal intensity distribution of the pulsed pump radiation beam is such that in the measurement time period a signal to background ratio is greater than a signal to background ratio achieved using a single pulse of the pulsed pump radiation beam, the signal to background ratio being a ratio of: (a) signals generated at the surface by reflections of acoustic waves from the feature to (b) background signals generated at the surface by reflections of acoustic waves which have not reflected from the feature.

28 . A method for determining a temporal intensity distribution of a pulsed pump radiation beam for irradiating a surface of an object having a feature disposed below the surface with a pulsed pump radiation beam so as to produce an acoustic wave in the object, the method comprising:
determining a temporal intensity distribution of the pulsed pump radiation beam such that in a measurement time period a signal to background ratio is greater than a signal to background ratio achieved using a single pulse of the pulsed pump radiation beam, wherein the signal to background ratio is a ratio of: (a) signals generated at the surface by reflections of acoustic waves from the feature to (b) background signals generated at the surface by reflections of acoustic waves which have not reflected from the feature.

29 . The method of claim 28 , wherein the measurement time period corresponds to a time period during which a portion of an acoustic wave generated by an initial pulse of the pulsed pump radiation beam which is reflected from the feature and not from any other interfaces within the object arrives at the surface.

30 . The method of claim 28 , wherein the temporal intensity distribution of the pulsed pump radiation beam is determined such that in the measurement time period there is at least partial constructive interference between: (i) a reflected portion of the acoustic wave generated by a first pulse, the reflected portion of the acoustic wave generated by the first pulse having reflected from the feature; and (ii) a reflected portion of the acoustic wave generated by a second pulse, the reflected portion of the acoustic wave generated by the second pulse having also been reflected from the feature.

31 . The method of claim 28 , wherein the temporal intensity distribution of the pulsed pump radiation beam is determined such that in the measurement time period there is at least partial destructive interference between: (i) a reflected portion of the acoustic wave generated by a first pulse which is not incident on the feature; and (ii) a reflected portion of the acoustic wave generated by a second pulse which is not incident on the feature.

32 . The method of claim 28 comprising:
determining a plurality of acoustic pathways away from and back to the surface based on the structure of the object;
for each determined acoustic pathway, determining a time taken for an acoustic pulse to propagate along the acoustic pathway, and an attenuation factor and a phase change for an acoustic pulse propagating along the acoustic pathway;
for a pulsed pump radiation beam, determining an acoustic signal at the surface as a superposition of contributions from each pulse propagating along each pathway and determining one or more parameters of the temporal intensity distribution, such that in a measurement time period: the ratio of signals generated at the surface by reflections of acoustic waves from the feature to background signals generated at the surface by reflections of acoustic waves which have not reflected from the feature is enhanced.

33 . The method of claim 32 , wherein the one or more parameters of the temporal intensity distribution are determined such that:
there is at least partial constructive interference between one or more contributions from pathways that reflect from the feature; and/or there is at least partial destructive interference between one or more contributions from pathways that are not incident on the feature.

34 . The method of claim 28 , comprising:
irradiating a surface of the object with a pulsed pump radiation beam so as to produ

Assignees

• Asml Netherlands Bv

Inventors

• Witte Stefan Michiel
• Antoncecchi Alessandro
• Zhang Hao
• Edward Stephen
• Planken Paulus Clemens Maria
• Goorden Sebastianus Adrianus
• Huisman Simon Reinaid
• Setija Irwan Dani
• Vles David Ferdinand

Classifications

• G03F9/7084

  Position of mark on substrate, i.e. position in (x, y, z) of mark, e.g. buried or resist covered mark, mark on rearside, at the substrate edge, in the circuit area, latent image mark, marks in plural levels · CPC title

• G03F9/7053 Primary

  Non-optical, e.g. mechanical, capacitive, using an electron beam, acoustic or thermal waves · CPC title

• G03F7/70133 Primary

  Measurement of illumination distribution, in pupil plane or field plane · CPC title