Metrology apparatus and metrology methods based on high harmonic generation from a diffractive structure
Disclosed is a metrology apparatus and method for measurement of a diffractive structure on a substrate. The metrology apparatus comprises a radiation source operable to provide first radiation for excitation of the diffractive structure such that high harmonic second radiation is generated from said diffractive structure and/or substrate; and a detection arrangement operable to detect said second radiation, at least a portion of which having been diffracted by said diffractive structure.
1 . A metrology apparatus for measurement of a diffractive structure on a substrate for control of a lithography process, comprising:
a radiation source configured to provide a first radiation for excitation of the diffractive structure such that high harmonic second radiation is generated from the diffractive structure and/or substrate;
a detection system configured to detect the second radiation, at least a portion of that having been diffracted by the diffractive structure; and
a processor configured to use the second radiation to determine a parameter of the diffractive structure or a parameter of the lithographic process.
2 . The metrology apparatus of claim 1 , wherein the first radiation is pulsed radiation.
3 . The metrology apparatus of claim 2 , wherein a length of each pulse is in the range of 1 fs to 500 fs.
4 . The metrology apparatus of claim 1 , wherein the first radiation comprises a wavelength in the range of 100 nm to 3000 nm.
5 . The metrology apparatus of claim 1 , wherein at least some harmonics of the second radiation comprise wavelengths shorter than 200 nm.
6 . The metrology apparatus of claim 1 , further comprises a dispersive element configured to spectrally resolve the second radiation on the detection system.
7 . The metrology apparatus of claim 1 , wherein the processor is further configured to determine a ratio of an intensity of a zeroth order and an intensity from at least one higher diffraction order of the second radiation; and
use the ratio to determine a height of the diffractive structure in the direction perpendicular to the substrate plane.
8 . The metrology apparatus of claim 1 , wherein the processor is further configured to determine overlay, focus, alignment, critical dimension and/or one or more other profilometry parameters from the second radiation.
9 . The metrology apparatus of claim 1 , wherein the radiation source comprises:
a high harmonic generation source comprising a gas source for generating a gas medium thereby is able to generate high harmonic third radiation from excitation of the gas medium by the first radiation; and
radiation delivery optics for delivering the third radiation to a structure on the substrate.
10 . The metrology apparatus of claim 9 , wherein the high harmonic generation source is operable to generate the third radiation such that the detection system is configured to detect both the second radiation and the third radiation, at least a portion of the second radiation and the third radiation having been diffracted by the diffractive structure.
11 . The metrology apparatus of claim 10 , wherein the processor is further configured to determine interference between the second radiation and third radiation; and determine the phase of the second radiation from the interference.
12 . The metrology apparatus of claim 1 , wherein the diffractive structure comprises a structure formed by a lithographic process on a semiconductor substrate.
13 . The metrology apparatus of claim 1 , wherein the metrology apparatus is configured such that the first radiation is incident on and the second radiation is emitted from the same side of the substrate.
14 . A method for measurement of a diffractive structure on a substrate, comprising:
exciting the diffractive structure with first radiation to generate high harmonic second radiation from the diffractive structure and/or substrate; and
detecting the second radiation, at least a portion of that having been diffracted by the diffractive structure to obtain a measured data,
wherein the measured data corresponding to the second radiation is used to determine a parameter of the diffractive structure or to control a lithography process.
15 . A lithographic cell comprising a metrology apparatus for measurement of a diffractive structure on a substrate for control of a lithography process, comprising:
a radiation source configured to provide first radiation for excitation of the diffractive structure such that high harmonic second radiation is generated from the diffractive structure and/or substrate;
a detection system configured to detect the second radiation, at least a portion of that having been diffracted by the diffractive structure; and
a processor configured to use the second radiation to determine a parameter of the diffractive structure or a parameter of the lithographic process.
16 . The metrology apparatus of claim 1 , wherein at least some harmonics of the second radiation comprise wavelengths shorter than 100 nm.
17 . The metrology apparatus of claim 1 , wherein at least some harmonics of the second radiation comprise wavelengths shorter than 70 nm.
18 . The metrology apparatus of claim 1 , wherein at least some harmonics of the second radiation comprise wavelengths shorter 30 nm.