Apparatus and method for enhanced critical dimension scatterometry
Scatterometers and methods of using scatterometry to determine several parameters of periodic microstructures, pseudo-periodic structures, and other very small structures having features sizes as small as 100 nm or less. Several specific embodiments of the present Invention are particularly useful in the semiconductor industry to determine the width, depth, line edge roughness, wall angle, film thickness, and many other parameters of the features formed in microprocessors, memory devices, and other semiconductor devices. The scatterometers and methods of the invention, however, are not limited to semiconductor applications and can be applied equally well in other applications.
1 . A scatterometer for evaluating microstructures on workpieces, comprising:
a radiation source configured to produce a beam of radiation having a wavelength;
an optical system having a first optics assembly and an object lens assembly, wherein the first optics assembly is configured to condition the beam of radiation such that beam is diffuse and randomized, and wherein the object lens assembly is configured to (a) focus the beam to an area of at object focal plane through at least a 15° range of altitude angles and at least a 90° range of azimuth angles simultaneously and (b) present a return radiation scattered from a microstructure in a radiation distribution at a second focal plane;
a detector positioned to receive the radiation distribution of the return radiation and configured to produce a representation of the radiation distribution; and
a computer operatively coupled to the detector to receive the representation of the radiation distribution, wherein the computer includes a database having a plurality of simulated radiation distributions corresponding to different sets of parameters of the microstructure and a computer-operable medium containing instructions that cause the computer to identify a simulated radiation distribution that adequately fits the representation of the radiation distribution produced by the detector.
2 . The scatterometer of claim 1 , further comprising a navigation system including a light source separate from the radiation source and navigation optics having a low magnification capability for locating a general area of the microstructure and a high magnification capability for accurately aligning the object lens with the microstructure.
3 . The scatterometer of claim 1 wherein the object lens assembly is configured to focus the conditioned beam to a spot size not greater than 30 μm.
4 . The scatterometer of claim 1 wherein the radiation source comprises a laser configured to generate a first beam having a first wavelength and a second beam having a second wavelength different than the first wavelength.
5 . The scatterometer of claim 4 wherein the first wavelength is approximately 266 nm and the second wavelength is approximately 405 nm.
6 . The scatterometer of claim 1 wherein the wavelength is approximately 200 nm to approximately 475 nm.
7 . The scatterometer of claim 1 wherein the wavelength is approximately 375 nm to approximately 475 nm.
8 . The scatterometer of claim 1 wherein the first wavelength is approximately 244 nm and the second wavelength is approximately 457 nm.
9 . The scatterometer of claim 1 wherein the wavelength is approximately one of 405 nm or 457 nm.
10 . The scatterometer of claim 1 , wherein the computer-operable medium further comprises instructions that cause the computer to acquire data from only selected pixels of the detector having sensitivities above a threshold level.
11 . The scatterometer of claim 1 , further comprising:
a calibration member having a first reflectivity of the wavelength located proximate to a workpiece site; and
a computer operatively coupled to the detector, wherein the computer includes a computer-operable medium containing instructions that determine a reference reflectance using a first detected reflectance from the first calibration member and a second detected reflectance from an area separate from the calibration member.
12 . The scatterometer of claim 11 wherein the calibration member comprises a mirror having a reflectance greater than approximately 95% and capable of reflecting radiation through a range of altitude angles of 0° to 89°, and the second reflectance is from free space.
13 . (canceled)
14 . The scatterometer of claim 1 wherein the first optics assembly comprises a diffuser that produces a diffuse randomized beam.
15 . The scatterometer of claim 1 wherein the first optics assembly comprises an order selector configured to limit the angular range of various diffraction orders.
16 . The scatterometer of claim 1 wherein the scatterometer further comprises a field stop having an aperture and an illumination lens through which the diffused and randomized beam pass.
17 . The scatterometer of claim 1 wherein the object lens assembly comprises a plurality of achromatic lenses.
18 . The scatterometer of claim 1 , further comprising a plurality of optical heads, wherein individual optical heads are suitable for a unique bandwidth of radiation.
19 . The scatterometer of claim 1 , further comprising a reference detector configured to measure changes in the beam from the irradiation source.
20 . The scatterometer of claim 1 wherein the object lens assembly is configured to simultaneously focus the conditioned beam at the object focal plane through a range of incidence angles having (a) altitude angles of 0° to at least about 45° and (b) azimuth angles of 0° to at least about 90°.
21 . The scatterometer of claim 20 wherein the altitude angles are 0° to at least 70° and the azimuth angles are 0° to at least 180°.
22 . The scatterometer of claim 20 wherein the altitude angles are 0° to at least 80° and the azimuth angles are 0° to at least 360°.
23 . The scatterometer of claim 1 , further comprising a polarizing beam splitter in a path of the return radiation between the object lens assembly and the detector to separate the p- and s-polarized components of the return radiation from each other.
24 . The scatterometer of claim 23 , further comprising a single detector to receive both the p- and s-polarized components of the return radiation, and wherein the polarizing beam splitter comprises a cube-type polarizing beam splitter.