Patent Application
20230204422
This application claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2021-0189237, filed on Dec. 28, 2021 in the Korean Intellectual Property Office (KIPO), the contents of which are herein incorporated by reference in their entirety.
Example embodiments relate to an imaging assembly and a spectral imaging ellipsometer including the same. More particularly, example embodiments relate to an imaging assembly for imaging reflected light from a wafer surface and a spectral imaging ellipsometer including the same.
Spectral elliptic polarization analysis technology is a technology that irradiates polarized light to a sample and measures a change in a polarization state of the reflected light. The change in polarization (spectrum) according to the wavelength depends on physical properties and a structure of the sample. The physical properties and structure information of the sample may be extracted and measured using the spectrum obtained through the spectral imaging ellipsometer. The spectral imaging ellipsometer may include an imaging lens optical system including lenses to image the light reflected from the sample. However, there are problems in that a large number of lenses are used in order to satisfy optical performance in a broadband wavelength, so that the transmittance is lowered, the measurement speed is lowered, and chromatic aberration occurs, which causes a focus deviation for each wavelength.
Example embodiments provide an imaging assembly of a broadband high-efficiency spectral imaging ellipsometer that provides improved transmittance and avoids chromatic aberration.
Example embodiments provide a spectral imaging ellipsometer including the imaging assembly.
According to example embodiments, an imaging assembly of a spectral imaging ellipsometer includes an analyzer configured to polarize reflected light reflected from a sample surface, an imaging mirror optical system disposed on an optical path of the reflected light passing through the analyzer and including a first mirror having a concave surface and a second mirror having a convex surface, and a light detector configured to receive light passing through the imaging mirror optical system to collect spectral data. The reflected light is firstly reflected by the first mirror, the firstly reflected light is secondarily reflected by the second mirror and travels toward the first mirror again, and then thirdly reflected by the first mirror to be imaged on a light receiving surface of the light detector.
According to example embodiments, a spectral imaging ellipsometer includes a light irradiator configured to irradiate a polarized light whose direction changes on a sample surface to generate reflected light, an analyzer configured to polarize the reflected light reflected from the sample surface, an imaging mirror optical system disposed on an optical path of the reflected light passing through the analyzer and including a first mirror having a concave surface and a second mirror having a convex surface, a light detector configured to receive light passing through the imaging mirror optical system to collect spectral data, and a controller configured to control operations of the light irradiator and the analyzer. The centers of the radii of curvature of the first mirror and the second mirror are arranged to coincide with one point, and at least three reflections of the reflected light are provided in the first and second mirrors.
According to example embodiments, a spectral imaging elliptic spectrometer may include a light irradiator configured to irradiate light having a polarization component to multiple points on a wafer surface and an imaging assembly configured to receive the reflected light reflected from the wafer to obtain an image according to the polarization state at each of the plurality of points.
The light irradiator may include a monochromator for separating a narrow wavelength band (i.e., a specific spectrum range) from a broadband wavelength, and the image assembly may include an analyzer for polarizing the reflected light, an imaging mirror optical system disposed on an optical path of the reflected light passing through the analyzer and a two-dimensional image sensor as a light detector for receiving the light passing through the mirror optical system to collect the spectral data.
The imaging mirror optical system may be a mirror-based imaging optical system composed of at least two mirrors. When the mirror-based imaging optical system is used, transmittance of the optical system may be increased to improve measurement sensitivity in a narrow wavelength band (i.e., a specific spectrum range) and measurement speed in a broad wavelength band, and the occurrence of chromatic aberration may be reduce to thereby minimize focus deviation for each wavelength.
Example embodiments will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings.
Hereinafter, example embodiments will be explained in detail with reference to the accompanying drawings.
Referring to
In example embodiments, the spectral imaging ellipsometer 10 may be an imaging elliptic spectroscopy apparatus (e.g., spectroscopic elliptic spectrometer) of a surface measurement type that measures multiple points instead of one point on the wafer surface. In addition, the spectral imaging elliptic spectrometer 10 may irradiate the wafer surface with light having a broadband wavelength in order to obtain desired information on a miniaturized semiconductor structure, thickness, physical properties, etc. For this imaging elliptic spectroscopy apparatus, the light irradiator 20 may include a monochromator 23 configured to select and transmit a narrow wavelength band from a wide wavelength band, and a light detector 36 may include a camera as a two-dimensional image sensor.
The wafer W may be a semiconductor substrate. For example, the semiconductor substrate may include or may be formed of silicon, strained silicon (strained Si), silicon alloy, silicon carbide (SiC), silicon germanium (SiGe), silicon germanium carbide (SiGeC), germanium, germanium alloy, gallium arsenide (GaAs), indium arsenide (InAs) and III-V semiconductors, II-VI semiconductors and a combination thereof. In addition, if necessary, the wafer may be an organic plastic substrate rather than the semiconductor substrate.
The wafer W may be supported on the stage 50. The stage 50 may move the wafer W to a specific position during a measurement process. For example, the stage 50 may move the wafer W in a first direction or a second direction perpendicular to the first direction.
As illustrated in
The light source 22 may generate broadband light. For example, the light source 22 may emit visible light. The wavelength band of the light generated by the light source 22 may vary depending on the object to be measured, and may generally have a bandwidth ranging from Ultraviolet (UV) band to Near Infrared (NIR) band. The monochromator 23 may extract light of a specific wavelength from the light generated from the light source 22. For example, the monochromator 23 may extract monochromatic light from broadband light and illuminate the monochromatic light through the illumination assembly 24.
The light emitted from the light source assembly 21 may travel along a path of the incident light Li in the illumination assembly 24. Light emitted from the light source assembly 21 into the illumination assembly 24 may be converted into parallel light by a collimator lens of the illumination optical system 25. An illumination body of the illumination assembly 24 may extend in the same direction as the path of the incident light Li, and the polarizer 26 and the compensator 28 may be fixedly installed in the illumination body. The incident light Li may be irradiated to a measurement area A of the wafer W placed on the stage 50 through the polarizer 26 and the compensator 28.
The polarizer 26 may adjust a polarization direction of the incident light Li. The polarizer 26 may include a rotating part that can adjust the polarization direction, and may rotate at a first angle. The first angle of the polarizer 26 may be maintained to have a constant value. Alternatively, the polarizer 26 may be electrically connected to the controller 40, and the controller 40 may adjust the first angle of the polarizer 26.
The compensator 28 may adjust a phase difference of the incident light Li. The compensator 28 may include a rotating part, and may rotate at a second angle. The compensator 28 may adjust the phase difference of the incident light Li by using the rotating part. The compensator 28 may be electrically connected to the controller 40. The controller 40 may adjust the second angle of the compensator 28. Accordingly, the incident light Li as monochromatic light extracted from the light generated from the light source 22 may be irradiated to the measurement area A on the wafer W, and the reflected light Lr reflected from the wafer W may be collected into an imaging assembly 31 of the detector 30.
The detector 30 may receive the light Lr reflected from the wafer W to detect a two-dimensional image of the sample surface A according to a polarization change. The detector 30 may include an analyzer 32 as a third polarizer provided in the imaging assembly 31, an imaging mirror optical system 34 and the light detector 36. The analyzer 32, the imaging mirror optical system 34 and the light detector 36 may be fixedly installed in an emitting body of the imaging assembly 31.
The analyzer 32 may adjust a polarization direction of the reflected light Lr reflected from the wafer W. The analyzer 32 may include a rotating part, and may rotate at a third angle. The analyzer 32 may be electrically connected to the controller 40. The controller 40 may adjust the third angle of the analyzer 32. The analyzer 32 may transmit only a linearly polarized light component corresponding to the third angle.
The imaging mirror optical system 34 may image the reflected light Lr passing through the analyzer 32 on a light receiving surface of the light detector 36. The imaging mirror optical system 34 may have an object plane and an imaging plane as conjugate planes. The object plane of the imaging mirror optical system 34 may be positioned on the wafer surface, and the imaging plane of the imaging mirror optical system 34 may be positioned on the light receiving plane of the light detector 36.
The imaging mirror optical system 34 may have a relatively long working distance WD. The analyzer 32 may be positioned between the object plane and the imaging mirror optical system 34. The rotating part of the analyzer 32 may include a hollow type motor for adjusting the third angle. In this case, in consideration of a size of the hollow type motor, the imaging mirror optical system 34 may be designed to have a relatively long working distance.
In example embodiments, the imaging mirror optical system 34 may be a mirror-based imaging optical system including at least two mirrors. In the case of an existing lens-based optical system, since a large number (eg, 8 to 16) of lenses are used to satisfy optical performance of a broadband wavelength, transmittance may be reduced and chromatic aberration may occur. However, when the mirror-based imaging optical system is used, it may be possible to minimize chromatic aberration and secure transmittance in a specific wavelength region.
The light detector 36 may detect a spectral image from the reflected light Lr passing through the imaging mirror optical system 34. For example, the light detector 36 may detect a spectral image for a particular wavelength. The light detector 36 may include a camera as a two-dimensional image sensor capable of detecting the reflected light Lr.
The controller 40 may be connected to the monochromator 23, the polarizer 26, the compensator 28, the analyzer 32, the photo detector 36 and the processor 42 to control operations thereof. The controller 40 may receive a Polarizer, Compensator and Analyzer (PCA) angle set from the processor 42. The PCA angle set may include a first angle that corresponds to the rotation angle of the polarizer 26, a second angle that corresponds to the rotation angle of the compensator 28, and a third angle that corresponds to the rotation angle of the analyzer 32. The controller 40 may change the first to third angles by controlling the polarizer 26, the compensator 28 and the analyzer 32 according to the received PCA angle set.
The controller 40 may also generate a PCA angle set by changing the first to third angles according to a preset value. For example, while the first and second angles of the polarizer 26 and the compensator 28 are maintained at constant values, the third angle of analyzer 32 may be changed to generate a plurality of PCA angle sets.
The processor 42 may receive spectral images (see
In addition, the processor 42 may generate a spectrum 70 (see
The processor 42 may be a central processing unit (CPU), a microprocessor, an application processor (AP), or any processing device similar thereto. The processor 42 may execute software or instructions that perform functionality of data analysis or optical critical dimension (OCD) operations including a spectrum recognition algorithm. The optical critical dimension operations may extract physical parameters of the inspection area of the wafer W from spectral data. The spectrum recognition algorithm of the optical critical dimension operations may use a Rigorous coupled-wave analysis (RCWA) algorithm. The rigorous coupled-wave analysis algorithm may be usefully used to explain diffraction or reflection of electromagnetic waves from a surface of a grating structure. However, it may not be limited thereto, and the processor 42 may apply a spectral image ellipse analysis technique, a multi-point high-speed measurement spectral ellipse analysis technique, etc. to monitor a profile change trend in the wafer W. In addition, the processor 42 may perform a variable separation algorithm such as a correlation analysis algorithm for extracting a profile change value from a plurality of spectra, a principal component analysis algorithm, a rank test, etc.
Measurement variables that can be measured by the spectral imaging ellipsometer 10 may include a critical dimension, a height of a pattern, a recess, an overlay, a defect, etc.
In the spectral imaging ellipsometer 10, when light having a polarization component is irradiated on the sample W to be inspected, reflectivity and phase values are changed according to the polarization directions (p-wave, s-wave). The spectral imaging ellipsometer 10 may measure electromagnetic field values of p-wave and s-wave while changing a combination of the PCA angle sets. The first angle of the polarizer 26 may determine the polarization direction of the light incident on the sample, and the second angle of the compensator 28 may determine the phase difference between the p-wave and the s-wave. The third angle of the analyzer 32 may determine the polarization direction of the light incident on the light detector 36 after being reflected from the sample.
The set of PCA angles may be selected depending on the measurement parameters. For example, it may be possible to select a different set of PCA angles for each wavelength λ. The PCA angle set may be selected randomly, in a predetermined order, or using a PCA angle set selection algorithm.
As illustrated in
As illustrated in
The PCAR spectral matrix 60 may be named I(x, y, λ) as coordinates. The spectral image 20 may be referred to as a spectral domain. The PCAR spectral matrix 60 may include the spectral images with spatial coordinates of each pixel P captured by a Field Of View (FOV) of a light sensor included in the light detector 36, and a spectrum of each pixel P according to a wavelength. That is, the PCAR spectral matrix 60 may include a plurality of spectral images and a spectrum representing a change in the light intensity according to wavelengths in each pixel P of the spectral images.
As illustrated in
Hereinafter, the imaging mirror optical system 34 will be explained in detail.
Referring to
In example embodiments, the imaging mirror optical system 34 may image the reflected light Lr passing through the analyzer 32 on a light receiving surface of the light detector 36. The imaging mirror optical system 34 may have an object plane and an imaging plane as conjugate planes. The object plane of the imaging mirror optical system 34 may be positioned on the wafer surface A, and the imaging plane of the imaging mirror optical system 34 may be positioned on the light receiving plane of the light detector 36.
As illustrated in
The object plane may be positioned at a first conjugation point, and the imaging plane may be positioned at a second conjugation point. That is, the reflected light Lr from the first conjugate point may be incident and primarily reflected to the first mirror 100 of the imaging mirror optical system 34, and the primarily reflected light may be may be secondary reflected by the second mirror 110 and proceed toward the first mirror again, and then, may be thirdly reflected by the first mirror 100 and travel toward the second conjugate position. A reference axis SA of the optical system may be orthogonal to a plane passing through the point P, the first conjugation point and the second conjugation point.
The reflected light Lr reflected from the wafer surface A may pass through the analyzer 32, and the reflected light Lr that has passed through the analyzer 32 may impinge on a first portion 102 of the first mirror 100. The reflected light Lr passing through the analyzer 32 may be incident off-axis on the first portion 102 of the first mirror 100. The first portion 102 of the first mirror 100 may firstly reflect the reflected light to be directed toward the second mirror 110. The second mirror 110 may secondary reflect the reflected light to be directed toward a second portion 104 of the first mirror 100. The second portion 104 of the first mirror 100 may thirdly reflect the reflected light, and the thirdly reflected light Lc from the second portion 104 of the first mirror 100 may be focused on the light receiving surface of the light detector 36. The light Lc thirdly reflected from the second portion 104 of the first mirror 100 may be emitted off-axis. The first and second portions 102 and 104 may partially overlap.
In example embodiments, the imaging mirror optical system 34 may further include a third mirror 120. The third mirror 120 may be a plane mirror. The third mirror 120 may deflect the light Lc reflected from the second portion 104 of the first mirror 100 toward the light detector 36. The third mirror 120 may redirect the light Lc reflected from the second portion 104 of the first mirror 100 in order to change a position of the light detector 36.
As described above, the imaging mirror optical system 34 may be the mirror-based imaging optical system including at least two mirrors 100 and 110. Since it is composed of reflective mirrors, it may be possible to improve the transmittance of the optical system to improve measurement sensitivity in a narrow wavelength band (i.e., a specific spectrum range) and a measurement speed in a broad wavelength band, and to minimize the focus deviation for each wavelength by reducing the occurrence of chromatic aberration.
Referring to
In example embodiments, the imaging mirror optical system 34 may further include the compensation lens 130 configured to compensate for chromatic aberration. The compensation lens 130 may be disposed on a path of the light Lc thirdly reflected from the first mirror 100.
When the analyzer 32 includes a glass substrate or a crystal-type polarizer, chromatic aberration may occur in the reflected light passing through the analyzer 32. The compensation lens 130 may compensate for the chromatic aberration generated by the analyzer 32.
Since the analyzer 32 includes a very thin substrate, the number of lenses of the compensation lens 130 for compensating for chromatic aberration may be very small. Accordingly, the decrease in transmittance by the compensation lens may be insignificant.
Referring to
In example embodiments, the imaging mirror optical system 34 may further include the fourth mirror 102 configured to redirect reflected light Lr passing through an analyzer 32. The fourth mirror 102 may be a plane mirror. The fourth mirror 102 may be configured to deflect the reflected light Lr passing through the analyzer 32 toward the first mirror 100 in order to change positions of the first to third mirrors 100, 110 and 120.
Referring to
In example embodiments, the imaging mirror optical system 34 of the imaging assembly of the spectral imaging ellipsometer may further include the second compensation lens 132 configured to compensate for chromatic aberration. The second compensation lens 132 may be disposed on a path of reflected light Lr reflected from the fourth mirror 102. The second compensating lens 132 may compensate for the chromatic aberration caused by the analyzer 32.
Referring to
In example embodiments, the analyzer 32 may be a reflective polarizer. The analyzer 32 may have high reflectivity for broadband wavelengths. Since the analyzer 32 is a reflection type polarizer (i.e., a reflective polarizer), chromatic aberration may not occur. Accordingly, since all optical elements are constituted by mirrors, it may possible to constitute an imaging optical system having no chromatic aberration.
The above spectral imaging ellipsometer may be used to manufacture a semiconductor package including semiconductor devices such as logic devices or memory devices. The semiconductor package may include logic devices such as central processing units (CPUs), main processing units (MPUs), or application processors (APs), or the like, and volatile memory devices such as DRAM devices, HBM devices, or non-volatile memory devices such as flash memory devices, PRAM devices, MRAM devices, ReRAM devices, or the like.
The foregoing is illustrative of example embodiments and is not to be construed as limiting thereof. Although a few example embodiments have been described, those skilled in the art will readily appreciate that modifications are possible in example embodiments without materially departing from the novel teachings and advantages of the present invention. Accordingly, all such modifications are intended to be included within the scope of example embodiments as defined in the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2021-0189237 | Dec 2021 | KR | national |
