CN103575661A

CN103575661A - Optical measurement system with vertical and oblique incidence measurement functions

Info

Publication number: CN103575661A
Application number: CN201210281800.6A
Authority: CN
Inventors: 李国光; 赵江艳; 刘涛; 吴文镜
Original assignee: BEI OPITCS TECHNOLOGY Co Ltd
Current assignee: BEI OPITCS TECHNOLOGY Co Ltd
Priority date: 2012-08-09
Filing date: 2012-08-09
Publication date: 2014-02-12

Abstract

The application discloses an optical measurement system with vertical and oblique incidence measurement functions. The optical measurement system comprises a light source, an optical fiber bundle, a refection focusing system, a first light focusing unit, a second light focusing unit, a third light focusing unit, a fourth light focusing unit, a first polarizer, a second polarizer and an optical spectrometer. The optical measurement system provided by the application comprises an oblique incidence measurement device and a vertical incidence measurement device; the measurement accuracy of a sample is improved.

Description

Optical measurement system comprising normal incidence and oblique incidence

Technical Field

The present application relates to the field of optical technology, and more particularly, to an optical measurement system including normal incidence and oblique incidence.

Background

With the rapid development of the semiconductor industry, it becomes very important to accurately measure the Critical Dimension (Critical Dimension), the spatial morphology and the material characteristics of a three-dimensional structure formed by a single-layer or multi-layer thin film on a wafer by using an optical measurement technology. In order for the measurement results to be effective, the measurement system used should be capable of measuring the film thickness and/or film composition with high accuracy. Among the well-known non-destructive detection techniques are photometry and ellipsometry, which obtain reflectance data by measuring the electromagnetic radiation reflected by a sample. In spectroscopic ellipsometers, incident light having a certain polarization state is reflected by a sample (typically at a large incident angle), and the properties of the sample can be obtained by analyzing the polarization state of the reflected light. Since the incident light contains a multi-frequency composition, a spectral profile can be obtained. In particular, the polarization state of the incident light is time-dependent (passing the incident light through a rotating polarizer), or the method of analyzing the reflected light is time-dependent (passing the reflected light through a rotating analyzer).

Generally, a semiconductor thin film needs to be measured to obtain the thickness d, the refractive index n and the extinction coefficient k of the thin film. While ellipsometry can only measure two ellipsometric parameters, namely: ψ and Δ, the optical parameters of the sample film cannot be accurately given based on only two ellipsometric equations (Vol.59, No.4 in Physics), and can be solved only by a computer fitting method. In order to increase the measurement accuracy and obtain additional information about the target sample, researchers in this field have proposed a Variable Angle Spectroscopic Ellipsometer (VASE). Theoretically, the measurement device can give an ellipsometry equation under a plurality of angles, and the measurement accuracy can be increased to a certain extent. However, in practice this is often not very effective, as described in Critical Reviews of Optical Science and Technology Volume CR72, pages 14-16, where the film thickness was found to be 330-

Can obtain a substantially identical fitted curve. For a hypothetical film thickness, the optical constants of the film will change in a compensatory manner to give an equally good fit, since the film thickness and the optical constants of the film material are often correlated in the fit. It is difficult to precisely measure the film thickness and the optical constants only by the elliptical polarization method. In order to accurately measure a sample, for example, the thickness and optical parameters of a thin film of the sample, a plurality of optical measuring devices are generally integrated into a complex optical measuring system, i.e., the sample is measured simultaneously by two optical measuring systems at normal incidence and oblique incidence (see U.S. Pat. nos. US5608526 and US 6713753). Generally, a measurement system integrating a plurality of optical measurement devices is complicated, requires a plurality of broadband light sources and detection devices, and is expensive. If, as described in US6713753, a beam splitter is used to couple an optical path, although the requirements of reducing light sources and reducing cost can also be met, in practical applications, optical path adjustment is not easy to implement, and when the beam splitter is used to perform splitting and combining, the light transmission efficiency is low, for a light beam with vertical incidence, at least two times of passing through the beam splitter is required, the theoretical light transmission efficiency is only 25% at most, and a light beam with oblique incidence also needs to pass through a primary beam splitter, which reduces the accuracy of system measurement, so that the optical measurement system including vertical incidence and oblique incidence is not widely popularized in practical applications.

On the other hand, it is well known to those skilled in the art that it is advantageous to focus the broadband probe beam to a relatively small size spot on the sample surface, since the small size allows measurement of the microstructure pattern and the broadband probe beam improves the measurement accuracy. In this case, a key element in the optical measurement is to focus the broadband probe beam on the surface of the sample, and when a lens is used, chromatic aberration is usually generated, so that the light focusing positions of different wavelengths are different, and the error is increased. In the achromatic lens, although chromatic aberration caused by the refractive index of the lens is reduced within a certain range, the chromatic aberration cannot be completely eliminated, and in addition, the structure of the lens is complex and the cost is high. There are also proposals in the art to use aspheric mirrors such as toroidal mirrors, off-axis parabolic mirrors, which, although they use reflective focusing, achieve achromatic color over a broad spectral wavelength range and have high reflectivity over a broad wavelength range, aspheric mirrors are complex to process and expensive to manufacture. Although paraxial parallel light parallel to the main shaft of the spherical reflector can be converged at the focal point of the spherical reflector, the spherical reflector which is simple to process and low in price is inconvenient to focus because the focal point of the spherical reflector is positioned on the main shaft. In practical applications, the incident light is usually slightly deviated from the principal axis, but because the focal point adjustment range is very limited, and the size of a general sample is usually large, several hundreds of millimeters, the direct use of the sample to focus the broadband light beam on the surface of the sample is not easy to realize.

Disclosure of Invention

The technical problem that this application will be solved provides a simple structure, measures the accuracy, and the optical measurement system of vertical incidence and oblique incidence that the integrated level is high.

In order to solve the above technical problem, the present application provides an optical measurement system, including a light source, a spectroscopic ellipsometer, and a spectrophotometer; the light source emits a first detection light beam and a second detection light beam; the spectroscopic ellipsometer measures the polarization change of the first detection beam after being reflected by the sample; the spectrophotometer measures the light intensity change of a second detection light beam which is vertically or nearly vertically incident to the surface of the sample after being reflected by the sample.

The application provides an optical measurement system contains two measuring device of spectrum ellipsometer and spectrophotometer, has improved the precision of sample measurement, and simultaneously, this optical measurement system carries out the beam split through the optical fiber bundle and closes light, can make two sets of optical measurement device sharing light source and spectrometer, has greatly reduced the cost of system, and simultaneously, relative spectrometer uses the system light-passing efficiency of optical fiber bundle coupling higher. In addition, the spectrophotometer in the optical measurement system adopts the spherical reflector which is low in price and simple to process for focusing, so that the broadband chromatic aberration-free effect can be achieved, and the equipment cost is not increased.

Drawings

Fig. 1 is a schematic structural diagram of a focusing system provided in an embodiment of the present application;

FIG. 2 is a schematic diagram of the optical achromatic focusing of the present application;

FIG. 3 is a schematic structural diagram of a W-shaped optical fiber bundle provided in the present application;

FIG. 4a is a schematic diagram of the arrangement of the I sub-fiber and the II sub-fiber at the port 2 of the fiber bundle in FIG. 3;

FIG. 4b is a schematic diagram of the arrangement of the II sub-fiber and the III sub-fiber at the port 3 of the fiber bundle in FIG. 3;

FIG. 4c is a schematic diagram of the arrangement of the III-th sub-fiber and the IV-th sub-fiber at the port 4 of the fiber bundle in FIG. 3;

FIG. 5 is a schematic optical path diagram of a light beam entering a III-th sub-fiber provided by the present application;

FIG. 6 is a structural diagram of a periodic shallow trench of monocrystalline silicon.

FIG. 7 is a spectrum of the amplitude ratio of the TM and TE reflectivities and the phase difference between the TM and TE.

FIG. 8 is a schematic diagram of an optical measurement system provided herein;

fig. 9a is another schematic structural diagram of the optical measurement system provided in the present application.

FIG. 9b shows a preferred arrangement of the III-, IV-and V-sub-fibers of the bundle used in FIG. 9a at port 4.

Detailed Description

The method and the device realize the chromatic aberration-free focusing of the detection light beam through the cheap spherical reflector. As shown in fig. 1, the focusing system is composed of two spherical mirrors and one plane mirror. Preferably, the curved surface mirror SPR1 and the curved surface mirror SPR2 have the same curvature radius, the point light source S0 is located at the focal point of the spherical surface mirror SPR1, the divergent light beam emitted from the point light source is reflected by the spherical surface mirror SPR1, and forms a parallel light beam after being deflected by an angle α, the parallel light beam is incident on the plane mirror M and then deflected by an angle β, and then is incident on the curved surface mirror SPR2, and the parallel light beam is deflected by the angle α by the curved surface mirror SPR2, and then is vertically incident and focused on the surface of the sample. The normal lines of the curved mirrors SPR1 and SPR2 and the plane mirror M are in the same plane. As can be seen from fig. 1, with this specially designed structure, the incident beam deflected at a small angle on the spherical mirror can be made to be incident perpendicularly to the surface of the sample, and under the precondition that a proper working distance is obtained, the optical path is not blocked by each optical element. The deflection angle of the main beam of the incident beam on the curved mirror SPR2 may be different from that of the curved mirror SPR 1.

As shown in fig. 2, if the angle between the main beam of the incident probe beam and the horizontal plane is t, it can be known from geometrical knowledge that the main beam of the converging beam reflected by the curved mirror SPR2 should be perpendicular to the surface of the sample: 2 α + β -t =90 °.

For the spherical reflector, the larger the angle of the parallel incident light direction deviating from the main axis is, the poorer the focusing effect is, so the deflection angle alpha of the light beam is not too large, in the application, the incident angle of the light beam on the spherical reflector is preferably 5-15 degrees, so that a system formed by the two spherical reflectors and the plane reflector can focus the detection light beam to a proper light spot size, and meanwhile, a proper working distance is obtained. Further, as can be seen from 2 α + β -t =90 °, β =90 ° -2 α + t, i.e., the deflection angle β of the incident light on the above-mentioned plane mirror M can be determined according to the direction of the incident light beam and the set α angle.

If the position of the three-sided mirror is fixed and only the incident direction of the incident beam is changed, for example, the included angle between the incident beam and the horizontal plane is t + Δ t, the deflection angle of the beam on the curved mirror SPR1 is α +2 Δ t, the deflection angle on M is β -2 Δ t, the deflection angle on the curved mirror SPR2 is α -2 Δ t, and it can be known from the above formula that 2 α '+ β' -t =90 ° +2 Δ t, that is, the included angle of the main beam of the convergent beam reflected by the curved mirror SPR2 from the vertical direction is 2 Δ t. Therefore, as is understood from the above-mentioned conclusion, if the incident light beam incident on the sample SA deviates from the vertical direction by 2 Δ t, the direction of the convergent light beam reflected by the SPR2 can be adjusted to be incident again perpendicularly to the sample surface by changing the incident direction of the main light beam of the divergent light beam incident on the SPR1 by Δ t. The focusing system of the present application can change the emitting direction of the emergent light by fine-tuning the direction of the incident light.

The spherical reflector utilizes reflection to focus, is irrelevant to the refractive index of a material, and can achieve the effect of no chromatic aberration of a broadband.

The optical beam coupling in the optical measurement system of vertical incidence and oblique incidence can be realized through the optical fiber bundle, the structure that two measurement devices share one light source and the spectrometer is achieved, and the effect of reducing the system cost is achieved while the measurement accuracy is improved. The "W" shaped fiber bundle used for beam coupling in the present application is described below.

As shown in fig. 3, the optical fiber bundle is formed by optical fiber bundle sub-fibers I, II, III, iv and optical

fiber bundle ports

1, 2, 3, 4, 5, which are shaped like a W-shape, that is, each two optical fiber bundle sub-fibers share one port, which is as follows: the optical fiber bundle sub-fiber I and the optical fiber bundle sub-fiber II share the optical fiber bundle port 2; the other end of the optical fiber bundle sub-fiber II and the optical fiber bundle sub-fiber III share an optical fiber bundle port 3, the other end of the optical fiber bundle sub-fiber III and the optical fiber bundle sub-fiber IV share an optical fiber bundle port 4, in addition, the other end of the optical fiber bundle sub-fiber I is connected with the optical fiber bundle port 1, and the other end of the optical fiber bundle sub-fiber IV is connected with the optical fiber bundle port 5. Wherein, the length of each segment of the optical fiber sub-fiber is about 1 m.

The port of the W-shaped optical fiber bundle consists of a sleeve and an optical fiber, and the optical fiber is arranged in the sleeve.

Preferably, the bundle sub-fibers I, II, iv comprise only one fiber and the bundle sub-fiber III comprises six fibers. To achieve higher coupling efficiency, the fiber ports may be arranged as follows:

at the port 2, the cross sections of the sub-optical fibers I and II of the optical fiber bundle form a side-by-side close-packed structure, as shown in FIG. 4 a;

at the port 3, the optical fiber bundle sub-fiber II is located at the central part, and six optical fibers constituting the optical fiber bundle sub-fiber III are symmetrically arranged around the central part to form a regular hexagon, as shown in fig. 4 b;

at the port 4, six optical fibers constituting the optical fiber bundle sub-fiber III and one optical fiber constituting the optical fiber bundle sub-fiber iv are arranged side by side in a straight line, and the optical fiber bundle sub-fiber iv is located in the middle, and the six optical fibers constituting the optical fiber bundle sub-fiber III are divided into two parts, and symmetrically distributed on both sides thereof, as shown in fig. 4c, such a shape can be matched with a slit entrance of a spectrometer, so that both beams of reflected light can enter the spectrometer with high efficiency.

As can be seen from the above description, if an incident beam enters the fiber bundle from the fiber bundle port 2, the beam passes through the fiber bundle sub-fibers I and II and then is split into two beams, which are respectively emitted from the

fiber bundle ports

1 and 3 and can be used as probe beams of different optical measurement systems, for example, if the beam emitted from the fiber bundle port 1 is used as a probe beam of an obliquely incident spectroscopic ellipsometer and the beam emitted from the fiber bundle port 3 is used as a probe beam of a spectrophotometer which is perpendicularly incident on a sample surface to measure reflectivity, a reflected beam from the sample surface will return to the port 3 along the original path, if the probe beam reflected by the sample by the vertically incident sample surface enters the fiber bundle sub-fiber III from the port 3 and the probe beam reflected by the sample by the spectroscopic ellipsometer is simultaneously entered into the fiber bundle sub-fiber iv from the port 5, two probe beams respectively passing through different optical measurement devices and containing optical characteristic information of the sample material are emitted from the same optical fiber beam port 4, and the same spectrometer can detect different probe beams only by aligning the spectrometer with the optical fiber beam port 4. In order to make the probe beam vertically incident on the sample surface and reflected by the sample surface enter the optical fiber bundle sub-fiber III with high efficiency when returning to the optical fiber bundle port 3, the focusing lens L before fine-tuning the sample or the optical fiber bundle port 3 is generally adjusted to slightly defocus the beam focused on the sample surface, and the optical path of the probe beam of the spectrophotometer returning along the original path enters the optical fiber outside the port 3, i.e. the optical fiber bundle sub-fiber III, is shown in fig. 5, and the specific implementation method can be referred to chinese patent application 201110005913.9. In the invention, because the off-axis use of the spherical reflector (even if the incident light direction deviates from the main axis) causes the light spot focused on the sample to have spherical aberration, and the light beam reflected by the sample has spherical aberration when returning to the optical fiber port 3 of the W-shaped optical fiber, the spherical aberration can be just utilized, so that most of the reflected light beam on the surface of the sample can enter the sub-optical fiber III through the optical fiber port 3 of the W-shaped optical fiber rather than returning to the optical fiber sub-optical fiber II along the original path, the theoretical light transmission efficiency of the vertical incidence part can reach more than 50 percent, and the oblique incidence part does not pass through the optical splitter, so that the light transmission efficiency is basically not lost in the light beam coupling process.

The optical fiber bundle sub-fiber described above may be a bundle of a plurality of optical fibers arranged closely. Furthermore, if a further sub-fibre is coupled at port 4, this fibre bundle can be used for the reception of the probe beam by other optical measurement devices in the system, for example the transmission beam through the sample in a spectrophotometer.

The use of fiber bundles to couple multiple beams of light allows for easier calibration of the optical path compared to a beam splitter because the separate ends of the fiber bundles are independent of each other. For example, if two beams of light need to be combined, it can be achieved by only aligning the

fiber bundle ports

3 and 5 in fig. 3 with the two beams of light, respectively.

Elliptical polarization measurement method:

the spectroscopic ellipsometer in this application may be a polarizer-sample-analyzer (PSA) configuration ellipsometer. The Fourier coefficient can be calculated by rotating the polarizer P and the fixed analyzer A, or rotating the analyzer A and the fixed polarizer P, or rotating the polarizer P and the analyzer A according to a certain frequency ratio, and then the measured sample is calculated by comparing with a numerical simulation result and numerical regression. The principle OF measurement can be briefly described in the book HANDBOOK OF ELLIPSOMETRY, Harland G.Tompkins, 2005, Spectroscopic Ellippage protocols and Applications, Hiroyuki Fujiwara, 2007 and the principle formula described in the document Liang-Yao Chen, Xing-Wei Feng, Yi Su, Hong-Zhou Ma, and You-Hua Qian, "Design OF a scanning ellipsometer by synchronization OF the polar analyzer and analyzer," applied. Opt.33, 1299-:

the sample Jones matrix can be expressed as

From L_out＝AR(A)J_sR(-P)PL_inIt is possible to obtain,

[\begin{matrix} E_{A} \\ 0 \end{matrix}] = E_{in} [\begin{matrix} 1 & 0 \\ 0 & 0 \end{matrix}] [\begin{matrix} \cos A & \sin A \\ - \sin A & \cos A \end{matrix}] [\begin{matrix} r_{pp} & r_{ps} \\ r_{sp} & r_{ss} \end{matrix}] [\begin{matrix} \cos P & - \sin P \\ \sin P & \cos P \end{matrix}] [\begin{matrix} 1 & 0 \\ 0 & 0 \end{matrix}] [\begin{matrix} 1 \\ 0 \end{matrix}] .

ignoring the proportionality constant, one can derive:

E_A＝(ρ_pp+ρ_pstanP)cosA+(ρ_sp+tanP)sinA，

detected light intensity:

I＝|E_A|²＝I_O(1+αcos2A+βsin2A)

wherein alpha and beta are Fourier coefficients of the light intensity I, and experimental values can be obtained through calculation. Corresponding to the expression as

When r is_ps=r_sp=0, i.e. ρ_ps=ρ_spWith =0, the calculation formula for the usual isotropic film sample can be obtained:

wherein tan ψ is r_pp、r_ssAmplitude of the ratio, Δ being r_pp、r_ssThe phase difference of the ratio.

By ellipsometry, the spectral lines of two fourier coefficients α and β can be calculated, which are directly related to the ellipsometric parameters Ψ and Δ of the sample.

The detailed operation of ellipsometry consists of the following three main steps: 1) due to the presence of the rotating system, the system needs to be calibrated to exclude measured light intensity deviations caused by the rotation of the polarizer. The calibration method is to use a standard uniform sample, such as a silicon wafer, to measure the light intensity of the uniform sample at different polarizer angles; theoretically, the light intensities should be identical; the variation relation of the light intensity and the angle can be used as a reference value, and the light intensity influence of the system at different polarizer angles is removed through the ratio. Specifically, the reflected light intensity spectrum of the silicon wafer at each angle is recorded every time the polarizer rotates by 1 degree, and all 360-degree scanning is completed, and the data are stored as reference values. 2) During measurement, the reflected light intensity of each angle is compared with a reference value, and a relative true value of the light intensity at each angle is obtained. 3) And obtaining a result through mathematical model calculation and curve regression fitting.

Taking the one-dimensional grating as shown in fig. 6 as an example, when the measurement parameters phi =0 and theta is 60, i.e., the angle r is set at this point_ps=r_spThe amplitude ratio and phase difference of =0 are shown in fig. 7.

The spectroscopic ellipsometer of the present application may also be an ellipsometer comprising a phase compensator, constituting a polarizer-compensator-sample-analyzer (PCSA) structure or a polarizer-sample-compensator-analyzer (PSCA) structure. The spectrum obtained by measurement can be obtained by rotating the phase compensator C, fixing the polarizer P and the analyzer A or rotating the analyzer A, fixing the polarizer P and the phase compensator C, and the Fourier coefficient is obtained by calculation, so that the ellipsometry parameters psi and delta of the sample are obtained, and the sample is measured by comparison with a numerical simulation result and numerical regression calculation. The following is a brief description of the case of a Rotary Compensator (RCE) under the PSCA architecture:

L_out＝AR(A)R(-C)CR(C)J_sR(-P)PL_in，

namely: assume that the system P =45 ° and a =0 °, i.e.:

it can be derived that when δ =90 degrees:

detected light intensity:

I＝|E_A|²＝I_O(2-cos2 ψ +2sin2 ψ sin Δ sin2C-cos2 ψ cos4C + sin2 ψ cos Δ sin4C)/2 in this case, the stokes vector corresponding expression after the probe light is reflected by the sample is:

S₀＝1

S₁＝-cos2ψ

S₂＝sin2ψcosΔ

S₃＝-sin2ψsinΔ

detected light intensity expressed in stokes vector:

I = I_{0} (1 + \frac{S_{1}}{2} - S_{3} \sin 2 C + \frac{S_{1} \cos 4 C}{2} + \frac{S_{2} \sin 4 C}{2})

by ellipsometry, S can be calculated from experimental values₁、S₂、S₃Three fourier coefficient lines that are directly related to the ellipsometric parameters Ψ and Δ of the sample, and that allow the specific angle of Δ to be calculated, increasing the accuracy of the measurement compared to the ellipsometer described above that does not include a compensator.

Because the reflectivity R and the transmissivity T of the sample are determined by the film thickness, the optical constant, the three-dimensional shape and other characteristics, the reflectivity R and/or the transmissivity T of the sample are measured by the vertical incidence spectrophotometer while the ellipsometry parameters of the sample are measured by the oblique incidence spectroscopic ellipsometer, so that more related information of the sample can be provided, the calculation and the regression fitting of a mathematical model are facilitated, and more accurate measurement results are obtained. Or more Fourier coefficient spectral lines can be obtained through an optical measurement system comprising the oblique incidence spectroscopic ellipsometer and the vertical incidence spectroscopic ellipsometer, so that a more accurate measurement result can be obtained.

After the ellipsometric parameters, as well as the reflectivity and/or transmissivity of the sample are measured, the optical constants, film thickness, and/or Critical Dimension (CD) or three-dimensional morphology of the sample for analysis of periodic structures can be calculated by calculating spectral lines and curve regression fits through mathematical models.

Example one

An optical measurement system of a first embodiment of the present application is shown in fig. 8. The optical parameter measuring system comprises a light source SO, a curved surface reflector CM, an optical fiber bundle FB, a spherical reflector SPR1, an SPR2, a plane reflector M, an achromatic lens L1, an L2, an L3, an L4, a polarizer P, an analyzer A and a spectrometer SP, wherein the components form two different optical measuring devices of an oblique incidence spectrum ellipsometer SPE and a vertical incidence spectrophotometer SPM.

The light beam emitted by the broadband point light source SO enters a port 2 of the W-shaped optical fiber bundle after passing through a curved surface reflector CM for focusing, is divided into two beams of light by an optical fiber bundle sub-optical fiber I and an optical fiber bundle sub-optical fiber II, and is respectively used as a detection light beam of an optical measuring device spectrum ellipsometer SPM and a spectrophotometer SPE. The optical paths of the two probe beams are described below:

(1) enters the optical fiber bundle sub-optical fiber II, the light beam emitted from the optical fiber bundle port 3 is used as a probe light beam in the spectrophotometer, the probe light beam is incident to the spherical reflector SPR1, forms a parallel light beam after being reflected by the spherical reflector SPR1, and deflects, the parallel light beam is incident to the plane reflector M, deflects once again and then is incident to the spherical reflector SPR2, the spherical reflector deflects the parallel light beam by a certain angle, the light reflected by the spherical reflector is a convergent light beam with the main light vertical to the sample, the convergent light beam is vertically incident and focused on the O point on the surface of the sample, the reflected light on the surface of the sample sequentially passes through the spherical reflector SPR2, the plane mirror M and the spherical reflector SPR1 to form a convergent light beam, enters the optical fiber bundle sub-optical fiber III through the optical fiber bundle port 3, is transmitted by the optical fiber bundle sub-optical fiber III, and is emitted from the optical fiber bundle port 4, and then into the spectrophotometry SP.

(2) The light beam emitted from the optical fiber bundle port 1 enters the optical fiber bundle sub-fiber I as the probe light beam of the spectroscopic ellipsometer, the light beam is incident to the achromatic lens L1, the optical fiber port 1 is located at the focal point of the achromatic lens L1, the divergent light beam passes through the lens L1 and becomes a parallel light beam, the parallel light beam passes through the polarizer P and is incident on the achromatic lens L2, and the achromatic lens L2 converges the parallel light beam and then enters and focuses the sample surface at a large incident angle (for example, 70 degrees). The reflected light on the sample surface sequentially passes through an achromatic lens L3, an analyzer A and an achromatic lens L4, enters an optical fiber bundle sub-fiber IV through an optical fiber bundle port 5, then exits from an optical fiber bundle port 4, and enters a spectrometer SP.

The spectrometer SP is connected with a processor or a computer, and the signals detected by the spectrometer SP are analyzed, so that the thickness, the optical parameters, the three-dimensional morphology and other characteristics of the sample film are calculated through a curve fitting process of numerical value regression.

In this embodiment, although chromatic aberration is not caused by off-axis use (the incident light direction deviates from the main axis) of the spherical mirror in the vertical incidence optical system, a spot focused on a sample has spherical aberration, in this example, the spherical aberration is just utilized, so that most of the reflected light beams on the surface of the sample can enter the sub-optical fiber III through the W-shaped optical fiber beam port 3, rather than return to the optical fiber beam sub-optical fiber II along the original path, and compared with the use of a spectrometer in the prior art, the optical transmission efficiency is improved.

Embodiments of the present application also include an adjustable sample stage for holding a sample, examples of which include sample stages in X-Y-Z-Theta or R-Theta-Z coordinates. In the semiconductor industry, the size of a sample is typically an 8 inch (200 mm) or 12 inch (300 mm) diameter wafer. In the flat panel display industry, samples typically have dimensions of 1 meter or more. For wafers, the surface may not be flat due to thin film layer stress on the wafer, and the like. For large scale samples, the sample surface may be distorted, or the sample platform may not be flat. Therefore, when a sample is inspected, each measurement point can be refocused in order to achieve high-precision measurement and ensure rapid measurement of the yield of a semiconductor production line.

In the actual measurement process, in order to accurately focus the probe beam in the SPE and the probe beam in the SPM on the sample to the same point, the measurement can be performed by moving the sample platform, that is, after the experimental data is obtained by the measurement of the spel, the sample platform is moved to align the probe beam in the SPM to the same point on the sample.

Preferably, this embodiment may further include a phase compensator, as shown in fig. 8, the compensator C may be located between the polarizer P and the analyzer a in the optical path of the SPE of the spectroscopic ellipsometer, and the spectroscopic ellipsometer of this application is equivalent to an ellipsometer with a polarizer-compensator-sample-analyzer (PCSA) or polarizer-sample-compensator-analyzer (PSCA) structure. Under the structure, 1) the PSCA is formed by rotating the analyzer A, fixing the polarizer P and the compensator C_ROr PCSA_RMeasurement mode, 2) forming PSC by rotating compensator C, fixed analyzer A and polarizer P_RA or PC_RAnd (6) SA measuring mode. From the above ellipsometry, a line of fourier coefficients is calculated, which is directly related to the ellipsometric parameters Ψ and Δ of the sample.

In addition, in the present embodiment, the oblique incidence spectroscopic ellipsometer may also be an oblique incidence polarimeter (polarimeter).

In addition, the present embodiment may further include a polarizer rotation control device for controlling the polarization direction of the polarizer and/or a wave plate rotation control device for controlling the optical axis direction of the wave plate.

In addition, the achromatic lenses L1, L2, L3, and L4 in this embodiment may also be curved mirrors, such as off-axis parabolic mirrors, so that the spectroscopic ellipsometer in this embodiment can achieve broadband achromatic effect.

In this embodiment, an imaging system may also be included, the imaging system including an illumination unit and an imaging unit. The measuring reflected light beam on the surface of the sample and the reflected light beam of the illuminating unit are reflected by the movable plane mirror and captured by the imaging unit, and then the detection light spot is aligned with the measured pattern of the sample through the movable sample platform.

In the present application, the spectrophotometer SPM and the spectroscopic ellipsometer SPE share one spectrometer, so that the measurement of the ellipsometric parameters and the measurement of the reflectivity of the sample cannot be performed simultaneously, and diaphragms, such as diaphragms D1 and D2 in the figure, may be disposed in the optical path. During measurement, a sample is loaded, after the sample platform aligns to a measurement point, the diaphragm D1 is opened, the diaphragm D2 is closed, and the reflectivity of the sample is measured by a photometry method; then, the diaphragm D1 is closed, the diaphragm D2 is opened, the sample is measured by an elliptical polarization method, after the measurement is finished, the measured data is input into a processor, and the characteristics of the optical constant, the film thickness, the three-dimensional morphology and the like of the sample material can be obtained by calculation and fitting.

The optical parameter measurement system described in the embodiment of the present application includes two different optical measurement devices, namely, an oblique incidence spectroscopic ellipsometer SPE and a vertical incidence spectrophotometer SPM, so that the thickness of the sample thin film and its optical constants can be accurately measured. The optical parameter measuring system comprises a W-shaped optical fiber beam, SO that the spectroscopic ellipsometer SPE and the spectrophotometer SPM of the optical measuring device can share the light source SO and the spectrometer SP, the effects of reducing cost and simplifying a light path are achieved, and in addition, the optical fiber beam can also collect a detection light beam which is vertically incident to the surface of a sample and is reflected by the sample and returns along the original path in the spectrophotometer SPM measuring device with higher light transmission efficiency. In addition, in this embodiment, the system formed by two spherical mirrors and one plane mirror is used in the spectrophotometer SPM to replace an achromatic lens or an aspheric mirror (such as an off-axis parabolic mirror) to focus the light beam, which not only eliminates chromatic aberration, but also reduces the expensive cost caused by using the aspheric mirror.

Example two

An optical measurement system of the present application comprising a spectroscopic ellipsometer SPE and a spectrophotometer SPM is shown in fig. 9 a. In the optical parameter measurement system of this embodiment, on the basis of embodiment 1, a fiber bundle sub-fiber V is added to the port 4 of the W-shaped fiber bundle, and the other end of the fiber bundle sub-fiber V, i.e. the port 6, is placed below the sample and aligned with the focused spot of the probe beam in the spectrophotometer on the sample, so as to receive the beam transmitted through the sample, and then the transmitted light can be transmitted to the port 4 through the fiber bundle sub-fiber V, thereby entering the spectrometer SP for detection. The arrangement of the optical fibers at the port 4 of the optical fiber bundle is shown in the figure, that is, the ports of the sub-optical fibers IV and V of the optical fiber bundle can be located at the center of the port 4, the optical fiber port of the sub-optical fiber III of the optical fiber bundle is divided into two parts and arranged at the two sides of the two parts in parallel, and the arrangement of the optical fibers at the port 4 of the optical fiber bundle is shown in the figure 9 b.

Compared with the first embodiment, the embodiment can measure the ellipsometric parameter and the reflectivity spectrum of the sample by the spectroscopic ellipsometer SPE and the spectrophotometer SPM only by adding one optical fiber, and simultaneously measure the transmittance spectrum of the sample by the spectrophotometer SPM, so that the thickness and the optical constant of the sample film can be measured more accurately. The embodiment can realize that three measuring ways simultaneously share one spectrometer and one light source, thereby simplifying the structure of the device and achieving the effect of reducing the cost.

In addition, this embodiment also includes a lens L5 disposed below the sample for focusing the transmitted beam in the spectrophotometer into the optical fiber V, which may be an achromatic lens or a curved mirror instead.

In addition, in this embodiment, since the spectroscopic ellipsometer and the spectrophotometer share the spectrometer SP and the light source SO, diaphragms need to be arranged in each optical path, and different measurement methods can be implemented by controlling the switches of the diaphragms. The arrangement of the diaphragms is shown as D1, D2 and D3 in the figure. During measurement, after a sample is loaded, the diaphragm D2 is opened, the diaphragms D1 and D3 are closed, and the sample is measured by an elliptical polarization method to obtain the spectral intensity I₁(t); the diaphragm D1 was then opened, the diaphragms D2 and D3 were closed and the reflectance spectrum I measured by the spectrometer SP was recorded₂(ii) a Finally, diaphragms D1 and D3 are opened, diaphragm D2 is closed, and the spectrum I measured by spectrometer SP is recorded₃The transmission spectrum of the sample is I = I₃-I₂。

In the application, the spectrometer SP is connected with the processor, the measured data can be input into the processor, and the optical constant, the film thickness, the Critical Dimension (Critical Dimension) of the three-dimensional structure, the spatial morphology and the like of the sample material can be obtained through computer calculation fitting.

In this application, the light source may be a light source including multiple wavelengths. In particular, the spectrum of the light source may be in the vacuum ultraviolet to near infrared light range, i.e. in the wavelength range of 150nm to 2200 nm. The light source may be a xenon lamp, a deuterium lamp, a tungsten lamp, a halogen lamp, a mercury lamp, a composite broadband light source containing a deuterium lamp and a tungsten lamp, a composite broadband light source containing a tungsten lamp and a halogen lamp, a composite broadband light source containing a mercury lamp and a xenon lamp, or a composite broadband light source containing a deuterium tungsten halogen, and typically the light beam of such light sources is natural light. Examples of such light sources include Oceanoptics, HPX-2000, HL-2000 and DH2000, and Hamamatsu, L11034, L8706, L9841 and L10290. The light source can also be natural light formed by converting partially polarized light or polarized light by using a depolarizer. For example, the depolarizer can be a Lyot depolarizer (U.S. patent No. 6667805). The spectrometer may in particular be a spectrometer comprising a grating, a mirror, and a Charge Coupled Device (CCD) or a photodiode array (PDA), for example an Ocean Optics QE65000 spectrometer or a B & W Teck Cypher H spectrometer. The optical fiber sub-fiber can be a ultraviolet change resistant fiber (standing fiber) with a wavelength range of 200-1100 nm.

Further, the optical measurement system of the present application may further include a calculation unit for calculating optical constants, film thickness, and the like of the sample material.

In addition, the optical measurement system in the present application may further include an imaging system that generates a distribution pattern on the patterned sample surface, measures a specified position, and observes a focusing state of the probe beam on the sample.

In addition, in the present application, when the reflectance or transmittance of a sample is measured by a spectrophotometer, it is also necessary to measure the reflectance spectrum of a reference sample of which the absolute reflectance is known and the transmittance spectrum in the absence of the sample before the measurement.

It is noted that those skilled in the art, in light of the teachings of the present specification, will appreciate that the optical measurement system of the present application, including spectroscopic ellipsometers and spectrophotometers, is not limited to the specific form disclosed in the above embodiments, as various modifications can be made to the measurement system of the present application while remaining within the general concept of the present application. The measuring system can be applied to detecting the thickness and the optical constant of a semiconductor film, an optical mask, a metal film, a dielectric film, glass (or a coating film), a laser reflector, an organic film and the like, and the critical dimension and the three-dimensional appearance of a periodic structure formed by the materials, and particularly can be applied to measuring all dimensions of a three-dimensional structure which is formed by a plurality of layers of films and has one-dimensional and two-dimensional periodicity in a plane and the optical constant of each layer of material.

While the present application has been described with reference to exemplary embodiments, it is to be understood that the application is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Finally, it should be noted that the above embodiments are only for illustrating the technical solutions of the present application and not for limiting, and although the present application is described in detail with reference to examples, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present application without departing from the spirit and scope of the technical solutions of the present application, which should be covered by the claims of the present application.

Claims

1. An optical measurement system including normal incidence and oblique incidence, comprising:

the device comprises a light source, an optical fiber bundle, a reflection focusing system, a first light focusing unit, a second light focusing unit, a third light focusing unit, a fourth light focusing unit, a first polarizer, a second polarizer and a spectrometer;

the reflection focusing system comprises a first reflection element, a second reflection element and a plane reflection unit;

wherein,

the light emitted by the light source is divided into a first detection light beam and a second detection light beam through the optical fiber bundle, wherein the second detection light beam vertically enters the surface of the sample after sequentially passing through the first reflecting element, the plane reflecting element and the second reflecting element; the first detection beam obliquely enters the surface of the sample through the first light-gathering unit, the first polarizer and the second light-gathering unit in sequence;

the vertical incident light reflected by the surface of the sample and sequentially passing through the second reflecting element, the plane reflecting element and the first reflecting element, and the oblique incident light reflected by the surface of the sample and sequentially passing through the third light condensing unit, the second polarizer and the fourth light condensing unit are transmitted by the optical fiber bundle and then output to the spectrometer through the same port.

2. The optical measurement system of claim 1, wherein the first, second, third, and fourth condensing units are achromatic lenses or curved mirrors; the first reflecting element and the second reflecting element are spherical reflectors; the plane reflecting element is a plane reflector; the first polarizer is a polarizer, and the second polarizer is an analyzer.

3. The optical measurement system of claim 1, wherein the fiber bundle comprises:

the first sub-fiber, the second sub-fiber, the third sub-fiber and the fourth sub-fiber;

the I sub-fiber and the II sub-fiber share an input port;

the III sub-fiber and the IV sub-fiber share an output port;

the output port of the II sub-fiber is connected with the input port of the III sub-fiber in a binding manner to form an input/output port;

and the other ends of the I sub-optical fiber and the IV sub-optical fiber are respectively connected with an optical fiber port.

4. An optical measurement system according to claim 3,

the I sub-optical fiber, the II sub-optical fiber and the IV sub-optical fiber comprise one optical fiber, and the III sub-optical fiber consists of six optical fibers;

at the input and output ports of the optical fiber bundle, the II sub optical fiber is positioned at the central part, and the six optical fibers forming the III sub optical fiber are symmetrically arranged around the II sub optical fiber to form a regular hexagon;

at the output port of the optical fiber bundle, the III sub-optical fiber and the IV sub-optical fiber are arranged in a straight line; the IV sub-optical fiber is positioned in the middle, and the six optical fibers forming the III sub-optical fiber are divided into two parts and symmetrically distributed on two sides of the IV sub-optical fiber.

5. The optical measurement system of claim 3, wherein the fiber bundle is a W-shaped fiber bundle; the optical fiber bundle is an ultraviolet change resistant optical fiber with the wavelength range of 200 and 1100 nm; the light source is a xenon lamp, a deuterium lamp, a tungsten lamp, a halogen lamp, a mercury lamp, a composite broadband light source comprising a deuterium lamp and a tungsten lamp, a composite broadband light source comprising a tungsten lamp and a halogen lamp, a composite broadband light source comprising a mercury lamp and a xenon lamp, or a composite broadband light source comprising a deuterium tungsten halogen.

6. The optical measurement system of claim 2, further comprising a compensator;

the compensator is located between the polarizer and the sample or between the sample and the analyzer.

7. The optical measurement system of claim 3, further comprising a first optical stop and a second optical stop;

the first diaphragm is arranged in an optical path between the II sub-optical fiber and the first reflecting element;

the second diaphragm is arranged in an optical path between the I sub-fiber and the first light-gathering unit.

8. The optical measurement system of claim 7, wherein the fiber bundle output port to which the spectrometer is connected further comprises a vth sub-fiber;

and the Vth sub-optical fiber transmits the part of the second detection beam which is transmitted through the sample into the spectrometer.

9. The optical measurement system of claim 8, further comprising a fifth light condensing unit;

and the fifth light-condensing unit focuses the part of the detection beam penetrating through the sample into the Vth sub-fiber, and is a curved reflector or an achromatic lens.

10. The optical measurement system of claim 9, further comprising a third diaphragm;

the third diaphragm is arranged in an optical path between the fifth light-condensing unit and the sample.

11. Optical measurement system according to any of claims 1-10, characterized in that the optical measurement system further comprises a calculation unit for calculating optical constants of the sample material, the film thickness and/or critical dimension properties or three-dimensional topography for analyzing periodic structures of the sample.