JP5370155B2 - Surface inspection apparatus and surface inspection method - Google Patents

Description

The present invention relates to a surface inspection apparatus and a surface inspection method .

For example, as a surface inspection apparatus for inspecting the surface of a substrate on which a fine pattern is formed in a process of manufacturing a semiconductor device, as disclosed in JP 2006-343102 A (Patent Document 1), There has been proposed a method for detecting a defect based on the amount of leakage light from a crossed Nicol optical system based on a change in polarization state due to structural birefringence. According to this method, even if the pattern has a fine period such that diffracted light is not generated with respect to the illumination wavelength, a defect in the pattern is detected by capturing the change in the polarization state of regular reflected light (0th order diffracted light). Therefore, it is possible to detect a defect without shortening the wavelength of light used for inspection.
JP 2006-343102 A JP 2006-179660 A Tatsuta Tatsuo "Applied Optics II-Baifukan" Edmund Optics Japan Co., Ltd. 2007 Optical Parts and Product General Catalog (Catalog Code No. J074A) O plus E Vol. 29, no. 9 (September 2007)

  However, in the means disclosed in Japanese Patent Application Laid-Open No. 2006-343102, a change in polarization state is a scalar quantity called a leakage light quantity from the crossed Nicols system (for example, when the polarization state is expressed by a Stokes parameter, only the S1 component is Therefore, it is impossible to know how the polarization state has changed, and the amount of information for defect determination is small and high-precision defect detection cannot be performed. There was a problem.

  Therefore, the present invention has been made in view of such circumstances, and detects the polarization state of specularly reflected light from the substrate itself, and increases the amount of information used for pattern defect determination to detect defect detection accuracy. It is an object of the present invention to provide a surface inspection apparatus capable of improving the quality.

The first means for achieving the above object includes two-dimensional imaging by receiving polarized light illumination means for illuminating the inspected substrate on which the pattern is formed, and specularly reflected light regularly reflected by the inspected substrate. A light receiving unit that forms a surface image of the substrate to be inspected on an element; a polarization state modulating unit that modulates a polarization state of the specularly reflected light disposed in at least one of the polarization illumination unit and the light receiving unit; with a polarization state modulation means, wherein the output signal or these from the two-dimensional image pickup device of the surface image obtained while modulating the polarization state of the regularly reflected light, prior Symbol plurality representing the polarization state of the regularly reflected light calculated parameters, the calculated amount of change from said plurality of parameters representing the polarization state of the polarized illumination to detect defects of the inspected substrate by comparing the value stored in advance and the variation amount detected have a means, said A surface inspection apparatus and generates the converted image of the amount of brightness.

The second means for solving the problem is the first means, based on the polarization state of the polarized illumination measured using a reference substrate on which a pattern is not formed, instead of the substrate to be inspected. Storage means for storing a change amount (correction value) of the regular reflection light to the polarization state by the reference substrate;
And correction means for correcting the amount of change in the polarization state using the correction value stored in the storage means.

  The third means for solving the problem is the first means or the second means, and further, a rotating means for rotating the substrate to be inspected about an axis parallel to a normal line of the surface. It is characterized by having.

  A fourth means for solving the problem is any one of the first means to the third means, and the polarization state varying means is arranged in the light receiving optical system and is centered on an optical axis. A quarter-wave plate that is rotatable, and an analyzer, and the specularly reflected light using an output signal from the two-dimensional image sensor of the surface image acquired while rotating the quarter-wave plate The polarization state is detected.

  A fifth means for solving the problem is any one of the first to fourth means, wherein the wavelength of the illumination light emitted from the polarized illumination means is formed on the substrate to be inspected. It is characterized by being longer than twice the period of the periodic pattern.

  A sixth means for solving the problem is any one of the first to fifth means, wherein the wavelength of illumination light emitted from the polarized illumination means is variable. It is what.

  A seventh means for solving the problem is any one of the first to sixth means, wherein the polarization state uses a Stokes parameter having a linearly polarized component and a circularly polarized component as parameters. The detection means separates the change amount of the polarization state into the change amount of the linearly polarized light component and the change amount of the circularly polarized light component, and the obtained change amount of the linearly polarized light component and the circularly polarized light are obtained. The defect of the substrate to be inspected is detected by using at least one of the component change amounts and comparing with the previously stored value.

  An eighth means for solving the problem is any one of the first to sixth means, wherein the polarization state uses a Stokes parameter having a linearly polarized component and a circularly polarized component as parameters. The detection means converts the amount of change in the polarization state into a brightness scalar quantity and displays it on the image display means.

  A ninth means for solving the problem is any one of the first to sixth means, wherein the polarization state is expressed using an ellipse, and the detection means is the polarization state. Are separated into a major axis azimuth component and an ellipticity component, or separated into a major axis azimuth component and an ellipticity component, and compared with the previously stored value. The present invention is characterized in that a defect of a substrate to be inspected is detected.

A tenth means for solving the problem is any one of the first to sixth means, wherein the polarization state is expressed using a Jones vector, and the detection means is the polarization The state change amount is separated into an amplitude term and a phase term of a complex amplitude, or separated into a real term and an imaginary term of a complex amplitude, and the defect of the inspected substrate is compared with the previously stored value. It is characterized by detecting.
An eleventh means for solving the above-mentioned problem is that a substrate to be inspected on which a pattern is formed is polarized and illuminated, the specularly reflected light that is specularly reflected by the substrate to be inspected is received, and the two-dimensional imaging device is received by the specularly reflected light. plural said imaged surface image of the inspected substrate above the polarization state of the regularly reflected light is modulated, based on the modulation, representing the polarization state before Symbol specular reflected light from the output signal of the two-dimensional image pickup device Determination of parameters, the calculated amount of change from said plurality of parameters representing the polarization state of the polarized illumination, by comparing the value stored in advance and the variation amount detecting a defect in the inspected substrate A surface inspection method characterized by generating an image obtained by converting the amount of change into brightness .
A twelfth means for solving the problem is the eleventh means, in which a measurement is performed using a reference substrate on which a pattern is not formed instead of the substrate to be inspected, and the reference substrate is used. A change amount of a plurality of parameters representing the polarization state is corrected based on a measurement result.

  According to the present invention, it is possible to improve the defect detection accuracy by detecting the polarization state of the specularly reflected light from the substrate and increasing the amount of information used for pattern defect determination. Even if there is a change, it is possible to provide a surface inspection apparatus capable of accurately measuring a change in polarization state due to a pattern. In addition, by modulating the polarization, the amount of light passing through the analyzer increases, so it is possible to measure with less illumination than the conventional technology, and a light source that is as bright as the conventional technology is required. And not.

It is a figure which shows the outline | summary of the surface inspection apparatus which is an example of embodiment of this invention. It is a figure which shows the example of the arrangement | sequence of the pattern formed on the wafer. It is the figure which expressed Stokes parameter visually using the Poincare sphere. It is a figure showing the conditions for the structural birefringence by a pattern to become the maximum. It is a figure which shows the change of the polarization state in the pattern in which the line and the space were located in a line. It is a figure which shows the detail of a light source.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light source, 2 ... Polarizer, 3 ... Concave mirror, 4 ... Wafer, 5 ... Concave mirror, 6 ... Quarter wave plate, 7 ... Analyzer, 8 ... Lens, 9 ... Two-dimensional image sensor, 10 ... Signal processing Unit: 11 ... monitor, 12 ... shot, 13 ... resist pattern (pattern), 14 ... line, 101 ... mercury lamp, 102 ... elliptical mirror, 103 ... lens, 104 ... wavelength selection filter, 105 ... neutral density filter, 106 ... Lens 107 ... Random fiber 107a ... Ejection end

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an outline of a surface inspection apparatus which is an example of an embodiment of the present invention. The divergent light emitted from the light source 1 is converted into linearly polarized light by the polarizer 2 and becomes substantially parallel light by the concave mirror 3 to illuminate the entire wafer 4 that is the substrate to be inspected. As shown in FIG. 2, a plurality of shots 12 are arranged on the wafer 4, and an exposed / developed resist pattern 13 (hereinafter simply referred to as a pattern) is formed in the shot 12. Further, the patterns in one shot 12 are not necessarily arranged in the same fine pattern, and may be composed of different fine patterns depending on places. These patterns 13 have a fine pattern whose period is half or less of the wavelength of the illumination light. That is, it is a fine pattern that does not generate diffracted light and cannot be inspected by an inspection apparatus using diffracted light.

  The light regularly reflected by the wafer 4 undergoes a change in polarization state due to the structural birefringence of the pattern 13. Here, the change in the polarization state due to the structural birefringence of the pattern 13 differs depending on the state of the pattern 13, for example, the line width, the trapezoidal degree of the cross section, the edge roughness, and the like, and can be used for pattern defect inspection. Since the Stokes parameter of the illumination light is known, if the Stokes parameter of the reflected light is measured, the amount of change in the polarization state due to the pattern 13 can be known. Here, the Stokes parameters (S0, S1, S2, S3) are one of parameters indicating the polarization state. As is well known, S0 is the light intensity (normalized to 1), the S1 and S2 components correspond to the amount and the azimuth of the linearly polarized component, and the S3 component corresponds to the amount of the circularly polarized component. It becomes possible to detect separately the change of the component and the change of the circularly polarized light component.

  FIG. 3 is a diagram visually expressing the Stokes parameters using a Poincare sphere.

  If S1, S2, and S3 are taken on the respective axes of the three-dimensional coordinates xyz of the Poincare sphere, the polarization state is always represented by one point on the Poincare sphere in the case of complete polarization.

  If the Poincare sphere is considered to be the Earth, it represents linearly polarized light on the equator, the north pole represents clockwise circularly polarized light, and the south pole represents counterclockwise circularly polarized light. The linearly polarized light at the intersection of the equator and S1 rotates 180 degrees while making a round on the equator (see Non-Patent Document 1, pages 202 and 203).

  On the wafer 4, the light specularly reflected while being changed in the polarization state by the pattern 13 becomes convergent light by the concave mirror 5, passes through the quarter-wave plate 6 and the analyzer 7 as a rotational phase shifter, and is supplied with a lens 8. An overall image of the wafer 4 is formed on the two-dimensional image sensor 9 via

  By the way, what is generally used as a quarter-wave plate is that two birefringent crystal plates are laminated so that their crystal axes are orthogonal to each other, and the quarter-wave plate has a quarter-wavelength due to the difference in thickness. The optical path difference is created, for example, as shown on page 184 of Non-Patent Document 1. However, this type of wave plate acts as a quarter-wave plate when the incident light beam is perpendicularly incident, but when light is incident obliquely, the optical path difference changes greatly and does not act as a quarter-wave plate. There is. In the present invention, in order to avoid this problem, a very thin birefringent material is used to generate an optical path difference of a quarter wavelength with a single plate. For example, when a quarter-wave plate for a wavelength of 546 nm is made of a single crystal plate, the thickness is about 15 μm. In this case, since the wave plate is very thin and weak in strength, it is preferable to adhere or optically contact the wave plate to a substrate having no birefringence. Moreover, you may use what formed the thin polymer which has a birefringence on a non-birefringent substrate as what has the same effect. As this type of wave plate using a polymer, “Polymer Wave Plate True Zero Order Type” published on page 79 of Non-Patent Document 2 is known. It is also effective to use a wave plate having a reduced incident angle dependency by combining a positive crystal and a negative crystal as shown on pages 927 to 928 of Non-Patent Document 3. Specifically, Non-Patent Document 3 discloses an example in which crystal quartz (quartz) and sapphire are combined.

  When the quarter-wave plate 6 is rotated 360 degrees, the polarization state of the specularly reflected light is modulated, and the output signal of each pixel of the two-dimensional image sensor 9 changes. The Stokes parameter for each pixel can be calculated using the transition phaser method. The Stokes parameter measurement by the rotational phase shifter method is introduced in various books and magazines. For example, Non-Patent Document 1 on page 233 introduces “Method by Rotating λ / 4 Plate”. Briefly describing the Rotational Transition Phase Method, if the signal component obtained by rotating 360 degrees when the rotation angle of the phase shifter is θ is Fourier series expanded, S0 is a bias component and cos 4θ component, and S1 is The cos 4θ component, S2 corresponds to the sin 4θ component, and S3 corresponds to the sin 2θ component, and the Stokes parameters can be obtained from these Fourier coefficients. A more detailed explanation of this calculation is also described in Japanese Patent Application Laid-Open No. 2006-179660 by the same applicant as the present application.

Here, since the polarization state of the reflected light is expressed using Stokes parameters, if the Stokes parameter of the reflected light from the wafer is measured in advance for a wafer without the pattern 13, it changes due to the optical system. Since only the polarization state to be detected can be known, this is used as a correction parameter. That is, by subtracting the Stokes parameter of each pixel when measuring the substrate without the pattern from the Stokes parameter of each pixel when the substrate with the pattern 13 is measured, the change (amount) of the polarization state caused by the optical system is eliminated. Is possible. That is, it is possible to detect only the polarization state change due to the pattern 13. In addition, when subtracting the Stokes parameter in this way, it is preferable to use a Stokes parameter in which S0 is normalized to 1.
The means disclosed in Japanese Patent Application Laid-Open No. 2006-343102 has a problem that the amount of leakage light changes due to a change in the polarization state generated in the optical system itself. In other words, when there is no pattern on the substrate and the polarization state does not change, if the substrate is two-dimensionally imaged in a crossed Nicol arrangement, the entire light source should be essentially zero. Since the system is not perfect, when the substrate is two-dimensionally imaged, the entire light amount does not become zero, and different light amounts are detected depending on the location. When the change in polarization state due to the pattern is small, there is a problem that sufficient defect detection accuracy cannot be achieved by detection with the amount of light leaked from the crossed Nicols system.

  Next, a method for determining the presence or absence of a pattern defect from the detected polarization state change will be described below.

  Store the change distribution for each component of the Stokes parameter for each pixel of a shot that has been determined to be non-defective by a scanning electron microscope in advance, and compare it with each shot to determine whether each shot is non-defective or defective. It is determined whether or not.

  Here, when imaging the polarization state (Stokes parameter) change (amount), it is converted into a single scalar amount called brightness and visualized on the monitor 11 to display a wafer image. This is achieved by, for example, matching the linear distance between two points on the Poincare sphere with Stokes parameters as shown in Fig. 3 or the distance along the spherical surface between two points on the Poincare sphere to the brightness. it can. In addition, as an image to be displayed, it is possible to independently display the amount of change of each component of the Stokes parameter, that is, the amount of change of S1, S2, and S3.

  As a result, if there is a defective shot in which the line width of the pattern is changed due to an exposure amount error or a focus error at the time of exposure of the pattern 13, only the defective shot is displayed with a different brightness. . In addition, when a part of one shot is partially defective, only the defective part is displayed with a partially different brightness.

  In addition, since a polarization change due to structural birefringence appears in the S3 component (circular polarization component), it is also effective to view only the amount of change in the S3 component. In this case, the change amount of the S3 component is displayed in correspondence with the brightness. Also, depending on the shape of the pattern, it is also effective not to convert the Stokes parameter into one scalar quantity, but to calculate the amount of change in each parameter S1, S2, S3 as described above, and judge whether the product is good or defective. It is.

  In the above description, the Stokes parameter is obtained for each pixel of the two-dimensional image pickup device. However, for example, an average of signals of a plurality of pixels may be taken in order to reduce sensitivity error and electrical noise of each pixel. . For example, an average of signals of 2 × 2 pixels may be taken, and in this case, the number of pixels of the finally obtained image is ¼ of the original number of pixels.

  FIG. 4 is a diagram showing conditions for maximizing structural birefringence due to the pattern 13. In the pattern 13 in which the line 14 and the space are arranged as shown in the figure, the effective refractive indexes in the x direction and the y direction shown in the figure are different. Therefore, when linearly polarized light having a vibration direction that forms an angle of 45 degrees with respect to the line 14 is incident as shown in FIG. 3, the change in the polarization state becomes maximum, and the S3 component is generated as shown in FIG. It becomes elliptically polarized light. Here, for the sake of simplicity, it is described as normal incidence, but in the case of oblique incidence, a difference occurs in the reflectance between the vibration component in the x direction and the vibration component in the y direction, so that the S2 component also occurs at the same time. It becomes elliptically polarized light inclined more than 45 degrees. Therefore, in the case of oblique incidence, the angle of the vibration direction of linearly polarized light that maximizes the change in polarization state may deviate from 45 degrees, and the angle depends on the structure of the pattern 13.

  There are two types of methods for rotating the polarizer 2 and rotating the wafer 4 in order to make the incident polarization vibration direction and the pattern 13 have a desired angle. In this embodiment, the polarizer 2 is They are arranged so that the vibration direction is in the plane of the paper, and the wafer 4 is rotated by a wafer rotating device (not shown) to form a desired angle. But essentially it doesn't matter. The wafer 4 may be rotated by setting the wafer rotating device on a stage on which the wafer is placed and rotating the wafer on the stage, or once removing the wafer from the stage, the wafer rotating device. Alternatively, the wafer may be transferred to the stage and rotated by the wafer rotating apparatus, and then placed on the stage again.

  FIG. 6 shows the light source 1 in detail. The light emitted from the mercury lamp 101 is collected by the elliptical mirror 102, collimated by the lens 103, passes through the wavelength selection filter 104 and the neutral density filter 105, and then collected by the lens 106 and enters the random fiber 107. .

  107a which is the emission end of the random fiber 107 corresponds to the emission end of the light source 1 in FIG. Here, the wavelength selection filter 104 is switchable so that the emission line of the mercury lamp can be selected, and e-line, g-line, h-line, i-line, j-line (313 nm), and 248 nm filters can be selected. . For structural birefringence, the shorter the wavelength, the greater the change in the polarization state. Therefore, it is preferable to use a shorter wavelength. There are some elements that do not exist, and various wavelengths can be used properly depending on the pattern conditions. The neutral density filter 105 can also switch various transmittances according to the situation.

In addition, when the wavelength is changed, the phase shifter is shifted from the quarter wavelength, so that the phase shifter may be exchanged according to the wavelength. Further, for example, a broadband wave plate in which a quartz wave plate and an MgF ₂ wave plate are combined may be adopted, and a system that is not exchanged may be used. In this case, the phase shifts slightly from the quarter wavelength depending on the wavelength, but the amount of deviation is known in the rotational phase shifter method even if the phase shift angle of the phase shifter is not exactly 90 degrees (quarter wavelength). If so, there is no problem because it can be corrected. Even if the extinction ratio of the analyzer is not so high, it can be corrected similarly if the extinction ratio itself is known.

In the above description, an example in which the Stokes parameter is used as an index representing the polarization state is shown, but the index representing the polarization state is not limited to the Stokes parameter. There are various indexes indicating the polarization state. For example, (1) the major axis azimuth and ellipticity or the major axis azimuth and ellipticity angle when the polarization state is represented by an ellipse. Amplitude term and phase term of complex amplitude when represented by Jones vector (3) A method such as a real term and an imaginary term of complex amplitude when the polarization state is represented by Jones vector. In essence, these may be used as an index representing the polarization state, but it is preferable to use the Stokes parameter as the most easily understood index.

Claims (12)

Polarized illumination means for illuminating polarized light on the substrate to be inspected with the pattern formed thereon;
Light receiving means for receiving specularly reflected light regularly reflected by the inspected substrate and forming a surface image of the inspected substrate on a two-dimensional image sensor;
Polarization state modulation means for modulating the polarization state of the specularly reflected light disposed in at least one of the polarization illumination means and the light receiving means;
Using the polarization state modulation means, a plurality representing the polarization state of the output signal or these from the two-dimensional image pickup device of the surface image obtained with the polarization state of the regularly reflected light is modulated, before Symbol specular light seek parameters, the calculated amount of change from said plurality of parameters representing the polarization state of the polarized illumination to detect defects of the inspected substrate by comparing the value stored in advance and the variation amount It has a detection means,
A surface inspection apparatus that generates an image obtained by converting the amount of change into brightness . Stores the distribution of the amount of change (correction value) from the polarization state of the polarized illumination measured using a reference substrate on which no pattern is formed instead of the substrate to be inspected to the polarization state of specularly reflected light from the reference substrate. Storage means for
The surface inspection apparatus according to claim 1, further comprising: a correction unit that corrects a change amount of a plurality of parameters representing the polarization state using the correction value distribution stored in the storage unit.   3. The surface inspection apparatus according to claim 1, further comprising a rotating means for rotating the substrate to be inspected about an axis parallel to a normal line of the surface.   The polarization state varying means is a quarter-wave plate that is arranged in the light-receiving optical system and that can rotate around the optical axis, and an analyzer, and is acquired while rotating the quarter-wave plate. 4. The surface inspection apparatus according to claim 1, wherein a polarization state of the regular reflection light is detected using an output signal of the surface image from the two-dimensional imaging device. 5. .   The wavelength of the illumination light irradiated from the polarized illumination means is longer than twice the period of the periodic pattern formed on the substrate to be inspected. The surface inspection apparatus described in 1.   The surface inspection apparatus according to claim 1, wherein the wavelength of illumination light emitted from the polarized illumination unit is variable.   The polarization state is expressed using Stokes parameters having a linearly polarized component and a circularly polarized component as parameters, and the detecting means determines the change amount of the polarization state as the change amount of the linearly polarized component and the change of the circularly polarized component. And using at least one of the change amount of the linearly polarized light component and the change amount of the circularly polarized light component obtained, and comparing the previously stored value with the defect of the substrate to be inspected. The surface inspection apparatus according to any one of claims 1 to 6, wherein   The polarization state is expressed using a Stokes parameter having a linearly polarized component and a circularly polarized component as parameters, and the detecting unit converts the amount of change in the polarization state into a scalar amount of brightness and displays it on an image display unit. The surface inspection apparatus according to any one of claims 1 to 6, wherein:   The polarization state is expressed using an ellipse, and the detection means separates the amount of change in the polarization state into a major axis azimuth component and an ellipticity component, or a major axis azimuth component and an ellipticity. 7. The surface according to claim 1, wherein a defect of the substrate to be inspected is detected by being separated into corner components and being compared with the value stored in advance. 8. Inspection device.   The polarization state is expressed using a Jones vector, and the detection means separates the amount of change of the polarization state into an amplitude term and a phase term of complex amplitude, or separates into a real term and an imaginary term of complex amplitude. The surface inspection apparatus according to any one of claims 1 to 6, wherein a defect of the substrate to be inspected is detected by comparing with the value stored in advance. The substrate to be inspected with the pattern is polarized and illuminated,
Receiving regular reflection light regularly reflected by the substrate to be inspected, and forming a surface image of the substrate to be inspected on a two-dimensional image sensor by the regular reflection light;
Modulating the polarization state of the specularly reflected light;
Based on the modulation obtains a plurality of parameters representing the polarization state before Symbol specular reflected light from the output signal of the two-dimensional image pickup device, to calculate the change amount from the plurality of parameters representing the polarization state of the polarized illumination, surface inspection method characterized by comparing the value stored in advance and the variation amount detecting a defect in the inspected substrate, and generates an image obtained by converting the amount of change in brightness. In place of the substrate to be inspected, measurement is performed using a reference substrate on which no pattern is formed, and based on the measurement result using the reference substrate, the amount of change in a plurality of parameters representing the polarization state is corrected. The surface inspection method according to claim 11, wherein:

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