Optical inspection device and control method for same

Abstract

Provided are: an optical inspection device capable of increasing the numerical aperture of an objective lens; and a method for controlling the optical inspection device. This optical inspection device comprises: a light irradiation unit that irradiates a sample with first irradiation light and second irradiation light, which are two linear light beams; an objective lens that condenses scattered light from the sample; a detection unit that detects the scattered light condensed by the objective lens; and a control unit that determines, on the basis of a signal output from the detection unit, whether the sample contains a defect or foreign matter, and that controls each unit. The optical inspection device is characterized in that the control unit sets the directions of the first irradiation light and the second irradiation light so that first reflected light, which is the first irradiation light reflected by the sample, and second reflected light, which is the second irradiation light reflected by the sample, are in the same position in a longitudinal direction of the linear light or in a direction orthogonal to the longitudinal direction, with respect to the pupil position of the objective lens.

Description

Optical inspection device and control method thereof

[0001] The present invention relates to an optical inspection apparatus that irradiates a sample with light and detects scattered light from the sample to determine whether or not there are defects or foreign matter in the sample, and a control method for the same.

[0002] Optical inspection equipment is used in conjunction with scanning electron microscopes (SEMs) to inspect semiconductor devices, which are becoming increasingly miniaturized. Optical inspection equipment generates observation images used to determine the presence or absence of defects or foreign particles by detecting scattered light from a sample irradiated with light. When high-intensity laser light sources are used in optical inspection equipment, speckle noise generated by light interference reduces the detection accuracy of defects and foreign particles.

[0003] Patent Document 1 discloses that, in order to suppress speckle noise, linear light is irradiated onto a sample from multiple directions and the detection signals of scattered light for each irradiated light are averaged. In other words, by averaging the detection signals of multiple scattered lights, the signal related to speckle noise decreases, but the signal related to defects or foreign matter does not decrease, thereby improving the detection accuracy of defects and foreign matter.

[0004] JP 2008-275540 A

[0005] However, Patent Document 1 does not sufficiently consider increasing the numerical aperture of the objective lens that collects scattered light from the sample. Since direct reflection light from the sample interferes with the detection of defects and foreign particles, it is necessary to prevent the direct reflection light from entering the objective lens. When the direct reflection light generated by irradiating the sample with light from multiple directions is at different positions, the numerical aperture of the objective lens is reduced to prevent the direct reflection light from entering the objective lens. A smaller numerical aperture of the objective lens reduces the amount of scattered light collected, thereby reducing the accuracy of detecting defects and foreign particles.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical inspection apparatus capable of increasing the numerical aperture of an objective lens, and a control method thereof.

[0007] In order to achieve the above object, the present invention provides an optical inspection device comprising a light irradiation unit that irradiates a sample with two linear beams of light, namely, a first irradiation beam and a second irradiation beam; an objective lens that collects scattered light from the sample; a detection unit that detects the scattered light collected by the objective lens; and a control unit that determines whether the sample contains defects or foreign matter based on a signal output from the detection unit and controls each unit, wherein the control unit sets the directions of the first irradiation beam and the second irradiation beam so that first reflected light, which is light from the first irradiation beam reflected by the sample, and second reflected light, which is light from the second irradiation beam reflected by the sample, are at the same position at the pupil position of the objective lens in the longitudinal direction of the linear beams or in a direction perpendicular to the longitudinal direction.

[0008] The present invention also provides a control method for an optical inspection device that includes a light irradiation unit that irradiates a sample with two linear beams of light, namely, a first irradiation beam and a second irradiation beam, an objective lens that collects scattered light from the sample, a detection unit that detects the scattered light collected by the objective lens, and a control unit that determines whether the sample contains defects or foreign matter based on a signal output from the detection unit and controls each unit, wherein the control unit sets the directions of the first irradiation beam and the second irradiation beam so that first reflected light, which is light from the first irradiation beam reflected by the sample, and second reflected light, which is light from the second irradiation beam reflected by the sample, are at the same position at the pupil position of the objective lens in the longitudinal direction of the linear beams or in a direction perpendicular to the longitudinal direction.

[0009] According to the present invention, it is possible to provide an optical inspection apparatus capable of increasing the numerical aperture of an objective lens and a control method thereof.

[0010] FIG. 1 shows an example of the overall configuration of the optical inspection device of Example 1. FIG. 1 shows an example of the configuration of the light source unit. FIG. 1 shows an example of the configuration of the first irradiation unit. FIG. 1 shows an azimuth angle of irradiation light and a circuit pattern having periodicity. FIG. 2 shows the positions of directly reflected light and diffracted light of the first irradiation light and the second irradiation light. FIG. 3 shows the positions of diffracted light of the first irradiation light and the second irradiation light, and a spatial filter. FIG. 4 shows the positions of diffracted light of the first irradiation light and the third irradiation light, and a spatial filter. FIG. 5 shows the positions of diffracted light of the first irradiation light, the fourth irradiation light, and the fifth irradiation light, and a spatial filter. FIG. 2 shows an example of the relationship between the amount of scattered light and the angle of incidence for different film thicknesses of a transparent thin film. FIG. 3 shows an example of the detection unit. FIG. 4 shows another example of the detection unit. FIG. 5 shows an inspection area at low magnification and an inspection area at high magnification. FIG. 6 shows a magnification adjustment unit that changes the magnification in the X direction without changing the magnification in the Y direction. FIG. 6 shows another example of the detection unit. FIG. 7 shows an example of the timing chart of the detection unit in FIG. 15. FIG. 8 shows an example of a timing chart of light reception and light irradiation by the detection unit. FIG. 9 shows an example of the effect of suppressing aliasing.

[0011] An embodiment of an optical inspection device according to the present invention will be described below with reference to the accompanying drawings. The optical inspection device is a device that irradiates a sample to be inspected with light from multiple directions and detects scattered light from each irradiated light to determine whether or not there are defects or foreign matter in the sample.

[0012] An example of the overall configuration of the optical inspection apparatus of Example 1 will be described using Figure 1. The optical inspection apparatus 100 includes a sample stage 102, a stage driving unit 103, a light source unit 110, a first irradiation unit 111, a second irradiation unit 112, a detection optical system 120, a detection unit 130, and a control unit 140. The sample stage 102 holds a sample 101 such as a semiconductor wafer. The stage driving unit 103 drives the sample stage 102 to move and rotate the sample 101 in the X, Y, and Z directions.

[0013] The light source unit 110 emits light that is incident on the first irradiating unit 111 and the second irradiating unit 112. Details of the light source unit 110 will be described later with reference to FIG.

[0014] The first irradiator 111 forms linear light from the incident light and irradiates the sample 101 with the first irradiation light L1, while controlling the incident angle θ1 and azimuth angle of the first irradiation light L1. Details of the first irradiator 111 will be described later with reference to FIG. 3. The second irradiator 112 forms linear light from the incident light and irradiates the sample 101 with the second irradiation light L1, while controlling the incident angle θ2 and azimuth angle of the second irradiation light L2. The incident angles θ1 and θ2 are angles relative to the normal to the surface of the sample 101, i.e., the Z axis. The first irradiation light L1 and the second irradiation light L2 are parallel to each other on the surface of the sample 101, and are irradiated at the same position or adjacent positions. The azimuth angles of the first irradiation light L1 and the second irradiation light L2 will be described later with reference to FIG. 4.

[0015] The detection optical system 120 has an objective lens 121, a spatial filter 122, an analyzer 123, a magnification adjustment unit 124, and an imaging lens 125 to collect scattered light generated from the sample 101 by irradiation with the first irradiation light L1 and the second irradiation light L2 and form an image on the detection unit 130. The objective lens 121 collects the scattered light from the sample 101. The spatial filter 122 blocks diffracted light contained in the scattered light. The magnification adjustment unit 124 adjusts the magnification of the scattered light incident on the detection unit 130. The imaging lens 125 forms an image of the scattered light on the detection unit 130.

[0016] The detection unit 130 detects the incident scattered light and outputs a signal corresponding to the amount of the detected scattered light to the control unit 140. Note that the scattered light is detected in accordance with the movement of the sample stage 102 in the minor axis direction of the first irradiation light L1, thereby generating a two-dimensional image of the sample 101.

[0017] The control unit 140 is a device, such as a general-purpose computer, that controls the operation of each unit, generates an observation image based on a signal output from the detection unit 130, and determines whether the sample 101 contains defects or foreign matter. A storage device, a display device, and an input device may be connected to the control unit 140. The storage device stores various programs, data, observation images, etc. The display device displays the observation image, the determination results of the presence or absence of defects or foreign matter, etc. The input device allows the user to input data, etc.

[0018] The presence or absence of defects or foreign matter is determined using the generated observation image and a reference image that contains the same circuit pattern as the observation image. For example, a difference image between the observation image and the reference image is calculated, and if the pixel value of the difference image is greater than a predetermined threshold, it is determined that a defect or foreign matter is present. Note that, prior to calculating the difference image, a registration process between the observation image and the reference image may be performed.

[0019] An example of the configuration of the light source unit 110 will be described using Fig. 2. The light source unit 110 has a laser light source 201, a half-wave plate 202, a polarizing beam splitter 203, a diffuser 204, a half-wave plate 205, a polarizing beam splitter 206, and a mirror 207. The laser light source 201 emits linearly polarized light having a specific wavelength toward the half-wave plate 202.

[0020] The half-wave plate 202 is set at a desired angle in a plane perpendicular to the direction of the incident light, and changes the polarization direction of the light according to the set angle. The polarizing beam splitter 203 splits the light that has passed through the half-wave plate 202 into light that heads toward the light-absorbing diffuser 204 and light that heads toward the half-wave plate 205. The intensity ratio of the light split by the polarizing beam splitter 203 is adjusted by the set angle of the half-wave plate 202.

[0021] Similar to the half-wave plate 202, the half-wave plate 205 is set at a desired angle in a plane perpendicular to the direction of the incident light, and changes the polarization direction of the light according to the set angle. The polarizing beam splitter 206 splits the light that has passed through the half-wave plate 205 into light that travels toward the first irradiation unit 111 and light that travels toward the second irradiation unit 112 via the mirror 207. The intensity ratio of the light split by the polarizing beam splitter 206 is adjusted by the set angle of the half-wave plate 205.

[0022] An example configuration of the first irradiating unit 111 will be described with reference to Fig. 3. The second irradiating unit 112 has the same configuration as the first irradiating unit 111. The first irradiating unit 111 includes a concave cylindrical lens 301, a convex cylindrical lens 302, a Dove prism 303, a half-wave plate 304, a quarter-wave plate 305, and a condenser lens 306.

[0023] The concave cylindrical lens 301 and the convex cylindrical lens 302 constitute a cylindrical beam expander, which forms linear light from incident light and outputs it to the Dove prism 303. The Dove prism 303 rotates around the axis corresponding to the direction of incidence of the linear light, changing the azimuth angle of the linear light depending on the rotation angle. The half-wave plate 304 is set at a desired angle in a plane perpendicular to the direction of the incident light and changes the polarization direction of the light depending on the set angle. The quarter-wave plate 305 is set at a desired angle in a plane perpendicular to the direction of the incident light and converts linearly polarized light into circularly polarized light or elliptically polarized light depending on the set angle. The condenser lens 306 adjusts the size of the first irradiation light L1 irradiated onto the sample 101.

[0024] In order to prevent interference between the first irradiation light L1 and the second irradiation light L2, it is preferable to stagger the irradiation timings of the two beams. For example, when pulsed light having a pulse width PW is emitted from the light source unit 110, optical interference can be prevented by making the difference between the optical path from the polarizing beam splitter 206 via the first irradiation unit 111 to irradiate the sample 101 and the optical path via the second irradiation unit 112 larger than the product PW·c of the pulse width PW and the speed of light c. Furthermore, when multi-longitudinal mode laser light is emitted from the light source unit 110, the coherence length is several meters or less, so optical interference can be prevented by making the difference between the two optical paths larger than the coherence length.

[0025] The azimuth angles of the irradiation light and the periodic circuit pattern will be described with reference to Figure 4. The azimuth angle φ1 of the first irradiation light L1 and the azimuth angle φ2 of the second irradiation light L2 are angles relative to the X-axis in a plane parallel to the surface of the sample 101. That is, the direction of the first irradiation light L1 is determined by the incident angle θ1 and the azimuth angle φ1, and the direction of the second irradiation light L2 is determined by the incident angle θ2 and the azimuth angle φ2.

[0026] The semiconductor device, which is the sample 101, includes a periodic circuit pattern. The circuit pattern has, for example, a memory portion 401, an X-direction portion 402, and a Y-direction portion 403. The memory portion 401 is formed with a repeat pitch of several tens of nanometers or less, so it is difficult to confirm the pitch state when irradiated with ultraviolet light having a wavelength of 200 nanometers or more. In the X-direction portion 402, peripheral circuits of the memory portion 401 are formed lined up in the X-direction, and in the Y-direction portion 403, peripheral circuits are formed lined up in the Y-direction. The repeat pitch is coarser than that of the memory portion 401, and the pattern also includes an irregular pattern. Therefore, diffracted light is generated when light is irradiated onto the X-direction portion 402 or the Y-direction portion 403.

[0027] Incidentally, since light directly reflected from the sample 101 interferes with the detection of scattered light, it is necessary to prevent it from entering the objective lens 121. When the positions of the directly reflected light generated by irradiating the sample 101 with light from multiple directions are varied, the numerical aperture of the objective lens 121 is reduced to prevent the directly reflected light from entering the objective lens 121. However, when the numerical aperture of the objective lens 121 is reduced, the amount of scattered light that is collected decreases, and the accuracy of detecting defects and foreign matter decreases.

[0028] Therefore, in Example 1, the directions of the first irradiation light L1 and the second irradiation light L2 are set so that the first reflected light, which is the light of the first irradiation light L1 directly reflected by the sample 101, and the second reflected light, which is the light of the second irradiation light L2 directly reflected by the sample 101, are positioned at the same position in the longitudinal direction of the linear light. Alternatively, the directions of the first irradiation light L1 and the second irradiation light L2 are set so that the first reflected light and the second reflected light are positioned at the same position in a direction perpendicular to the longitudinal direction of the linear light.

[0029] The positions of the directly reflected light and diffracted light of the first irradiation light L1 and the second irradiation light L2 will be described using Figure 5. In Figure 5(a), diffracted light 510-513 of the first irradiation light L1 is shown at the position of the pupil 500 of the objective lens 121. Note that if the sample 101 includes an X-direction portion 402 and a Y-direction portion 403, the diffracted light spreads in the X and Y directions, and therefore, X and Y are added to the end of the reference symbols for the diffracted light spreading in each direction. That is, diffracted light 510X-513X spreads in the X direction, and diffracted light 510Y-512Y spreads in the Y direction. The intersection of diffracted light 510X and diffracted light 510Y is the position of the directly reflected light of the first irradiation light L1, and is outside the pupil 500.

[0030] 5B shows diffracted light beams 520X to 523X and 520Y to 522Y of the second irradiation light beam L2 at the position of the pupil 500. The intersection of the diffracted light beam 520X and the diffracted light beam 520Y is the position of the directly reflected light of the second irradiation light beam L2, which is outside the pupil 500.

[0031] 5(c) is a diagram in which FIG. 5(a) and (b) are superimposed, and shows diffracted light 510X to 513X and 510Y to 512Y of the first irradiation light L1 and diffracted light 520X to 523X and 520Y to 522Y of the second irradiation light L2. Furthermore, in order to increase the size of the pupil 500 and the amount of scattered light that is collected, the directly reflected light of the first irradiation light L1 and the directly reflected light of the second irradiation light L2 are set to the same position in the Y-axis coordinate, which is the longitudinal direction of the linear light. For the two directly reflected light beams to be at the same position in the Y-coordinate, for example, the following equation may be satisfied:

[0032] sin θ1·sin φ1=sin θ2·sin φ2 (Equation 1) Here, θ1 is the angle of incidence of the first irradiation light L1, φ1 is the azimuth angle of the first irradiation light L1, θ2 is the angle of incidence of the second irradiation light L2, and φ2 is the azimuth angle of the second irradiation light L2.

[0033] The positions of the diffracted light of the first irradiation light L1 and the second irradiation light L2 and the spatial filter 122 will be described using FIG. 6 . (a) of FIG. 6 is the same as (c) of FIG. 5 and shows diffracted light 510X to 513X and 510Y to 512Y of the first irradiation light L1 and diffracted light 520X to 523X and 520Y to 522Y of the second irradiation light L2. Since the directly reflected light of the first irradiation light L1 and the second irradiation light L2 are set to the same position in the Y coordinate, the diffracted light 510X to 513X and the diffracted light 520X to 523X are also set to the same position in the Y coordinate. The diffracted light 510Y to 512Y and the diffracted light 520Y to 522Y have different X coordinates. Because these diffracted lights reduce the detection accuracy of defects and foreign matter, they are preferably blocked to prevent them from entering the pupil 500.

[0034] 6B shows the spatial filter 122 that blocks the diffracted light of the first irradiation light L1 and the second irradiation light L2, with the diffracted light depicted by a dotted line. The spatial filter 122 has light-blocking rods 601X to 603X and 601Y to 602Y. The rods 601X to 603X are long in the X direction, and the rods 601Y and 602Y are long in the Y direction. Because the diffracted light 521Y and the diffracted light 511Y are at different positions on the X coordinate, the rod 601Y blocks the diffracted light 521Y, and the rod 602Y blocks the diffracted light 511Y. On the other hand, because the diffracted light 511X and the diffracted light 521X are at the same position on the Y coordinate, the rod 601X blocks the diffracted light 511X and the diffracted light 521X. Similarly, rod 602X blocks diffracted light 512X and diffracted light 522X, and rod 603X blocks diffracted light 513X and diffracted light 523X. In other words, since one rod blocks multiple diffracted light beams, the area of ​​pupil 500 that is not blocked expands, and more scattered light is detected.

[0035] The positions of the diffracted light of the first irradiation light L1 and the third irradiation light L3 and the spatial filter 122 will be described using FIG. 7 . The third irradiation light L3 is a linear light irradiated from a different direction from the first irradiation light L1 and the second irradiation light L2, and has an incident angle θ3 and an azimuth angle φ3. (a) of FIG. 7 shows diffracted light 510X to 513X and 510Y to 512Y of the first irradiation light L1 and diffracted light 530X to 533X and 530Y to 532Y of the third irradiation light L3. Furthermore, in order to increase the size of the pupil 500, the directly reflected light of the first irradiation light L1 and the directly reflected light of the third irradiation light L3 are set to the same position on the X-axis coordinate, which is perpendicular to the longitudinal direction of the linear light. For the two directly reflected light beams to be at the same position on the X-coordinate, for example, the following equation may be satisfied:

[0036] sin θ1·cos φ1=sin θ3·cos φ3 (Formula 2) Because the directly reflected light of the first irradiation light L1 and the directly reflected light of the third irradiation light L3 are set to the same position on the X coordinate, the diffracted light beams 510Y to 512Y and the diffracted light beams 530Y to 532Y are also set to the same position on the X coordinate. Note that the diffracted light beams 510X to 513X and the diffracted light beams 530X to 533X are set to different positions on the Y coordinate.

[0037] 7B shows the spatial filter 122, which blocks the diffracted light of the first irradiation light L1 and the third irradiation light L3, with the diffracted light depicted by a dotted line. The spatial filter 122 has rods 601X to 606X that are long in the X direction and a rod 601Y that is long in the Y direction. Because the diffracted light 510X to 513X and the diffracted light 530X to 533X are at different positions on the Y coordinate, each of the rods 601X to 606X blocks the diffracted light 533X, 511X, 532X, 512X, 531X, and 513X, respectively. Meanwhile, because the diffracted light 511Y and the diffracted light 531Y are at the same position on the X coordinate, one rod 601Y blocks the diffracted light 511Y and the diffracted light 531Y. This expands the area of ​​the pupil 500 that is not blocked, and more scattered light is detected.

[0038] The positions of the diffracted light of the first irradiation light L1, the fourth irradiation light L4, and the fifth irradiation light L5 and the spatial filter 122 will be described using Figure 8. The fourth irradiation light L4 is a linear light that is irradiated from a direction different from the first irradiation light L1 to the third irradiation light L3, and has an incident angle θ4 and an azimuth angle φ4. The fifth irradiation light L5 is a linear light that is irradiated from a direction different from the first irradiation light L1 to the fourth irradiation light L4, and has an incident angle θ5 and an azimuth angle φ5. However, the fourth irradiation light L4 and the fifth irradiation light L5 are irradiated from a direction closer to the first irradiation light L1 than the second irradiation light L2 and the third irradiation light L3.

[0039] 8A shows diffracted light beams 510X to 513X and 510Y to 512Y of the first irradiation light beam L1, diffracted light beams 540Y to 542Y of the fourth irradiation light beam L4, and diffracted light beams 550Y to 552Y of the fifth irradiation light beam L5. The first irradiation light beam L1, the fourth irradiation light beam L4, and the fifth irradiation light beam L5 are irradiated so as to satisfy the following formula:

[0040] sin θ1·sin φ1=sin θ4·sin φ4=sin θ5·sin φ5 (Equation 3) When the first irradiation light L1, the fourth irradiation light L4, and the fifth irradiation light L5 are irradiated so as to satisfy Equation 3, the three directly reflected beams are at the same position in the Y-axis coordinate, which is the longitudinal direction of the linear light, and the diffracted beams spreading in the X-direction also overlap at the same Y-coordinate.

[0041] 8B shows the spatial filter 122, which blocks the diffracted light of the first, fourth, and fifth irradiation light beams L1, L4, and L5, with the diffracted light beams depicted by dotted lines. The spatial filter 122 has rods 601X to 603X that are long in the X direction and rods 601Y to 603Y that are long in the Y direction. Because the diffracted light beams 551Y, 541Y, and 511Y are at different positions on the X coordinate, the rods 601Y to 606Y block the diffracted light beams 551Y, 541Y, and 511Y, respectively. Meanwhile, because the diffracted light beams of the fourth and fifth irradiation light beams L4 and L5 overlap with the diffracted light beam 511X, the rod 601X blocks the diffracted light beam that overlaps the diffracted light beam 511X and the diffracted light beam 511X. Similarly, rod 602X blocks the diffracted light that overlaps with diffracted light 512X and diffracted light 512X, and rod 603X blocks the diffracted light that overlaps with diffracted light 513X and diffracted light 513X. This expands the area of ​​pupil 500 that is not blocked, and more scattered light is detected.

[0042] Incidentally, if a transparent thin film is formed on the surface of the sample 101 and a foreign particle is present on the transparent thin film, the amount of scattered light detected will vary depending on the film thickness of the transparent thin film and the angle of incidence of the irradiated light. Although the film thickness of the transparent thin film may be unknown or may vary, it is desirable to maintain a substantially constant detection accuracy for defects and foreign particles even in such cases. Therefore, the intensity of each irradiated light is adjusted so that the total amount of scattered light generated by irradiated light from multiple directions falls within a predetermined range.

[0043] 9 shows a transparent thin film 901 formed on the surface of silicon 900 and a foreign particle 902 on the transparent thin film 901, along with an example graph of the amount of scattered light from the foreign particle 902. The vertical axis of the graph represents the amount of scattered light, and the horizontal axis represents the angle of incidence of the irradiated light, and the graph shows cases where the film thickness t of the transparent thin film 901 is 105 nm, 120 nm, and 135 nm. As shown in the graph of FIG. 9, even a change in film thickness t of just 15 nm changes the angle of incidence at which the amount of scattered light peaks. Specifically, when t = 105 nm, the amount of scattered light peaks at an incident angle of approximately 78 degrees, whereas when t = 120 nm, the amount of scattered light peaks at an incident angle of approximately 73 degrees, and when t = 135 nm, the amount of scattered light peaks at an incident angle of approximately 65 degrees.

[0044] To maintain a substantially constant detection accuracy for defects and foreign particles, the intensity of each irradiated light beam may be adjusted so that the total amount of scattered light generated by irradiated light beams from multiple directions falls within a predetermined range. For example, the intensity ratio of each irradiated light beam may be adjusted so that the difference between the values ​​calculated by the following three equations falls within a predetermined range.

[0045] I1·S(θ1, t1) + I2·S(θ2, t1) + I3·S(θ3, t1) ... (Equation 4) I1·S(θ1, t2) + I2·S(θ2, t2) + I3·S(θ3, t2) ... (Equation 5) I1·S(θ1, t3) + I2·S(θ2, t3) + I3·S(θ3, t3) ... (Equation 6) Here, I1, I2, and I3 are the intensities of the first irradiation light, second irradiation light, and third irradiation light, respectively; S(θ, t) is the amount of scattered light per unit amount of incident light when the angle of incidence is θ and the film thickness is t; and θ1, θ2, and θ3 are the angles of incidence of the first irradiation light, second irradiation light, and third irradiation light. Furthermore, t1, t2, and t3 are different film thicknesses, and are values ​​within the range of expected variations, for example, t1=105 nm, t2=120 nm, and t3=135 nm.

[0046] If possible, it is desirable to adjust I1, I2, and I3 so that the values ​​calculated by Equations 4 to 6 are equal. When the values ​​calculated by Equations 4 to 6 are equal, the total amount of scattered light does not change even if the film thickness t varies, so the detection accuracy for defects and foreign particles is maintained constant. When adjusting I1, I2, and I3, it is important to note that I1, I2, and I3 ≥ 0.

[0047] An example of the detection unit 130 will be described using Fig. 10 . The detection unit 130 has a detection element 1001, an AD conversion unit 1002, and a transmission line 1003. The detection element 1001 is an element that outputs an electric charge according to the amount of incident light. The AD conversion unit 1002 is an element that converts an analog signal into a digital signal and outputs the digital signal. The transmission line 1003 transmits the digital signal output from the AD conversion unit 1002 to the control unit 140.

[0048] 10 , a plurality of rectangular detecting elements 1001 are arranged along the Y axis, and an AD conversion unit 1002 is connected to each of the detecting elements 1001. Because the detecting elements 1001 are arranged in a row, it is necessary to irradiate the same position on the sample 101 with irradiation light from multiple directions, which requires highly accurate position adjustment.

[0049] Another example of the detection unit 130 will be described with reference to Fig. 11. Similar to Fig. 10, the detection unit 130 illustrated in Fig. 11 includes a detection element 1001 that outputs an electric charge according to the amount of incident light, an AD conversion unit 1002 that converts an analog signal into a digital signal and outputs the digital signal, and a transmission line 1003 that transmits the digital signal output from the AD conversion unit 1002.

[0050] In the detection unit 130 illustrated in FIG. 11 , multiple square-shaped detector elements 1001 are arranged two-dimensionally on the XY plane. The multiple detector elements 1001 arranged in the Y direction are referred to as a line. The detector elements 1001 are TDI (Time Delayed Integration) sensors, and an AD converter 1002 is connected to each of the detector elements 1001 on the rightmost line. Each detector element 1001 transfers charge generated by receiving light to its adjacent detector element 1001 in the X-axis direction, and the integrated value of the charge generated by each detector element 1001 arranged along the X-axis is output to the AD converter 1002. The sample stage 102 moves in the X-axis direction as charge is transferred to the adjacent detector element 1001 in the X-axis direction. The amount of movement of the sample stage 102 is the size on the surface of the sample 101, which corresponds to the pitch of the detector elements 1001 in the X-axis direction. Furthermore, since the plurality of detecting elements 1001 are arranged two-dimensionally on the XY plane, highly accurate position adjustment is not required within the range in which scattered light from irradiation light coming from multiple directions enters the detecting unit 130 .

[0051] When a plurality of square detecting elements 1001 are arranged two-dimensionally on the XY plane, the magnification in the X direction and the magnification in the Y direction must be aligned, and therefore, inspection takes a long time in high-magnification imaging. Fig. 12(a) shows a low-magnification inspection region 1201 and a high-magnification inspection region 1202, which are regions inspected by the detecting unit 130 in Fig. 11.

[0052] The low magnification inspection area 1201 is an area inspected by low magnification imaging while the specimen stage 102 moves per unit time, and is scanned by a low magnification one-line area 1203, which is an area imaged at low magnification by one line in the detection unit 130 in Fig. 11. The high magnification inspection area 1202 is an area inspected by high magnification imaging while the specimen stage 102 moves per unit time, and is scanned by a high magnification one-line area 1204, which is an area imaged at high magnification by one line in the detection unit 130 in Fig. 11.

[0053] When the magnification ratio between low magnification and high magnification is R, the area ratio between a one-line region 1203 at low magnification and a one-line region 1204 at high magnification is R^2. In other words, when inspecting regions of the same area, high-magnification imaging requires R^2 times the time of low-magnification imaging.

[0054] The reduction of inspection time will be described using (b) of Figure 12. (b) of Figure 12 shows a low-magnification inspection area 1205 and a high-magnification inspection area 1206, which are areas inspected per unit time, and a low-magnification one-line area 1207 and a high-magnification one-line area 1208, which are areas where one line is imaged. The low-magnification inspection area 1205 is scanned by the low-magnification one-line area 1207, and the high-magnification inspection area 1206 is scanned by the high-magnification one-line area 1208. The low-magnification inspection area 1201 and the low-magnification inspection area 1205 are the same size. The high-magnification inspection area 1206 has the same size in the Y direction as the low-magnification inspection area 1205 and the same size in the X direction as the high-magnification inspection area 1202.

[0055] The high magnification one line region 1208 includes square pixels of the same size as the square pixels included in the high magnification one line region 1204, and a greater number of square pixels are arranged in the Y direction than in the high magnification one line region 1204. In other words, the high magnification one line region 1208 allows the high magnification inspection region 1206, which is a wide region in the Y direction, to be inspected by high magnification imaging.

[0056] The low-magnification one-line region 1207 has rectangular pixels arranged in the Y direction, the same number as the square pixels included in the high-magnification one-line region 1208. The rectangular pixels of the low-magnification one-line region 1207 have the same size in the Y direction as the square pixels included in the high-magnification one-line region 1204, and the same size in the X direction as the square pixels included in the low-magnification one-line region 1203. In other words, the low-magnification one-line region 1207 allows the low-magnification inspection region 1205, which is a wide region in the X direction, to be inspected by high-magnification imaging in the Y direction. Note that to achieve both the high-magnification one-line region 1208 and the low-magnification one-line region 1207, it is necessary to change the magnification in the X direction without changing the magnification in the Y direction.

[0057] The magnification adjustment unit 124, which changes the magnification in the X direction without changing the magnification in the Y direction, will be described using Fig. 13. Fig. 13(a) shows an XZ cross section, and Fig. 13(b) shows a YZ cross section. The magnification adjustment unit 124 illustrated in Fig. 13 includes a convex cylindrical lens 1301, a concave cylindrical lens 1302, and a convex cylindrical lens 1303. The concave cylindrical lens 1302 is disposed between the convex cylindrical lens 1301 and the convex cylindrical lens 1303.

[0058] Convex cylindrical lens 1301 and convex cylindrical lens 1303 have convex curved surfaces in the XZ cross section, so light converges, but they do not have curved surfaces in the YZ cross section, so parallel light is maintained. Also, concave cylindrical lens 1302 has a concave curved surface in the XZ cross section, so light diverges, but they do not have a curved surface in the YZ cross section, so parallel light is maintained. In other words, when concave cylindrical lens 1302 moves between the solid line position and the dotted line position, the magnification in the X direction changes, but the magnification in the Y direction does not change.

[0059] Since the convex cylindrical lens 1301, the concave cylindrical lens 1302, and the convex cylindrical lens 1303 are not rotationally symmetrical, it is difficult to increase their size, and therefore it is preferable to keep the light beam passing through them as narrow as possible. However, when the magnification is changed, the light beam may become larger in the X direction.

[0060] Therefore, as illustrated in Figure 14, the detecting elements 1001 of the detecting unit 130 are made rectangular, with a larger size in the X direction than in the Y direction. The detecting elements 1001 of the detecting unit 130 illustrated in Figure 14 have a size in the X direction that is 1.5 to 2 times the size in the Y direction. By using a detecting unit 130 in which rectangular detecting elements 1001 are arranged two-dimensionally, it becomes possible to reduce the size of the cylindrical lens used in the magnification adjusting unit 124, which changes the magnification in the X direction without changing the magnification in the Y direction. Note that the method of changing the magnification in the X direction without changing the magnification in the Y direction is not limited to the one described using Figures 13 and 14.

[0061] An example of a detection unit 130 that performs binning will be described using Fig. 15. Similar to Fig. 11, the detection unit 130 in Fig. 15 has a plurality of detection elements 1001 arranged two-dimensionally on the XY plane, an AD conversion unit 1002, and a transmission line 1003. Binning is a process in which a plurality of detection elements 1001 are regarded as a single detection element 1001, and by performing binning in the X direction, the magnification in the X direction can be reduced.

[0062] The detection unit 130 in FIG. 15 further includes a binning buffer 1501 and an accumulation buffer 1502. The binning buffer 1501 is connected to the detection elements 1001 on the rightmost line and bins the charges for two lines. The accumulation buffer 1502 is connected to the binning buffer 1501 and accumulates the charges transferred from the binning buffer 1501 before outputting them to the AD conversion unit 1002. The AD conversion unit 1002 converts the charges for two lines output from the accumulation buffer 1502 into digital signals and outputs them to the transmission line 1003.

[0063] 15, the speed at which charges generated by light reception are transferred in the X direction can be increased. That is, by having the binning buffer 1501 and the accumulation buffer 1502, binning and AD conversion can be performed in a pipeline, thereby increasing the charge transfer speed.

[0064] The timing chart of the detection unit 130 in Fig. 15 will be described using Fig. 16. Note that Fig. 16(a) shows a comparative example in which the binning buffer 1501 and the accumulation buffer 1502 are not provided, and Fig. 16(b) shows a comparative example in which the binning buffer 1501 and the accumulation buffer 1502 are provided.

[0065] 16A, the first stage is charge transfer between lines, the second stage is charge reset, the third stage is CDS (Correlated Double Sampling) reference voltage sampling, the fourth stage is CDS signal sampling, and the fifth stage is the timing of AD conversion. Charge transfer cannot be performed during the CDS signal sampling period, so the charge transfer speed cannot be increased.

[0066] In (b) of Fig. 16, the first row shows the charge transfer between lines, and the second row shows the timing of the charge transfer from the binning buffer 1501 to the accumulation buffer 1502. Note that the third to sixth rows in (b) of Fig. 16 are the same as the second to fifth rows in (a) of Fig. 16. By providing the binning buffer 1501 and the accumulation buffer 1502, charge transfer can be performed during the CDS signal sampling period, thereby increasing the charge transfer speed.

[0067] FIG. 17 illustrates a timing chart of light reception and light irradiation by the detection unit 130, which includes the detection element 1001 in which the foreign particle 902 is captured. In FIG. 17 , the first row shows the light reception timing for the first line in the detection unit 130, and charges are generated during a light reception period t_scan, which is the period during which the detection element 1001 receives light. The light reception period t_scan is on the order of μs. The second row shows the light reception timing for the second line adjacent to the first line, the third row shows the light reception timing for the third line, and the fourth row shows the light reception timing for the Nth line. The charges generated on the first line are transferred sequentially to the second line, the third line, ..., the Nth line. The Nth line is the line closest to the AD conversion unit 1002. Light reception on each line is repeated with a non-light reception period t_off interposed therebetween.

[0068] The fifth row in Figure 17 shows the irradiation timing of the first irradiation light L1, and the sixth row shows the irradiation timing of the second irradiation light L2. The first irradiation light L1 and the second irradiation light L2 are irradiated onto the sample 101 every light-receiving period t_scan. The irradiation of the first irradiation light L1 and the second irradiation light L2 is repeated at an irradiation period T_L. During the light-receiving period t_scan, the sample 101 moves in the X direction. Therefore, if the pulse width PW of the first irradiation light L1 and the second irradiation light L2 is too long or the irradiation period T_L is too short, image blurring occurs. Furthermore, if the pulse width PW is too short, the intensity of the first irradiation light L1 and the second irradiation light L2 increases, which may damage the sample 101. Therefore, the pulse width PW is set to the order of nanoseconds.

[0069] To prevent interference between the first and second irradiation beams L1 and L2, a time difference Δt may be set between the irradiation timings of the two beams. The time difference Δt is longer than the pulse width PW and sufficiently shorter than the light-receiving period t_scan.

[0070] If a foreign particle 902 is captured in the detector element 1001-1 in the first line, the foreign particle 902 will also be captured in the detector element 1001 in the second line adjacent to the detector element 1001-1, and similarly, the foreign particle 902 will also be captured in the detector element 1001 in the third line and the detector element 1001-N in the Nth line. If the position of the foreign particle 902 captured in the detector elements 1001 of each line is the same, aliasing will occur, reducing the detection accuracy of defects and foreign particles. Therefore, aliasing is suppressed by shifting the position of the foreign particle 902 captured in the detector elements 1001 of each line. To shift the position of the foreign particle 902 captured in the detector elements 1001 of each line, the control unit 140 can set the magnification Mx in the X direction and the movement amount Px of the sample 101 in the X direction between the lines, for example, using the following equation:

[0071] Mx=Sx / {Px(G / N+1)} (Equation 7) Here, Sx is the size of the detecting element 1001 in the X direction, G is the amount of deviation within Sx, and N is the number of lines, where G<1. When the magnification Mx and the amount of movement Px are set using (Equation 7), the position of the foreign substance 902 captured in the detecting element 1001 is shifted by G / N between adjacent lines, and is shifted by G between the detecting element 1001-1 and the detecting element 1001-N, so aliasing can be suppressed.

[0072] The aliasing suppression effect will be explained using Figure 18. The graph in Figure 18 shows the distribution of foreign object signal strength versus foreign object position, with the curve showing a peak when the foreign object is located at the center of the detecting element 1001. Note that since the foreign object signal strength is obtained by detecting scattered light, it can be obtained even when the foreign object is located outside the size of the detecting element. Aliasing can be suppressed when the curve in Figure 18 is close to a sinc function.

[0073] A first curve 1801 is the case when t_scan>>T_L, a second curve 1802 is the case when t_scan+t_off=T_L and G=0, and a third curve 1803 is the case when t_scan+t_off=T_L and G=0.5. When t_scan>>T_L, the number of irradiations during the light-reception period t_scan is multiple, and when t_scan+t_off=T_L, the number of irradiations during the light-reception period is one.

[0074] In the first curve 1801, the foreign object signal strength decreases due to the influence of the movement of the foreign object 902 during the light receiving period. In the second curve 1802, the foreign object signal strength increases within the size of the detecting element and decreases sharply outside the size of the detecting element compared to the first curve 1801 because it is not influenced by the movement of the foreign object 902 during the light receiving period. Furthermore, since the profile of the second curve 1802 is far from a sinc function, aliasing is likely to occur. In the third curve 1803, the foreign object signal strength within the size of the detecting element decreases more than the second curve 1802, but is improved more than the first curve 1801. Furthermore, since the profile of the third curve 1803 is close to a sinc function, aliasing is easily suppressed.

[0075] 18 shows the case where the deviation amount G is 0.5, but it is preferable to adjust G according to the magnification Mx. For example, G may be increased at low magnifications that are susceptible to the effects of aliasing, and decreased at high magnifications that are less susceptible to the effects of aliasing. Alternatively, G may be calculated to provide a profile close to a sinc function in the graph of FIG. 18, and the magnification Mx and the movement amount Px of the sample 101 in the X direction between the lines may be set using the calculated G and Equation 7.

[0076] Note that the suppression of aliasing is not limited to using (Equation 7), and the position of the foreign substance 902 captured by the detecting element 1001 in each line may be shifted by making t_scan+t_off≠T_L. However, to avoid the influence of movement of the foreign substance 902 during the light-receiving period t_scan, the number of irradiations during the light-receiving period is limited to one. In other words, aliasing can be suppressed by adjusting the light-receiving period t_scan and the irradiation cycle T_L while keeping the magnification Mx fixed.

[0077] The above describes the embodiments of the present invention. The present invention is not limited to the above embodiments, and the components can be modified and embodied without departing from the spirit of the invention. Furthermore, multiple components disclosed in the above embodiments may be combined as appropriate. Furthermore, some components may be omitted from all the components shown in the above embodiments.

[0078] 100: Optical inspection device, 101: Sample, 102: Sample stage, 103: Stage driving unit, 110: Light source unit, 111: First irradiation unit, 112: Second irradiation unit, 120: Detection optical system, 121: Objective lens, 122: Spatial filter, 123: Analyzer, 124: Magnification adjustment unit, 125: Imaging lens, 130: Detection unit, 140: Control unit, 201: Laser light source, 202: Half-wave plate, 203: Polarizing beam splitter, 204: Diffuser, 205: Half-wave plate, 206: Polarizing beam splitter , 207: mirror, 301: concave cylindrical lens, 302: convex cylindrical lens, 303: Dove prism, 304: ½ wavelength plate, 305: ¼ wavelength plate, 306: condenser lens, 401: memory section, 402: X direction section, 403: Y direction section, 500: pupil, 510: diffracted light of L1, 511: diffracted light of L1, 512: diffracted light of L1, 513: diffracted light of L1, 520: diffracted light of L2, 521: diffracted light of L2, 522: diffracted light of L2, 523: diffracted light of L2, 530: diffracted light of L3, 5 31: diffracted light of L3, 532: diffracted light of L3, 533: diffracted light of L3, 540: diffracted light of L4, 541: diffracted light of L4, 542: diffracted light of L4, 550: diffracted light of L5, 551: diffracted light of L5, 552: diffracted light of L5, 601: rod, 602: rod, 603: rod, 604: rod, 605: rod, 606: rod, 900: silicon, 901: transparent thin film, 902: foreign substance, 1001: detecting element, 1002: AD conversion unit, 1003: transmission line, 1201: inspection area at low magnification, 12 02: Inspection area at high magnification, 1203: 1 line area at low magnification, 1204: 1 line area at high magnification, 1205: Inspection area at low magnification, 1206: Inspection area at high magnification, 1207: 1 line area at low magnification, 1208: 1 line area at high magnification, 1301: convex cylindrical lens, 1302: concave cylindrical lens, 1303: convex cylindrical lens, 1501: binning buffer, 1502: accumulation buffer, 1801: first curve, 1802: second curve, 1803: third curve.

Claims

1. An optical inspection device comprising a light irradiation unit that irradiates a sample with two linear beams of light, namely, a first irradiation beam and a second irradiation beam, an objective lens that collects scattered light from the sample, a detection unit that detects the scattered light collected by the objective lens, and a control unit that determines whether the sample contains defects or foreign matter based on a signal output from the detection unit and controls each unit, wherein the control unit sets the directions of the first irradiation beam and the second irradiation beam so that first reflected light, which is light from the first irradiation beam reflected by the sample, and second reflected light, which is light from the second irradiation beam reflected by the sample, are at the same position at the pupil position of the objective lens in the longitudinal direction of the linear beams or in a direction perpendicular to the longitudinal direction.

2. An optical inspection device according to claim 1, wherein the control unit sets the directions of the first irradiation light and the second irradiation light so as to satisfy sin θ1·sin φ1 = sin θ2·sin φ2 or sin θ1·cos φ1 = sin θ2·cos φ2 when the incident angle of the first irradiation light is θ1, the azimuth angle is φ1, and the incident angle of the second irradiation light is θ2, the azimuth angle is φ2.

3. An optical inspection device according to claim 1, wherein the sample includes a periodic circuit pattern, and further comprising a spatial filter that blocks diffracted light generated from the circuit pattern when the first illumination light and the second illumination light are irradiated onto the sample.

4. An optical inspection device as described in claim 1, wherein the sample has a transparent film on its surface, and the control unit adjusts the intensity ratio between the first irradiation light and the second irradiation light so that the total amount of scattered light falls within a predetermined range even when the film thickness of the transparent film varies.

5. An optical inspection device according to claim 1, characterized in that the optical path difference between the first irradiation light and the second irradiation light is greater than the product PW·c of the pulse width PW of the first irradiation light and the second irradiation light and the speed of light c.

6. An optical inspection device according to claim 1, characterized in that the optical path difference between the first irradiation light and the second irradiation light is greater than the coherence length of the first irradiation light and the second irradiation light.

7. An optical inspection device according to claim 1, further comprising a magnification adjustment unit that changes the magnification in a direction perpendicular to the longitudinal direction without changing the magnification in the longitudinal direction, wherein the detection unit has a plurality of detection elements arranged two-dimensionally, and the size of the detection elements in the direction perpendicular to the longitudinal direction is larger than the size in the longitudinal direction.

8. An optical inspection device according to claim 1, wherein the detection unit has a plurality of detection elements arranged two-dimensionally, and the control unit bins the electric charges generated in the detection elements in a direction perpendicular to the longitudinal direction.

9. An optical inspection device according to claim 8, wherein the detection unit further has a binning buffer and an accumulation buffer, the binning buffer bins the charges of two of the detection elements aligned in a direction perpendicular to the longitudinal direction, and the accumulation buffer accumulates the charges transferred from the binning buffer.

10. An optical inspection device according to claim 1, wherein the detection unit has a plurality of detection elements arranged two-dimensionally, and the control unit sets the magnification in a direction perpendicular to the longitudinal direction or the amount of movement of the sample so that the position of the object reflected in each of the detection elements arranged in a direction perpendicular to the longitudinal direction is shifted.

11. An optical inspection device according to claim 10, wherein the control unit sets Mx and Px using Mx = Sx / {Px(G / N+1)}, where Mx is the magnification in the direction perpendicular to the longitudinal direction, Sx is the size of the detection element in the direction perpendicular to the longitudinal direction, Px is the amount of movement of the sample in the direction perpendicular to the longitudinal direction, G is the amount of positional deviation of the object, and N is the number of the detection elements lined up in the direction perpendicular to the longitudinal direction.

12. An optical inspection device as described in claim 1, wherein the detection unit has a plurality of detection elements arranged two-dimensionally, and the control unit sets the light receiving period of the detection elements or the irradiation cycle of the first irradiation light and the second irradiation light so that the positions of the objects reflected in each of the detection elements arranged in a direction perpendicular to the longitudinal direction are shifted.

13. A control method for an optical inspection device comprising a light irradiation unit that irradiates a sample with two linear beams of light, namely, a first irradiation beam and a second irradiation beam, an objective lens that collects scattered light from the sample, a detection unit that detects the scattered light collected by the objective lens, and a control unit that determines whether the sample contains defects or foreign matter based on a signal output from the detection unit and controls each unit, wherein the control unit sets the directions of the first irradiation beam and the second irradiation beam so that first reflected light, which is light from the first irradiation beam reflected by the sample, and second reflected light, which is light from the second irradiation beam reflected by the sample, are at the same position at the pupil position of the objective lens in the longitudinal direction of the linear beams or in a direction perpendicular to the longitudinal direction.

Images