Defect Inspection Equipment

Abstract

To provide a defect inspection apparatus capable of simultaneously inspecting the height and pitch of a small step defect and a waviness defect on a sample surface with high sensitivity and high throughput.SOLUTION: A defect inspection apparatus according to the present invention is equipped with a first sensor for detecting a differential interference signal and a second sensor for detecting a pupil plane image of an irradiating optical system, and detects a step defect using the differential interference signal and detects a waviness defect using signals detected by the first sensor and the second sensor.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a defect inspection apparatus that detects defects on a sample using light. [Background technology]

[0002] As the data capacity of hard disks (HDs) continues to increase, the surface condition, defect size, and shape of HDs have a significant impact on performance and yield. To maintain and improve yield, it is necessary to inspect for low-aspect-ratio, low-step defects (heights of a few nanometers, widths of a few tens of micrometers) and waviness defects (periods of a few tens of micrometers, heights of a few nanometers) caused by surface polishing or foreign matter contamination. Low-aspect-ratio defects are low-step defects that generate almost no scattered light. Interferometric measurements, such as differential interference contrast (DIC) inspection, which uses the principles of differential interference microscopy, are used to detect low-step defects. Scattered light inspection is used, which can detect waviness defects as surface roughness (haze) without including defect height or period information.

[0003] Patent Document 1 below discloses an optical system that simultaneously performs scattered light inspection and DIC inspection by scanning a wafer surface with laser light illumination. The document describes the following technology (see abstract): "An inspection apparatus for simultaneous dark field (DF) and differential interference contrast (DIC) inspection includes an illumination source and a sample stage configured to fix a sample. The inspection apparatus includes a first sensor, a second sensor, and an optical subsystem. The optical subsystem includes an objective lens and one or more optical elements arranged to direct illumination from one or more illumination sources to the surface of the sample via the objective lens. The objective lens is configured to collect signals from the surface of the sample, and the collected signals include signals based on scattering from the sample and / or signals based on phase. The inspection apparatus includes one or more separation optical elements arranged to spatially separate the collected signals into DF signals and DIC signals by directing the DF signals and DIC signals along DF paths and DIC paths, respectively." [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2017-531162 Summary of the Invention [Problem to be solved by the invention]

[0005] Due to surface polishing during the HD manufacturing process, the surface of HDs has randomly periodic undulation defects that are difficult to detect using conventional scattered light detection. As HD capacity increases, the distance between the magnetic head and the HD surface becomes shorter, creating a need to inspect undulation defects, which were previously outside the scope of control. In addition, there is a similar need to detect non-periodic, low-level step defects. High-sensitivity, high-throughput inspection is required for both undulation and low-level step defects.

[0006] DIC-based inspection equipment is suitable for detecting low-level step defects. Therefore, it would be ideal if waviness defects could also be detected using a DIC-based inspection equipment. However, when detecting waviness defects using a DIC-based inspection equipment, the DIC signal intensity varies depending on the period of the waviness defects (the interval between defects: pitch), and in particular, the signal amount for a period of shear amount × 1 / n is zero or very weak, making it difficult to detect. Therefore, it is difficult to detect waviness defects with an arbitrary period simply by using a DIC-based optical defect inspection equipment.

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a defect inspection device that can simultaneously inspect the height and pitch of low-level step defects and waviness defects on a sample surface with high sensitivity and high throughput. [Means for solving the problem]

[0008] The defect inspection device according to the present invention includes a first sensor that detects a differential interference signal and a second sensor that detects a pupil plane image of an irradiation optical system, and detects step defects using the differential interference signal and waviness defects using the signals detected by the first sensor and the second sensor. [Effects of the Invention]

[0009] The defect inspection device according to the present invention can simultaneously inspect the height and pitch of low-level step defects and waviness defects on a sample surface with high sensitivity and high throughput. Problems, configurations, and effects other than those described above will become clear from the following description of the embodiments. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic configuration diagram of a defect inspection device 1 according to a first embodiment. [Figure 2] FIG. 10 is a diagram illustrating a rotation inspection of the surface of the disk 2. [Figure 3] The arrangement of the detection elements of the sensors 14 and 17 is shown. [Figure 4] 1A and 1B are a cross-sectional view and a top view of a bump defect 40 and a waviness defect 42, respectively. [Figure 5] 10A and 10B are diagrams illustrating the relationship between a wavy defect along the θ direction and a height signal. [Figure 6] 10 shows the intensity ratio between the height signal 61 and the height signal 62 obtained by simulation with respect to the period of the undulation defect. [Figure 7] FIG. 2 is a functional block diagram of a processor 105. [Figure 8] 10A and 10B are diagrams illustrating a method for determining the height of a waviness defect in the θ direction. [Figure 9] FIG. 2 is a diagram illustrating data output by the defect inspection device 1. [Figure 10] FIG. 1 is a system block diagram of a defect inspection device 1. [Figure 11] FIG. 1 is a configuration diagram of a defect inspection device 1 according to a second embodiment. [Figure 12]FIG. 10 is a functional block diagram of a processor 105 according to a second embodiment. [Figure 13] 10 shows the configuration of a detection element of a sensor 17 in embodiment 3. [Figure 14] 1A and 1B are a cross-sectional view and a top view of an R-direction waviness defect 142. [Figure 15] FIG. 11 is a functional block diagram of a processor 105 according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] <First Embodiment> FIG. 1 is a schematic diagram of a defect inspection device 1 according to a first embodiment of the present invention. The defect inspection device 1 is a device that detects step defects and waviness defects present on the surface of a sample by irradiating the sample with light. Here, as an example of a sample, a case where surface defects of a hard disk are inspected will be described. Each of the components of the defect inspection device 1 shown in FIG. 1 will be described below.

[0012] The light source 3 is composed of a coherent single-wavelength laser. A longer wavelength allows for a wider detection range. A shorter wavelength increases sensitivity to minute heights. The illumination optical system 4 is positioned to optimize the beam shape that is irradiated onto the disk 2. For example, to achieve a thin linear beam spot, as described below, the illumination optical system 4 can be realized by using two cylindrical lenses and an anamorphic prism. The mirror 5 is assumed to be a general reflecting mirror. It is desirable to use a multilayer film designed to prevent phase change within the plane of the beam as the mirror 5.

[0013] Beam splitters 6 and 7 are beam splitters that split the beams. Beam splitter 6 transmits light from light source 3 to disc 2 and reflects light reflected from disc 2 toward sensor 17. Beam splitter 7 transmits light from light source 3 to disc 2 and reflects light reflected from disc 2 toward sensor 14 and also transmits it toward beam splitter 6. It is desirable that each beam splitter distributes intensity appropriately so that the optimal amount of light is obtained at sensor 14 and sensor 17, respectively. Here, we assume that the light amount from light source 3 is sufficient and assume a beam splitter that splits the intensity at 1:1.

[0014] The quarter-wave plate 8 is provided to adjust the light intensity to 1:1 when the beam is separated into P-polarized light and S-polarized light by the polarization separation element 9. The polarization separation element 9 separates the incident beam into P-polarized light and S-polarized light. For example, the polarization separation element 9 can be realized by a Nomarski prism or a Wollaston prism.

[0015] The focusing optical system 10 is an optical system that focuses the light separated by the polarization separation element 9 onto the disc 2. To obtain a differential interference signal, the focusing optical system is set so that the split point of the light on the polarization separation element 9 and the focusing point on the disc 2 are at their focal points. As a result, the P-polarized and S-polarized light reflected from the disc 2 are combined again by the polarization separation element 9. For ease of implementation, the focusing optical system can be easily designed by using a relay optical system.

[0016] The detection optical system 11 is an optical system set up so that the beam spot on the disc 2 is imaged on the sensor 14. It is assumed that the magnification will be converted to be optimal for the size of the sensor 14. The sensor 14 is preferably placed at a position conjugate with the beam spot on the disc 2. This allows for accurate detection of differential interference signals.

[0017] The detection optical system 16 is an optical system arranged so that the intensity of the image on the pupil plane of the focusing optical system 10 can be detected by a sensor 17. It is desirable to set the pupil position of the focusing optical system 10 and the sensor 17 so that they are conjugate, but it is sufficient if the pupil image of the focusing optical system 10 can be detected by the sensor 17. The detection optical system 16 may be subjected to magnification conversion so as to match the size of the sensor 17.

[0018] Light output from light source 3 is irradiated towards disk 2. The beam is split into two light beams, S-polarized and P-polarized, by polarization splitter 9, and these are irradiated onto the surface of disk 2. Light reflected from disk 2 is detected by sensors 14 and 17. Sensor 14 detects differential interference contrast (DIC) signals of the two light beams, S-polarized and P-polarized. Sensor 17 detects an image on the pupil plane of focusing optical system 10.

[0019] The processor 105 uses the DIC signal detected by the sensor 14 to detect minute, low-level defects on the surface of the disk 2. Furthermore, the processor 105 uses the pupil plane beam intensity detected by the sensor 17 and the DIC signal detected by the sensor 14 to detect waviness defects on the surface of the disk 2 according to a principle that will be described later.

[0020] The pupil plane intensity has a slight tilt in the ray direction of the light reflected from the undulation defects on the surface of the disk 2 compared to the light reflected from a flat surface. This tilt is so small that it cannot be detected on the imaging plane, but on the pupil plane it can be calculated as an intensity ratio of a few percent from the center. This intensity ratio depends on the height and period (pitch) of the undulation defects. Therefore, by determining the intensity ratio on the pupil plane, the processor 105 can calculate the height and period of the undulation defects.

[0021] FIG. 2 is a diagram illustrating the rotational inspection of the surface of a disk 2. During the inspection of the disk 2, the disk 2 is rotated in the θ direction by a stage 103 (described later). Light beams 20 and 21 are irradiated onto the surface of the disk 2. Light beams 20 and 21 are S-polarized and P-polarized, respectively, as shown in FIG. 1. The detected signal does not change regardless of whether light beam 20 or light beam 21 is S-polarized or P-polarized, and these can be in any order. Light beams 20 and 21 are long in the radial (R) direction 22 and short in the θ direction 23 (rotation direction) (thin line shape). By making them long in the radial (R) direction, surface defects can be detected over a wide area at once, enabling high-throughput full-surface inspection.

[0022] When inspecting the surface of the disk 2, the light beams 20 and 21 are not moved, and the disk 2 is rotated along the θ direction arrow 23 while being moved along the radial direction arrow 22, thereby inspecting the entire surface of the disk 2. By increasing the beam diameter in the R direction, it is possible to inspect the entire surface without overlooking even small defects.

[0023] 3 shows the arrangement of detecting elements in each of the sensors 14 and 17. The sensors 14 and 17 have detecting elements arranged on the detection surface as shown in FIG. 3 according to the properties of the light beam to be detected.

[0024] The surface of the sensor 14 is conjugate with the disk 2, and imaging light 30 of the area being observed is incident thereon (the collected light forms an image on the sensor surface). The sensor 14 has N pixels (N detection elements) arranged in the R direction, from sensor pixels S1_1 to S1_N, and can detect DIC signals for each pixel. This makes it possible to simultaneously detect DIC signals over a wide range without reducing the detection sensitivity for each pixel. In other words, it is possible to detect small step defects on the disk 2 without overlooking them.

[0025] The sensor 17 detects the pupil plane intensity of the focusing optical system 10. Since the NA (Numerical Aperture) is larger in the thin line direction (θ direction) on the surface of the disc 2, the size of the beam spot 31 on the pupil plane is larger in the θ direction. Therefore, the sensor 17 has two pixel detection elements arranged along the θ direction. The processor 105 (or the sensor 17 itself) detects the signal intensity difference between pixels S2_1 and S2_2.

[0026] FIG. 4 shows a cross-sectional view and a top view of a bump defect 40 and a wavy defect 42, respectively. Low-level step defects include protruding defects on the surface of the disk 2, such as bump defect 40, and recessed defects (not shown). Low-level step defects are assumed to have heights and surface sizes of 0.1 μm to several μm. A fine beam is used to ensure that these defects are not overlooked. As shown in the figure, a wavy defect 42 is a wavy surface with small steps (heights of about 1 nm). In hard disks, wavy defects with a wavy period 43 (wavy pitch) in the range of about 20 μm to 100 μm are said to cause bad sectors.

[0027] The DIC signal can detect a phase step 41 between the irradiation positions of the light beams 21 and 20. By detecting the phase step 41, it is possible to detect a bump defect 40 and a waviness defect 42. However, in the case of a waviness defect 42, it is important to note that the detected phase step changes not only depending on the height of the waviness defect but also on the waviness period 43. This will be explained next.

[0028] FIG. 5 is a diagram illustrating the relationship between a waviness defect and a height signal along the θ direction. The upper part of FIG. 5 shows the relationship between P / S polarized light beam 20, light beam 21, and waviness. The disk 2 is shown in cross section. The horizontal direction in the figure corresponds to the θ direction. The lower part of FIG. 5 shows the waveforms in the θ direction of a height signal 50 obtained from DIC and a height signal 51 obtained from the pupil intensity distribution.

[0029] When the waviness period is out of phase with respect to the distance (shear amount) between light beam 20 and light beam 21 (left in the figure), when light beam 20 is irradiated onto the bottom of the waviness, light beam 21 is irradiated onto the top of the waviness, as shown in the figure. In this case, light beam 20 and light beam 21 are at different heights on disk 2, so a DIC signal is generated. That is, height signal 50 generates a signal corresponding to the disk position, as shown in the figure. On the other hand, the pupil intensity distribution obtained from light beam 20 and the pupil intensity distribution obtained from light beam 21 are also out of phase with each other. After reflecting off disk 2, light beam 20 and light beam 21 are combined by polarization separation element 9, so they cancel each other out and no amplitude is generated for height signal 51, as shown in the figure.

[0030] When the waviness period is in phase with the spacing (shear amount) between light beam 20 and light beam 21 (right side of the figure), when light beam 20 is irradiated onto the top of the waviness, light beam 21 is irradiated onto the top of the waviness, as shown in the figure. In this case, light beam 20 and light beam 21 are at the same height on disk 2, so the DIC signal is zero. In other words, no signal corresponding to the disk position is generated in height signal 50, as shown in the figure. On the other hand, the pupil intensity distributions obtained from light beam 20 and light beam 21 are also in phase with each other. After reflecting off disk 2, light beam 20 and light beam 21 are combined by polarization separation element 9, but because they are in phase, they do not cancel each other out. Therefore, height signal 51 becomes a signal corresponding to the disk position, as shown in the figure.

[0031] As described above, the DIC height signal 50 and the pupil intensity distribution height signal 51 have a complementary relationship with respect to the waviness period. The present invention utilizes this feature to provide a waviness signal detection method that is independent of the waviness period. Note that, because the amplitudes of the height signals 50 and 51 depend on the waviness height and period, they can be converted into height information based on the correction method described in FIG. 8.

[0032] Figure 6 shows the intensity ratios of height signals 61 and 62 obtained by simulation with respect to the period of the undulation defect. Height signal 61 is a DIC signal, and height signal 62 is an optical pupil plane intensity distribution signal. In this simulation, the distance (shear amount) between light beam 20 and light beam 21 is set to 175 μm, and the undulation defect has the same height but is changed in period. Height signals 61 and 62 are normalized with the maximum value of each detection signal set to 1.

[0033] The height signal 61 (DIC signal) is maximum at the waviness defect period 63 and minimum at the waviness defect period 64. The waviness defect period 63 is in the opposite phase state described in FIG. 5 and is equal to the shear amount × 2 / (2n+1) (n is a natural number). The waviness defect period 64 is in the same phase state described in FIG. 5 and is equal to the shear amount × 1 / n (n is a natural number). The simulation results show that the height signal 61 (DIC signal) differs for each waviness defect period. In contrast, the height signal 62 (optical pupil plane intensity signal) is minimum at the waviness period 63 because it is in the opposite phase. The height signal 62 is maximum at the waviness period 64 because it is in the same phase. This shows that by detecting the height signals 61 and 62, all waviness defects with periods of 20 to 100 μm can be detected.

[0034] The relative intensities of the height signals 50 and 51 detected by the inspection device change for each period, but the relative intensity ratio for each period of the waviness defect obtained by this simulation can be used to correct the height signal to the actual defect.

[0035] 7 is a functional block diagram of processor 105. Current signals from the light-receiving surfaces of sensors 14 and 17 are converted into digital signals by an I / V converter 70 and an A / D converter 71. The I / V converter 70 and the A / D converter 71 are common technologies and will not be described in detail here, but in order to improve the inspection speed, it is advisable to design them with attention to frequency characteristics.

[0036] The DIC signal converted by the A / D converter 71 has an amplitude that changes at a certain intensity level, like the height signal 50 shown in Fig. 5. The offset removal unit 72 removes the intensity level and obtains only the amplitude.

[0037] The unevenness evaluation unit 73 evaluates minute defects using the acquired amplitude-only signal. The unevenness evaluation unit 73 extracts signals that have changed and determines whether the amplitude is positive or negative to determine unevenness. Furthermore, by measuring the length of the amplitude in the θ direction, it is possible to obtain information on the length of the defect. Furthermore, by measuring how many light-receiving surfaces have changed, it is possible to obtain information on the length of the defect in the R direction. The unevenness evaluation unit 73 sends amplitude information along with length information of the minute defect in the R and θ directions to the unevenness height evaluation unit 74.

[0038] The unevenness height evaluation unit 74 acquires height information based on the amplitude and defect size. Height information can be acquired using DIC with standard techniques, so details are omitted here. As described above, the sensor 14 can detect the unevenness, size, and height of minute step defects.

[0039] The signal addition processing unit 75 adds all the light receiving surface information from which the intensity levels have been removed by the offset removal unit 72. Here, an example will be described in which all spot signals in the R direction on the disc 2 are detected together, but the spot signals may also be evaluated individually. If evaluated individually, the waviness period in the R direction can be evaluated in detail.

[0040] The digital signal obtained by the sensor 17 is subjected to the following calculation by the signal calculation unit 77, which can output a signal S corresponding to the waviness height in the θ direction from the pupil plane intensity distribution: S=(S2_1)-(S2_2).

[0041] The FFT processing unit 76 performs Fourier transform on the signals generated by the signal addition processing unit 75 and the signal calculation unit 77 using the rotation speed corresponding to the R direction position of the disc 2, and calculates the modulation degree (signal level) corresponding to the waviness period. The frequency evaluation unit 78 extracts waviness periods with large modulation degrees.

[0042] A signal selection unit 79 selects the larger of the modulation degree obtained from DIC (sensor 14) and the modulation degree obtained from the pupil intensity distribution (sensor 17) from the extracted waviness period. A θ-direction waviness height evaluation unit 80 converts the modulation degree into height information by comparing the signal selected by the signal selection unit 79 with an ideal height curve (described later). As a result, the period and height of the waviness in the θ direction at the specified R position can be determined.

[0043] The processor 105 can distinguish between minute step defects and waviness defects by separately outputting information on the irregularities, size, and height of minute step defects and information on the period and height of waviness defects.

[0044] FIG. 8 is a diagram illustrating a method for determining the height of a waviness defect in the θ direction. The upper part of FIG. 8 shows the modulation depth of the DIC signal after FFT for three cases. The lower part of FIG. 8 shows the modulation depth of the height signal obtained from the pupil intensity distribution for the same three cases. In each graph, the horizontal axis represents the waviness frequency (pitch) and the vertical axis represents the modulation depth. The modulation depth obtained by DIC is height signal 50, and the modulation depth obtained from the pupil plane intensity distribution is height signal 51.

[0045] Case 1 is a case where the swell period in the θ direction is out of phase with the interval between the light beams 20 and 21 (left side of FIG. 5). Case 2 is a case where the swell period in the θ direction is in phase with the interval between the light beams 20 and 21 (right side of FIG. 5). Case 3 is an intermediate case between the two.

[0046] Ideal height curve 81 and ideal height curve 82 each show the ideal height signal obtained at a specified height. Each ideal height curve describes the ratio of the signal level to the defect height for each pitch value of the waviness defect. Curve 81 is for the DIC signal, and curve 82 is for the pupil plane intensity signal. The height evaluation unit 80 can calculate the waviness defect height by comparing the signal level with the ideal height curve. Data describing each ideal height curve may be stored in advance in a storage device provided in the defect inspection device 1.

[0047] In case 1, the DIC signal has a large modulation degree due to the reverse phase. Therefore, the signal selector 79 selects the DIC signal. The height evaluator 80 determines the height from the ideal height curve 81 and the height signal 50 using the following formula: Height=Hs1 / Hi.

[0048] In case 2, the signals are in phase, so the modulation depth of the pupil intensity distribution signal is large. Therefore, the signal selector 79 selects the pupil intensity distribution signal. The height evaluator 80 determines the height from the ideal height curve 82 and the height signal 51 using the following formula: Height=Hs2 / Hi.

[0049] In Case 3, the signal selection unit 79 selects the larger of the DIC signal and the pupil plane intensity signal. In the example of FIG. 8, the modulation depth of the DIC signal is larger. Therefore, the signal selection unit 79 selects the DIC signal. The height evaluation unit 80 determines the height from the ideal height curve 81 and the height signal 50 using the following formula: Height=Hs1 / Hi.

[0050] As described above, by using the signal with the larger modulation degree out of the DIC signal and the pupil plane intensity signal, it is possible to easily determine the height and period of the undulation defect regardless of the period of the undulation defect.

[0051] 9 is a diagram illustrating data output by the defect inspection device 1. Information indicated by this data can be provided, for example, on a GUI (graphical user interface) displayed on a monitor by the processor 105. The left side of FIG. 9 is a defect map, and the right side of FIG. 9 is a waviness distribution in the θ direction.

[0052] The defect inspection device 1 can display defect information corresponding to height levels on the disk 2, indicating where on the disk 2 the defect information is located. FIG. 9 shows an example in which three levels—a first defect level 92, a second defect level 93, and a third defect level 94—are displayed according to height and size. For example, a defect level outside the tolerance range may be preset, and only defects outside the tolerance level may be displayed. Although the disk reference line 91 is not on the disk 2, displaying it on the screen allows for a visually easy-to-understand display of the disk position, defect size, and height. If the disk reference line 91 cannot be set, the defect size and height relative to the disk radial position may be displayed. For waviness in the θ direction, it is preferable to plot the disk radius on the horizontal axis and the waviness height on the vertical axis. A judgment level 95 may also be set, and an alarm may be issued if the waviness height 96 exceeds that level.

[0053] The position of a defect on the surface of the disk 2 can be identified based on the coordinates at the time of irradiation with the light beams 20 and 21. The processor 105 can display the defect position on the screen by reflecting the coordinates on the GUI of Fig. 9. The numerical values of the defect coordinates may also be displayed.

[0054] 10 is a system block diagram of the defect inspection apparatus 1. The defect inspection apparatus 1 includes a control panel 101, a controller 102, a stage 103, an optical system 104, a light source 3, sensors 14 and 17, a processor 105, and a monitor 106.

[0055] The control panel 101 corresponds to a GUI that the host 100 operates when it wants to use the device. When the host 100 wants to refer to the results of an inspection, the GUI can be displayed on the monitor 106. Based on the command received by the control panel 101, the information required for the inspection is sent to the controller 102.

[0056] The controller 102 drives the stage 103 to rotate the disk 2 and turn on the light source 3. The stage 103 has the functions of switching the front and back of the disk 2, exchanging the disk 2, and transporting the disk, and can inspect the front and back of multiple disks consecutively. This makes it possible to inspect the front and back of multiple disks 2 at high speed and detect minute low-level defects and surface waviness.

[0057] The light source 3 may continuously emit light in CW (continuous wave) or may emit light only when inspecting the disc 2 to reduce power consumption. The optical system 104 is each optical system shown in FIG. 1. The beam emitted from the light source 3 is focused onto the disc 2 by the optical system 104, and defect information on the disc 2 is detected by the sensors 14 and 17. The detection signals detected by the sensors 14 and 17 are processed by the processor 105 to obtain the defect information. The procedure for obtaining the defect information is as described above. The defect information is displayed on the monitor 106.

[0058] <First embodiment: Summary> In the defect inspection apparatus 1 according to the first embodiment, for a waviness defect pitch that cannot be detected by the DIC signal detected by the sensor 14, the pupil plane intensity difference signal detected by the sensor 17, which is installed conjugate with the pupil plane, is the largest. For a waviness defect pitch at which the DIC signal intensity is the largest, the pupil plane intensity signal cannot be used to detect it. By combining such a DIC signal and a pupil plane intensity distribution signal in a mutually complementary manner, the defect inspection apparatus 1 can detect step defects as well as waviness defects of all periods.

[0059] <Embodiment 2> 11 is a configuration diagram of a defect inspection device 1 according to embodiment 2 of the present invention. Compared to embodiment 1, it newly includes a half-wave plate 12, a polarizing beam splitter 13, and a sensor 15. The other configurations are the same as those of embodiment 1.

[0060] The half-wave plate 12 has the function of converting the incident polarized light into light polarized at a 45° angle relative to the polarizing beam splitter 13. The polarizing beam splitter 13 has the function of transmitting P-polarized light and reflecting S-polarized light. In the second embodiment, the DIC signal is detected by two sensors, sensors 14 and 15. Specifically, the reflected light from the disc 2 is condensed into one beam by the polarization separation element 9, and then split again into two beams by changing the phase of the polarization and detected.

[0061] Sensor 15 is the same type of sensor as sensor 14, with the detection element divided into N parts as shown in Figure 3. After taking the difference and sum of the sensor signals from sensors 14 and 15, a signal is generated by dividing the difference by the sum. This signal processing makes it possible to detect height information that is not dependent on changes in laser intensity and is subject to strong external disturbances.

[0062] FIG. 12 is a functional block diagram of the processor 105 in the second embodiment. Compared to FIG. 7, a new block for processing the detection signal from the sensor 15 has been added. The signal calculation unit 120 performs the following calculation: S = (S1 - S3) / (S1 + S3), where S1 is the signal from the sensor 14 and S3 is the signal from the sensor 15. At this time, multiple signals are obtained for each light-receiving surface. The signal calculation unit 120 obtains the difference using the above formula, thereby eliminating the intensity level in the same way as the offset removal unit 72. Furthermore, because the signals corresponding to height are generated in opposite phases between the sensors 14 and 15, the amplitude is effectively doubled. Furthermore, because division is performed by the signal obtained by adding S1 and S3, laser intensity information can be removed, and a signal independent of laser intensity fluctuations can be obtained. Thus, in the second embodiment, a DIC signal that is more resistant to external disturbances can be detected compared to the first embodiment.

[0063] <Third Embodiment> FIG. 13 shows the configuration of a detection element of sensor 17 in embodiment 3 of the present invention. In the element configuration shown in FIG. 13, the detection element is divided into four parts in the R direction as well as the θ direction. The height and period signals of a waviness defect in the R direction are detected by calculating the sum signal of sensor pixels S4_1 and S4_4 and the sum signal of S4_3 and S4_2, respectively, and then calculating the difference between these signals. At the same time, the height and period signals of a waviness defect in the θ direction are detected by calculating the sum signal of sensor pixels S4_1 and S4_2 and the sum signal of S4_4 and S4_3, respectively, and then calculating the difference between these signals. This makes it possible to detect the period and height information of a waviness defect in the R direction as well as the waviness defect in the θ direction.

[0064] 14 shows a cross-sectional view and a top view of an R-direction undulation defect 142. The R-direction undulation defect 142 has a undulating surface with small steps (about 1 nm), similar to the undulation defect 42. In hard disks, undulation defects with a undulation period 143 in the range of about 20 μm to 100 μm are said to cause bad sectors.

[0065] Since the beam spots on the surface of the disk 2 are spaced apart from each other in the θ direction (see the middle part of FIG. 14), the height and period of defects undulating along the θ direction can be obtained by the configuration of embodiment 1. On the other hand, for defects undulating along the R direction, there is no difference in signal level between the beam spots (see the middle part of FIG. 14). Therefore, for an R-direction waviness defect 142, the phase step difference between the irradiation positions of the light beam 20 and the light beam 21 is zero. In other words, the height signal 140 cannot be used to detect the height and period signals of the R-direction waviness defect 142. In contrast, the height signal 141 calculated from (S4_1+S4_4)-(S4_3+S4_2) changes in the R direction, and defect height and period information can be detected.

[0066] Fig. 15 is a functional block diagram of the processor 105 in the third embodiment. Compared to Fig. 7, signal calculation units 150 and 151 and an R-direction waviness height evaluation unit 152 are newly added. The signal output by the signal calculation unit 150 is equivalent to that of the signal calculation unit 77, and the FFT processing unit 76 and subsequent units are the same as those in Fig. 7. The signal output by the signal calculation unit 151 is used by the R-direction height evaluation unit 152 to determine the period and height of waviness in the R direction. For waviness defects in the R direction, the period and height can be detected from the signal intensity, so the period and height signals can be determined by the R-direction height evaluation unit 152 without performing FFT signal processing.

[0067] <Modifications of the present invention> The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0068] In the above embodiments, the controller 102 and the processor 105 can be configured by hardware such as a circuit device that implements these functions, or by a computing device such as a CPU (Central Processing Unit) that executes software that implements these functions.

[0069] In the above embodiment, the present invention has been described as being applied to an inspection device used for defect inspection carried out in the manufacturing process of semiconductors, etc. However, the application of the present invention is not limited to this, and the present invention can be applied to other defect inspection devices that optically detect both minute step defects and waviness defects. [Explanation of symbols]

[0070] 1: Defect inspection equipment 9: Polarization separation element 10: Condensing optical system 14: Sensor 17: Sensor 105: Processor

Claims

1. A defect inspection apparatus that inspects a sample using light, comprising: a light source that emits a light beam; a polarization splitter element for splitting the light beam into a first beam and a second beam having orthogonal polarized light; an optical system for irradiating the sample with the first beam and the second beam in a narrow linear shape; a first sensor arranged at a position conjugate with the irradiation positions of the first beam and the second beam on the sample; a second sensor arranged at a position capable of detecting an image of a pupil plane of the optical system; a processor that detects defects on the specimen using the signal detected by the first sensor and the signal detected by the second sensor; Equipped with the processor obtains a differential interference signal of the first beam and the second beam using a signal detected by the first sensor, and detects a step defect on the sample using the differential interference signal; The processor detects a waviness defect on the sample using the signal detected by the first sensor and the signal detected by the second sensor. A defect inspection device characterized by:

2. the first sensor includes two or more first detection elements arranged along a longitudinal direction of a beam spot having the thin line shape of the light beam reflected from the sample; The processor simultaneously detects one or more step defects included in one of the beam spots by detecting the step defect for each of the first detection elements.

2. The defect inspection apparatus according to claim 1.

3. the second sensor includes two second detection elements arranged along a short direction of the narrow linear beam spot of the light beam irradiated onto the sample, The processor detects the height and period of the undulation defect based on the signal detected by each of the second detection elements.

2. The defect inspection apparatus according to claim 1.

4. the processor extracts a first signal detected by the first sensor and a second signal detected by the second sensor for each period of the waviness defect; the processor identifies the larger of the extracted first signal and the extracted second signal as a height signal; The processor detects the height of the waviness defect using the identified height signal.

2. The defect inspection apparatus according to claim 1.

5. the processor obtains ideal height curve data describing a relationship between the height of the wavy defect and the intensity per period of the first signal or a relationship between the height of the wavy defect and the intensity per period of the second signal; The processor calculates the height of the waviness defect by using the intensity of the first signal or the intensity of the second signal and referring to the relationship described by the ideal height curve data.

5. The defect inspection apparatus according to claim 4.

6. the defect inspection apparatus further includes a first beam splitter that transmits the light beam from the light source toward the sample and reflects the light reflected from the sample toward the first sensor; The defect inspection apparatus further includes a second beam splitter that transmits the light beam from the light source toward the sample and reflects the reflected light from the sample toward the second sensor.

2. The defect inspection apparatus according to claim 1.

7. the defect inspection apparatus further includes a rotation mechanism that rotates the sample, the optical system irradiates the first beam and the second beam onto the sample at intervals along a rotation direction of the sample; The optical system forms the thin line shape by extending the first beam and the second beam in a direction perpendicular to the rotation direction.

2. The defect inspection apparatus according to claim 1.

8. The processor detects the waviness defect having periodicity along the rotation direction.

8. The defect inspection device according to claim 7.

9. the defect inspection apparatus further includes a third beam splitter that splits the light beam directed toward the first sensor into a first polarization component and a second polarization component that are orthogonal to each other; the first sensor detects the first polarization component output by the third beam splitter; the defect inspection apparatus further includes a third sensor that detects the second polarized light component output by the third beam splitter; The processor detects the step defect using a result obtained by dividing the difference between the first polarization component and the second polarization component by the sum of the first polarization component and the second polarization component.

2. The defect inspection apparatus according to claim 1.

10. the second sensor includes four detection elements arranged along the short-side direction and the long-side direction of the thin linear beam spot of the light beam irradiated onto the sample, The processor detects the height and period of the waviness defect based on the signals detected by each of the detection elements.

4. The defect inspection apparatus according to claim 3.

11. the processor detects heights of the waviness defects having periodicity along the short-side direction using two of the detection elements arranged along the short-side direction, The processor detects the height of the undulation defect having periodicity along the longitudinal direction using the two detection elements arranged along the longitudinal direction.

11. The defect inspection apparatus according to claim 10.

12. the second sensor includes a first detection element and a second detection element arranged along the longitudinal direction, the second sensor includes a third detection element adjacent to the second detection element in the short-side direction, the second sensor includes a fourth detection element adjacent to the first detection element in the short-side direction, the processor detects the waviness defect having periodicity in the short-side direction by using a result obtained by subtracting a sum of a third detection signal output by the third detection element and a fourth detection signal output by the fourth detection element from a sum of a first detection signal output by the first detection element and a second detection signal output by the second detection element; The processor detects the undulation defect having periodicity in the longitudinal direction by using a result obtained by subtracting the sum of the second detection signal and the third detection signal from the sum of the first detection signal and the fourth detection signal.

12. The defect inspection apparatus according to claim 11.

13. the defect inspection apparatus further includes a rotation mechanism that rotates the sample, the optical system irradiates the first beam and the second beam onto the sample at intervals along a rotation direction of the sample; the optical system extends the first beam and the second beam along a direction perpendicular to the rotation direction, thereby forming the thin line shape whose short-side direction is the rotation direction and whose long-side direction is the perpendicular direction; When detecting the height of the undulation defect along the rotation direction, the processor extracts a signal intensity corresponding to the period of the undulation defect by performing a Fourier transform using the number of rotations for each position along the orthogonal direction; When detecting the height of the waviness defect along the orthogonal direction, the processor detects the period and height of the waviness defect without performing the Fourier transform.

12. The defect inspection apparatus according to claim 11.

14. The processor identifies the coordinates of the detected waviness defect and step defect, and outputs the results.

2. The defect inspection apparatus according to claim 1.

15. The processor discriminates the period and height information of the detected undulation defect and the height information of the step defect, and outputs the results.

2. The defect inspection apparatus according to claim 1.

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