Leveling method of light intensity of line laser light, laser light source device and surface state inspection apparatus using the same

Abstract

To provide a method for leveling a light intensity distribution in a longitudinal direction of linear laser by alleviating influence of a bright / dark pattern (interference fringe) generated by interference of laser light radiated from a slit arranged on a front surface of a cylindrical lens in a light source of line laser used in a light source of a light scattering-type surface inspection apparatus.SOLUTION: In a leveling method of light intensity of line laser light that expands with a prescribed width by irradiation with laser light in a direction orthogonal to a travel direction of the laser light via a slit, the laser light with aligned phases passing through the slit is assumed as point light sources with aligned phases that are arranged in close-contact with each other, a distance from the point light source to the line laser light is changed with the shape of the slit, and the light intensity of the line laser light is leveled by adjusting the phase at an irradiation point of the point light source.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a method for leveling the light intensity of a line laser beam, a laser light source device in which the light intensity of a line laser beam is standardized, and a surface condition inspection device using the laser light source device. [Background technology]

[0002] Inspection of the surface condition of various substrates such as semiconductor substrates, liquid crystal substrates, and disk substrates is essential because defects such as foreign matter, scratches, and cracks on the surface can have a significant impact on product quality and the occurrence of defective products.

[0003] One method for inspecting the surface condition of a substrate is the laser light scattering inspection method, which irradiates the substrate surface with laser light and detects the intensity of the scattered light reflected from the surface with a light receiving device. This method is based on the principle that the intensity of the scattered light changes if there is a defect or foreign matter on the substrate surface.

[0004] In surface condition inspection equipment using the laser light scattering method, since the range of the irradiated laser light is narrow, a means for scanning the laser light source and the light receiving device in conjunction with each other is provided to scan so as to cover the entire substrate.The location, size, shape, etc. of foreign objects and defects are determined by statistically processing the intensity data of the scattered light reflected from the substrate.

[0005] A spot light source is one of the laser light sources for surface inspection devices using the laser light scattering method. However, a spot light source has a problem that the irradiation range of the laser light is narrow, and it takes a long time to scan the entire surface of the substrate. For this reason, the inventor uses a line laser light as the laser light source for the laser light scattering method.

[0006] Line laser light is produced by using a cylindrical lens as a focusing lens for the laser light. By focusing only the axial direction, which has the curvature of the cylindrical lens, a short axis is created, and the unfocused side becomes the long axis, forming a line-shaped laser light. In addition, a slit is often provided in front of the cylindrical lens to limit the range of the light beam. When such a line laser beam is irradiated onto the surface of the substrate, a linear (line-shaped) light beam spreading with a predetermined width becomes the irradiation range, and the area of ​​the irradiation range is significantly enlarged compared to the case of a spot, so the time required to scan the entire surface of the substrate can be significantly reduced.

[0007] However, when a line laser beam is used in a surface condition inspection device, there is a problem that the light intensity of the line laser beam varies in the longitudinal direction of the irradiation range (intensity distribution), which reduces the detection accuracy of foreign matter and defects. This problem will be described in more detail later in the section on problems to be solved.

[0008] Surface condition inspection and evaluation methods using the laser light scattering method have long been widely used for inspecting various substrates, films, etc., and many applications have been submitted regarding specific means thereof, etc. The present applicant has also previously proposed a means for distinguishing between convex defects and concave defects in substrate surface inspection using the laser light scattering method (Patent Document 1).

[0009] In addition, in semiconductor manufacturing equipment, laser light may be used for heat treatment. That is, in order to promote the crystallization of a semiconductor thin film and improve its electrical characteristics, a laser light is irradiated onto the surface of the thin film to perform annealing (laser annealing method). In such a laser annealing method, a case has been disclosed in which a linear laser is used to enlarge the irradiation area of ​​the laser light (Patent Document 2).

[0010] Furthermore, Patent Document 2 points out that the light intensity of the laser light varies greatly between the center and both ends of the linear laser beam, which makes it easy for the effect of laser irradiation to become non-uniform. As a method for dealing with this problem, this example reports that it is possible to improve quality by dividing the laser irradiation into two stages, a preliminary irradiation and a main irradiation. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 6476580 [Patent Document 2] JP 2007-251196 A Summary of the Invention [Problem to be solved by the invention]

[0012] It is a well-known fact that when two or more light sources of light with a single wavelength (monochromatic light), such as laser light, are placed close to each other and radiate light in the same direction, a light interference pattern (interference fringes) is formed on the irradiated surface.

[0013] If we consider the light source of the line laser light as being roughly a number of point light sources arranged closely spaced along the longitudinal direction of the slit, it is expected that interference of the laser light may result in the formation of a wavy change in light intensity (a pattern of light and dark) along the longitudinal direction of the irradiation surface of the line laser light.

[0014] To confirm this, the applicant carried out the following experiment. Figure 1 is a schematic diagram of an experimental device for measuring the intensity distribution of the light flux of line laser light. This device is composed of a light source device 1, a light receiving device 2 that measures the light intensity at a measurement point P on a virtual light receiving surface 3, and a data recording device 4. The light source device 1 comprises a laser light source 5, a pickup lens 6 placed in front of it for focusing the laser light, a cylindrical lens 7 placed in front of it at a predetermined distance, and a light source side slit 8 placed in front of it. The distance between the light source side slit 8 and the line laser light is L mm.

[0015] The light receiving device 2 is composed of an opening 9 and a condenser lens 10 on the front side, and a photomultiplier 11 on the rear side, and forms a rectangular virtual light receiving area (field of view) on the virtual light receiving surface 3, and the linear laser light 12 emitted from the light source device 1 is included in this field of view. If there is a foreign object on the surface of the substrate to be inspected within the field of view of the linear laser 12, the foreign object will generate scattered light. Since the intensity of this scattered light is proportional to the size of the foreign object, the size of the foreign object can be estimated by measuring the intensity of the scattered light.

[0016] A pair of focusing lenses 10 in the light receiving device 2 picks up the light on the linear laser 12 and makes it incident on the photomultiplier 11, thereby measuring the light intensity. Furthermore, a scanning device (not shown) scans the light receiving device so that the measurement point P covers the entire area of ​​the linear laser 12, thereby measuring the light intensity distribution in the longitudinal direction of the linear laser 12. That is, by inspecting the entire substrate with the linear laser 12, the positions and sizes of foreign objects distributed on the substrate surface can be identified from the intensity of the scattered light and the corresponding positions (distribution).

[0017] 1 is a conceptual diagram showing the arrangement of each part, and the actual shape of the device may differ from that shown in the diagram. The following describes the results of examining the effect of the presence or absence of the light source side slit 8 using this device.

[0018] Figure 2 shows the change in the intensity distribution of the line laser light with and without a slit, with Fig. 2(a) showing the case where there is no slit 8 on the light source side, and Fig. 2(b) showing the case where a rectangular slit 0.7 mm wide and 3.0 mm long is placed on the light source side. As can be seen in Fig. 2(a), the light intensity measured on the virtual light-receiving surface 3 shows a mountain-like distribution with a broad base (normal distribution).

[0019] If a light source with such a large spread and intensity difference is used for the laser light scattering method, as will be described in detail later, it is undesirable because it reduces the accuracy of distinguishing the size of foreign matter and defects and the accuracy of detecting minute defects. On the other hand, if there is a rectangular slit as shown in Figure 2(b), the base part of the mountain-shaped distribution is blocked and only the high-intensity light near the peak is extracted, which significantly improves the suitability as a light source for the laser light scattering method. Therefore, it is necessary to use a slit.

[0020] However, even when a slit is provided, it was found that another problem occurred, as described below. Figure 3 shows an enlarged view of the waveform in Figure 2(b). As mentioned above, the slit used was a rectangle of 0.7 x 3.0 mm. This figure shows that there are irregularities in the intensity distribution of the line laser light. Although the shape of the wave is distorted due to the effects of noise, a wavy intensity change with almost uniform intervals can be seen.

[0021] The reason for this wavy intensity change is believed to be the light and dark pattern caused by the interference of light, as mentioned in the previous paragraph (0013). In other words, it is safe to say that the previous prediction has been experimentally confirmed.

[0022] When a line laser beam with such a light and dark pattern is used, the following problems are thought to occur: That is, in the laser light scattering method, the change in intensity of scattered light (hereinafter sometimes simply referred to as "intensity change") due to the presence or absence of a foreign object or defect (hereinafter simply referred to as a foreign object) at the laser light irradiation position is measured, the location of the foreign object is identified from the detected position of the intensity change, and the size of the foreign object is determined from the amount (magnitude) of the intensity change.

[0023] However, the intensity of scattered light depending on the presence or absence of a foreign object depends basically on the size of the foreign object, but also on the intensity of the laser light irradiated at the measurement position, and the change in intensity increases or decreases in proportion to the strength of the incident laser light. Therefore, even if a foreign object is the same size, if it is in an area where the intensity of the laser light is high (a bright part of a light-dark pattern), it will be judged as a large foreign object, and conversely, if it is in an area where the intensity of the incident laser light is low (a dark part of a light-dark pattern), it will be judged as a small foreign object, which reduces the accuracy of determining the size of the foreign object.

[0024] It is also thought that this will have an effect on the detection sensitivity of minute foreign objects. Even if a foreign object is very small, it will be detected as a foreign object when it is in a light area of ​​a light-dark pattern, but when it is in a dark area, the change in scattered light intensity will be below the judgment threshold and it will not be detected as a foreign object, which may lead to a problem of instability in the foreign object detection limit.

[0025] In order to avoid these problems, it is desirable to realize a means for reducing the effect of interference of laser light in a light source of a line laser light that limits the irradiation range of the line laser light by a slit, thereby eliminating the bright and dark pattern, or reducing the difference in light intensity between bright and dark patterns. However, such a means has not yet been obtained.

[0026] Therefore, the object of the present invention is to provide a means for reducing wavy changes in light intensity at the line laser light irradiation surface and leveling out the light intensity in the longitudinal direction in a laser light source device having a cylindrical lens in front of a laser light source and a slit in front or rear of the cylindrical lens.

[0027] Furthermore, by using the above-mentioned line laser light as a light source in a laser light scattering type surface condition inspection device, it is possible to improve the accuracy of foreign body inspection, for example, to improve the accuracy of foreign body size determination and to improve the stability of the detection limit for minute foreign bodies. [Means for solving the problem]

[0028] In order to solve the above problems, the applicant came up with the following idea. That is, the light source of the line laser light can be considered as a collection of many closely spaced virtual light sources (also referred to as point light sources in this specification) arranged within the slit. Each of these virtual light sources has the function of forming a light and dark pattern due to the interference of light, and the composite of these light and dark patterns can be considered as an interference fringe that is observed as a whole.

[0029] In the case of a rectangle with a constant slit width, the positions of the peaks of the brightness patterns of each divided virtual light source are the same, and by combining these, a pattern with strong brightness is formed. However, if the width of the slit in the longitudinal direction is changed, it is possible that the positions of the brightness peaks will differ between the wide and narrow parts of the slit, and it is expected that by combining these lights, a line laser light with fewer brightness patterns overall (light intensity in the longitudinal direction (long axis) of the irradiation range is leveled) can be obtained.

[0030] To confirm this, the applicant has simulated the distribution of light intensity by changing the shape of the slit in various ways using a numerical calculation model, as described in detail in the examples below. Also, an experiment was carried out to measure the distribution of light intensity in the longitudinal direction on the virtual light receiving surface 3 by changing the shape of the slit in various ways using the device of Fig. 1. As a result, it was found that a line laser light with a leveled light intensity and less wavy intensity can be obtained with a slit of a certain shape.

[0031] Based on this finding, the present invention provides a method for leveling the light intensity of a line laser beam, which is a method for leveling the light intensity in a longitudinal direction of a line laser beam that spreads on an irradiation surface by irradiation with the laser beam in a direction perpendicular to the traveling direction of the laser beam through a slit, comprising the steps of: The coherent laser light passing through the slit is assumed to be a plurality of closely spaced coherent point light sources, The shape of the slit is used to change the distance from the point light source to the line laser light, and the phase at the irradiation point of the point light source is adjusted, thereby leveling out the light intensity of the line laser light.

[0032] Further, the laser light source device of the present invention based on this finding is a laser light source device which forms a light flux spreading with a predetermined width in a direction perpendicular to the traveling direction of the laser light by using a laser light source, a cylindrical lens arranged in front of the laser light source, and a slit arranged in front of or behind the cylindrical lens, and The light intensity in the longitudinal direction of the light beam spreading over the specified width is leveled out by the longitudinal width of the slit, which changes over a specified width, and / or the lateral width, which also changes over a specified width.

[0033] The slit is desirably formed in a vertically elongated hexagonal shape whose width increases linearly from both short sides toward the center in the longitudinal direction. The slit may also be formed in an hourglass shape whose width decreases linearly from both short sides toward the center in the longitudinal direction.

[0034] Furthermore, the slit may have a long side formed into a trapezoid shape by inclined portions on both sides and a parallel portion in the center, and the left and right long sides may be arranged symmetrically about the central axis of the slit, forming a vertically elongated octagonal shape.

[0035] The surface condition inspection device of the present invention is a substrate surface condition inspection device comprising: a laser light source device which includes a laser light source, a cylindrical lens arranged in front of the laser light source, and a slit arranged in front or rear of the cylindrical lens, and which forms a light beam which spreads with a predetermined width in a direction perpendicular to the traveling direction of the laser light; a scattered light receiving device; scanning means configured so that the laser light source device and the light receiving device can work together to scan the entire surface of an inspection target; and means for processing and recording a signal from the light receiving device, The light intensity in the longitudinal direction of the light beam spreading over the specified width is leveled out by the longitudinal width of the slit, which changes over a specified width, and / or the lateral width, which also changes over a specified width. Effect of the Invention

[0036] The laser light source device of the present invention reduces the influence of interference of the laser light irradiated through a slit, and makes it possible to obtain a line laser light with little change in light intensity (leveled).

[0037] This makes it possible to use a line laser light source in a light scattering type surface condition inspection device, making it possible to increase the inspection speed by several to several dozen times compared to the case of a point light source.

[0038] Furthermore, in surface condition inspection using a line laser light source, the improvements to the laser light source device of the present invention have made it possible to improve inspection accuracy, for example, improve the accuracy of foreign object size discrimination and stabilize the detection limit for minute foreign objects, compared to the case before the improvements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] As mentioned above, by using a slit to form the line laser beam used in the laser light scattering method, it is possible to block the base part of the line laser beam that has a mountain-shaped light intensity distribution. Also, since it is possible to extract only the laser beam with high light intensity near the peak, the suitability as a light source for the laser light scattering method is significantly improved, and the use of a slit is considered to be indispensable.

[0040] On the other hand, when a slit is placed, uneven changes occur in the light intensity distribution in the longitudinal direction of the line laser light. As described above, the intensity of scattered light due to the presence or absence of a foreign object also changes depending on the intensity of the laser light irradiated to the measurement position, and the change in intensity increases or decreases in proportion to the strength of the incident laser light. Therefore, the change in the intensity of the laser light reduces the accuracy of determining the size of the foreign object.

[0041] Therefore, a numerical calculation model was devised to determine how the shape of the slit affects the light intensity distribution of the line laser light, and the light intensity distribution of the line laser light was obtained for each of the slit shapes shown in Figure 12.

[0042] The simulation using the numerical calculation model assumed that a large number of point light sources were closely arranged in a two-dimensional lattice pattern to match the shape of the slit opening provided at the end of the laser light source. In other words, the slit was considered to be a collection of minute slits, and the light passing through each minute slit was replaced with the light output from the point light source.

[0043] Next, since the laser light source emits laser light with a wavelength of λmm and an initial phase that is aligned, it is assumed that the laser light that passes through the slit is also output from the slit with a aligned phase. The slit is assumed to be a collection of tiny slits (point light sources), and the energy distribution of the point light sources is assumed to be an elliptical Gaussian distribution.

[0044] The laser light (electromagnetic wave) with a wavelength of λ mm emitted from each point light source of the minute slit is a spherical wave. In other words, the solution of Maxwell's equations in polar coordinates for r≫λ is a spherical wave. Here, i and q are i 2 = -1, and the wave number expressed as q = 2π / λ. The refractive index of air (atmosphere) is n ≒ 1. (The permittivity and permeability of air are approximated to the permittivity ε_0 and permeability μ_0 of a vacuum, respectively.)

[0045] Next, the two-dimensional electric field distribution at a position z=Lmm away from the slit opening (on the line z=Lmm: corresponding to the line laser P Lmm away from the slit 8 in Figure 1) is calculated as a superposition of the light (spherical waves) propagated from each point light source in the minute slit. The focusing effect of the cylindrical lens (focusing light in one axial direction and shaping the light into a line shape) is approximated as a superposition of two-dimensional electric fields in one axial direction. The y-axis component of the two-dimensional electric field distribution at the position z=Lmm calculated above is added together to find the electric field component in the x-axis direction. Then, the light intensity of the line laser light (longitudinal direction) at the position z=Lmm is calculated. If the electric field E and the dielectric constant of vacuum are ε_0, the light energy is given by The result is TIFF2024044913000003.tif1073.

[0046] Based on the above prerequisites, the mathematical formula for the electric field of a point source of a minute slit is set as follows:

number

[0047] Above, σ x ,σ y : Variance of the Gaussian distribution on the x and y axes. This is a parameter that indicates the spread of the laser light, and was set from the laser profile data of the actual device. I 0 : is a normalization constant, which is a parameter set so that the result of surface integration of the light intensity, i.e., the actual laser light output, is obtained. However, since the normalization of the light intensity is performed after the final calculation (after the light intensity distribution of the line shape is calculated), in the numerical calculation, I 0 =1.

[0048] The mathematical formula for the electric field distribution of the light output from the minute slits (each point light source) was set as follows:

number

[0049] The electric field at the position of the slit, i.e., the z=0 plane (coordinates (x,y,0): inside the slit) is E in (x,y) = E 0 (x,y,0), and if the coordinate (x,y,0) is outside the slit opening, then E in (x,y) = 0. In other words, when creating a numerical calculation program, the repeated (loop) calculation part of the superposition of the electric field to be calculated later is not rewritten every time the slit shape is changed, but is set under the condition that light does not pass through anything other than the slit opening, and the electric field other than the slit opening is E in =0 was set.

[0050] To calculate the electric field on the line L mm (Z = L mm) from the slit, we use the point source (x m, The electric field at the position of the line laser light (x, y, L) output from the laser diode (x, y, 0) is expressed by the following formula 3.

number

[0051] The electric field at a distance of L mm (Z=L mm) from the slit can be calculated by adding up the electric fields from all the point light sources (Equation 4 below).

number

[0052] where x max ,y max are flat areas that are slightly larger than the slit opening. Originally, x n ,y n It would be sufficient to calculate the sum only over the internal area of ​​the slit opening, but the calculation part of the program would have to be rewritten every time the slit shape is changed. Therefore, the sum is calculated over an area slightly larger than the slit opening, and an equivalent calculation is performed by setting Ein(x,y) = 0 outside the slit.

[0053] The electric field distribution of the line laser light at Z=L mm (on the line) can be calculated by calculating the electric field for all coordinates (x, y, L) using the above calculation. That is, The electric field distribution of the line laser light can be obtained by calculating the entire area of ​​TIFF2024044913000013.tif673 and obtaining the electric field distribution E(x,y,L) on the Z=Lmm line. This is equivalent to calculating the optical interference effect caused by the slit when there is no cylindrical lens. Strictly speaking, It is necessary to calculate the entire area of ​​TIFF2024044913000014.tif640, but since spherical waves attenuate as 1 / r, it is thought that it is sufficient to calculate over an area slightly larger than the slit opening.

[0054] When taking into account the effect of the cylindrical lens, it can be found using the following simplified equation 5, which adds up in the y-axis direction. Strictly speaking, since the electric field is a vector, it would not be correct unless all of the calculations up to this point are calculated as vectors and the cylindrical lens is set up so that the direction of travel of the spherical wave changes (the vector direction changes); however, this is a complicated concept, so it has been replaced by a simplistically calculated sum in the y-axis direction.

number

[0055] The light intensity of the line laser light can be calculated by the following formula 6 within the range of x. Here, E(x) is the calculated electric field including the effect of the cylindrical lens, TIFF2024044913000016.tif511 is its complex conjugate.

number

[0056] The above TIFF2024044913000019.tif673 Maximum light intensity calculated in the area Find TIFF2024044913000020.tif712 and calculate the following formula 7. A graph of the light intensity of the line laser light can be obtained by plotting the CSV file in which the values ​​of TIFF2024044913000021.tif918 are recorded using Excel or the like.

number

[0057] Using the theoretical calculations described above, the slit shape was changed in various ways to determine the longitudinal light intensity distribution of the line laser light. The light intensity at each point of the line laser light and the maximum value among them were normalized using the above formula 7, and the results were displayed in graphs as shown in Figures 4 to 11. Figure 12 shows eight types of slit shapes used in the numerical calculation model. We will now explain the various slit shapes and the longitudinal light intensity distribution of the line laser light corresponding to the slit shapes.

[0058] The simulation results for rectangular slit No. 1 are shown in Figure 4. The light intensity of this slit has a wave-like intensity with a nearly uniform period in the longitudinal direction of the linear laser (hereinafter also referred to as the "width direction"), and if the intensity at the peaks is 100%, the intensity at the valleys is about 60 to 70%.

[0059] The simulation results for hexagonal slit No. 2 are shown in Figure 5. In this case, there are some deep valleys on both sides in the width direction, but in other parts the intensity distribution is leveled with barely noticeable wavy changes. The difference in intensity between the peaks and valleys is at most 6-7%, which can be considered to be sufficiently leveled for use as a light source for laser light scattering methods.

[0060] The simulation results for curved hexagonal slit No. 3 (hexagonal No. 2 whose four long sides are not straight but are concavely curved) are shown in Figure 6. Compared to the hexagonal case in Figure 5, the valleys near both ends in the width direction are deeper, and wavy unevenness can be seen in the center. Therefore, in the case of a hexagonal slit, it is clear that it is preferable for the long sides to be straight, not curved.

[0061] The simulation results for the hourglass-shaped slit No. 4 are shown in Figure 7. In this case as well, there are some rather deep valleys on both sides in the width direction, but in other parts the wavy changes are barely noticeable and the difference in strength between the peaks and valleys is at most about 6 to 7%, resulting in an intensity waveform very similar to that of the hexagonal slit No. 2. It is believed that this slit can also be used in practice without any problems.

[0062] Figure 8 shows the simulation results for curved hourglass-shaped slit No. 5 (the hourglass-shaped slit No. 3 has curved rather than straight indentations on its sides). As can be seen in the figure, a fairly strong wavy waveform remains, and the waveform is similar to that of a rectangular slit. The reason for such a large difference in the light intensity waveform between the straight-shaped indentations on the sides and the curved indentations is unclear, but it is thought to be an interesting phenomenon.

[0063] The simulation results for diamond-shaped slit No. 6 are shown in Figure 9. As can be seen in Figure 9, no wavy irregularities due to light interference are visible at all, and the shape resembles a simple normal distribution. The only difference between the diamond-shaped slit and the hexagonal slit shapes is that either both ends in the longitudinal direction are pointed, or one has a portion of both ends cut off to form a short side. It is surprising that this difference in slit shape results in completely different light intensity distribution waveforms.

[0064] The simulation results for the elliptical slit No. 7 are shown in Figure 10. As can be seen in the figure, in this case, the overall shape is a wave shape with wavy projections and recesses that are thought to be due to optical interference superimposed on a normal distribution-type shape resembling a mountain with base.

[0065] It is true that the light and dark pattern caused by light interference appears to have been alleviated, but the waveform overall remains largely normal distribution, and the difference in light intensity between the peaks and the bases is too large, making it unsuitable as a light source for a laser light scattering method.

[0066] The simulation results for octagonal slit No. 8 are shown in Figure 11. In this case too, the wavy unevenness caused by light interference is greatly alleviated, and an almost uniform intensity waveform is obtained overall. There is an intensity difference of about 10% between the peaks and valleys, but this level is likely to be suitable as a light source for the light scattering method.

[0067] To summarize the above results, the hexagonal slit (number 2) provides the most suitable intensity distribution waveform, and the hourglass-shaped (number 3) and octagonal (number 8) slits are also considered to be suitable as light sources for the light scattering method.

[0068] Next, a comparative experiment was conducted between the longitudinal light intensity distribution of the line laser light due to differences in slit shapes based on a numerical calculation model and the longitudinal light intensity distribution of the line laser light generated by an actual inspection device. The experimental device shown in Fig. 1 was used, and the longitudinal light intensity distribution of the line laser light was measured for the three types of slits shown in Fig. 13. Fig. 13 is a table showing the shapes of the three types of slits used in the above measurements, and the table shows the slit number, shape diagram, slit dimensions, and the number of the diagram of the simulation results.

[0069] Figure 14 shows the measurement results for rectangular slit No. 1 in Figure 13. In the case of this slit, the light intensity of the line laser light is wavy with an almost uniform period, and if the intensity of the peaks is 100%, the intensity of the valleys is about 60 to 70%. When compared with the longitudinal intensity distribution of the line laser light from a numerical calculation model, although there are differences in the wavy unevenness in the center, the overall shape of the light intensity distribution is similar.

[0070] The measurement results for hexagonal slit No. 2 are shown in Figure 15. Comparing with Figure 5, which shows the intensity distribution based on the numerical calculation model, there are some differences in the intensity distribution in the center and the depth of the valleys on both ends in the width direction, but overall the light intensity distribution is similar.

[0071] The measurement results for the elliptical slit No. 3 are shown in Figure 16. Comparing it with Figure 10, which shows the intensity distribution based on the numerical calculation model, both have a mountain-like normal distribution shape with a base, although there are differences in how the base spreads.

[0072] From the above, the light intensity distribution of the line laser light due to the change in the shape of the slit can be simulated by a numerical calculation model. This means that the slit can be assumed to be a number of closely spaced point light sources with the same phase, and by changing the distance from such point light sources to the line laser light, the phase at the irradiation point irradiated by each point light source can be controlled. In other words, this shows that the light intensity of the line laser light can be leveled by adjusting the overlap of phases at the irradiation point by adjusting the shape of the slit. In this embodiment, the hexagonal slit No. 2 produced the most suitable intensity distribution waveform, and it is believed that the hourglass-shaped slit No. 3 and the octagonal slit No. 8 are also suitable as light sources for the light scattering method.

[0073] Next, a surface inspection device using the slit of the present invention will be described. Fig. 17 is a conceptual diagram showing an outline of the configuration of the device in one embodiment. This device is composed of a laser light source device 1, a light receiving device 2, a scanning device that scans the entire surface to be inspected, and a data processing and recording device 4 for scattered light.

[0074] The laser source device 1 generates a line laser light using a cylindrical lens 7 and a slit 8, and irradiates the surface of a circular substrate 13, which is the object to be inspected. In this embodiment, a hexagonal slit 8 shown in Table 1 is used as the slit 8. The light scattered on the substrate surface enters the light receiving device 2, passes through a condenser lens 10, and the scattered light intensity is measured by a photomultiplier 11. The light is then converted into data by a data processing and recording device 4.

[0075] The scanning mechanism of this device will be described below. The circular substrate 13 to be inspected is placed on a rotating table 14, and a rotating shaft 15 of the rotating table 14 is rotated at a predetermined speed by a rotating device 16. At this time, the center of the circular substrate 13 is positioned so as to coincide with the axis of the rotating shaft 15.

[0076] Meanwhile, the laser light source device 1 and the light receiving device 2 are fixed to a support member 18 by an attachment member 17. The support member 18 is configured to be movable back and forth (in the direction of the arrow in the figure) by a feed mechanism 20 attached to a support 19. During this movement, the attachment of the laser light source device 1 and the light receiving device 2 is adjusted so that the irradiation position of the laser light source device 1 passes on a radial line passing through the center of the circular substrate 13.

[0077] Moreover, the cylindrical lens 7 and the slit 8 are attached and adjusted so that the longitudinal direction of the linear scratch of the line laser light coincides with the radial direction of the circular substrate 13. In this state, when the center of the laser light is fixed at the position of radius r and the circular substrate 13 is rotated, the inspection of the annular portion (annular portion of radius r-Δr / 2 to r+Δr / 2) of the longitudinal width (hereinafter referred to as Δr) of the linear scratch of the line laser light is completed.

[0078] Next, the center of the laser light is moved to position r+Δr, and measurement is performed by rotating the circular substrate 13 once. In this way, by moving the center of the laser light from the center to the outer edge of the circular substrate 13 and performing measurement, it is possible to inspect the entire surface of the substrate.

[0079] In this embodiment, Δr is approximately 500 μm. In the case of a spot light source, the width of the laser mark is usually 100 μm or less. If this is taken to be 100 μm, for example, the area that can be measured in one revolution of the circular substrate 13 is 500 μm / 100 μm=5 times that of the spot light source in the case of a line laser light source. Therefore, the time required to inspect one substrate is reduced to 1 / 5.

[0080] Furthermore, as already mentioned, when the hexagonal slit of the present invention is used for slit 8, it is possible to improve inspection accuracy, for example, to improve the accuracy of distinguishing foreign object size and to stabilize the detection limit for minute foreign objects, compared to when a conventional rectangular slit is used. [Brief description of the drawings]

[0081] [Figure 1]FIG. 1 is a schematic diagram of an experimental device for measuring the intensity distribution of a light flux of a line laser light. [Diagram 2] 11A and 11B are diagrams showing changes in intensity distribution of line laser light depending on whether or not there is a slit. [Diagram 3] FIG. 13 is a diagram showing the intensity distribution of a line laser light when the slit is rectangular. [Figure 4] FIG. 13 is a diagram showing a simulation result of intensity distribution when the slit is rectangular. [Diagram 5] FIG. 13 is a diagram showing a simulation result of the intensity distribution when the slit is hexagonal. [Figure 6] FIG. 13 is a diagram showing a simulation result of the intensity distribution when the slit is a curved hexagon. [Figure 7] FIG. 13 is a diagram showing a simulation result of intensity distribution when the slit is hourglass-shaped. [Figure 8] FIG. 13 is a diagram showing a simulation result of the intensity distribution when the slit is a curved hourglass shape. [Figure 9] FIG. 13 is a diagram showing a simulation result of the intensity distribution when the slit is rhombic. [Figure 10] FIG. 13 is a diagram showing a simulation result of the intensity distribution when the slit is elliptical. [Figure 11] FIG. 13 is a diagram showing a simulation result of intensity distribution when the slit is octagonal. [Figure 12] This is a diagram (table) showing eight types of slit shapes used in the numerical calculation model. [Figure 13] This is a diagram (table) showing three types of slit shapes installed on an actual machine. [Figure 14] FIG. 13 is a diagram showing measurement results for a rectangular slit using an actual device. [Figure 15] FIG. 13 is a diagram showing measurement results of a hexagonal slit using an actual device. [Figure 16] FIG. 13 is a diagram showing measurement results of an elliptical slit using an actual device. [Figure 17] 1 is a schematic diagram showing a configuration of a surface inspection device according to an embodiment of the present invention; [Explanation of symbols]

[0082] 1: laser light source device, 2: light receiving device, 3: virtual light receiving surface, 4: data processing and recording device, 5: laser light source, 6 pickup lens, 7: cylindrical lens, 8: light source side slit, 9: opening, 10: condenser lens, 11: photomultiplier, 12: linear laser (line laser light), 13: circular substrate, 14: Rotary table, 15: Rotary shaft, 16: Rotating device, 17: Mounting member, 18: Support member, 19: Support column, 20: Feeder

Claims

1. A method for equalizing the longitudinal light intensity of a line laser beam that spreads on an irradiation surface by irradiation with the laser beam in a direction orthogonal to the traveling direction of the laser beam passing through a slit, characterized in that: assuming that the laser beam with aligned phases passing through the slit is a plurality of closely arranged point light sources with aligned phases; changing the distance from the point light source to the line laser beam according to the shape of the slit and adjusting the phase at the irradiation point of the point light source to equalize the light intensity of the line laser beam. A method for equalizing the light intensity of a line laser beam.

2. In a laser light source device that forms a light beam spreading with a predetermined width in a direction orthogonal to the traveling direction of the laser beam by a laser light source, a cylindrical lens disposed on the front surface thereof, and a slit disposed on the front or rear surface thereof, the laser light source device is characterized in that the longitudinal light intensity of the light beam spreading with the predetermined width is equalized by a change in the width in the longitudinal direction and / or the short-side direction of the slit.

3. The laser light source device according to claim 2, wherein the slit is formed in a vertically long hexagonal shape whose width linearly expands from both short sides on both sides toward the center in the longitudinal direction.

4. The laser light source device according to claim 2, wherein the slit is formed in an hourglass shape whose width linearly decreases from both short sides on both sides toward the center in the longitudinal direction.

5. The laser light source device according to claim 2, wherein the long side of the slit is formed in a trapezoidal shape from the inclined portions on both sides and the parallel portion in the center, and the left and right long sides are arranged axially symmetrically with respect to the central axis of the slit, and is formed in a vertically long octagonal shape.

6. A surface state inspection apparatus for a substrate, comprising: a laser light source device that forms a light beam spreading with a predetermined width in a direction orthogonal to the traveling direction of the laser beam by a laser light source, a cylindrical lens disposed on the front surface thereof, and a slit disposed on the front or rear surface of the cylindrical lens; a scattered light receiving device; scanning means configured such that the laser light source device and the receiving device are interlocked to scan the entire surface of the inspection target; and means for processing and recording the signal of the receiving device. The surface state inspection apparatus is characterized in that the longitudinal light intensity of the light beam is equalized by a change in the width in the longitudinal direction and / or the short-side direction of the slit to a predetermined width.

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