JP5578329B2 - Line light source - Google Patents

Description

  The present invention relates to a line light source, and more specifically to a technique for reducing variation in luminance at each position in the longitudinal direction of the line light source.

  Many line light sources in which a plurality of light emitting elements such as LEDs are arranged in a row on a substrate have already been put into practical use. In such a line light source, variations in luminance at each position in the longitudinal direction of the line light source occur due to variations in characteristics of individual light emitting elements, or positional deviation (offset) when the light emitting elements are mounted on the substrate.

  When a line light source is used as a light source for inspection such as surface defect inspection, the luminance variation (non-uniformity) adversely affects the inspection. In particular, in the case of a wide-range inspection that requires high detection accuracy, such as when a defect in a fine pattern is inspected macroscopically, the influence of the non-uniformity of the brightness becomes greater.

  Conventionally, luminance unevenness has been reduced by diffusing light by providing a diffusion plate or a microlens in front of a light emitting element of a line light source. Alternatively, it is possible to control the drive current of each light emitting element (LED) so that the luminance is uniform.

  As another method, for example, published patent application 2004-101311 discloses an illumination device for a line sensor camera. In this illuminating device, a plurality of illumination units in which a plurality of LEDs are arranged in a line at a predetermined pitch interval are provided, and illumination by the other illumination unit is applied to a portion where the illumination intensity is weak in the linear illumination range of one illumination unit. The portions with high luminance are arranged so as to be shifted along the pitch interval direction so as to overlap each other. Thereby, when the LEDs that are point light sources are combined in a line, unevenness in luminance that occurs due to darkening of the location between adjacent LEDs is suppressed.

JP 2004-101311 A

  In the conventional method of reducing luminance unevenness by providing a diffusion plate or microlens, the luminance unevenness is not necessarily sufficiently reduced for a wide range of inspections that require high detection accuracy. In addition, a predetermined control circuit is required to control the drive current of each light emitting element. In particular, as the number of light emitting elements increases, the control becomes more complicated, and there is a possibility that sufficient brightness uniformity cannot be achieved.

  In the lighting device of Patent Document 1, at least two or more lighting units are necessary, which leads to an increase in size and cost of the lighting device. In addition, in the illumination device of Patent Document 1, the luminance at each position in the longitudinal direction of the line light source due to variations in the characteristics of individual light emitting elements or positional deviations (offsets) when the light emitting elements are mounted on the substrate. Insufficient to reduce the variation.

  Therefore, an object of the present invention is to provide a line light source capable of reducing variations in luminance at each position in the longitudinal direction.

  The present invention includes a plurality of light emitting elements arranged in a line at predetermined intervals on a substrate, at least one diffusion plate provided on an upper part of the substrate for diffusing light from the plurality of light emitting elements, A mask provided on or near the surface of the plate for setting the light quantity distribution of the emitted light in the longitudinal direction of the diffusion plate according to the luminance distribution in the longitudinal direction of the diffusion plate in the diffused light from the diffusion plate; A line light source is provided.

  According to the present invention, by controlling the light quantity distribution of the diffused light in the longitudinal direction of the diffuser plate, it is possible to reduce the variation in luminance at each position in the longitudinal direction of the line light source.

  In one embodiment of the present invention, the mask sets the light amount distribution so as to cancel the luminance distribution.

  According to one embodiment of the present invention, it is possible to reduce (uniformize) luminance variation in accordance with the luminance distribution in the longitudinal direction actually measured or simulated.

  In one embodiment of the present invention, the mask uses a curve representing an inverse function of a function corresponding to the curve of the luminance distribution as a mask pattern for shielding diffused light.

  According to one aspect of the present invention, it is possible to form a mask pattern for uniquely (automatically) shielding diffused light from an inverse function of a function corresponding to a luminance distribution curve.

  In one embodiment of the present invention, the mask pattern is formed from a film, a thin plate, or a tape that can block light.

  According to one embodiment of the present invention, a mask pattern that faithfully reflects a curve representing an inverse function of a function corresponding to a curve of a luminance distribution can be formed using a film, a thin plate, or a tape.

It is a figure which shows one Embodiment of a structure of the line light source of this invention. It is a figure which shows the measurement result of the luminance distribution of the line light source of this invention. It is a figure which shows one Embodiment of the structure of the mask of this invention. It is a figure which shows the measurement structure of the wafer surface using the line light source of this invention. It is a figure which shows the measurement result of the luminance distribution by the structure of FIG.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a configuration of a line light source 100 of the present invention. 1A is a top view of the line light source 100, and FIG. 1B is a side (cross-sectional) view. A plurality of light emitting elements 12 are arranged in a line at a predetermined pitch L1 on the long substrate 10. The size of the substrate 10 can be arbitrarily selected, but is, for example, 15 mm × 700 mm. The pitch L1 can be arbitrarily selected according to the size of the light emitting element 12, and is several mm, for example. A diffusion plate 20 is disposed on the substrate 10, that is, on the light emitting element 12. At both ends of the substrate 10, there are connector portions 14 and 16 connected to a power source / controller for controlling the light emission of the light emitting element 12. The lower surface of the substrate 10 is connected to a heat sink 18 for releasing heat from the light emitting element 12. The heat sink 18 is made of, for example, aluminum (Al), and is bonded to the lower surface of the substrate 10 via a heat conductive adhesive layer (not shown).

  The substrate 10 is selected according to the output of the light emitting element 12. For a relatively small output (eg, “mW” level), a general circuit board such as a printed wiring board can be used. When the heat generation amount of the light emitting element 12 is small, the heat sink 18 may be unnecessary. When the output of the light emitting element 12 is relatively large (for example, “W” level), the substrate 10 is made of a material having a large thermal conductivity, such as a metal (such as aluminum (Al) or copper (Cu)).

  The light emitting element 12 can basically be arbitrarily selected from not only semiconductor elements such as currently available light emitting diodes (LEDs) and laser diodes (LD) but also light emitting elements that will newly appear in the future. However, it is desirable that the light-emitting element has a relatively high output, in other words, a high luminance, for the purpose of the present invention. In the following description, a case where a high-intensity LED is used as the light emitting element 12 will be described. That is, the description will be made assuming that the light emitting element 12 is the high brightness LED 12. Here, high brightness means that the output is about several watts (W), for example.

  The high-intensity LED 12 means one formed as a chip (elementized) one by one, and is different from a form such as an LED array formed by a semiconductor process. Accordingly, the high-intensity LEDs 12 are mounted at a predetermined pitch L1 while being positioned one by one on the substrate 10. The luminescent color of the high-intensity LED 12 can be arbitrarily selected, and can be basically arbitrarily selected from visible, near ultraviolet, near infrared, and the like. For example, from the viewpoint of increasing the amount of light, a white LED having a wide emission wavelength band can be used, but it goes without saying that other three primary colors (red, blue, green) may be used.

  The diffusing plate 20 is used for diffusing and uniformizing the light from the high-intensity LED 12, and the material thereof can be arbitrarily selected. There may be at least one diffusion plate 20, and the number thereof can be arbitrarily selected. Further, the diffusing plate 20 may be used in combination with other means having a light diffusing function such as a microlens. In the present invention, as will be described in detail later, a mask for further uniformizing light is installed on or near the surface of the diffusion plate 20.

  Next, the use principle (concept) of the luminance distribution in the present invention will be described with reference to FIG. 2A shows the measurement configuration of the luminance distribution of the line light source 100, and FIG. 2B shows the measurement result and the like. As shown in (a), the luminance distribution is measured by the line sensor camera 25 installed on the line light source 100. The line sensor camera 25 may be any camera that can acquire an image for each dimension by arranging light receiving elements (pixels) in a line. The line sensor camera 25 includes, for example, a one-dimensional CCD. Although not shown, the output signal of the line sensor camera 25 is input to a signal (image) processing system such as a PC, where it is processed to have a luminance distribution.

  The line light source 100 emits light with a predetermined output, moves at a predetermined pitch in the X direction in the figure, and the line sensor camera 25 measures the average luminance at each position on the X axis. Here, the average luminance means an average of luminance values in the short (width) direction of the line light source 100 at each position (X) of the line light source 100. Curve A in FIG. 2B is a measurement result of the luminance distribution. It can be seen that the average luminance varies depending on the position (X) of the line light source 100. A curve B is a curve representing an inverse function of the function when the curve A is viewed as one function. In the present invention, the variation in luminance is reduced by canceling the amplitude of the luminance (curve) using the curve B representing the inverse function of the average luminance distribution (curve). Specifically, as described later in detail, the light amount from the line light source 100, more precisely the light amount from the diffusion plate 20 (diffused light amount) is controlled using the curve B. This is because the amount of light received by the line sensor camera 25 is an integrated value of light, and thus the amount of light on the light output side is increased or decreased depending on the position (X) to cancel out the magnitude (variation) of the luminance value. ing.

  FIG. 3 is a diagram showing an embodiment of the configuration of the mask 30 of the present invention. 3A and 3B are top views of the mask 30, and FIGS. 3C to F are side (cross-sectional) views of the mask 30. FIG. The mask 30 has a light shielding region 310 and a transmission region 312. The light shielding area 310 constitutes one mask pattern, and its shape (pattern) is determined based on the curve (for example, B in FIG. 2) representing the inverse function of the luminance distribution described above. That is, the light quantity at each position (X) of the line light source 100 is increased or decreased by the shielding shape 310 reflecting the curve representing the inverse function of the luminance distribution. In practice, the mask shielding shape 310 is formed while changing the scale of the curve in the long (X) direction or the short (Y) direction according to the size of the line light source 100.

  The light shielding region 310 is provided at one end (FIG. 3A) or both ends (FIG. 3B) of the mask 30 in the short side (Y) direction. When the light shielding region 310 is provided at one end, it may be provided at the upper end as shown in FIG. 3A or at the lower end on the lower side of the figure. When providing the light shielding region 310 at both ends as shown in FIG. 3B, the shape (pattern) of the shielding region 310 is inverted up and down. At the time of the reversal, a fine difference may be provided between the two shapes from the viewpoint of promoting uniform luminance. The mask 30 is formed on a transparent substrate or directly on the surface of the diffusion plate 20. The light shielding region 310 is formed by patterning a thin film, tape, thin plate or the like that does not transmit light. Here, patterning means processing into a shape corresponding to the curve representing the inverse function of the luminance distribution described above. In the case of a thin film, it is formed by a film forming technique such as vapor deposition of metal on a transparent substrate. In the case of a tape or a thin plate, it is cut into a shape corresponding to the curve. Alternatively, a shape corresponding to a curve may be drawn on a transparent substrate using a laser processing machine or the like, and the light transmittance of the drawing area may be reduced.

  As shown in FIGS. 3C and 3D, the mask 30 is provided on one surface of one diffusion plate 20, that is, on the incident side surface of light from the high-intensity LED 12 or the exit side surface of diffused light from the diffusion plate. Installed or formed directly on each surface. The mask 30 may be provided on both sides of one diffusion plate 20 as shown in FIG. At that time, the mask 30 of FIG. 3A is installed on the upper surface side of the diffusion plate 20, and the mask 30 in which the mask 30 of FIG. 3A is inverted (the light shielding region 310 is on the lower side). A mask) may be installed. When two diffuser plates 20 are used in an overlapping manner, a mask 30 can be provided between the two diffuser plates 20 as shown in FIG. Note that the number of the diffusion plates 20 is not limited to one or two, and a plurality of three or more diffusion plates can be stacked or combined. In that case, the mask 30 can be selectively provided on the surface of one or two or more diffusion plates.

  Next, the results of measuring the Si wafer surface using the line light source 100 of the present invention will be described with reference to FIGS. FIG. 4 is a diagram showing a wafer surface measurement system using the line light source 100 of the present invention. FIG. 5 is a diagram showing the measurement result of the luminance distribution according to the configuration of FIG.

  4A is a top view of the measurement system, and FIG. 4B is a side view of the measurement system. The line light source 100 is placed above the Si wafer 40 on the table 45 at a predetermined distance. The line sensor camera 25 is also installed above the Si wafer 40 at a predetermined angle with respect to the surface of the Si wafer 40. As in the case of FIG. 2, although not shown, the output signal of the line sensor camera 25 is input to a signal (image) processing system such as a PC, where it is processed to have a luminance distribution. The table 45 can be moved horizontally or vertically in a predetermined step. While the line light source 100 emits light with a predetermined output, the table 45 on which the Si wafer 40 is placed moves in a predetermined step, and the line sensor camera 25 moves each position (X) on the predetermined line of the Si wafer 40. The average brightness of was measured.

  In FIG. 5, a curve C is a measurement result of the luminance distribution when the mask 30 of the present invention is not used, and a curve D is a measurement result of the luminance distribution when the mask 30 of the present invention is used. As is clear from the comparison between the two curves, it can be seen that the variation in the average luminance at each position (X) of the Si wafer 40 is smaller in the curve D when the mask 30 of the present invention is used. The difference Δc = Q2−Q1 between the curve C and the difference Δd = P2 between the curve C and the difference Δc = Q2−Q1 between the curve C and the difference Δ between the maximum value and the minimum value of the average luminance in each curve based on the actual measurement values. The ratio (Δd / Δc) to −P1 was about 53%, and it was confirmed that the variation in average luminance was reduced by about half. That is, the uniformity of the luminance distribution at the position (X) of the light emitting element is improved by about 50%.

  The embodiment of the present invention has been described with reference to FIGS. However, the present invention is not limited to these embodiments. The present invention can be implemented in variously modified, modified, and modified embodiments based on the knowledge of those skilled in the art without departing from the spirit of the present invention.

10 Substrate 12 Light emitting element (High brightness LED)
14, 16 Connector portion 18 Heat sink 20 Diffuser 25 Line sensor camera 30 Mask 40 Si wafer 45 Stage 100 Line light source 310 Light shielding area 320 Light transmission area

Claims (5)

A line light source,
A plurality of light emitting elements arranged in a line at predetermined intervals on the substrate;
At least one diffusion plate provided on the substrate for diffusing light from the plurality of light emitting elements;
A light amount distribution of the emitted light in the longitudinal direction of the diffuser plate is set according to a luminance distribution in the longitudinal direction of the diffuser plate in the diffused light from the diffuser plate provided on or near the surface of the diffuser plate. and a mask for,
The mask uses a curve representing an inverse function of a function corresponding to the curve of the luminance distribution as a mask pattern for shielding the diffused light so as to cancel the luminance distribution . The line light source according to claim 1 , wherein the mask pattern is provided along a longitudinal direction of the mask at at least one end in a short direction of the mask. The line light source according to claim 1 , wherein the mask pattern is formed of a light shielding film, a thin plate, or a tape. The line light source according to claim 1, wherein the mask is provided between two diffusion plates. The line light source according to any one of claims 1 to 4 , wherein the light emitting element is formed of a high brightness LED and is provided on a substrate having high thermal conductivity.

Images