JP2006018040A - Corner cube array formation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a corner cube reflector having a plurality of unit structures arranged at fine pitches, and ensuring excellent retroreflection. <P>SOLUTION: The corner cube array formation method includes steps of: (A) preparing a layer 31 to be etched having a crystal structure; (B) forming a mask layer which is constituted of a plurality of masks 32a and has a pattern for regulating the arrangement of corner cubes on the layer 31 by the use of a material different from that of the layer 31; and (C) providing the layer 31 with a shape 33 for regulating the retroreflection of the corner cube arrays, by etching the layer 31 from the area not covered with masks 32a. The step (C) includes steps of: (C1) obtaining reflected light by emitting light 34 to the areas including the areas where the mask parts 32a of the layer 31 are formed and the areas where the mask parts 32a are not formed; (C2) detecting, on the basis of the reflected light, a point of time when the masks 32a are peeled from the layer 31; and (C3) stopping the etching of the layer 31. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for forming a corner cube array.

  In recent years, development of very small optical elements (micro optical elements) such as microlenses, micromirrors, and microprisms has been promoted, and they are used in the fields of optical communication and display devices. The realization of such a micro optical element is expected to further develop and enhance the fields of optical technology and display technology.

  As such an optical element, there is known a corner cube array obtained by regularly arranging corner cubes having shapes corresponding to one corner of a cube and having three surfaces orthogonal to each other. The corner cube array can be used, for example, for a retroreflector of a reflective display device. The retroreflecting plate refers to a reflecting plate that reflects light in the original direction regardless of the incident direction by reflecting incident light on a plurality of reflecting surfaces.

  A corner cube array used for a retroreflector of a reflective display device is required to be composed of corner cubes having a very small size (for example, 100 μm or less). This is because if the size of the corner cube (unit element) is larger than the pixel of the display device, the retroreflected light may pass through an undesired pixel, which causes a problem of color mixing.

  Conventionally, a corner cube array has been mechanically manufactured using a cutting method (plate method, pin bundling method, etc.). However, in a method of mechanically preparing a corner cube, a fine corner cube as described above is used. It is difficult to form. In addition, when a corner cube reflector is manufactured using the method described above, the specularity of each reflecting surface is lowered, and the corner curvature (R) at the intersection of the reflecting surfaces is increased, so that the efficiency of retroreflecting is low. The problem that becomes.

  On the other hand, Patent Document 1 and the like describe a method of producing a corner cube array using a photochemical technique. Non-Patent Document 1 describes a method of manufacturing a corner cube array using selective growth of silicon. However, with these methods, it is difficult to control the shape of the corner cube with high accuracy, and it is difficult to obtain a corner cube array having excellent retroreflection characteristics.

  Therefore, the present inventors have a shape controlled with high accuracy by performing anisotropic etching on the surface of the substrate having a crystal structure in Patent Document 2 and the like, the applicant of which is the same as the present application. A method of fabricating a corner cube array is proposed.

  When a corner cube array is manufactured by etching, it is extremely important to quickly detect the end point of etching. If the etching is continued beyond the point where the etching should be finished, or if the etching is stopped before the point where the etching should be finished, a deviation from the ideal corner cube array shape will occur, reducing the recursive characteristics. May be a factor.

  By the way, as a general technique for detecting the end point of etching, there are the following two methods.

  The first method is a method of embedding an etching stop layer inside an object to be etched. For example, when a gallium arsenide (GaAs) layer is etched using a mixed solution of sulfuric acid and hydrogen peroxide as an etching solution, indium phosphide (InP) having etching resistance to the etching solution is formed inside the GaAs layer. Pre-embed layers. Thus, the etching can be terminated when the etching of the GaAs layer proceeds and reaches the position of the InP layer.

  The second method is a method of detecting an optimum etching end point by observing the surface of the object to be etched by some method in the etching process. For example, when etching is performed in a vacuum, a method of observing the surface of an object to be etched using an electron beam is known. In a method called reflection light velocity electron diffraction, the surface state of the object to be etched can be observed by making electrons incident at a low angle on the surface of the object to be etched and projecting the reflected electron pattern on the fluorescent screen. On the other hand, in dry etching or wet etching performed in a pressure atmosphere close to atmospheric pressure, a method of observing the surface of an object to be etched using light is known. For example, Patent Document 3 discloses a method of observing temporal changes in light reflection intensity at a plurality of locations on the surface of the object to be etched when the etching process is performed by spraying an etching solution on the surface of the object to be etched. This method utilizes the phenomenon that the gloss of the metal film, which is an object to be etched, is lost as the etching progresses, and the amount of reflected light is reduced.

Japanese Patent Laid-Open No. 7-205322 JP 2003-066211 JP 2003-105568 A Applied Optics Vol.35, No19 pp3466-3470 "Precision crystal corner cube arrays for optical gratings formed by (100) silicon planes with selective epitaxial growth"

  However, it is difficult to apply these techniques for detecting the end point of etching to etching for processing into a complicated shape such as a corner cube array.

  Thus, in the method of manufacturing a corner cube array by etching, a new method capable of accurately detecting the end point of etching is required in order to improve the shape accuracy of the corner cube array.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to accurately detect a point where etching should be terminated in a method of manufacturing a corner cube array by etching.

  The corner cube array forming method of the present invention includes (A) a step of preparing an etching target layer having a crystal structure, and (B) a corner using a material different from the material of the etching target layer on the etching target layer. A step of forming a mask layer having a pattern that defines an arrangement of cubes; and (C) a retroreflective surface of the corner cube array is defined by etching the etched layer from a region not covered by the mask layer. A method of forming a corner cube array including a step of providing a shape to be etched to the layer to be etched, wherein the step (C) is not formed with the region of the layer to be etched in which the mask layer is formed. Irradiating a region including the region with light to obtain reflected light (C1), and based on the reflected light, the mask layer is subjected to etching. And step (C2) for detecting when peeled from ring layer, and a step (C3) for stopping the etching of the layer to be etched.

  In a preferred embodiment, the step (B) includes a step of forming the mask layer using a material having a reflectance different from that of the material of the layer to be etched with respect to the light. C2) includes a step of measuring the intensity of the reflected light.

  In a preferred embodiment, the step (C1) includes a step of irradiating monochromatic light as the light to obtain reflected light, and the step (C2) includes reflected light by the mask layer and reflection by the etched layer. A step of observing an interference state with light.

  In a preferred embodiment, the step (B) includes a step of forming the mask layer using a material having a reflection spectrum different from that of the material of the layer to be etched, and the step (C2) includes the step (C2). Measuring the spectrum of the reflected light.

  The corner cube array may be composed of cubic corner cubes.

  In the step (C), the etching rate of the etched layer preferably depends on the crystal plane orientation of the etched layer.

  The step (C) is preferably a step of chemically etching the layer to be etched.

  The step (C) may include a step of performing wet etching of the layer to be etched using an etching solution and a step of causing the etching solution to flow.

  In a preferred embodiment, the layer to be etched is made of a cubic crystal material and has a surface substantially parallel to the {111} plane of the crystal material.

  The crystalline material may be gallium arsenide.

  The etching apparatus of the present invention is an apparatus for etching a layer to be etched, on which a mask layer having a predetermined pattern is formed, from a region not covered with the mask layer, wherein the mask of the layer to be etched is A light irradiating unit configured to irradiate light to a region including a formed region and a region not formed to form reflected light; a light receiving unit that receives the reflected light; and the mask based on the reflected light. Includes a control unit that detects that the layer is peeled from the layer to be etched.

  In a preferred embodiment, a region including an etching tank in which an etching solution for etching the layer to be etched is placed and a region where the mask is formed and a region where the mask is not formed of the layer to be etched is included in the etching solution. And a means for causing the etching solution to flow, and a flow rate controller for controlling the flow rate of the etching solution.

  According to the present invention, in the method for producing a corner cube array by etching, the end point of etching can be accurately and easily detected, so that a corner cube array with high shape accuracy can be obtained. Since such a corner cube array has excellent retroreflection characteristics, it can be suitably used for a retroreflection plate of a display device.

  An example of a method for forming a corner cube array by etching will be described with reference to FIG.

  First, as shown in FIG. 1A, a mask layer 2 covering a selected region is formed on an etching target layer 1 having a crystal structure. As the layer 1 to be etched, a single crystal substrate made of a cubic crystal material (for example, GaAs) and having a surface substantially parallel to the {111} plane of the crystal material can be used. The mask layer 2 has a pattern that defines the arrangement of corner cubes, and is formed using, for example, a resist material.

  Subsequently, when the etched layer 1 is etched under the condition that the etching rate is different depending on the crystal plane in the etched layer 1, as shown in FIG. Anisotropic etching proceeds from a region not covered by layer 2.

  As a result, as shown in FIG. 1C, a corner cube array shape 3 is formed on the surface of the layer 1 to be etched. The corner cube array shape 3 is composed of three (100) faces of the crystal material in the etched layer 1. At this time, a convex portion is formed in a region covered with the mask layer 2 in the layer to be etched 1, and the contact area between the mask layer 2 and the surface of the layer to be etched 1 becomes extremely small. Peel from the surface of the etching layer 1.

  In order to form a corner cube array with high shape accuracy using the above method, it is important to detect with high accuracy the point in time at which the etching process should be stopped (etching end point). As a result of studies by the present inventors, in the above method, the corner cube array shape 3 is formed in the etched layer 1 when the mask layer 2 is peeled off from the surface of the etched layer 1, and the mask layer 2 is It has been found that the shape accuracy of the corner cube array shape 3 decreases as the etching continues even after peeling.

  Therefore, the corner cube array forming method according to the present invention is characterized in that the time when the etching mask is peeled off in the etching process is detected, and the etching is stopped at that time.

  Hereinafter, the etching process in the present invention will be described more specifically.

  Similar to the method shown in FIG. 1, after the mask layer 2 is formed on the surface of the etching target layer 1, the etching target layer 1 is etched. While etching is performed, light is irradiated to a region including a region where the mask layer 2 is formed and a region where the mask layer 2 is not formed in the etching target layer 1, and the mask layer 2 is etched based on the reflected light. The time when peeling from 1 is detected. By stopping the etching at this point, the corner cube array shape 3 is given to the layer 1 to be etched.

  The “layer to be etched” in the present invention may have a crystal structure, but is preferably a single crystal substrate made of a cubic crystal material (hereinafter sometimes referred to as “cubic single crystal substrate”). ). As the cubic single crystal substrate, for example, a substrate formed from a compound semiconductor having a zinc flash structure (such as GaAs) or a substrate formed from a crystal material having a diamond structure (such as germanium crystal) can be used. Such a cubic single crystal substrate preferably has a surface substantially parallel to the {111} plane of the crystalline material. Here, the “substrate having a surface substantially parallel to the {111} plane of the crystal material” is not only a substrate having a surface parallel to the {111} plane of the crystal material, but also inclined by 0 ° to 10 °. A substrate having a curved surface.

  The “corner cube array shape” may be a shape that defines the retroreflective surface of the corner cube array. The etched layer to which the corner cube array shape is given by etching may be used as it is as a corner cube array for a retroreflector or the like, or may be used as a master for producing the corner cube array by transfer. . Alternatively, the corner cube array may be formed by forming a reflective metal layer on the surface of the layer to be etched with the corner cube array shape.

  In the present specification, the “corner cube array” only needs to have a structure in which corner cubes having three surfaces orthogonal to each other are arranged. For example, the corner cube array has a structure in which concave portions having a triangular pyramid shape are arranged. May be. Preferably, the corner cubes have a structure in which cubic corner cubes each having a square shape are arranged. Such a corner cube array (cubic corner cube array) is advantageous because it can realize particularly high retroreflection characteristics.

  Hereinafter, the method for detecting the etching end point in the present invention will be described more specifically with reference to the drawings. Here, three detection methods (first detection method to third detection method) will be described as an example.

  In the first detection method, the difference in reflectance between the layer to be etched and the mask layer is used to detect when the mask layer is peeled from the layer to be etched, that is, the point at which etching is to be completed.

  FIGS. 2A and 2B are diagrams for explaining the first detection method. As shown in FIG. 2A, the object to be etched 100 includes an etched layer 1 having a crystal structure and a mask layer 2 formed so as to cover a selected region on the surface of the etched layer 1. is doing. The mask layer 2 is patterned into a shape corresponding to the corner cube array shape to be formed. While the etching target layer 1 is being etched, the light 10 is incident on the surface of the object to be etched 100 on which the mask layer 2 is formed, and the intensity of the reflected light is observed.

  In the first detection method, the reflectance of the etched layer 1 with respect to the light 10 and the reflectance of the mask layer 2 with respect to the light 10 are different. For example, a material having a relatively low reflectance is used as the material of the layer 1 to be etched, and a material having a higher reflectance than that of the material of the layer 1 to be etched is used as the material of the mask layer 2.

  As the light 10, it is preferable to select light having a wavelength such that a difference between the reflectance of the etching target layer 1 and the reflectance of the mask layer 2 becomes large. Depending on the combination of the material to be etched 1 and the material of the mask layer 2, white light may be used as the incident light 10. Further, the light 10 may be set to enter perpendicularly to the surface of the layer 1 to be etched, or may be set to enter at a predetermined angle. However, when the etching is started, it is necessary to make the light 10 incident not only on the region of the surface of the layer to be etched 1 that is not covered with the mask layer 2 but also on the surface of the mask layer 2.

  As the etching progresses, as shown in FIG. 2B, a corner cube array shape 3 is formed on the etched layer 1, the contact area between the mask layer 2 and the etched layer 1 decreases, and finally the mask layer. 2 peels from the surface of the layer 1 to be etched. When the mask layer 2 is peeled off, the light 10 is reflected only on the surface of the etched layer 1. As a result, the reflected light intensity changes rapidly, and this point is detected. In this example, since the reflectance of the material of the mask layer 2 is higher than the reflectance of the material of the layer 1 to be etched, a point where the reflected light intensity rapidly decreases is detected.

  An example of observation of the reflected light intensity in the first detection method is shown in FIG. The vertical axis in FIG. 3 is the intensity of reflected light (A.U .: arbitrary unit), and the horizontal axis is the etching time (seconds). As described above, the point e1 at which the intensity of the reflected light sharply decreases is the point at which the mask is peeled off, and it is preferable that the etching is terminated immediately after the point e1 is detected.

  Depending on the material of the layer 1 to be etched, a change in retroreflection characteristics depending on the shape of the layer 1 to be etched may be used. The case where the retroreflective property is used will be specifically described below.

  When light 10 is incident on the surface of the layer 1 to be etched from an oblique direction during etching, the layer 1 to be etched before the corner cube array shape is formed does not exhibit retroreflection characteristics. It does not return to the incident direction of the light 10. When the etching progresses and the corner cube array shape 3 is formed from the etched layer 1 and the mask layer 2 is peeled off at the same time, the light 10 is recursively reflected by the corner cube array shape 3. The amount (intensity) of reflected light increases rapidly. After detecting this point, the etching is immediately terminated.

  Next, the second detection method will be described. In this detection method, interference between reflected light from the layer to be etched and reflected light from the mask layer is used.

  4A and 4B are diagrams for explaining the second detection method. As shown in FIG. 4A, as in the case of the first detection method, a mask layer 2 is formed so as to cover a selected region on the surface of the etching target layer 1, and the etching target layer 1 is etched. . During the etching, the light 10 is incident on the surface of the object to be etched 100 on which the mask layer 2 is formed, and the reflected light intensity is observed. In the second detection method, monochromatic light is used as the light 10.

  The incident angle of the light 10 with respect to the surface of the etched layer 1 and the angle of the reflected light to be observed are the light reflected by the surface of the mask layer 2 and the light reflected by the bottom surface of the recess formed in the etched layer 1. As long as it can be observed simultaneously. Preferably, the light 10 is made incident on the surface of the layer 1 to be etched, and the intensity of the light reflected in the vertical direction is observed. Here, “the bottom surface of the recess formed in the etched layer 1” means a recess formed around the region of the etched layer 1 that is not covered with the mask layer 2 by etching of the etched layer 1. This refers to the bottom surface 1s, and this bottom surface 1s is typically substantially parallel to the surface of the etched layer 1 before etching. As the etching progresses, the level of the bottom surface 1s decreases and the area of the bottom surface 1s decreases.

If the corner cube pitch in the shape of the corner cube array to be formed is sufficiently small (for example, 50 μm or less), when light 10 is incident on the object 100 to be etched, the light reflected from the surface of the mask layer 2 and the recesses in the layer 1 to be etched Interference occurs with the light reflected from the bottom surface 1s of the. This is because the height (level) h ₂ of the surface of the mask layer 2 is constant (when the etching time is “t”, dh ₂ / dt = 0), but the level of the bottom surface 1 s of the concave portion of the etched layer 1 This is because h ₁ decreases as etching progresses (dh ₁ / dt <0). Since the interference state periodically changes due to the change in the optical path difference, the intensity of the reflected light is ½ the wavelength λ of the light 10 on which the level h ₁ of the bottom surface 1 s of the etched layer ₁ is incident. It vibrates with the time changing as one period.

  When the etching progresses and the corner cube array shape 3 is formed in the etched layer 1 and the mask layer 2 is peeled off from the surface of the etched layer 1 as shown in FIG. Intense periodic vibrations do not occur. The reason why periodic vibration does not occur due to the peeling of the mask layer 2 is that the level of the region covered by the mask layer 2 (hereinafter referred to as “region 1 m”) on the surface of the layer 1 to be etched is also the progress of etching. Accordingly, the level of the bottom surface 1s decreases at substantially the same speed as the level of the bottom surface 1s, so that interference does not occur between the light reflected by the region 1m and the bottom surface 1s.

  An example of observation of reflected light intensity in the second detection method is shown in FIG. The vertical axis in FIG. 5 is the intensity of reflected light (A.U.), and the horizontal axis is the etching time (seconds). The point e2 at which the periodic vibration of the reflected light intensity does not occur is the point at which the mask layer 2 is peeled off, and it is preferable to stop the etching promptly when the point e2 is detected. The reflected light intensity shown in FIG. 5 decreases as the etching progresses. This is because the area of the bottom surface 1s in the etched layer 1, that is, the area of the region that regularly reflects the light 10 is increased as the etching progresses. This is because the regular reflectance is decreased.

  Next, the third detection method will be described. In this detection method, the difference in wavelength between the light reflected by the etched layer and the light reflected by the mask layer is used. Therefore, it is necessary to select materials for the etched layer and the mask layer so that the spectra of the light reflected by the etched layer and the mask layer are different from each other.

  Also in the third detection method, as in the other detection methods described above, a mask layer is formed so as to cover a selected region on the surface of the etching target layer, and the etching target layer is etched. During the etching, white light is incident on the surface of the object to be etched on which the mask layer is formed, and the spectrum of the reflected light is measured.

  Measurement examples of the reflected light spectrum in the third detection method are shown in FIGS. As shown in FIG. 6A, the spectrum of reflected light when etching is started has a peak P1 caused by light reflected by the mask layer and a peak P2 caused by light reflected by the etched layer. On the other hand, when the etching progresses and the mask layer is separated from the layer to be etched, the peak of the spectrum of the reflected light is only the peak P2 due to the light reflected by the layer to be etched, as shown in FIG. Therefore, it is preferable to detect the point where the spectrum of the reflected light changes abruptly and stop the etching quickly.

  In the present invention, any one of the detection methods described above may be used, or two or more detection methods may be used in combination. Etching in the present invention may be chemical etching, and may be dry etching using an etching gas or wet etching using an etching solution.

  Hereinafter, a configuration example of an etching apparatus used for etching in the present invention will be described with reference to the drawings. The etching apparatus described below can be used for etching using any of the above detection methods.

  FIG. 7 is a diagram showing the configuration of the chamber 11 in the dry etching apparatus. In the chamber 11, an object to be etched 100, a light irradiation part 13 for making light incident on the object to be etched 100, and a light receiving part 15 for receiving the light reflected by the object to be etched 100 are arranged. The object to be etched 100 includes a layer to be etched 1 and a mask layer 2 formed on the surface thereof. The etching target layer 1 is etched by bringing an etching gas into contact with the surface of the etching target 100 on which the mask layer 2 is formed.

  In the configuration shown in FIG. 7, the light from the light irradiation unit 13 is incident on the surface of the object to be etched 100 from an oblique direction. However, the light may be incident perpendicular to the surface of the object to be etched 100. 15 is arranged so as to receive light vertically reflected by the object 100 to be etched.

  FIG. 8 is a top view for explaining the configuration of the etching tank 21 in the wet etching apparatus. In the etching tank 21, an object to be etched 100, a light irradiation unit 13 for making light incident on the object to be etched 100, and a light receiving unit 15 that receives light reflected by the object to be etched 100 are arranged. The object to be etched 100 includes a layer to be etched 1 and a mask layer 2 formed on the surface thereof. Etching of the etching target layer 1 is performed by bringing the surface of the etching target 100 on which the mask layer 2 is formed into contact with an etching solution. The angle at which the light from the light irradiation unit 13 is incident on the surface of the object to be etched 100 is not particularly limited, but is, for example, approximately 90 degrees. In the configuration shown in FIG. 8, the light irradiation unit 13 is installed so that light enters perpendicularly to the surface of the object to be etched 100, and the light receiving unit 15 is installed at substantially the same position as the light irradiation unit 13. . In addition, the light irradiation part 13 and the light-receiving part 15 may be provided in an etching liquid, and one or both may be provided in the position which does not contact an etching liquid.

  7 and 8, the light irradiation unit 13 is disposed so that light is incident on the surface of the object to be etched 100 on which the mask layer 2 is formed. The light emitted from the light irradiation unit 13 is preferably incident on a plurality of locations on the surface of the object to be etched 100. On the surface of the object to be etched 100, the incident position of light is not particularly limited, and may be selected at random. However, it is necessary to irradiate with light the area | region including the area | region in which the mask layer 2 was formed, and the area | region in which the mask layer 2 was not formed among the surfaces of the to-be-etched object 100. Typically, the spot diameter of light formed on the surface of the object to be etched 100 is at least twice the pitch of the corner cube array to be formed.

  In addition, the light receiving unit 15 is disposed so as to be able to receive the light reflected by the surface of the object to be etched 100, and typically the light from the light irradiation unit 13 is regularly reflected by the mask layer in the object to be etched 100. Arranged in the direction. However, when the method of detecting the etching end point using the retroreflective property of the corner cube shape among the first detection methods is used, the light receiving unit 15 is arranged in the light incident direction regardless of the light incident direction. It arrange | positions so that the reflected light which returns may be received.

  Further, in a measurement unit (not shown), the intensity of light received by the light receiving unit 15 is measured, and the temporal change in intensity is recorded. Further, a control unit (not shown) detects that the mask layer is peeled based on the recorded measurement result of the reflected light intensity. When the peeling of the mask layer is detected, the etching of the etching target layer is stopped.

  Here, the material of the layer 1 to be etched removed by etching and the mask layer 2 that has been peeled off do not affect the measurement of the reflected light intensity, and the surfaces of the light irradiation unit 13, the light receiving unit 15, and the object 100 to be etched. It is desirable to be surely excluded from the space.

  In the etching apparatus having the configuration shown in FIG. 7, the removed material of the layer 1 to be etched and the peeled mask layer 2 are discharged from the chamber 11 by gas flow, or the reflected light intensity measurement in the chamber 11 is affected. It may be collected electrically in a place where it does not exist.

  On the other hand, in the etching apparatus having the configuration shown in FIG. 8, when the etching solution is flowed inside the etching tank, the material of the layer 1 to be etched and the mask layer 2 that has been peeled off do not affect the reflected light intensity measurement. It is advantageous because it can be moved to or discharged from the etching tank 21. The flow of the etching solution is, for example, provided with an etching solution supply port and a discharge port in the etching tank 21, and the etching solution flowing into the etching tank 21 from the supply port is brought into contact with the object to be etched 100 and then etched from the discharge port. This can be done by flowing out of the tank 21. The etchant that has flowed out may be supplied to the etching tank 21 again after filtering.

  When the etching solution is caused to flow inside the etching tank, it is preferable to control the flow rate of the etching solution inside the etching tank. As the etching end point is approached, by increasing the flow rate of the etching solution, the peeled mask layer 2 reattaches to the surface of the etched layer 1 or floats between the etched layer 1 and the light receiving portion 15. Since it is possible to prevent the measurement of the reflected light intensity from being affected, the etching end point can be detected more reliably.

  When the etching apparatus having the configuration shown in FIG. 7 or FIG. 8 is used, two or more detection methods among the first to third detection methods can be simultaneously performed. For example, when the first and second detection methods are to be performed, a material having a low reflectance is used as the material of the etching target layer 1, and a higher reflectance than the material of the etching target layer 1 is used as the material of the mask layer 2. The material which has is used. For the measurement of the reflected light intensity, monochromatic light having a wavelength such that the difference between the reflectance of the layer to be etched 1 and the reflectance of the mask layer 2 becomes large is used. The light irradiation unit 13 is installed so that such monochromatic light is perpendicularly incident on the surface of the object 100 to be etched, and the light receiving unit 15 receives light reflected in the vertical direction on the surface of the object 100 to be etched. To be installed. By measuring the temporal change in the intensity of the received light, it is possible to detect the point at which the intensity rapidly decreases and / or no periodic interference of the intensity occurs as the etching end point.

  In the case where the first detection method and the third detection method are performed simultaneously, monochromatic light having a specific wavelength and white light are emitted from the light irradiation unit 13 to the surface of the object 100 to be etched, and the reflected light thereof. By observing the time change of the spectrum of the spectrum, the peak of the spectrum due to the material characteristics of the mask layer 2 does not occur, and / or the intensity of the light having the specific wavelength of the reflected light changes abruptly Can be detected.

(Embodiment 1)
Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In this embodiment, a corner cube array composed of three {100} planes orthogonal to each other is produced by using a substrate formed of GaAs crystal and performing wet etching on the substrate. The end point of wet etching is detected by using the first and second detection methods described above together.

  First, as shown in FIG. 9A, a GaAs substrate 31 whose surface is substantially parallel to the {111} B plane is prepared. The {111} plane formed by gallium is the {111} A plane, and the {111} plane formed by arsenic is the {111} B plane. The surface of the substrate 31 is finished to a mirror surface.

  Next, as shown in FIG. 9B, a positive photoresist film 32 'having a thickness of about 1 μm is formed on the substrate surface by spin coating. As a material of the photoresist film 32 ′, for example, a resist material having a reflectance of 50% for monochromatic light having a wavelength of 670 nm is used. Note that the reflectance of GaAs with respect to this monochromatic light is about 30%.

  After pre-baking the photoresist film 32 ′ at about 100 degrees for 30 minutes, a photomask is placed on the photoresist film 32 ′ and exposure is performed.

  After the exposure, the photoresist film 32 ′ is developed to form a patterned resist layer 32 on the substrate 31 as shown in FIG. 9C. The resist layer 32 has a plurality of mask portions 32 a that cover selected regions of the substrate 31, and a plurality of openings 32 b that expose the surface of the substrate 31. In the present specification, of the resist layer 32, a layer composed of a plurality of mask portions 32a is called a mask layer.

  The planar shape of the resist layer 32 in the present embodiment is shown in FIG. The resist layer 32 has an equilateral triangular mask portion 32a and an opening 32b, and these regions 32a and 32b are alternately arranged in opposite directions in each of the side directions of the triangle. In addition, one of the equilateral triangles defining these regions 32a and 32b is arranged on the substrate 31 so as to be parallel to the <01-1> direction of the GaAs crystal. In the present embodiment, the length of one side of the equilateral triangle that defines the mask portion 32a and the opening portion 32b (the pitch Pm of the mask layer 2) is about 10 μm.

  In the present embodiment, the size (arrangement pitch) of corner cubes to be formed can be controlled according to the arrangement pattern of the mask portions 32a and the openings 32b in the resist layer 32. More specifically, the size of the corner cube to be formed is substantially the same size as the pitch Pm (here, about 10 μm) of the resist layer 32.

Next, wet etching of the substrate 31 is performed using an etching solution. As the etchant, for example, a mixed solution of NH ₄ OH: H ₂ O ₂ : H ₂ O = 1: 2: 7 can be used, and the temperature of the etchant is about 20 degrees.

  The wet etching in the present embodiment can be performed using, for example, an etching apparatus 200 as shown in FIG. The etching apparatus 200 includes an etching tank 42, a water supply pipe 48 for supplying the etching liquid 46 to the etching tank 42, and a drain pipe 50 for discharging the etching liquid 46 from the etching tank 42. An etching solution 46 is held in the etching tank 42, and the substrate 31 that is an object to be etched is fixed in the etching solution 46. A light observation device 44 is installed inside the etching tank 42. The light observation device 44 includes a light irradiation unit that irradiates light onto the surface of the substrate 31 to be etched, a light receiving unit that receives the reflected light, a measurement unit that measures the intensity of the received light, and the like. Yes. The etching solution 46 in the etching tank is discharged from the etching tank 42 by the drain pipe 50 or the overflow tank 52 for removing the top, filtered by the filter 55, and returned to the etching tank 42 from the water supply pipe 48 again. Further, the water supply pipe 48 is provided with a valve 56, and a pump 54 is provided between the drain pipe 50 and the water supply pipe 48, and the flow rate (flow rate) of the etching solution 46 inside the etching tank by the valve 56 and the pump 54. Can be controlled. Further, the material of the substrate 31 removed by etching and the mask portion 32a peeled off from the substrate 31 are removed from the etching tank 42 via the drain pipe 50 or the overflow tank 52 by the specific gravity, and then removed by the filter 55. Is done.

  When the substrate 31 on which the resist layer 32 is formed is fixed to the etching tank 42 of the etching apparatus 200 and the substrate 31 is etched, it is exposed through the opening 32b in the substrate 31 as shown in FIG. Etching progresses from the area where it is. In the present embodiment, the {100} plane ((100) plane, (010) plane, and (001) plane) of the gallium arsenide crystal is less likely to be etched than other crystal planes. Anisotropic etching proceeds so as to be exposed.

  During the etching, the surface of the substrate 31 on which the resist layer 32 is formed is observed using the light observation device 44. As shown in FIG. 9D, the observation is performed by measuring the intensity of light that is incident on the surface of the substrate 31 perpendicularly to the surface of the substrate 31 and the light reflected in the direction perpendicular to the surface of the substrate 31 as shown in FIG. .

  The measurement result of the reflected light intensity is shown in FIG. As can be seen from FIG. 12, when etching is started, periodic oscillation of the reflected light intensity is observed. One period of vibration indicates a time during which the bottom surface of the concave portion formed in the substrate 31 is deepened by 335 nm by etching. As the etching progresses, the reflected light intensity drops sharply and the reflected light intensity does not vibrate (point e3 shown in FIG. 12). At this point, the substrate 31 is pulled up from the etchant 46.

  Note that it is preferable to increase the flow rate of the etching solution 46 in the etching tank 42 in the vicinity of the etching end point. Accordingly, it is possible to prevent the mask portion 32a peeled off from the substrate 31 from reattaching to the substrate 31 or floating in the vicinity of the substrate 31 or the light observation device 44 to interfere with the measurement of the reflected light intensity.

  Thereafter, the substrate 31 is subjected to ultrasonic cleaning for about 10 minutes to remove unnecessary mask portions 32 a remaining on the substrate 31. Furthermore, it substitutes with ethanol and performs pure water running water washing for about 10 minutes. In this way, the corner cube array shape 3 is formed on the surface of the substrate 31 as shown in FIG.

  The method of forming the corner cube array according to the present invention is not limited to the above method. In the above method, the GaAs substrate 31 is used as the layer to be etched, but the layer to be etched in the present invention may be a single crystal substrate made of another cubic crystal material. Furthermore, the layer to be etched may be a layer formed on a support substrate made of an amorphous or polycrystalline material, and not only a flat plate but also various three-dimensional shapes as long as it includes a flat surface. Can have.

  Further, the pattern of the resist layer 32 is not limited to the pattern shown in FIG. However, in order to suitably manufacture the corner cube array, it is desirable that predetermined points (for example, the position of the center of gravity) in the mask portion 32a of the resist layer 32 are arranged on the honeycomb lattice points. Here, the honeycomb lattice point refers to a point corresponding to the vertex of each regular hexagon and the center of gravity of each regular hexagon when congruent regular hexagons are laid without gaps. Alternatively, a plurality of parallel lines at equal intervals (predetermined intervals) extending in the first direction and a plurality of equal intervals extending in a second direction different from the first direction by 60 ° and the same intervals as the predetermined intervals The point corresponding to the intersection with the parallel line. The mask portion 32a of the resist layer 32 preferably has a three-fold rotational symmetry shape such as a triangle or a hexagon.

  The corner cube size (corner cube arrangement pitch) in the corner cube array obtained by the present invention is not particularly limited because it varies depending on the application of the corner cube array, but the corner cube array is used as a retroreflector for a reflective liquid crystal display device. For example, the thickness is 2 μm or more and 50 μm or less.

  According to the present invention, since the end point of etching can be detected with high accuracy in a method for producing a corner cube array by etching, a corner cube array with high shape accuracy can be provided. Since such a corner cube array has excellent retroreflection characteristics, it can be suitably used for a retroreflection plate of a display device.

  Furthermore, according to the present invention, an etching apparatus that can easily produce a corner cube array with high shape accuracy can be provided.

(A)-(c) is process sectional drawing for demonstrating the method of producing a corner cube array. (A) And (b) is a cross-sectional schematic diagram for demonstrating the 1st detection method in this invention. It is a graph which illustrates the measurement result of the reflected light intensity at the time of using the 1st detection method in the present invention. (A) And (b) is a cross-sectional schematic diagram for demonstrating the 2nd detection method in this invention. It is a graph which illustrates the measurement result of the reflected light intensity at the time of using the 2nd detection method in the present invention. (A) And (b) is a graph which illustrates the measurement result of the reflected light spectrum at the time of using the 3rd detection method in the present invention. It is a figure for demonstrating the structure of the chamber in the dry etching apparatus used by this invention. It is a top view for demonstrating the structure of the etching tank in the wet etching apparatus used by this invention. (A)-(e) is sectional process drawing for demonstrating the formation method of the corner cube array of embodiment by this invention. It is a figure which shows the shape of the resist layer in embodiment by this invention. It is a figure for demonstrating the structure of the etching apparatus used with the manufacturing method of the corner cube array of embodiment by this invention. It is a graph which illustrates the measurement result of the reflected light intensity in the embodiment by the present invention.

Explanation of symbols

1 Substrate 2 Mask layer 3 Corner cube array shape 31 Substrate (GaAs substrate)
32 'resist film 32 resist layer 32a mask part 32b opening 33 corner cube array shape 34 light (monochromatic light)

Claims (12)

(A) preparing a layer to be etched having a crystal structure;
(B) forming a mask layer having a pattern defining an arrangement of corner cubes on the etched layer using a material different from the material of the etched layer;
(C) a step of etching the layer to be etched from a region not covered with the mask layer, thereby providing the layer to be etched with a shape defining a retroreflecting surface of the corner cube array. An array forming method comprising:
The step (C)
Irradiating light to a region including a region where the mask layer is formed and a region where the mask layer is not formed in the etched layer to obtain reflected light (C1);
A step (C2) of detecting when the mask layer is peeled off from the layer to be etched based on the reflected light;
A method of forming a corner cube array including a step (C3) of stopping etching of the etching target layer. The step (B) includes a step of forming the mask layer using a material having a reflectance different from that of the material of the layer to be etched with respect to the light,
The method of forming a corner cube array according to claim 1, wherein the step (C2) includes a step of measuring an intensity of the reflected light. The step (C1) includes a step of obtaining reflected light by irradiating monochromatic light as the light,
3. The method of forming a corner cube array according to claim 1, wherein the step (C2) includes a step of observing an interference state between the reflected light from the mask layer and the reflected light from the etching target layer. The step (B) includes a step of forming the mask layer using a material having a reflection spectrum different from that of the material of the layer to be etched,
The method of forming a corner cube array according to claim 1 or 2, wherein the step (C2) includes a step of measuring a spectrum of the reflected light.   The corner cube array forming method according to any one of claims 1 to 4, wherein the corner cube array includes a cubic corner cube.   6. The method of forming a corner cube array according to claim 1, wherein in the step (C), the etching rate of the etching target layer depends on the crystal plane orientation of the etching target layer.   The said process (C) is a formation method of the corner cube array in any one of Claim 1 to 6 including the process of performing the chemical etching of the said to-be-etched layer.   The method of forming a corner cube array according to claim 7, wherein the step (C) includes a step of performing wet etching of the etching target layer using an etching solution and a step of causing the etching solution to flow.   9. The method of forming a corner cube array according to claim 1, wherein the etching target layer is made of a cubic crystal material and has a surface substantially parallel to the {111} plane of the crystal material.   The method for forming a corner cube array according to claim 9, wherein the crystal material is gallium arsenide. An apparatus for etching a layer to be etched, on which a mask layer having a predetermined pattern is formed on a surface, from a region not covered with the mask layer,
A light irradiation unit configured to irradiate light to a region including a region where the mask is formed and a region where the mask is not formed of the layer to be etched to form reflected light;
A light receiving unit for receiving the reflected light;
An etching apparatus comprising: a control unit that detects that the mask is peeled from the etching target layer based on the reflected light. An etching tank into which an etching solution for etching the layer to be etched is placed;
Means for bringing a region including the region where the mask is formed and the region where the mask is not formed into contact with the etching solution;
Means for flowing the etching solution;
The etching apparatus according to claim 11, further comprising a flow rate control unit that controls a flow rate of the etching solution.

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