JP4269189B2 - Optical element, optical film planarization method, and optical element manufacturing method - Google Patents

Description

  The present invention provides an optical element that relaxes the stress of the optical film acting on the substrate and planarizes the surface on which the optical film is formed when an optical film is formed on one surface of the substrate, and relaxes the film stress. The present invention relates to an optical film planarizing method for planarizing the surface of a substrate and a method for manufacturing the optical element.

  Optical devices such as liquid crystal projectors and optical pickups are composed of various optical elements, and an optical film is generally formed on one surface of a transparent substrate such as a glass material. As optical films, there are various optical films such as a dielectric single layer film, a dielectric multilayer film, and a metal film. These optical films have internal stress (film stress). After being formed on the transparent substrate, the entire transparent substrate is deformed by the film stress. As a result, the performance of the optical film is deteriorated or lost.

  Since optical devices in recent years are highly demanded to be compact, it is required to reduce the thickness of the transparent substrate. If it does so, the influence which it has on the transparent substrate by the membrane stress will become remarkable. For this reason, (1) It is necessary to correct the deformation of the shape of the transparent substrate while satisfying the request for reducing the plate thickness.

As a method for simultaneously satisfying the above requirements (1) and (2), for example, a film for correcting deformation of the substrate due to the film stress of the optical film (on the opposite surface on which the optical film of the transparent substrate is formed) There is a method of forming a thin film for correction. This technique is disclosed in Patent Document 1, in which a thin film having internal stress is formed on the non-optical functional surface (back surface) of the optical element, and the optical element is applied to the optical element using the action of the internal stress (film stress) of the thin film. Deformation is caused, thereby correcting the shape of the optical functional surface of the optical element. That is, a thin film that corrects the action of the film stress is formed on the surface opposite to the optical film formed on one surface of the substrate to correct the shape of the entire element.
Japanese Patent Laid-Open No. 2005-19485

  By the way, in Patent Document 1, it is necessary to form a thin film on a substrate (non-optical functional surface) for correcting the substrate shape, but in general, fine control is required to obtain a desired thin film. On the other hand, it is necessary to make the substrate thin, and for a thin substrate, the degree of deformation due to the film stress by the optical film is large, but at the same time, the film stress of the thin film for correction acts strongly. In this case, the thin film formation accuracy must be very finely controlled so as to correct the film stress caused by the optical film accurately and with high accuracy, which is extremely difficult.

  Further, the correction thin film basically exhibits only the function of correcting the substrate shape and does not exhibit other optical functions. Such a thin film is an unnecessary element from the viewpoint of the optical function, and thus becomes a surplus cost. Moreover, since it takes a relatively long time to form a thin film, if this process takes a long time, a problem of a decrease in production efficiency is caused. Furthermore, since a thin film for correction which is originally unnecessary is formed on a thin substrate, there is a problem in terms of resistance to stress.

  Accordingly, an object of the present invention is to reduce the film stress caused by the optical film and to planarize the optical film without forming a thin film for correction.

  In order to achieve the above object, the optical element according to claim 1 of the present invention has a difference in surface roughness between the front surface and the back surface of the substrate, and the surface of the front surface or the back surface has a smaller roughness. An optical film is formed on the surface, and stress of the optical film is relieved.

  When the substrate is very thin, if there is a difference in surface roughness between the front surface and the back surface of the substrate, there is an effect that a convex distortion occurs in the direction of the rough surface of the substrate (so-called Twiman effect). On the other hand, the optical film has a film stress that causes a convex distortion in the direction of the film formation surface of the substrate. Therefore, if an optical film is formed on the surface with the finer roughness, the direction of distortion due to the action of the film stress and the direction of distortion due to the Twiman effect have a relationship of opposite convex directions. Cancel each other's stress. If it does so, the shape as the whole board | substrate will be corrected and an optical film can be planarized.

  Here, the optical film may not be completely planarized as long as it is within an allowable error range. In other words, if the sliding surface is formed, the film stress of the optical film is canceled and the degree of planarization can be increased, but if it is within an allowable error range that exhibits the optical function, it is not completely planarized. Alternatively, it may be in a slightly curved state.

  An optical element according to a second aspect of the present invention is the optical element according to the first aspect, wherein the surface with the finer roughness is finished by mirror polishing to form a film forming surface, which is opposite to the film forming surface. The surface is formed as a sliding surface.

  By performing mirror polishing to form a film formation surface and forming a sliding surface on the opposite surface, a difference in surface roughness can be provided. Here, the formation of the sliding surface means that one surface of the substrate is slid using an abrasive having a coarse particle size, and the sliding surface means a surface on which the sliding surface is formed. As a means for forming the sliding surface (sliding surface forming means), there are various other methods such as grinding using a grinding agent, sandblasting that blows an abrasive onto the substrate surface, cutting with diamond, sandpaper, brushing, etc. Means can also be applied. In other words, the formation of the sliding surface refers to forming minute scratches, that is, minute irregularities on the substrate surface, and means forming satin on the surface.

  On the other hand, mirror polishing is a method for mirror-finishing the surface of a substrate (removing irregularities on the surface of the substrate), and so-called lapping, burnishing, polishing, or the like can be applied. When an abrasive is used in the formation of the sliding surface, sliding surface polishing is performed. However, the same term “polishing” is used for sliding surface polishing and mirror polishing. However, the sliding surface polishing is a technique for forming minute irregularities on the substrate surface, and the mirror polishing is a technique for eliminating the minute irregularities on the substrate surface.

  The surface before the sliding surface is formed (the surface to be slid) does not need to be mirror-finished in advance, but the surface to be slid and the surface on which the optical film is formed (the surface to be formed) are based on the plane state. The surface to be slid is preferably mirror-finished in the same manner as the film formation surface in that the amount of bending is controlled. That is, it is preferable to match the criteria of the bending amount.

  Basically, the substrate has a flat plate shape, but may have a shape other than the flat plate shape. In the sense that the sliding surface cancels the film stress of the optical film, as long as the sliding surface and the film forming surface are parallel, not only a rectangular flat plate shape but also any plate-like substrate such as a circle or a triangle Can be applied to. Here, the film-forming surface must have a high degree of planarization in order to exhibit a predetermined optical function, but the sliding surface that is the opposite surface basically does not exhibit an optical function. Its shape can be arbitrary. Therefore, if the film stress of the optical film can be canceled and the optical film can be planarized, the sliding surface may be somewhat irregular even if it is not flat.

  An optical element according to a third aspect of the present invention is the optical element according to the second aspect, wherein the sliding surface is slid with a particle size such that the optical film is planarized. . If the surface to be slid is formed, the film stress can be relieved, but the optical film can be made closer to flattening by forming the surface to be slid with an optimum particle size. When the sliding surface is formed, the particle size is large when the stress is large, and when it is fine, the stress is small. Therefore, if an optimum particle size corresponding to the film stress of the optical film is selected, it is possible to approach planarization.

  An optical element according to a fourth aspect of the present invention is the optical element according to any one of the first to third aspects, wherein the optical film is a reflective multilayer film that reflects light in a predetermined wavelength range. Features. Basically, since the sliding surface is a surface that is not used optically, the optical element to which the present invention can be applied most among various optical elements is a reflection mirror.

  When functioning as a reflection mirror, a reflective multilayer film made of a metal film may be used instead of the dielectric multilayer film. However, although the metal film reflects light in all wavelength regions, the reflection efficiency is slightly lowered because of the high light absorption rate. Therefore, it is preferable to apply a reflective multilayer film made of a dielectric multilayer film from the viewpoint of suppressing light loss. The metal film may be a single-layer film, but a reflective multilayer film made of a dielectric multilayer film requires a relatively large number of film layers in order to obtain an extremely high reflectance in a desired wavelength region. As a result, the film stress on the substrate becomes strong, so that a particularly advantageous effect is obtained in the case of a reflective multilayer film made of a dielectric multilayer film.

  In addition, when the sliding surface can be used for other purposes, the present invention can be applied as an optical element other than the reflection mirror. Since minute irregularities are formed on the sliding surface, the light distribution can be made uniform by utilizing light scattering by transmitting light to the sliding surface. Further, it can be used as, for example, APC (Auto Power Control) for measuring the intensity of light using scattered light. In such a case, the optical film is not a reflective multilayer film, but can be applied as a film having a transmission characteristic that transmits light of a predetermined condition, for example.

  The optical film planarization method according to claim 5 of the present invention includes a mirror polishing step of mirror polishing at least one surface of a substrate, and a sliding surface forming step of forming a sliding surface by sliding an opposite surface of the mirror polished surface. And an optical film forming step for forming an optical film on the mirror-polished one surface, and the stress of the optical film on the substrate is The sliding surface is relaxed, and the optical film is planarized.

  An optical film planarization method according to a sixth aspect of the present invention includes a mirror polishing step of mirror polishing at least one surface of a substrate, an optical film formation step of forming an optical film on the mirror polished surface, and the optical film formation step. A sliding surface forming step of forming a sliding surface by sliding the surface opposite to the surface on which the optical film is formed, and the stress of the optical film with respect to the substrate, The sliding surface is relaxed to planarize the optical film.

  The optical film planarization method according to claim 5 and the optical film planarization method according to claim 6 are the same in that the film stress of the optical film is canceled to form the optical film by forming a sliding surface. However, in the optical film planarizing method of claim 5, the sliding surface forming step is performed before the optical film forming step (tip sliding), and in the optical film planarizing method of claim 6, the sliding surface forming step is performed. Is different after the optical film forming step (post-slip).

  In the case of tipping, the surface to be slid is formed with a particle size corresponding to the amount of curvature of the substrate when the optical film is formed in advance. That is, the amount of bending of the substrate due to the film stress is anticipated, and that amount is relaxed in advance by the stress due to the formation of the sliding surface. In this case, since the sliding surface can be formed in advance with a uniform particle size, it is suitable for mass production.

  On the other hand, in the case of rearing, when the optical film is formed on the substrate, the substrate is bent in the convex direction on the optical film side due to the stress of the optical film. And according to the curvature state of a board | substrate, the sliding surface for performing correction | amendment according to ex post facto can be formed. For this reason, it is possible to finely planarize the optical film according to the degree of curvature of each substrate.

  Here, in the case of tip sliding, when the sliding surface is formed, in the case of rear sliding, when the optical film is formed, the substrate is bent by the stress due to the Twiman effect or the film stress of the optical film. In this case, in a state where the substrate is not fixed, the substrate tends to bend in one direction due to stress due to the Twiman effect or film stress of the optical film. For this reason, the substrate is fixed to a fixing jig or the like in which the planar state is maintained using an adhesive or the like, and the substrate is forcibly maintained in the planar state. By forming the optical film or the sliding surface in this state, it can be performed accurately.

  An optical film planarization method according to claim 7 of the present invention is the optical film planarization method according to claim 5 or 6, wherein the substrate is planarized when the sliding surface is formed. It is characterized by sliding. If the sliding surface is formed with an optimum particle size, the optical film can be brought close to a flat surface.

  The optical film planarization method according to claim 8 of the present invention is the optical film planarization method according to claim 7, wherein the particle size is coarser or finer than the particle size formed by the sliding surface forming step. A fine adjustment step is performed in which fine adjustment is performed to bring the film-forming surface closer to a flat surface by sliding the sliding surface.

  When the sliding surface is slid again after forming the sliding surface, when polishing with a grain size coarser than the grain size when the sliding surface is formed, a stress that relaxes the film stress acts, and when polishing with a fine grain size Acts to relieve stress due to the Twiman effect. That is, when the sliding surface is polished again with a coarser grain size, stress that causes convex distortion in the direction of the sliding surface acts, and when the sliding surface is polished again with a finer grain size, A stress causing a convex distortion in the direction is applied. Therefore, in the case of post-sliding, if convex distortion still occurs in the direction of the film formation surface, the sliding surface is polished again with a coarser grain size, and stress due to the Twiman effect is applied to the plane of the optical film. Plan

  On the other hand, if the stress due to the formation of the sliding surface exceeds the film stress and the convex surface is distorted on the rough surface (opposite to the film forming surface), the sliding surface is re-adjusted with a finer particle size. Polishing is performed to reduce the stress due to the formation of the sliding surface and to flatten the optical film. If the stress due to the formation of the sliding surface is insufficient or excessively applied, after the sliding surface is formed, the surface is again polished with a coarse particle size or a fine particle size so that fine fine adjustment is possible. Correction can be performed, and planarization of the optical film can be achieved. That is, polishing the sliding surface with a coarse particle size or a fine particle size after forming the sliding surface means that the excess or deficiency of the stress is finely adjusted and corrected.

  The optical element manufacturing method according to claims 9 to 12 of the present invention is characterized in that the optical element is manufactured by applying the optical film planarization method.

  The substrate material is mainly a transparent glass material, but it can also be applied to a transparent plastic material. Further, when used as a reflection mirror, since light does not pass through the substrate, it can be applied to non-transparent materials.

  As the optical film, a dielectric multilayer film composed of a plurality of dielectric films, a dielectric single layer film composed of a single dielectric film, a metal film, or the like can be applied. Among these, the dielectric multilayer film, particularly the dielectric multilayer film having a large number of film layers, has a strong film stress. Therefore, the present invention is particularly effective for such a dielectric multilayer film.

  Various methods such as vacuum deposition, ion plating, ion assist, sputtering, CVD (Chemical Vapor Deposition), spraying, and printing are applied as means for forming an optical film on the substrate. can do.

  When the optical element of the present invention is applied as a reflection mirror, for example, an optical pickup, a liquid crystal projector (projection display apparatus), or the like can be applied as an optical apparatus having the optical element as a component.

  By forming a sliding surface on the surface opposite to the surface on which the optical film is formed, the present invention cancels the film stress of the optical film due to the formation of the sliding surface, and does not form a special correction thin film. However, the planarization of the optical film can be achieved. In particular, when the substrate is thin, the film stress tends to be strong, and the optical film is greatly distorted. Even if the film stress is increased, the optical film is formed by forming a sliding surface on the opposite surface. In this case, a particularly advantageous effect can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, a reflection mirror that reflects light as an optical element will be described. In FIG. 1, the reflecting mirror 1 is mainly composed of a flat transparent substrate 10 such as a glass plate. A reflective multilayer film 12 is formed as an optical film on one surface of the transparent substrate 10 (deposition surface 10S). From the viewpoint of guaranteeing the optical accuracy of the reflective multilayer film 12, the film formation surface 10 </ b> S needs to maintain strictly flatness. For this reason, the film-forming surface 10S is mirror-polished in advance. The surface opposite to the film formation surface 10 </ b> S of the transparent substrate 10 is a sliding surface 13. Here, it is assumed that the sliding surface is formed by a coarse abrasive.

  Since the reflective multilayer film 12 has internal stress (film stress), when the reflective multilayer film 12 is formed on the transparent substrate 10, the reflective multilayer film 12 is curved in a convex direction (a direction in which the reflective multilayer film 12 is convex). A force acts on the transparent substrate 10. However, the slidable surface 13 is formed on the surface (the slid surface 10R) opposite to the surface on which the reflective multilayer film 12 is formed.

  When one surface of the thin transparent substrate 10 (the surface to be slid 10R) is slid with an abrasive, the transparent substrate 10 protrudes in the convex direction (the direction in which the transparent substrate 10 protrudes toward the sliding surface 13: when the reflective multilayer film 12 is formed on the transparent substrate 10). It tries to bend in a direction opposite to the direction to bend). This bending stress is called the Twiman effect. In particular, when the transparent substrate 10 is thin, the stress (sliding surface formation stress) that tends to bend increases. Since the reflecting mirror 1 is an extremely thin optical element due to a demand for compactness, the transparent substrate 10 having a very thin plate thickness is used. Then, since the film stress and the formation stress of the sliding surface are in opposite directions, both stresses can be canceled.

  Here, the final purpose is not to make the shape of the entire transparent substrate 10 the original shape, but to planarize the reflective multilayer film 12. Therefore, unlike the reflective multilayer film 12, the shape of the sliding surface 13 may be somewhat distorted. Since the reflective multilayer film 12 is formed on the film formation surface 10S, if the reflective multilayer film 12 is planarized, the film deposition surface 10S is naturally planarized.

  The sliding surface 10R is mirror-polished in advance in the same manner as the film formation surface 10S so that the surface 10R is parallel to the film formation surface 10S. Since the amount of curvature due to the film stress of the reflective multilayer film 12 is based on the plane, the slidable surface 10R is also based on the plane, thereby matching the two standards. Thereby, the measurement of the amount of bending can be facilitated.

  Next, the film stress will be described. The film stress varies depending on the material, plate thickness, and the like of the transparent substrate 10 as well as the factors of the film itself such as the film thickness, the number of film layers, and the material of the reflective multilayer film 12 formed on the transparent substrate 10. Here, a case where the thickness of the transparent substrate 10 is “1.5 mm” and the reflective multilayer film 12 is formed on the transparent substrate 10 by vacuum deposition will be described. For example, the reflective multilayer film 12 is compatible with three wavelengths (light in the wavelength range of CD (light near the wavelength of 780 nm), light in the wavelength range of DVD (light near the wavelength of 650 nm), and light of the large-capacity optical disc (wavelength near 405 nm). In the case of a reflective multilayer film in which the reflectance of light in the three wavelength regions of light is increased), the case of two wavelengths (a reflective multilayer film in which the reflectance of light in the wavelength range of CD and DVD is increased) or one wavelength The film stress tends to be stronger than in the case of the correspondence (reflective multilayer film in which the reflectance of light in the CD wavelength region is increased).

  On the other hand, the stress acting on the transparent substrate 10 by forming the sliding surface (stress due to the Twiman effect) varies depending on the particle size of the abrasive when an abrasive is used. Here, as an example of the particle size of the abrasive, three particles having a particle size of 7 μm, a particle size of 16 μm, and a particle size of 23 μm are used. Since the stress due to the formation of the sliding surface becomes stronger as the particle size of the abrasive becomes coarser (as the particle size becomes larger), the strongest stress acts when polishing with a particle size of 23 μm, and as the particle size becomes smaller (as the particle size becomes smaller). ) Since it becomes weak, the stress becomes the weakest when polished with a particle size of 7 μm.

  Therefore, if the reflective multilayer film 12 forms a sliding surface with a grain size that is balanced with the film stress acting on the transparent substrate 10, the stresses of the two are stresses that tend to bend in opposite directions. Can be canceled. Even when a particle size that is not balanced with the film stress is used, the film stress relaxation function is exhibited until the film stress cannot be completely canceled. For this reason, after forming a sliding surface, if the degree of planarization of the reflective multilayer film 12 is within an allowable error range, an arbitrary particle size can be used.

  Next, the relationship between the thickness of the transparent substrate 10, the grain size of the abrasive, and the degree of planarization of the reflective multilayer film 12 after the formation of the sliding surface will be described with reference to the graph of FIG. The figure is a graph showing the degree of planarization of the reflective multilayer film 12 when the sliding surface is formed with different particle sizes after the reflective multilayer film 12 is formed on the transparent substrate 10. In the figure, the degree of planarization is indicated by center displacement (μm), the horizontal axis in the figure indicates the plate thickness, and the vertical axis indicates the center displacement.

  When the center displacement is 0 μm, the reflective multilayer film 12 is ideally in a planar state, and the amount of curvature of the reflective multilayer film 12 increases as the value of the center displacement increases from 0 μm. The bending direction is opposite between a positive value and a negative value. Further, as the reflective multilayer film 12, an approximately laminated multilayer film of about 30 layers of titanium oxide and silicon dioxide is assumed, and the film thickness is about 3.5 nm.

  The normal state among the graphs shown in the figure is a case where no sliding surface is formed. That is, the amount of bending due to the film stress is purely shown. In this case, when the plate thickness is 1.5 mm, the center displacement is 3 μm, and when the plate thickness is 1 mm, the center displacement is approximately 7.5 μm. Accordingly, as the plate thickness is thinner, the transparent substrate 10 is more greatly curved by the film stress of the reflective multilayer film 12.

  Next, when the sliding surface 13 is formed with an abrasive having a particle size of 7 μm, as shown in the figure, when the plate thickness is 1.5 mm, the center displacement is approximately 1 μm, and when the plate thickness is 1 mm. The center displacement is approximately 3 μm. Accordingly, since the film stress of the reflective multilayer film 12 can be relaxed, the amount of curvature of the film formation surface 10S can be reduced as compared with the case where the sliding surface 13 is not formed. That is, planarization can be achieved.

  On the other hand, when the sliding surface 13 is formed with an abrasive having a particle diameter of 16 μm, the center displacement is approximately 0.7 μm when the plate thickness is 1.5 mm. Therefore, it is possible to further planarize the film formation surface 10S by forming the sliding surface 13 with an abrasive having a coarse particle size.

  When the sliding surface 13 is formed with an abrasive having a particle diameter of 23 μm, the center displacement is approximately −0.5 μm when the plate thickness is 1 mm. On the other hand, when the plate thickness is extremely reduced to about 0.3 mm, the film stress is superior to the stress due to the formation of the sliding surface, so the center displacement is approximately -2 μm. As is apparent from the figure, when a sliding surface is formed on the transparent substrate 10 having a plate thickness of about 0.7 mm using an abrasive having a particle size of 23 μm, the stress due to the sliding surface 13 and the film stress are just balanced. Therefore, the reflective multilayer film 12 can be completely planarized.

  As described above, the reflective multilayer film 12 is formed on one surface (deposition surface 10S) of the reflection mirror 1, and the slid surface 13 is formed on the opposite surface (the slid surface 10R). The reflective multilayer film 12 can be planarized by relaxing. Here, the amount of relaxation of the film stress differs depending on which of the formation of the reflective multilayer film 12 and the formation of the sliding surface 13 is performed first.

  First, a description will be given of the case where the reflective multilayer film 12 is formed after the sliding surface 13 is formed first. As shown in FIG. 3, first, as shown in FIG. 3A, both surfaces of the transparent substrate 10 are mirror-polished so that both the film formation surface 10S and the sliding surface 10R are in a planar state. (Mirror polishing process). Then, as shown in FIG. 6B, the sliding surface 13 is formed by sliding the sliding surface 10R (sliding surface forming step). At this point, the transparent substrate 10 is curved toward the sliding surface 13 due to the Twiman effect. Finally, as shown in FIG. 5C, by forming the reflective multilayer film 12 as an optical film on the transparent substrate 10 (optical film forming step), the film stress and the sliding surface of the reflective multilayer film 12 are formed. The film-forming surface 10S is planarized, and the reflective multilayer film 12 is planarized.

  When this method is employed, it is necessary to grasp in advance the amount of bending caused by forming the reflective multilayer film 12 on the transparent substrate 10. In anticipation of the film stress in advance, the transparent substrate 10 is curved in the opposite direction, thereby flattening when the reflective multilayer film 12 is formed. In this case, since the sliding surface can be uniformly formed on the transparent substrate 10 using an abrasive having a certain particle size, a number of transparent substrates 10 are previously formed with a certain particle size, Since the reflective multilayer film 12 can be formed later to manufacture a reflective mirror, it is suitable for mass production.

  Next, a method for forming the reflective multilayer film 12 first and then forming the sliding surface 13 will be described. Also in this case, first, both surfaces of the transparent substrate 10 are mirror-polished (mirror-polishing step). Then, as shown in FIG. 3D, a reflective multilayer film 12 as an optical film is formed on the film formation surface 10S (optical film forming step), and as shown in FIG. The sliding surface 13 is formed on the surface 10R (sliding surface forming step). In this case, the action of the film stress is achieved by forming the reflective multilayer film 12, and the sliding surface 13 is formed later to alleviate the effect. As a result, even when the amount of bending due to the film stress differs depending on the solid, the sliding surface 13 can be formed with a particle size matched to the actual amount of bending, so that planarization can be realized with fine accuracy.

  As shown in FIG. 4, compared to the case where the sliding surface 13 is not formed (without the sliding surface), the case where the sliding surface 13 is formed (the method in which the sliding surface 13 is formed first and the reflective multilayer film 12 is formed later) is used. The center displacement can be brought close to 0 μm, and the planarization accuracy is improved. However, post-slip (a method in which the reflective multilayer film 12 is first formed and the slide surface 13 is formed later) can further bring the center displacement closer to 0 compared to the front-slip, and the highest planarization accuracy is achieved. Yes. In other words, whether to use the front or rear sliding method is appropriately selected depending on whether mass production is important or flattening accuracy is important.

  In addition, in the case of adopting any of the tip sliding method or the post-sliding method, the sliding surface 13 is again formed with an abrasive having a coarser particle size or an abrasive having a finer particle size than that when the sliding surface 13 is formed. By doing so, the reflective multilayer film 12 can be planarized. After the sliding surface 13 is formed, when the sliding surface 13 is slid again with an abrasive having a coarser particle size, stress due to the Twiman effect acts, and stress in the direction opposite to the film stress of the reflective multilayer film 12 acts. On the other hand, after the sliding surface 13 is formed, if the sliding surface 13 is slid again with a finer grain abrasive, stress due to the Twiman effect is reduced, and stress in the same direction as the film stress of the reflective multilayer film 12 acts. .

  That is, when the reflective multi-layer film 12 is formed in the case of tipping, when the sliding surface 13 is formed in the case of post-slip, when the film stress of the reflective multi-layer film 12 is still prevailing, When the sliding surface 13 is slid again with a coarse particle size, and the stress due to the Twiman effect is greater than the film stress of the reflective multilayer film 12, the sliding surface 13 is slid again with a finer particle size to finely adjust the planarization. (Fine adjustment process). By performing this fine adjustment step, the reflective multilayer film 12 can be planarized. This fine adjustment step is a step of adjusting the excess / deficiency when excess or deficiency occurs when the film stress of the reflective multilayer film 12 is relaxed by the stress due to the formation of the sliding surface 13.

  As described above, by forming the sliding surface on the surface opposite to the film formation surface on which the optical film is formed, even if the film formation surface is curved due to the film stress of the optical film, the formation of the sliding surface is achieved. The stress due to the above can be relaxed, and the optical film can be planarized.

It is an external view of an optical element. It is a graph which shows the relationship between board thickness, a particle size, and center displacement. It is a figure which shows the flow of each manufacturing process when the formation process of a sliding surface is performed previously, and when an optical film formation process is performed previously. It is another graph which shows the relationship of the center displacement by a front sliding and a rear sliding.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reflection mirror 10 Transparent substrate 10R Sliding surface 10S Film forming surface 12 Reflecting multilayer film 13 Sliding surface

Claims (12)

  A difference in surface roughness is provided between the front surface and the back surface of the substrate, an optical film is formed on the surface with the finer roughness of the front surface or the back surface, and the stress of the optical film is relieved. An optical element. The optical element according to claim 1,
The optical element is characterized in that the surface with finer roughness is finished by mirror polishing to form a film-forming surface, and a surface opposite to the film-forming surface is formed as a sliding surface. The optical element according to claim 2,
The slidable surface is slid with a particle size such that the optical film is planarized. The optical element according to any one of claims 1 to 3,
The optical element is a reflective multilayer film that reflects light in a predetermined wavelength range. A mirror polishing step of mirror polishing at least one surface of the substrate;
A sliding surface forming step of forming a sliding surface by sliding the surface opposite to the mirror-polished one surface;
An optical film forming step for forming an optical film on the mirror-polished one surface, which is a step performed after the sliding surface forming step,
A method of planarizing an optical film, wherein the sliding surface relaxes the stress of the optical film with respect to the substrate to planarize the optical film. A mirror polishing step of mirror polishing at least one surface of the substrate;
An optical film forming step of forming an optical film on one mirror-polished surface;
A step performed after the optical film forming step, and a sliding surface forming step of forming a sliding surface by sliding the surface opposite to the surface on which the optical film is formed, and
A method of planarizing an optical film, wherein the sliding surface relaxes the stress of the optical film with respect to the substrate to planarize the optical film. An optical film planarization method according to claim 5 or 6,
An optical film planarization method, wherein the sliding surface is formed with a particle size such that the substrate is planarized. The optical film planarization method according to claim 7,
Performing a fine adjustment step of finely adjusting the film-forming surface to be closer to a flat surface by rubbing the sliding surface with a particle size coarser or finer than the particle size of the sliding surface formed in the sliding surface forming step. An optical film planarization method characterized by the above. An optical element for manufacturing an optical element in which an optical film is formed on one surface of a substrate that has been mirror-polished, and a sliding surface is formed on a surface opposite to the surface on which the optical film is formed, thereby reducing the stress of the optical film A manufacturing method of
A mirror polishing step of mirror polishing at least one surface of the substrate;
A sliding surface forming step of forming a sliding surface on the opposite surface of the mirror-polished one surface;
An optical element manufacturing method comprising: an optical film forming step for forming an optical film on the one mirror-polished surface, the step being performed after the sliding surface forming step. An optical film is formed on a mirror-polished surface of a substrate, and a sliding surface is formed by sliding the surface opposite to the surface on which the optical film is formed, thereby producing an optical element that relieves stress on the optical film. A method of manufacturing an optical element,
A mirror polishing step of mirror polishing at least one surface of the substrate;
An optical film forming step of forming an optical film on one mirror-polished surface;
A step that is performed after the optical film forming step, and includes a sliding surface forming step of forming a sliding surface on a surface opposite to a surface on which the optical film is formed, and
The method of manufacturing an optical element, wherein the sliding surface relaxes the stress of the optical film with respect to the substrate to planarize the optical film. It is a manufacturing method of the optical element according to claim 9 or 10,
When forming the sliding surface, the substrate is slid with a particle size such that the substrate is planarized. It is a manufacturing method of the optical element according to claim 11,
By sliding the sliding surface with a particle size coarser or finer than the particle size that formed the sliding surface in the sliding surface forming step, the stress due to the optical film is relieved and the film-forming surface is made closer to a flat surface. A method of manufacturing an optical element, comprising performing a fine adjustment step of performing fine adjustment.

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