Method for manufacturing a lens holding device, lens assembly, and elastic member for lens holding.

Abstract

To provide a flexure structure having sufficient flexibility even for a mount for a small-diameter lens.SOLUTION: A lens holding device includes a lens mount member 16 and an elastic body member 18. The elastic body member 18 has an annular shape that includes three or more slots 26 evenly distributed in a circumferential direction. An outer circumferential portion of the elastic body member is fixed to an inner circumferential portion of the lens mount member 16, and an inner circumferential portion of the elastic body member is fixed to an outer circumferential portion of a lens 12. When a dimension of the elastic body member 18 in an optical axis direction is defined as b, and a minimum dimension in a radial direction of a region of the elastic body member 18 on the inner side in the radial direction of the slots 26 is defined as h, the configuration satisfies b≤1 mm, and a ratio (h / b) satisfies 1 / 2≤(h / b)≤1.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a lens holding device, a lens assembly, and a method for manufacturing an elastic member for holding a lens.

Background Art

[0002] In a semiconductor inspection apparatus used for inspecting a wafer or a mask, a high-precision objective lens is used for the purpose of capturing a defect on an object illuminated by deep ultraviolet light as an image.

[0003] A high-precision objective lens used in a semiconductor inspection apparatus has characteristics different from those of commercially available objective lenses such as those for biological use and metal use. Typical differences are as follows.

[0004] First, the wavefront aberration is small. For a general objective lens, if the wavefront aberration in visible light is 0.07 waves rms, it is regarded as aberration-free. However, for a high-precision objective lens for a semiconductor inspection apparatus, it is required that the wavefront aberration in ultraviolet light be 0.03 waves rms or less. Since the wavelength of ultraviolet light is half or less of the wavelength of visible light, this standard means that the requirements for a high-precision objective lens are more than four times stricter than those for a commercially available objective lens.

[0005] Second, it is the performance stability of the high-precision objective lens with respect to the external environment. The objective lens is exposed to temperature changes and vibration shocks during transportation. The performance of a high-precision objective lens for a semiconductor inspection apparatus must not deteriorate (change) due to these disturbances. In addition, the objective lens is exposed to temperature changes due to absorption of illumination light and pressure changes such as low pressure. Therefore, the performance of a high-precision objective lens must not deteriorate due to such temperature changes and pressure changes.

[0006] As other differences, the following two can be mentioned. A high-precision objective lens must have resistance to the deposition of outgas due to irradiation with ultraviolet rays. In addition, since polarization may be used as a measurement method, the objective lens itself must not have polarization characteristics.

[0007] Thus, high-precision objective lenses used in semiconductor inspection equipment are required not only to have smaller aberrations than general objective lenses, but also to possess stable performance against various disturbances.

[0008] To satisfy these requirements, the elastomer mount structure has long been known as a holding structure for objective lenses. In this structure, the lens is bonded to a cell (mount) by an elastomer. The individual cells to which the lenses are bonded are inserted into the lens barrel or connected to each other to form the objective lens. Silicone-based potting material (hereinafter referred to as silicone adhesive) is a well-known elastomer used for bonding the lenses. Silicone adhesive has the advantage of being able to fix the lens without distortion and also producing relatively little outgassing.

[0009] While silicone adhesives offer significant advantages, their limitations have become increasingly apparent in recent years. For example, consider a high-precision mask defect inspection system. Such systems require limiting the allowable eccentricity of the objective lens to tens of nanometers or less. The eccentricity sensitivity of this type of objective lens is extremely high, and the required aberration level is stringent. Therefore, if the lens exhibits eccentricity exceeding these limits, it may be mistakenly detected as a false defect. Silicone adhesives are unsuitable for fixing lenses used in such applications. The reasons for this are explained below.

[0010] Temperature changes and vibrations can affect the lens assembly, causing forces to be applied to individual lenses, resulting in lens eccentricity. If the adhesive holding the lenses in place has sufficient fixing strength and resilience, the lenses should return to their original positions when the disturbance disappears.

[0011] However, fixing lenses with silicone adhesive is insufficient (shear strength of a few MPa), the adhesive is soft (Young's modulus of a few MPa), and it does not have positional recovery properties. Therefore, when fixing lenses with silicone adhesive, it cannot be expected that the lenses will return completely to their original position after the disturbance has disappeared.

[0012] To avoid this, a hard elastomer with a Young's modulus of several GPa is useful. Epoxy adhesives are an example of a hard elastomer with a Young's modulus of several GPa. Fixing lenses with epoxy adhesive exhibits high linearity with respect to dimensional changes and strong adhesive strength. In this case, even if force is applied to the lens due to temperature changes and vibration shocks, the lens will return to its original position when the disturbance disappears.

[0013] On the other hand, if a hard adhesive such as epoxy adhesive is used, a different problem arises. Adhesives generally exhibit a phenomenon called curing shrinkage, where their volume decreases during curing. Since the force applied to the lens due to curing shrinkage is proportional to Young's modulus, for example, the curing shrinkage stress when using epoxy adhesive can reach nearly a thousand times that when using silicone adhesive. As a result, deterioration of wavefront aberration occurs due to changes in the surface precision of the lens, and deterioration of polarization characteristics occurs due to the photoelastic effect of the lens, resulting in a degradation of imaging characteristics and polarization characteristics.

[0014] Thus, conventional elastomer mount structures have two conflicting requirements: positional stability and shape stability of the lens.

[0015] An improved lens holding structure is known in which the lens mount has flexibility (see, for example, Patent Document 1). A flexible structure is called a flexure structure. The difference in the coefficient of linear expansion between the lens and the mount due to temperature changes, as well as the curing shrinkage of the adhesive, are absorbed by the flexibility of the flexure structure itself, so the stress on the lens is kept to a minimum.

[0016] However, applying a flexure structure to small-diameter objective lenses with a diameter of 30 mm or less, such as those used in semiconductor inspection equipment, presents difficulties. The flexure structure is formed on the mount by machining, such as wire-cut electrical discharge machining. Therefore, the lens mount must be of a certain size for machining purposes. In addition, to increase the flexibility of the flexure structure, it is necessary to provide not only circumferential slots (slits) but also slots of complex shapes, which also leads to a larger mount. While it is conceivable to make the arms thinner to increase flexibility, the limitations of wire-cut electrical discharge machining impose restrictions on the diameter and width of the arms.

[0017] In addition, two other structures are known for stably holding lenses. One is a structure that absorbs the difference in linear expansion by using a thick elastomer adhesive layer (Non-Patent Literature 2), and the other is a structure that absorbs the difference in linear expansion by using a resin ring provided between the lens and the mount (Non-Patent Literature 3).

[0018] Since the adhesive layer and resin ring can be configured to any size, these lens holding structures are suitable for small-diameter lenses. However, the resin is unstable in terms of dimensional changes with temperature, and the expected effect may not be achieved. In addition, ultraviolet irradiation used in semiconductor measuring equipment can cause chemical damage to the mount, potentially impairing dimensional stability and the cleanliness of the lens interior, making it unsuitable for advanced semiconductor measuring equipment. [Prior art documents] [Patent Documents]

[0019] [Patent Document 1] U.S. Patent No. 4,733,945 [Non-patent literature]

[0020] [Non-Patent Document 1] M. Bayer, Lens barrel optomechanical design principles, Opt. Eng., 1981

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0021] In view of the above background, an object of the present invention is to provide a lens holding device that realizes a flexure structure having sufficient flexibility to contribute to the stability of a lens even in the mounting of a small-diameter lens and stably holds the lens.

Means for Solving the Problems

[0022] In order to solve the above problems, an aspect of the present invention is a lens holding device (10) for holding a lens (12), which has a lens mounting member (16) and an elastic member (18, 30) provided separately from the lens mounting member. The elastic member has an annular shape having three or more equally distributed slots (26, 38) in the circumferential direction, the outer periphery is fixed to the inner periphery of the lens mounting member, and the inner periphery is fixed to the outer periphery of the lens. When the dimension of the elastic member in the optical axis direction is b and the minimum dimension in the radial direction of the region (28, 40) of the elastic member inward in the radial direction of the slot is h, b ≦ 1 mm and the ratio (h / b) satisfies 1 / 2 ≦ (h / b) ≦ 1.

[0023] According to this configuration, even in the mounting of a small-diameter lens, a flexure structure having sufficient flexibility to contribute to the stability of the lens is obtained, and the lens is stably held.

[0024] In the above aspect, each slot may be on one virtual circle concentric with the elastic member and have an arc shape.

[0025] According to this configuration, the lens is stably held evenly over the entire circumference.

[0026] In the above embodiment, the elastic member (30) may be composed of a plurality of elastic thin plates (32) stacked in the optical axis direction, each having a slot portion (34) that constitutes a part of the slot.

[0027] This configuration facilitates the etching of slots in individual thin elastic sheets.

[0028] In the above embodiment, the slots of the elastic thin plate may overlap each other in the optical axis direction.

[0029] With this configuration, even if the elastic member is composed of multiple elastic thin plates, the flexural performance will not differ from that of an elastic member with a single structure.

[0030] In the above embodiment, the lens mount member and the elastic member may be made of stainless steel.

[0031] This configuration reduces the thermal stress caused by the difference in linear thermal expansion coefficients between the lens mount member and the elastic member.

[0032] To solve the above problems, one aspect of the present invention is a lens assembly (50) having at least one lens holding device according to the above aspect.

[0033] With this configuration, the lens is held stably in the assembled lens.

[0034] To solve the above problems, one aspect of the present invention is a method for manufacturing an elastic member used in a lens holding device according to the above aspect, wherein the slot is formed by etching.

[0035] According to this manufacturing method, a highly accurate elastic member can be produced with minimal residual strain due to processing stress during slot formation. [Effects of the Invention]

[0036] According to the above embodiment, even with a small-diameter lens mount, a flexure structure with sufficient flexibility to contribute to the stability of the lens can be obtained, and the lens is held stably. [Brief explanation of the drawing]

[0037] [Figure 1] Exploded perspective view showing Embodiment 1 of the lens holding device according to the present invention [Figure 2] Cross-sectional view of the lens holding device of Embodiment 1 [Figure 3] Front view of the elastic member used in the lens holding device of Embodiment 1 [Figure 4] Front view illustrating the manufacturing method of the elastic member used in the lens holding device of Embodiment 1. [Figure 5] Exploded perspective view showing Embodiment 2 of the lens holding device according to the present invention [Figure 6] Cross-sectional view of the lens holding device of Embodiment 2 [Figure 7] A half-sectional view showing one embodiment of the lens assembly according to the present invention. [Modes for carrying out the invention]

[0038] An embodiment of the lens holding device according to the present invention will be described below with reference to the figures.

[0039] (Embodiment 1) Figures 1 to 3 show the lens holding device 10 of Embodiment 1. The lens holding device 10 holds a circular lens 12 when viewed from the front, and has a lens mount member 16 (cell) including a cylindrical portion 14, and a ring-shaped elastic member 18 (elastic member for lens holding) provided separately from the lens mount member 16 between the lens 12 and the cylindrical portion 14. The lens mount member 16 is made of a metal such as stainless steel. The lens 12 is made of synthetic quartz or the like, and is a small optical lens with an outer diameter of about 30 mm or less.

[0040] The elastic member 18 is made of a material having a coefficient of thermal expansion equivalent to that of the lens mount member 16, for example, the same metal (stainless steel) or the same type of metal as that which constitutes the lens mount member 16. The elastic member 18 has an annular shape and is made of an annular flat plate (stencil) with a dimension (plate thickness) in the optical axis direction of 1.0 mm or less.

[0041] If the lens mount member 16 and the elastic member 18 are made of equivalent stainless steel, the thermal stress acting between the lens mount member 16 and the elastic member 18 due to the difference in linear thermal expansion coefficients will be reduced.

[0042] The outer diameter of the elastic member 18 is slightly smaller than the inner diameter of the cylindrical portion 14. The inner diameter of the elastic member 18 is slightly larger than the outer diameter of the lens 12. As shown in Figure 2, the outer circumference of the elastic member 18 is bonded to the inner circumference of the cylindrical portion 14 by an annular adhesive layer 20 provided between the outer surface 18A of the elastic member 18 and the inner surface 14A of the cylindrical portion 14. The inner circumference of the elastic member 18 is bonded to the outer circumference of the lens 12 by an annular adhesive layer 22 provided between the inner surface 18B of the elastic member 18 and the outer surface 12A of the lens 12. Suitable adhesives for the adhesive layers 20 and 22 include epoxy adhesives.

[0043] The lens mount member 16 has an annular flange portion 24 extending radially inward from the cylindrical portion 14. One end face 24A of the flange portion 24 is in contact with one end face 18C of the elastic member 18. This contact determines the position of the elastic member 18 in the optical axis direction relative to the lens mount member 16.

[0044] Each elastic member 18 has three arc-shaped slots 26 that penetrate in the direction of the optical axis. Each slot 26 is formed by etching or the like and is arranged at equal intervals in the circumferential direction on a virtual circle concentric with the elastic member 18. Each slot 26 has the same arc length and is evenly distributed in the circumferential direction of the elastic member 18.

[0045] The elastic member 18 constitutes a flexure beam 28 in the radially inward region of each slot 26. Each flexure beam 28 has a rectangular cross-sectional shape defined by both end faces 18C, 18D of the elastic member 18, the radially inward inner surface 26A of the corresponding slot 26, and the inner circumferential surface 18B of the elastic member 18, as shown in Figure 2. In a front view, each flexure beam 28 extends circumferentially on a virtual circle concentric with the elastic member 18, with a concentric arc shape.

[0046] Each flexure beam 28 has a flexure beam length L (see Figure 3) determined by the length measured along the arc of the slot 26, and is considered a cantilevered beam (beam fixed at both ends), forming a flexure structure that is elastically deformable in the radial direction. In the following description, the beam length L may be referred to as the flexure length L.

[0047] An important factor in the flexural performance of the flexure beam 28 here is its radial bending stiffness. This stiffness is determined by the Young's modulus E of the flexure beam 28, the cross-sectional shape (rectangular) of the flexure beam 28, and its dimensions, which are correlated with the second moment of area.

[0048] The optical axis dimension b of the flexure beam 28 is determined by the plate thickness of the elastic member 18 and is 1.0 mm or less. The minimum radial dimension h of each flexure beam 28 is a value within the range of 1 / 2 or more of the optical axis dimension b and less than or equal to the optical axis dimension b. The minimum radial dimension h is the minimum radial dimension of the flexure beam 28 in the region of the elastic member 18 radially inward of the slot 26.

[0049] The ratio of the optical axis dimension b to the minimum radial dimension h (flexure blade thickness) of each flexure beam 28. (h / b) It is sufficient that it satisfies equation (1) below. 1 / 2 ≤ (h / b) ≤1 ...(1)

[0050] If n is the number of flex beams 28, and r is the radius of the virtual circle connecting the flex beams 28 to each other, which is concentric with the elastic member 18, then the total length n·L of the flex beams 28 is given by the following equation (2). (2π·r)=k(n·L) ...(2) However, k is a coefficient. The coefficient k may be around 0.3 to 0.5, and preferably k = 0.4. The smaller this coefficient k, the shorter the flex length L of each flex beam 28 becomes.

[0051] In the lens holding device 10, the flexure structure is formed on an annular flat plate that constitutes an elastic member 18, separately from the lens mount member 16. The elastic member 18 provides a flexure structure with sufficient flexibility even for small-diameter lens mount structures, without requiring complex-shaped slots, unlike a flexure beam 28 with simple-shaped slots 26 extending in the circumferential direction.

[0052] With this configuration, the flexure structure is formed separately from the lens mount member 16, on a flat, elastic member 18 with a plate thickness of 1.0 mm or less. As a result, even if the flexure length L of the flexure beam 28 is short, its rigidity is sufficiently low. This enables the realization of a good flexure structure with sufficient flexibility in a small mount for small-diameter lenses.

[0053] This can be explained using a mechanical model that considers the flexure structure as a cantilevered beam (a beam fixed at both ends).

[0054] The displacement δ [mm] when a load P [N] is applied to a beam fixed at both ends is given by the following equation (3). δ=(PL 3 ) / 192EI ...(3)

[0055] Here, E is the Young's modulus of the flexure beam 28 (in MPa), and I is the second moment of area of ​​the flexure beam 28 (in mm²). 4) Since the flexure beam 28 has a rectangular cross-section, the second moment of area I of the flexure beam 28 is given by the following equation (4). I=(bh 3 ) / 12 ...(4)

[0056] Next, we will compare the stress applied to the lens using the above formula in the case where a 20mm diameter synthetic quartz lens 12 is mounted on a SUS303 lens mount component, using examples and comparative examples.

[0057] Table 1 shows the dimensions, specifications, and loads acting on the lens when a 1°C temperature change occurs in the lens holding device of the embodiment (results of stress calculation).

[0058] [Table 1]

[0059] Table 2 shows the dimensions, specifications, and loads acting on the lens (results of stress calculation) of each part of a comparative example lens holding device that has been empirically recognized as effective, when a 1°C temperature change occurs.

[0060] [Table 2]

[0061] In the comparative example, the optical axis dimension b of the flexure beam is larger than in the example, resulting in higher rigidity of the flexure beam. Therefore, the strain due to processing stress on the elastic member is smaller, and the flexure beam is less prone to deformation even with a small minimum radial dimension h. Furthermore, in the comparative example, diametrical slots can be provided, allowing the flexure length L, which is provided in three equally spaced circumferential directions, to be set to the largest possible value (here, 80% of 1 / 3 of the circumference). Consequently, even with a relatively thick flexure beam, the load acting on the lens can be kept sufficiently small.

[0062] On the other hand, when attempting to miniaturize the elastic member, it is not possible to provide diametrical slots, and therefore the flexure length L cannot be increased. For example, if the flexure length is half that of the case in Table 2, the load P acting on the lens will be eight times that of the case in Table 2 according to equation (3) above. To reduce the load P acting on the lens, it is effective to reduce the second moment of area I. One way to achieve this is to form the flexure structure with a thin plate with a thickness of 1.0 mm, thereby reducing the optical axis dimension b.

[0063] The differences between the example and the comparative example will be explained. The biggest difference between the two is the coefficient k for the flexure length. In the comparative example shown in Table 2, k = 0.8, while in the example shown in Table 1, k = 0.4. As a result, the rigidity of the flexure structure due to the flexure beam is eight times greater in the comparative example than in the example, and consequently, the force acting on the lens is also eight times greater. To absorb this, the optical axis dimension b was 10.0 mm in comparative example 1, but was set to 0.7 mm in the example. Accordingly, the minimum radial dimension h was 0.35 mm in the comparative example, but was set to 0.30 mm in the example.

[0064] These parameter settings allow the load P acting on the lens in the examples shown in Table 1 to be reduced to the same extent as that in the comparative examples shown in Table 2, even when the coefficient k changes from 0.8 to 0.4.

[0065] In the lens holding device 10 of Embodiment 1, each slot 26 of the elastic member 18 is located on a single virtual circle concentric with the elastic member 18 and has an arc shape, so that the lens 12 is held evenly and stably around its entire circumference.

[0066] Next, with reference to Figure 4, one embodiment of a method for manufacturing the elastic member 18 will be described. In the manufacturing of the elastic member 18, as shown in Figure 4(A), first, an outer shape B and an inner shape C are formed coaxially on a metal plate A. By forming the outer shape B, an annular member D is produced having the outer circumferential surface 18A of the elastic member 18, and by forming the inner shape C, an annular member D having the inner circumferential surface 18B of the elastic member 18. The outer shape B and the inner shape C can be formed by any of the following processing methods: punching, laser processing, electrical discharge machining, or etching.

[0067] Next, as shown in Figure 4(B), a predetermined number of slots 26 are formed in the annular member D by etching. The formation of these slots 26 completes an elastic member 18 having a flexure beam 28 with a double-supported fixed beam in the barbering area radially inward of each slot 26.

[0068] In this manufacturing method, the slots 26 are formed by etching rather than by mechanical processing such as punching, resulting in less processing stress remaining in the elastic member 18 and less distortion of the elastic member 18 due to processing stress. As a result, a flexure beam 28 with high shape accuracy can be obtained, and consequently, a flexure beam 28 with the required flexure performance can be accurately obtained, and a high-performance elastic member 18 can be accurately manufactured.

[0069] (Embodiment 2) Figures 5 and 6 show the lens holding device 10 of Embodiment 2. In Figures 5 and 6, parts corresponding to Figures 1 to 3 are denoted by the same reference numerals as those used in Figures 1 to 3, and their descriptions are omitted.

[0070] In Embodiment 2, the elastic member 30 is composed of a laminate of multiple, in the illustration, four elastic thin plates 32. Each elastic thin plate 32 has the same shape and has slot portions 34 and flexure beam portions 36 of the same shape. The thickness of each elastic thin plate 32 is b / 4 so that a predetermined optical axis dimension b is obtained by the total thickness of the four elastic thin plates 32. The slot portions 34 of each elastic thin plate 32 form a slot 38 assembled in the optical axis direction when the four elastic thin plates 32 are laminated in the optical axis direction. That is, each slot portion 34 constitutes a part of the slot 38 in the optical axis direction. The flexure beam portions 36 of each elastic thin plate 32 form a flexure beam 40 assembled in the optical axis direction when the four elastic thin plates 32 are laminated in the optical axis direction.

[0071] The etching of the slot portion 34 may be performed individually for each elastic material thin plate 32. This reduces the etching depth for forming the slot 38 compared to the case in Embodiment 1. This facilitates the etching of the slot 38. As a result, in Embodiment 2, it becomes possible to obtain a flexure portion with the required thickness while keeping the flexure structure thin enough for manufacturing.

[0072] Embodiment 2 is substantially identical to Embodiment 1, except for the configuration of the elastic member 30 described above.

[0073] Multiple elastic thin plates 32 are stacked such that the circumferential positions of their respective slot portions 34 and flex beam portions 36 are identical. In other words, the slot portions 34 and flex beam portions 36 of the multiple elastic thin plates 32 are aligned with each other in the circumferential direction and overlap each other in the optical axis direction.

[0074] As a result, slot 38 becomes equivalent to slot 26 in Embodiment 1, and flex beam 40 also becomes equivalent to flex beam 28 in Embodiment 1. Even if the elastic member 30 is a laminated structure, a flex structure with substantially the same characteristics as when the elastic member 18 is a single-piece structure, as in Embodiment 1, can be obtained. In other words, even if the elastic member 30 is composed of multiple elastic thin plates 32, the flex performance does not differ from that of a single-piece elastic member 18.

[0075] As a result, the lens holding device 10 of Embodiment 2 operates in the same manner as the lens holding device 10 of Embodiment 1 and produces the same effect.

[0076] Next, one embodiment of the lens assembly according to the present invention will be described with reference to Figure 7.

[0077] As shown in Figure 7, the lens assembly 50 has a cylindrical lens barrel 52 and several lenses, seven in this example, arranged in the optical axis direction within the lens barrel 52. Each lens 541-547 is fixed to the lens barrel 52 by lens holders 561-567.

[0078] Each lens holder 561 to 567 is fitted into the lens barrel 52, thereby determining its radial position relative to the lens barrel 52.

[0079] The lens barrel 52 has an inner flange portion 52A that protrudes radially inward from one end in the optical axis direction. Each lens retaining device 561 to 567 is inserted sequentially into the lens barrel 52 from the other end in the optical axis direction. A female thread 52B is formed on the radially inward side of the other end of the lens barrel 52. An annular set screw member 58 is screw-engaged into the female thread 52B. The lens retaining devices 561 to 567 are fixed to the lens barrel 52 in the optical axis direction by being sandwiched between the inner flange portion 52A and the set screw member 58 in the optical axis direction. In this way, the optical axis position of each lens retaining device 561 to 567 relative to the lens barrel 52 is determined.

[0080] In this lens assembly 50, the lens retaining devices 562 to 566, excluding the lens retaining devices 561 and 567 for the lenses 541 and 547 located at both ends of the lens barrel 52 in the optical axis direction, each have a structure equivalent to the lens retaining device 10 having the elastic member 18 of Embodiment 1.

[0081] As a result, the operation and effects of the lens holding device 10 of Embodiment 1 can be effectively obtained in the lens assembly 50.

[0082] In addition, in other embodiments, lens holding devices 562 to 566 may have a structure equivalent to the lens holding device 10 having the elastic member 30 of Embodiment 2. Furthermore, all of the lens holding devices 561 to 567 may have a structure equivalent to the lens holding device 10 of Embodiment 1 or Embodiment 2.

[0083] Although the present invention has been described above in terms of preferred embodiments, the present invention is not limited to these embodiments and can be modified as appropriate without departing from the spirit of the invention. For example, the number of slots 26 and 38 and the number of flex beams 28 and 40 thereon are not limited to three, but may be three or more. The number of elastic thin plates 32 in Embodiment 2 is not limited to four, but may be any other number.

[0084] Furthermore, some or all of the above embodiments may be combined and implemented. Also, not all of the components shown in the above embodiments are necessarily essential, and they can be appropriately selected and omitted as long as they do not depart from the spirit of the present invention. [Industrial applicability]

[0085] A small and highly precise flexure can be constructed from an annular, flat, elastic member, and by interposing this between the lens and the mount via adhesive, it can be applied to stabilize the lens's orientation due to temperature changes without increasing the lens's size. [Explanation of symbols]

[0086] 10: Lens holding device 12: Lens 16: Lens mount component 18: Elastic member 26: Slot 28: Flexor beam 30: Elastic member 32: Elastic material thin plate 34: Slot section 36: Flexor beam section 38: Slot 40: Flexure beam 50: Lens Assembly

Claims

1. A lens holding device for holding a lens, It has a lens mount member and an elastic member provided separately from the lens mount member, The elastic member has an annular shape with three or more slots evenly distributed in the circumferential direction, its outer circumference is fixed to the inner circumference of the lens mount member, and its inner circumference is fixed to the outer circumference of the lens. A lens holding device in which, when the optical axis dimension of the elastic member is b and the minimum radial dimension of the region of the elastic member radially inward of the slot is h, b ≤ 1 mm and the ratio (h / b) satisfies 1 / 2 ≤ (h / b) ≤ 1.

2. The lens holding device according to claim 1, wherein each slot lies on a virtual circle concentric with the elastic member and has an arc shape.

3. The lens holding device according to claim 1 or 2, wherein the elastic member has a slot portion that constitutes a part of the slot and is composed of a plurality of elastic thin plates stacked in the optical axis direction.

4. The lens holding device according to claim 3, wherein the slot portions of the elastic thin plate overlap each other in the optical axis direction.

5. The lens holding device according to claim 1 or 2, wherein the lens mount member and the elastic member are made of stainless steel.

6. A lens assembly having at least one lens holding device according to claim 1 or 2.

7. A method for manufacturing an elastic member used in a lens holding device according to claim 1 or 2, wherein the slot is formed by etching.

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