Method and device for depositing a thin layer on a curved surface

Abstract

Method for producing a thin layer of material on a surface (S) of a substrate (O), comprising the steps of projecting particles of material from a source (3) of particles of material, moving the support (4) on a closed trajectory around a first axis of rotation (A1), pivoting the substrate (O) on itself around a second axis of rotation (A3) corresponding to an axis of symmetry of the surface (S) of the substrate (O). The method comprises the step of moving the support to expose different portions of the surface (S) of the substrate (O) to a direct projection of the particles of material for an exposure time depending on the desired thickness of material on said surface portions. Device for implementing this method. FIGURE OF THE ABSTRACT: Fig. 1

Description

Title of the invention: Method and device for depositing a thin layer on a curved surface

[0001] The present invention relates to the field of manufacturing optical components such as lenses, in particular those used in missile guidance systems.

[0002] BACKGROUND OF THE INVENTION

[0003] In the field of optics, it is known to cover a surface of an optical substrate (such as a lens or a blade) with at least one thin layer of material - commonly with a thickness of between approximately 10 nm and 500 nm or even 1 pm - forming constructive or destructive interference. These thin layers have, for example, the following functions: an anti-reflection function; a dichroic or interference filtering function; a high-pass, low-pass or band-pass filtering function. The optics used in missile guidance systems commonly comprise such thin layers in order to benefit from these functions.

[0004] Thin layers are most often produced by projecting the material onto the surface of the optical substrate. In particular, well-known techniques of vacuum evaporation or cathodic sputtering of the material intended to form the thin layer are used.

[0005] A thin-film material deposition installation generally comprises a frame, a source of material, and a substrate holding support opposite the source. The frame is provided with a hermetic enclosure connected to a vacuum circuit in which the source of material and the substrate holding support are placed. One of the main constraints on the deposition is the homogeneity of the thickness of the thin layer, which must be identical at every point on the surface of the substrate covered by the thin layer. Indeed, a variation in the thickness of a thin layer induces a variation in the expected optical effect, for example a shift in the transmitted wavelengths. To obtain a uniform thickness, the ideal would be for the material particles to arrive on a flat surface like a vertical rain, homogeneous over the entire surface. However, the material particles arrive in a projection cone from the source.

[0006] It is known to mount the support on the frame so as to be able to move the holding support along a circular path centered on a first axis of rotation and to pivot the holding support on itself about a second axis of rotation which is perpendicular to a plane containing the circular path and corresponds to an axis of symmetry of the surface of the substrate. This makes it possible to ensure the deposition of a layer of material of uniform thickness on the surfaces having zero curvature or slightly pronounced. The thickness deposited varies in fact according to the local inclination of the surface to be covered, and more particularly according to the cosine of the value of the local inclination angle. However, certain substrates have a surface, concave or convex, with a very pronounced curvature, close, for some, to the hemisphere. The thickness of material deposited will then be almost zero for the portions of surfaces with a quasi-vertical inclination.

[0007] It is also known to interpose a mask between the source and the holding support to block some of the particles directly above certain areas of the surface of the substrate and allow the particles to pass directly above other areas of the surface of the substrate. The mask is thus arranged to modify the distribution of the particles deposited on the surface of the substrate. Even if the use of a mask improves the uniformity of the deposition, the deposition of material in the areas of the surface having the steepest inclination remains problematic and the constitution of the mask can be complex.

[0008] SUBJECT OF THE INVENTION

[0009] The invention aims in particular to facilitate the production of thin layers, in particular on surfaces comprising at least one zone having a strong local inclination. Summary of the invention

[0010] For this purpose, a method is provided for producing a thin layer of material on a surface of a substrate, the method comprising the steps of: holding the substrate on a support so that at least a portion of the surface is oriented towards a source of material particles, projecting the material particles from the source of material particles, moving the support on a closed trajectory around a first axis of rotation, pivoting the substrate on itself around a second axis of rotation corresponding to an axis of symmetry of the surface of the substrate.According to the invention, the method comprises the step of moving the support between two extreme positions on a trajectory in an arc of a circle around a third axis of rotation parallel to a direction locally tangential to the closed trajectory to expose to a direct projection of the material particles different portions of the surface of the substrate during an exposure time depending on the desired thickness of material on said surface portions.

[0011] Thus, a third rotation is added to the two existing ones. This third rotation being carried out around an axis substantially tangential to the closed trajectory, it makes it possible to expose to the source, in other words to the projection of the particles of material, portions of surface which would be difficult to reach by the particles of material with the methods of the prior art. It is understood that the thickness of the deposit of material on a portion of surface is proportional to the time during which this portion of surface is exposed to the projected material particles. This exposure time depends on the speed of movement of the holding support. This speed may not be constant around the third axis of rotation depending on the shape of the surface, for example to increase the exposure time of the periphery of the surface compared to the exposure time of the center of the surface so as to uniform the thickness of material deposited over the entire surface.

[0012] The invention also relates to a device for implementing this method.

[0013] The device for depositing a material on a surface of a substrate comprises a frame delimiting a hermetic enclosure and, in said hermetic enclosure, a source of material, and a support for holding at least a portion of the surface of the substrate opposite the source. The substrate holding support is mounted on the frame to be moved along a closed trajectory around a first axis of rotation and to pivot on itself around a second axis of rotation corresponding to an axis of symmetry of the surface of the substrate. The holding support is mounted on the frame to be moved between two extreme positions on an arcuate trajectory around a third axis of rotation parallel to a direction tangential to the closed trajectory.The device comprises at least one actuator for moving the holding support and an electronic unit for controlling the actuator which are arranged to move the holding support so as to orient different portions of the surface of the substrate towards the source at a speed depending on the desired thickness of material on said portions.

[0014] Optionally, the device comprises a plate mounted on the frame to rotate around the first axis of rotation, the plate being driven in rotation by a motor forming at least in part the actuator, the holding support being mounted to pivot on a rocker mounted movably on the plate to move the holding support on the arcuate trajectory.

[0015] Optionally then: - the frame comprises a cam path extending substantially opposite the closed trajectory with a variable spacing relative to the plate and the rocker is connected by at least one rod to a carriage traveling along the cam path so as to bring the rocker between two extreme positions corresponding to the extreme positions of the support on the arcuate trajectory; - the frame is provided with a rail extending opposite the closed path with a constant spacing relative to the plate and a roller is mounted on the rocker coaxially with the holding support to be applied against the rail and is rotatably linked to the holding support in such a way that the placing the holding bracket along the closed path causes the bracket to rotate around the second axis of rotation.

[0016] Other characteristics and advantages of the invention will emerge from reading the following description of a particular and non-limiting embodiment of the invention. Brief description of the drawings

[0017] Reference will be made to the accompanying drawings, among which:

[0018] [Fig-1] [Fig.l] is a schematic axial sectional view of an optical element produced by implementing the method of the invention;

[0019] [Fig.2] [Fig.2] is a schematic sectional view of a device according to the invention;

[0020] [Fig.3] [Fig.3] is a schematic perspective view showing the means of de placement of the holding support around the third axis of rotation;

[0021] [Fig.4] [Fig.4] is a schematic perspective view, according to a viewing angle different from that of [Fig.3], showing the means of moving the holding support around the third axis of rotation;

[0022] [Fig.5] [Fig.5] is a schematic perspective view, according to a viewing angle different from that of figures 3 and 4, showing the means of moving the holding support around the third axis of rotation;

[0023] [Fig.6] [Fig.6] is a schematic elevation view, showing the means of de placement of the holding support around the third axis of rotation when the rotation support is in an intermediate position between its two extreme positions;

[0024] [Fig.7] [Fig.7] is a view similar to that of [Fig.6], showing the means of moving the holding support around the third axis of rotation when the rotation support is in a first of its two extreme positions;

[0025] [Fig.8] [Fig.8] is a view similar to that of [Fig.6], showing the means of movement of the holding support around the third axis of rotation when the rotation support is in a second of its two extreme positions. DETAILED DESCRIPTION OF THE INVENTION

[0026] The invention relates to the production of a thin layer C of material on a surface S of a substrate O to form an optical element E (shown in [Fig.l]). The surface S is in the form of a spherical cap, here convex, having a central axis of symmetry S'.

[0027] The method implemented comprises the steps of: - maintain the substrate O so that at least a portion of the surface S is oriented towards a source of material particles, - project material particles from a material particle source, - moving the substrate O on a closed trajectory, here circular, around a first axis of rotation while pivoting the substrate O on itself around a second axis of rotation corresponding to an axis of symmetry of the substrate O, - moving the substrate O between two extreme positions on a trajectory substantially in an arc of a circle around a third axis of rotation locally tangential to the closed trajectory to orient different portions of the surface S of the substrate O towards the source at a speed depending on the desired thickness of material on said surface portions.

[0028] The method of the invention is implemented by means of a device for depositing a material on the surface S of the substrate O.

[0029] The device ([Fig.l]) comprises a frame 1 delimiting a hermetic enclosure 2 in which a source 3 of material is arranged, and a support 4 for holding at least a portion of the surface S of the substrate O opposite the source 3.

[0030] The hermetic enclosure 2 is connected to a vacuum circuit, symbolized at 5, comprising for example a pump.

[0031] The source 3 is for example a crucible which contains the material to be deposited and which is provided with a heating element for the material allowing the evaporation of particles of the material. The heating element comprises for example an electrical resistance and / or a laser emitter directed onto the material. The electrical resistance and / or the laser emitter are connected to an electrical power supply source. It will be noted that the source 3 is represented symbolically in [Fig.l], whether for its structure or its positioning. Other techniques for producing and projecting particles can of course be used.

[0032] The device comprises a horizontal plate 6, mounted on the frame 1 to rotate on itself around a vertical axis of rotation A1. The plate 6 is driven in rotation by a motor 7.

[0033] A slide 8 is fixed at the periphery of the plate 6 to extend in a radial plane of the plate 6. The slide 8 extends in an arc of a circle around an axis of rotation A2 (figures 3 to 5) parallel to a tangential direction locally to the plate 6 at the point of fixing of the slide 8 (the tangential direction is perpendicular to the radial plane of the plate 6 in which the slide 8 extends). The slide 8 here comprises a vertical plate provided with a groove 8.1 extending in an arc of a circle over 180° around the axis of rotation A2.

[0034] On the slide 8 is mounted a rocker 9 (figures 4, 5 and 6 to 8) having the form of a carriage comprising two rollers 10 rolling in the groove 8.1 of the slide 8 so that the rocker 9 has two extreme positions, namely a high position (figures 2 and 8) and a low position (figures 3, 5 and 7), in such a way that the rocker 9 has a part which is substantially oriented upwards when the rocker 9 is in the high position and this same part is oriented downwards when the rocker 9 is in the low position. The rocker 9 is driven along a circular trajectory around the axis of rotation A1 by the slide 8 itself driven along this trajectory by the plate 6 itself driven in rotation on itself by the motor 7. During this movement along the circular trajectory, the rocker 9 is simultaneously moved along an arc-shaped trajectory around the axis of rotation A2 between its two extreme positions by a rod 11 having a first end articulated to the rocker 9 and a second end articulated to a carriage 12 carried by wheels 13 each engaged in a rail 14 (figures 2, 6 to 8). The rails 14 extend coaxially and parallel to each other above the periphery of the plate 6: they have at least one high section 14.1 and a low section 14.2 connected to the high section by two inclined intermediate sections 14.3, the high sections being spaced from the plate 6 by a first distance dl greater than a second distance d2 separating the low sections from the plate 6 ([Fig.2]). The carriage 12 is driven along the rails 14 by the rod 11, the carriage 9, the slide 8, the plate 6 and the motor 7. It is understood that: when the carriage 12 has its wheels 13 engaged in the high section of the rails 14, the rocker 9 is in its high position ([Fig.7]); when the carriage 12 has its wheels 13 engaged in the low section of the rails 14, the rocker 9 is in its low position ([Fig.6]). The rails 14 thus form a cam path extending opposite the circular trajectory with a variable spacing relative to the plate 6. The rails 14 may comprise several high sections and several low sections, for example two symmetrically opposite high sections and two symmetrically opposite low sections..

[0035] The support 4 is mounted on the rocker 9 which moves the support 4 on the arc-shaped trajectory defined by the slide 8 around the axis of rotation A2. The support 4 is mounted on the rocker 9 to pivot on itself around an axis of rotation A3. The substrate O (shown in double dot-and-dash lines in Figures 3 to 5 and in strong lines in Figures 2 and 6 to 8) is mounted on the support 4 in such a way that the central axis of symmetry of the surface S coincides with the axis of rotation A3. A rail 15 ([Fig.2]) integral with the frame 1 extends opposite the circular path with a constant spacing relative to the plate 6 and a roller 16 (figures 3 to 5) is mounted on the rocker 9 coaxially with the support 4 to be applied against the rail 15 and is linked in rotation to the support 4 in such a way that the movement of the support 4 along the circular path causes the roller 16 to roll on the rail 15 and therefore the rotation of the support 4 around the axis of rotation A3. The rail 15 has a circular cross-section in such a way that the roller can cooperate with the rail 15 whatever the position of the rocker 9 relative to the plate 6. It can be seen in figures 6 to 8 that the . roller 16 is caused to move from the outer periphery of the rail 15 to the inner periphery of the rail 15 without losing contact with it.

[0036] Thus, when the motor 7 drives the plate 6 in rotation around the axis of rotation A1 (or first axis of rotation), the support 4 and therefore the substrate O: - moves along the circular trajectory corresponding to the trajectory of the slide 8 resulting from the rotation of the plate 6 around the axis of rotation Al; - pivots on itself around the axis of rotation A3 (or second axis of rotation) corresponding to the central axis of the surface S of the substrate O; - moves between two extreme positions on the arc-shaped trajectory around the axis of rotation A2 (or third axis of rotation) tangential to the circular trajectory around the axis of rotation Al.

[0037] It will be noted that the length of the upper 14.1 and lower 14.2 sections of the rails 14, the length and the inclination of the intermediate sections 14.3 connecting the upper and lower sections, and the diameter of the roller 16 will determine the time of presentation of each portion of the surface S towards the source 3 of material or, in other words, the time of direct exposure of each portion of the surface S to the particles of material emitted by the source 3 of material. For example, it may be decided that each of the upper 14.1 and lower 14.2 sections has a length such that the support 4 makes a number x of turns on itself when the carriage 12 travels along said section over its entire length, taking into account the diameter of the roller 16 and the length of rail 15 traveled by the roller 16 while the carriage 12 has traveled along said section.

[0038] The motor 7, the rails 14, the carriage 12, the rod 11 and the rocker 9 thus form an actuator for moving the support 4 which is arranged with the control unit 20 ([Fig.l]) to move the support 4 so as to orient different surface portions of the substrate towards the source at a speed depending on the desired thickness of material on said surface portions.

[0039] Of course, the invention is not limited to the embodiment described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0040] In particular, the emission of the material particles can be obtained by implementing a vacuum evaporation or cathode sputtering technique for example, but other techniques conventionally used for the deposition of thin layers on optical substrates can be used, for example techniques using a laser. The invention can also be applied for the compaction of thin layers by ion gun for example.

[0041] Although the motorization 7 has been shown on the same side of the plate 6 as the source 3, the motorization 7 can be positioned on the side of the plate 6 opposite the source 3.

[0042] It is possible to use a dedicated actuator, such as an electric motor, for moving the support 4 along the arcuate trajectory or for pivoting the support 4 on itself.

[0043] Although no mask is shown between the source 3 of material and the support 4, one or more masks can obviously be used depending on the requirements.

[0044] The plate 6 may comprise one or more arms each carrying a support 4 for holding a substrate.

[0045] The upper and lower sections are here flat and can have a very short length; it is possible to provide for the sections to have a variable slope along their length or to be curved upwards or downwards.

Claims

1.

2.

3. Claims Method for producing a thin layer of material on a surface (S) of a substrate (O), comprising the steps of holding the substrate on a support (4) so ​​that at least a portion of the surface (S) is oriented towards a source (3) of material particles, projecting the material particles from the source (3) of material particles while moving the support (4) on a closed trajectory around a first axis of rotation (A1) and pivoting the substrate (O) on itself around a second axis of rotation (A3) corresponding to an axis of symmetry of the surface (S) of the substrate (O), characterized in that the support (4) is also moved, during the projection,between two extreme positions on a trajectory in an arc of a circle around a third axis of rotation (A2) parallel to a direction locally tangential to the closed trajectory to expose to a direct projection of the particles of material different portions of the surface (S) of the substrate (O) during an exposure time depending on the desired thickness of material on said surface portions., The method of claim 1, wherein the closed path is circular. Device for depositing a material on a surface (S) of a substrate (O), comprising a frame (1) delimiting a hermetic enclosure (2) and, in said hermetic enclosure (2), a source (3) of material, and a support (4) for holding at least a portion of the surface (S) of the substrate (O) opposite the source (3), the support (4) for holding the substrate being mounted on the frame (1) to be moved along a closed trajectory around a first axis of rotation (A1) and to pivot on itself around a second axis of rotation (A3) corresponding to an axis of symmetry of the surface (S) of the substrate (O), characterized in that the holding support (4) is mounted on the frame (1) to be moved between two extreme positions on an arcuate trajectory around a third axis of rotation (A2) parallel to a direction tangential to the closed trajectory,and in that the device comprises at least one actuator for moving the holding support and an electronic unit (20) for controlling the actuator which are arranged to move the holding support around the three axes of rotation so as to orient towards the source (3) different portions of the surface (S) of the substrate at a speed depending on the thickness of the material, desired on said portions.

4. Device according to claim 3, comprising a plate (6) mounted on the frame (1) to rotate around the first axis of rotation (A1), the plate being driven in rotation by a motor (7) forming at least in part the actuator, the holding support (4) being mounted to pivot on a rocker (9) mounted movably on the plate (6) to move the holding support on the arcuate trajectory.

5. Device according to claim 4, in which the frame (1) comprises a cam path (14) extending substantially opposite the closed trajectory with a variable spacing relative to the plate (6) and the rocker (9) is connected by at least one rod (11) to a carriage (12) traveling along the cam path so as to bring the rocker between two extreme positions corresponding to the extreme positions of the support on the arcuate trajectory.

6. Device according to claim 5, in which the cam path (14) comprises at least one high section (14.1) and one low section (14.2) connected to each other by two intermediate sections (14.3); the high and low sections having a length, and the intermediate sections having a length and an inclination, determined as a function of a desired direct exposure time of each portion of the surface (S) to the particles of material coming from the source (3) of material.

7. Device according to claim 4, in which the frame (1) is provided with a rail (15) extending opposite the closed path with a constant spacing relative to the plate (6) and a roller (16) is mounted on the rocker (9) coaxially with the holding support (4) to be applied against the rail (15) and is rotationally linked to the holding support (4) in such a way that the movement of the holding support (4) along the closed path causes the rotation of the support around the second axis of rotation (A3).

8. Device according to claim 7, in which the rail (15) has a circular cross-section such that the roller (16) can cooperate with the rail (15) whatever the position of the rocker (9) relative to the plate (6).

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