Abstract:
The invention relates to a test glass changing system ( 10 ) for selectively coating and optically measuring a test glass ( 24, 24 ″) in a coating chamber ( 1 ) of a vacuum coating installation ( 3 ). In the coating chamber, a movable turntable ( 2 ) is used to guide substrates ( 7 ) on a path through a stream of a coating material. The test glass changing system ( 10 ) comprises a test glass holder ( 8, 8 ″) with a test glass plate ( 26 ) for holding the test glass ( 24, 24 ″), and a cover ( 28, 28 ″) for selectively covering the test glass plate ( 26 ). The test glass changing system ( 10 ) also comprises a rotary apparatus ( 34 ) for rotating the test glass plate ( 26 ) about an axis ( 51 ) which is oriented approximately parallel to the axis of rotation ( 5 ) of the turntable ( 2 ). The test glass holder ( 8, 8 ″) can be positioned on the turntable ( 2 ) and removed from the coating chamber ( 1 ) in the form of a unit.

Description:
TECHNICAL FIELD 
     The invention relates to a test glass changing system for selectively coating and optically measuring a test glass plate in a vacuum coating installation. 
     BACKGROUND 
     The production of optical multilayer systems, which are also referred to as interference layers, plays an important role in, for example, optical products such as band-pass filters, edge filters, cold mirrors, beam splitters, and antireflection coatings. The goal of such a coating is to achieve transmission or reflection at the multilayer system that is as complete as possible within a prescribed wavelength range but achieve negligible transmission or reflection in the wavelength ranges outside thereof, with the smallest transition region possible. Meeting these demands requires a large number of individual layers, wherein, for example, layers with high and low refractive index are alternately applied to the substrate; however, it is also possible for two layers with a high refractive index or two layers with a low refractive index to follow one another directly. 
     When producing such complex layer systems, more particularly when producing multilayers with specific functional properties, a regular measurement or check of the functional layers applied to the substrates is necessary in order to ensure the desired layer thicknesses and layer properties. To this end, use is made of test glasses, on which in each case a single layer is deposited and checked. In the case of complex optical filters, a plurality of test glass changes are required in order to achieve the filter specifications. In order to achieve the required accuracy, the test glass must be arranged on the site of the substrates and substantially experience the same coating as the substrate; furthermore the test glass change between the individual coating sequences should be as automated as possible, i.e. without manual replacement of the test glasses by an operator. 
     DE 36 04 624 A1 has disclosed a test glass changer that allows a test glass change when the coating chamber is sealed. A holder for holding a plurality of test glasses is mounted on a rotary disk, which is used to guide the substrates along a path through at least one coating material flow. The holder is moved with the rotary disk and is mounted such that it can rotate with respect to the rotary disk. An intermittent motion system, which is arranged along the path of the rotary disk, switches respectively one test glass into a position that is stationary with respect to the rotary disk, in which position said test glass, along with the substrates, is alternately guided through the beam path of the measurement device and the coating material flow for a prescribable number of revolutions of the rotary disk. The holder is covered by a cover, which is attached to the rotary disk in a stationary fashion and in each case only exposes a single test glass in its coating and measurement position. The holder is rotated by a moveable shift finger, which is arranged in the interior of the coating chamber and protrudes into the orbit of the rotary disk and interacts with projections on the holder. When the shift finger engages into a projection on the holder, a test glass is rotated out of its congruent position with the measurement window and the next test glass takes its place. Hence, the test glass changer in DE 36 04 624 A1 permits a test glass change with a sealed coating chamber. However, loading the test glass changer is very complicated because the individual test glasses must be inserted into the holder of the test glass changer through the substrate lock. Furthermore, the test glass changer shown in DE 36 04 624 A1 can only hold a comparatively small number (four) of test glasses, and so (at least) one manual replacement of the test glasses is necessary when producing a multilayer system. 
     BRIEF SUMMARY 
     The invention further develops the known prior art such that a larger number of test glasses are provided, which can be changed in the interior of the coating chamber without manual intervention. Furthermore, it should be possible to insert the test glasses into the coating chamber as simply as possible. 
     According to this, the test glass changing system comprises a test glass holder with a test glass plate for holding one or more test glasses and a cover, which covers the test glass plate and protects the test glasses held therein from being coated. The cover is provided with a measurement window, which only exposes a small region of the test glass plate to being coated. Provision can also be made for a plurality of measurement windows and/or reference windows. The test glass plate can be rotated with respect to the cover by means of a rotation device, which forms a part of the test glass changing system; this moves different test glasses attached to the test glass plate into the region of the measurement window, where they are coated and measured. Compared to the generic DE 36 04 624 A1, the test glass changing system according to the invention differs in that the test glass holder (with the test glass plate and the cover) forms a closed unit that—like the substrates to be coated—can be introduced into the coating chamber through the substrate lock and can be positioned on the rotary disk. This allows a particularly simple and time-saving loading of the rotary disk: instead of equipping the test glass changing system (which is fixedly connected to the rotary disk) with test glasses, as necessary in DE 36 04 624 A1, which test glasses must be introduced individually though the substrate lock and have to be positioned on the test glass plate there, use of the test glass changing system according to the invention allows the equipping and preparation of the test glass holder to be carried out outside of the coating chamber and temporally independently of the substrate change. This is advantageous from an ergonomic point of view and saves time. Furthermore, it is possible to arrange a comparatively large number of test glasses on the test glass holder. 
     The cover of the test glass holder is embodied such that it can be rotated and lifted with respect to the test glass plate. A test glass change within the coating chamber is carried out in such a manner that the cover of the test glass holder is lifted, the test glass plate is rotated with respect to the cover by a prescribed angle, and the cover is subsequently put back down again. The rotation device used to rotate the test glass plate is preferably embodied as a lift/rotation device, with the aid of which it is possible to carry out rotations around an axis parallel to the rotational axis of the rotary disk and lift movements in the direction of this axis. A test glass change is then carried out such that the test glass plate is lifted off the rotary disk (or a base body of the test glass holder resting on the rotary disk) in the axial direction and the cover is lifted off the test glass plate in the axial direction; these two lift motions can be carried out at the same time or with a time offset with respect to one another. The test glass plate is subsequently rotated, as a result of which the region of the test glass plate situated under the measurement window of the cover is replaced and a new region of the test glass plate comes to rest below the measurement window of the cover. Test glass plate and cover are put down in this new relative angular position. If the test glass holder is now moved on the rotary disk through the coating station of the coating chamber, the region of the test glass plate just rotated to be under the measurement window is coated. 
     For the purpose of the test glass change in the case of circular or cylindrical test glass plates, the lift/rotation device expediently has two concentric annular bodies, which can both (preferably together) be adjusted in terms of their height; one of the two annular bodies can be rotated in a controlled fashion. The rotatable annular body serves for lifting and rotating the test glass plate, while the other annular body serves to lift the cover. 
     The lift/rotation device can be arranged in a stationary fashion in the processing chamber and can for example be located in the region of the coating station. In this case, a test glass change can only take place in a prescribed rotational position of the rotary disk, to be precise when the test glass holder is exactly above the lift/rotation device. Alternatively, the test glass rotation device can be arranged on the rotary disk (or on a revolving stage rotating in synch with the rotary disk); the advantage of this is that the test glass change can take place without changing the speed of the rotary disk and at any position in the coating chamber (for example during the transport of the test glass holder between measurement station and coating station). 
     In a first embodiment of the invention, the test glass plate is a circular-disk-shaped monitor glass. In this embodiment, the entire test glass plate or any selected region of the test glass plate can serve as test glass. The monitor glass is advantageously provided with a central cutout, through which a reference beam can be routed during the optical measurement in order to monitor a drift of the measurement light. 
     In a second embodiment of the invention, the test glass plate is provided with a multiplicity of holding regions for holding individual test glasses. In this case, the test glass plate is rotated by a prescribed angle with respect to the cover during a test glass change so that the test glass comes to rest directly below the measurement window of the cover. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following text, the invention will be explained in more detail on the basis of an exemplary embodiment illustrated in the figures, in which: 
         FIGS. 1   a ,  1   b  show sectional views of a coating installation with a rotary disk; 
         FIG. 2  shows a schematic plan view of the rotary disk in  FIGS. 1   a  and  1   b;    
         FIG. 3  shows a test glass changing system according to the invention with a test glass holder and a lift/rotation device in a first embodiment: 
         FIG. 3   a  shows a plan view of the test glass holder; 
         FIG. 3   b  shows a sectional view of the test glass holder; 
         FIG. 3   c  shows a sectional view of the associated lift/rotation device; 
         FIG. 4  shows a test glass changing system according to the invention with a test glass holder and a lift/rotation device in a further embodiment: 
         FIG. 4   a  shows a plan view of the test glass holder; 
         FIG. 4   b  shows a sectional view of the test glass holder; and 
         FIG. 4   c  shows a sectional view of the associated lift/rotation device. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1   a  and  1   b  show schematic sectional views through a coating chamber  1 , which forms part of a vacuum coating installation  3 . Within the coating chamber  1  there is a rotary disk  2 , which can be rotated around a rotational axis  5  with the aid of a rotation apparatus  4  that can be subject to open-loop or closed-loop control. A plan view of the rotary disk  2  is illustrated in  FIG. 2 . A plurality of recesses  6  are provided on the rotary disk  2 , which recesses are arranged on a common great circle  23  around the axis  5 . The recesses  6  can selectively be equipped with a disk-shaped substrate  7  or with a test glass holder  8 ; an oxide layer is deposited under residual gas on these substrates  7  and on the test glass holder  8  in the coating chamber  1 . Together with a test glass rotation device  9 , the test glass holder  8  forms part of a test glass changing system  10 . 
     The rotary disk  2  is equipped with substrates  7  or test glass holder  8  through a substrate lock  20  in a side wall of the coating chamber  1 . In order to remove the substrates  7  or test glass holder  8 , a lift device  21  with a stamp  22  that can be displaced in the axial direction  5  is arranged in the coating chamber  1 , directly opposite the substrate lock  20 . During a substrate change, the stamp  22  of the lifting device  21  is guided from below through an aperture  6 ′ in the region of the recess  6  of the rotary disk  2  and in the process lifts the substrate disk  7  or test glass holder  8  situated in the region of the recess  6  out of the rotary disk  2 , and so the substrate disk  7  or test glass holder  8  can be removed via the substrate lock  20 . The substrate lock  20  can easily be used to replace a second, etc. test glass holder  8  and hence a sufficient number of monitor glasses can be provided, even in the case of a very large number of layers, without breaking the vacuum or losing much space to test glass holders. 
     The coating chamber  1  comprises a coating station  11  and a measurement station  13 , which are preferably delimited from one another by diaphragms, and are only interconnected through slits in the diaphragms. In the coating station  11  there is a sputtering apparatus  12 , in which—in a known fashion—sputtering material of a target is sputtered by reactive sputtering, with a sputtering material/oxygen compound precipitating onto the walls of the coating chamber  1  and on the substrates  7  and the test glass holder  8 .—In the measurement station  13  there is an optical measurement apparatus  14 , by means of which optical properties, more particularly transmission and/or reflection, of the growing layers can be determined. The optical measurement apparatus  14  comprises a measurement light source arranged above the coating chamber  1  and detectors  16 , arranged below and/or above the coating chamber  1 , for measuring the transmitted and/or reflected radiation. Windows  19  have been inserted in the top  17  and/or the base  18  of the coating chamber  1  in a vacuum-tight fashion and the measurement light beam  15  is guided through the coating chamber  1  via said windows. The optical measurement apparatus  14  is preferably a single wavelength or multi-wavelength spectrometer, more particularly a spectral photometer or a spectral ellipsometer. With the aid of the optical measurement apparatus  14 , it is possible to measure the optical losses after deposition of a prescribed layer thickness and set layer properties depending on a signal from the optical measurement apparatus  14 . If use is made of a spectral photometer, it is easily possible to establish transmission, absorption, and reflection in a prescribed spectral range and as a function of the layer thickness. 
     In addition to the coating station  11  shown in  FIG. 1 , provision can be made for further processing regions (e.g. plasma processing regions, further sputtering apparatuses, etc.) in the coating chamber  1 . Furthermore, provision can be made for further measurement stations. 
     The rotary disk  2  in the coating chamber  1  is rotated around the rotational axis  5  in a controlled or regulated fashion with the aid of the rotation apparatus  4 . In the process, the substrates  7  and the test glass holder  8  are successively moved at least once through the coating station  11  and the measurement station  13  on a circular orbit. As indicated in  FIG. 2 , the test glass holder  8  has approximately the same diameter as the substrate disks  7 , and so the test glass holder  8 —like the substrate disks  7 —can be held in any recess  6  in the rotary disk  2  and can be removed from the rotary disk  2  using the lifting device  21 . 
     In order to monitor the coating applied to the substrates  7  regularly, the measurement apparatus  13  is used to carry out measurements on test glasses  24  that are held in the test glass holder  8 .  FIGS. 3   a  and  3   b  show a plan view ( FIG. 3   a ) and a sectional view ( FIG. 3   b ) of the test glass holder  8  from  FIG. 1 . The test glass holder  8  comprises a tubular basic body  25 , on which there is a circular-disk-shaped test glass plate  26 . The test glass plate  26  has a central cutout  27 . In the exemplary embodiment shown in  FIGS. 3   a  and  3   b , the test glass plate  26  is embodied as a monitor glass  26 ′, i.e. as a continuous disk-shaped glass plate with a central cutout  27 . In order to achieve a targeted coating of selected regions of the monitor glass  26 ′, the monitor glass  26 ′ is covered by a removable circular cover  28 . The cover  28  is provided with two openings, a measurement window  29  and a reference window  30 . If the test glass holder  8  is moved on the rotary disk  2  though the coating station  11 , the region  31  of the monitor glass  26 ′ situated below the measurement window  29  is coated, while the remaining regions of the monitor glass  26 ′, which are covered by the cover  28 , remain uncoated. 
     The measurement window  29  serves for the optical measurement in the measurement station  13  of the layer thickness or the layer properties of the region  31  of the monitor glass  26 ′ situated in this window  29 . The reference window  30 , arranged in the center of the cover  28 , serves for the 100% measurement of the layers applied to the monitor glass  26 ′, as a result of which a drift of the measurement light is avoided. In the exemplary embodiment in  FIG. 3 , the two windows  29 ,  30  have a rectangular shape; however, they can also be circular, elliptical, etc. If the test glass holder  8  is brought into the coating station  11 , the region  31  of the monitor glass  26 ′ situated below the measurement window  29  is exposed to the sputtering medium and is coated; the thickness and composition of this coating is established in the measurement station  13 . In a changer station  32 , the monitor glass  26 ′ located in the test glass holder  8  is rotated through a prescribed angle  33  in order to place a further (previously uncoated) region  31 ′ of the monitor glass  26 ′ below the measurement window  29 . This rotation of the monitor glass  26 ′ is brought about with the aid of the rotation device  9 , which is arranged in the changer station  32 , which is preferably embodied as a lift/rotation device  34  and—as shown in  FIG. 1   b —attached to the base  18  of the coating chamber  1  below the rotary disk  2 . In the exemplary embodiment in  FIG. 1   b , the changer station  32  is situated in the same region of the coating chamber  1  as the coating station  11 , and so the lift/rotation device  34  is arranged below the sputtering apparatus  12 . 
     The lift/rotation device  34  comprises two concentrically arranged annular bodies  35 ,  37  (see  FIG. 3   c ) and is arranged in such a position in the coating chamber  1  that the common center  39  of the annular bodies  35 ,  37  is situated directly below the great circle  23  of the substrate disks  7  mounted on the rotary disk  2 . The inner annular body  35  can be rotated around an axis  5 ′ with the aid of a control apparatus (not illustrated in the figures), which axis runs through the center  39  of said annular body and is aligned approximately parallel to the rotational axis  5  of the rotary disk  2 . Furthermore, the annular bodies  35 ,  37  can together be displaced parallel to the axis  5 ′ with the aid of the control apparatus. The lift/rotation device can also be embodied such that the two annular bodies  35 ,  37  can be displaced individually, however this requires an additional movement axis; therefore it is more advantageous to provide a common advance movement of the two annular bodies  35 ,  37 . 
     Each annular body  35 ,  37  is provided with a set of lifting elements  36 ,  38  (pins  36 ′,  38 ′ in the present exemplary embodiment), which protrude from the annular bodies  35 ,  37  in the displacement direction  5 ′. If a test glass change should be carried out (i.e. if the monitor glass  26 ′ in the test glass holder  8  should be rotated by an angle  33 ), the test glass holder  8  is, with the aid of the rotary disk  2 , positioned with respect to the lift/rotation device  34  such that the center  40  of the test glass holder  8  comes to rest above the center  39  of the annular bodies  35 ,  37 . Then the two annular bodies  35 ,  37  are moved upward until the pins  38 ′ of the outer annular body  37  penetrate into the cavities  41  in the base body  25  of the test glass holder  8 , while the pins  36 ′ of the inner annular body  35  are held in the interior  42  of the base body  41 . The lengths of the pins  36 ′,  38 ′ are calculated such that if the annular bodies  35 ,  37  are advanced further, the pins  38 ′ of the outer annular body  37  lift the cover  28  of the test glass holder  8  while the pins  36 ′ of the inner annular body  35  lift the monitor glass  26 ′, to be precise such that the monitor glass  26 ′ is lifted off the base body  25  while the cover  28  is lifted off the monitor glass  26 ′ such that monitor glass  26 ′ and cover  28  rest on the pins  36 ′ and  38 ′ without touching one another—and without touching the base body  25 . In this position the monitor glass  26 ′ is rotated through the angle  33  by a rotation of the inner annular body  35 , while base body  25  and cover  28  remain in their positions. As a result of this, another region  31 ′ of the monitor glass  26 ′ now comes to rest under the measurement window  29  instead of the monitor glass region  31  originally situated below the measurement window  29 . Thus, this rotation of the monitor glass  26 ′ so to speak carries out a “test glass change”: successive rotations of the monitor glass  26 ′ with respect to the cover  28  afford the possibility of moving different regions  31 ,  31 ′ of the monitor glass  26 ′ into the region of the measurement window  29 . The lift/rotation device  34  therefore allows a fully automatic test glass change within the sealed coating chamber  1 . 
     The size and position of the measurement window  29  is calculated such that the monitor glass  26 ′ can be moved into at least six different measurement positions, advantageously eight (or even more) different measurement positions by rotation. In the exemplary embodiment in  FIGS. 3   a  and  3   b , the monitor glass  26 ′ has a diameter of 125 mm, while the measurement window  29  has a dimension of 38 mm×15 mm. 
     A coating sequence is brought about as follows: at first, the substrates  7  and a test glass holder  8 , which contains an uncoated monitor glass  26 ′, are instated in the coating chamber  1  through the substrate lock  20  and placed into the positions  6  of the rotary disk  2  provided therefor. In a first coating sequence, the substrates  7  and the region  31  of the monitor glass  26 ′ lying below the measurement window  29  are subjected to a first coating in the sputtering apparatus  12 ; the changing intensity of transmission and/or reflection is measured in situ in the measurement station  13  during the coating and hence the thickness and composition of the layer deposited in the region  31  of the monitor glass  26 ′ is determined optically. After this first coating process, which comprises the deposition of at least one layer but in general comprises the deposition of a multiplicity of layers, the test glass holder  8  is positioned with respect to the lift/rotation device  34  and—as described above—a test glass change is performed by rotating the monitor glass  26 ′ such that now a new region  31 ′ of the monitor glass  26 ′ lies below the measurement window  29  instead of the region  31 . A second coating sequence is subsequently carried out with a second in situ measurement. This is repeated up to the last coating sequence. If the number of desired coating sequences is larger than the number of coating regions  31 ,  31 ′ that can be placed on the monitor glass  26 ′, the test glass holder  8  can be replaced by a new uncoated test glass holder through the substrate lock  20 . 
       FIGS. 4   a - 4   c  show a further embodiment of the test glass changing system according to the invention. This test glass changing system  10 ″ comprises a test glass holder  8 ″, the test glass plate  26  of which is formed by a support plate  26 ″ that has cutouts for individual measurement glasses  24 ′,  24 ″. In the present exemplary embodiment, the measurement glasses  24 ′,  24 ″ are formed by elongate glass platelets  24 ″ that are rounded off at the ends, have a length of 40 mm, and a width of 16 mm, which glass platelets are arranged symmetrically on the support plate  26 ″; in the exemplary embodiment shown in  FIG. 4   b , the support plate  26 ″ can hold eight measurement glasses  24 ″, which are each rotated by an angle  33 ″ of 45° with respect to the adjacent measurement glass. In the center, the support plate  26 ″ has a cutout  27 ″. In order to bring about a targeted coating of a selected measurement glass  24 ′, the support plate  26 ″ is covered by a removable circular cover  28 ″. It is possible to identify in the plan view of  FIG. 4   b  that the cover  28 ″ has a measurement window  29 ″ (to allow access to a selected measurement glass  24 ′) and a reference window  30 ″ (for the reference measurement during the optical measurement in the measurement station  13 ). If the test glass holder  8 ″ is moved through the coating station  11  on the rotary disk  2 , the measurement glass  24 ′ situated below the measurement window  29 ″ is coated while the further measurement glasses  24 ″ covered by the cover  28 ″ remain uncoated. The thickness and composition of this coating is established in the measurement station  13 . In the changer station  32 , the support plate  26 ″ of the test glass holder  8  is rotated by a prescribed angle  33 ″ in order to place a further measurement glass  24 ″ below the measurement window  29 ″ in the cover  28 ″. This rotation of the support plate  26 ″ is brought about with the aid of the rotation device  9 ″, embodied as a lift/rotation device  34 ″, which is attached to the base  18  of the coating chamber  1  and comprises two concentrically arranged annular bodies  35 ″,  37 ″ (see  FIG. 4   c ). The center  39 ″ of the annular bodies  35 ″,  37 ″ is situated directly below the great circle  23  of the substrate disks  7  mounted on the rotary disk  2 . The outer annular body  35 ″ can be rotated around the axis  5 ′ in a controlled fashion, while the annular bodies  35 ″,  37 ″ can together be displaced parallel to the axis  5 ′. Each annular body  35 ″,  37 ″ is provided with lifting elements  36 ,  38  in the form of an annular web  36 ″,  38 ″ protruding upward. The two annular bodies  35 ″,  37 ″ are moved upward during a test glass change, with the web  38 ″ of the inner annular body  37 ″ meeting a downwardly protruding tube section  43 ″ of the cover  28 ″ and pressing the cover  28 ″ upward, while the web  36 ″ of the outer annular body  35 ″ meets the lower edge  44 ″ of the support plate  26 ″ and lifts the support plate  26 ″. Here, the lengths of the webs  36 ″,  38 ″ are calculated such that during the common advance of the annular bodies  35 ″,  37 ″, the support plate  26 ″ is lifted off the rotary disk  2  while the cover  28 ″ is lifted off the support plate  26 ″ such that support plate  26 ″ and cover  28 ″ rest on the webs  36 ″ and  38 ″ without touching one another—and without touching the rotary disk  2 . In this position, the support plate  26 ″ is rotated by the angle  33 ″ by a rotation of the outer annular body  35 ″ while the cover  28 ″ held on the annular body  38 ″ remains in its position, and so another test glass  24 ″ now comes to rest under the measurement window  29 ″ instead of the test glass  24 ′ originally situated below the measurement window  29 ″. Hence, different test glasses  24 ′,  24 ″ can be moved into the region of the measurement window  29 ″ by successive rotations of the support plate  26 ″ with respect to the cover  28 ″. The lift/rotation device  34 ″ thus allows a fully automatic test glass change within the sealed coating chamber  1 .