Patent Application
20100266747
A coating system for optical components generally is housed in a vacuum or partial vacuum chamber within which a number of elements reside. The elements may include: a source of material to be deposited as a coating; an energy source for vaporizing the source material; a support such as a planetary support for simultaneously moving and supporting objects to be coated; and a monitoring system for monitoring the thickness or other characteristic of a material deposited as a coating. Generally, the planetary support moves within the vacuum chamber, with some or all of the other elements being fixed at least during the coating process.
In a typical coating system, target objects to be coated are moved within the vacuum chamber as the coating material is vaporized. Using the planetary system, objects move around both their own axis of rotation and the axis of rotation of the support; moving through the space of the vacuum chamber in this manner corrects for any spatial variations in the vapor of the deposition material and allows even coating of the target objects. A monitor within the vacuum chamber is coated at roughly the same rate as the target objects and a signal from the monitor reflects the extent to which it is coated. This monitor signal is then used to control the rate and/or extent of coating that occurs for both the monitor and the target objects. Typically, the monitor extends vertically or horizontally from a wall of the vacuum chamber toward its middle.
Having accurate information regarding the thickness of a material deposited on a coated object can be an important factor in the later use of that object for its intended purpose. For example, precise control of the characteristics of an optical coating on an optical component, such as a camera lens, may be an important factor in determining the operational characteristics of that component. Transmission through and reflection from an optical component can be affected by a number of parameters, including the identity and nature of a transparent coating material provided on that component and the construction of the component itself.
Typically, light interacts with a thin-film coating by an interference effect whereby light rays reflected from the coating interfere with rays that pass through the coating and reflect from an underlying surface. In a coating having multiple types of layers, each with a thickness and a refractive index, a portion of the incident light may reflect from the interface between each successive layer, resulting in a complicated interference effect that determines the characteristics of both the light that is ultimately reflected from the coated component and the light that is transmitted through it. The different interactions between the layers of a coating and an incident light wave can be exploited by using a defined coating “recipe” to manufacture an optical component having distinct operational characteristics in a given spectrum of light.
Many techniques exist for monitoring the characteristics of an optical film deposited on an optical component. Two common techniques are optical monitoring and quartz crystal monitoring.
Optical monitoring generally involves detecting and responding to changes in the interaction of light with an optical coating on an optical monitor component. An optical monitoring system usually includes a light projector to send a light beam, an optical component to reflect the light beam (and to which a coating layer is applied), and a light receiver or detector to receive and detect the reflected light. A user of the system can track the deposition of an optical coating onto the optical component by following changes in the reflectance of the light beam sent by the projector and received at the detector. Deposition of the coating onto the optical component ideally should be comparable to deposition of the coating onto a target object in the same vacuum chamber, and the user will have pre-determined the change in the characteristics of the reflected light that corresponds to a desired optical layer thickness. Thus, to make a single-layer coating on a target object, the user can follow the deposition of that coating onto an optical component using the monitor. To make a multi-layer coating on a target object, the user can follow the deposition of the layers sequentially, applying and monitoring deposition of one layer at a time to an optical component used for monitoring until the desired multi-layer coating is finished. To accomplish accurate monitoring of each layer's deposition, the user can discard each optical component used as a monitor after it is used to monitor a given layer, providing a new optical component for monitoring at each layering step.
Quartz crystal monitoring involves detecting and responding to changes in the resonance frequency of a quartz crystal as an optical coating or other material is deposited on the crystal. An electrically energized quartz crystal resonates at a given frequency. The resonance frequency of the crystal depends substantially upon the mass and geometry of the crystal, and thus a change in mass of the crystal will result in a change in its resonance frequency. A user of a coating system can calculate, in advance, the amount (mass) of material that must be deposited onto the crystal to cause a given change in the crystal's resonance frequency. The user can then monitor and measure the deposition of a material layer by watching for the predetermined change in the resonance frequency of the crystal.
In a simple construct, a quartz thickness monitor may include two crystals, one experimental crystal and one reference crystal. A monitor of this type is used in the SPI-MODULE™ quartz crystal thickness monitor sold by Structure Probe, Inc. of West Chester, Pa. Typically, the experimental crystal resides in a vacuum chamber with the target objects to be coated with a material layer, whereas the reference crystal resides outside the vacuum chamber, or at least in a location where it is not coated by a material layer. At the beginning of a coating process, the difference between the resonance frequencies of the two crystals (if there is one) can be set to zero. During material deposition, the mass of the experimental crystal will rise and, thus, its resonance frequency will drop. At the same time, changes in resonance frequency of the reference crystal may be monitored and used to correct for changes in resonance frequency of the experimental crystal that are not due to material deposition, such as changes due to ambient conditions. This allows a more accurate determination of the actual addition in mass to the experimental crystal. Given the measured change in mass on the experimental crystal, and a known density of the material, the thickness of a material layer deposited on the crystal (and the target objects) can be derived. Accordingly, the rate of mass deposition can be decreased as a desired thickness is approached, and deposition can be stopped when the desired thickness is achieved. Other methods of monitoring material deposition on a reference component, such as that disclosed in U.S. Pat. No. 5,112,642 to Wajid (Measuring and Controlling Deposition on a Piezoelectric Monitor Crystal) could also be used.
Although quartz is discussed as a typical crystal used in monitoring and controlling a material deposition process, it should be appreciated that any appropriate piezoelectric crystal can be used. For example, ceramic resonators like barium titanate, lead zirconium titanate, and zirconium-toughened alumina, among others, may also be used for crystal monitoring. Desirable features in a crystal monitor material include a precise resonance frequency that can be readily monitored, and a low temperature dependence of the crystal's resonance frequency so that temperature variations occurring during the coating process will have a relatively small effect on the resonance frequency compared to the effect of mass changes resulting from material deposition.
The present teachings provide systems, including apparatus and methods, for monitoring and controlling fabrication of thin-film coatings on a target substrate, thereby providing coatings with highly accurate thicknesses and optical characteristics.
The present teachings provide systems, including apparatus and methods, for monitoring and controlling fabrication of thin-film coatings on a target substrate, thereby providing coatings with highly accurate thicknesses and optical characteristics. The systems may include a crystal holder assembly configured to monitor a first material deposition event and an optical component holder configured to monitor a second material deposition event, where the crystal holder and the optical component holder are arranged about a shared axis of rotational symmetry. The crystal holder assembly might be constructed of several components, including a crystal holder and a base plate, with both the crystal holder and the base plate having rotational symmetry. The described systems provide for accurate and repeatable deposition of optical coatings on optical components at relatively low cost and with a relatively high degree of performance.
In an illustrated embodiment, the crystal holder and the base plate are arranged coaxially, such that central openings in each of the holder and the base plate are aligned. The crystal holder assembly might include a plurality of crystal sites, each configured to support at least one quartz crystal. With the central openings of the holder and base plate being aligned, an optical component holder may be arranged in the center of the crystal holder assembly, resulting in a central optical monitor being surrounded by a plurality of quartz crystal monitors. This combined crystal/optical monitoring system can provide real time, highly accurate information regarding coating deposition rates and measurements of optical coating thickness.
In one embodiment, the crystal holder has eight-fold rotational symmetry, and the base plate is substantially circular. Furthermore, the crystal holder and base plate may be arranged in a stacked orientation, with the crystal holder residing above the base plate. In such an arrangement, the base plate may include exposure openings that allow exposure of at least a portion of the crystal holder to an atmosphere in a vacuum chamber used for a material deposition process. Optimally, the openings in the base plate allow exposure of a crystal held in the crystal holder to a source of material deposited on a target object in the vacuum chamber.
In some embodiments, each crystal might be held reversibly in a crystal drawer, with the drawer being configured for easy placement in and removal from the crystal holder. This design may allow for replacement of crystals in the monitor with no disassembly of the monitoring and controlling system, resulting in consistency of tooling factors (the ratio between the film thicknesses on the target object and the crystal or optical monitor) over a number of runs.
Because the monitoring and controlling assembly 10 may span a wall 15 of a vacuum chamber 11, it may be important to maintain the integrity of a vacuum induced within the chamber while still allowing control of elements of the assembly 10 within the chamber. Pass-through 16 may thus include a flange 22 coupled to the vacuum chamber wall and to a pass-through body 24, to avoid any undesirable leaking of atmospheric gases into chamber 11. In the illustrated embodiment, a single pass-through body 24 may accommodate an optical component assembly opening 25, one or more communication openings 26, and one or more cooling apparatus openings 27.
So that the resonance frequency of a crystal residing in each crystal drawer can be monitored, a crystal wire connection 46 (see
Crystal sites 32 may be arranged about the crystal holder 28 with radial symmetry. For example, in the illustrated embodiment, eight crystal sites are arranged around a central axis 50 of the holder, with each site separated from its neighbor sites by an angle 52 of about forty-five degrees, as may be seen in
A crystal holder 28 may have a substantially circular central passage 53 with a size described by radius 51. In some embodiments, passage 53 of the holder may be configured so that the crystal holder 28 sits around the collar 60 the base plate 30. Similarly, the crystal holder's lower surface 54 may be shaped to have a close fit with an upper surface 68 of the base plate. Although difficult to see in
When provided, cooling pipes such as pipes 64 may originate outside the vacuum chamber, cross the chamber pass-through 16, and loop in the base plate 30, as shown in
The base plate depicted in
As depicted, for example, in
As one example, in some vacuum chambers the emitters 17 are oriented such that they are directed at an angle α of about 20 degrees from the vertical rather than being directed vertically (see
Coupling of the Geneva gear only to the crystal holder means that the base plate's position may be substantially static and that its exposure openings may always be in alignment with the emitters. In other words, rotation of the Geneva driver in the illustrated embodiment causes movement only of the Geneva gear and its associated crystal holder, while the base plate remains stationary. Because it is stationary, the base plate, which serves as a shield to protect the crystal holder (and its supported crystals) from the emitters, can be of either simple or highly complex design depending on the required performance parameters and protection needs.
Recalling
An optical component 86 in the optical chamber 84 may serve as a target for a light source 88, with light reflected from the component being received at a light detector 90. Light 92 may be projected from the light source 88, reflected from the optical component 86, and received at detector 90. As noted earlier, measuring one or more properties of the light reflected from, or transmitted through, the optical component can allow a user to determine an amount of material deposited on that component.
Optical chamber 84 may be constructed as a substantially cylindrical body having a chamber radius 94 as measured from an axis 96 oriented along the length of the assembly 12. As is apparent from a consideration of the figures, the optical chamber 84 may be configured with a radius 94 sufficiently small to allow the chamber to reside within base plate passage 58 (and, thus, holder passage 53). In some embodiments, axes 50, 56 and 96 may overlap, meaning the crystal holder 28, base plate 30 and optical chamber 84 are coaxial. In other embodiments, axes 50, 56 and 96 may not overlap (for example, if any of the elements are shaped irregularly, or if the optical chamber is substantially smaller than the base plate and/or crystal holder passages) and/or the optical chamber may be offset from one or more of axes 50 and 56.
An optical component 86 in optical chamber 84 may be exposed to an optical coating until its performance deteriorates to the point at which it no longer can be used as an optical monitor. At this time, an internal switching mechanism (such as a simple sweeper arm, not shown) may be used to remove a used optical component from the stack of optical components, leaving a fresh (unused) optical component for exposure to the light source. An exemplary optical component switcher of this type is the Intellevation Test Glass Changer manufactured by Intellevation Ltd. of Scotland, United Kingdom.
Semi-cylindrical shield 98 may generally be discontinuously cylindrically shaped, meaning that the shield follows a roughly cylindrical path around the optical component assembly but that it does not form an enclosed cylinder. As well, the semi-cylindrical shield may not have a fixed position, but may rest on an upper portion of the base plate 30. In this way, the semi-cylindrical shield 98 may be substantially freely rotated around the glass changer axis 96 of the optical component assembly 12. That the semi-cylindrical shield 98 is not fully closed and is freely rotatable has the benefit that the open portion of the shield 98 may be rotated to provide access to any given crystal site 32 in a crystal holder 28. The semi-cylindrical shield 98 may, of course, be mounted in various other ways and still allow relatively free rotation of the shield and relatively free access to the crystal holder.
As noted, the shielding system 97 may include a static cylindrical shield 100 and static shield plate 102 that protect the bottom of the base plate and prevent emitted coating chemicals from being projected up onto the optical component assembly 12. Because one requirement for proper functioning of the monitoring/controlling assembly 10 is that it receive some amount of the emitted coating chemicals 13 from the emitters 17, the shield plate 102 may include one or more shield tubes 104 that each provide a shield tube passage 106 defining a pathway from an emitter (not shown) to a crystal exposure opening 66 associated with a particular shield tube. Each shield tube 104 is generally coupled to the shield plate 102 so that tube passage 106 is directed along angle β toward the emitters (as discussed above for the base plate), allowing coating chemicals to follow a relatively direct path from an emitter to a sensing crystal at a crystal site 32.
In some embodiments, the static cylindrical shield 100 and shield plate 102 may be coupled via one or more suspension brackets 108 to a support plate 110. For example, an upper portion of a suspension bracket 108 may be welded or bolted to support plate 110. A lower portion of the suspension bracket 108 may be welded or bolted to the static cylindrical shield 100. In this way, shield 100 may be held below the crystal holder 28 and the base plate 30 by the suspension bracket's attachment to support plate 110. Shield plate 102 may, in turn, be kept in place by being welded or bolted to static cylindrical shield 100. Alternatively, shield plate 102 may be welded or bolted directly to suspension bracket 108. Although in each case a shielding component may be described as being welded or bolted to another component, the interacting components may be coupled in any appropriate manner, such as via welding or bolting or through the use of adhesives, friction fittings, etc.
The support plate may be further coupled to a support cylinder 112, providing a stable structure from which the shield system 97 may be suspended. The support plate 110 and support cylinder 112 may be coupled to the optical component assembly 12 or to another portion of the monitoring/controlling assembly 10, or to a portion of the chamber 11. In any case, the assembly including the static cylindrical shield 100, shield plate 102, suspension brackets 108 and support plate 110 may form a “cage” within which the semi-cylindrical shield 98 may rotate.
Free rotation of the shield 98 within its “cage” may allow, as noted above, relatively free access to any given crystal site 32. This ease of access, in turn, may allow a user of the monitoring/controlling assembly 10 to relatively conveniently change out individual crystals from the crystal holder 28. The user may do so by rotating the open portion of the shield 98 to a location in front of a crystal site 32 in which a crystal to be replaced resides. The user may then withdraw the crystal drawer from the crystal site, replace the crystal in the drawer, and then reinsert the drawer to the site, all without major (or any) disassembly of the monitoring/controlling assembly.
The described system elements may be used in a method of monitoring and controlling material deposition. First, as noted in the background discussion, a quartz crystal (or other appropriate crystal) can be used to detect material deposition events, since material deposition on the crystal changes its mass and therefore its resonance frequency. According to the present disclosure, the crystal may be held at one of many crystal sites arranged about a central opening of a crystal holder, with the crystals being rotatably indexed by a Geneva gear mechanism. This mechanism allows a “new” crystal to be moved to a monitoring location above a material emitter when an “old” crystal accumulates so much deposited material that it can no longer accurately reflect deposition events.
Second, the described system may incorporate an optical component to detect material deposition events. Deposition of material on the optical component may change one or more characteristics of the light reflected by or transmitted through that component, and those characteristics can be monitored by a detector. Advantageously, as seen in the illustrated embodiment, the optical component is configured to reside within the central opening of the crystal holder. Constructing the system in this way allows both the quartz crystal and optical monitors to be supported by a single pass-through coupled to a wall of the vacuum chamber, and minimizes the area within the chamber obstructed or utilized by chamber monitoring systems.
In monitoring and controlling material deposition on a target object, a user may place into a vacuum chamber, via a single chamber pass-through, a combined crystal/optical monitor. The monitor may include a crystal holder assembly 14 having a crystal holder 28 and a base plate 30. The combined monitor may include, disposed coaxially or otherwise within a central passage 53 of the crystal holder, an optical chamber 84 of an optical component assembly 12. The user may arrange one or more target objects 18 on one or more planetary assemblies 19 in the vacuum chamber. Finally, the user may couple to one or more emitters 17 one or more materials 13 to be deposited on the target objects.
The user may also index the crystal holder 28 so that one or more of its crystal sites 32, with an associated crystal 42, is exposed to the emitters 17 through an exposure opening 66 of the base plate. The user may also ensure that a fresh (i.e. not previously exposed to a material deposition event) optical component 86 is arranged in the optical chamber 84 of the optical component assembly.
The user may begin the deposition process by causing the emitters 17 to vaporize materials 13 so that they enter the atmosphere of the vacuum chamber and become deposited on the target objects 18, any exposed crystal 42, and optical component 86. The user may monitor deposition of materials 13 onto the optical component 86 and a crystal 42 by monitoring a signal from a light detector 90 (giving the reflection from the optical component) and from the crystal 42 (giving the resonance frequency of the crystal). The user may control the rate of vaporization of the materials 13 by the emitters 17 in response to the change in resonance frequency of the crystal and the extent of material deposition by the change in reflectance from the optical component.
In one embodiment according to the present disclosure, the quartz crystal monitors may function to control a rate of material vaporization from the emitters in response to their being coated via material deposition. In the same embodiment, the optical monitors may be used in conjunction with the quartz crystal monitors, with the optical monitors being used to control an extent of material deposition (i.e. the endpoint of the process) in response to their being coated via material deposition. Alternatively, both the crystal and optical monitors may be used to control deposition rates, or both may be used to signal an endpoint to the deposition process. Furthermore, the roles of the different monitors may be reversed, with the crystal monitors used to signal an endpoint and the optical monitor used to control the deposition rate.
The disclosure set forth above may encompass multiple distinct inventions with independent utility. Although each of these inventions has been disclosed in its preferred form(s), the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense, because numerous variations are possible. The subject matter of the inventions includes all novel and nonobvious combinations and subcombinations of the various elements, features, functions, and/or properties disclosed herein. The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. Inventions embodied in other combinations and subcombinations of features, functions, elements, and/or properties may be claimed in applications claiming priority from this or a related application. Such claims, whether directed to a different invention or to the same invention, and whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the inventions of the present disclosure.
