CN1037703Y - PCVD process for making an approximately dome-shaped dielectric cold light mirror coating and equipment for performing the process - Google Patents

Abstract

The present invention describes a PCAD method for making near-dome-like substrates, in particular reflectors with an inner dielectric cold mirror coating, and a particularly suitable apparatus for implementing the method. A moving body is used to adjust the thickness of the gas layer to be reacted over the surface to be coated so that the degree of homogeneous reaction that occurs in the gas layer during the plasma phase is not detrimental to the desired coating quality. This method can provide a uniform coating of the highest optical quality and mechanical, thermal and chemical stability on the inside and/or outside surfaces of large area and fully dome-shaped substrates of virtually any shape without substrate complexity movement. As with the PPCVD method, a coating thickness distribution with a specific axial and horizontal direction can be superimposed in a known manner by suitably shaping the moving body.

Description

PCVD process for making an approximately dome-shaped dielectric cold light mirror coating and equipment for performing the process

The present invention relates to a plasma chemical vapor deposition method (PCVD method) for preparing an approximately dome-shaped dielectric cold light mirror coating, providing a substrate inner and/or outer surface with a dielectric coating system, and It also relates to a device implementing the method.

Typically the reflector consists of an arched glass substrate, typically dome-like in shape, with an inner reflective coating. The reflective coating may consist of a metallic coating or, on the other hand, a dielectric coating system if a specific spectral change in reflectivity is desired. It is thus possible to manufacture, for example, so-called cold light mirrors, such as those used in dentistry, which have a high reflectivity only in the visible spectral range, but which transmit thermal radiation.

Dielectric coating systems with selective spectral reflectance generally consist of a number of coatings alternately placed on top of another, one with a high reflectance and another with a low reflectance. The details of the construction of such coating systems, how many coating pairs must be arranged, one on top of the other, and how to determine the coating thickness to achieve the desired optical effect, are well known to those skilled in the art and have been described, for example, by HAMacleod, Thin Film Optical Filters, A. HiLger Ltd., London.

Typically, dielectric coating systems are applied to the substrate by means of high vacuum methods such as high vacuum vapor deposition, sputtering or electron beam spraying. In order to obtain a uniform coating on the inner surface of the substrate without complex motion of the highly arched substrate, a "gas scattering method" is usually used (K.Steinfelder et al., Vakuumtechnik 28 (1979), Page 48). In this way, vapor deposition is achieved at elevated additional gas pressure (approximately 10-3 mbar), which acts to block vapor particle self-evaporation by multiple collisions of vapor particles with additional particles The rectilinear motion of the source towards the substrate so that the motion of the vapor particles no longer has any particular direction. In this way it is possible to produce so-called "soft" coating systems consisting of ZnS/MgF2 coating pairs, which are susceptible to machining, and so-called "semi-hard" coating systems consisting of ZnS/SiO2 and ZnS/Al2O3 coating pairs The latter, although resistant to processing, cannot be mechanically loaded.

Besides the gas scattering method, another high-vacuum vapor deposition method is known (HKPulker, Coatings on Class, Elsevier, Amsterdam 1984), in which in order to achieve a uniform coating, the substrate is A double rotational movement is performed on the star-shaped bracket. However, reflectors with the coating systems described above (dome base about 5 cm in diameter) have the disadvantage that they fail very quickly at high atmospheric humidity and are not thermally stable enough to withstand even the commonly used halogen incandescent lamps in Under normal circumstances, the high heat generated cannot even withstand more than 50 watts of electrical power.

Electron beam evaporation in high vacuum produces SiO2/TiO2 coating systems that meet high demands in terms of mechanical, chemical and thermal load bearing capacity and are therefore generally described as so-called "hard" coating systems. However, since such coating systems are quite difficult to manufacture (eg, complex substrate motion, heating of the substrate), these coating systems are more expensive than soft coatings for highly arched substrates several times higher.

It is an object of the present invention to provide a simple and inexpensive method of providing a dielectric and/or a dielectric and/or on the inner and/or outer surface of a large area substrate with a high degree of camber, such as a dome. or metal coating systems with the highest optical quality and mechanical, thermal and chemical stability. In particular, the method is suitable for making reflectors with inner dielectric cold mirror coatings.

Another object of the present invention is to find a device suitable for implementing this method.

As far as the method is concerned, in order to achieve the object of the present invention, a PCVD method is provided according to the invention for the production of an approximately dome-shaped substrate, in particular a reflector with a cold mirror coating of an inner dielectric, on which The inner and/or outer sides of the sheets are provided with a dielectric and/or metallic coating system, characterized in that the thickness of the gas layer to be reacted over the surface of the substrate to be coated is adjusted by means of a moving body, so that in the plasma The degree of homogeneous reaction that occurs in stages ("glass soot formation") does not adversely affect the desired coating quality; the present invention also provides a PCVD method for producing approximately dome-shaped substrates, particularly is to manufacture a reflector with an inner dielectric cold mirror coating, providing a dielectric coating system on the inner surface of a substrate, the substrate having an open dome neck, and the dome base having a diameter of at least 2 cm, It is characterized in that the coating is done in a container, which is assembled by two substrates to form a vacuum tank, the two substrates are air-tightly joined to each other, through a hole in the neck of the dome. The openings feed the reaction gas in a continuous gas flow along the surface to be coated to generate plasma in the entire reaction space bounded by the two substrates; the present invention provides an optimum apparatus for implementing the method of the present invention , characterized in that there is a vacuum tank, a device for mounting one or more substrates in the vacuum tank, and one or more moving bodies, so that their (their) positions in the vacuum tank define the gas to be reacted layer thickness, and it (they) are detachably arranged relative to the surface(s) to be coated, there are gas inlets and outlets in the vacuum tank, which are connected to a gas source or vacuum pump, and which connect them Arranged to allow the passage of the reactive gas in a continuous gas flow along the surface(s) to be coated, and also means for activating a plasma zone in the gas layer to be reacted; for carrying out the method according to the invention, press The present invention also provides an optimal apparatus for coating the inside and/or outside of a substrate, characterized by a vacuum canister which is composed of the dome-shaped substrate and a canister section Formed together, the two are connected in a gas-tight manner, the half side of the edge of the tank is open, and there is a moving body, so that its position defines the gas layer to be reacted in the vacuum tank, the moving body is relative to the tank. The surface to be coated is detachably arranged, and there are also means for fixing a mobile body in the tank part, in the mobile body there is a channel opening on the side of the mobile body facing the surface to be coated at least as much as A gas inlet or gas outlet is open and there are means for connecting the passage to a gas source or a vacuum pump external to the vacuum tank, and there is at least one gas inlet or gas outlet in the tank part, which is connected to a gas source or a vacuum pump. a vacuum pump is connected and together with the gas inlet or gas outlet in the moving body makes it possible to form a continuous flow of the reactive gas along the surface to be coated, and also means for exciting a plasma zone in the gas layer to be reacted; for For carrying out the method according to the present invention, the present invention provides another optimal apparatus which Ready for coating the inside of a substrate having an open dome neck, characterized by a vacuum tank consisting of the dome-shaped substrate and a half-side open tank part, the substrate and the tank part being The edges are assembled and gas-tightly connected, and a moving body, whose position in the vacuum tank defines the gas layer to be reacted, is removably positioned relative to the surface to be coated, and Means for mounting a moving body in the tank part, in which there is also a gas inlet or gas outlet for supplying or removing the reactive gas which can be supplied or removed through the dome neck of the opening, and also for A device for exciting a plasma region in a gas layer to be reacted.

In the manufacture of optical fibers, the PCVD method commonly used for coating the inside of tubular glass blanks is known per se. For example, there is a basic description on page 122 of the journal "Optical Communications", Vol. 8 (1987).

As far as these methods are concerned, the plasma pulsed CVD (Chemical Vapor Deposition) method (in this regard, see, for example, the journal "Optical Communications", Vol. 8 (1987), p. 130) is particularly suitable for producing optical properties with defined optical properties. dielectric coating system. The plasma pulsed CVD method makes it possible to produce extremely thin uniform coatings on substrates, all the way down to monomolecular coatings.

in the content of the invention

Here, the term "plasma CVD method" includes plasma pulsed CVD methods. Even the plasma pulse CVD method is well used.

The coatings produced by the PCVD method feature not only high optical quality, but also excellent chemical, mechanical and thermal stability. They possess these beneficial properties due to the properties of solid materials that they actually possess in terms of stoichiometry and morphology.

The present invention takes advantage of the fact that the PCVD method itself is particularly suitable for coating parts with complex shapes due to its strong scattering effect. Uniform coatings can be achieved by these methods without having to rotate or move the substrate in some other way. Leaving aside this advantage, so far only small-area, high-camber domed substrates have been coated with PCVD.

For example, European Patent Specification 0,017,296 describes a PCVD method for the manufacture of spherical microlenses, in which a glass plate is provided with grooves about 35 [mu]m deep to accommodate the lens. During the ensuing coating, a plasma region is created across the glass sheet that extends just into the groove. As a result, a coating material is deposited not only on the surface of the glass sheet but also in the grooves, by changing the composition of the reactive gas during coating, it is possible to produce a desired coating in the deposited coating in a manner known per se. Distribution of reflection coefficients. As disclosed above, coating is only stopped when the grooves are completely filled with coating material. According to some further process steps (planar grinding of the surface and bonding to another coated plate, in each case combining the two hemispheres to form a sphere), the coated glass plate was removed from the Produces spherical lenses embedded in a glass frame.

However, it is not possible to generalize the above method to coating substrates with very large cambers of considerable size (~5mm at the base of the dome), for example, cannot be used for dome-like, rounded substrates in most general-purpose applications. On a reflector surface with a top base diameter of at least 20 mm, this is because the thickness of the plasma region suitable for coating is usually limited to a few tens of mm above the surface to be coated, so the plasma cannot surround the surface to be coated. Coat the entire object on that side, which is necessary to produce a uniform inner or outer coating. For larger thickness plasma regions, not only at the interface of the substrate/gas space, but also in the entire gas space of the so-called homogeneous reaction is formed in the form of glass soot deposited on the surface of the substrate and added to the deposition The chance of accumulating particles in the coating is also increased. This greatly impairs the quality of the coating and renders the coating unusable.

The method according to the invention is described below with an example of a coating on the inside of a substrate, which is particularly useful for applications such as the manufacture of reflectors. Without substantial limitation, the following description is also valid for the coating of the outside of the substrate according to the method of the present invention. In particular, the devices described for the inner coating can be transferred to the outer coating in a simple manner by arranging the substrate in reverse and a suitably shaped moving body. The only exception is a method that is specifically suitable for medial application.

In order to apply an approximately dome-shaped substrate (also referred to as a dome in the following) on the inside, according to the invention a so-called moving body is placed in the half-open space bounded by the dome-shaped substrate and The surface to be coated is spaced apart and removably positioned relative to the surface. By means of this moving body, the thickness of the gas layer to be reacted over the surface to be coated is adjusted so that the degree of homogeneous reaction that occurs in the plasma phase (“glass soot formation”) is dependent on the desired coating quality will not have adverse effects.

Generally, the coating quality of the dielectric interference coating system making the reflector will be good enough if the separation distance does not exceed 20mm. On the other hand, this distance should not be made less than 2 mm, because otherwise too high demands are placed on the accuracy of the positioning of the moving body.

In order to achieve the coating, the reaction gas is fed into the reaction space in a manner known per se and the plasma forming the coating is excited.

The reactive gases used in the PCVD method are usually metal chlorides, metal organic compounds, oxygen, nitrogen, and ammonia. For depositing "hard" SiO2/TiO2 coating systems suitable for reflectors with a luminescent silver luster, SiCl4 and TiCl4 can be used as reactive gases in addition to oxygen. The disadvantage of using SiCl4, however, is that high substrate temperatures are required to prevent chlorine from entering the coating. For coating domes by the method of the present invention, hexamethyldisiloxane is preferably used instead of SiCl4, since this eliminates the need for high substrate temperatures and is therefore more economical.

For activating the plasma, all methods known for this purpose are suitable, for example high frequency, low frequency, microwave, direct voltage or pulsating direct voltage excitation. High or low frequency excitation can be capacitive, or inductive.

In the method of the present invention, microwave excitation is preferred. The advantages of microwave excitation are: low risk of radiation damage to deposited coatings, plasma power necessary for a process decreases with increasing frequency, microwave plasma emission efficiency is high and over a wide range of pressures (approximately 10 -3 to 50 mbar) are operable.

In addition to these more general advantages applicable to each PCVD method, the use of microwave plasma for the method of the present invention has particular advantages, since the plasma region is confined to the smallest possible volume, the use of low Inexpensive components that consume power, such as magnetrons, act as microwave generators. Thus, for example, during the coating of small domes with a diameter of the dome base not greater than 50 mm, the electrical power supplied by one magnetron (100 watts) is sufficient to excite and maintain the plasma regions in at least 4 domes.

For the inner coating of the reflector, glass substrates are preferably used. Although the method according to the invention can in principle be fully used for coating plastic substrates, most plastics are not suitable for use as reflectors due to their generally low thermal load bearing capacity. In addition, the above-mentioned coating systems adhere better to glass than to plastics, especially under thermal loads.

Since the positioning of the moving body is relatively simple, the method of the present invention is particularly suitable for coating highly arched substrates with rotationally symmetrical shapes, such as domes, or objects with elliptical or parabolic shapes. By suitably shaped moving bodies, irregularly shaped substrates, such as elongated dome-shaped substrates, such as those used in the manufacture of dental mirrors, can also be applied without difficulty.

The method of the present invention makes it possible to coat multiple substrates simultaneously in one container. To limit the volume of the reaction space, it is convenient to counter-sink a plurality of domes in suitable grooves on the substrate holder or eg in the base plate of the vessel, with their openings facing the interior of the reaction space. Preferably, the lid of the container is provided with a raised structure which cooperates with the structure of the substrate, and when the container is closed, the projection of the lid sinks as a moving body into the cavity defined by the substrate. However, in order to adjust the thickness of the gas layer to be reacted, it is preferable to arrange the moving body by means of suitable supports so that the separation distance relative to the surface to be coated is variable. According to this configuration, the new reactive gas and the reactive gas discharged from the coating material can pass through the gas inlet and gas outlet located on the side wall of the container and connected to one or more gas sources or vacuum pumps outside the container to be substantially parallel to the gas inlet and outlet. A continuous air flow of the surface to be coated is passed through the container.

In the case of capacitive excitation consisting of the metal cover plate and the base plate of the container, the above structure is applicable, especially for depositing metal coatings or hybrid coatings consisting of a metal and a dielectric, for example It is also applicable that the transition from a purely metallic coating to a purely dielectric coating occurs continuously.

For the manufacture of reflectors with cold light mirrors, press-formed glass substrates are usually used, which are provided in advance with lamp connection points, so-called dome necks, for electrical connections on the outer domed surface of the substrate . Before coating, the substrate is subjected to a cleaning step that includes certain cleaning processes, such as flowing a cleaning solution through the dome. Such cleaning processes must remove the seal created by the molding at the neck of the dome after pressing. agent.

When coating these so-called open domes, each dome is preferably supplied individually with fresh reactive gas during the deposition process using the opening in the neck of the dome. This avoids coating thickness variations from dome to dome, which would otherwise occur due to a gradual increase in reactive gases emitted from the coating material in the direction of the gas flow. The spent reaction gas can be withdrawn through the opening in the side wall of the container.

As for closed domes, it is proposed to supply each dome with a new reactive gas through an appropriate channel in the moving body. However, the open dome can also be supplied with new reactive gases in this way.

If multiple substrates are to be coated simultaneously in a container, in addition to the substrates, the walls of the container are inevitably also coated. This not only leads to a higher consumption of coating material, but also has the further disadvantage that, depending on the coating thickness and material in a coating process, as well as on the requirements for coating quality, the container must also undergo an expensive cleaning steps. This cleaning cannot always be done so thoroughly that virtually none of the original old coating residue sticks to the wall. During subsequent coating processes these residues may separate from the walls and deposit in the form of microscopic particles on the inside surfaces of the substrates to be coated, thus rendering the coating of these substrates unusable.

To avoid these problems, in one version of the preferred method, each substrate is coated one by one, and each substrate itself is used simultaneously as part of the vacuum tank. For this purpose, the dome-shaped substrate is combined and hermetically joined to form a closed container with an appropriately sized canister having half-side openings, such as a glass tube melt-sealed at one end. As long as both parts are made of glass, it is generally sufficient for an airtight connection to join the polished edges to each other and to vacuum the tank. The tightness is further improved if an O-ring made of Viton or Silicone rubber is placed between the two tank sections. However, the use of sealing rings made of organic materials limits the substrate temperature to about 200°C, and fluorocarbon resins and fluororubbers can withstand continuous temperatures up to 260°C.

In a method of the type described above, it is convenient to confine the plasma to the interior space of the dome during coating. Thus, the can portion added to the dome is only slightly coated at the same time as coating, so either a cleaning step is not required, or if a simple cleaning step is to be performed the can be reused for coating subsequent domes tank part. Since a part of the vacuum tank is always renewed in any case of changing substrates, cleaning costs are greatly reduced compared to coating substrates in a container. In order to be absolutely certain that the coating is not damaged by coating particles detaching from the walls of the re-used can part, the vacuum can is positioned so that the dome is as high as possible over the re-used can part during coating maintain a vertical position.

The moving body is suitably spaced and removably mounted with respect to the surface to be coated on the tank wall applied to the substrate, for example by means of a glass tube fused to the tank wall, Its free end carrying the moving body faces the inner space of the substrate. For example, the moving body can be screwed or inserted into the end of the glass tube. This has the advantage that the distance of the moving body relative to the inner surface of the substrate can be easily adjusted in the event of replacement of the substrate.

Depending on whether the dome to be coated has a closed or an opening, the feeding of the reaction gas to the neck of the dome varies.

When coating a closed dome, the reactive gas is passed in a continuous gas flow along the surface to be coated, through the gas inlet or gas outlet in the tank section added to the dome, and through the moving Another gas outlet or gas inlet in the body on the side facing the surface to be coated, which side is connected via a channel in the moving body to a gas source outside the vacuum tank or to a vacuum pump. Preferably for this purpose the moving body is mounted so that the passage of the moving body is continuous in the glass tube leading to the outside and carrying the moving body.

For reasons of flow technology, the gas flow direction is preferably chosen so that new reaction gas is introduced into the reaction space through channels in the moving body, while the reaction gas discharged in the coating material passes through the tank part which is connected to the dome. The gas outlet is excluded. With airflow in the opposite direction, it is difficult to maintain the low pressure required for coating within the container due to the pressure drop in the nozzle of the moving body.

The above air flow directions are recommended, especially if substrates that are not rotationally symmetrical are to be coated. Since in this case it is extremely difficult to produce exactly the same flow conditions for the reactive gases at every point on the surface to be coated, to obtain a uniform coating, it is most convenient to Fresh reactive gas is fed into the reaction space, these gas inlets are evenly distributed on the end face of the moving body opposite the surface to be coated, and are connected via a central channel in the moving body to a gas source outside the vacuum tank.

These conditions become especially simple when coating open domes. In this case, the gas flow need not be fed through the moving body, but the open dome neck itself can be connected to a suitable feed line connected to a gas source or vacuum pump. There is no optimum direction for the direction of airflow in this embodiment.

In the case of an "open" dome, it may be beneficial to seal the neck of the dome and effect application in a similar manner to a closed dome. The equipment used to coat the closed dome may be relatively simple to seal for mass production, since each vacuum tank has to be sealed in only one place.

For "open" domes that are not overly large, eg no greater than 20 mm in diameter at the base of the dome, the reaction space volume is still small enough to achieve coating without moving the volume. According to the invention, in this case, conditions are provided for the coating to be carried out in a container which consists of two domes combined to form a vacuum tank and which are connected to each other in a gas-tight manner. In this case, let the reactant gas flow through the necks of the two open domes. In this type of method, if a pulsed method is used, the closer the shape of the substrate is to a hemispherical shape, the more uniform the coating will be.

In the method according to the invention, substrate temperatures customary in PCVD methods can be established. The limit in this regard is mainly determined by the thermal resistance of the substrate material. It is well known that higher substrate temperatures result in greater densities of deposited material, so higher substrate temperatures are preferred if there are special requirements for the mechanical, thermal, and chemical stability of the coating.

When coating the domes for the production of reflectors, the substrate temperature is preferably between room temperature and 200°C. The quality of the coating thus obtained is good enough for use as a reflector and the method is economical. Another advantage is that without additional heating, plasma pretreatment alone, such as gas discharge of O2, can establish substrate temperatures in this order of magnitude, allowing the substrate surface to be coated prior to actual coating. Achieving the desired state typically involves the use of the above-mentioned plasma pretreatment. The length of plasma pretreatment time also determines the temperature reached by the substrate.

The moving body is conveniently fabricated from materials that are dimensionally stable and usable at least in vacuum up to the selected substrate temperature. "Vacuum usable" here means that at the selected temperature the material does not evolve any gas that would be detrimental to the process. This involves two aspects, one is the possible pressure deterioration, and the other is the concentration of substances that damage the coating quality in the atmosphere within the vessel.

For the above-mentioned coating, it is sufficient if the moving body consists of a material that is dimensionally stable, usable in a vacuum at temperatures up to about 200°C, and resistant to substances generated in the discharge. Materials that meet these requirements are, for example, metallic materials, such as Al, Ti, stainless steel, or dielectric materials, such as glass, ceramics, glass-ceramics, or even plastics, especially fluorocarbon resins, preferably polytetrafluoroethylene.

The coating is preferably carried out at a pressure in the vessel of 0.03 to 10 mbar. At pressures less than 0.03 mbar, the coating speed is significantly reduced so that the method can no longer function economically. Furthermore, the plasma may not be stable enough, with the result that more expensive magnetic field assisted methods must be used. Although high pressure is beneficial for coating speed, as pressure increases, so does the probability of a homogeneous reaction. As a result, the distance between the moving body and the substrate must be appropriately reduced. In order not to operate at too small a distance, it has proven beneficial not to increase the pressure above 10 mbar.

In the PCVD process, the plasma is typically generated at low power to convert only about 1% to 4% of the reactant gas into the coating material. This recovery is the result of a compromise between the cost-effectiveness of the process and the risk of non-uniform coating that the reactive gases pass over the surface to be coated too violently in the coating material The result of emitting reactive gases.

The coating is preferably carried out by plasma pulsed CVD, in which case the coating is carried out on an area element of a portion of the substrate surface in the gas volume - the number of particles forming, in a manner known per se, is Each point of the substrate determines the thickness of the coating deposited on that area of the substrate surface during a plasma pulse. Thus the utilization of the reactive gas is improved, even including the complete discharge of the gas during one plasma pulse, so the deposition rate is much higher than that of the continuous wave method, not only that, the plasma pulse CVD method has another advantage, That is, by means of the shape change or arrangement of the moving body, a coating thickness distribution with specific axial and horizontal directions can be produced.

Thus, when a dome is used as a reflector, for example, it is generally desirable to produce a uniform reflective color in a plan view of the dome viewed from the front of the entire reflector surface, regardless of the central arrangement within the dome. How the angle of incidence of the light emitted by the light source is different.

Bearing in mind the fact that the interference phenomenon that produces a particular reflected color is related to the path of light as it travels through the individual layers of a dielectric coating system, the necessary coatings to produce a uniform reflected color can be easily determined using simple geometric relationships. A functional relationship between the layer thickness distribution and the shape of the inner surface of the substrate, and converting the above thickness distribution into a "spacing distribution" between the inner surface of the substrate and the moving body. In this respect, it is recommended that the pressure loss of the reaction gas in the flow direction be taken into account when determining the spacing distribution.

The advantages that can be obtained with the aid of the invention are in particular that for the production of, for example, the inner coating of highly arched substrates of reflectors, a reliable coating method known to the advantage of PCVD can also be used. Apply method. The use of the PCVD method makes it possible to have a uniform, high optical quality, and also mechanically, chemically, and thermally stable coating for domed substrates of virtually any shape, with a high degree of camber, without the need for substrate motion, if Using the plasma pulse method, a suitably shaped moving body can be superimposed with a coating thickness distribution with a specific axial or horizontal direction.

During each coating of a substrate, virtually no other surface is coated except for the substrate and the moving body, which are also part of the reaction vessel. Coating can be accomplished within a pressure range that is easily controllable and inexpensive. The conversion of the reactive gas into the coating material can be practically complete, as a result of which not only optimum utilization of the reactive gas is possible but also a high coating speed. If the intensity of the excitation field exceeds a (easy to determine) threshold at which the value converted into the coating material reaches its maximum value, local irregularities in the excitation field, such as microwave fields, are observed in the plasma pulse method. In this case, it is not always necessary to deviate the coating thickness from a predetermined value.

The invention and the advantages that can be obtained are described in more detail below with reference to a specific schematic diagram and two specific embodiments. in:

Figure 1 is a schematic longitudinal cross-section of an apparatus for coating a plurality of domes in a vessel using the plasma pulse method of the present invention; Figure 2 is an apparatus of the same representation for coating a A single dome with a closed dome neck; Figure 3 shows a device for coating a single dome with an open dome neck; Figure 4 shows a moving body designed as a gas injector , for coating a substrate of a rotationally asymmetric shape; Figure 5 shows the apparatus derived from Figure 2, where the dome is surrounded by another vacuum tank to avoid damage caused by leakage; and Figure 6 shows two small Hemispherical domes that combine to form a vacuum tank for application without moving bodies.

In Fig. 1 a plurality of domes 1 can be seen, which are placed one after the other in a grid on the base plate 2 of the container 3 so that the plasma pulse method can be used for coating. In order to keep the volume of the reaction space as small as possible, the dome 1 is sunk into the mounting recess 4 in the base plate 2 . The cover plate 5 of the container 3 has a plurality of mobile bodies 6 which sink into a cavity 8 bounded by the dome-shaped inner surface 7 to be coated, ie to cooperate with the grooves 4 in the base plate 2 . For supplying the reactive gas, each moving body 6 is provided with a central channel 9 which can be connected to a gas source not shown in the figure. It is on the side wall of the container 3 that a plurality of gas outlets 10 are provided, through which the reaction gas discharged in the coating material can be sucked off by means of a vacuum pump (not shown in the figures).

The distance between the inner surface 7 of the dome and the side 11 of the relative moving body 6 opposite it is determined so that the particle formation process in the gas space between the two surfaces during a plasma discharge does not impair the quality of the coating . Furthermore, in the embodiment shown, in order to compensate for the pressure drop of the reactive gas in the direction of gas flow in order to obtain a uniform coating, the end of each dome 1 at the gas outlet end (ie at the edge of the dome) The moving body 6 is made wider than the dome neck at the gas inlet end.

The device for generating the plasma zone in the vessel is known per se and is therefore not shown in the figures. Thus, for example, the base plate and the cover plate of the container can be made of one metal and a plasma can be excited capacitively by applying a voltage between the two plates. With this arrangement, both a coating of a dielectric material and a coating of a metallic material can be deposited, as well as a mixed coating of a dielectric material and a metallic material. Likewise, a microwave antenna can be placed above the cover plate or below the substrate of dielectric material, and the plasma can be excited and maintained by irradiation with microwave energy.

To implement the coating method, the reaction gas is fed in a continuous gas flow through the moving body 6 into the cavity 8 bounded by the inner surface 7 of the dome and the moving body 6 . In this way, after the air flow enters the cavity 8 bounded by the dome, it turns back at the neck 12 of the dome and exits the dome 1 again transversely along the surface to be coated and the moving body 6 (continuous drawing in the figure). arrows indicate the direction of airflow). As a result of activating a gas discharge, the coating material is deposited on the inner surface 7 of the dome and on the surface of the moving body 6 , and on the entire inner wall of the container 3 . The length of time between the two plasma pulses and the flow rate of the gas are properly coordinated (as is usual in plasma CVD methods) so that the reaction space above the inner surface of the dome is completely refilled before each plasma pulse New reactive gas.

By changing the composition of the gas in a manner known per se, it is possible to deposit thin layers of different compositions on top of each other, one layer on top of the other.

To heat the substrate, the apparatus shown in Figure 1 can be placed in a furnace. It is simpler to bring the substrate to the desired substrate temperature by means of plasma pretreatment techniques.

Figures 2 and 3 show the apparatus for coating individual domes. As can be seen from the figures, in each case the dome 1 is always combined with a half-open can 13 to form the container 3 . A gas-tight connection is achieved by a sealing ring 14 between the edges of the two tank parts.

The apparatus in Figure 2 is suitable for the application of domes with closed dome necks. The reaction gas is supplied through a gas inlet 15 added to the tank portion 13 of the dome.

The gas supplied follows the surface to be coated through the moving body 6 to the dome neck 12, at which point it turns back and is sucked out through the channel 16 in the moving body 6 and the cornered glass tube 17, which supports the moving body 6 and connected to a vacuum pump not shown in the figure. In order to fix the moving body, it is also possible to use a straight glass tube which is placed axially in the vacuum tank and melted into the tank wall opposite the dome. The supply of gas in this case can take place, for example, through a number of gas inlets gathered around the melting point. The airflow directions described above are beneficial if there is concern that the coating material will clog the passages 16 .

In the device shown, the plasma is excited by irradiation with microwave energy. For this purpose, the dome 1 is fitted with a waveguide 18 whose outer conductor 19 extends just to the edge of the dome and whose inner conductor 20 terminates just in front of the closed dome neck 12 . With this structure, the plasma region can be easily confined within the reaction space 21 bounded by the inner surface 7 of the dome and the end face 11 of the moving body 6 . It is true that in these cases the plasma also extends partially into the channel 16 in the moving body 6; however, since only the reactive gases discharged in the coating material are fed through this channel, the coating material is largely avoided Progressive blockage of openings and passages.

Other aspects of this coating were performed as previously described.

The apparatus shown in Figure 3 was used to coat domes with open dome necks. In this embodiment, the main way of realizing the coating is similar to the embodiment shown in FIG. 2 . One difference is that the spent reaction gas is removed not by the moving body 6 but by the open domed neck 12 . For this purpose, a glass tube 22 connected to a vacuum pump is mounted on the dome 1 from the outside, and the glass tube 22 is securely sealed from the external space by means of the sealing ring 14 . For example, the plasma can be excited by irradiation of microwave energy (see arrows drawn in dashed lines) by means of microwave antennas (not shown) that are laterally focused around the dome.

The moving body 6 in FIG. 2 does not necessarily have to have a central channel 16, but as shown in FIG. 4, it can be provided with some small channels 23 (_≤1 mm) evenly distributed over the entire surface, such as a sinter.

In order to avoid failure due to leaks at the dome seal 14, it may be beneficial to provide a second vacuum tank 24 on the dome as shown in Figure 5, incorporating a vacuum that neither interacts with the dome material but is itself A coating gas (eg, O 2 ) that does not participate in the plasma is added to the vacuum tank 24 . When the size of the leak is constant, the smaller the pressure difference between the inside and outside of the dome, the smaller the amount of gas flowing into dome 1. The pressure in the vacuum tank 24 is preferably adjusted precisely so that a plasma (P≧50 to 100 mbar) is not excited in the plasma coating of the inner surface 7 of the dome at this pressure.

The above measures may be important in the case of simultaneous coating of many domes by the same gas supply system. Without this measure, a single leak could jeopardize the coating of all domes.

Two small hemispherical domes 1 can be seen in FIG. 6 , which are combined to form a vacuum tank 25 . Since the vacuum tank 25 is spherical, there is the same amount of gas per area element of the substrate surface. Therefore, if the plasma pulse CVD method is used, a uniform coating can be ensured even without moving bodies. The volume defined by the two domes is small enough to exclude the homogeneous phase in the gas space from adversely affecting the coating quality.

In the embodiment shown, the gas flow is produced through the open dome neck 12, and similar to the apparatus of FIG. 3, gas inlet and outlet pipes 26, 27 are added to the neck 12 in a gas-tight manner. In this version, the plasma can also be excited in a simple manner by irradiation with microwave energy by means of microwave antennas that are concentrated laterally around the vacuum vessel.

It can be easily seen from these figures that, in principle, the applicator body and the moving body can be substituted for each other. For example, in the embodiment shown in FIG. 3 , the dome to be coated can be moved to the position of the moving body, so as to achieve the purpose of external coating. In order to avoid simultaneous internal and external coating, it is only necessary to ensure that the inner space of the dome is free of any coating material. For this purpose, the dome can be, for example, part of another vacuum tank placed in the container.

The apparatus shown in Figure 2 is particularly suitable for coating domes in mass production, since the vacuum tank needs to be sealed in only one place. It is recommended that multiple vacuum tanks be placed in contact with the dome, always one after the other in a grid. The gas supply and the connection to the vacuum pump take place via a common feed line system.

For coating, the dome is mounted on a permanently fixed vacuum tank hemisphere, using a sealing ring if necessary, and the vacuum tank so formed is evacuated. In a simple manner, the plasma can be excited by irradiation with microwave energy by means of, for example, a waveguide mounted on top of a dome. After coating, the vacuum tank was vented, after which the coated dome could be fully lifted and replaced with a new substrate.

Example 1 The pressed edge of a dome made of borosilicate glass No. 8486 produced by the Schott Glaswerke factory, having a diameter of 50 cm, was applied to a tube also having a diameter of 50 cm. A Viton O-ring placed on the polished end of the tube ensures a gas-tight connection between the tube and the dome. The tube is made of a dielectric material, in the present case borosilicate glass No. 8330 produced by the Schott Glaswerke factory. The reaction gas can be fed into the reaction space formed in this way through a glass tube with a diameter of 10 mm which is fused laterally into it. The spent reaction gas is removed through a cone at the end of the tube. Its dimensions can be derived from Figure 2, which is drawn on a 1:1 scale. The gas inlet tube is angled along the axis of the larger tube; it terminates at an axially perforated Teflon moving body. The diameter of the hole is 5mm; but this value is not very critical. The reaction gas can enter the reaction space through this hole. The shape of the moving body is such that the distance between its surface and the inner surface of the dome is the same everywhere, ie 7 mm except for the neck area of the dome.

In order to bring the inner surface of the dome to be coated in the desired state, a gas discharge of O2 is excited in the reaction space formed by the dome and the moving body before coating. The desired substrate temperature is established by the intensity and duration of the O2 gas discharge. Microwave energy is radiated from above to the dome by a microwave antenna.

The gas discharge parameters of O2 are specified as follows: Mass flow of O2 (ml/min): 200 Pressure in vessel (mbar): 0.7 Pulse duration (ms): 0.6 Inner pulse period (ms): 20 Microwave frequency (GHz ): 2.45 Average microwave power (Watts): 75 Substrate temperature (°C): 90 Then, the microwave irradiation was interrupted and the gas mixture was adjusted to produce the first TiO2 coating. This gas mixture is first allowed to flow into the branch line for about 0.5 minutes; then the mass flow becomes stable. The cooling of the dome during this period was not significant.

A TiO2 coating was produced with the following parameters: TiCl4 flow rate (ml/min): 3 λ = 550 nm λ/4 coating application time (sec): 25 Other parameters were unchanged compared to the O2 gas discharge parameters.

The microwave irradiation is then interrupted and the gas mixture is adjusted to produce the first SiO2 coating; the SiO2 coating is produced by means of a steady mass flow (see above).

The process parameters are as follows: C6H18OSi2 flow rate (ml/min): 3.6 λ=550nm λ/4 coating coating time (seconds): 25 Other parameters have not changed compared with the gas discharge parameters of O2.

Alternately adding a total of 31 TiO2/SiO2λ/4 coatings and adjusting their thicknesses according to existing optical standards, the resulting interference coating system is a so-called cold light mirror. Example 2 A 50 mm diameter dome made of borosilicate glass No. 8486 manufactured by Schott Glaswerke was placed on the lower electrode of a 13.56 MHz plasma generator in a vessel. The upper electrode is designed as a gas sprayer and moving body. At each point on the substrate, the distance between the moving body and the inner surface of the substrate to be coated was 15 mm.

The vessel was evacuated to 0.03 mbar, at which pressure the dome was pretreated with a gas discharge of O2. Then, the coating was achieved at the same pressure; for this, a mass flow was established: 1 ml/min of TiCl4 and 35 ml/min of O2, and a TiO2 coating was applied at a high frequency power of 50 watts. C6H18OSi2 (hexamethyldisiloxane) at a flow rate of 0.5 ml/min and O2 at 35 ml/min were then determined to be established, and a SiO2 coating was applied at a high frequency power of 50 watts.

Thirty-one TiO2/SiO2λ/4 coatings were applied alternately, the thickness of which was adjusted according to known optical standards, so that the interference coating system was a cold light mirror.

Claims (11)

1. a PCVD method (plasma chemical deposition method), for the manufacture of an approximate dome-shaped dielectric cold light mirror coating, the coating system of dielectric is provided on the inner and/or outer surface of its substrate, it is characterized in that The thickness of the gas layer to be reacted on the surface of the substrate to be coated is adjusted by means of a moving body, and the thickness of the gas layer to be reacted is adjusted to 2 to 20 mm. 2. A method as claimed in claim 1, characterized in that the moving body used to adjust the thickness of the gas layer to be reacted is made of a material that is dimensionally stable and usable in a vacuum at temperatures up to 200[deg.]C. 3. A method as claimed in claim 2, characterized in that the moving body for adjusting the thickness of the gas layer to be reacted is made of a metallic material, in particular Al, Ti, stainless steel, or of a dielectric material made of, especially glass, ceramic, glass-ceramic, or of a plastic, especially fluorocarbon resin. 4. An apparatus for carrying out the method according to at least one of claims 1 to 3, characterized in that there is a vacuum tank 3 in which one or more dome-shaped substrates are installed 1, one or more moving bodies 6 so that its (their) position in the vacuum tank 3 defines the thickness of the gas layer to be reacted, and it (they) relative to the surface to be coated (one or more A) 7 are removably arranged, there are gas inlets and outlets in the vacuum tank 3, which are connected to a gas source or vacuum pump, and they are arranged so that the reaction gas can flow in a continuous flow along the surface to be coated ( one or more) through, and means for activating a plasma region in the gas layer to be reacted. 5. A device for carrying out the method according to at least one of claims 1 to 4 for the inner and/or outer coating of a substrate, characterized in that there is a vacuum tank 3, which It is formed by a combination of a dome-shaped substrate 1 and a tank part 13, which are connected in an air-tight manner, and then the half side of the edge (the tank part 13) is opened, and there is a movable body 6, which makes it The position defines the gas layer to be reacted in the vacuum tank 3, the moving body 6 is detachably arranged with respect to the surface 7 to be coated, and there are also means for fixing the moving body 6 in the tank part 13, in There is a channel 16 in the moving body 6, the opening of the channel 16 on the side 11 of the moving body 6 facing the surface to be coated is open to at least one gas inlet or gas outlet, and there is a connecting channel 16 with the outside of the vacuum tank 3. A gas source or vacuum pump connected device, there is at least one gas inlet or gas outlet in the tank part 13, which is connected to a gas source or a vacuum pump, and together with the gas inlet or gas outlet in the moving body 6 makes the reaction gas A continuous flow along the surface to be coated becomes possible, as well as means for exciting the plasma zone in the gas layer to be reacted. 6. The apparatus of claim 5, wherein a pipe 17 connected to a gas source or a vacuum pump is allowed to extend into the wall of the tank part 13 for supplying or removing the reaction at its end protruding from the vacuum tank 3 Gas, at the other end of the tube 17 facing the inner space of the substrate, a moving body 6 is arranged so that it can move in the axial direction, and the passage 16 in the moving body is continuous in the tube 17. 7. Apparatus according to claim 6, characterized in that the pipe 17 is connected to a gas source for supplying the reaction gas. 8. The apparatus of claim 6, characterized in that the pipe 17 is connected to a gas source for supplying the reaction gas, and the moving body 6 is designed as a gas injector at that end of the moving body 6 that faces the surface 7 to be coated . 9. A device for carrying out the method of at least one of claims 1 to 4 for coating the inside of a substrate with an open dome neck, characterized by a vacuum tank 3. It is composed of a dome-shaped substrate 1 and a tank part 13 with a half-side opening, the substrate 1 and the tank part 13 are combined together at the edge and air-tightly connected, and there is a moving body 6, which changes it. a distance position in order to define the gas layer to be reacted in the vacuum tank 3, the movable body 6 to be removably arranged with respect to the surface 7 to be coated, and the means for mounting the movable body 6 in the tank part 13, There is also a gas inlet or gas outlet 15 in the tank part 13 for supplying or removing the reactive gas which can be supplied or removed through the dome neck of the opening, and also for exciting the plasma in the gas layer to be reacted body area device. 10. Device according to at least one of claims 4 to 8, characterized in that the moving body 6 consists of a dimensionally stable material that can be used in vacuum at temperatures up to 200[deg.]C. 11. Device according to claim 10, characterized in that the moving body 6 consists either of metallic materials, in particular Al, Ti, stainless steel, or of dielectric materials, in particular glass, ceramics, glass-ceramics, or of plastics, in particular Fluorocarbon resin composition.