METHOD AND DEVICE FOR THE OUTER-WALL AND/OR INNER-WALL COATING OF HOLLOW BODIES

Abstract

Apparatus and method for outer wall and/or inner wall coating of hollow bodies made of an electrically nonconductive material in which the hollow body is inserted into a process chamber which is divided by the hollow body into an internal and external reaction space, wherein at least one process gas is introduced into one of the two reaction spaces under a process pressure, and a plasma is generated in the reaction space and fragments and/or reaction products formed in the plasma from the at least one process gas are deposited to form a layer on the side of the wall of the hollow body that faces the plasma, the plasma being influenced with regard to at least one operating parameter by a magnetic field that permeates the two reaction spaces.

Claims

1. A method of outer wall and/or inner wall coating of a hollow body made of an electrically nonconductive material, comprising inserting the hollow body into a process chamber which is divided by the hollow body into an internal reaction space and an external reaction space, introducing at least one process gas into one of the two reaction spaces under a process pressure while the other of the two reaction spaces is being kept at a pressure of less than or greater than the process pressure, and generating a plasma in the reaction space into which the process gas has been introduced while keeping that reaction space under process pressure, whereby fragments and/or reaction products formed in the plasma from the at least one process gas are deposited to form a layer on the side of the wall of the hollow body that faces the plasma, wherein the plasma is influenced with regard to at least one operating parameter by means of an active magnetic field that permeates the two reaction spaces.

2. The method as claimed in claim 1, wherein a parameter influenced by the active magnetic field is at least one of the following: a. homogeneity of the plasma viewed at a constant distance along the wall of the hollow body to be coated, where greater homogeneity under the action of the active magnetic field is achieved compared to a plasma without an active magnetic field, b. energy density of the plasma where a greater energy density is achieved under the action of the active magnetic field compared to a plasma without an active magnetic field, c. spatial position of the plasma where the plasma, by the action of the active magnetic field, is kept at a greater distance from a wall of the process chamber and/or elements in the process chamber compared to the distance without an active magnetic field.

3. The method as claimed in claim 2, wherein the active magnetic field is generated by superimposition of the magnetic fields of multiple magnetic field-generating elements comprising multiple coils or permanent magnets.

4. The method as claimed in claim 3, wherein magnetic field lines of the active magnetic field, by powering of the coils in a manner dependent on the hollow body shape, are matched in terms of their profile at least in regions to the profile of the wall of the hollow body to be coated.

5. The method as claimed in claim 3, wherein at least two groups of the coils are used successively in time to generate the same plasma-influencing magnetic field with a temporary overlap in the powering of the two groups.

6. The method as claimed in claim 3, wherein at least one sensor is used to contactlessly detect spatial position of the plasma generated while the influence by the magnetic field is being detected, and at least one the magnetic field-generating elements is actuated depending on the data detected by the at least one sensor in order to influence the magnetic field depending on the data.

7. An apparatus for outer wall and/or inner wall coating of a hollow body made of an electrically nonconductive material, comprising a. a process chamber configured for insertion therein of the hollow body and which is divided by the hollow body into an internal reaction space and an external reaction space, b. at least one vacuum pump configured to selectively evacuate the reaction spaces, c. at least one process gas feed configured to selectively introduce at least one process gas into one of the reaction spaces by means of which a process pressure can be established in one of the reaction spaces with the at least one process gas in conjunction with the at least one vacuum pump, d. at least one microwave generator configured to selectively introduce energy into one of the two reaction spaces for generation of a plasma, and further comprising at least one element configured to generate a magnetic field that permeates the process chamber and influences with regard to at least one parameter of the plasma.

8. The apparatus as claimed in claim 7, wherein the at least one element comprises a plurality of elements configured to generate a magnetic field that permeates the process chamber by superimposition of the magnetic fields generated by the respective elements.

9. The apparatus as claimed in claim 7, wherein the at least one element comprises a coil configured to be supplied with power or comprises a permanent magnet.

10. The apparatus as claimed in claim 9, wherein a plurality of the coils are arranged successively in a direction of axial extent of the process chamber corresponding to the longitudinal direction of the hollow body to be coated.

11. The apparatus as claimed in claim 10, wherein at least one of the coils is disposed an axial ends of the process chamber opposite from an axial end face of the hollow body to be coated, wherein the at lease one coil has a shorter winding diameter than the other coils, the other coils being disposed outside of the process chamber or being disposed within the process chamber and configured to surround the outside of the hollow body.

12. The apparatus as claimed in claim 11, wherein at least one hollow conductor configured to introduce energy into the process chamber is disposed in an axial margin between axially adjacent coils or between axially adjacent winding sections of the same coil.

13. The apparatus as claimed in claim 7, further comprising at least one sensor configured to contactlessly detect spatial position of the plasma generated while the plasma is being influenced by the magnetic field, and wherein the at least one magnetic field-generating element is configured to be actuated depending on measurements from the sensor.

14. The apparatus as claimed in claim 8, wherein the plurality of elements that generate the influencing magnetic field are configured as at least two groups of coils that can be supplied with power and each of the two groups of coils is configured to generate a same plasma-influencing magnetic field.

15. The apparatus as claimed in claim 14, further comprising a control unit configured to successively power the two groups of coils with a partial powering of two groups at the same time in a temporary overlap.

Description

[0047] A working example of the invention is elucidated by the figures that follow.

[0048] The apparatus of the invention as shown in FIG. 1 permits application of a sequential, and in each case exclusive, inner and/or outer coating to a hollow body 4 made of plastic, for example to large-volume containers 4 made of plastic. For generation of a layer, at least one process gas is introduced into the respective reaction space 4a or 4b via one of the respective hollow antennas 3 and excited to a plasma, which generates plasma polymerization. The reaction space 4a is defined here by the interior of the hollow body 4. The reaction space 4b by the space between the outer wall of the hollow body 4 and the process chamber 12.

[0049] The coating process overall is effected under low pressure, i.e. a pressure lower than the surrounding atmospheric pressure. The necessary pressure may be generated by means of a vacuum pump 15 for each of the two reaction spaces 4a/4b. The ignition of the plasma is generated with pulsed microwave excitation which is generated by the signal generators 1 and released via hollow antennas 3 and/or hollow conductors 5. According to the invention, the plasma here is influenced by a magnetic field which is generated by the coils 13, 16 and 17 that are supplied with power.

[0050] In the method, the hollow body 4 is fixed in a gas-tight manner in the process chamber 12. Once the process chamber has been closed, by way of example for the outer coating, process gases are first introduced into the outer reaction space 4b via a gas probe 3 in the reactor lid 2, which is simultaneously a microwave antenna for the inner coating, and a process pressure of, for example, 10 to 30 Pa is established.

[0051] The inner reaction space 4a of the container 4 here preferably remains under atmospheric pressure or close to atmospheric pressure. Microwave radiation is introduced into the process chamber 12 via an antenna 3, especially matched to the container geometry, which is especially also a gas probe for the inner coating. The radiation passes through the inner reaction space 4a of the hollow body 4 virtually without loss. The significantly higher pressure in the inner reaction space 4a here prevents the ignition of a plasma. The microwave radiation reaches the outer reaction space 4b of the hollow body 4, where it encounters suitable conditions for a plasma state, as a result of which the deposition process is initiated on the outer wall of the hollow body 4.

[0052] At the same time, a magnetic field is generated by means of a coil arrangement composed of coils 16 and 17, which homogenizes the plasma along the field lines by means of the acceleration generated in the charged particles and simultaneously keeps it away from the chamber walls of the process chamber 12 by means of a magnetic enclosure. In FIG. 1, based on the longitudinal axis A of the hollow body 4, an axially terminal coil 17 which is at the opposite end from the upper axial end wall of the hollow body 4 and has a smaller diameter than the coil 16 is provided, which creates a constriction of the field lines at the axial end, and hence the effect of a magnetic mirror for the plasma. Such a coil 17 is disposed here only at an axial end, the upper end of the hollow body 4 here. It may also be the case in the invention that such a coil 17 is also provided at the other end, the lower end here, of the hollow body, especially as shown in FIG. 2.

[0053] FIG. 2 visualizes the field line profile for an execution in schematic form with coils 17 arranged at both axial ends. The field line profile of the effective magnetic field is shown and illustrates the magnetic pole spacing in the axial direction A. What is clearly apparent is the constriction of the field lines at the axial ends, which is brought about by the coils 17 having smaller winding diameter than the coils 16, which are arranged radially around the hollow body 4 based on the axis A. The field lines of the magnetic field here are forced into a bottleneck-shaped profile, especially such that the field lines are for the most part bent back together in the interior of the enclosure volume. This apparatus can be used to restrict the plasma to the direct environment of the face of the hollow body to be coated and keep it away from the process chamber walls. In addition, the plasma is homogenized and preferably compressed, which increases the energy density and hence the layer deposition rate.

[0054] The magnetic influence on the plasma is based here on the Lorentz force, which keeps the charged plasma particles, electrons and ions on screw-shaped paths in the magnetic field, and especially thereby restricts the possible local dwelling regions, homogenizes the plasma and preferably also increases the local energy density.

[0055] This magnetic enclosure, here in this example, but also with general validity for the invention, can be achieved with cylinder coils since the magnetic field of such a coil is directed parallel to the coil axis, which prevents the loss of particles in radial direction.

[0056] If an inner coating that sequentially follows the outer coating is desired, after the process of outer coating, for the subsequent inner coating, the gas supply in the outer reaction space 4b may be ended and latter may be evacuated down to a pressure level below the process pressure, preferably to about 5 Pa.

[0057] In the inner reaction space 4a of the hollow body 4, process gas is introduced via the gas probe 3 and adjusted to a process pressure, for example a pressure of about 10 to 30 Pa. Microwave radiation, which is then introduced into the process chamber 12 via the opposite antenna 3 and the laterally slotted hollow conductor 5, passes through the outer space without loss as a result of the significantly lower pressure that corresponds to an increased free path length.

[0058] The radiation in the interior 4a of the hollow body 4 then encounters suitable conditions for a plasma state, as a result of which the layer deposition process on the inner wall of the hollow body 4 is initiated. Again, the magnetic field is switched on, this time preferably solely for homogenization of the plasma, which is especially advantageous in the inner coating of large hollow bodies.

[0059] The total cycle time for the inner and outer coating, depending on the hollow body volume, is, for example, 10 to 120 seconds, especially with 1-30 seconds being required in each case for the coating. The remaining seconds are required for the evacuating and the change of sample.

[0060] FIG. 3 shows a further working example of the invention. The cylinder coils 13 and 22 in this example, by comparison with coils 16 to 21, may be executed with a smaller diameter, and preferably with a core made of a ferromagnetic material, such that high magnetic flux densities are possible at low currents. These coils 13 and 22 are therefore less critical in relation to thermal stress.

[0061] The cylinder cons 16 to 21 by contrast, for process- and system-related reasons, have a greater inner radius (especially corresponding to or larger than the outer radius of the process chamber 12) and, in this execution, preferably do not have a core.

[0062] In an alternative execution, the antenna/gas probe 3 may preferably be formed from a ferromagnetic material in order to achieve an increase in magnetic flux density of the outer coils 16 to 21. This execution is of interest particularly for the magnetic enclosure of the plasma ignited around the outside of the container wall, i.e. in the reaction space 4b, since the field lines here run through and to the antenna 3.

[0063] The kinetic energy of the ions E.sub.kin in a microwave plasma may typically assume values of up to 30 eV or 4.8E-18 J and is dependent on the coating process and system type. In order to steer these charged particles with a magnetic field, depending on E.sub.kin, a magnetic flux density of up to 0.01 T to 1 T is required. The internal diameter of the process chamber 12, for a 10 L container may, by way of example, be about 350 mm. With a cylinder coil having this internal diameter, preferably without a core, and having 5000 windings, for example, and a power supply of 3 A, it is possible to achieve, by way of example, a magnetic flux density of about 0.05 T. The strength of this magnetic field can also be enhanced by the coils 13 and 22 depending on the power required. In this example, the coil, with inclusion of energy loss via convection (laminar flow at v=2 m/s), achieves a temperature of 90° C., for example, which is critical for sustained stability after about 30 seconds. After the coil has been switched off, a few minutes may be required until it has sufficiently cooled down again. There are various options for taking account of the cooling times of the coils in the process. Possible use examples are: [0064] 1. Different Groups of Coils are Used in Each Coating Cycle

[0065] Loading and removal operations, vacuum generation and introduction of gas are preferably included in the total cycle time, such that this is fixed depending on the vessel size and may, for example, be 10 s to 120 s. In each coating operation, only the coils of a particular group of coils are switched on in order to generate the plasma-influencing magnetic field, such that the coils of at least one other group of coils, especially the coils used previously, can cool down. For example, it would be possible in the first coating process first to use coils 16, 18 and 20 of a first group and then, in the subsequent process, coils 17, 19 and 21 of another group. In this way, it is possible in each case to generate a uniform magnetic field, especially in each case an at least essentially identical magnetic field, and the coils in the groups undergo sufficient cooling to be reused in the subsequent process. [0066] 2. The Groups of Coils are Switched on and off in Alternation Within a Coating Cycle

[0067] In this case in particular, processes of coil charging and discharging should be noted. A current accentuated by induction will always act against the cause of its formation (change in magnetic field). During the charging operation, the flow of current is inhibited by the self-induced voltage of the coil. The processes of coil charging and discharging may, depending on their configuration size, last for a few milliseconds, but also a few tens of seconds. Taking account of these charging and discharging processes, groups of coils are alternately supplied with current during the coating process, especially such that a sufficiently high average magnetic flux density is achieved at sufficiently low maximum operating temperature. The inductivities can be taken into account via a mutually adjusted increase in current over time in one group, while the current is reduced in another group, until one group has displaced the other group for generation of the magnetic field. It is preferably ensured here that the superimposed magnetic fields of the two groups, at the times when two groups are simultaneously supplied with current, correspond to the magnetic field that each group also generates on its own after the other has been switched off.

[0068] Thus, both in the case of sole operation of one group and during the time interval of switchover of operation from one group to another, the same magnetic field is generated.

[0069] FIG. 3 additionally shows, by reference numeral 23, an optical sensor for detection of the plasma during operation, in order to regulate this using the sensor measurements, especially with regard to the plasma position or the distance between plasma and process chamber wall or plasma and hollow body wall.

LIST OF REFERENCE NUMERALS

[0070] 1.) Signal generator

[0071] 2.) Lid of the process chamber, especially movable by guide rod (e.g. pneumatically driven)

[0072] 3.) Gas probe/antenna (electively made of ferromagnetic material)

[0073] 4.) Hollow body

[0074] 5.) Hollow conductor arc

[0075] 6.) Energy distribution

[0076] 7.) Hollow conductor

[0077] 8.) Guide rod made, for example, of PEEK or similar materials that have high transparency to microwaves and magnetic fields

[0078] 9.) Valve

[0079] 10.) Gas flow regulator

[0080] 11.) Gas reservoir

[0081] 12.) Process chamber, for example with radial wall of borosilicate glass or similar materials that have high transparency to microwaves and magnetic fields

[0082] 13.) Base of process chamber with sealing surface for accommodation of the hollow body, and optionally coil with core of ferromagnetic material for magnetic mirror action at the axial end

[0083] 14.) Pressure measurement

[0084] 15.) Pump stand with at least one vacuum pump

[0085] 16.) Coil for generation of a magnetic field

[0086] 17.) Coil for generation of a magnetic field

[0087] 18.) Coil for generation of a magnetic field

[0088] 19.) Coil for generation of a magnetic field

[0089] 20.) Coil for generation of a magnetic field

[0090] 21.) Coil for generation of a magnetic field

[0091] 22.) Coil for generation of a magnetic field, especially with core of ferromagnetic material, for magnetic mirror action at the axial end of the hollow body

[0092] 23.) Sensor for detection of the spatial spread of the plasma