DE102008044024A1 - Coating method and coating device - Google Patents

Abstract

The invention relates to a PE-CVD coating method for coating metallic workpieces (7), in particular of components of fuel injection systems, wherein the metallic workpieces (7) acted upon by a high-frequency AC voltage or a pulsed or non-pulsed DC voltage and a plasma stream (9) a gas distributor (2) are exposed. According to the invention, it is provided that the workpieces (7) are arranged in a stationary manner relative to the gas distributor (2). Furthermore, the invention relates to a coating device (1).

Description

State of the art

The The invention relates to a PE-CVD coating process (PE-CVD = plasma-assisted chemical vapor deposition) according to claim 1 and a coating device according to the preamble of claim 14.

High-quality protective coatings are nowadays deposited in plasma-aided processes in batch systems or in clocked multi-chamber batch plants. The in-line coating processes are aimed at the largest possible batch sizes in order to keep the coating costs low. In the known coating devices, the workpieces (up to several 10000 pieces) are rotatably arranged in a coating chamber by up to three axes, wherein the coating chamber can be charged with process gas to form a plasma. During the coating, the workpieces are rotated relative to the gas outlet openings (gas distributor, gas shower) in order to achieve a uniform deposition. The coating is usually carried out in pressure ranges between about 10 ^-1 to about 10 ^-3 mbar, wherein deposition rates of typically between 1 and 2 microns / h can be realized.

adversely in the in-line coating processes, it is that with these are not economically small, at prefabrication steps adapted batch sizes are feasible. One Another major disadvantage is the long cycle time in known Coating process of up to several hours.

From the DE 10 2007 035 518 A1 It is known to coat elongated, cylindrical components with an electrically induced plasma current.

Disclosure of the invention

Of the Invention is based on the object, a coating method and to propose a coating apparatus with which also small batch sizes economically coatable are. In particular, with the method and the device short cycle times can be realized.

These Task is with regard to the coating method with the features of claim 1 and in terms of the coating device with the features of claim 14 solved. Advantageous developments The invention are specified in the subclaims. In the scope of the invention covers all combinations at least two of in the description, the claims and / or features disclosed in the figures. To avoid repetition should also be disclosed according to the method apply as disclosed according to the device and be claimable. Likewise, according to the device disclosed features as disclosed according to the method and claim claimable be.

Of the Invention is based on the idea, the workpieces not as in the prior art rotatable to arrange, but preferred stationary relative to the gas distributor (gas shower), that is stationary relative to the gas outlet openings, through the process gas and / or Process liquid flows out to form a plasma stream. Due to the fixed arrangement of the workpieces can reached high deposition rates of over 20 microns / h be, which in total very short cycle times are feasible. The cycle times can be further optimized if the Coating chamber volume (process chamber volume) is minimized especially by placing the workpieces in one as possible small distance to the gas distributor can be arranged. By a Minimizing the coating chamber volume can take the time needed is evacuated to evacuate the coating chamber to a minimum be reduced. With a trained according to the concept of the invention Method and a suitably trained coating device can a significantly increased deposition rate at least consistent Layer quality can be realized. Overall, you can comparatively inexpensive coating devices be created because no elaborate cathode technology and no high vacuum neces sary. The invention Coating method and one according to the concept of the invention trained coating device are suitable for integration in production lines. Within the scope of the invention also an embodiment in which the workpieces Although not rotated, but one, preferably very slow, translational relative movement between the workpieces and the gas distributor is realized. The workpieces are preferred while translational to the gas distributor and / or away from it emotional.

Preferably, the protective layer obtained by means of the coating process is resistant to abrasion and protects the workpieces from corrosion and / or serves as diffusion protection against oxygen and / or water / water vapor and / or serves as protection against other chemical attacks of acidic or basic media. Additionally or alternatively, the at least one applied layer can be realized as, in particular, a coloring and / or structuring, decorative layer. If necessary, the workpieces can successively by means of the method formed by the concept of the invention or by means of the device several layers in the same coating chamber preferably first an adhesive layer onto which the actual protective layer based on hydrocarbons and / or silanes (dopings with, for example, N, O, F are possible by adding further gases) is applied. The adhesive layer can be realized, for example, with silane, tetramethylsilane (TMS), hexamethyldisilazane (HMDS), hexamethyldisilazane oxide (HMDSO) or organometallic compounds. Suitable as process gas for the formation of the plasma stream for the actual coating process are in particular halogen-, silicon-, carbon-containing and / or organometallic monomers, ie low molecular weight, crosslinkable substances. Particularly advantageous is the use of acetylene and / or methane to obtain a low-friction, diamond-like carbon layer (DLC layer). In addition to the gaseous precursors, it is also possible to introduce highly fluid starting materials with a high proportion of the layer-forming species in the total molecular weight, such as, for example, gasoline or pentane.

at Demand can be assigned to the workpieces a counter electrode where both the counter electrode and the gas distributor can be used potential-free or potenzialbehaftet. It is especially preferred if only the Workpieces form a voltage-loaded electrode, d. H. the means electrically contacting the workpieces not directly supplied with process gas and / or plasma to To realize a deposition concentration on the workpieces.

All Particularly preferred is an embodiment in which the used gas distributor several outlet openings having, wherein the outlet openings advantageously such are such that the process gas leaving them directly after exiting the exit openings as plasma is activated, d. H. is ignited. These outlet openings can optionally be tapered towards the workpieces widening be formed.

Especially it is preferred if each workpiece has at least one, preferably only one, outlet opening is assigned to the direct (direct) flow. Preferably, the particular rotationally symmetrical workpiece is included coaxial with a longitudinal center axis passing through the outlet opening arranged. Uncoated surfaces of the workpiece can as in conventional coating methods be masked with conductive and non-conductive material. With advantage is the workpiece or in the coating chamber projecting portion flows directly from the plasma stream. There are also component geometries in which the flow not directly above the longitudinal center axis of the workpiece must be done. So it may be for pistons that are not on the Face to be coated are also useful, the outlet openings in the gas distributor just in the grid offset from the components or to be arranged as a ring gas coaxial with the component.

The Coating chamber volume can be reduced to a minimum, if the workpieces are at a close distance to them associated outlet openings are arranged. Prefers is the distance of a workpiece to him associated outlet opening less than 50 mm, preferably less than 30 mm. Due to the resulting, direct flow of the workpieces with the plasma stream can be high Separation rates are achieved.

Especially it is preferred to arrange the workpieces such that these extend counter to the flow direction, d. H. that the longitudinal extent of the components parallel to Flow direction of the plasma stream or the Plas maströme is aligned to the direct flow as well as the immediate To achieve flow around the workpieces with plasma flow.

by virtue of the high recoverable deposition rate, it is sufficient if the workpieces be exposed to the plasma stream for less than 20 minutes. Particularly preferred is the length of time that the workpieces be subjected to plasma current, from a range of values between less than 10 seconds and 20 minutes.

In a development of the invention, coating rates of more than about 3 μm, preferably of more than 20 μm, per hour are advantageously achieved. Optimum coating results are obtained when the workpieces are pretreated and / or cleaned in the coating chamber in which they are subsequently coated. Preferably, the pretreatment and / or cleaning by the use of cleaning gases, which are activated by high frequency or pulsed DC voltage to a plasma. Very particularly preferably hydrogen, halogen, oxygen, fluorine and / or nitrogen-containing gases are used, which are activated by means of high frequency to a plasma. Particularly preferred is the use of noble gases. Advantageously, the pressure in the pretreatment and / or cleaning phase is between about 0.01 mbar and 50 mbar. The excitation of the cleaning or pretreatment gas in the plasma or by its fragmentation gives rise to radicals and / or ions which permit intensive surface cleaning and / or activation. In addition, the pre-treatment allows a good connection (adhesion) of the actual wear protection coating or a primer layer. For the later function of the layer is a good adhesion on the substrate desirable. A poorly adhering layer would become detached from the substrate after the first movements of the component relative to the counter body and would only inefficiently protect the component against wear. As an alternative to a direct irradiation with cleaning gas, a diffuse distribution of the cleaning gas in the chamber is possible - in contrast to the actual process gas described above. The entire pretreatment time is preferably a few seconds to a few minutes - depending on the base material and layer type. The pressure setting in the pretreatment chamber depends in particular on the gas flow and the suction power of the gas pump.

Particularly preferred is an embodiment of the method in which the workpieces are subjected to an AC voltage frequency from a value range between about 10 kHz and 6 GHz. Most preferably, the frequency is selected from a frequency range between about 20 kHz and 400 MHz, and it is more preferable for the power to be coupled to be about 0.01-100 watts per cm ^{2 of} workpiece area.

The invention also leads to a coating apparatus for coating metallic workpieces, in particular nozzle needles for fuel injectors. Most preferably, the coating device is designed for carrying out a method described above. The device comprises a gas distributor, that is to say a multiplicity of gas outlet openings for pressurizing the workpieces with a plasma stream which is produced by activation of process gas flowing out through the outlet openings and / or process liquid to be evaporated. Furthermore, the coating device comprises means for applying a high-frequency alternating voltage to the workpieces, wherein the power to be coupled in preferably corresponds to between about 0.01 W and about 100 W per cm ² workpiece surface. The coating device is characterized in that the workpieces can be positioned in a stationary manner relative to the gas distributor. Alternatively, there is a translational (non-rotatory) relative movement possibility between the workpieces and the gas distributor. The coating device is further characterized by an optimal scalability, in particular when the workpieces, as will be explained later, are arranged on an electrode plate (workpiece carrier). The size of the electrode plate can be adapted to the process. It is conceivable to use electrodes with an areal extent of 1 cm × 1 cm to> 1 m × 1 m. The workpieces are preferably arranged in the form of a die in and / or on the electrode plate.

Especially For this purpose, the workpieces are preferred on an electrode plate arranged, which are preferably aligned parallel to the gas distributor (gas shower) is, so that the workpieces with their longitudinal extension aligned parallel to the plasma stream.

Prefers the workpieces are directly impinged by the plasma stream, to further optimize the deposition rate.

All particularly preferred is an embodiment of the coating device, in which only the workpieces with Voltage, in particular high-frequency alternating voltage or pulsed DC voltage, forming the applied electrode. This can be done be achieved, that the workpieces carrying electrode plate such is isolated, that the plasma current the electrode plate (carrier plate) can not act directly, but exclusively impinges on the workpieces. As a result, the deposition process be focused on the workpieces. If necessary, the preferably exclusively from the workpieces formed electrode associated with a counter electrode.

at Demand, the plasma flow by means of auxiliary electrodes advantageous be shaped to reduce inhomogeneities. there it is possible to have at least one auxiliary electrode between the workpieces and / or in the region of the outlet openings of the Gas distributor to arrange. In this case, the auxiliary electrodes both on the potential of the workpieces, or on the one of the Gas distributor or on the suction of holes. It is also conceivable, the auxiliary electrodes on a separately controlled Potential to lay, preferably from a frequency range between about 0 and 400 MHz.

Further Advantages, features and details of the invention will become apparent the following description of preferred embodiments as well as from the drawings.

These show in:

1 a first embodiment of a coating device with vertically arranged workpieces and

2 an alternative embodiment with suspended workpieces.

In The figures are the same elements and elements with the same Function marked with the same reference numerals.

In 1 is highly schematic a coating device 1 to carry out a PE-CVD coating process shown. The coating device 1 includes a metallic gas distributor 2 (Gas shower) with a gas inlet 3 and a distribution chamber 4 , from which a large number of outlet openings 5 open out. The outlet openings 5 are conically shaped in cross-section and expand towards a coating chamber 6 (Process chamber) into which the outlet openings 5 open out.

In the coating chamber 6 are a variety of metallic workpieces 7 , here nozzle needles for fuel injectors, arranged. The workpieces 7 are in an electrode plate 8th held in the area of the coating chamber 6 is electrically isolated or provided with an insulation, so that from the outlet openings 5 emerging process gas and / or exiting, to be evaporated process liquid, the / to a plasma stream 9 is activated, not in direct contact with the electrode plate 8th can come. The electrode plate 8th is with known means 10 for applying the electrode plate 8th contacted with a voltage. The gas distributor 2 lies on earth.

As it turned out 1 results is every workpiece 7 an outlet opening 5 associated with each workpiece 7 coaxial with an imaginary, not shown longitudinal central axis of the associated outlet opening 5 is arranged so that each workpiece 7 directly with plasma current 9 can be acted upon. There are also component geometries in which the outlet openings offset advantageous to the longitudinal center axes of the workpieces 7 are arranged. The individual plasma streams overlap in a region between two adjacent workpieces 7 and run parallel to the workpieces 7 ,

It can also be seen that the workpieces 7 at a small distance to the associated outlet openings 5 , are arranged by about 40 mm in this embodiment.

In the electrode plate 8th are each between two workpieces 7 suction 11 for sucking off process gas and / or process fluid and / or plasma and for evacuating the coating chamber 6 before the actual coating process.

The over the nozzle-like outlet openings 5 supplied process gas is excited in the plasma, partially fragmented and ionized, and forms the plasma streams 9 made up, in part, on the workpieces 7 precipitate as a layer. Pumping out the plasma from the suction openings 11 provides a plasma stream 9 on the outside of the workpieces 7 moving along the workpieces 7 extends. If necessary, the plasma currents 9 be influenced and controlled via appropriate control surfaces. In the plasma stream 9 forms, depending on the coupled power, the total pressure and the area ratios between that of the workpieces 7 formed electrode and the gas distributor 2 as well as an optionally provided counterelectrode (not shown here) a potential (self-bias). This potential causes an acceleration in the plasma stream 9 located charged ions on the surface of the workpieces 7 , This ion bombardment causes a compaction of the layer and an increase in the layer hardness. Important for the functionality of the workpiece 7 is the layer thickness and the hardness of up to 50 GPa of the layer. The one in the coating chamber 6 set pressure depends on the process gas flow and the suction power of a not shown, on the coating chamber via the suction openings 11 connected vacuum pump from. It is preferably between about 0.01 mbar and 50 mbar.

Before the coating process described above, the workpieces can 7 directly in the coating chamber 6 pretreated and / or cleaned, in which case via the gas distributor 2 appropriate cleaning gas, in particular noble gas, is supplied, as a plasma stream 9 is activated. Alternatively, the workpieces 7 not directly flowed with the cleaning gas, but the latter becomes diffuse in the coating chamber 6 distributed. Preferably, the pressure during this pretreatment and cleaning phase is 0.01 mbar to 50 mbar.

With the in 1 shown coating device 1 Coating times of less than 10 or 5 minutes can be realized. The cycle time including pumping time is about 10 minutes. First, the electrode plate 8th (Goods carrier) introduced. The residual gas (air) is pumped to the pre-treatment pressure and then brought to working pressure by the inlet of a noble gas. The high frequency or the pulsed DC voltage is turned on for about 1 to 10 minutes. By admixture of initially silicon-containing process gases, an adhesive layer (transition layer) is deposited. In the next step, the reaction gas acetylene is fed. The power of the injected radio frequency can be varied during the process. The gas supply is then stopped and the residual gas is evacuated.

2 shows an alternative coating device 1 , The difference from the embodiment according to 1 is that the workpieces 7 hanging in the coating chamber 6 on an electrode plate 8th (Workpiece holder) are arranged. The workpieces 7 enforce the electrode plate 8th , On the from the gas distributor 2 abge turned side of the workpieces 7 there is a counter electrode 12 , into the suction holes 11 are introduced. The counter electrode 12 lies together with the gas distributor 2 (Gas shower) optional on ground, while the electrode plate 8th with funds 10 connected to a high-frequency voltage or a pulsed DC voltage. In the case of high-frequency excitation of the counter electrode 12 is a phase adjustment with the high frequency of the workpieces 7 necessary.

Alternatively to one in the 1 and 2 shown planar design of the electrode 8th it is alternatively conceivable to shape them, for example, cylindrical. It is particularly preferred if the then cylindrically contoured electrode 8th radially inside the, preferably then also cylindrical, gas distributor, so that not as in the embodiments shown, a plasma current is achieved from top to bottom, but in the radial direction.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 102007035518 A1 [0004]

Claims (22)

PE-CVD coating process for coating metallic workpieces ( 7 ), in particular of components of fuel injection systems, wherein the metallic workpieces ( 7 ) with a high-frequency AC voltage or a pulsed or non-pulsed DC voltage and a plasma stream ( 9 ) from a gas distributor ( 2 ), characterized in that the workpieces ( 7 ) not rotating, preferably stationary, relative to the gas distributor ( 2 ) to be ordered. Method according to claim 1, characterized in that the workpieces ( 7 ) directly from the plasma stream ( 9 ) are flown. Method according to one of claims 1 or 2, characterized in that the plasma stream ( 9 ) via at least one suction opening ( 11 ) is sucked, preferably for each individual workpiece ( 7 ) or for each group of workpieces ( 7 ) a suction opening ( 11 ) is provided. Method according to one of the preceding claims, characterized in that the gas distributor ( 2 ) a plurality of outlet openings ( 5 ), which are preferably designed in such a way that they are conically widening, are that from the outlet openings ( 5 ) emerging process gas at the outlet openings ( 5 ) is activated as plasma. Method according to claim 4, characterized in that each workpiece ( 7 ) at least one, preferably only one, outlet opening ( 5 ). Method according to one of the preceding claims, characterized in that the workpieces ( 7 ) each less than 50 mm, preferably less than 30 mm apart from the respective, their associated outlet opening ( 5 ) to be ordered. Method according to one of the preceding claims, characterized in that the workpieces ( 7 ) with its longitudinal extent parallel to the flow direction of the plasma stream ( 9 ) to be ordered. Method according to one of the preceding claims, characterized in that the workpieces ( 7 ) less than 15 minutes, preferably less than 10 minutes, preferably less than 5 minutes with the plasma stream ( 9 ). Method according to one of the preceding claims, characterized in that the workpieces ( 7 ) are coated at a coating rate ranging from 2 μm to 100 μm per hour. Method according to one of the preceding claims, characterized in that the workpieces ( 7 ) in the coating chamber ( 6 ) are pretreated and / or cleaned in a plasma before the coating process. Method according to one of the preceding claims, characterized in that the workpieces ( 7 ) are applied with an AC voltage frequency from a value range between 10 kHz and 6 GHz, preferably between about 200 kHz and 400 MHz and / or with a pulsed DC voltage, in particular with time constants between 0.01 μs and 100 μs. Method according to one of the preceding claims, characterized in that already coated workpieces are stripped by means of suitable process gases, in particular by adding Ar, O ₂ , N ₂ , H ₂ , hydrocarbons and / or at least one fluorine compound. Method according to one of the preceding claims, characterized in that the gas distributor with changing Gas mixtures and / or plasmas is applied, and thus the workpieces be both purified in a process and, in particular, after that is coated with at least one, in particular graded, layer. Coating device for coating metallic workpieces ( 7 ), in particular of components of fuel injection systems, preferably for carrying out the method according to one of the preceding claims, with a gas distributor ( 2 ) for applying the workpieces ( 7 ) with a plasma stream ( 9 ) and with funds ( 10 ) for applying the workpieces ( 7 ) with a high-frequency AC voltage or pulsed or non-pulsed DC voltage, characterized in that the workpieces ( 7 ) is not rotatable, preferably stationary, relative to the gas distributor ( 2 ) are positionable. Coating device according to claim 14, characterized in that the workpieces ( 7 ) can be arranged such that their longitudinal extent parallel to the plasma stream ( 9 ) is aligned. Coating device according to one of claims 14 or 15, characterized in that the workpieces ( 7 ) can be arranged in such a way that they are directly separated from the plasma stream ( 9 ) are vorströmbar. Coating device according to one of Claims 14 to 16, characterized in that the gas distributor ( 2 ) a plurality of outlet openings ( 5 ), and that the workpieces ( 7 ) at a distance of less than 50 mm, preferably less than 30 mm, relative to the outlet openings ( 5 ) can be arranged. Coating device according to one of claims 14 to 17, characterized in that the outlet openings ( 5 ) are such, in particular are conically widening formed and / or profiled that from the outlet openings ( 5 ) emerging process gas at the outlet openings ( 5 ) is activated as plasma. Coating device according to one of claims 17 or 18, characterized in that each workpiece ( 7 ) at least one, preferably only one, outlet opening ( 5 ) assigned. Coating device according to one of claims 14 to 19, characterized in that the workpieces ( 7 ) in and / or on one, in particular as an electrode plate ( 8th ), tool holders are arranged, and that only the workpieces ( 7 ) one with plasma current ( 9 ) formable electrode. Coating device according to one of claims 14 to 20, characterized in that the electrode has a counter electrode ( 12 ), which is preferably optionally with a high frequency between 100 kHz and 6 GHz or alternatively with a DC voltage, in particular with time constants between 0.01 microseconds and 100 microseconds, can be acted upon. Coating device according to one of the claims 14 to 21, characterized in that the workpiece holder with arranged in a grid workpieces, preferably with defined increments, translationally adjustable relative to the gas distribution is, and that the workpieces, especially during the adjustment movement, with different gases and / or precursors and / or, in particular caustic and / or coating, Plasmas are acted upon.