WO2012164050A1

WO2012164050A1 - Apparatus and method for coating and/or for removing material by means of pecvd/cde

Info

Publication number: WO2012164050A1
Application number: PCT/EP2012/060318
Authority: WO
Inventors: Dirk REINER
Original assignee: Surcoatec Ag
Priority date: 2011-05-31
Filing date: 2012-05-31
Publication date: 2012-12-06

Abstract

The subject matter of the invention is an apparatus (10) for coating at least one surface region (28) and/or for removing material from at least one surface region (28) of a workpiece (22) having any desired shape by means of plasma-enhanced chemical vapour deposition, with a chamber (14), which has a radiofrequency electrode (22), a reference electrode (29) and an electrically conductive workpiece holder (24), and with a circuit arrangement (30) for feeding radiofrequency, which circuit arrangement has at least one radiofrequency generator (32) and radiofrequency line paths (36, 38, 40), wherein the radiofrequency generator (32) is connected via radiofrequency line paths (36, 38, 40) to feed points (42, 44, 46) of the radiofrequency electrode (22) which are physically separated from one another. Provision is made for the radiofrequency electrode (22) to be electrically conductively connected to the workpiece holder (24) at the plurality of feed points (42, 44, 46).

Description

Device and method for coating and / or removing material by means of

PECVD / CDE

The invention is based on a device for coating at least one

Surface area and / or for removing material from a surface area of an arbitrarily shaped workpiece by means of plasma-enhanced chemical

Vapor deposition. The device has a chamber containing a high-frequency electrode (RF electrode), a reference electrode and an electrically conductive

Workpiece holder includes and a circuit arrangement for feeding

High frequency, in turn, at least one high-frequency generator and

Having high-frequency line paths, wherein the high-frequency generator via the

High-frequency line paths is electrically connected to spatially separate feed points of the high-frequency electrode. The invention further starts from a corresponding method for coating at least one surface area and / or for removing material from a surface area of an arbitrarily shaped workpiece by means of plasma-assisted chemical vapor deposition.

An apparatus for coating at least one surface area and / or for removing material from a surface area of a workpiece and a

corresponding method is known for example from US 2004/0168770 AI. Such methods are also known under the generic names plasma coatings (PECVD,

"Plasma Enhanced Chemical Vapor Deposition") or ion etching and plasma etching (CDE: Chemical Dry Etching) known. Here, a workpiece is placed in a vacuum chamber and fixed there. The chamber is evacuated to a residual gas pressure in the high vacuum or ultrahigh vacuum range and an inert working gas admitted. By feeding an RF field via an RF electrode arranged in the vacuum chamber, a low-pressure plasma is then ignited. Here, an ionized gas is generated, which contains a noteworthy proportion of fast-moving free charge carriers such as ions or electrons.

In the case of the PECVD, in addition to the working gas, further so-called reaction gases are fed into the chamber, which in particular can contain carbon or silicon. In the low-pressure plasma, the electrons have such high energies that chemical reactions between the gas components and components of the surface of the workpiece are possible, which are not possible in thermal equilibrium. In this way, layers are formed on the surface of the workpiece which, depending on the reaction gas, e.g. can consist of carbon or silicon oxide. For example, it is possible to produce high-strength, low-friction and biocompatible diamond-like carbon coatings (DLC, "diamond-like carbon") used in implants, gears, etc. However, ion etching and plasma etching are about removing material from the surface For this purpose, the ions of the low-pressure plasma generated must have a certain minimum energy.The acceleration of argon ions in high or ultra-high vacuum in the direction of the substrate to be machined, resulting in the impulse transmission of the In plasma etching, the etching is also carried out by a chemical reaction in which instead of pure argon, a reactive gas such as oxygen is supplied to the plasma.

The object of the present invention is to provide a device and a method for

Coating at least one surface area and / or for removing material from at least provide a surface region of a workpiece by means of plasma-assisted chemical vapor deposition or plasma etching, in which the coating / ablation is possible even in inaccessible areas. This object is achieved with a device and a method having the features of claims 1 and 10, respectively. The subclaims indicate preferred embodiments.

In the device according to the invention it is provided that the workpiece holder is electrically conductively connected to the high-frequency electrode having the plurality of feed points. In such a device is a in the chamber

placed workpiece in the vicinity of the high-frequency electrode (RF electrode) and also electrically (or dielectrically) connected to this. The reference electrode with the mostly constant electrical potential is - apart from electrical conduction via charge carriers of the plasma - electrically isolated from the workpiece. By this arrangement, the resulting potential variation varies greatly in the region of the workpiece, wherein the plasma / plasmas inductively / capacitively by irradiation of an electromagnetic

Alternating field can be generated in the region of the workpiece. Due to the different feed points on the same RF electrode, an at least temporary formation of this plasma in inaccessible surface areas, such as cavities formed as recesses is achieved. Workpiece holder and RF electrode can also be integrally formed.

In principle, any number of feed-in points is conceivable. However, high-frequency generators (RF or RF generators) often have three or six different high-frequency outputs, so that a corresponding number of injection points on the

High frequency electrode is preferred. According to a preferred embodiment of the invention it is provided that the high-frequency electrode is formed flat. The feed points are formed distributed over the corresponding area, so are arranged to each other objectionable. In particular, it is advantageously provided that the feed points are arranged linearly. Preferably, the feed points are arranged on an imaginary, over the surface centrally extending straight spaced from each other. Alternatively, it is also advantageously provided that the feed points are arranged in the form of an n-corner (polygon), in particular an equilateral n-corner, with n = 3, 4. This n-corner or polygon is preferably arranged centrally on the surface of the HF electrode.

According to a preferred embodiment of the invention it is provided that the

Circuit arrangement is arranged such that it can feed high frequency sequentially in the individual feed-points. This sequential feeding results in a temporal sequence of the feed-in location, in particular a feed-in cycle. If, for example, three linearly arranged feed points are provided, which are designated in succession from one side starting with a, b and c, the result is a preferred wiring in the sequence... B, c, b, a, b, ... in which there is a back and forth movement of the entry point with regard to the (imaginary) straight line. At a

Arrangement of the feed points, which gives a polygon, for example, a circumferential movement of the feed point is preferred.

According to a further preferred embodiment of the invention, the

Circuit arrangement at least one matching circuit part for impedance matching of the RF feed. Such a matching circuit part is conventional

Devices are known, for example, as the circuit of a matching unit (or "match box"), the corresponding matching circuit part being associated with a specific HF electrode Trimming capacitor preferred embodiment of the invention, the circuit arrangement has one each

Matching circuit part per feed-point.

According to yet another preferred embodiment of the invention, it is provided that the high-frequency line paths to the feed points in the region of the adaptation

Circuit part are capacitively coupled. This coupling is in particular by means of RC elements, more preferably by means of series connections of resistors and

Capacitors, realized. The coupling can avoid harmful feedbacks via the respective non-active feed-in points. Such feedbacks would interfere with operation and could damage the circuitry.

It is advantageously provided that the workpiece holder has a plurality of spatially separate electrical connection paths to different locations of the

High frequency electrode has. This results in several possibilities of electrical connection of the workpiece to the RF electrode.

According to a further preferred embodiment of the invention, the chamber has electrically conductive inner walls which form an interior of the chamber and at the same time form the reference electrode or at least form part of the reference electrode. In the simplest case, therefore, the arrangement of the electrodes consists only of the

Interior forming inner walls, which forms the reference electrode, and -elektrisch isolated thereof-the RF electrode in the interior.

In the method according to the invention it is provided that the coating is carried out by means of a device mentioned above. In this case, it is possible, in particular, for the surface area to be coated or the surface area in the material to be removed, a surface area in at least one cavity of the workpiece. In other words, the invention thus encompasses the use of an abovementioned device for coating at least one surface area and / or for Removal of material from a surface area of a workpiece, in particular from a surface area in at least one cavity of the workpiece.

In this way, an alternating field with very high field strengths can be generated in the chamber, as is necessary for the formation of the cavity plasma. An alternating field generated in this way has a sufficiently high penetration depth, so that even hollow bodies with large wall thicknesses can be penetrated and coated on the inside. The workpiece itself does not have to function as an electrode and can therefore also consist of a non-metallic material.

It is preferably provided that the circuit arrangement, the high frequency (the

High-frequency signal) in the individual feed-points successive feeds. This results in particular a feed cycle. This feed cycle also allows the plasma to penetrate into cavity (s) of the workpiece.

According to a preferred embodiment of the invention, the method comprises the following method steps:

(i) inserting the workpiece into the chamber and positioning the workpiece in the chamber, wherein an all-round minimum distance between the outer wall of the workpiece and the inner wall of the chamber is observed,

(ii) closing the chamber and evacuating it to a residual pressure of 0.001-20 Pascal,

(Iii) introducing an inert working gas and one or more reaction gases via a gas supply device and / or a gas lance in the interior of the chamber, and

(iv) igniting a plasma by applying a high frequency electric field to the high frequency electrode.

A gas lance is preferred for workpieces designed as cavities

Recesses additionally used. The gas lance protrudes preferably into the cavity of the Workpiece into it. The hollow body to be coated is not earthed or provided with any other reference potential.

The workpiece may be formed in particular as a hollow body. As hollow bodies to be coated, in principle all possible hollow bodies are possible, ie hollow bodies closed on one side (such as vessels, cans etc.) as well as tubular hollow bodies without bottom, such as e.g. Cannulas, bodies with a through-hole or tubes. The latter hollow bodies must be closed with a lid or stopper on one side before coating.

Preferably, the minimum distance between the outer wall of the workpiece and the inner wall of the chamber is 15 cm. The maximum distance is, however, by the

Dimensioning of the used chamber given. This feature is particularly advantageous in that in the method the temperatures inside the coating chamber usually do not exceed 200 ° C. Due to these low temperatures, plastic hollow bodies can therefore also be provided with a highly resistant inner coating. This is particularly advantageous because even non-metallic hollow bodies can be coated due to the non-required electrically conductive connection between the hollow body and the high-frequency electrode with the method according to the invention.

It is preferably provided that the working gas is a gas selected from the group comprising argon, helium, hydrogen, oxygen or another noble gas.

Furthermore, it is particularly preferably provided that the reaction gas is a gas selected from the group containing oxygen.

Such a method for plasma-assisted chemical vapor deposition for

Material removal is also referred to as plasma etching. As a reaction gas for this Oxygen is particularly suitable method, since the oxygen ions produced in the plasma are particularly heavy and therefore particularly effective in the accelerated state

Cause surface erosion. By means of the method in which a plasma is ignited after supplying oxygen under high energy supply, it is possible to clean the surface of the substrate absolutely residue-free ("etching") .This is due in particular to the high atomic weight of the oxygen atoms, with sufficient acceleration In a further preferred embodiment of the process according to the invention, it is provided that the reaction gas is a gas selected from the group comprising hydrocarbon gases such as methane, ethane, ethene, ethyne, propane or silane gases such as tetramethylsilane or hexamethyldisiloxane are suitable for forming a DLC layer, the latter, for example, suitable for forming a SiCV layer.

The term DLC ("diamond-like carbon") is understood as meaning layers of molecular carbon which hybridize a network or lattice of sp ² and sp ³

Have carbon atoms. The ratio of the two variants depends on the coating conditions. If the former predominates, the coating has graphite-like properties (low coefficient of friction), the latter predominate, the hardness and the transparency of the coating increase. Mixed coatings containing both variants often combine both advantages.

Applicants' investigations have shown that with this method, the inner surfaces of bulk cans and other hollow bodies can be effectively coated with a DLC layer. In the method according to the invention, the plasma is preferably ignited by applying a high-frequency field with the following parameters:

1st frequency: 10 kHz - 100 GHz

2. Electrical power: 500 - 5000 W

3. Gas supply: 0 - 90 scm ³ .

The frequency is preferably in the range of 10 - 15 MHz. Particular preference is the frequency 13.56 MHz (RF, radio frequency).

The electrical power to be applied is calculated according to the following formula: Power (watts) = area to be coated (m ² ) x 1750. The latter factor can be between 1500 and 2200 and is empirically determined in practice. A hollow body with an inner surface of 0.85 m ² to be coated would therefore have to be coated with an energy of about 1500 watts.

Surprisingly, the bias voltage which occurs under these circumstances is in the range of 0V, namely on all supply lines. Moreover, this value is independent of whether the hollow body to be coated is in electrically conductive contact with the high-frequency electrode or not.

The gas supply is regulated gas-specific and depending on the object and desired

Layer properties controlled in a range of 0-90 sccm. It is preferably provided that the amount of reaction gas for the coating to be introduced amounts to 0.1 to 10 sccm reaction gas per 10 cm ² of internal surface to be coated.

The unit sccm denotes standard cubic centimeters, ie the volume of the gas to be introduced in cubic centimeters per minute (minute volume). For the adjustment, a valve with a mass flow controller is used. At a given pressure of the gas supply so decides the opening state of the valve on the inflowing minute volume. With hydrocarbon gases, the more gas is used, the harder the layer becomes, as the proportion of available carbon atoms increases. In the case of silane gases, on the other hand, the ratio of silane gas to oxygen determines the hardness of the layer. For hard coatings, for example, the ratio is 100 sccm of HMDSO (hexamethyldisiloxane) to 400 sccm of oxygen. A reduction of the oxygen content, however, leads to softer layers. Particularly preferably, the amount of the reaction gas to be introduced is 0.5-5 sccm of reaction gas per 10 cm ² of internal surface to be coated.

Furthermore, it is preferably provided that the reaction gas is doped with one or more gases containing Si, N, F, B, O, Ag, Cu, V or Ti. These dopants can help to specifically influence the properties of the applied coating. For example, the doping of the reaction gas with a gas containing Si (e.g.

Hexamthyldisiloxan) to reduce friction even under wet conditions and to a higher thermal stability. Doping with N, F, B, or O affects the surface tension, wettability, and hardness of the coating. Doping with metals helps to affect the conductivity of the coating, while doping with Ag, Cu, V or Ti affects the biological behavior of the coating, particularly biocompatibility, e.g. is immensely important for implants.

With the method according to the invention, layer growth rates of up to 4 μητ / h and layer thicknesses of up to 7 μιη are achieved.

According to the invention, there is further provided a hollow body having an inner surface, which is characterized in that the latter has been treated by a method according to one of the preceding claims, such that on the inner surface a

Material removal was made and / or provided with a coating has been. As mentioned above, the coating can be, for example, a DLC, a TiOx or a SiO ₂ bond direction.

Particularly preferably, this hollow body is a hollow body selected from the group comprising vessels, bottles, cans, cannulas, hollow needles, syringes, inner walls of cylinder or piston bores in internal combustion engines, inner sides of bearings, in particular ball or roller bearings.

With the method according to the invention u. a. Achieve the following advantages: a) improved cleaning of three-dimensional hollow bodies, in particular bulk cans, at the same time with reduced expenditure;

b) improved corrosion protection of the coated surfaces;

c) no inward diffusion of a substrate located in the hollow body into the inner surface layer of the hollow body;

d) reduction of the friction coefficient of the inner surface; and

e) improved heat dissipation.

The present invention will be explained in more detail by the figures shown and discussed below. It should be noted that the figures have only exemplary character and are not intended to limit the invention in any way.

1 shows an apparatus 10 for coating at least one surface area and / or for removing material from at least one surface area of a workpiece 12 by means of plasma-assisted chemical vapor deposition PECVD or plasma etching (CDE). The device 10 has a vacuum chamber designed as a chamber 14, which is shown in Fig. 1 in a sectional view. The chamber 14 forms with its inner walls 16 an inner space 18 which can be evacuated. In the lower region of the inner space 18, a high-frequency electrode (HF electrode) 22 which is electrically insulated from the inner walls 16 by means of insulators 20 is arranged. On the surface trained High-frequency electrode 22 is a workpiece holder 24 made of metal, on which in turn is held to be coated workpiece 12. This workpiece 12 is formed as a hollow body with a recess formed as a blind hole 26 recess. This cavity 26 is formed by a hard surface area 28 of the workpiece 12 formed by the inner wall of the hollow body.

The workpiece 12 is positioned spaced from the inner walls 16. Namely, the inner walls 16 at the same time form a reference electrode 29 of the device and carry as electrical reference potential e.g. Ground potential.

The device 10 further comprises a circuit arrangement 30 for feeding high-frequency signals or high-frequency voltage. For this purpose, the

Circuit arrangement 30 at least one high-frequency generator 32, at least one matching circuit part 34 for impedance matching in a matching unit ("match box") and a plurality of high-frequency line paths 36, 38, 40. The high-frequency generator 32 is on the High-frequency line paths 36, 38, 40 at spatially separate feed points 42, 44, 46 (or a, b, c) of the high-frequency electrode 22 connected.

About the switched between the high frequency generator 32 and the RF electrode 22 controllable matching circuit parts 34 in the so-called "match box", with the help of trim capacitors, the individual high frequency paths 36, 38, 40 to the feed points 42, 44, 46th be controlled separately to produce a homogeneous alternating field with uniformly high field strengths in the entire chamber.The high-frequency line paths 36, 38, 40 to the feed points 42, 44, 46 are capacitive in the region of the matching circuit part 34, The circuit arrangement 30 is set up for feeding the high-frequency voltage in succession into the individual feed-in points 42, 44, 46 of the HF-electrode, in particular by means of RC elements (not shown). Such a successive feeding of the high frequency into the individual feed points 42, 44, 46 of the HF electrode 22 produces a spatially varying plasma in the region of the workpiece 22. This plasma also extends into the cavity 26 of the workpiece 12 or 12 formed as a hollow body even forms preferentially in this cavity.

Fig. 2 shows the rough circuit diagram of the circuit arrangement 30 with the

High frequency generator 32, one of the three matching circuit parts 34 with

Trim capacitors, the interconnection of the three high-frequency line paths 36, 38, 40 and a supply line to the reference electrode 29, which is in the embodiment at ground potential (or neutral potential). The capacitive coupling of the matching circuit parts 34 with each other is not shown, since only one matching circuit parts 34 is shown.

Claims

Claims:

Device (10) for coating at least one surface region (28) and / or for removing material from at least one surface region (28) of an arbitrarily shaped workpiece (12) by means of plasma-enhanced chemical vapor deposition, with a chamber (14) having a high frequency -Electrode (22), a reference electrode (29) and an electrically conductive workpiece holder (24) and

radio frequency power supply circuit (30) comprising at least one high frequency generator (32) and high frequency line paths (36, 38, 40), said high frequency generator (32) having high frequency line paths (36, 38, 40) at spatially separate feed points (42, 44, 46) of the high-frequency electrode (22) is connected,

characterized in that the workpiece holder (24) is electrically connected to the plurality of feed points (42, 44, 46) having high frequency electrode connected (22).

2. Apparatus according to claim 1, characterized in that the high-frequency electrode (22) is formed flat.

3. Apparatus according to claim 1 or 2, characterized in that the feed points (42, 44, 46) are arranged linearly.

4. Apparatus according to claim 1 or 2, characterized in that the feed points (42, 44, 46) in the form of an n-corner, in particular an equilateral n-corner, with n = 3, 4, 5 ... arranged are.

5. Device according to one of claims 1 to 4, characterized in that the circuit arrangement (30) for sequentially feeding the high frequency in the individual feed points (42, 44, 46) is arranged.

6. Device according to one of the preceding claims, characterized in that the circuit arrangement (30) at least one matching circuit part (34) for

Has impedance matching of the RF feed.

7. The device according to claim 6, characterized in that the matching circuit part (34) has a trimming capacitor.

8. Device according to one of the preceding claims, characterized in that the high-frequency line paths (36, 38, 40) capacitively coupled to the feed points (42, 44, 46) in the region of the matching circuit part (34), in particular by means of RC elements are.

9. Device according to one of the preceding claims, characterized in that the chamber (14) has electrically conductive inner walls (16) which form an interior of the chamber (14) and at the same time form the reference electrode (29) or at least part of the reference electrode ( 29) form.

10. A method for coating at least one surface area and / or for

Removal of material from at least one surface region of a workpiece (12), in particular from a surface region (28) in at least one cavity (26) of the workpiece (12), by means of plasma-assisted chemical vapor deposition, characterized in that the coating by means of a device (10) is carried out according to one of the preceding claims.

11. The method according to claim 10, characterized in that the circuit arrangement (30) successively high frequency in the individual feed points (42, 44, 46) feeds.

12. The method according to claim 10 or 11, comprising the following steps:

Inserting the workpiece (12) into the chamber (14),

Positioning the workpiece (12) in the chamber (14), wherein a mutual minimum distance between the outer wall of the workpiece (12) and the inner wall (16) of the chamber (14) is to be observed,

Closing the chamber (14) and evacuating it to a residual pressure of 0.001 - 20 Pascal,

Introducing an inert working gas and one or more reaction gases via the gas supply device and / or a gas lance, and

Igniting a plasma by applying an electrical high frequency to the high-frequency electrode (22).