DE102004004177A1 - Producing controlled hardness diamond-like carbon layers on substrates, e.g. machine parts or implants, by ion-supported deposition from mixture of carbon-containing gas and carrier gas - Google Patents

Abstract

Ion-supported deposition method for producing diamond-like carbon layers (DLC's) of thickness d involves depositing the layer onto a substrate (cleaned by plasma etching and heated to 50-300[deg]C) from a gas phase of carbon-containing gas(es) and carrier gas at a base pressure of 0.1-100 mPa and a working pressure of 0.01-10 Pa, while forming an ion stream using a plasma discharge and applying a negative, pulsed potential U of -0.5 to -30 kV at a pulse frequency of 50-5000 Hz and pulse frequency 0.5-50 mu s to give an ion flux F to the substrate, where the hardness of the DLC is adjustable in the 1-30 GPa range via the process parameter Ein = F.U/d and the layer deposition rate is 0.5-5 mu m/h.

Description

The The invention relates to a method for producing diamond-like Carbon films (DLC) by means of an ion-based deposition process.

It is well known, a variety of substrate materials with thin films to coat from diamond-like carbon. Diamond-like carbon layers are layers of amorphous, hydrogen-containing carbon (a-C: H), the one big one Hardness and high elasticity, a good corrosion protection, a high chemical resistance, very low coefficient of friction and a smooth surface morphology can have. These properties make the DLC coatings attractive for industrial use Applications such as as low-friction and wear-resistant layers at high mechanical loads. Examples of potential tribological Applications of DLC coatings are the coating of drive components such as gears or shafts and the coating of press and Molds for the forming technique. Their good biocompatibility also allows for a use in the medical field, e.g. as a coating for endoprostheses in the anchoring or joint area and other implants.

Pure DLC layers can today in spite of their fundamentals excellent properties due to their high residual stress, their poor adhesion especially on steel substrates, for example, and their low thermal stability, especially as wear protection only with low, for many Applications are deposited inadequate layer thicknesses or but require elaborately prepared, e.g. with adhesive layers provided, substrates or special dopants. For many Applications therefore only have the option instead of a simple one DLC layer only multilayer coating systems deposit, but on the one hand to a lower hardness and on the other hand leads to a much more complex process.

In the DE 198 26 259 various examples of C-MeC multilayer structures prepared by a plasma CVD method are given. Whereby, for example, the metal (Me) in the metal carbide layer (MeC) may be tungsten, chromium or titanium and the carbon layer consists of amorphous hydrogen-containing carbon (aC: H). However, the need to manufacture the two single-layer systems in separate gas spaces renders this process unsuitable for industrial production.

Also in the EP 0 971 048 For example, a Me-C: H layer and a method for producing such a layer will be described. However, that is in the EP 0 971 048 described method a combination of conventional PVD method, such as DC magnetron sputtering or arc evaporation and plasma-enhanced CVD method by a plasma is ignited by pulsed DC voltage to the substrate.

adversely however, in all known methods, the processes are very sensitive to even the smallest changes the boundary conditions react and thus the results, so the Layers, partially different properties, e.g. different Layer thickness, hardness or adhesive strength. The reproducibility of the layer properties is in any case a high challenge. A disadvantage, the PVD method bring along, is in the process occurring occurring, strong directed particle transfer. The material to be deposited leaves the target perpendicular to the target surface. Complex three-dimensional workpieces must therefore in any case be moved through the coating plasma consuming, to be homogeneously coated. This results in a low dynamic coating rate, which is responsible for the economy Process, however, is crucial.

Furthermore is the target positioning, dimensioning and operation also very complicated, for example, a spatial and stoichiometric uniform target removal to ensure sputtering or arc cathodes. A removal of solids targets also always brings the risk of droplets (solid droplets) with them, which are completely prevented only by elaborate filter techniques can be. Another disadvantage with almost all conventional PVD such as CVD methods are the necessary high process temperatures during deposition wear protection layers, often far beyond 200 ° C lie. This is a coating of temperature-sensitive materials not possible.

task The invention is an economical process for the production of diamond-like carbon layers.

These Task is carried out according to the invention the subject of the independent Claim 1 solved. Advantageous developments emerge from the subclaims.

In the method according to the invention - claim 1 - for producing diamond-like carbon layers (DLC layers) of a thickness d by means of an ion-based deposition method with its process steps, a substrate is provided: This substrate may, for example, an arbitrarily shaped steel substrate (eg: cold work steel 1.2379 (X155CrVMol2-1), stainless steel 1.4305 (X 8 CrNiS 18 9), high speed steel 1.3343 (5 6-5-2), bearing steel 1.3505 (100Cr6)), as for example for components in drive technology or used for forming tools in plastics or metalworking. It may also be of another titanium, magnesium, aluminum or cobalt based metal alloy, as well as of glass, silicon or of a ceramic material.

The Liability problem, which in all common procedures exclusively on the Introduction of a bonding agent layer stored between substrate and DLC layer for example, is dissolved from Ti, Cr or Si, can in the inventive method technically relevant substrates, such as some steel grades, alone already by the high particle energy in the initial phase of the process solved become. This results in an implantation of ions and ion mixing of deposited layer and substrate material on the interface, which leads to improved adhesion in many substrates. Furthermore can by a pure implantation step, the coating process In-situ still can be preceded, the workpiece surface on the subsequent coating chemically or mechanically prepared (Pretreatment). On some substrates, both the pretreatment and also the ion mixing process also using additional Elements next to C and H take place, such as O, N or Si. By the high-energy particle bombardment in the pretreatment and Ion mixing phase of the process can also be a graded transition be constructed from substrate material to the layer material. properties like the thermal stability and the optical transmission can also over Doping be solved with elements such as O or Si. The latter, for example, on Values of over 90%.

Before the actual coating process, the surface of the substrate must be cleaned. After the prepurification under atmospheric pressure with, for example, alcoholic (isopropanol), ketonic or aldehydic (acetone) or aqueous solutions (on an alkaline basis), the substrate is introduced into the vacuum chamber and there at a base pressure between 1 × 10 ^-4 to 1 × 10 ^-1 Pa and a working pressure between 1 × 10 ^-2 to 10 Pa exposed to a noble gas ion bombardment. To generate the noble gas ions, eg Ar ^{(+ n)} (n> = 1), noble gas is introduced into the vacuum chamber and a plasma discharge via a microwave (eg 2.45 GHz) or high / radio frequency (eg 13, 56 MHz) ignited. In order to further improve the layer adhesion during the subsequent coating and to reduce layer stresses, the substrate can be brought to temperatures of up to 300 ° C. by means of an external heater (generally radiant heating) and / or the plasma power introduced. In the particularly advantageous embodiment of the method, the temperature remains below 200 ° C to gently coat material and temperature-sensitive substrates. These low treatment temperatures compared to conventional PVD or CVD processes are made possible by the high to very high particle energies (1 to 30 keV) of the process in the plasma.

As starting materials (precursor) for the preparation of aC: H layers can be a variety of gaseous or liquid hydrocarbons with or without hydrogen substituents (Si, F, B, N, O, metals), as well as carbonaceous solids (eg graphite), which then Solid source sources such as vacuum evaporator arc or sputtering cathodes are placed in the gas / sublimation phase, can be used. To synthesize the diamond-like carbon layers is a process atmosphere of at least one hydrocarbon-containing gas, such as methane or acetylene or heavy hydrocarbons such as the aromatic benzene (C ₆ H ₆ ), methylbenzene (C ₇ H ₈ ) or trimethylbenzene (C ₉ H ₁₂ ) and Ar, N, CO, or CO ₂ or mixtures thereof, wherein the base pressure during the deposition process in a range between 1 · 10 ^-4 Pa and 1 · 10 ^-1 Pa, advantageously at 5 · 10 ^-3 Pa and the working pressure in a range between 1 × 10 ^-2 Pa and 10 Pa, advantageously at 1 Pa. The process gas is introduced to the working pressure in the process chamber and at the ignition point (1 · 10 ^-2 Pa - 1 Pa), the plasma source at a power of 200 to 1400 W, advantageously 600 W ignited. The excitation of the gas molecules by the electromagnetic radiation leads to a splitting of the bonds of the process gases, whereby it comes to the generation of a plasma with high proportions of reactive ionized atoms, molecules and / or molecular clusters. The plasma spreads via diffusion in the process chamber. The reactivity of the plasma alone already allows the deposition of a layer on the substrate surrounded on all sides by the plasma. In addition, the plasma can still influence the energetic states of the surface of the substrates to be coated.

Without the application of a high voltage to the substrate, however, only a deposition of soft polymer films is possible when using hydrocarbons (plasma polymerization). In the method described here, in a pulsed mode, a negative high voltage in the range from -0.5 to -30 kV is applied to the conductive workpiece or, in the case of insulating substrates, to the conductive substrate holder arranged behind it. The growing layer on the substrate, which can be arbitrarily shaped, is thus bombarded by the positively charged and accelerated to the workpiece ions from the plasma. By the high elek As a result of the stress applied to the workpieces, the charged particles are always accelerated perpendicular to the equipotential surfaces and thus the workpiece surface. Thus, an attack from all sides is equally guaranteed. The bombardment with the high-energy ions leads to a densification of the deposited material, to a modification of the H-content of the layer as well as a modification of the bonding states in the layer (hybridizations) and thus to a greater hardness.

F:

Fluenz

U:

Spannung

d:

Schichtdicke ist,

konstant gehalten wird.Due to the high energy of the ions, the deposition rate can be increased compared to conventional deposition methods such as the sputtering or vacuum arc coating method or the CVD method and yet the necessary high hardness can be achieved, the process temperature, as mentioned, less than or equal to 200 ° C. The decisive factor is that the particle energy offered for more deposited layer volumes is increased, ie (FU / d), where

F:

fluence

U:

tension

d:

Layer thickness is,

is kept constant.

This can by the appropriate litigation in the case described here Procedure done.

The highest deposition rates with simultaneous high hardness could be achieved by ignition of an Ar plasma with methylbenzene feed. The use of other gas species such as CH ₄ or N ₂ or even a gas mixture with Ar or CO _{2 also} led to diamond-like carbon layers but with lower growth rate or lower hardness. The significantly lower deposition rate when using light hydrocarbons such as methane or acetylene as a carbon source is due to the less favorable C: H ratio or the higher proportion of free H radicals when using these precursors. In this case, both less C is released for deposition and at the same time more reactive H ⁺ ions, so that there is a higher etch rate. In total, this results in a low deposition rate of max. 1 μm / h.

conventional Plasma CVD methods can for procedural reasons offer only small particle energies from the plasma. When used of heavy hydrocarbons as precursors is therefore only one Deposition of soft polymer films possible because the decisive Parameter of particle energy is clearly too low and therefore only little energy during the deposit can be deposited in the layer, but for the necessary Modification of the bonding conditions, Breaking chains and rings as well as hybridization is needed. High rate deposition of hard a-C: H layers from this type of precursor is therefore not possible with conventional plasma CVD methods.

The Frequency of the high voltage pulses may be as described herein Method can be set between 50 Hz and 5000 Hz, advantageously 2000 Hz are used, the rising edge of the pulses advantageously 130 ns long and the duration of the pulses is approximately 0.5-50 μs, advantageously 1 μs.

The ion bombardment can be expressed by an ion fluence F in the unit [particle / cm ² ]. Typical deposition rates for DLC layers in this process are between 0.5 μm / h and 5 μm / h. The advantage of this method is above all in the high-rate deposition, ie greater than 2 μm / h.

Surprisingly, it was possible to establish a relationship between the particle energy E _in offered per deposited layer volume, which is composed of the fluence F of the ions, the applied pulse voltage U and the layer thickness d: e i n = F · U / d results and the layer hardness are found. The layer hardness was determined dynamically with the help of a nanoindenter based on the principle of Oliver and Pharr with a Berkovich diamond tip. This now allows the reproducible production of diamond-like carbon layers with a hardness in an interval of 1 to 30 GPa. Depending on the application of such carbon layers, different hardnesses are necessary since other properties such as abrasion resistance, etc. are also associated with the hardness. It is therefore indispensable for the economical production of diamond-like carbon layers to be able to adapt the method for producing such layers quickly and reliably to the respective requirement and thus also to realize deposition of hard layers with high rates at moderate coating temperatures.

In an advantageous method - claim 2 - is the Substrate prior to deposition of the carbonaceous layer with pretreated with an ion implantation step (pretreatment). This additional Process step increased u. a. the adhesion of the layer to the substrate.

In a further advantageous method - claim 3 - is also with the provision of a process atmosphere of a carbon-containing gas mixture of at least one carbon-containing gas and a carrier gas also Doping gas provided. This has the advantage, above all in applications in the field of semiconductor electronics, that the purchaser of the layers produced by this process receives a starting material with a homogeneous base doping for his further own processes. For mechanical or optical applications, for example in the field of automotive engineering or optics, it is possible to set properties that are necessary for these applications, such as coefficient of friction or transparency, in accordance with the application.

In a further advantageous method claim 4 - the carbonaceous gas is carbon (C), methane (CH ₄ , acetylene (C ₂ H ₂ ), an aromatic such as benzene (C ₆ H ₆ ), methylbenzene (C ₂ H ₈ ) or trimethylbenzene (C ₉ H ₁₂ ), or another heavy CH compound, all of which are industrially easy to produce and, in addition to being carbon donors, are therefore particularly suitable for an economical coating process.

In a further advantageous method - claim 5 and 6 - is as a carrier gas, a noble gas such as argon (Ar), or a gas such as nitrogen (N ₂ ), oxygen (O ₂ ), carbon monoxide (CO) or carbon dioxide (CO ₂ ) and as doping silane, silazane or siloxane, in particular SiH ₄ , HMDS, HMDSO and derivatives, or fluorine precursors such as hexafluorobenzene, fluorobenzene, tetrafluoroethylene, hexafluoroethane, and other fluorohydrocarbons, or organometallic precursors or a combination of these carrier and / or doping gases used , The advantage of using gaseous or liquid precursors is that the necessary doping elements are therefore available homogeneously in the gas space and do not flow from the source in a highly directional manner, as in the case of solid sources.

In a further advantageous method - claim 7 - is the carbonaceous gas mixture over Electromagnetic alternating fields ionized. This procedure has the advantage that the energy to be introduced for ionization is very easy to adapt to the respective gas species.

In a further advantageous method - claim 8 - is the carbon-containing gas mixture additionally via a vacuum arc discharge or transferred a Ionenabtrag in the plasma state. This method is suitable especially when using carbon solids, such as. Graphite, then over Vacuum evaporator arc or sputtering cathodes in the gas / sublimation phase is brought. In this way, additional carbon can be made available for example, to further increase the C: H ratio. Even if here from an additional Procedural step, the exclusive use of Carbon solids to provide the carbonaceous process atmosphere not be excluded.

In further advantageous methods, the substrate - claim 9 and 10 - of steel, magnesium, a titanium or aluminum alloy, a cobalt or cobalt-chromium alloy, silicon, glass or ceramic. For example, to increase the service life of forming or cutting tools, of bearing components such as balls or housings, or of drive components such as shafts and gears, usually made of steels such as 100Cr6 / 52100, X155CrVMo12-1 / D2, X8CrNiS189 / 303 or 42CrMoS4 It is advantageous to provide the steel products with low friction and hard wear protection layers such as DLC coatings. But also for optical components such as lenses, lenses and windows for optical systems, or for large-scale applications such as window glass, etc., a wear-resistant and chemically inert surface, as they form DLC layers, required by many industries. An increase in long-term stability is becoming increasingly important, especially in medicine in the field of human implants due to the ever-increasing life expectancy of the population. It is therefore particularly advantageous with the inventive method also typically used for implants materials, such as titanium alloys (eg TiAl ₆ V ₄ , TiAl ₆ Nb ₇ , TiNi), CoCr alloys, medical steels (eg 316L) or ceramic workpieces (eg Al ₂ O ₃ ) to coat.

In Another advantageous method - claim 11 - is the Process temperature kept below 200 ° C. Especially with substrates that already have a certain pretreatment obtained, such as hardened steels, may be too high a substrate temperature in coating basic properties of the substrate, such as. the hardness, ductility or breaking strength by phase transformations and / or microstructural transformations disadvantageous change. Below 200 ° C the risk of such processes is very low, leaving the original ones Properties of the substrate are retained as core properties but the surface properties adapted to the respective application requirements and thus sustainable can be improved.

In further advantageous methods - claim 12 - the ion current strikes the substrate surface almost perpendicularly at any point on the substrate. Due to the high electrical voltage of -0.5 kV to -30 kV, which is applied to the workpieces, the positively charged particles are always accelerated perpendicular to the equipotential surfaces and thus the workpiece surface. Thus, a uniform fire is guaranteed from all sides. Especially when coating komple xer three-dimensional objects, such as forming tools, gears, shafts or hip implants, is a uniform surface coating without having to move the workpiece and the high deposition rate is particularly economical.

An exemplary embodiment of a series of measurements on the surprisingly found relationship between layer hardness and E _in is illustrated in more detail below with reference to the drawing. It shows

1 Development of the layer hardness as a function of the particle energy introduced per volume.

In 1 the dependence of the layer hardness as a function of the particle energy introduced per volume is shown. The dashed line is only for better clarity. F is the ion fluence determined by Rutherford Backscattering Spectroscopy (RBS), U is the pulse voltage and d is the total layer thickness. It can be seen that with higher per volume of introduced particle energy, the layer hardness increases until it finally reaches a maximum. If the particle energy introduced per volume is further increased, the hardness of the layer decreases again. Corresponding determinations of the hydrogen content of the measured layers show that in area 1 of the 1 Thus, before the maximum hardness, an increase in the particle energy introduced per volume leads to a decrease in the hydrogen content and formation of new CC bonds. These bonds are both sp ² and sp ³ bonds. The latter lead to an increase in the layer hardness. In area 2 of 1 , ie after the maximum hardness, the increase in the particle energy introduced per volume leads to a destruction of the sp ³ bonds, which then converted into sp ² bonds again lead to a reduction in hardness.

In order to obtain the maximum achievable for a given working gas composition (hydrocarbons and other carrier gases) hardness with increasing deposition rate, simultaneously with the Abscheideratensteigerung and the deposited per shift volume energy must be increased, which is synonymous with the constant hold of the E _in parameter.

1

Area increasing hardness

2

Area decreasing hardness

Claims (12)

Method for producing diamond-like carbon layers (DLC layers) of thickness d by means of an ion-supported deposition method with the method steps - Providing a substrate - Cleaning the substrate by means of a plasma etching process - Heating the substrate to a process temperature, wherein the process temperature in the range between 50 ° C and 300 ° C - providing a process atmosphere of a carbon-containing gas mixture of at least one carbon-containing gas and a carrier gas, wherein the base pressure of the process in a range between 1 · 10 ^-4 Pa and 1 · 10 ^-1 Pa, and the working pressure in a range between ^{1.10 -2} Pa and 10 Pa. - depositing a carbon-containing layer from the gas phase on the substrate - generating an ion current by means of a plasma discharge and applying a negative, pulsed voltage U to the substrate, the voltage being in a range of - 0.5 kV to -30 kV, the Wiede repetition rate of the voltage pulses between 50 Hz and 5000 Hz, the pulse length between 0.5 μs and 50 μs and the ion current to an ion fluence F on the substrate characterized in that the hardness H of the diamond-like carbon layer in a range of 1 GPa to 30 GPa via the process parameters F, U, d formed. Parameter E _in = F · U / d is adjustable and the deposition rate of the layer between 0, 5 .mu.m / h and 5 .mu.m / h is. Method according to claim 1, characterized that the substrate before deposition of the carbonaceous layer is pretreated with an ion implantation step. Method according to claim 1 or 2, characterized that with the provision of a process atmosphere of a carbonaceous Gas mixture of at least one carbon-containing gas and a carrier gas also at least one doping gas is provided. Method according to one of claims 1 to 3, characterized in that the carbonaceous gas carbon (C), methane (CH ₄ ), acetylene (C ₂ H ₂ ), an aromatic such as benzene (C ₆ H ₆ ), methylbenzene (C ₇ H ₈ ) or trimethylbenzene (C ₉ H ₁₂ ) or another heavy CH compound. A method according to claim 3, characterized in that as doping silane, silazane or siloxane, in particular SiH ₄ , HMDS, HMDSO and derivatives, fluorine precursors such as hexafluorobenzene, fluorobenzene, tetrafluoroethylene, hexafluoroethane, and other Fluorokohlenwaasserstoffe, organometallic precursors or a combination of carrier and / or these doping gases is used. Method according to one of claims 1 to 5, characterized in that the carrier gas used is a noble gas such as argon (Ar), or nitrogen (N ₂ ), oxygen (O ₂ ), carbon monoxide (CO), or carbon dioxide (CO ₂ ). Method according to one of Claims 1 to 6, characterized that the carbon-containing gas mixture ionizes via alternating electromagnetic fields becomes. Method according to one of claims 1 to 7, characterized that the carbon-containing gas mixture additionally via a vacuum arc discharge or an ion removal is transferred to the plasma state. Method according to one of claims 1 to 8, characterized that the substrate steel, magnesium, a titanium or aluminum alloy, a Cobalt or cobalt-chromium alloy, silicon, glass or ceramic is. Method according to one of claims 1 to 9, characterized that the substrate is a component of the automotive or mechanical engineering, the drive, bearing or engine technology, a tool for forming, Cutting or other material processing, a component of pharmaceutical or chemical industry, a medical implant or an optical component. Method according to one of claims 1 to 10, characterized that the process temperature is kept below 200 ° C. Method according to one of claims 1 to 11, characterized that the ion current at each point of the substrate is nearly vertical on the substrate surface incident.