DE4210508C1 - Mixed diamond - silicon carbide coating with good adhesion - consists of intimate mixt. of diamond phase and cubic beta silicon carbide phase, which can vary across coating thickness - Google Patents

Abstract

Mixed diamond-SiC coating consists of an intimate mixt. of diamond phase and cubic beta-SiC phase, with a compsn. expressed by (beta-SiC) x (diamond)1-x, (where x is the molar fraction of SiC), which can vary across the coating thickness. The zones of individual phases of the mixt. consist of grains with dimensions in the micron range. ADVANTAGE - Physical and mechanical properties are varied over a wide range, good adhesion

Description

The invention lies in the field of artificially produced diamond layers and Process for the deposition of these layers from the gas phase.

The special physical properties of diamond, such as

• - extreme hardness and rigidity,
• - optical transparency from UV to millimeter wave range,
• - a thermal conductivity that exceeds copper by a factor of 5, such as
• - Excellent properties as a semiconductor material

lead to a multitude of possible applications in the most varied of ways Fields of technology.

It has been known since the early 1980s that diamond, one of the Normal conditions compared to graphite metastable carbon modification, through activated CVD processes (chemical vapor deposition: chemical Vapor phase deposition) bypassing graphite formation Separate gaseous hydrogen / carbon mixtures as a layer leaves. In these CVBD processes, the gas phase is usually replaced by a plasma or thermally activated, instead of the thermodynamically stable graphite the diamond phase is formed.

So far, pure diamond layers have been produced with these processes, whose physical and chemical properties predominantly through the intrinsic diamond properties can be determined. The variability of  Layer properties are therefore low. The currently known pure Diamond layers also show insufficient adhesion Substrate materials such as B. on hard metal or substrates that are not contain larger amounts of silicon.

JP-A62-2 18 566 and JP-A62-1 33 068 describe diamond-SiC composite layers described. These layers are multiple layers and consist of so-called layer stacks with sharp interfaces. Here too is the Variability of the layer properties low and the adhesion on different substrate materials are not optimal.

The object of the present invention is to achieve a layer for To make available, their range of properties, in particular the thermal and mechanical data, based on the properties of a pure diamond layer is variably adjustable in certain areas. The layer is also said to have good adhesion to a variety of substrate materials have, especially on such as. B. Fe, Co, Ni, on which pure Diamond layers adhere insufficiently.

The object is achieved in that a diamond-silicon carbide mixed layer is produced which consists of an intimate mixture of the diamond phase and the cubic β-silicon carbide phase. In this way, a novel material of the composition (β-SiC) _x (diamond) _{1-x is created} , the molar β-SiC component x being in the range 0 <x <1 and, depending on the application, varying over the layer thickness can.

In a preferred embodiment of the mixed layer according to the invention, the regions of the individual phases of the layer are formed from grains with dimensions in the μm range or smaller. According to the invention, grains are understood to mean homogeneously deposited, contiguous areas of the diamond or the β-SiC phase, which can look as shown in FIG. 1.

Another embodiment is a mixed layer according to the invention, in which the molar proportion of β-SiC x starting from an almost pure β-SiC Layer changes continuously over the layer thickness from x to 0, so that the Layer surface is formed by an almost pure diamond layer.

The mixed layer according to the invention preferably has a layer thickness of 20 nm to 1 mm.

Further embodiments can be applied by applying the invention Mixing layer on substrates consisting in particular of Fe, Co, Ni or contain these elements.

The mixed layer according to the invention can be obtained by deposition from the Gas phase with a CVD process in which a gas mixture of hydrogen, Tetramethylsilane (TMS) and hydrocarbons, preferably methane, in Reactor of the CVD process is used, and the process parameters like this that the growth conditions for diamond and β-SiC are fulfilled at the same time. It does not matter whether the gases are already as Mixtures passed into the reactor or by separate feeding only in the reactor be mixed.

In the preferred embodiment of the method, the Substrate temperature in the range of 400 ° C to 1000 ° C, the gas flow in the range from 10 sccm (cm³ / min under standard conditions) to 5 slm (l / min under Standard conditions), the concentration of hydrocarbons, preferably of methane, in the range up to 2 vol .-% and the concentration of Tetramethylsilane in the range up to 1 vol .-%, both concentrations unequal 0 vol .-% are.

The level of the molar β-SiC component x of the mixed layer according to the invention can in the manufacturing process described here by the value of Tetramethylsilane concentration set in the reactor of the CVD process will. Due to the level of the tetramethylsilane concentration, the SiC Deposition rate and the layer quality significantly affect.  

In a special embodiment of the method according to the invention the tetramethylsilane concentration in the reactor by varying the feed Amount changed during the deposition process, so that a Mixing layer according to the invention is obtained in which the molar β-SiC Proportion x varies over the layer thickness.

In a further development of this embodiment, during the Deposition process the concentration of tetramethylsilane in the reactor continuously or gradually from approx. 1 vol .-% to a value less than 0.001 vol. = To be reduced. This allows a mixed layer to be produced whose molar proportion of β-SiC x is based on the layer thickness starting from one almost pure β-SiC layer reduced from x to 0.

A preferred embodiment of the method according to the invention is shown in using a microwave plasma CVD process or one Hot wire CVD process ("hot filament" CVD) for the deposition of Mixed layer according to the invention from the gas phase.

The diamond-silicon carbide mixed layer according to the invention is used in the production of thin layers, especially in the component or Tool coating as well as for manufacturing or coating electronic components.

With the solution of the problem according to the invention, there is a Series of advantageous effects over the previously known state of the Technology.

Through the intimate mixture of the diamond and the β-SiC phase and with it given possibility of varying the molar proportion of β-SiC x the Mixed layer according to the invention can be within the range 0 <x <1 affect a variety of properties of the layer, particularly thermal and mechanical data, such as B. thermal Expansion coefficient or modulus of elasticity. So that is within certain limits  an adaptation of the layer to substrate properties is possible. This variability the properties cannot be achieved with the previously known layers. Diamond layers usually show insufficient adhesion Substrate materials that do not contain large amounts of silicon (Si itself, Si₃N₄ etc.). The new layer material can play the role of a adhesion-promoting intermediate layer, e.g. B. on carbide or on Steel tools, play. SiC layers are on different metals (with Layer thickness up to a few 100 m) can be produced with good adhesion (Gmelin Handbook Si, Suppl. Vol. B2, SiC, Part 1, s. 272). Starting from an almost pure SiC layer can be a good by steadily reducing x to 0 adhesive diamond layer obtained on a variety of substrate materials will.

A number of metals, especially iron, cobalt and nickel, promote the Deposition of graphite instead of diamond. A mixed layer of SiC and Diamond can also help here, since the SiC-rich intermediate layer Graphite formation suppressed.

Pure diamond layers oxidize noticeably in air above 600 ° C. It's closed expect the oxidation in the mixture with SiC, for example when used as Tool coating, inhibited by the formation of SiO₂ protective layers becomes. In spite of the lattice constant difference, β-SiC can under certain Conditions (removal of the SiO₂ surface layer by hydrogen Plasma etching, precarburization of the Si) are epitaxially applied to Si. A diamond layer can be obtained by continuously reducing x to 0 be, whose orientation by the orientation of the SiC component in the Mixing layer is determined. This possibility is of great importance for everyone Areas of application, especially for electronic applications.

The invention is explained in more detail below with the aid of exemplary embodiments and FIGS. 1 and 2. It shows

Fig. 1 is a schematic representation of the microstructure of the diamond-silicon carbide-mixed layers,

Fig. 2 is an X-ray diffraction diagram of diamond-silicon carbide mixed layers (No. 151 091).

The diamond-silicon carbide mixture layers were in a microwave Plasma CVD reactor in a gas mixture of hydrogen, methane and Tetramethylsilane (TMS) manufactured. Since TMS is one at room temperature Liquid phase with a relatively high vapor pressure was initially a 1% TMS / hydrogen gas mixture used.

In each experiment, two silicon wafers were used as the substrate; one of them was pretreated with ultrasound using diamond particles (70 μm, aqueous suspension). Both were cleaned in an acetone ultrasonic bath prior to the deposition experiment. After positioning the substrate in the reactor, the vacuum chamber was evacuated to 10 ^-2 mbar and the substrate was heated to 900 ° C. The process gases were then fed in and the plasma ignited.

Table 1 shows the deposition parameters from three experiments. "a" means with Diamond pretreatment and "b" without pretreatment. The deposition was at a total gas flow of approx. 500 cm³ / min (under standard conditions) in Pressure range from 20 mbar to 30 mbar.

The samples were characterized by X-ray diffraction, IR absorption, electron beam microsensor and Raman scattering. The results show that the layers consist of a fine-grained mixed phase of diamond and β-SiC crystals with a grain size in the μm range or smaller. Fig. 1 shows a schematic representation of the layer structure on the basis of the microstructure analysis. Fig. 2 shows a high resolution x-ray diffraction; one can clearly see the strong lines of β-SiC 5 and diamond crystals 6.

Since under normal conditions diamond hardly any germs on non-pretreated As silicon forms, it is difficult to achieve diamond deposition. Therefore SiC was predominantly formed on an untreated substrate. Man therefore receives a significantly lower growth rate and due to this also a smaller layer thickness.  

Table 1 shows the difference between pretreated and non-pretreated Substrates.

Table 1

Manufacturing conditions

Since the SiC deposition rate is strongly dependent on the TMS concentration (with the increasing TMS content from 0.006 vol .-% to 0.2 vol .-% decreases Deposition rate from 2 nm / min to approx. 8 nm / min) can be achieved by Change in TMS concentration during the process the proportion of β- SiC phase vary over the layer thickness. In experiment no. 22 1091 we have set and reached a relatively high TMS content in the gas phase therefore a relatively high deposition rate with an almost pure β-SiC phase.  

In Fig. 1, the layer structure of the diamond-silicon carbide mixed layer 1 is shown schematically on a substrate 4 on the basis of the microstructure analysis. The diamond-silicon carbide mixture layer 1 consists of an intimate mixture of the diamond phase 2 and the β-silicon carbide phase 3 . The areas of the individual phases are formed from grains, ie from homogeneously deposited, contiguous areas of the diamond phase 2 and the β-SiC phase 3 , which can look as shown in FIG. 1.

FIG. 2 shows a high-resolution X-ray diffraction diagram, which was recorded by one of the diamond-silicon carbide mixed layers produced in the exemplary embodiment (No. 15 1091, see Table 1). The strong lines of β-SiC (111) 5 and diamond (111) 6 can be clearly seen.

Claims (12)

1. Diamond-silicon carbide mixture layer ( 1 ), which consists of an intimate mixture of the diamond phase ( 2 ) and the cubic β-silicon carbide phase ( 3 ) of the composition (β-SiC) _x (diamond) _1-x with 0 <x <1, where x indicates the molar proportion of β-SiC, which may vary over the layer thickness. 2. Mixing layer according to claim 1, wherein the areas of the individual Phases of the intimate mixture of grains with dimensions in μm Area or smaller. 3. Mixing layer according to claim 1 or 2, in which the molar β-SiC- Proportion x starting from an almost pure β-SiC layer over the Layer thickness changes continuously from x to 0. 4. Mixed layer according to one of claims 1 to 3 with a layer thickness which is preferably in the range from 20 nm to 1 mm. 5. Mixing layer according to one of claims 1 to 4 on substrates ( 4 ) which in particular consist of Fe, Co, Ni or contain these elements. 6. A method for producing the mixed layer according to one of the claims 1 to 5 by deposition from the gas phase using a CVD process, characterized in that a gas mixture consisting of Hydrogen, tetramethylsilane and hydrocarbons, preferably Methane, which is used in the reactor of the CVD process, and that Process parameters are set so that the growth conditions for diamond and β-SiC are fulfilled at the same time. 7. The method according to claim 6, characterized in that the substrate temperature in the range of 400 ° C to 1000 ° C, the gas flow in the range of 10 cm³ / min (under Standard conditions) up to 5 l / min (under standard conditions)  Concentration of hydrocarbons, preferably methane, in Range up to 2 vol .-% and the concentration of tetramethylsilane in Range up to 1 vol .-%, both concentrations not equal to 0 vol .-% are. 8. The method according to claim 6 or 7, characterized in that the molar proportion of β-SiC x the Mixing layer by the value of the tetramethylsilane concentration in Reactor is set. 9. The method according to claim 8, characterized in that during the deposition process Tetramethylsilane concentration in the reactor by varying the supplied amount is changed so that the molar proportion of β-SiC x changes over the layer thickness. 10. The method according to claim 9, characterized in that during the deposition process Tetramethylsilane concentration in the reactor as a function of time is changed so that the molar proportion of β-SiC x in the layer starting from an almost pure β-SiC layer, continuously from x to 0 changes. 11. The method according to any one of claims 6 to 10, characterized in that preferably a microwave plasma CVD process or a hot wire CVD process for deposition from the Gas phase is used. 12. Use of the mixed layer according to one of claims 1 to 5 for Production of thin layers, especially in the component or Tool coating as well as for the production or coating of electronic components.