EP1784524A2 - Layered composite comprising cubic boron nitride - Google Patents

Abstract

The invention relates to a layered composite on a substrate, at least one individual layer of the layered composite containing cubic boron nitride and being produced by deposition. The aim of the invention is to provide a layered composite of this type with improved adhesive qualities. To achieve this, the cubic boron nitride contains oxygen, which is added during the deposition stage.

Description

Layered composite with cubic boron nitride

The invention relates to a layer composite on a substrate according to the preamble of claim 1. At least one layer of the composite layer contains cubic boron nitride.

Cubic boron nitride (BN) is due to its excellent Materi¬ aleigenschaften and especially as a superhard material - after the diamond, the hardest material ever - particularly suitable as a wear protection layer for chip-giving tools such as chisels, cutting, milling or drilling tools and for forming tools to increase their service life and / or the processing speed in use. The big advantage of cubic boron nitride over diamond is its chemical resistance to ferrous materials.

The synthesis of thin cubic boron nitride layers, i. with a layer thickness between 50 nm and 300 nm, is only possible by means of PVD or PECVD methods, because ion bombardment is an indispensable prerequisite for the formation of the superhard, cubic phase during layer growth. Due to the ion bombardment, however, such negative residual effects result in such high residual stresses that the layers fail above a certain thickness, typically between 50 nm and 300 nm, depending on the condition, ie. flake off of substrate. Therefore, despite their high potential, such layers could not yet be used.

By way of example, the following publications are referenced for the deposition of thick cubic boron nitride layers:

[1] describes cubic boron nitride layers, which are deposited via a plasma torch. With this technique, however, only small areas in the range of a few mm ^{2 can be} coated. Also within this small coating area, the layer thickness distribution and the layer structure method are conditional extremely inhomogeneous. The layer thickness drops continuously to zero in the furrow region, and on the other hand there are coated regions in which the boron nitride is almost exclusively not deposited in the cubic region. Furthermore, a limited reproducibility is observed, which manifests itself in considerable fluctuation ranges of the growth rate. With regard to the tool and component coating, the required targeted rastering of the plasma torch jet in accordance with the complex tool and component geometries is extremely costly and practically impossible for above-mentioned reasons in a high quality.

In [2] the production of thick cubic boron nitride layers with a boron carbide target in oxygen-free atmosphere is proposed. However, the layers containing carbon and no oxygen have a high residual stress level of up to 17 GPa.

In [3] the deposition of thick cubic boron nitride layers at high temperatures of typically 1200 ° C is described. In this case, residual stresses in the layer are degraded by incipient flow of the silicon substrate. This mechanism for reducing the residual stresses and the ¹ high substrate temperatures preclude the coating of tools.

In [4] cubic boron nitride layers are produced without oxygen addition, whereby their residual stress was decomposed by high-energy argon ion implantation with an energy of 300,000 eV. By alternating coating and ion implantation, which takes place in two different apparatuses, cubic boron nitride layers with thicknesses of 1.3 μm could be produced. The area that can be exposed to the ion implantation is typically 1 cm ² , the substrate volume is limited to 1 cm ³ and the range of the ions is about 180 nm. For the deposition of a 1.3 micron thick layer with an area of 1 cm ² is then required for 7 cycles, consisting of coating,

Ion implantation and heat post-treatment, half a month.

The object of the invention is therefore to suggest a layer composite in which boron nitride of at least one single layer is present in a cubic modification, has improved adhesion, and the abovementioned limitations and disadvantages, in particular for the coating of tools or other components, even with layer thicknesses above 2 μm or not at larger lateral dimensions.

The object is achieved by a layer composite with the characterizing features of claim 1. Subclaims give advantageous embodiments of the invention again.

An essential feature of the invention relates to the targeted addition of oxygen in the deposition of a cubic boron nitride layer by adding oxygen into the process gas. For better

Metering control, the addition can be made, for example, by argon (Ar) and by an Ar: C> ₂ gas mixture, where Ar is replaceable by another process gas, for example by helium (He), neon (Ne), krypton (Kr), xenon ( Xe) or nitrogen (N ₂ ). Furthermore, the oxygen can also be converted by an oxygen-containing target via a PVD process in the gas phase and separated from there.

The oxygen occupies the N sites of the cubic boron nitride lattice, intercalates lattice sites, or accumulates in the grain boundaries between the crystallites. Basically, the oxygen influences the deposition kinetics in a positive way, so that surface and volume diffusion processes can be optimized and thus the residual stresses are reduced even more during the layer growth.

As a result of the addition, the intrinsic stresses in the deposited coating can be reduced to such an extent and the Increase adhesive strength so far that layers with one for the

Wear protection relevant thickness of at least 2 microns can be produced. The targeted addition of oxygen preferably takes place during the entire coating process.

Oxygen-containing, cubic boron nitride layers can be prepared in principle with all PVD processes and all plasma-assisted CVD processes.

With these PVD and plasma mentioned CVD methods support layer-forming particles with a certain current density and a certain energy as neutral particles or as ionized particles on the substrate or on the growing layer and thereby become part of the lattice of the layer surface - or grown. Preferably, but not necessarily, the substrate serves as an electrode for the aforementioned electric field. The layer-forming particles may be:

Boron (B): neutral, mono- or poly-ionized,

Nitrogen (N): neutral, single or multiple ionized,

Oxygen (0): neutral, single or multiple ionized,

Molecules or clusters composed of boron, nitrogen and oxygen atoms: neutral, mono- or poly-ionized,

Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr) or Xenon (Xe), i. the elements of group 0 of the Periodic Table (noble gases, plasma atmosphere), neutral, mono- or poly-ionized,

• Foreign atoms, ions, molecules or clusters which, in addition to boron, nitrogen, oxygen, helium, neon, argon, krypton or xenon, also contain other elemental constituents, neutral, mono- or poly-ionized.

Furthermore, ions with a certain energy Ei _0n and a certain current density Φ _{on must} hit the substrate or the growing layer. These ions can be: Boron: single or multiple ionized,

Nitrogen: single or multiple ionized,

Oxygen: single or multiple ionized,

Helium, Neon, Argon, Krypton or Xenon, single or multiple ionized,

• Foreign ions, foreign molecule ions or foreign cluster ions which contain other elemental constituents in addition to boron, nitrogen, oxygen or noble gases, single or multiple ionized.

In this case, the current densities and the energy need of the layering particles and the ions are chosen such that with regard to the ele¬ commentaries composition of the layer the following conditions are met ^•

• the ratio of boron to nitrogen [B]: [N] must be between 0.85 and 1.15: 0.85 ≤ [B]: [N] <1.15,

• the oxygen concentration [O] must be between 3 At% and 15 At%: 3 At% <[0] <15 At%,

• the sum of the concentrations of helium [He], neon [Ne], argon [Ar], krypton [Kr] or xenon [Xe] may be up to 7 At%: [He] + [Ne] + [Ar] + [Kr] + [Xe] <7 At%

• the concentration of other elementary particles except boron, ^'Stick¬ material, oxygen, helium, neon, argon, krypton or xenon may be up to 5 at%, however, must be kept low if the particle formation of the cubic phase at a certain Concentration prevented and this concentration should be below 5 At%.

Furthermore, all particles which strike the substrate or the growing layer with a certain current density and are incorporated in the layer define the total flux of the layer-forming particles Φ _o . By averaging over the energy of these particles, the average energy E _{0 is} defined. All ions that are on the surface of the substrate or the growing layer with a meet certain current density, define the flow of ions Φi _on .

By averaging over the energy of these particles, the average ion energy E _{10n is} defined. The ratio Φi _on / Φo and di> e energies E ₀ and Ej _0n must be chosen so that the cubic phase forms.

It is within the scope of the invention to use oxygen for the reduction of residual stresses in composite materials (Corαposites and Nanocomposites), multilayer, multilayer and nanolaminierte multilayer layers and any combination of these layer concepts which wholly or partly of cubic boron nitride (c -BN). Furthermore, the two first layers are not a necessary prerequisite for the deposition of thick c-BN: O layers.

With the coating of tools with cubic boron nitride, the highest processing speed and the greatest increase in tool life are expected, especially in the machining area of iron-containing alloys, compared with all coatings available hitherto.

The invention will be explained in more detail with reference to an exemplary series of experiments with the following figures. Show it

1 shows an experimentally determined parameter field for the deposition of oxygen-containing, cubic boron nitride layers,

2 a and b AES overview spectra of a 500 nm thick oxygen-containing cubic boron nitride layer,

3 shows an AES overview spectrum of a 2550 nm thick oxygen-containing cubic boron nitride layer,

Fig. 4 shows an FTIR spectrum of a 1800 nm thick oxygen-containing, cubic boron nitride layer and Fig. 5 is an X-ray diffraction pattern of 1800 nm thick

Oxygen-containing cubic boron nitride layer.

With a CVD / PVD hybrid coating apparatus, oxygen-containing cubic boron nitride layers were successfully produced on planar silicon substrates, with layer thicknesses of 500 nm, 1.8 μm and 2.5 μm. The coating sources were magnetron sputtering units, an ECR ion gun and an ECR plasma source. The rotatable substrate holder was charged with a DC voltage or a high-frequency substrate bias and heated to 85O ⁰ C.

All layers were grown on a silicon substrate as a three-layer system consisting of a boron-rich ion energy-graded adhesion layer (hexagonal boron nitride-oxygen layer, h-BN: O layer), a composition-graded boron nitride oxygen nucleation layer, and a cubic boron nitride Oxygen cover layer (c-BN: O cover layer) prepared in the order mentioned. In the present case, there is thus a layer system with three individual layer types in three individual layers (individual layers). It is quite possible, as part of a multilayer system, to provide at least two of the single-layer types in periodic order as further individual layers.

Due to the selected process control, the adhesive strength was increased by the deposition of the first single layer, the nucleation of the cubic phase was controlled by the deposition of the second single layer and the actual growth of c-BN: O was optimized by depositing the third single layer.

The experimentally determined individual layer thicknesses and the deposition times of the three-layer system are reproduced below in Table 1. The individual layer thicknesses were realized solely by varying the coating times for the individual layers.

Tab. 1: Individual and total layer thicknesses and the deposition times of the oxygen-containing cubic boron nitride layers.

The production and process parameters for the individual layers listed in Tab. 1 are as follows, wherein the layer thicknesses are determined with the aid of scanning electron-sectional images and with the aid of surface profilometric measurements.

Process parameters for boron-rich, ion-energy-graded h-BN: O layer:

The stoichiometric, hexagonal boron nitride target of a magnetron sputtering unit is subjected to 500 W HF target power and atomized in an Ar-C> ₂ mixture. The gas mixture consists of 45 sccm Ar, 0 sccm N ₂ , 3 sccm of an Ar-C> ₂ gas mixture with a mixing ratio of Ar to O ₂ of 80% to 20%. The working gas pressure is 0.26 Pa and the substrate temperature 350 ^° C. The negative substrate bias amount has been increased from 0V in 30V increments to 330V at equidistant time intervals, and then to 350V.

Process Parameters for Composition-Graded BN: 0 Nucleation Layer:

The stoichiometric, hexagonal boron nitride target of a magnetic atomizing unit is irradiated with 500 W HF target power. aufschlagt and atomized in an Ar-N ₂ -O ₂ mixture. The Substrat¬ temperature is 350 ° C and the amount of the negative Substrat¬ prestress 350 V. The gas mixture consists of 45 sccm Ar and 3 sccm of an Ar-O ₂ gas mixture with a mixing ratio of Ar to O ₂ from 80% to 20% , The nitrogen gas is increased at equidistant time intervals from 0 sccm in 0.5 sccm increments to 5 sccm and then in 1 sccm increments to 10 sccm. The working gas pressure is initially at 0.26 Pa and at the end at 0.29 Pa.

Process Parameters for c-BN: O Topcoat:

The stoichiometric, hexagonal boron nitride target of a magnetron sputtering unit is exposed to 500 W HF target power and atomized in an Ar-N ₂ -O ₂ mixture. The substrate temperature is 350 ° C and the amount of negative substrate bias is 350 V. The gas mixture consists of 45 sccm Ar, 3 sccm of an Ar-O ₂ gas mixture with a mixing ratio of Ar to O ₂ of 80% to 20% and 10 sccm N ₂ . The working gas pressure is 0.29 Pa.

For the determination of the possible deposition parameters, the following procedure can be used in principle. If the layer does not contain a cubic phase for a chosen combination of Φi _on / Φo ^ Eo and Ei _0n , then the ratio Φ _Ion / Φ _o and / or the energies Eo and E _{10n must} be chosen larger until the cubic Phase forms, but not so large that by sputtering effects on the surface no more auf¬ growing (see Fig. 1).

Fig. 1 shows a diagram of the experimentally determined in the context of the embodiment relationship between the ion flux Φi _on i ^m ratio to the flow of the layer-forming particles Φ _BN (corresponding to the aforementioned generally held flow of the layer-forming particles Φ _o ) in dependence on the middle _Ion energy Ei _0n - The diagram shows three parameter _ranges 1 to 3. A cubic boron nitride oxygen layer (c-BN: O) deposits in the region 1, in a certain flux _ratio Φ _IOΠ / Φ _BN or the average ion energy Eion reach a certain level. If this level is not reached (range 2), then either the energy or / and the flow ratio is no longer sufficient for conversion in the direction of the cubic BN: O during the deposition; Thus, the hexagonal modification is deposited (h-BN: O). In area 3, on the other hand, either the energy and / or the ratio Φ _Ion / Φ _{BN is} too large, ie the layer-forming particles are atomized again, so that no BN: O layer builds up any more.

The substrate temperature T ₃ must meet the following conditions during the coating process:

During the nucleation process it must be at least 120 ^° C.: T ₃ > 120 ^° C.,

• be less than 90% of the melting temperature of the substrate T _M , s: T ₃ <T _M , s

• less than 90% of the melting temperature of the oxygen-containing cubic boron nitride layer T _{M / C} _ _B N _: O are: T _s <T _M , _C -BM _: O

The composition of the aforementioned individual layers was determined by means of AES (Auger electron spectroscopy). 2 a shows, by way of example, an overview spectrum (c / s = signals per second about the kinetic energy in eV) of the 300 nm oxygen-containing cubic boron nitride layer of the layer composite given in Tab. 1 with a total thickness of 500 nm after a removal of 20 nm for the purpose of surface cleaning. The spectrum shows three signals that can be assigned to the elements boron, nitrogen and oxygen. The elemental concentration results for boron at 48.6 at%, for nitrogen at 46.5 at% and for oxygen at 4.9 at%.

2 b shows, by way of example, an AES depth concentration profile of a layer composite given in Tab. 1 with a total thickness of 500 nm. From this, the homogeneous distribution of the element concentrations in the 300 nm thick oxygen-containing, cubic boron nitride cover layer can be determined as well as the element distribution in the adhesion promoter and the

Determine nucleation layer.

As the layer thickness increases, the electrical charge also increases in this analysis method. This complicates measurement and an accurate evaluation of the AES spectra, even if the charging of the analysis surface is at least partially compensated by the ion bombardment in combination with the offer of electrons. Therefore, in the composite layer with a total thickness of 2.55 μm, the BN: O layer had to be locally atomized by the ion beam down to the silicon substrate, forming a crater with a cross section similar to Gaussian distribution (crater profile). By scanning this mathematically describable crater profile, an accurate depth profiling could be performed, whereby charges are much easier degradable by a surface current over the crater profile to the silicon.

Fig. 3 shows the above-mentioned overview spectrum on the crater profile, i. the elemental composition of the 2 micron thick oxygen-containing, cubic boron nitride cover layer of the listed in Tab. 1 2.55 micron thick BN: O layer. Here, the boron concentration results to 49 At%, the nitrogen concentration to 46.3% and the Sauerstoff¬ concentration to 4.6 At%. Within the measurement accuracy, this is in very good agreement with the elemental composition of the oxygen-containing, cubic boron nitride cover layer of the 500 nm thick BN: O layer and corresponds to the expectations due to the process in the deposition of the cover layers.

The detection of the sp ³ -hybridized binding states takes place by means of infrared spectroscopy (FTIR, FIG. 4) and the detection of the cubic crystal structure by X-ray diffraction (XRD, FIG. 5). 4 shows a transmission infrared spectrum in the wavenumber range between 400 cm ^-1 and 8400 cm ^-1 . Evident is the pronounced residual beam band of the 1405 nm thick c-BN: O cover layer at 1080 cm ^-1 . Furthermore, the BNB flexural vibration at approximately 780 cm ^-1 and the BN Stretching vibration observed at 1380 cm ^"1 , mainly from the

Adhesive layer and the nucleation caused wer¬ the.

The oscillations are caused by layer thickness interferences. The 5 maxima at 7850 cm ^-1 , 6400 cm ^-1 , 5080 cm ^-1 , 3690 cm ^-1 and 2295 cm ^-1 and the four minimums between them can clearly be seen be estimated:

_ Number of periods _ 4 ^total ^ average refraction sin dex ■ wavenumber range 2 • 2 • (7850 cm ^"1 - 2295 cm ^{~ x} J

The X-ray diffraction pattern, which was taken in the grazing incidence, shows three signals which can be assigned to the c-BN: O. They correspond to the signals of (111) c-BN at 43.3 °, (220) c-BN at 74.1 ° and (311) c-BN at 89.8 °. Thus, the detection of the cubic, oxygen-containing boron nitride phase was provided by means of FTIR and XRD.

With the aid of a nanoindenter from Hysitron, the hardness was measured on an approximately 2 .mu.m thick, oxygen-containing, cubic boronitride layer. The layer hardness was found to be 59.2 GPa ± 2.3 GPa at a maximum load of 2 mN, 59.6 GPa ± 1.9 GPa at 5 mN and 60.5 GPa ± 1.6 GPa at 10 mN, which corresponds to the theoretically expected value.

literature

[1] S. Matsumoto, W. Zhang: Jpn. J. Appl. Phys. 39 (2000) L442

[2] K. Yamamoto, M. Keunecke, K. Bewilogua: Thin Solid Films, 377/378

(2000) 331

[3] D. Litvinov, CA. Taylor, R. Clarke: Diamond Relate. Mater. 7

(1998) 360

[4] H. -G. Boyen, P. Widmayer, D. Schwertberger, N. Deyneka, P.

Ziemann: Appl-Phys. Lett. 76, (2000) 709

Claims

claims 1. Layer composite on a substrate, wherein at least one individual layer of the composite layer contains cubic boron nitride and is produced via a deposition, characterized in that the cubic boron nitride contains oxygen, which during the Deposition is added. 2. Layer composite according to claim 1, characterized in that the layer composite consists of a single layer. 3. Layer composite according to claim 1 or 2, characterized in that the deposition takes place by means of PVD- or plasma-assisted CVD method. 4. Laminate according to one of the preceding claims, characterized in that the substrate is wholly or partially formed by the surface of a cutting tool or a Umformwerk¬ tool. 5. Laminate according to one of the preceding claims, characterized in that the composite layer a boron-rich ion energy-graded adhesive layer, a composition-graded boron nitride oxygen nucleation layer and a cubic boron nitride oxygen cap layer on a substrate in said Order includes. 6. Laminate according to one of the preceding claims, characterized in that comprises a periodic sequence of at least two types of individual layers and contains at least one of the single-layer types of oxygen-containing cubic boron nitride. Laminate according to one of the preceding claims, characterized in that at least one single layer is a nanocomposite in which a component contains oxygen-containing cubic boron nitride.