WO1997008360A1

WO1997008360A1 - Method for forming a metallic or ceramic deposition coating

Info

Publication number: WO1997008360A1
Application number: PCT/IB1996/000824
Authority: WO
Inventors: Jean-Marc Agullo; Muriel Touanen; Dominique Richon
Original assignee: M3D Societe Anonyme
Priority date: 1995-08-25
Filing date: 1996-08-22
Publication date: 1997-03-06
Also published as: FR2738017A1

Abstract

A method for coating a metallic or ceramic substrate (15) with a complex metallic or ceramic material from two or more organometallic precursors by chemical vapour deposition includes decomposing the two organometallic precursors by sublimation in two separate crucibles (16) in a reactor (6) into which a suitable gas is fed, while simultaneously rotating said substrates (15) above the two crucibles (16), and reacting these components at the surface of the substrate, heated to a temperature of about 650° to 850 °C. Each of the precursors is sublimated at a suitable temperature according to the desired proportion of the two components in the coating.

Description

PROCESS FOR FORMING A METAL OR CERAMIC DEPOSIT

CERAMIC FROM AT LEAST TWO METAL PRECURSORS

The present invention relates to a method of forming a complex deposit containing at least two metallic or ceramic elements by chemical vapor deposition (CVD) on a metallic or ceramic substrate, as well as to a device intended to form a deposit. complex from at least two metallic or ceramic precursors by the CVD technique.

The complex coatings, in particular ceramics, produced by the CVD technique are well known. The precursors used to make these coatings are generally in the form of halides which are decomposed hot and the metal elements of which are reacted with oxygen, a hydrocarbon and / or nitrogen to form oxides, carbides, nitrides or carbonitrides. The advantage of this coating technique is to give excellent adhesion of the coating to the substrate. This is the reason why CVD is used in particular for coating cutting tools.

The disadvantage of this technique is that it requires heating the substrate to temperatures of the order of 1300 ° K and more, thereby limiting the nature of the substrates on which CVD coatings can be produced.

It has been proposed to lower the temperature of the substrate by replacing the precursors in the form of halides with organometallic precursors. This is how J. Slifirski

(Perpignan thesis, 1993, N ° 257C) proposed to deposit TiC, TiN or TiCN on a metallic substrate starting from an organometallic precursor Ti (C ₅ H ₅ ) ₂ Cl ₂ sublimed in a reactor supplied with H ₂ with a certain percentage of NH ₃ .

This type of precursor has also been proposed in EP-A1-0 387 113, according to which it is proposed to precede the deposition with an ionic pickling.

US-2,898,235 proposes to deposit metals or alloys from organometallic type precursors. However, it is not proposed to react these metals with gases, these are only used as neutral vector elements with respect to the metals to be deposited.

It has been proposed in "Thin Solid Films" ¹ September 1994, Vol. 249, no 1, Lausanne (CH), Poirier L. et al: "Vanadocene used as a precursor for the chemical vapor deposition of vanadium carbide at atmospheric pressure", to carry out the pyrolysis of a precursor (C ₅ H ₅ ) ₂ V for the deposition by CVD of crystalline vanadium carbide, on a steel substrate at a temperature of 973 ° K in a cold-walled reactor. JP-A-62 218574 published as an abstract in "Japanese Abstracts of Japan" vol. 012, no. 082 (C-481), March 15, 1988, relates to a device for CVD deposition assisted by plasma under reduced pressure from two precursors in the form of halides each disposed in a vaporization chamber in direct communication with a reaction arranged below. The vapors of these precursors are brought by a carrier gas onto substrates mounted on a rotary support. This is a relatively conventional CVD installation, using a carrier gas to bring the reaction products to the substrate. The precursors in liquid form are evaporated and the vapors are transported from top to bottom on the substrates by the gas stream. The system can only operate at reduced pressure. In addition, the efficiency of such a system is very low, a large part of the reactive gas being deposited on the walls of the reactor or of the evaporation chambers. It is also known that a solid solution of mixed carbonitride of Ti and Zr makes it possible to further increase the mechanical properties, in particular, the hardness. It is further assumed that it has excellent resistance to hot oxidation, even in an aggressive medium and gives good resistance to aqueous corrosion.

The object of the present invention is to make it possible to produce a complex deposit from at least two metallic or ceramic precursors with the possibility of varying the concentrations of the metallic or ceramic complexes deposited.

To this end, the subject of the present invention is a process for forming a complex deposit according to claim 1. The advantage of this process lies in the possibility of allowing a dosage of the components, of being able to work at atmospheric pressure depending on the case. , to have a high deposition efficiency, to work at lower temperatures than with halogen precursors, while retaining the advantages inherent in CVD.

The appended drawing illustrates the process and the results obtained using the deposition process which is the subject of the present invention.

Figure 1 is a schematic sectional view of the experimental enhancer used to produce the examples.

Figure 2 is a diagram of% at. of Zr with respect to Ti as a function of the lattice parameter determined by RX.

Figure 3 is an X-ray image showing the distribution of the elements in the repository. Figure 4 is a schematic sectional elevation view of the enhancer for the implementation of the method of the invention.

The examples which follow were carried out in a CVD deposition apparatus with cold walls with a sublimator in the reactor. The distance between the sublimator and the substrate is 40 mm. FIG. 1 illustrates the sublimator used to carry out these examples and which comprises two crucibles of Al ₂ 0 ₃ , an external crucible 1 and an internal crucible 2. A space is provided between the two crucibles to receive the precursor TiCp ₂ Cl ₂ (Cp : cyclo pentadienyl C ₅ H ₅ ), while the precursor ZrCp ₂ Cl ₂ is placed in the interior crucible

2. The crucibles are surrounded by a heated coil

3. A cover 4 of Al ₂ 0 ₃ pierced with a central opening 5 is placed on the external crucible 1 while the edge of the internal crucible 2 is located at a distance from the cover 4 in order to allow the passage of the vapor of the precursor TiCp ₂ Cl ₂ to the substrate placed 40 mm above.

The examples were carried out according to the following protocol: The substrate and the precursors are introduced into the reactor which is placed under vacuum for approximately 2 hours. Pumping is then stopped to fill the reactor with hydrogen until the pressure reaches atmospheric pressure at which the deposition process takes place. The sublimator is heated until the temperature reaches 513 ° K using the heating coil 3.

In parallel, the substrate is heated using an HF generator until its temperature T _s reaches between 923 ° and 1123 ^β K. When the temperature of the precursor reaches 513 "K, the flow rate of ammonia is adjusted by gas phase at the desired value and the process lasts 3 hours from this point in. The voltage across the heating winding 3 must be monitored at least for the first hour in order to achieve good thermal equilibrium.

During the cooling phase following the shutdown of the HF generator and the voltage across the heating coil 3, the hydrogen and ammonia flow rates are stopped and replaced by 1.67.10 ~ ⁶ m ³ / s d 'argon for at least% hour so as to purge the ammonia flow meter and the reactor before dismantling. The experimental sublimator, illustrated in FIG. 1, made it possible to sublimate fractions of precursors of the order of 10 ^~ . The melting temperature of TiCp ₂ Cl ₂ is 538 ° - 543 ° K (supplier: Fluka) and an optimal sublimation speed is obtained at 513 ^β K without any decomposition of the precursor (a first fragmentation is observed at from 563 ° K). By analogy, we assume that there is no decomposition of ZrCp ₂ Cl ₂ below its melting temperature which is given by the supplier (Aldrich) at 513 ° K. Under these conditions, the two precursors are sublimated at the same temperature.

All the above parameters being fixed, the examples given in the table below only vary as a function of the temperature T _s of the tungsten carbide substrate with cobalt binder and of the% of ammonia in the gas phase mixed with hydrogen . It is indeed these two parameters which have the greatest influence on the composition of the deposit. The results of the examples come from RX and MEB-EDX analyzes (at the surface). SEM-EDX: the atomic percentages come from a surface (magnification 100) located in the center of the sample. The growth rates were measured on polished sections.

RX: the mesh parameter is calculated from the only line (200) of the deposit which is not disturbed by the lines of the substrate. Beforehand, the spectrum is readjusted on the line (110) of the WC of the substrate (20 = 63.977 °).

TABLE I

The atomic percentages shown in this table come from a surface analysis. It has been verified that the results are identical on a polished cut, which shows uniformity of the distribution of elements in depth We were able to plot Figure 2 which represents the atomic percentage of Zr as a function of the lattice parameter, using an assay of Ti and Zr on a polished section and RX results. The boundaries, delimited by the theoretical parameters, of TiN, ZrN, TiC and ZrC are also indicated on this diagram in FIG. 2.

The results of Table I above and of the diagram in FIG. 2 make it possible to make various observations: The growth rates are overall lower than those observed during the deposition of Ti carbonitride from the same precursor. This suggests that the conversion rate of ZrCp ₂ Cl ₂ is lower than that of TiCp ₂ Cl ₂ at the same pyrolysis temperature. A percentage of NH ₃ of 10% seems to be quite sufficient, because at 1123 ° K an additional excess has a growth-inhibiting effect as has been observed during the deposition of titanium carbonitride alone, from the same precursor . The area covered by the examples is located in the zone rich in Zr which is linked to the physiognomy of the assembly which does not allow the two precursors to be heated independently. On the other hand, the variation of the temperature of the substrate intervenes only on the growth rate and not on the Zr content of the deposit. Under these conditions, the sublimation temperature of the products would affect the Zr / (Zr + Ti) ratio, while that of the substrate would only influence the growth rate.

FIG. 3 is an X-ray image made on a sample according to example 1 of the table above and showing a good distribution of the elements of the deposit.

The foregoing examples all relate to mixed carbonitrides of Ti and Zr. It is obvious to those skilled in the art that mixed carbides of Ti and Zr can also be obtained. For this purpose, it suffices simply to suppress the supply of ammonia in the H ₂ . As indicated, the sublimator illustrated in FIG. 1 was used to obtain the above examples. Another type of sublimator is contemplated or even the use of two sublimators, one for each precursor, in order to vary the concentrations of Ti and Zr in the deposit.

FIG. 4 schematically illustrates the installation used with a view to making it possible to vary the proportions of Ti and Zr, given that the previous examples, produced using the reactor of FIG. 1, do not allow the ratio Zr / Ti which remains around 9/1. The reason is that the sublimation temperature of Ti is significantly higher than that of Zr. This is the reason why the precursor of Ti was put in the outside crucible and that of Zr in the inside crucible. However, this measure was not sufficient. Putting the two precursors in two separate crucibles, separated from each other poses a problem of homogenization of the mixed compound Ti, Zr. In this case, on the one hand, TiC or TiCN is obtained, on the other hand, ZrC or ZrCN. If the two crucibles are too close to each other, the problem is not resolved however and in addition there is heat transfer by radiation between the two crucibles.

The installation illustrated in FIG. 4, making it possible to solve the problem of the variation of the Zr / Ti ratio, in the coatings of carbides or carbonitrides from solid organometallic precursors comprises a tubular enclosure 6 made of quartz, the base of which is fixed sealingly known to a base plate 7 pierced with several openings including in particular the openings 8,9 to supply this enclosure with gas. In this example, these gases, in the case of carbonitride, are H ₂ and the nitrogen precursor NH ₃ . Other openings are provided for the connection of the heating of crucibles and that of thermocouples as will be seen later. The upper end (not shown) is connected in the usual way to a vacuum pump. An opening 10, formed in the center of the base plate 7, serves for the sealed passage of a shaft 11, the internal part 11a of which is made of alumina, extending coaxially to the axis of revolution of this tubular enclosure 6. The lower end of the internal part 11a is engaged with a sleeve connection 12, while the upper end carries a disc 13 for supporting substrates. This disc 13 is in steatite. In this example, it has 4 openings 14 each having a shoulder 14a serving to support the substrate 15 to be coated. The substrate 15 is held in the housing 14 by a graphite cylinder 14a. An electrical winding 27 connected to a high-frequency HF current source surrounds the tubular enclosure 6 at the level of the disc 13 in order to heat the substrates 15 via the graphite cylinders 14a. Crucibles 16, four in number in this example, are distributed at equal angular distance from each other around the axis of revolution of the tubular enclosure 6. These crucibles 16 are positioned in indentations 17 formed in a support 18 fixed to four feet 19 placed in blind positioning holes 20 formed on the base plate 7, A steatite cover 21 pierced with openings 22 corresponding to the openings of the crucibles 16 is placed on these. Heating bodies 23 and thermocouples 24 are used for controlled heating of each of the crucibles. These heating bodies and these thermocouples are connected to the outside of the sealed tubular enclosure 6 by openings made through the base plate 7, the passage of the connection wires through these openings being made in leaktight manner by the means usually used in CVD reactors.

The connection sleeve 12 comprises several screws 25 which allow the shaft 11a to be fixed at variable heights and therefore to adjust the author of the disc 13 for supporting the substrates 15 and thus to vary the distance between the crucibles 16 and the substrates 15. The lower end of the connection sleeve 12 is fixed the shaft 11 which is that of a variable speed motor 26. In the case present, this speed can vary from 30 to 300 rpm in order to rotate the disc 13 and consequently the substrates 15 to be coated with respect to the crucibles and thereby produce a combined deposit of the various precursors contained in the crucibles by reacting or not also with a gaseous precursor, in this example, with NH ₃ . Using the installation of FIG. 4, TiZrCN coatings were carried out at atmospheric pressure from the aforementioned precursors TiCp ₂ Cl ₂ and ZrCp ₂ Cl ₂ disposed respectively in two of the four crucibles 16 located at 180 ° l of each other. The enclosure 6 is supplied with H ₂ and 5% NH ₃ .

TiCp ₂ Cl ₂ was heated to 513 ° K, ZrCp ₂ Cl ₂ to 483 ° K while the substrates were heated to 973 ° K. The disc 13 carrying substrates 15 is driven at a speed of the order of 1 to 2 revolutions / second, or from 0.2 to 0.4 m / s, which makes it possible to obtain a TiZrCN coating in which:

% atTi

= 1% atZr

% atTi

% atC

Generally, the temperature of TiCp ₂ Cl ₂ can vary between 513 ° and 543 ° K, that of ZrCp ₂ Cl ₂ between 483 ° and 513 ° K and that of the substrate between 923 ° and 1123 ° K. The speed of rotation of the disc 13 can vary between 30 and 300 rpm, which corresponds, given the diameter at the center of the substrate to 0.1 to 1 m / s. In general, by increasing the temperature of one of the precursors relative to the other, the proportion of the metal of this precursor in the coating is increased relative to the metal of the other precursor. The variation in the temperatures of the precursors and of the substrate also makes it possible to modify the growth rate of the coating. The rotation of the disc 13 makes it possible to better homogenize the gaseous system originating from sources separated and distant from each other by so that each substrate does not alternately receive one gas then the other and so on, but constantly a mixture caused by the mixing caused by the rotation of the disc. Therefore, it is possible to obtain a homogeneous coating and not formed of successive layers of TiCN and ZrCN.

Among the substrates capable of being coated using the method described, mention may be made of WC-Co for cutting tools with a view to increasing their hardness, alloys for electrical resistances to increase, in addition to their hardness, their resistance to oxidation at high temperature and / or their resistance to aqueous corrosion for heating elements in aggressive media such as fluidized beds or for chemical or underwater installations. It is also possible to coat steel or cast iron substrates, in particular to produce cast iron molds for polymers or glass. Of course, the substrates mentioned here, as well as the applications are not limiting, but only cited as examples. Among the advantages of the process described above, in addition to the possibility of varying the ratios Ti, Zr at will, one can also point out the fact of working at atmospheric pressure and even 100 to 200 Pa above, the continuous entry of H ₂ gas, NH ₃ causing a slight overpressure. This avoids the risk of a leak accidentally entering oxygen which would cause oxidation of the coating. Given the very slight overpressure, a leak would result in a gas outlet from the enclosure 6 thereby avoiding the risk of oxidation. In the case of coatings of substrates of complex shapes, the disc 13 can be replaced by a tubular cylinder, the internal wall of which has suitable attachment means for the substrates to be coated.

In addition to the process mentioned above, the installation of FIG. 4 can be used for any deposition of ceramic layers on substrates from two solid precursors. Alternatively, it is possible, by rotating the substrate holder 13, disc or cylinder, and that passing ne ¹ once in front of each crucible 16 to form several successive layers, as many as there crucibles with different precursors. This is how we could form two superimposed layers TiN / Al ₂ 0 ₃ as we find on cutting tools.

We will now describe in detail several examples relating to the complex deposits from two organometallic precursors produced using the installation illustrated in FIG. 4.

The substrates to be covered are made of 42CD4 steel or tungsten carbide / cobalt. They are polished with diamond paste up to grade lμm. They are then ultrasonically cleaned in ethanol for 5 min. The substrates 15 are placed in the housings 14 as well as the graphite cylinders 14a and the precursors of titanium (TiCp ₂ Cl ₂ , Cp: cyclopentadienyl) and of zirconium (ZrCp ₂ Cl ₂ ) are placed in the crucibles 16. The enclosure is subjected to argon vacuum-filling cycles to remove all traces of oxygen, then it is put under vacuum for 1 hour. The motor 26 is started to drive the substrate holder 13 at a speed selected between 10 and 160 rpm. The gases are introduced into the enclosure through the supply conduits 8 and 9. In this example, the flow rate of hydrogen N50 is 2.4 1 / min and that of ammonia N45 is 0.267 1 / min, and pumping is stopped. The enclosure then reaches atmospheric pressure.

The heating windings 23 are then energized. Power is supplied by alternating current (30V). Discontinuous regulators provide the set temperature (503 ° to 573 ° K) and the rise speed (15 ° K / min). Simultaneously, the substrates are heated by high frequency induction to their set temperature (923 ° to 1023 ° K). After stabilization of the temperatures (≈15 min), the deposition operation lasts 3 hours. 12

The other deposition parameters are indicated in Table II below:

TABLE II

The crucible / substrate distance is fixed at 4 cm. The results were measured in the same way as for the examples in Table I and are shown on the diagram in Figure 2.

All the above-mentioned examples relate to deposits of TiZrCN. It is obvious that the method as well as the apparatus can be used for complex deposits from other metallic or ceramic precursors. According to data from the literature, a YBa _{! 6} ^Cu _2, ₈ ^was produced on a substrate Zirconia. The atomic percentages were measured by an X-ray energy electron microprobe. The precursors are of the form: M (thd) _x with M≈metal and thd = 2,2,6,6-tetramethyl-3,5-heptanedionate

The operating conditions are collated in table III: TABLE III

The crucible / substrate distance is fixed at 4 cm.

In the same way as before, a very thin deposit

(≈0.2μm) of Cu ₂ In was produced on a zirconia substrate from Cu (thd) ₂ and In (tfac) ₃ = 1, 1, 1-trifluoroacetylaceous tonate. The conditions are listed in the following Table IV:

TABLE IV

The crucible / substrate distance is fixed at 4 cm.

Claims

1. A method of forming a complex deposit containing at least two metallic or ceramic elements by chemical vapor deposition (CVD) on a metallic or ceramic substrate, characterized in that there is an organometallic precursor of each of said elements in a crucible, which each of these elements is brought to its sublimation temperature, in a reactor supplied with at least one gas, reactive or not, suitable for the complex to be formed, that said substrate is placed above the respective openings of said crucibles, at a distance of less than 10 cm and a relative displacement is produced between the precursors of said elements on the one hand, and the heated substrate between approximately 650 ° and 850 ° on the other hand, for alternately bringing this substrate to each of said precursors, the speed of this displacement being chosen so that the reaction between the components forms on this substrate a complex deposit of es two elements in a determined proportion.

2. Method according to claim 1, characterized in that a carbide or a mixed carbonitride of Ti and Zr is formed by supplying the reactor with H ₂ and, in the case of the deposition of carbonitride, with NH ₃ as as a nitrogen precursor by fixing the proportion of NH ₃ between 0 and 20% of the flow of H ₂ .

3. Method according to claim 1, characterized in that it takes place at atmospheric pressure.

4. Method according to claim 2, characterized in that the organometallic precursors are respectively Zr (C ₅ H ₅ ) ₂ Cl ₂ and Ti (C ₅ H ₅ ) ₂ C1 ₂ .

5. Method according to claim 4, characterized in that the Zr precursor is heated between 210 ° and 240 ° and the Ti precursor between 240 ° and 270 ° C.

6. Method according to claim 1, characterized in that said displacement speed is between 0.1 and 1 m / s.

7. Device intended to form a mixed ceramic or metallic coating from at least two solid metallic precursors by chemical vapor deposition (CVD) on a metallic or ceramic substrate inside a sealed enclosure provided with openings intended to connect this enclosure to determined gas sources in order to create a controlled atmosphere in this enclosure, characterized in that it comprises: a support member for said substrate, guide means engaged with this support defining a trajectory determined displacement located substantially in a horizontal plane, drive means engaged with this support to move it along this trajectory, a crucible for each of said precursors disposed below a portion of said trajectory of the heating means each of said crucibles and means for heating said substrate.