Body coated with cubic boron nitride and method for manufacturing the same

Abstract

A body coated with cubic boron nitride is disclosed which includes a base material, a first interlayer formed on the base material, a second interlayer formed on the first interlayer, a third interlayer formed on the second interlayer, and a cubic boron nitride film formed on the third interlayer. Each of the first and second interlayers comprises nitride or boride mixed with an adding element chosen from the IVb, IIIb, Vb, IVa, Va and VIa groups of the periodic table. In one embodiment of the invention, the composition ratio of the adding element to the nitride or boride decreases towards the surface between the second interlayer and the third interlayer. The third interlayer also contains nitride or boride mixed with an adding element chosen from the IVb, IIIb, Vb, IVa, Va and VIa groups of the periodic table. In one embodiment of the invention, the total mixing amount of the adding element in the third interlayer is 0.01 atomic % to 10 atomic %, and shows an absorption peak at the wave number of 950 cm.sup.-1 to 1150 cm.sup.-1 according to infrared absorption spectrum.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a body coated with cubic boron nitride, and a method for manufacturing the same.

2. Description of the Prior Art

Recently a film-making technique has been remarkably developed. Various coating techniques of the cubic boron nitride have been developed for coating a part, a tool or the like which requires corrosion-resistance, wear-resistance and high hardness.

Methods disclosed in the Japanese Patent Opening Gazettes Nos. 204370/1986, 47472/1987 and 77454/1987 are given as examples for the coating techniques.

In the method disclosed in the Japanese Patent Opening Gazette No. 204370/1986, prasma abundant in electrons is produced by hollow cathode discharge, and a part of the electrons are attracted towards a reaction gas inlet. Gas is activated, and so reactivity for physical vapour deposition has been improved.

In the method disclosed in the Japanese Patent Opening Gazette No. 47472/1987, a DC or AC bias voltage is applied to a reaction gas introducing nozzle which is called "activation nozzle", so that plasma is produced with high density. Ions are injected to a body to be coated, from the plasma of high density. Radio frequency (rf) bias voltage is applied to the body to be coated. Thus, a cubic boron nitride film is formed on the body.

In the Japanese Patent Opening Gazette No. 77454/1987, such a method for forming a cubic boron nitride film is disclosed that a DC or AC bias voltage is applied to the activation nozzle to produce a plasma of high density, a rf bias voltage is applied to a body to be coated, and a reaction gas such as Nitrogen gas or hydronitrogen gas and a discharge base gas such as Argon are mixed and introduced into the vacuum chamber through the activation nozzle, or concurrently introduced thereinto.

In both of the above described second method (Japanese Patent Opening Gazette No. 47472/1987) and third method (Japanese Patent Opening Gazette No. 77454/1987), the bias voltage is applied to the gas introducing nozzle so that plasma of high density is produced adjacent to the opened portion of the gas introducing nozzle, while the rf bias voltage is applied to the body to be coated, and ions are injected into the body from the plasma of high density so as to form a cubic boron-nitride film on the body.

Besides the above-described methods, a sputtering method, an ion-beam deposition method and an ion plating method are well known for forming a cubic boron nitride film.

The X-ray diffraction method is used for judging the structure of the film. It was reported that the cubic boron nitride film was judged to be formed by the fact that only one peak was obtained nearly at the diffraction angle 2.theta.=43.degree.within the range of 20.degree. to 50.degree. as shown in FIG. 1.

However, the structure of the boron nitride film which was judged to be cubic-crystalline by the fact that the maximum peak was obtained nearly at the diffraction angle 2.theta.= 43.degree. according to the X-ray diffraction method, is classified into two kinds according to the infrared absorption spectrum method. One of the two kinds shows the absorption peaks at the wave numbers of about 1400cm.sup.-1 and 800cm.sup.-1 , as shown in FIG. 2. The other of the two kinds shows the absorption peak at the wave number of about 1050 cm.sup.-1. The Vickers hardness of the film of the latter characteristic is 5000 to 6000 kg/mm.sup.2. The base material coated with such a film, which requires high wear resistance and high hardness, can have a further longer life.

Hitherto, the boron nitride films which were judged to be cubic-crystalline by the X-ray diffraction method, show the absorption peaks at the wave numbers of about 1400 cm.sup.-1 and 800cm.sup.-1 according to the measurement of the X-ray absorption spectrum. Their Vickers hardness is 2000 to 4000 kg/cm.sup.2. Accordingly, it is considered that they include essentially graphite structure (hexagonal boron nitride). They cannot be judged to be cubic-crystalline from the measurement results of the infrared absorption spectrum.

On the other hand, the boron nitride film formed by the method disclosed in the Japanese Patent Opening Gazette No. 47472/1987 or 77454/1987 was confirmed to be cubic-crystalline both by the X-ray diffraction measurement and infrared absorption spectrum method.

However, the film of a few hundreds A thick near the surface boundary has graphite structure (h-BN film) which shows the absorption peaks at the wave-numbers of about 1400 cm.sup.-1 and 800cm.sup.-1 according to the infrared absorption spectrum measurement, even in the base material coated with the cubic boron nitride film which shows the absorption peak at the wave number of about 1050cm.sup.-1. The surface boundary between the base material and the film is instable to moisture in the atmosphere. Adherence strength between them is essentially low. Accordingly, when the base material coated with such a film is let alone in the atmosphere, it has been found that the film is easily peeled from the base material due to the internal stress of the film.

On the other hand, the boron nitride film containing excess boron (B/N>1) has graphite structure according to the infrared absorption spectrum measurement. However, the film strength can be improved, since B--B bonds exist therein. When such a film containing excess boron is interposed as an interlayer between the cubic boron-nitride film and the base material, the adhering strength of the film can be improved. However, when the thickness of the cubic boron nitride film is increased for a practical use, the peeling occurs at the surface boundary between the boron nitride film containing excess boron, and the cubic boron nitride film. Accordingly, it cannot be practically used.

SUMMARY OF THE INVENTION

Accordingly, it is an object of this invention to provide a body coated with cubic boron nitride film in which the film strength can be improved and so stable in the atmosphere that the adherence strength can be improved, and to provide a method for manufacturing such a body coated with cubic boron nitride film.

In accordance with an aspect of this invention, a body coated with cubic boron nitride comprising: (A) a base material; (B) a first interlayer of nitride or boride mixed with at least one adding element of IVb group, IIIb group, Vb group, IVa group, Va group and VIa group of the periodic table, and the composition ratio of said at least one adding element is decreased towards the surface, said first interlayer being formed on said base material; and/or a second interlayer of nitride or boride mixed with at least one element of IVb group, IIIb group, Vb group, IVa group, Va group and VIa group of the periodic table, the total mixing amount of the adding element being 0.01 atomic % to 10 atomic %, and shows an absorption peak at the wave number of 950cm.sup.-1 to 1150cm.sup.-1 according to the infrared absorption spectrum, said second interlayer being formed on said first interlayer or said base material; and (C) a cubic boron nitride film which shows the maximum absorption peak at the wave number of 950 cm.sup.-1 to 1150.sup.-1 according to the infrared absorption spectrum, said cubic boron nitride film being formed on said first interlayer or said second interlayer.

In accordance with another aspect of this invention, a body coated with cubic boron nitride comprising; (A) a base material, (B) a first interlayer of nitride or boride which contains at least one adding element of IVb group, IIIb group, Vb group, IVa group, Va group and VIa group of the periodic table, said first interlayer being formed on said base material; (C) a second interlayer of nitride or boride mixed with at least one adding element of IVb group, IIIb group, Vb group, IVa group, Va group and VIa group of the periodic table, and the composition ratio of said adding element is decreased towards the surface, said second interlayer being formed on said first interlayer, (D) a third interlayer of nitride or boride mixed with at least one adding element of IVb group, IIIb group, Vb group, IVa group, Va group and VIa group of the periodic table, the total mixing amount of said adding element being 0.01 atomic % to 10 atomic %, and shows an absorption peak at the wave number of 950cm.sup.-1 to 1150cm.sup.-1 according to the infrared absorption spectrum, said this interlayer being formed on said second interlayer and (E) a cubic boron nitride film which shows the maximum absorption peak at the wave number of 950cm.sup.-1 to 1150cm.sup.-1 according to the infrared absorption spectrum, said cubic boron nitride film being formed on said third interlayer.

In accordance with a further aspect of this invention, a method, for manufacturing a body coated with cubic boron nitride comprising the steps: (A) of preparing a base material in a vacuum chamber, (B) of preparing at least one element of IVb group, IIIb group, Vb group, IVa group, Va group and VIa group of the periodic table, being able to form a compound with boron and nitrogen, or said compound of said at least one element; (C) of introducing said elements or compound into said vacuum chamber under the control of the evaporation rate or supply speed of said elements or compound, and concurrently under the control of the evaporation rate of boron; and (D) of forming an interlayer of nitride or boride having a predetermined chemical composition between said base material and a cubic boron nitride film.

The foregoing and other objects, features, and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the preferred embodiments of the invention, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THF DRAWINGS

FIG. 1 is graph showing the results of the X-ray diffraction measurement of the boron nitride film produced by the prior method;

FIG. 2 is a graph showing the results of the infrared absorption spectrum measurement of the boron nitride film produced by the prior method.

FIG. 3 is a graph showing the infrared absorption spectrum of the cubic boron nitride film;

FIG. 4 is an enlarged view of a part of a body coated with cubic boron nitride according to this invention;

FIG. 5 is a graph showing an example of composition of an interlayer according to this invention;

FIG. 6 is a graph for explaining the method of this invention.

FIG. 7 is a schematic view of an apparatus for forming the film according to this invention; and

FIG. 8 is a graph showing another example of composition interlayer according to this invention.

DESCRIPTION OF THF PREFERRED EMBODIMENTS

FIG. 4 shows the structure of the body coated with cubic boron nitride according to this invention. In FIG. 4, a base material 1 is made of, for example, silicon, WC (tungsten carbide) or Al.sub.2 O.sub.3. An interlayer 2 which contains at least one element of IVb group, IIIb group, Vb group, IVa group, Va group and VIa group being able to form compounds with boron and nitrogen, is formed on the base material 1. A cubic boron nitride film or layer 3 is formed on the interlayer 2. The interlayer 2 and the cubic boron nitride film 3 are formed by the apparatus shown in FIG. 7 which is partially shown in the Japanese Patent Opening gazette Nos. 47472/1987 and 77454/1987. Next, the apparatus of FIG. 7 will be described. A first evaporation source 12 containing silicon, and a second evaporation source 13 containing boron are arranged in a vacuum chamber 11. Electron beams EB as shown by dash-lines, heat and evaporate silicon and boron in the sources 12 and 13. A partition wall 14 is arranged between the sources 12 and 13. Shutters 21 and 22 are arranged in face to the sources 12 and 13. A substrate or base material 18 to be coated is put directly over the sources 12 and 13. A shutter 20 is arranged under the substrate 18.

A thermal emitter 23 which consists of W(tungsten) filament, is arranged adjacent to the one side wall of the vacuum tank 11. An alternate current source 24 is connected through a transformer 25 to the thermal emitter 23. A rf power source 29 is connected through a matching circuit, which consists of capacitors and an inductance coil, to the substrate 18. A halogen lamp 19 for heating the substrate 18 is arranged above the substrate 18.

An activation nozzle 15 is fixed at the other side wall. Argon gas and nitrogen gas are supplied through a valve 16 into the activation nozzle 15. They are mixed and introduced into the vacuum tank 11 from the activation nozzle 15. Or they are concurrently introduced from the activation nozzle 15. A direct current source 26 is connected to the activation nozzle 15, and it is connected to the transformer 25. An exhausting opening 17 is made at the other side wall, and it is connected to not-shown trap and diffusion pump.

Quartz oscillator thickness monitors 27 and 28 are arranged at both sides of the substrate 18. Evaporation rates of silicon and boron from the sources 12 and 13 are measured by the monitors 27 and 28, respectively. Although not shown, output terminals of the monitors 27 and 28 are connected to the sources 12 and 13. A feed-back control is effected for obtaining predetermined evaporation speeds. FIG. 5 shows one example of the interlayer 2 obtained by the apparatus of FIG. 7, in which silicon (Si) is used as an adding element. A layer (A) most adjacent to the base material 1 consists of nitride of Si.sub.3 N.sub.4, and it is 0.3 .mu.m thick. The compositions of layers (B) and (C) change from Si.sub.3 N.sub.4 to BN through B.times.SiyNz (as Si.sub.3 N.sub.4 .fwdarw.B.times.SiyN.sub.2 .fwdarw.BN), where x,y and z represent mixing ratio of elements B. Si and N. respectively. The composition ratios of the adding element (Si) are decreased towards the surface in the interlayers (B) and (C). The decreasing gradient of the layer (C) is smaller than that of the layer (B). The composition of nitrogen (N) is omitted in FIG. 5.

FIG. 6 shows a parameter region in which the cubic boron film is formed according to this invention in use of the methods disclosed in the Japanese Patent Opening Gazette Nos. 47472/1987 and 77454/1987, or the apparatus of FIG. 7. As understood from FIG 6, the cubic boron nitride can be formed in the range over the thresholds of the RF power and activation nozzle current. The RF power is applied as a bias voltage to the base material 1.

FIG 8 shows another example of the interlayer 2 obtained by the apparatus of FIG. 7 in which silicon (Si) is similarly used as an adding element. In FIG. 8, the evaporation rate of the Si evaporation source is constant in the layer (A') which consists of silicon nitride and is 0.2 .mu.m thick. For the layer (B'), the heating of the boron evaporation source starts, while the evaporation rate of the Si evaporation source is reduced. The decreasing gradient of Si and the increasing gradient of boron are predetermined in FIG. 8. The layer (B') contains the mixture of silicon nitride and boron nitride, and it is 0.2 .mu.m thick. In the layer (C'), the decreasing gradient of Si evaporation becomes smaller than in the layer (B'), while the increasing gradient of boron evaporation becomes smaller than in the layer (B'). The table I shows the measurement results on the adherence strengths of the cubic boron nitride (C--BN) films in the atmosphere, in comparison with the prior art method. The cubic boron nitride films are formed through the interlayers 2 on the Si-substrate or WC-Co tip, respectively, at the different thicknesses. The interlayers 2 have the structure shown in FIG. 5.

TABLE I______________________________________ C--BN film thickFilm Construction 0.5 .mu.m 1 .mu.m 3 .mu.m______________________________________C--BN/Interlayer/Si .smallcircle. .smallcircle. .smallcircle.C--BN/Interlayer/ .smallcircle. .smallcircle. .smallcircle.WC--Co tipPrior Art x x x______________________________________ In the Table I, the mark .largecircle. represents good adherence, while the mark x represents bad adherence. In the prior art, the films were peeled in a very short time, in the atmosphere. The measurements were made on what element was effective for improving the adherence strength of the film besides silicon, as the adding element. Table II shows the measurement results of the cubic boron nitride films on the different adding elements. The thickness of the interlayer is constant and 2000 .ANG., in which the composition ratio of the adding element is decreased from the base material (Si) towards the cubic boron nitride film. TABLE II______________________________________ Adding element to InterlayerC--BN film Ib group IIb group IIIb group IVb groupthick Cu Zn Al C Si Ge______________________________________0.1 .mu.m x x .smallcircle. .smallcircle. .smallcircle. .smallcircle.0.3 .mu.m x x .smallcircle. .smallcircle. .smallcircle. .DELTA.______________________________________ Adding element to Interlayer Vb IVa Va VIa VIIIaC--BN film group group group group groupthick P Ti Nb Cr Ni______________________________________0.1 .mu.m .smallcircle. .smallcircle. .smallcircle. .smallcircle. x0.3 .mu.m .DELTA. .smallcircle. .DELTA. .DELTA. x______________________________________ In the Table II, the mark .largecircle. represents good adherence, the mark .DELTA. considerable bad adherence and the mark x bad adherence. In the mark .DELTA., the film is partially peeled in a very short time under the atmosphere. In the mark x, the film is entirely peeled in a very short time under the atmosphere.

It is confirmed from the table II that the elements of IIIb group, IVb group, Vb group, IVa group, Va group and VIa group of the periodic table are effective for improving the adherence strength of the film.

Table III shows the experimental results of the adherences on the different structures of the interlayers.

TABLE III__________________________________________________________________________ WC base Al.sub.2 O.sub.3 baseBase material Si wafer tip tip__________________________________________________________________________Structure of B C C/B C/B/A B C/B C/B/A B C/B C/B/A CInterlayerAdherence .DELTA. .smallcircle. .smallcircle. .smallcircle. .DELTA. .DELTA. .smallcircle. .DELTA. .smallcircle. .smallcircle. .DELTA.__________________________________________________________________________ In the Table III, the meanings of the marks .largecircle. and .DELTA. are equal to those in the Table II. The meanings of the layers A, B and C are equal to those of the layers (A) (B) and (C) in FIG. 5, respectively. B and C represent the single layer structure of (B) and (C), respectively. C/B represents that the layer (B) is formed on the base material, and the layer (C) is formed on the layer (B). C/B/A is equal to the structure (A) (B) (C) shown in FIG. 5. The thicknesses of the interlayers A, B and C are 2000.ANG., respectively. The thickness of the cubic-crystalline film is 1 .mu.m. The element Si was used as the adding element.

Generally defined, the interlayer A is equal to the nitride layer or boride layer which contains at least one kind of element of the IVb group, IIIb group, Vb group, IVa group, Va group and VIa group of the periodic table. The interlayer B is equal to the nitride layer or boride layer with which at least one kind of element of the IVb group, IIIb group, Vb group, IVa group, Va group and VIa group of the periodic table, is mixed and in which the composition ratio of said at least one kind of element is decreased from the base material towards the surface. And the interlayer C is equal to the nitride layer or boride layer with which at least one element of the IVb group, IIIb group, Vb group, IVa group, Va group and VIa group of the periodic table, is mixed at the total mixture amount of 0.01 atomic % to 10 atomic %, and which has the absorption peak at the wave number of 950 cm.sup.-1 to 1150 cm.sup.-1.

As understood from the table III, the good adherence can be obtained by the suitable selection of the interlayer structure in accordance with the kind of the base material. As above described, according to this invention, at least one element of the IVb group, IIIb group Vb group, IVa group, Va group and VIa group of the periodic table, is added to form the three-dimensional bonds in the graphite structure of the surface boundary. Thus, even when the base material is coated with a thick cubic boron nitride film, this film can resist sufficiently the internal stress, and the adherence can be greatly improved. Accordingly, this invention is very useful for parts or tools which require corrosion-resistance, wear-resistance and high hardness.

While the preferred embodiment has been described, variations thereto will occur to those skilled in the art within the scope of the present inventive concepts which are delineated by the following claims.

Claims

1. A body coated with cubic boron nitride comprising:

(A) a base material;

(B) a first interlayer formed on said base material wherein said first interlayer comprises nitride or boride, the nitride or boride comprising nitrogen or boron elements with an adding element chosen from the IVb, IIIb, Vb, IVa, Va and VIa groups of the periodic table;

(C) a second interlayer formed on said first interlayer wherein said second interlayer comprises nitride and boride, the nitride and boride comprising nitrogen and boron elements with an adding element chosen from the IVb, IIIb, Vb, IVa, Va and VIa groups of the periodic table, and further wherein the composition ratio of said adding element of the boride and nitride decreases towards the surface between a second interlayer and said third interlayer;

(D) a third interlayer formed on said second interlayer wherein said third interlayer comprises nitride and boride, the nitride and boride comprising nitrogen and boron elements with an adding element chosen from the IVb, IIIb, Vb, IVa, Va and VIa groups of the periodic table, and further wherein the total mixing amount of the adding element is 0.01 atomic % to 10 atomic %, and further wherein said third interlayer shows an absorption peak at the wave number of 950cm.sup.-1 to 1150cm.sup.-1 according to the infrared absorption spectrum;

(E) a cubic boron nitride film formed on said third interlayer wherein said cubic boron nitride film shows a maximum absorption peak at the wave number of 950cm.sup.-1 to 1150cm.sup.-1 according to the infrared absorption spectrum.

2. A body according to claim 1 wherein said adding element of said third interlayer has a composition ratio which decreases towards the surface between said third interlayer and said cubic boron nitride film.

3. A body according to claim 2 wherein the decreasing gradient of the composition ratio of said adding element in said second interlayer is larger than that in said third interlayer.

4. A body according to claim 1 wherein the ratio of boron elements to nitrogen elements is increased towards the surface between said second interlayer and said third interlayer in said second interlayer.

5. A body according to claim 4 wherein the ratio of boron elements to nitrogen elements is increased towards the surface between said third interlayer and said cubic boron nitride film in said third interlayer.

6. A body according to claim 5 wherein the increasing gradient of said ratio in said second interlayer is larger than that in said third interlayer.

7. A body according to claim 1 wherein the thickness of each of said first, second and third layers is on the order of 0.2.mu.m.

8. A body according to claim 1 wherein the ratio of nitrogen elements to boron elements is increased towards the surface between said second interlayer and said third interlayer in said second interlayer.

9. A body according to claim 8 wherein the ratio of nitrogen elements to boron elements is increased towards the surface between said third interlayer and said cubic boron nitride film in said third interlayer.

10. A body according to claim 9 wherein the increasing gradient of said ratio in said second interlayer is larger than that in said third interlayer.

11. A body according to claim 1 wherein the thickness of the cubic boron nitride film is from 0.01.mu.m to 3.mu.m.