WO2002070776A1

WO2002070776A1 - Deposition process

Info

Publication number: WO2002070776A1
Application number: PCT/AU2002/000246
Authority: WO
Inventors: Phil J. Martin; Avi Bendavid; Terence John Kinder; Edward Preston
Original assignee: Commonwealth Scientific And Industrial Research O Rganisation
Priority date: 2001-03-05
Filing date: 2002-03-05
Publication date: 2002-09-12
Also published as: AUPR353601A0

Abstract

The invention relates to a method of vapour depositing a mixed coating on a region of a substrate. The method involves concurrently providing a flux of material from a vacuum cathodic arc source and a flux of material from a magnetron cathode to a region of the substrate. The material may be conducted in the presence of a reactive gas if desired. Very hard films, useful as coatings, with complex chemical structures can be built from chemically simple cathodes.

Description

TITLE: DEPOSITION PROCESS

TECHNICAL FIELD

The invention relates to physical vapour deposition (PVD) processes and to

superhard films and coated surfaces prepared by those processes.

BACKGROUND ART

Surfaces coated with thin layer films have many applications, depending on the

nature of the coating, including uses as optical films, electrically conducting films,

magnetic storage films, as barriers to prevent the migration of copper from diffusing in

microchips, and more particularly as superhard or friction reducing coatings for

mechanical parts and tools subject to wear.

One particular material of interest as a superhard thin film is Ti(₁-_X)Si(_X)N_(y). Ti₍i_χ₎Si₍χ₎N₍y₎ films are extremely hard (usually in excess of 40GPa) but often have equivalent or lower stress than softer films. This combination of properties makes them

ideal candidates as coatings on machine tools for use in drilling, milling and the like.

Thin layer films may be deposited by vapour deposition processes such as

chemical vapour deposition (CVD) or physical vapour deposition (PND). Of the two,

CND requires the more severe conditions and it is often necessary for CND processes to

be run at temperatures of several hundred degrees Celsius, which in many cases is above

the annealing temperature of the steel substrate to be covered.

PND processes involve the use of energetic particles to deposit a coating on a

surface via evaporation or sputtering. In PVD processes, material is vaporised from a solid or liquid target source, transported through a vacuum and brought into contact with

a substrate. When the vaporised material contacts the substrate, it condenses. The

vaporised material may be a chemical element, a compound or an alloy. PND processes

have been used to deposit films with thicknesses of the order of between a few

nanometres up to thousands of nanometres and can even be used to form multilayer

coatings and thick deposits.

There are a number of different methods that can be used to carry out PVD. A

widely used method of deposition is magnetron deposition. Magnetron deposition is

used extensively in all branches of thin film technology as it is useful for uniform, large-

area coating such as for architectural glass, and for the deposition of electrically insulating materials such as carbides or nitrides by using RF techniques. Films deposited

by the use of magnetron deposition, however, suffer from inferior adhesion of the film to

the surface relative to other deposition techniques, such as vacuum arc evaporation. Magnetron deposited films have poor adhesion due to the relatively low energy of the particles sputtered from the magnetron cathode as they arrive at the substrate to be

coated. The energies of a particle arriving at the substrate are typically of the order of 5-

10 eN, even though the energy of the ionised atoms of the working gas may be much higher.

A further drawback of using magnetron deposition is the poisoning of the

cathode (source), hi the reactive deposition of thin films by a magnetron in DC mode,

for example, the deposition of a silicon nitride coating occurs by sputtering silicon in a

nitrogen or nitrogen/argon atmosphere and the surface of the magnetron cathode quickly

becomes "poisoned". "Poisoning" is a specific term that refers to the formation of a

surface layer on top of the cathode during operation, h the case of the Si/nitrogen, the

poisoning surface layer is a nitride layer. This has the effect of charging the surface of

the cathode source to such an extent that the ions required to cause sputtering are no longer attracted to it and eventually the deposition rate (sputtering rate) decreases or

ceases altogether until the reactive gas is reduced, the surface layer removed and a clean

cathode surface exposed again. The poisoning process may restart when the reactive gas

is reintroduced.

The conventional solutions to the problem of poisoning are either to apply RF fields, or more recently pulsed DC voltages, to the magnetron. These have the effect of

removing the charge from the surface in alternate cycles such that the ions can bombard

the cathode surface, clean it and sputter clean material once more.

An alternative known system to prevent poisoning also includes a precision feedback system where the nitrogen partial pressure (for the example of nitride deposition) is carefully monitored and used to control the poisoning effect. In such a

system, the magnetron is operated just on the edge of the poisoning curve but is prevented from being totally poisoned by starving the system of nitrogen at the required

time.

However, both the above solutions to the problem of poisoning require special

controls and/or power supply characteristics and add an additional layer of complexity to

the deposition apparatus and method.

Another popular method of physical vapour deposition is cathodic arc evaporation.

In this method, the particle energies are higher than those in the magnetron method, by as

much as a factor of 10, ie up to 100 eV, which results in enhanced film density and

adhesion of the deposited layer.

However, the cathodic arc method is not readily amenable to the deposition of film

with controlled "impurities" ie films having closely controlled compositions and

therefore closely controlled properties. These films typically have a predominant

component doped with a smaller amount of another component. It is well established

that in such surface mixtures, the addition of such impurities or dopants can greatly

modify the properties of the surface film.

For example, using the cathodic arc method to prepare a coating of titanium nitride

(TiN) with a silicon content of around 3 atomic % would require the prior preparation

and use of a special and expensive Ti-Si cathode, and the operation thereof in a nitrogen

containing gas composition, to produce the required coating on the substrate. Process

parameters such as gas composition and the nature of the bias potential applied to the

substrate during deposition would also require careful attention.

Any discussion of the prior art throughout the specification should in no way be

considered as an admission that such prior art is widely known or forms part of common

general knowledge in the field. It is an object of the present invention to provide a system to overcome at least one of the above-mentioned problems in the art, or which provides an economic alternative to the above method for producing PVD coated substrates. DESCRIPTION OF THE INVENTION

According to a first aspect the invention provides a method of vapour depositing a mixed coating on a region of a substrate, said method including the steps of: providing at least one flux of material from a magnetron cathode to said region of said substrate; and concurrently providing at least one flux of material from a vacuum cathodic arc source to said region of said substrate.

Two or more of either the magnetron or vacuum arc cathode may also be employed. For example, one magnetron with two arc sources or two magnetrons and two arc sources may be used. Either magnetron or arc device may be DC, pulsed-DC or RF powered. The arc source may be unfiltered, partially filtered or fully filtered type, where filtering refers to the removal of microdroplets of cathode material from the plasma stream.

The magnetron and vacuum cathodic arc sources may be operated in a vacuum, in a partial pressure of an inert gas, or in the presence of a reactive gas, or in a mixture of two or more inert gases, two or more reactive gases, or various mixtures of one or more inert gases and one or more reactive gases. Argon, for example, is a suitable inert gas. An example of a suitable reactive gas is nitrogen.

The amount of power supplied to the magnetron is used to control the flux of the sputtered material. The magnetron may be positioned closer to, or further from, the substrate to

increase or decrease the amount of sputtered material supplied to the growing film as

required.

The amount of power supplied to the arc source may also be varied to increase or decrease the amount of arc evaporated material. The arc beam, due to its high ionisation,

may also be deflected by scanning electromagnetic coils, magnetic arrays or the like to

modify or increase the area and pattern of deposition. This can be used to improve

uniformity of the films or decrease or increase the amount of arc deposited material in

order to achieve and maintain the desired balance between the magnetron flux and the

arc flux to reach the desired composition of the substrate

The magnetron or the cathodic arc source may be operated independently at either

a continuous flux, or at a variable flux. Alternatively one or both sources may be turned

on or off to form a multilayer film structure with predetermined properties.

Preferably, the magnetron is a DC magnetron or RF magnetron. The cathodic arc

source may be a DC or pulsed arc source. The vacuum cathodic arc source may be

operated in either the filtered or unfiltered mode.

The method has been found to be applicable to any size or shape of either the arc

cathode or the magnetron cathode.

The major and minor components of a film may be supplied from either a

magnetron or a variable arc cathode.

The method may also be used with any cathode composition with one or more arc

or magnetron sources of different elemental compound or alloy composition in order to

achieve the desired composition of the substrate. Preferably the magnetron sputter source and cathode arc source are independently selected from one or more of a chemical element, a compound, or an alloy cathode. Multiple sources using combinations of more than one of the above maybe used for highly complex film compositions.

In a preferred method of the present invention, the vacuum cathodic arc source is a metal M, the magnetron sputters silicon and the deposition takes place under a controlled pressure of nitrogen to provide a coating of the general foπnula: (₁._x)Si₍χ₎N(_y), herein M is a metal e.g.Ti, Ta, Mo or W, wherein x is from 0.001 to 0.999 and wherein y is from 0.001 to 10. Alternatively, M may also be carbon.

In one highly preferred embodiment, the magnetron sputters silicon and the cathodic arc sputters titanium concurrently towards a substrate. The deposition takes place under an atmosphere of nitrogen. The resultant mixture of compounds deposited on the surface is a mixture of TiN_x and SiN_y, where x and y may be such that the resultant compounds have super-stoichiometric, stoichiometric or sub-stoichiometric ratios.

According to a second aspect the invention provides a coated substrate including a mixed coating provided by at least one flux of material from a magnetron concurrently deposited with at least one flux of material from a vacuum cathodic arc source.

According to a third aspect, the invention provides an apparatus including a magnetron cathode and a vacuum cathodic arc source.

Surprisingly, in the present case, it was found that when a magnetron deposition source was used in conjunction with a cathodic arc source, poisoning did not occur.

The magnetron and cathodic arc source may be operated in conjunction, if desired, without the need for either special controls such as the control of gas partial pressures and without the need for special power supply characteristics such as pulsed

DC, or RF etc.

Surprisingly, the magnetron cathode surface remained clean for many hours when

operated in conjunction with an arc source. Without wishing to be bound by theory, it is believed that the ions generated in the plasma created by the arc source are sufficient to

sputter the cathode surface and prevent poisoning.

The reactive gas in the system e.g. nitrogen, is ionized by the plasma generated

by the arc source. The ions are then accelerated toward the magnetron cathode and can

sputter the surface, hi the absence of the arc plasma the majority of the neutral nitrogen

molecules are not influenced by potential on the magnetron cathode and will form a

nitride on the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 Shows a schematic drawing of an apparatus of the present invention

Figure 2 shows the variation of silicon present in the deposited films of the

present invention as a function of magnetron power.

BEST MODES OF CARRYING OUT THE INVENTION

The method of the present invention utilizes a combination of existing

components in a hitherto unknown fashion to produce highly useful superhard films. While it is thus unnecessary to describe each component of the apparatus, a general

schematic diagram of a preferred embodiment of the invention used to deposit Ti and Si

is given in Figure 1 by way of example.

The deposition takes place in chamber 1. Pump or pumps 2 are used to evacuate the chamber, and throttle valve 3 is used to control the operating pressure of the magnetron and arc source. A DC magnetron 4 is used to deposit silicon, and a DC arc source 5 is used to

deposit the Ti. Shutter 6 is used to measure the ion current from the arc source. Gas

source 8 is used to provide either a reactive gas, such as nitrogen, or an unreactive gas,

such as argon, or any other gas.

An ion etcher 7 is used in preferred embodiments to bombard the substrate 9 with

argon ions prior to deposition to ensure maximum adhesion.

A bias 10 is used to apply a negative potential of -10 to 1200 V to the substrate.

Heater 11 is used to heat the substrate to 350-400°C.

The vacuum window 12 allows observation of the operation of the sources.

As mentioned above, arcs provide sufficient particle energy to produce dense

adherent films at high rate and relatively low cost, however, they are not readily adapted

for the inexpensive production of doped or alloyed films, and nor do they work well on

silicon cathodes.

Magnetrons produce lower energy particles that result in films with less adhesion,

although they are a good source for silicon deposition but are readily poisoned when

used in the presence of reactive gases.

The combination of the present invention provides ideal control and variability of

the Si content by varying the magnetron power and or distance from the substrate as

described. The bias applied to the substrate will also influence the silicon content in the

deposited film. Increasing the bias will increase the sputtering of the depositing silicon from the surface by the titanium ions generated by the arc source. Further, not only do

the two allow controlled deposition, but the arc allows the magnetron to remain free

from poisoning in circumstances where, alone, it would normally become rapidly

poisoned. The method of the present invention may also be operated in such a manner as to

provide layered films, or films of a continuously variable nature. This can be achieved

by adjusting the balance of M (such as Ti) deposited as opposed to Si deposited, as well

as adjusting the partial pressure of a reactive gas. Switching rapidly between one set of

deposition parameters and another will produce a layered film, whereas moving from

one set of parameters to another slowly will produce a film where the composition of the

film changes as a function of the cross section. The thickness of each layer maybe

controlled by the deposition rate and time.

COMPARATIVE EXAMPLE

The compressive stress in certain arc deposited compound films, such as TiN, ZrN

and NbN is high and can result in reduced adhesion to the substrate. It is known that

the addition of a second material such as Cu, Ni or Si can be added to reduce this stress

and form films with useful properties.

It is known, for example, that nanosized grains of TiN surrounded by an

amorphous network of silicon nitride Si₃N₄ produce a nanocomposite super or ultra hard

coating. Typical nanocomposite coatings of Si₃N₄ and TiN contain 7-9 atomic percent

silicon corresponding to 16-21 mol. percent Si₃N₄ . Hardness values for such a coating of

1-5 micrometres thick may be as high as 50 GPa compared to 20-25 GPa for undoped

TiN. This material may be produced by a PVD process from a highly expensive alloy

cathode, or by the different technique of chemical vapour deposition, which has its own drawbacks. EXAMPLE ACCORDING TO THE INVENTION

A 2 inch diameter DC magnetron is used to deposit Si atoms from a silicon

cathode (commercial semiconductor quality polished wafer with a resistivity of around 2

ohm-cm). A filtered cathodic arc source ( 2 inch diameter partially filtered type

operating in the DC mode) is used to produce titanium on particles from a titanium

cathode (commercial grade 99.9 percent purity). The PVD methods are operated concurrently in a partial vacuum of nitrogen and argon gas (80:20 mixture at 5 millitorr

or 0.75 Pa) the deposition is carried out in a diffusion pumped chamber with a base

pressure of 10^"5 torr. The substrate is either a silicon wafer or polished steel substrate. A

negative bias voltage of -100 volts is applied to the substrate to improve film properties.

Deposition of titanium particles alone in the gas mixture gave a TiN film of 0.5 micrometres thick with a hardness of approximately 25 GPa. Turning the magnetron on

and allowing the second silicon flux to coat the surface in conjunction with the titanium

flux such that the final silicon content of the coating was from 5-10 atomic % (by control

of the magnetron power level), gave a surface film hardness of approximately 40 GPa

with no evidence of film delamination from the substrate indicating high adhesion and

lower stress.

The composition of such films is usually expressed in terms of the formula

Ti₍i.χ₎Si₍χ₎N_(y). The films are a mixture of titanium nitride and silicon nitride i.e. TiN

and Si₃N . The stoichiometry of the material will vary according to the elemental concentrations. The properties of the films are defined by the atomic percent of silicon

in the film that ranges from 1 % to 20 %. Conventionally only the silicon content is

given to define the material. Thus, going from a composition of Ti(l)Si(0)N(l) to a composition of from Ti(0.95)Si(0.05)N(0.95) - Ti(0.9)Si(0.1)N(0.9), hardness has doubled

The surface composition and film properties are comparable to that produced by chemical vapour deposition, or by deposition from a single complex cathode in combination with a reactive gas.

A number of films in accordance with the present invention were prepared by a method analogous to that described for Example 1. Thickness was about 0.5μm. The compositions and hardness properties are shown in Table 1.

TABLE 1. M(i._X)Si_(x)N_(y) Films

The percentage amount of silicon deposited can be controlled by controlling magnetron power. Figure 2 shows the amount of silicon deposited as a function of magnetron power for one set of experimental conditions. The bias used was -150V, the Ti ion current from the arc source was 5 A, the total pressure was 0.75Pa (150 seem N₂, 30 seem Ar) with a substrate temperature of 350°C. By adding a magnetron to achieve the dual flux as described, regular arc

machines can be adapted to produce these new "superhard" materials quite readily.

Tools such as cutting bits and the like can be readily placed in the apparatus and used as

deposition substrates.

The method of the present invention is applicable to a number of materials and

combinations but it is particularly valuable for the TiSiN new generation materials that

many in the field are trying to make. Moreover, the method of the present invention

avoid using high temperature CVD (500-800 centigrade ie > annealing point of high

speed steel tools), RF magnetrons (which do not involve the adhesion of arcs) or arcs

with alloy cathodes (which are expensive) and avoid poisoning.

Although the invention has been described with reference to a specific example, it

will be appreciated by those skilled in the art that the invention may be embodied in

many other forms.

Claims

THE CLAIMS OF THE INVENTION ARE AS FOLLOWS:

1. A method of vapour depositing a mixed coating on a region of a substrate, said

method including the steps of:

providing at least one flux of a first material from a magnetron cathode to said

region of said substrate; and

concurrently providing at least one flux of a second material from a vacuum

cathodic arc source to said region of said substrate.

2. A method according to claim 1 wherein the first material is non-identical to the

second material.

3. A method according to claim 1 or claim 2 wherein at least two magnetron cathodes

are employed.

4. A method according to any one of the preceding claims wherein at least two

vacuum cathodic arc sources are employed.

5. A method according to any one of the preceding claims wherein the magnetron

cathode is DC powered, pulsed-DC powered or RF powered.

6. A method according to any one of the preceding claims wherein the vacuum

cathodic arc is filtered.

7. A method according to any one of the preceding claims wherein the vacuum

cathodic arc is DC powered, pulsed-DC powered or RF powered.

8. A method according to any one of claims 1 to 7 wherein the vapour deposition

takes place under a partial pressure of an inert gas.

9. A method according to claim 8 wherein the inert gas is Argon.

10. A method according to any one of claims 1 to 7 wherein the vapour deposition

takes place in the presence of a reactive gas.

11. A method according to claim 10 wherein the reactive gas is Nitrogen.

12. A method according to any one claims 1 to 7 wherein the vapour deposition takes

place in a vacuum.

13. A method according to any one of the preceding claims wherein the amount of

power supplied to the magnetron is used to control the flux of the sputtered material.

14. A method according to any one of the preceding claims wherein the distance from

the substrate to the magnetron is used to control the amount of sputtered material

supplied to the substrate.

15. A method according to any one of the preceding claims wherein the amount of

power supplied to the arc source is used to control the flux of the sputtered material.

16. A method according to any one of the preceding claims wherein the arc beam is

deflected.

17. A method according to claim 16 wherein the arc bean is deflected by a scanning

electromagnetic coil.

18. A method according to claim 16 or 17 wherein the arc bean is deflected by a

magnetic array.

19. A method according to any one of claims 16 to 18 wherein the arc beam is

deflected to modify the area of deposition.

20. A method according to any one of claims 16 to 19 wherein the arc beam is

deflected to modify the pattern of deposition.

21. A method according to any one of the preceding claims wherein the at least one

flux from the magnetron cathode and the at least one flux from the vacuum cathodic arc

source provide coating having a predetermined composition on a substrate.

22. A method according to any one of the preceding claims wherein the magnetron

cathode provides a continuous flux of a first material.

23. A method according to any one of claims 1 to 21 wherein the magnetron cathode

provides a variable flux of a first material.

24. A method according to any one of the preceding claims wherein the vacuum

cathodic arc provides a continuous flux of a second material.

25. A method according to any one of claims 1 to 23 wherein the vacuum cathodic arc

provides a variable flux of a second material.

26. A method according to any one of the preceding claims wherein the first flux is

greater than the second flux.

27. A method according to any one of the preceding claims wherein the second flux is

greater than the first flux.

28. A method according to any one of the preceding claims wherein the magnetron

cathode is a chemical element

29. A method according to any one of the preceding claims wherein the magnetron

cathode is a chemical compound

30. A method according to any one of the preceding claims wherein the magnetron

cathode is an alloy

31. A method according to any one of the preceding claims wherein the vacuum

cathodic arc source is a chemical element

32. A method according to any one of the preceding claims wherein the vacuum

cathodic arc source is a chemical compound

33. A method according to any one of the preceding claims wherein the vacuum

cathodic arc source is an alloy.

34. A method according to any one of the preceding claims wherein the magnetron

cathode is silicon.

35. A method according to any one of the preceding claims wherein the vacuum

cathodic arc source is a M and the coating is of the general formula M₍₁._x)Si_(X)N₍y₎ and

wherein M is a metal or carbon.

36. A method according to claim 35 wherein M is Ti, Ta, Mo W.

37. A method according to claim 35 or 36 wherein M is Ti

38. A method according to any one of claims 35 to 37 wherein x is from 0.001 to

0.999

39. A method according to any one of claims 35 to 38 wherein y is from 0.001 to 1000

40. A method according to any one of the preceding claims wherein the vacuum

cathodic arc source is titanium.

41. A method according to any one of the preceding claims wherein the vacuum

cathodic arc source is titanium and deposition takes place under an atmosphere of nitrogen.

42. A method according to any one of the preceding claims wherein the vacuum

cathodic arc source is titanium and deposition takes place under an atmosphere of

nitrogen to provide a coating of Ti₍₁._x)Si_(X)N_(y)

43. A method according to claim 42 wherein x is from 0.001 to 0.999

44. A method according to claim 42 or 43 wherein y is from 0.001 to 10

45. A method according to claim any one of claims 35 to 44 wherein x and y are

independently selected to provide stoichiometric and/or substoichiometric ratios.

46. A substrate coating of the general formula M₍₁._X)Si_(X)N(_y).

47. A substrate coating according to claim 46 wherein M is Ti

48. A substrate coating according to claim 46 or 47 wherein x is from 0.001 to 0.999

49. A substrate coating according to any one of claims 46 to 48 wherein y is from 0.001 to 1000

50. A substrate coating according to any one of claims 46 to 49 wherein the Si content is 20%

51. A multilayer including at least one layer substrate coating deposited by a method according to any one of claims 1 to 45.

52. A coated substrate including a mixed coating provided by at least one flux of material from a magnetron concurrently deposited with at least one flux of material from a vacuum cathodic arc source.

53. A coated substrate according to claim 52 wherein the substrate is an article.

54. A coated article according to claim 53 wherein the article is a tool.

55. Apparatus for coating a substrate including a magnetron and a vacuum cathodic arc and wherein said magnetron and said vacuum cathodic arc are adapted for simultaneous deposition on to a substrate.