GB2401116A

GB2401116A - Plasma Assisted Chemical Vapour Deposition

Info

Publication number: GB2401116A
Application number: GB0309603A
Authority: GB
Inventors: Der Kolk Gerrit J Van; Arutiun P Ehiasarian; Papken Eh Hovsepian
Original assignee: Sheffield Hallam University; Hauzer Techno Coating BV
Current assignee: Sheffield Hallam University; IHI Hauzer Techno Coating BV
Priority date: 2003-04-28
Filing date: 2003-04-28
Publication date: 2004-11-03

Abstract

A PACVD process where the substrate is pretreated by bombardment using metal ions generated by a high power magnetic field supported pulsed magnetron discharge, with the horizontal component of the magnetic field in front of the cathode having a strength of 100-1500 Gauss (10<6>-1.5x10<7> T), and the power density of the discharge being more than 1000 W/cm<2>. After pretreatment a PACVD coating is applied. Preferably the pulse length of the discharge is between 10-1000žs, and the pulse interval is between 0.2ms - 1000s. The metal ions used for bombardment may be chosen from Ti, V, Cr, Zr, Nb, Mo, Hf, Ta or W. Preferably the pretreatment takes place at a pressure of 10<-5>-10<-1> mbar (0.001-10 N/cm<2>). The PACVD may deposit DLC, alloys containing carbon, boron nitride or combinations of carbon and nitrogen, and the plasma may be supported by mid, high or radio frequency discharges, microwave or active electron sources.

Description

A PACVD Process For The Coating Of Substrates And An Apparatus For The

Coating Of Substrates By A PACVD Process.

Plasma Assisted Chemical Vapour Deposition (PACVD) has been demonstrated to be a technology with a large potential. One of the industrial applications of PACVD is the production of low friction coatings on substrates. Such coating systems can e.g. be carbon based systems, such as diamond like carbon (DLC), silicon containing DLC, and boron containing DLC. One of the critical problems is to create a proper adhesion. One of the key issues for proper adhesion is to create a substrate surface with cleanness at atomic scale. To do so methods are avail- able like noble gas ion etching. Normally Ar is used with kinetic energies between and 400 eV. Higher kinetic energies are seldom used as they will result in the formation of an Ar rich layer in the outer atomic layers of the substrate; resulting in a mechanically weak and brittle layer just below the interface substrate/coating. An alternative method for etching is metal ion implantation such as is produced by a cathodic arc discharge. Quite often more than singly ionised metal-ions created in the vapour cloud of the cathodic arc discharge are utilised for low energy ion- implantation. Typical kinetic energies between 1000 eV and 3000 eV (determined by degree of ionisation and potential difference between the arc plasma cloud and the substrate) are utilised, the substrate is at so- called bias voltage potential. At these kinetic energies sputter yields are such that an etching effect is obtained. A second effect obtained by this implantation is the embedding of the metal ions in the substrate; see C. Schonjahn, L.A. Donohue, D.B. Lewis, W.-D. Munz, R.D. Twesten, I. Petrov, J. of Vacuum Science and Technology, Vol. 18, issue 4, 2000, p. 1718 -1723 [1], resulting in a change of surface structure and an increase of surface hardness.

It has been found that the most beneficial effects on adhesion are obtained with energies of around 1000 to 2000 eV. In some cases even local epitaxial film- growth can be obtained.

A:: À: À ...: . À À À l For metal ion implantation generated by cathodic arc discharge a problem is, that small droplets are generated at the cathode surface, and are ejected and that a fraction will land at the substrate surface. The quantities of droplets were found to be fairly low utilising Cr as target material, as compared to Ti or TiAI as target material. Therefore, for a number of applications, Cr ions are utilised specifically for the metal-ion etch or implantation phase, see W.-D. Munz, I.J. Smith, L.A.

Donohue, J.S. Brooks, US 6033734 patent, Method of coating metallic and ceramic substrates [2].

For a large number of applications the macro-particles (or droplets) at the inter- face substrate/coating do play a minor role. However, for applications involving low friction coatings such as WC-C:H and DLC the coefficient of friction and surface roughness are essential for a good performance of the coating. Hence etching by metal ions as generated by cathodic arc has never found an application for such coatings, due to the creation of additional surface roughness. Typical surface roughness that is required is Ra s 0.1,um. The starting surface is quite often highly polished before being coated. Surface preparation for these coatings takes place generally by a noble gas ion etch step, e.g. 300 eV Ar etching.

Until now a high metal ion density was achievable under usual industrial condi- tions only with cathodic arc discharge. Recently magnetic field supported high power impulse cathode sputtering has gained importance.

By application of a power density higher than 1000 W/cm2 on the cathode surface, it is possible to obtain a metal vapour in which 30 % or more of the metal vapour is ionised, see A. P. Ehiasarian, W.-D. Munz, L Hultman, U. Helmersson, V. Kouznetsov, Influence of high power densities on the composition of pulsed magnetron plasmas, Vacuum, 65 (2002) 147, [3]. Critical for this high power density is a crossed electric and magnetic field. This value is of the same order of magnitude as achieved in cathodic arc discharges. Fig. 1 shows an optical emission spectrum of a plasma generated in a high power impulse discharge with Cr as target material, with a : . . . . power density of 3000 W/cm2, a peak voltage of 1200 V, a pulse length of 50 ps and a pulse interval of 20 ms. The major advantage of this method of producing metal ions, is that macroparticles (droplets) are not formed, and consequently there is only a small additional surface roughness introduced by the coating proc- ess to the substrate interface.

An additional advantage is that after metal ion implantation a brittle surface inter- face, such as is formed after noble gas implantation is not formed. For noble gas implantation therefore the ion energy is limited. For metal ions this does not hold, a higher energy can be selected to achieve additional effects like surface harden- ing or surface amorphisation.

In the present invention the noble gas etch phase prior to plasma assisted chemi- cal vapour deposition is replaced by a metal ion implantation utilising a magnetic field supported high power cathode sputtering source. The processes taking place at the substrate are fundamentally different from those, taking place with noble gas ion implantation. With metal ions a higher ion energy can be used than with noble gas ions for the reasons described above, and next to sputter-cleaning (etching) metal ions are implanted at shallow depths resulting in changing sub- surface properties. Properties that can be influenced are nano-hardness, corrosion resistance and elasticity.

The metal ion energies are typically between 0.5 and 5 keV. The higher voltages can be used for implantation induced surface hardening.

The PACVD coating put on top can be deposited with plasma support by e.g. radio frequency, mid-frequency (20 to 10 kHz) or using additional means such as a microwave source or an electron cyclotron microwave source.

The High Power Pulsed Magnetron Process is a technology, that has been published very recently, see V. Kouznetsov, PCT application W098/40532, V. Kouznetsov, PCT applica- tion WO02/103078, V. Kouznetsov, PCT Application WO01/98553 [4, 5, 6]. The utilization À À a. . . À -

. . of metal ions produced by a high power pulsed magnetron for etching below physical vapour deposited coatings (PVD coatings) has been also been published recently, see W.-D. Munz, A. Ehiasarian, P. Hovsepian, EP 1 260 603 [7]. The utilization of high power pulsed magnetron generated metal ions for etching and surface preparation prior to plasma assisted chemical vapour deposition is an essentially new method...DTD: Literature [1] C. Schonjahn, L.A. Donohue, D.B. Lewis, W.-D. Munz, R.D. Twesten, l. Petrov, J. of Vacuum Science and Technology, Vol. 18, issue 4, 2000, p. 1718 1723.

[2] W. -D. Munz, l.J. Smith, L.A. Donohue, J.S. Brooks, US 6033734 patent Method of coating metallic and ceramic substrates.

[3] A. P. Ehiasarian, W.-D. Munz, L Hultman, U. Helmersson, V. Kouznetsov, Influence of high power densities on the composition of pulsed magnetron plasmas, Vacuum, 65 (2002) 147, [4] V. Kouznetsov, PCT application W098/40532 [5] V. Kouznetsov, PCT application WO02/103078 [6] V. Kouznetsov, PCT Application WO01/98553 [7] W.-D. Munz, A. Ehiasarian, P. Hovsepian, EP 1 260 603 À . À À e.

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Claims

Patent Claims 1. A PACVD process for the coating of substrates, wherein

the substrate is pre treated by metal ion bombardment, using metal ions generated by a high power magnetic field supported pulsed magnetron discharge, with the horizontal compo nent of the magnetic field in front of the magnetron cathode having a strength of to 1500 Gauss, and wherein, after the pre- treatment, a further coating takes place by means of plasma assisted chemical vapour deposition, with the power density of the pulsed discharge during pre-treatment being more than 1000 W/cm2.
2. A process in accordance with claim 1, wherein said power density is between 2000 and 3000 W/cm2.
3. A process in accordance with claim 1 or claim 2, wherein the pulse length of the pulsed magnetron discharge is between 10 and 1000 ps and the pulse interval is between 0.2 ms and 1000 s.
4. A process in accordance with claim 3, wherein the pulse length is preferably approximately 50 Us and the pulse interval 20 me.
5. A process in accordance with any one of the preceding claims wherein the dis charge during high power pulsed magnetron sputtering is distributed across the cathode surface, and extends over at least 50 % of the cathode surface.
6. A process in accordance with any one of the preceding claims wherein the dis charge current density is approximately 10 A/cm2.
7. A process in accordance with any one of the preceding claims wherein the metal ions used for surface preparation are one of Ti, V. Cr. Zr, Nb, Mo, Hf. Ta, W or combinations thereof. a.. a

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8. A process in accordance with any one of the preceding claims wherein the pre treatment takes place in an pressure regime of 10-5 to 10-' mbar and wherein the gaseous species is mainly a noble gas.
9. A process in accordance with any one of the preceding claims wherein the pre treatment takes place at a total pressure of 10 3 mbar.
10. A process in accordance with any one of the preceding claims, wherein the sub- strate is at a bias voltage of 0.5 to 5 keV during pre-treatment, and in such a way that an implantation and etch phase take place.
11. A process in accordance with any one of the preceding claims, wherein the sub- strate is at a bias voltage during pre-treatment that is changed from e.g. 0.5 keV to keV, to effect a transition from mainly etching to implantation.
12. A process in accordance with claim 11, wherein the substrate is at a bias voltage during pre-treatment that is changed from e.g. 0.5 keV to 5 keV and finally lowered again to 0.5 keV, to effect a transition from mainly etching to implantation, and fi- nally to form a surface layer having a concentration, especially a high concentra- ton, of the implanted metal species.
13. A process in accordance with any one of the preceding claims wherein the PACVD deposition process is used to deposit diamond like carbon, silicon containing dia- mond like carbon, alloys containing as main component carbon with other addi- tions, boron nitride or combinations of carbon and nitrogen.
14. A process in accordance with any one of the preceding claims wherein the PACVD process utilises plasma support by means of mid-frequency discharges, high fre- quency discharges, radio frequency discharges, microwave or active electron sources to stimulate the plasma.

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15. A process in accordance with any one of the preceding claims wherein one or more high power pulsed magnetron sources and devices for generating plasma are provided to realise the PACVD process.
16. Apparatus for the coating of substrates by a PACVD process, the apparatus including a treatment chamber having a substrate carrier, at least one pulsed magnetron associated with the chamber for generating a high power magnetic field supported pulsed magnetron discharge of metal ions from a magnetron cathode, said magnetic field having a maximum field component directly in front of said magnetron cathode of 100 to 1500 Gauss for pre-treating substrates present in said chamber by metal ion bombardment, said at least one pulsed magnetron hav- ing a power supply for operating said pulsed magnetron during said pre- treatment at a power density of more than 1000 W/cm2, and plasma generating means for effecting coating by plasma assisted chemical vapour deposition, the treatment chamber having inlet means for the admission of an inert gas and of at least one chemical participating in said chemical vapour deposition process.
17. An apparatus in accordance with claim 16 wherein said plasma generating means comprises the use of mid-frequency, radio frequency, high frequency or microwave energisation to produce the plasma.

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