Diamond-like nanocomposite compositions

Details Diamond-like nanocomposite compositions Diamond-like nanocomposite compositions

1999-03-15

2001-03-13

Turner, Archene (Department: 1775)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Physical dimension specified

C423S44500R, C423S415100, C427S249300, C427S530000, C427S570000, C427S574000, C427S577000, C427S578000, C428S408000

Reexamination Certificate

active

06200675

ABSTRACT:

FIELD AND BACKGROUND OF THE INVENTION
The invention relates to a diamond-like nanocomposite (DLN) composition having improved (lower) friction properties combined or not with improved (higher) hardness. The invention deals also with an improved process for covering substrates with a layer or film of such a composition in a modified plasma assisted chemical vapour deposition (PACVD) process in vacuum.
Diamond-like nanocomposite (DLN) materials are related or similar to diamond-like carbon (DLC). DLC films (a-C:H, a-C, i-C) display a good combination of high hardness and elasticity, high wear resistance and a low coefficient of friction. Furthermore, because of their chemical inertness, low surface energy and intrinsic smoothness, these films give access to appealing industrial applications such as hard, self-lubricating films, eg. for protection of magnetic discs and media, sliding parts in motors, space applications, optical components etc. However, deposited DLC films exhibit much higher internal stresses (above 1 GPa) than DLN films (200-400 MPa), thus impeding good adhesion to the substrate. DLC films on substrates may thus require the use of intermediate adhesion promoting layers which is not needed for DLN. Another disadvantage of DLC impeding fast commercialisation is the fact that the coefficient of friction of DLC in air increases up to about 0.2 to 0.3 when the relative humidity rises above 50%.
DLN and methods for its deposition on substrates, such as glass, metal or Si-wafers are described in U.S. Pat. Nos. 5,352,493 and 5,466,431. By using the deposition processes disclosed in this patent, diamond-like nanocomposites are produced which consist of an (amorphous)a-C:H diamond-like network and an (amorphous)a-Si:O glass-like network. These networks interpenetrate into each other and some Si-C-bonds may be present. This patent describes generally broad parameter ranges for the deposition processes. The physical characteristics of the resulting coating layers are thus also ranging between large boundaries. It is not obvious how to select these parameters in view of reaching certain predetermined and interesting properties, such as the production of deposited layers with a very high degree of hardness and/or with a very low coefficient of friction, even in humid air with a relative humidity above 50% or in water or solutions or emulsions in water.
OBJECTS AND SUMMARY OF THE INVENTION
The invention now has succeeded in designing an improved diamond-like nanocomposite composition than heretofore available and having in particular a coefficient of friction against steel which is smaller than 0.1 in air with a relative humidity (=RH) up to 90%, respectively in water. The friction test for determining this coefficient is described below. The composition comprises networks of a-C:H and a-Si:O wherein the H-concentration is preferably between 40% and 80% of the C-concentration. This is different from the composition claimed in U.S. Pat. No. 5,466,431.
The composition can include (be doped with) at least one transition metal of the group 1b to 7b and 8 as described in U.S. Pat. No. 5,352,493. The controlled incorporation of metals in the DLN structure leads to highly tailorable optical and electrical properties while retaining to a great extent the mechanical and thermal stability. As an example the electrical resistivity of the films can be varied. The metals Zr, Ti and W are preferred. The diamond-like nanocomposite composition according to the present invention, either doped or undoped with transition metals, comprises preferably 30 to 70 at % of C, 20 to 40 at % of H, 5 to 15 at % of Si and 5 to 15 at % of O, in particular 45 to 70 at % of C, 20 to 35 at % of H, 5 to 10 at % of Si and 5 to 10 at % of O.
It is also an object of the invention to provide a diamond-like nanocomposite composition which comprises 0.5 to 5 at % of an inert gas. It has indeed been found that the incorporation of eg. Ar or Kr or N by ion bombardment may increase the hardness of the composition, even outside the specified ranges or proportions of C, H, Si and O indicated above. This hardness can amount to between 10 and 21 GPa as measured by a nano indentation test described below.
The composition is generally formed by deposition onto a substrate of any shape and made of glass, ceramics, metal, plastics or semiconductors. It is thus another object of the invention to provide a substrate covered at least in part with a layer of the diamond-like nanocomposite composition. The thickness of the layer is generally between 0.01&mgr; and 10 &mgr;m although it can be higher than 10 &mgr;m. It has in particular been found that the DLN-composition of the present invention adheres much better to glass than DLC.
The invention sets also the process parameters for manufacturing a covered substrate with the diamond-like nanocomposite composition having the friction and hardness properties described above. The process according to the invention for manufacturing a covered substrate is carried out in an improved vacuum chamber and comprises the steps of
(a) introducing in said chamber a liquid organic precursor containing the elements C, H, Si and O to be deposited in the suitable proportions,
(b) forming a plasma from the introduced precursor by an electron assisted DC-discharge using a filament with a filament current of 50-150 A, a negative filament bias DC voltage of 50-300 V and with a plasma current between 0.1 and 20 A and
(c) depositing the composition on the substrate, to which a negative DC- bias or negative RF self-bias voltage of 200 to 1200 V is applied, in order to attract ions formed in the plasma.
To speed up and/or to better control the deposition process, the precursor can be evaporated in step (a) in said chamber during or after introduction, preferably by heating it between 30° C. and 150° C. This evaporation step is also useful for depositing other DLN-compositions outside the proportions specified above for C, H, Si and O. In step (c) the voltage is preferably between 250 and 1000 V and the frequency of the RF-voltage is best choosen between 30 and 1000 kHz.
The precursor is preferably an organosilicon compound, eg. a polyphenylmethylsiloxane such as triphenylnonamethylpentasiloxane.
When an inert gas is introduced in the vacuum chamber for incorporation into the deposited DLN-layer, it is ionised and incorporated by ion bombardment of the growing nanocomposite layer. Finally, when during the deposition process at least one transition metal is codeposited in the composition layer, then this is achieved by ion sputtering (eg. with argon) or by thermal evaporation.
The invention relates also to an improved apparatus as described below for carrying out the deposition process. In particular, new systems have been conceived for feeding the precursor to the vacuum chamber in a finely divided form, eg. as a vapour or mist and comprising optionally preheating arrangements for the precursor.


REFERENCES:
patent: 5352493 (1994-10-01), Dorfman et al.
TATF 96. 5THInternational Symposium on Trends and New Applications in Thin Films, Colmar, France, Apr. 1-3, 1996, No. 279, suppl. Issue, Vide Science, Technique Et Applications, Jan.-Mar. 1996, Soc. Francaise Due Vide, France, pp. 67-69, XP0000602985, Neerinck D Et Al: Tribological properties and structural investigation of diamondlike nanocomposites see the whole document.

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