FR2775005A1 - COATING BASED ON ULTRA-HARD AND FLEXIBLE CARBON NITRIDE AND PREPARATION METHOD THEREOF - Google Patents

Abstract

The carbon nitride-based coating has a hardness greater than 65 GPa and an elasticity greater than 160 GPa. To prepare a nitride-based coating, a microwave discharge is created in a nitrogen stream (8), one places a metal or semi-metal target (2) in a reaction chamber (1) at such a distance from the discharge zone (10) that the nitrogen plasma formed in the zone (12) where the target is located is under ionic form, a pulsed CO2 infrared laser beam is sent to this target (2) of said metal or semi-metal and said metal or semi-metal nitride is collected on a substrate (6) located under the target (2).

Description

Ultra carbon nitride coating
hard and flexible and its preparation process
The present invention relates to a coating based on carbon nitride having the characteristic of being both ultra hard, flexible and having a low coefficient of friction.

The invention also relates to the process for preparing the coating based on carbon nitride above and more generally a nitride coating of a metal or semi-metal of columns IIIa, IVa, IVb and
Vlb.

 The carbon nitride coatings prepared so far have the drawback of not combining flexibility, low coefficient of friction and high hardness.

 However, many industrial applications in electronics, optics, coatings on flexible plastic, require a coating that is both hard and flexible. For mechanical applications, the characteristic of a low coefficient of friction combined with hardness and flexibility is very important.

 The object of the present invention is to achieve this objective.

 According to the invention, this coating based on carbon nitride is characterized in that its hardness is greater than 65 GPa and its elasticity is greater than 160 GPa.

 The formula for this carbon nitride is CNx, x being greater than 0.3.

The process for preparing such a carbon nitride and more generally a nitride of a metal or semi-metal from columns IIIa, IVa, IVb and Vlb, is characterized by the following steps
A microwave discharge is created in a nitrogen flow, a target of said metal or semi-metal is placed in a reaction chamber at a distance such from the discharge zone that the nitrogen plasma formed in the zone where is located the target is in ionic form constituting the secondary ionization zone specific to the flowing nitrogen plasma as described in the ref (P. Supiot, O. Dessaux, P. Goudmand J. of Phys. D
Applied Physics 28, 1826-1840,1995). A pulsed CO2 infrared laser beam is sent to this target of said metal or semi-metal and said metal or semi-metal nitride is collected on a substrate located under the target.

 Preferably, the distance between the target and the discharge zone is less than about 0.7 m.

 When the target is located at this distance from the discharge zone, it is in the secondary ionization zone in which the nitrogen plasma is composed of ions.

 When the target is located at a greater distance from the discharge zone, for example at a distance equal to 0.9 meters, this target is situated in a so-called far discharge zone in which the nitrogen plasma is free of ions.

 In this case, the nitride coating obtained has poorer properties than in the case where it is formed in the secondary ionization zone.

The formation of the metal or semi-metal nitride according to the process according to the invention can be explained as follows
The laser beam upon reaching the metal or semi-metal target generates a molecular fragmentation of this metal or semi-metal, in the form of vapor which will react with the excited species of the nitrogen plasma to form a nitride of said metal or semi-metal.

 According to a preferred version of the invention, the target of said metal or semi-metal is placed 45 "from the direction of the laser beam.

 Preferably, the substrate is located under the target, in a horizontal plane, and parallel to the direction of the laser beam.

 Preferably also, the nitrogen flow and the discharge are formed in a horizontal tube perpendicular to the direction of the laser beam.

 Preferably the target is graphite.

 In this case, a carbon nitride coating is obtained which is both very hard, flexible and has a low coefficient of friction.

 According to the process according to the invention, the target can also be made of boron, aluminum, gallium, silicon, germanium, titanium or chromium.

 Boron, aluminum, gallium, silicon, germanium, titanium or chromium nitrides can thus be prepared.

 Other features and advantages of the invention will become apparent in the description below.

The accompanying drawings given by way of nonlimiting example
- Figure 1 is a schematic plan view of an installation for implementing the method according to the invention;
- Figure 2 is a view of this installation perpendicular to the plane of Figure 1.

 The installation represented in FIGS. 1 or 2 comprises a reaction chamber 1 inside which is placed a graphite target 2 which is arranged at 45 degrees from the direction of a pulsed CO2 infrared laser beam 3.

 The laser beam 3 is focused by a lens 4 in ZnSe and enters the chamber through a window 5 in Ba F2.

 Under the target 2 extends horizontally a substrate 6 which is parallel to the direction of the laser beam 3.

 Room 1 communicates at 7 with a vacuum pump.

 A nitrogen flow 8 (see FIG. 2) is created in a horizontal tube 9 which communicates with the chamber 1.

 A discharge is created in the zone 10 by means of a coupler 11.

 At a certain distance from the discharge zone 10 is located a zone 12 called secondary ionization, that is to say plasma composed of electrons, atom ions and excited nitrogen molecules.

 Target 2 is located at the end of this secondary ionization zone 12.

 Beyond this zone 12 the plasma is devoid of ions.

 A detailed description is given below of an example of implementation of the preparation process according to the invention.

 The deposition process has two stages which are linked without being released to the air: first of all, the substrate is subjected to a flow of nitrogen excited by an electric discharge created by a microwave generator for 5 min. The deposition phase begins with the vaporization of the target by the instantaneous concentration of infrared laser radiation in this atmosphere of excited nitrogen.

Operating conditions
A flow of nitrogen is excited via a coupler 11 connected to a microwave generator within a Pyrex tube 9 with a diameter of 30 mm, called a discharge tube. This tube 9 is connected to the reactor 1 by means of a sliding assembly. Continuous pumping provided by a 33 m3.h-1 pump leads the plasma to the reaction chamber. The post-discharge of the nitrogen plasma is introduced perpendicular to the reactor either in an ionic form also called secondary ionization, or either in an ion-free form, called distant post-discharge by varying the distance between the zones of deposition and discharge.

The presence of secondary ionization in the reaction chamber is obtained for very extensive power and pressure conditions.

Ablation of the carbon target 2 is carried out by the beam of a TEA infrared laser 3
Pulsed CO2 (LUMONICS) adjusted on the P20 line at the wavelength 10.54 µm. The pulse repetition frequency is 1Hz. The energy delivered by each pulse is 10 Joules for a duration of 50 ns. The laser beam is focused on the target 2 placed in the reactor provided with an input window 5 in BaF2 (infrared quality) using a convex plane lens 4 in Zinc Selenide. The target 2 is maintained at 45 "by a rotating aluminum support. The substrate 6 maintained at room temperature (can also be heated), is placed horizontally under this target. The target-substrate distance is 3 centimeters. deposition time is fixed at 15 min, the nitrogen flow rate is 4 1 / min, corresponding to a deposition pressure of 10 mbar.

 Some examples of industrial applications of the coating according to the invention are given below.

Electronic
Insulator, insulator and temperature conductor
Metal-Insulating-Semiconductor Structure (MIS).

 Barrier to diffusion in integrated circuits.

Thin Dielectric Films: Capacitors,
Very small capacitors for DRAMs (Dynamic Random Access Memories).

Optical
Protective coating for ophthalmic lenses, Anti reflection.

 Coating for laser optics, laser mirror, optical coatings on polymeric materials.

Electronics and Optoelectronics
Tribological applications
Solid lubricant, Slip, Protection
Coating on plastic materials.

 The list of other compounds which could be prepared according to the process according to the invention is given below.

Nitrides from metals and semi-metals in columns IIIa, IVa, IVb and Vlb.
examples
Cubic boron nitride from a boron or non-cubic boron nitride target;
Aluminum nitride from a target in
Aluminum
Gallium nitride from a Gallium target
Silicon nitride from a target of
Silicon;
Germanium nitride from a target no
Germanium.

Nitrides from transition metals
Examples
Titanium nitride from a target of
Titanium
Chromium nitride from a target in
Chromium.

Claims (9)

 1. Coating based on carbon nitride with a low coefficient of friction characterized in that its hardness is greater than 65 GPa and its elasticity is greater than 160 GPa and in that its formula is CNx x being greater than 0.3.  2. Process for preparing a coating based on the nitride of a metal or semi-metal of columns IIIa, IVa, IVb and Vlb, characterized by the following stages: a microwave discharge is created in a nitrogen flow (8), a target (2), of said metal or semi-metal, is placed in a reaction chamber (1) at such a distance from the discharge zone (10) that the nitrogen plasma formed in the zone (12) where the target is located is in ionic form, a metal or semi-metal is sent to this target (2) pulsed CO2 infrared laser beam (3) and said metal or semi-metal nitride is collected on a substrate (6) located under the target (2).  3. Method according to claim 2, characterized in that the distance between the target (2) and the discharge zone (10) is less than about 0.7m.  4. Method according to one of claims 2 or 3, characterized in that the target (2) of said metal or semi-metal is disposed at 45 "from the direction of the laser beam (3).  5. Method according to claim 4, characterized in that the substrate (6) is located under the target (2) in a horizontal plane and parallel to the direction of the laser beam (3).  6. Method according to one of claims 4 or 5, characterized in that the nitrogen flow (8) and the discharge (10) are formed in a horizontal tube (9) perpendicular to the direction of the laser beam (3) .  7. Method according to one of claims 2 to 6, characterized in that the wavelength of the laser beam (3) is equal to 10.54 µm  8. Method according to one of claims 2 to 7, characterized in that said target (2) is made of graphite.  9. Method according to one of claims 2 to 7, characterized in that said target is boron, aluminum, gallium, silicon, germanium, titanium or chromium.