Process and apparatus for coating the surface of a substrate

(42) Date of commencement of the patent: 15. 2.1997 (45) Date of issue: 25. 9.1997 (56) Documentation:

(73) Patent owner:

DE 4016352A1 WO 94 / 01595A1 DE 4035073C1 WO 92 / 01079A1 DE 4022817C1

EP 534505A2 '

DE 3914476C1 EP 445897A1 GB 2231587A EP 406871A2

JOANNEUM RESEARCH RESEARCH COMPANY HäH A-8010 GRAZ, STEIERMARK (AT).

VOEST-ALPINE STEEL LINZ GhfiH A-4031 LINZ, UPPER AUSTRIA (AT).

(72) Inventor:

EBNER REINHOLD DR.

TROFAIACH, STEIERMARK (AT). LENZ WOLFGANG DIPL.ING.

LEOBEN, STEIERMARK (AT). KÖSTER'S KURT DR.

PUOCNAU, UPPER AUSTRIA (AT). HAGLER JOSEF DIPL.ING.

LINZ, UPPER AUSTRIA (AT).

(54) METHOD AND DEVICE FOR COATING THE SURFACE OF A SUBSTRATE (57) Process for coating the surface of a substrate in vacuum or reactive gas atmosphere, wherein the substrate surface in a first step for better adhesion of the applied layer, eg by a coating etch, and then in a second step a layer of a material, eg by vapor deposition or sputtering, is applied to the treated surface, and wherein in the first step in a conventional manner by a high energy, ionized particle flow, a single or Mehratomlagenschicht is applied to the substrate surface.

CD

AT 402 945

DB SB7831ß

AT 402 945 Β

The invention relates to a method for coating the surface of a substrate in a vacuum or reactive gas atmosphere, wherein the substrate surface is treated in a first step for better adhesion of the applied layer, eg by a coating etch, and then in a second step a layer a material, for example by vapor deposition or sputtering, is applied to the treated surface.

Methods of this type are characterized by a particularly high degree of flexibility with regard to the deposition of various layers. Especially in the field of thin-film technology, the vacuum coating process allows a significant expansion of the possible coating systems, for example, compared to the galvanic coating, which also comes into question for the production of thin layers. The range of coating systems manufacturable by vacuum coating technologies includes plastics, metals and ceramics. The typical layer thicknesses are in the range of 0.3 to 3.0 μm. In special cases, larger layer thicknesses are produced, which can be several hundred μm thick.

According to Haefer: Surface and thin-film technology, Springer Verlag 1987, the vacuum coating technologies can be divided into two major groups, the CVD (Chemical Vapor Deposition) and the PVD (Physical Vapor Deposition) technology, which are clearly evident in the process principle and possible fields of application differ.

In the case of CVD technologies, the layer is produced by the chemical reaction of a gas mixture at the substrate surface, wherein the activation energy necessary for the chemical reaction is usually offered via the temperature of the surface to be coated. The part to be coated is heated either uniformly, coating the whole surface, or locally, producing a localized coating. This can be done for example by selective heating of the surface with a laser beam. This process is described, for example, in Molian, Janvrin: Laser Growth of Diamond Thin Films, TMS 1991 and in Steen: Laser Material Processing, Springer Verlag 1991. The temperatures necessary to control the chemical reaction are high, typically around 600 ° C to 1200 ° C. The deposited in this way metallic or ceramic layers therefore have mostly near-equilibrium structure and good adhesion by chemical reaction with the substrate surface. A disadvantage of this method is that high stresses form in the layer upon cooling after the coating due to differential thermal expansion of the layer and substrate. As a further disadvantage is to be considered that this method naturally only for temperature-insensitive materials, such as Hard metals, is suitable. Although low coating temperatures can be achieved by plasma activation according to Rie, Gebauer: Plasma-Assisted Chemical Vapor Deposition of Hard Coatings with Metallo-Organic Compounds, Plasma Surface Engineering, Elsevier 1991, such coating processes are predominantly still in the development stage.

In the PVD technologies, however, an atomic particle flow is generated by physical methods, which condenses on the substrate and thereby generates the layer (Reichelt: vapor deposition and sputtering of hard coatings, metal surface 40, 1986, 12, Carl Hanser Verlag 1986). About the gas space can during the coating of additional substances, eg by reactive gases such as nitrogen, oxygen or similar which precipitate on the growing layer and chemically react with the incoming particle beam, thus undergoing a reactive coating process, such as sputtering in Schiller et al: TiN hard coatings deposited on high seed steel substrates of Vacuum Science and Technology A5 (4) July, August 1987, American Vacuum Society 1987.

The generation of the Teiichenstromes can be done either by evaporation of the layer material in an evaporator boat, for example by conduction heating, or by the irradiation of a target surface with ions, electrons or photons.

FIG. 1 schematically shows the principle of beam-assisted coating technologies. In this case, starting from a particle beam generator 20, which particles 19, such as ions, electrons, photons, or the like. and thus bombarded a target 5, from which a vapor cloud propagates, which is deposited on a located in the direction of vapor propagation substrate 7. Ions are used in sputtering technology to atomize the surface of a solid target, electrons are used for Elelctronenstrahlverdarnpfung. For some time, lasers with suitable beam properties have been available to vaporize solids. For this purpose, pulsed laser radiation with extremely high pulse power is used. Such a method is referred to as LPVD (Laser Physical Vapor Deposition) or PLD (Pulsed Laser Depositionj method.

A major disadvantage of the conventional PVD coating technique is that it is not always possible to achieve a good adhesion of the layer to be applied with the substrate surface. For good adhesion it is necessary, among other things, to adsorb layers from the substrate surface

Remove AT 402 945 Β. Frequently, this is done in a glow discharge in a low pressure atmosphere ion etching processes, but these are time consuming and require a relatively complex process control, as about a plasma must be generated over the substrate surface. Despite these efforts, in many cases good adhesion can only be achieved after a long etching time of 1 to 20 minutes.

From DE-C1-42 28 573 a method for coating a preheated substrate using a pulsed laser source and a target has become known, wherein the substrate is rotatably mounted. Target and substrate holders with heating are arranged in a vacuum chamber having a quartz window for entry of the focused laser beam. The pulsed laser precipitate in the form of thin layers is removed from the target by evaporation of the material in the form of precipitation pulses. By the rotation of the substrate behind a screen in addition there is a shielding for a certain duration per revolution, whereby the film growth temperature can be positively influenced. However, this method does not provide an adhesion enhancing step prior to applying a layer of material.

The method described in DE-C1-40 35 073 relates to the layer production by means of pulsed deposition by laser ablation. In this case, a target is fired by means of a pulsed laser beam in a coating chamber, whereby a plasma cloud is formed, which deposits on a heatable substrate. Via a nozzle arranged laterally next to the substrate, a gas pulse is emitted onto the substrate, so that in each case the particles contained in the gas cloud can strike the substrate surface after the ablated particles and contribute to the formation of layers. A pretreatment of the surface of the substrate is not addressed in this document.

DE-C1-40 22 817 also discloses a coating method for producing a layer on a substrate, in which a coating material ablates from a carrier by means of a pulsed laser beam, transported in the form of a particle stream to the substrate and deposited thereon to form the layer, wherein the pulse duration and pulse intensity of the laser beam are selected to produce a thin precision layer that ionization and heating of the coating material takes place substantially in the interaction zone of the laser light with the coating material. About the coating of the substrate itself is only to be inferred in this document that several thin layers can be applied with the method described therein in different layers with different materials on the substrate. A pretreatment or However, activation of the substrate surface is not disclosed.

In the laser vapor deposition apparatus shown in DE-A1-40 16 352, a focused laser beam is directed into a vacuum chamber and directed to a rotating, cylindrical and heated target material. Opposite the target, a substrate is arranged, on which the sputtered target material is deposited. To the constant thermal decomposition or Reducing the depletion of the target, gas is passed through nozzles on the target, which there again causes the original composition of the target material. The orders of an activation layer to improve the adhesion of a layer of material on the substrate is not described in this document.

DE-C 1-39 14 476 has an arrangement for the removal of material of a target to the object, wherein a cylindrical target mounted on a rotatable holder and is rotatable about its cylinder axis. This avoids the formation of craters in the target material. Again, no pretreatment of the substrate is mentioned.

GB-A-2 231 587 discloses an evaporator having a cylindrical rotatably mounted target on which a laser beam is directed through a passage window of a vacuum chamber and a reactive gas line in the immediate vicinity of the target within the vacuum chamber to improve the surface quality. However, a two-step process of first applying an adhesion-promoting layer is not mentioned in this document.

Furthermore, from EP-A2-0 534 505 a laser evaporation method has become known in which a speed filter or an electric field is additionally arranged between the target and the substrate or is applied to form an amorphous metallic film on the surface of the substrate. This European patent application is a divisional application of EP-A2 406 871 and thus incorporates the same disclosure which merely discloses applying a multi-atomic layer by means of high energy particles but does not serve to apply a layer for adhesion promotion to the subsequent layer.

Furthermore, EP-A1-0 445 897 discloses a method for depositing thin layers, in which a laser beam impinges on a curved target surface at an angle. There are no details for producing a primer layer.

The dielectric film coating system shown in WO 94/01595 comprises a laser directed to a rotating target in an oxygen atmosphere and high energy

AT 402 945 Β

Produces particles that move away from the target to the substrate, which has been heated to about 200 ° C. It describes the cleaning of the surface in this document by conventional methods, a combination of a thin activation layer of a few atomic layers and a material layer applied thereto but is nowhere described in this document.

Finally, WO 92/01079 specifies a method for depositing thin layers by means of LPVD, in which no inhomogeneities in the layer thickness distribution occur. This is achieved by moving the laser beam on the target surface via a mirror system. However, there is no reference to a primer layer in this document.

The object of the invention is to provide a method of the type mentioned above, with which in a simple manner and very quickly a very good adhesion of the coating carried out in the second step is achieved.

Another object of the invention is to specify a method with which the highest possible flexibility with regard to the materials used and with regard to the layer composition can be achieved.

Furthermore, it is an object to provide a method which can be carried out with temperature-sensitive or large substrates at low temperatures.

According to the invention this is achieved in that in the first step in a conventional manner by a high energy, ionized particle flow, a single or Mehratomlagenschicht is applied to the substrate surface.

The impinging high-energy and ionized coating particles cause on the one hand the activation of the surface of the substrate, by which a cleaning of the same of adsorption and a chemical reaction with the impinging layer atoms is achieved, and on the other hand also form an adhesive layer. The application of this layer is preferably carried out at low pressure below 10^-3 mbar, so that adsorbed atoms or molecules can be efficiently removed and sucked through the vacuum pump system. Remaining particles react with the particles of the etch coating. Due to the high particle energies, an extremely good layer adhesion can be achieved at low coating temperatures.

By applying a mono- or polyatomic layer, which is formed of a different material than the subsequently applied layer, coatings tailored to the respective requirements can be produced. For example, the substrate may differ greatly from the actual material layer in the manner of the chemical bond, so that the single or Mehratomlagenschicht can effect a balance between them by this is chosen so that it lies with their type of bond between the two.

In a further development of the invention can be provided that the substrate, for example by washing, pickling, neutralization or the like. is pre-cleaned.

As a result, coarse impurities are removed before the application of the coating method according to the invention.

According to another variant of the invention it can be provided that the single or Mehratomlagenschicht is applied at the same location as the material layer.

This is advantageous in so-called batch processes, where a multiplicity of substrates are coated simultaneously, since this makes it possible to carry out the two coating steps for a large number of substrates without changing the orientation.

Furthermore, it can be provided that the single or Mehratomlagenschicht is applied to a different location as the material layer.

This type of application is very advantageous, for example, if a substrate with very large dimensions is to be coated and it is necessary for it to pass through the coating system. The continuous substrate can then be provided with a thin activation layer at one location by means of the first method step and, after passing through this step at another location, the actual material coating can be carried out by means of the second method step.

According to another embodiment of the invention it can be provided that the one or more atomic layer layer produced in the first step consists of a similar or alien material as the material layer applied in the second step.

In this case, the same target material can be used in both steps, whereby no intermediate step for changing the target material must be performed during the process.

Furthermore, it can be provided that in the second step, the material layer is applied by a high-energy and / or strongly ionized particle flow.

Thereby, the same technology for applying the single or Mehratomlagenschicht and the material layer can be used, whereby no further coating device must be provided.

AT 402 945 Β

In a further development of the invention can be provided that in the second step, the material layer is applied by a low-energy and / or low or non-ionized particle flow, which optionally a high-energy particle flow is superimposed.

As a result, differently structured layers can be applied to the adhesion or activation layer, which are very effectively influenced in their composition and density.

A particularly preferred embodiment of the invention may be that the high-energy, ionized particle flow is generated by the interaction of a pulsed laser radiation with the surface of a target material.

The high achievable energy density with a laser makes it possible to evaporate almost all materials, regardless of the nature of their chemical bond. This results in a high flexibility in the choice of coating materials.

A further object of the invention is to specify a device for coating surfaces, with which it is possible to carry out the method according to the invention in a simple manner.

This is in a device for coating surfaces, in which the surface to be coated in a vacuum chamber, eg a sputtering or sputtering device is arranged, wherein a laser beam of a, preferably pulsed laser for generating a high energy ionized particle stream is directed to a target material, so that the vapor cloud is deposited on the substrate surface, achieved in that the power density of the, preferably pulsed laser in a range of 10⁶ W / cm² until 10¹² W / cm² lies.

As a result, a high-energy particle stream is formed, which generates an activation or adhesive layer of one or more atomic layers on the substrate, to which then further layers can be applied.

It can be provided that the laser beam is focused by an optical lens.

As a result, the power density of the laser beam can be adjusted so that droplet formation is avoided on the substrate.

In this context, it can be provided that the lens is arranged sealingly in the wall of the vacuum chamber.

As a result, the optical focusing system can also be used as a transfer element of the laser beam from the room atmosphere into the recipient interior. A coating of the lens can be avoided by an inert or reactive gas flow opposite to the particle flow. This can be realized by a gas inlet in the region of the focusing lens. As a particularly advantageous protection against a coating of the focusing lens, which serves as a coupling window, the use of a diaphragm has been found, which is arranged between the focusing lens and target in the beam path.

For the application of an activation layer, which improves the adhesion of the subsequent material layer, it is advantageous if the laser is a pulsed laser, for example an Nd: YAG laser, an excimer laser, a TEA-CO₂Laser or a copper vapor laser is.

It can be provided that the pulse duration of the laser in a range of 10^-12 s to 10^-3 s is. A pulse time of the laser in this range is particularly advantageous for activation layers in which the proportion of droplets is to be kept small.

Particularly good adhesion properties are at a pulse duration of the laser, which is in a range of 10^_1° to 10^-7 s is reached.

Particularly preferred for many applications is when the power density of the pulsed laser is in a range of 10⁹ W / cm² until 10¹¹ W / cm² is.

To achieve a uniform erosion of the target, this can be moved during the laser bombardment. It is advantageous if the target material is cylindrical or disc-shaped. In this case, the target is rotated and additionally moved translationally.

Particularly advantageous is the relative movement between the target and the laser beam can be realized by movable mirror optics, which allow scanning and eroding the target surface.

For a very effective ejection of particles from the target material, it is particularly advantageous if the angle of incidence between the laser beam and the target surface normal lies in a range of 30 × to 90 ×.

According to a development of the invention it can be provided that the lens focal length of the focusing lens is in a range of 300 mm to 1000 mm.

This makes it possible to arrange the focusing lens in the wall of the recipient, and to focus the laser beam through it onto the target.

According to another embodiment of the invention can be provided that the vacuum chamber is a cylindrical or cubic recipient and the recipient pressure in a range between 5.10^-6mbar and 5.10^-2 mbar is located.

AT 402 945 Β

As a result, conventional vacuum chambers can be used for the production of particularly good adhesive layers. However, it is also possible to use any other recipient specially shaped for the process according to the invention.

For very effective Aktivierangsschichten consisting of single or Mehratomlagen, the target material may be preferably metallic, for example titanium, iron, chromium, silicon, zirconium, or non-metallic, for example, alumina, zirconia, lanthanum hexaboride.

For better adaptation of layer and substrate, activation layers with covalent or ionic bonding components are also used. These materials form a very good substrate for a subsequent layer. But this does not limit the target materials. All materials suitable for the coating purposes can be used.

Another feature of the invention may be that the reactive gas is formed from nitrogen, oxygen, a carbonaceous carrier gas or mixtures thereof.

According to another variant of the invention, provision may be made for the laser beam to be guided through a frequency multiplying device to match the absorption at the target and the interaction with the absorbing vapor before it hits the target material. Due to the frequency multiplication, in particular by the doubling, a targeted adaptation of the interaction of the laser beam with the outflowing steam can be realized. This makes it possible to vary the degree of ionization and the particle energy.

The invention will be explained in detail below with reference to the exemplary embodiments illustrated in the drawings. It shows

1 shows a schematic representation of a PLD method;

2 shows a layer structure produced by the process according to the invention;

3 is a schematic representation of the processes during the Verdampfüngsprozesses;

4 shows a diagram of the dependence of the power density on the pulse duration of the laser beam;

5 shows a schematic representation of an apparatus for carrying out the method according to the invention;

6 shows a scanning electron micrograph of an erosion trench caused by temporally successive laser pulses on a rotating target;

7 shows a scanning electron micrograph of the surface of a layer produced according to the invention: a) Fe layer, TiO 2_x-Layer;

8 shows a comparison of the X-ray spectra of TiN layers produced according to the invention with a TiN standard; and

9 shows scanning electron micrographs of the fracture surfaces of layers produced according to the invention on various substrates.

FIG. 2 shows in cross-section a layer which has been produced by coating the surface of a substrate 7 in a vacuum or reactive or inert gas atmosphere, wherein the substrate surface is treated in a first step for better adhesion of the layer to be applied and then In a second step, a layer 31 of a material, for example by vapor deposition or sputtering, has been applied to the treated surface.

In accordance with the invention, in the first step, a single or multiple atomic layer 30 has been applied to the substrate surface 7 by means of a high-energy, ionized particle flow. These deposits or multilayer atomic layer 30 is an activation layer and an adhesion layer for the subsequent material layer 31.

Depending on the substrates to be coated, the adhesive and material layers can either be applied at a location where many small substrates are to be coated, or at different locations, when a very large part to be coated is pulled through an installation in the form of a continuous process first process step is performed locally separated from the second process step.

In this case, the adhesive layer may be formed from the same or from a different material as the material layer. This can be adjusted as needed. In this case, large differences in the chemical bonding properties of the substrate surface and the material layer can be compensated, for example, by the adhesive layer. The material layer applied in the second step can also be generated by a high-energy and / or strongly ionized particle flow. However, it is also possible for the material layer to provide only low-energy and / or low-ionized particles, it being possible to build up a very well-adhering material layer on the base, which is formed by the adhesion layer, with a lower energy input.

Furthermore, a combination of these possibilities can be provided, so that in the second step, the material layer is applied by a low-energy and / or low or non-ionized particle flow, which is superimposed on a high-energy Teiichenstrom. This can be different

AT 402 945 Β

Materials are matched very closely, and the density, composition and properties of the material layer are combined as needed.

Particularly effective is a high-energy, ionized particle flow generated by the interaction of a pulsed laser radiation with the surface of a target material.

The use of laser beams for target evaporation brings significant advantages for the coating process. For example, the laser parameters are completely independent of the process conditions prevailing in the vacuum coating chamber. Furthermore, the simple and good focusability of laser beams and the resulting high power density means that virtually all materials can be evaporated regardless of the nature of the chemical bond. This results in an extraordinarily high flexibility in the choice of coating materials, which significantly exceeds the possibilities of other PVD processes.

For the entire coating process and the quality of the coating, the interaction of the laser radiation with the target is of crucial importance. The processes during the evaporation process (ablation process) are shown in FIG. 3 shown. It shows the interaction region with the incident and partially reflected laser beam, the heat front 39, the melt front 40, the evaporation front 41, and the outflowing steam or Plasma. The material vapor stream is directed towards the substrate surface.

The interaction phenomena change during the irradiation period. In the starting phase, part of the radiation is absorbed, the reflected portion is lost to the process. The absorbed radiation fraction first causes heating in the solid state, followed by melting and evaporation of the target surface. During the laser bombardment, the melting and evaporation front move into the solid base material of the target, which is eroded. As a consequence of the high power density, the explosive effluent exerts a high pressure on the underlying melt and causes atomization of the melt film.

In addition, evaporation takes place in atomic form, so that the result of the laser bombardment is a particle stream consisting of atoms, ions and a proportion of clusters.

In thin layers, droplets from the evaporation process are undesirable and should therefore be avoided wherever possible. The proportion of droplets in the evaporation process can be controlled via the power density in the interaction zone. In order to form as little as possible a molten phase, the temperature gradients should be as high as possible, which is ensured by a high power density and short laser pulses. It should be noted that as the pulse duration becomes shorter, the power density necessary to reach the vaporization temperature during laser irradiation greatly increases.

4 shows the result of model calculations for the laser evaporation of aluminum. It can be seen that for the onset of evaporation with the aid of a 10 ns pulse, a power density of at least 10⁹ W / cm² is necessary, using even shorter pulse durations such as 0.1 ns is a power density of 10¹⁰ W / cm² necessary. For efficient evaporation, these power densities should be significantly exceeded since the warm-up phase should only account for a small portion of the duration of a laser pulse.

For the application of an activation layer, which improves the adhesion of the subsequent material layer, it is advantageous if the pulsed laser is an Nd: YAG laser, an excimer laser, a TEA-CO2 laser or a copper vapor laser. But other pulsed lasers are also suitable if the necessary power densities and pulse densities can be achieved. The pulse duration of the laser should be within a range of 10 "s to 10^-3 s, preferably 10^-10 s to 10⁷ s are lying. A pulse time of the laser in this range is particularly advantageous for activation layers in which the proportion of droplets is to be kept small. The proportion of droplets in the activation layer is in a range of 10 at a power density of the pulsed laser⁶ W / cm² until 10¹² W / cm², preferably 10⁹ W / cm² up to 10 W / cm², low.

The use of LPVD (Laser Physical Vapor Deposition) or PLD (Pulsed Laser Deposition) technology therefore requires lasers with high pulse peak powers and short pulse times. The most important lasers available today are summarized in Table 1. Table 1 shows that Nd: YAG lasers have the greatest flexibility in terms of process conditions variation.

3 shows that the incident laser beam strikes the outflowing vapor. Due to the high power density occurs a very intense interaction between the laser beam and the steam. A noteworthy part of the irradiated light energy is converted into steam after the onset of evaporation and causes on the one hand the high kinetic energy of the outflowing steam at a speed of up to some 10 km / s and on the other hand an intensive ionization. Although these amounts of energy appear as a loss in the energy balance of the evaporation process, but with respect to the

AT 402 945 Β

Layer quality of advantage. The high particle energy and the efficient activation of the effluent vapor are a special feature of the LPVD process. Both are of crucial importance for the coating process according to the invention and promote the adhesive strength of the layer and the necessary surface diffusion to improve the layer structure. The LPVD (PLD) process is particularly suitable for coating at low temperatures.

In Fig. 5 is a schematic representation of an apparatus for performing the method according to the invention shown, wherein the surface to be coated is arranged in a vacuum chamber 4, which, for example may be a sputtering or sputtering device. A laser beam 2 generated by means of a preferably pulsed laser 1 is guided via an optical laser beam guide 3 into the vacuum chamber 4, where it strikes a target 5. The vapor 6 flowing out of this leaves the target 5 in the direction of the substrate 7 and deposits there. The vacuum chamber 4 is evacuated during this process via a vacuum pump system 10. Instead of the vacuum, a reactive gas, such as oxygen, nitrogen, a carbonaceous carrier gas, their mixtures or an inert gas can be introduced into the vacuum chamber 4, whereby a corresponding chemical reaction with the target vapor is established in the presence of a reactive gas and the reaction product is reflected.

Advantageously, an ND: YAG laser can be used as the laser light source, which is very well suited for this purpose in terms of pulse peak power, pulse duration and wavelength. Some typical beam characteristics of this laser are summarized in Tab.

The laser can be operated with an electro-optical Q-switch, which achieves pulse durations of 8 ns. In addition, in mode-locked operation, a shortening of the pulse duration into the picosecond range at high pulse power is possible. Due to the high pulse power, the unfocussed beam already has a high power density, which necessitates the use of high-quality coated optics in the beam guidance system. The coupling of the laser beam in the vacuum chamber via a focusing lens 9, wherein advantageously the lens 9 is arranged sealingly in the wall of the vacuum chamber. In this case, the planar surface of a plano-convex lens used can be used as a sealing surface. The use of a plane-parallel window is also possible. A coating of the optical elements by the installation of a diaphragm 11 in the beam path between the lens (or. Window) and the target prevented.

The targets used are cylinders or discs with a maximum diameter of 50 mm. The target is rotated relative to the laser beam so that an erosion trench is formed during the coating trial. The angle of incidence between the laser beam and the target surface normal is between 30 'and 90 "selectable. The distance between the target and the substrate is dependent on this angle, but can basically be set between 20 and 100 mm. Target and substrate are integrated into the vacuum chamber so that lens focal lengths of about 300 up to 600 mm are possible.

Laser 1, beam guiding system 3 and focusing optics 9 are matched to one another such that the largest possible parameter range can be covered. Highest flexibility in terms of pulse peak power, pulse duration and wavelength was achieved with an Nd: YAG laser with electro-optical Q-switch with the possibility of mode locking and frequency multiplication. Some typical beam characteristics of such a laser are summarized in Tab.2. When operating the laser with electro-optical Q-switch pulse durations of 8 ns can be achieved. In addition, in mode-locked operation, a shortening of the pulse duration to 30, 100 and 200 ps at high pulse power is possible. Special emphasis is placed on the achievable power density. By selecting the laser 1, the beam guide 3 and the focusing optics 9 are power densities of 10 '° W / cm² achievable, in individual cases, the maximum power density close to 10¹¹W / cm² come close.

The coating process takes place in a cylindrical recipient 4, to which the vacuum pumping station 10 is flanged, consisting of an oil-feed pump and a rotary pump. Other pumping systems can also be used. Furthermore, a gas inlet system is installed, which has a stable adjustable receiver pressure between 5.10^-5 mbar and 5.10^-2 mbar guaranteed. Both reactive and inert gases can be used as gases.

With the illustrated device, starting from metallic targets, both metallic layers in a non-reactive process and connecting layers in a reactive process can be produced.

In a predominantly reactive layer in the titanium-nitrogen system, a cylinder 5 of pure titanium, which is rotated relative to the laser beam, serves as a target. Before the actual coating, the recipient is at a pressure of less than 2. 10^-5 evacuated, then the etching coating is applied. Subsequently, the flooding is carried out with the reactive gas nitrogen. After reaching the preselected partial pressure of nitrogen, the start of the coating run takes place, which typically lasts between 30 and 60 minutes.

AT 402 945 Β

The reactive experimental design places high demands on the plant stability, since changes in the ratio of the impacting titanium atoms and nitrogen atoms also result in changes in the layer composition and in the layer structure. For this reason, the stability of the laser during the coating runs is constantly monitored and readjusted as needed. The laser is frequency multiplied, in the special case frequency doubled, ie operated at a wavelength of 532 nm. Under these conditions, the pulse energy is 550 mJ with a pulse duration of 8 ns. By measuring the width of the erosion trench, the focus diameter was determined for the experiments. FIG. 6 shows the scanning electron microscopic image of the erosion trench, the focus diameter is about 400um. The power density is therefore about 5 for titanium nitrogen. 10¹⁰ W / cm²,

By scanning electron microscopic layer studies, which can be seen in Figure 7, it was demonstrated that at power densities of greater than 10¹⁰ W / cm² Only very occasional droplet formation occurs. There are only a few droplets in the size of a few to determine.

For the titanium-nitrogen system, numerous coating experiments were performed with the substrate at room temperature. At constant laser parameters, a variation of the nitrogen partial pressure took place. The layers changed their color from a metallic gray to a gold tone with increasing nitrogen partial pressure, which already indicates the formation of titanium nitride. The continuous change of the coating color in coating experiments with increasing nitrogen partial pressure shows the high stability of the coating system, which was also confirmed by repeated layers.

In one series of coatings, X-ray fine structure investigations were carried out to determine the layer lattice. Despite the low coating temperature, a crystalline structure of the layers could be detected, the nitrogen atmosphere has led to the formation of a TiN layer. 8 shows the comparison of the X-ray spectrum of the titanium nitride layer produced according to the invention with the lines of the TiN standard. This shows a slight line shift and a pronounced (111) texture of the layer.

To assess the layer structure, coated glass substrates were broken and examined in the scanning electron microsphere. A scanning electron micrograph of the fracture surface of the layer is shown in FIG. The layer shows up as a homogeneous coating on the glass substrate, droplets could not be found. The structure of the fracture surface of the layer and glass substrate differs only slightly, the layer thus behaves bruchamorph, which indicates a very fine layer structure, which is also to be expected due to the low coating temperature.

The target material may be metallic, eg, titanium, iron, chromium, silicon, zirconium, or nonmetallic, eg, alumina, zirconia, lanthanum hexaboride.

The coating method according to the invention is characterized by a very high flexibility with respect to possible layer systems. Due to the process-related high kinetic energy and strong activation of the vapor stream, the method is also suitable for coating at relatively low temperatures.

In the following, various embodiments of adhesion or activation layers produced according to the invention are indicated with their process parameters.

Table 1

<td colspan="6">Typical beam characteristics for pulsed lasers</td>

<td>laser type</td><td>comment</td><td>Pulse power [MW]</td><td>Pulse duration [ns]</td><td>average power [W]</td><td>Wavelength [nm]</td>

<td>excimer</td><td>ArF, KrF, XeCI</td><td>-20-50</td><td>-10-40</td><td>-20-500¹'</td><td>-193-308</td>

<td>Nd: YAG</td><td>EO Q-switch mode locking</td><td>-20-150²'-50-600²'</td><td>-5-10 -0,03-0,2</td><td>-2-50²'-0.05-1.0²⁾</td><td>1064, 532 355, 266³⁾</td>

<td>TEA CO2</td><td>-</td><td>-10-30</td><td>Spike - 100 Tail - 2000</td><td>- 200-2000</td><td>- 10600</td>

'' depending on the laser gas used ²⁾ depending on pulse duration and wavelength ³¹ Fundamental wave and harmonics

AT 402 945 Β

Table 2

<td colspan="4">Beam data of the installed laser</td>

<td>Wavelength [nm]</td><td>Pulse duration [ns]</td><td>Pulse energy [mJ]</td><td>Puisleistung [MW]</td>

<td>1064</td><td>8th</td><td>1100</td><td>140</td>

<td>532</td><td>8th</td><td>550</td><td>70</td>

<td>355</td><td>8th</td><td>250</td><td>30</td>

<td>266</td><td>8th</td><td>80</td><td>10</td>

<td>1064</td><td>0.1</td><td>60</td><td>600</td>

<td>532</td><td>0.1</td><td>30</td><td>300</td>

<td>355</td><td>0.1</td><td>15</td><td>150</td>

<td>266</td><td>0.1</td><td>5</td><td>50</td>

Examples:

1. Activation layer for the coating of plastic films

Adhesion of SiO₂ or AI₂O₃ Vapor deposition layers (thermal evaporation, laser beam evaporation, electron beam evaporation) on plastic films can be significantly improved by PLDAaktivierungsschichten invention in a thickness of several atomic layers. In particular, activation layers of silicon, aluminum, as well as silicon and aluminum oxide have proven to be suitable.

Favorable deposition conditions for such an activation layer are:

Non-reactive process: receiver pressure p = 10^-5mbar to 10^_3mbar Reactive process: receiver pressure p = 10^-3 mbar to 10^-2 mbar thickness of the activation layer: 5 to 100 atomic layers

Laser radiation: Nd: YAG frequency doubled Pulse duration: 7 to 8 ns

Power density at the substrate: 5.10⁹ until 7.10⁹ W / cm²Laser pulse rate: 10 Hz

Coating rate: 0.1 to 1 atomic layer / laser pulse

Second Activation layers for the coating of glass with hard coatings at low temperatures

The layer adhesion to glass can be increased so far by intermediate layers according to the invention that very well adhering hard material layers can be produced at room temperature. The adhesion is so strong that it does not come to a detachment of the layer at the interface but at a breaking of the glass substrate at large layer thicknesses. The breaking of the glass can be avoided by applying thicker metallic intermediate layers, which not only improve the adhesion but also reduce the stress in the glass substrate as a result of plastic adaptation.

For the coating of glass with titanium nitride, the following process variants have proven particularly suitable:

Titanium activating layer + Titanium metallic intermediate layer + Titanium nitride sputtering layer Titanium activating layer + Titanium (thermal evaporator) metal vapor deposition layer + Titanium nitride sputtering layer

Favorable deposition conditions for a titanium activation layer are:

Pretreatment: Cleaning in ultrasonic bath (alcohol, acetone) and drying of receiver pressure p: 10 ~⁵ mbar to 10^-3 mbar

Substrate temperature · room temperature or above Thickness of activation layer: 1 to 500 atomic layers Laser radiation: Nd.YAG frequency doubled Pulse duration: 7 to 8 ns

Power density at the substrate: 7.10⁹ until 10¹° W / cm²

AT 402 945 Β

Laser pulse rate: 10Hz

Coating rate: 0.1 to 1 atomic layer / pulse

Third Activation layers for the electron beam coating of steel strip with zinc and zinc alloy layers as well as with multilayer layers at low temperatures

In order to realize well-adherent electron beam vapor deposition layers on steel strip, coating temperatures of 400 ° C. to 600 ° C. are generally required to activate the surface. By applying an activation layer according to the invention, well adhering electron beam vapor deposition layers can be produced even at low temperatures up to room temperature. Activation layers of iron, titanium or chromium have proven favorable.

Favorable deposition conditions for the activation layer of iron, titanium or chromium are:

Pretreatment: dry cleaning, pickling, neutralizing, drying

Recipient pressure p: 10^-5 mbar to 10^-3 mbar

Substrate temperature: room temperature or above

Thickness of the activation layer: 2 to 10 atomic layers

Laser radiation: Nd: YAG frequency doubled

Pulse duration: 7 to 8 ns

Power density at substrate: 8.10⁹ until 2.10¹⁰ W / cm²

Laser pulse rate: 10 Hz

Coating rate: 0.1 to 1 atomic layer / pulse

4th Activation layers for the hard coating of permanent molds made of hot-work steel

The life of permanent molds (die casting molds, low-pressure chill casting or the like) can be significantly increased by applying thin layers. By using activation layers according to the invention, well-adhering hard material layers can be deposited at extremely low temperatures between room temperature and about 200 ° C. The coating with titanium boride and with titanium carbonitride has proved to be particularly advantageous. As an adhesive layer, titanium has been outstandingly suitable. The hard material layers can be produced particularly favorably by sputtering. It has proven favorable for the layer properties to superimpose a high-energy particle stream on the actual coating particle stream in order to improve the layer structure.

Favorable deposition conditions for the titanium activation layer are:

Pretreatment: Degrease in Uitraschallbad, drying pressure of the recipient p: 10^-5 mbar to 10^-3 mbar Substrate temperature: room temperature or above Thickness of the active layer: 2 to 10 atomic layers Laser radiation: Nd: YAG frequency doubled Pulse duration: 7 to 8 ns

Power density at substrate: 8.10⁹ to 2.10 '° W / cm²Laser pulse rate: 10 Hz

Coating rate: 0.1 to 1 atomic layer / pulse