DD294511A5 - METHOD AND DEVICE FOR REACTIVE GAS FLOW SPUTTERING - Google Patents

Abstract

The invention relates to a method and a device for coating technology, in particular for the production of layers of high perfection from difficult to deposit materials. In this case, initially inert gas ions of low energy are directed onto the substrate from an inert gas-swept hollow cathode discharge and cause its surface cleaning without or with only minor structural damage (eg lattice construction defects); Subsequently, by altering the operating parameters, material is deposited from the targets representing the hollow cathode, which is deposited on the substrate. This results in layers of high purity, which can be produced as layer sequences of different materials. sputtering; Gasfluszsputtern; hollow cathode; hollow cathode discharge; inert gas; substrate; Cleaning; target; Structural damage; lattice defects; Layer purity; Layer sequence; Layer composition}

Description

For this 3 pages drawings

Field of application of the invention

The invention can be used in coating technology, in particular for applying thin layers in microelectronics, the optical and metallurgical industries.

Characteristic of the known state of the art

Molecular Beam Epitaxy (MBE) produces very clean and structurally perfect surfaces by heating in a vacuum. This process is very complicated because of the required vacuum (p <10 " ⁹ Pa) and the high thermal load of the molecular beam sources and does not permit the deposition of high-melting compounds Rossnagel (Thin Solid Films 171 [1989], p The main drawback of this system is the impossibility of introducing inert gas ions with energies below 100 eV in sufficient current density to the substrate, resulting in higher energy ions in the surface cleaning process and in the process of electron-beam evaporation also in the film deposition irreversible structural damage.

In addition, the system is very expensive, has a high energy consumption and causes in the case of the deposition of refractory substances a considerable Substrataufheizung. Finally, the electron beam evaporator generates harmful X-rays as well as a large number of stray, fast electrons and has a short life in the presence of oxygen as it is necessary when producing oxide layers.

Harper et al. (J. Appl. Phys. 58 (1985), p.550) describe a film deposition arrangement consisting of ion gun 1 (directed at the substrate) and ion gun 2 (directed at a sputtering target). Apart from the above-mentioned disadvantage of high ion energy of the ions directed directly onto the substrate, the problem of high-energy particles which arise in the sputtering process (sputtered target atoms and ions, scattered primary ions) and often cause considerable compositional and structural film damage is added. Keeping away these particles is only conditionally possible for the charged particles.

This is a fundamental problem not only in ion beam sputtering but also in diode, triode and magnetron sputtering. This also applies to that of Ohmi u.a. (Appl. Phys. Lett. 53 [1988], p.45) described method for homoepitaxy of silicon by magnetron sputtering, where a surface cleaning is achieved by targeted bombardment with low energy ions by means of suitable substrate voltage. Another disadvantage is also here that the intensity of the RF glow discharge i. a. is so low that only a small ion current density can be achieved on the substrate surface, which is why the pre-cleaning must be done under very clean conditions (high gas purity and very low residual gas pressure) to keep the recontamination sufficiently low. Although this method is in principle also suitable for the reactive sputtering of compounds, here - as in the other abovementioned sputtering methods - problems arise due to the interaction of the reactive gas with the target surface during the substrate pre-cleaning, in particular in the case of oxygen (for the purpose of producing oxide films). After completion of the substrate cleaning, stable sputtering conditions result only after removal of the chemically modified target topcoat, ie. h., a smooth transition from surface cleaning to coating is difficult to control.

K. Ishii (J.Vac.So., Technol. A7 [1989], p. 256) describes a coating process in which argon gas stream at a pressure of 0.25 to 1 Torr catalyzed by a hollow cathode (Ti , Fe, Cu) is deposited at a high rate on a substrate arranged via cathode opening. This method has the advantage over the other sputtering methods that thermalized the sputtered particles on their way to the substrate, compared to the evaporation processes that only a moderate substrate heating takes place.

Key drawbacks are that insulator films can not be made, that there is no in-situ surface cleaning, and that no ion bombardment is possible during film deposition, which is required for dense films of optimum structure if only average substrate temperatures are allowed. Other disadvantages are the limitation in the size of the surface to be coated, the limitation on the tube geometry of the target and the restriction to only one target material.

Object of the invention

The aim of the invention was to find a method and an apparatus for carrying out the method of surface coating, wherein it should be ensured that the applied layer is deposited on a very pure substrate surface, that by the cleaning and coating process, no structural change of the substrate surface or ., The substrate material is carried out and that the substrate is exposed to the lowest possible temperature load. In addition, it should be possible to deposit dense and structurally perfect layers of chemically bonded compounds, multicomponent layers and layer sequences of high homogeneity and purity, to change the layer composition during the coating process abruptly or arbitrarily graduated as well as the deposition rate and the ion energy and fire rate in a wide Easy to control area. The device should be distinguished by a simple structure, uncomplicated handling, low risks to operators and the environment and great operational stability and reproducibility of the operating parameters.

Explanation of the essence of the invention

The invention had the object of finding a method and an apparatus for surface coating, wherein a cleaning of the substrate in the system and the subsequent coating without impurities causing process interruption take place. In this case, the energy of the particles impinging on the target for cleaning and stimulating the formation of film during the coating should not exceed a few 10 eV at sufficient current density in order to avoid lattice defects. In addition, a low temperature load should be ensured by a thermal decoupling of substrate and particle source.

Furthermore, the coating source should be capable of coating even firmly bonded compounds, whereby individual components of the coating material located in the source from the outside should be able to be included separately or simultaneously in the particle beam generation process. The deposition rate as well as ion energy and ion rate should be determinable by parameters that are easy to influence. According to the invention this object is achieved in that strike by a small negative substrate bias from a hollow cathode in the direction of substrate of inert gas in which a glow discharge burns inert gas ions of low energy to the substrate, where they cause a removal of material, without causing significant structural damage, that By reducing the pressure in the recipient or increasing the gas flow rate or electrical displacement of the discharge in the substrate ¹ facing end of the hollow cathode or increase the discharge voltage sputtered Hohlkatoden particles enrich the substrate and thus a faster and uninterrupted transition from the substrate cleaning to the coating takes place by suitably changing the substrate bias, ion bombardment of the growing layer, discharge voltage and current, and gas pressure and current, the layer deposition rate and addition of a reactive gas to the inert gas The chemical composition of the layer can be adjusted.

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The discharge voltage and current must be so large that sufficient cathode material is removed. The voltage should be at 200 to 500V ücyen, on the one hand to achieve a stable and intense discharge and on the other hand, the substrate is not energetically exposed to neutral particles. The current is 10 ... 1000mA or even higher, depending on the size of the cathode surface. The gas pressure should not be significantly lower. 1 Pa to ensure complete thermalization of the sputtered particles on their way to the substrate, and not significantly above 20 Pa, to minimize the energy loss of those ions that are to strike the substrate. The gas flow rate is determined to be several tens to several hundreds of minutes, mainly related to the pressure, the layer growth rate, which varies between 0 and very high values, e.g. B. BOO nm / min, is adjustable. To realize the required glow discharge source and substrate must be arranged in a vacuum space. Since the inert working gas, z. As argon, displaced by its flow, the residual gas in the vacuum space from the substrate surface, the purity of the layers is determined mainly by that of the working gas. The costs for the vacuum space are therefore lower than in comparable methods.

The source consists of one or more gas-tight cavities which have at one end a gas inlet opening for the working gas (inert gas, possibly mixed with reactive gas) and at the other end an outlet opening directed onto the substrate. The inner surface and other internals, which should not hinder the flow of gas, consist of one or more parts of target material and may partially consist of insulating material. The various parts of the target material are electrically isolated from each other and individually provided with electrical connections. In operation, a DC or AC voltage is applied to these terminals from the outside, so that a glow discharge takes place, which causes a removal of the target material. In the case of DC voltage, the anode can be made of any conductive material and can also be arranged outside the cavities, which leads to increased purity and stability in the coating process. The spatial extent of the cavities transverse to the gas flow must be so large that a glow discharge can form (at least about 1 mm) and should not be greater than a few cm in order to exploit the Hohlkatodeneffekt can. For this purpose, for a given external size, an intensification of the discharge can be achieved by a uniformly angled design of the cross section, z. B. in the form of a packet of parallel tubes, the extent parallel to the gas flow should not be much less than the transverse extent to obtain the Hohlkatodeneffekt. Too large an expansion, based on the Bertriebparameters, is inappropriate because it leads to increased Redeposition already sputtered target material within the source and thus to a low efficiency.

The substrate is located in the gas flow near the exit opening of the cavities and should have a freely selectable electrical potential. Between the source and the substrate should be a pivoting aperture, z. B. to not change the substrate surface during the pre-cleaning of the source. In reactive deposition, the reactive gas exit port should be near the substrate-side source port (s) and directed at the substrate if reaction of this gas with the target is undesirable. Due to the relatively high working pressure results in a good heat dissipation for the cathode, so that even with average deposition rates can be dispensed with an additional cooling. As the process does not use high voltages, high frequency or toxic gases, it is safe and environmentally friendly.

embodiments

The invention will be explained in more detail below with reference to three embodiments. Show it

1 shows a device according to the invention for coating planar, conductive substrates. FIG. 2 shows a device with multiple hollow cathodes

3 shows a device for internal coating of pipes.

In Fig. 1, the substrate 3 is in electrical and thermal contact with the substrate holder 2, which is brought from the heater 1 to the intended temperature. The material to be applied is removed from the latter by a hollow cathode glow discharge which burns between the anode 21 or 22 and the cathodes 8 and 9, and taken along by the inert gas flowing through the tube 18, so that it forms those formed from the cathodes 8 and 9 Leaves Hohlkatodenraum, together with the inert gas passes through the truncated pyramid 5 and is reflected in large part on the substrate 3. If two different materials are to be deposited simultaneously or one after the other, the targets 8 and 9 must each consist of one of these materials. The deposition rates of both materials are controlled individually by the voltages Ui and U ₂ . If additional voltage sources are present, then with the arrangement described up to four different materials can be deposited simultaneously. The insulator hollow profiles 19 ensure the permanent electrical insulation of the targets with each other and the lateral gas tightness of the hollow cathode chamber. In the case of an intensive discharge to achieve very high rates, it is expedient for the tube coil 10, which is in thermal but not electrical contact with the targets, to flow through coolant in order to avoid overheating of the targets. If chemical compounds are to be separated with the assistance of reactive gases, these gases can be admixed with the inert gas or fed separately through the tube 16 into the bottom of the hollow cathode. In these cases, a reaction already occurs on the target surface. If this is undesirable, then the gas is to be introduced into the tube 17 (which is made of insulating material on the outside), which leaves it outside the hollow cathode only, directed directly onto the substrate. It receives a certain amount of thermal activation, since the tubular anode 22, which is likewise accommodated on the tube 17, is heated by the electron bombardment at the glow discharge. If this activation is not sufficient, by switching to 'anode 21, which is located in the interior of the tube 17, a dissociation and electrical excitation of the reactive gas can be achieved by means of a switch 20, without generating high-energy ions.

If very clean inert gas is required, then the hollow cathode can be extended downwards around the insulating body 12, the getter target 13, the anode 14 and the insulator base plate 15. The voltage source U ₄ here causes a second hollow cathode glow discharge which acts similarly to an ion getter pump, the insulator 12 and the insulator diaphragm 11 preventing transfer of getter material into the upper hollow cathode by lengthening the path and increasing the pressure.

The laterally gas-tight truncated cone 5, which is gas-tightly connected by means of insulating body 7 with the cathodes 8 and 9, but is electrically insulated, causes an alignment dos gas flow to the substrate and by cross-sectional widening against de; Hollow cathode and Querschnittsvorengung at its substrate holder side edge a reduction in the gas flow velocity, which leads to an increase in the outdiffusion of the entrained target material and thus to higher deposition rate, material utilization and inert gas savings. In addition, the process inherent in the process of repelling the residual gas is significantly enhanced. In the case of a coating of insulating substrates, it is expedient to arrange a fine-meshed metal net between the source and the substrate, which takes over the acceleration of the ions onto the substrate. Since the process works with a relatively high gas pressure, a mapping of the mesh to the layer thickness is not to be expected.

Before starting the feed, evacuate the vacuum system, adjust the inert gas flow, and heat the substrate as desired. When the pivot panel 4 is closed and the flap 6 is open, the voltages Ui, U ₂ , U _{4 are} switched on. Through the flap 6 source contaminants can escape effectively. If the source cleaning is completed, then flap 6 is closed and such a high gas pressure is set that, given the gas throughput, no target particles can reach the substrate but still deposit within the hollow cathode or within the truncated cone 5. Then, the voltage U _{3 is} turned on and the pivot panel 4 is opened. This leads to ion bombardment of the substrate surface by ions from the hollow cathode. The energy of the ions is closely related to U ₃ and, depending on the gas pressure, is on average slightly smaller than e _o · U ₃ . If Ui and U _{2 are} sufficiently small, the ion current consists almost exclusively of inert gas ions. The current density can be changed independently of the energy by changing U _{) (} U ₂ or by a slight change in the gas pressure.) The ions cause a surface cleaning of the substrate by material removal, whereby no structural damage occurs, if their energy is only a small multiple of the chemical binding energy After surface cleaning, the coating is transferred without interrupting the glow discharge by reducing the gas pressure or increasing the gas flow rate or increasing the voltages Ui, U _2. These three parameters are simultaneous the deposition rate determined. All three parameters are simple and stable adjustable. U ₃ is set so that the optimum for film formation ion energy is achieved and, if provided, are that or take in the reactive gases, unless they are already during the superficiality purge flowed. The termination of the deposition after reaching the desired layer thickness can be done by closing the pivot panel 4 or by turning off Ui, U ₂ .

In Fig. 2, the substrates 25 are on the substrate holder 24. In the gas-tight box 26, which has a collar 27 at the edge and the open side to the substrates 25 and is closely adjacent to them, through the tube 33, the working gas fed. The perforated plate 31 represents a flow resistance, whereby a uniform pressure is formed in the storage space 32 and the working gas flows uniformly through all the holes of the perforated plate 31, then through the anode space 29, through the hollow cathode matrix 28 and past the substrates 25. The hollow cathode matrix 28 consists of several groups, e.g. 3, of hollow cathodes, each consisting of a specific material, electrically connected to each other, of which other groups are isolated and distributed simultaneously on the opening surface of the box 26. The corona discharge causing the removal of material burns between these cathodes and the common anode 30.

By switching on and off or changing the voltages Ui, U ₂ , U _{3, it is} possible to produce layer systems with abrupt or graduated transitions, with retained voltage values resulting in mixed layers of specifiable composition. The size of the cathode matrix 28 and thus the size or number of the substrates 25 to be coated at the same time is not subject to any fundamental restriction.

In Fig.3 the application of the invention for the inner coating of pipes is described.

The existing from the tube 36 with gas inlet 34, anode 35, hollow cathode 39 and guide 40 source is first fully inserted into the tube 38 to be coated. This tube is connected by means of seal 41 to the Verkuumpumpe 42 and is evacuated from this. The other end of the tube 38 is closed by the source in communication with the sliding seal 37, which can slide on the tube 36 or tube 38. By the gas feed 34, the working gas is now admitted. Reactive gas can be admixed by the anode 35, which is embodied as a fugitive. By applying a suitable voltage to the anode 35 and the cathode 39 ignites the Hohlk.iiodenglimmentladung. To avoid parasitic discharges, the supplies of anode and cathode must be sufficiently isolated. The working gas conveys the atomized cathode material into the tube 38, on the inner wall of which it precipitates. By a negative bias of the tube 38 relative to the anode 35, an ion bombardment of the tube, which contributes to the surface cleaning, as well as for connection and structure formation of the growing layer.

To achieve a complete and uniform inner coating of the tube 38, the source installed in the tube 36 is uniformly withdrawn from the tube 38, as long as the seal 37 can ensure its tightness.

Claims (7)

1. A method for reactive Gasflußsputtern, characterized in that are directed from a inert gas flow through Hohlkatodenentladung by means of a low negative substrate bias inert gas ions for the purpose of surface cleaning on the substrate, that after a sufficient Oberflächenabtrag by reducing the pressure in the recipient and / or increasing the gas flow rate and / or electrical displacement of the discharge into the substrate-facing end of the hollow cathode and / or increase of the discharge voltage from the inner hollow cathode surface material particles are dusted and transported by the gas flow to the substrate and deposited there, wherein by changing the substrate bias of the ion bombardment of the growing layer, by discharge voltage and current and gas pressure and current, the Schichtabscheiderate and by adding a reactive gas and electrical switching from one to another target from which the Hohlk Atode is formed, the chemical composition of the layer is regulated. 2. A device for reactive Gasflußsputtern, characterized in that one of a plurality of mutually electrically isolated targets (8,9) formed hollow cathode is provided at its rear end with an inlet opening for inert gas (18) or with a Gaseinströmöffnung for reactive gas (16) in that the targets (8, 9) are connected separately to voltage sources (U ₁ , U ₂ ) which can be individually switched on, that an elongate anode (21) is located in the hollow cathode and / or a cavity located near the substrate-side opening of the hollow cathode Anode (22) is arranged in front of the hollow cathode, a substrate (3) on a substrate holder (2), which is by a voltage source (U ₃ ) on a negative bias relative to the anode (21,22) is that between Hollow cathode and substrate (3) a pivoting aperture (4) is arranged and that the substrate holder (2) is in contact with a heater (1). 3. A device according to claim 2, characterized in that in the substrate-side opening of the hollow cathode remote end of the hollow cathode opposite the targets (8.9) isolated gate target (13) and an anode (14) are located, with a voltage source (U ₄ ), the hollow cathode being terminated by an insulator bottom plate (15). 4. Apparatus according to claim 2 and 3, characterized in that the targets (8,9) are in thermal contact with a cooling device (10). 5. Apparatus according to claim 2-4, characterized in that arranged at the substrate side end of the hollow cathode with this gas-tight, but electrically isolated funnel-shaped body (5) for aligning the gas flow to the substrate (3) with a side flap (6) is. 6. Apparatus according to claim 2-5, characterized in that between hollow cathode and substrate (3) a pivoting aperture (4) is arranged and that the substrate holder (2) is in contact with a heater (1). 7. The device according to claim 2, characterized in that a common anode (30) and a matrix-arranged plurality of hollow cathodes (28) which are connected individually or in groups with separate voltage sources, in a gas-tight box (26) are arranged the box (26) has a rear gas inlet (33) for the inert gas and the single cathodes consist of individually or in groups different materials.