Method for depositing a cathode in a vacuum arc deposition apparatus

Abstract

The present invention relates to a method of depositing a cathode by an arc evaporation process in a vacuum chamber that ignites an arc and affects the speed and movement of the cathode spot of the arc on a predetermined track on the surface of the cathode to be deposited by a magnet. According to the present invention, the arc is ignited at the center (12) of the cathode, and then the cathode spot moves outward along an arc-shaped track (13) and then moves along a circular track (14) around the center of the target.

Description

Technical Field

[0001] The present invention relates to a method of depositing a cathode by an arc evaporation process in a vacuum chamber, which ignites an arc and affects the speed and movement of the cathode spot of the arc on a predetermined track on the surface of the cathode to be deposited by a magnet.

Background Art

[0002] In arc evaporation, the material to be evaporated must be a conductive material and is placed at the cathode potential, while the special electrode is used as the anode, or the wall of the coating chamber is connected to the anode of the current source. To initiate a vacuum arc discharge, as a common method, an ignition mechanism is used to short-circuit the anode potential and the cathode target for a short time to generate a small ignition arc, which is sufficient for a vacuum arc to form between the actual anode and the target and continue to burn independently. The vacuum arc impinges on the so-called cathode spots on the target with a high energy density. The cathode spots move across the surface of the target according to the material, magnetic field, and current, and the target material transitions from a solid to a glassy phase. In particular, when depositing carbon, typically the cathode spots for the material move very slowly across the surface of the target and there is a risk of sticking in one place. The locally high current generated by the very slow movement of the cathode spots can also cause potential melting of the anode material. The slow movement of the cathode spots also leads to very non-uniform target consumption in a short process time. This is particularly the case when a very thin carbon layer is deposited on the substrate. Carbon layers can be manufactured to have a wide range of properties due to their different structures. The layer hardness of the carbon layer can vary from hard and diamond-like hardness to soft and graphite-like hardness. The deposition of a thin layer requires only a short process time, during which the cathode spots only sweep a part of the arcs on the target. For example, a carbon layer on the order of 100 nm is deposited within a period of <1 minute, and even <10 seconds. In any case, normal ignition at the outer edge of the target means that the cathode spots cannot represent the desired complete circular track. In any case, using only a part of the surface of the target has the drawback that the target is only "consumed" partially and has to be changed frequently. However, the change of the target is related to the downtime of the system, which further increases the process cost. Summary of the Invention Problems to be Solved by the Invention

[0003] An object of the present invention is to provide a method for better utilization of a target material.

Means for Solving the Problems

[0004] To solve this problem, in the method described at the beginning, it is proposed that the arc is ignited at the center of the cathode, and then the arc cathode spot moves outward along an arc-shaped track and then moves along a circular track around the center of the target. This is achieved by maximizing the normal component of the magnetic field at the center of the target, which induces the outward movement of the cathode spot. For example, in the edge region where 35 mm < R ≦ 50 mm, the radial component of the magnetic field is maximized so that the cathode spot moves at an acceleration rate of > 10 mm / s.

[0005] Preferred embodiments of the present invention are described in the dependent claims.

[0006] Therefore, the cathode spot draws an arc-shaped track, particularly a track that sweeps an angle of ≧ 160°. The method according to the present invention can be used particularly for targets made of carbon.

Brief Description of the Drawings

[0007] Further embodiments of the present invention are described with reference to the drawings.

[0008]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0009] As shown in FIG. 1, the arc is ignited by the ignition wire 10, causing a short circuit on the surface of the target 11. The ignited arc vaporizes the target material, generating a plasma phase in front of the target that can condense on a sample placed in the reaction chamber, thereby forming a layer. In this case, the target consists of a disk-shaped carbon body. However, unlike the prior art, according to the present invention, the arc is ignited at the center 12 of the target. However, since this position is not an equilibrium position, the cathode spot is guided along a stable circular track around the center of the target due to the existing electromagnetic force (Lorentz force) and based on the conductivity of the target material. Prior to this, the cathode spot traces an arcuate track 13.

[0010] In an example of a specific embodiment, a graphite target 11 is used.

[0011] The target 11, i.e., the material that is vaporized during the process and condenses on the surface of the substrate having specific properties, is installed on the cathode in the vacuum chamber. The target has a diameter of 100 mm and a thickness of <20 mm.

[0012] The substrate, which is the sample to be coated, is transferred to the vacuum chamber. The vacuum chamber is pumped to a pressure range of <1×10 -3 Pa by a connected pump system. Argon is introduced into the vacuum chamber using gas flow control hardware. The argon is ionized and accelerated towards the substrate by the voltage applied to the substrate. By momentum transfer, surface impurities and oxides on the substrate are removed, and the surface of the substrate is activated. Here, the sample is prepared for the actual coating process. Depending on the process, the sample can also be brought to an appropriate temperature by a heater.

[0013] In the subsequent coating process, an argon stream is introduced into the vacuum chamber at a low level such that the argon pressure becomes <1 Pa. An ignition voltage of 88 V is applied to the target. The trigger finger at the anode potential for ignition is directed onto the surface of the target such that the contact point is approximately 40 mm from the center of the target, thereby causing a short circuit.

[0014] When the trigger finger is removed from the surface of the target, the short circuit generates an electric arc that deposits the target material and creates a conductive gas phase (plasma) within the vacuum chamber, enabling the plasma to burn between the cathode and the anode (chamber wall). After plasma ignition, a stable process can be achieved with a target voltage of approximately 20 V - 25 V and a target current of <80 A.

[0015] The cathode spot is actuated by a modified magnet located behind the target and a self-induced E-field caused by the target current. The magnetic field is optimized such that the normal component of the magnetic field component is maximized within the region of the center of the target and the radial component of the magnetic field component is maximized at a radius of 35 mm < R ≤ 50 mm. As a result, the cathode spot ignited at the center of the target is guided along a stable edge track along an arc-shaped track that sweeps an arc of radius ≥ 160° and is accelerated to a speed of > 10 mm / s.

[0016] The arc first travels on an arc-shaped track 13, which is described in simplified terms from a radius of approximately 22 mm outward from the center of the target (see Figure 2) to a radius R of approximately 45 mm. Since the initial direction of this arc track is statistically random, the arc can travel in different directions after each ignition. When it reaches the equilibrium position at a radius of approximately 40 mm, the arc starts a normal circular motion on the surface of the target at a quasi-static radius. Due to the modified magnet configuration, the arc requires approximately 30 seconds (approximately 10 mm / second) to complete one full revolution.

[0017] The process time depends on the deposition rate and is usually shorter than 1 minute. Depending on the process, the sample is cooled to a specific temperature. Next, the system is ventilated and the sample is removed from the vacuum chamber.

[0018] However, when the arc is dispersed and ignited at a target at a distance of 35 mm to 45 mm from the center of the cathode under the same process conditions with a standard magnet configuration, that is, when the cathode spot takes an equilibrium position and is ignited at a point on the circular track moving on the circular track, the arc requires 180 seconds to 240 seconds for one revolution of the circular track, that is, it moves at a speed of about 1 mm / second. In the case of a short coating time (<1 minute), this leads to the cathode spot moving only on a part of the circular track in the state-of-the-art process. As a result, the target is removed unevenly and has to be changed more frequently, leading to an undesirable longer downtime of the system.

[0019] The present invention is particularly applicable to the deposition of very thin carbon layers on the order of 100 nm. Such carbon layers are applied in a short period of up to 1 minute, preferably less than 10 seconds. Within this time, the arc can only move over a part of the surface of the target. In the case of arc ignition at the outer edge of the target, which is common in the prior art, the erosion profile is only arranged on a part of the surface of the target because only a partial section of the circular track can be traversed during the carbon vapor deposition. The present invention eliminates the drawback that the target has to be replaced even when the target is only partially worn. By igniting the arc at the center of the target and then moving the arc outward on the arc track, it is possible to ensure that the target is uniformly removed by vapor deposition.

[0020] The magnetic field that induces the arc is optimized with respect to the arc intensity and equilibrium position. The strength of the magnetic field has a great influence on the speed of the arc, and as a result, the arc generally moves faster over the target. The arc represents a strong negative charge that burns between the target and the anode arranged around the target. When the arc moves slowly, this current melts the anode. This can be minimized or further prevented by faster movement. Furthermore, the arc covers a longer distance in a shorter process time.

[0021] The equilibrium position of the arc also depends on the magnetic field. By modifying the magnetic field, the track of the arc on the surface of the target can be set accordingly.

Claims

Claim 1 A method of depositing a cathode by an arc evaporation process in a vacuum chamber that ignites an arc and affects the speed and movement of the arc cathode spot on a predetermined track on the surface of the cathode to be deposited by a magnet, wherein the arc is ignited at the center (12) of the cathode, and then the cathode spot moves outward along an arc-shaped track (13) and then moves along a circular track (14) around the center of the target. The method is characterized by this. Claim 2 The magnetic field on the surface of the target induces the outward movement of the cathode spot on an arc-shaped path by maximizing the normal component of the magnetic field at the center of the target, and by maximizing the radial component, the cathode spot has an acceleration speed of > 10 mm / s. The method according to claim 1, wherein the method is modified by obtaining a stable end position on a circular track with a radius of 35 mm < R ≦ 50 mm. Claim 3 The arc-shaped track (13) sweeps an angle of ≧ 160°. The method according to claim 1 or 2, characterized by this. Claim 4 The cathode is made of carbon (graphite). The method according to claim 1, 2 or 3, characterized by this.

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