RU2138094C1 - Facility for applying thin-film coatings - Google Patents

Abstract

FIELD: plasma engineering; coating large-area sheets of insulating materials. SUBSTANCE: unit comparing mean values of power and rate of current and voltage variation with reference signals is introduced in power system of magnetron phytosystem. Its output is connected to current interrupter and, through delay line, to starting device of adjustable regulated- voltage supply. When using phytosystem with small working chamber for coating large-area sheets, it will be good practice to make output sluice chamber in the form of blind pocket. For multiple-cathode phytosystems with long working chamber, multichannel gas admission system is used to pass gas through injection holes spaced maximum 100 cm apart. When such working chamber is divided by diaphragms into separate compartments and injection holes in each compartment are connected to separate gas admission system, such arrangement can apply multilayer coats simultaneously. Ionic cleaning functions are implemented by means of electrodes installed in sluice camber and connected to additional high-voltage supply. The latter may be of pulse type. EFFECT: provision for avoiding transfer of glow discharge into arc discharge thereby preventing failure of facility and coatings. 6 cl, 4 dwg

Description

 The invention relates to a plasma vacuum technique and is intended for coating on the surface of predominantly dielectric materials in the form of thin films of metals, their oxides, nitrides and other compounds synthesized by the interaction of a working gas with atomized cathode atoms.

 The source of the deposited material is the magnetron sputtering system (MPC). It contains a target cathode, an anode, and a magnetic system. The magnetic field lines are located near the target surface. When a constant voltage is applied between the cathode and the anode, a glow discharge is ignited. Electrons emitted from the target surface under the influence of electric and magnetic fields move along it along complex cyclic trajectories, ionizing atoms many times. This leads to an increase in the concentration of ions in the plasma and an increase in the cathode sputtering rate. A magnetic field localizes the plasma directly at the target surface.

 A very complete description of the possible designs of the MPC is presented in the monograph Danilina B.S., Syrchina V.K. Magnetron Spray Systems. - M .: Radio and communications, 1982, p. 72.

 Conventionally, they can be divided into coaxial and planar.

Coaxial structures (Krivobokov VP, Kuzmin OS, Legostaev VN Magnetron sputtering system. RF patent application N 95121032, 12/13/95) have a very large specific (per unit area of target) productivity. They are distinguished by a high material utilization rate. They provide high uniformity in length, are easy to install and have a number of other advantages, but some disadvantages are also characteristic of similar systems, the most significant of them are the following:
a) a cathode in the form of a tube has a relatively high cost;
b) when processing flat sheet materials, a significant part of the sprayed particles flies at an acute angle to the surface to be treated. As a result of the large path in the working gas medium, they are thermalized and therefore have relatively low energies, which creates problems of providing the necessary adhesion of the films with respect to the substrate.

 Planar magnetron systems have higher deposition rates due to the directional pattern of the sputtered particles, but in them the cathode erosion region is a narrow band in the form of a closed track, and the material utilization never exceeds 26%. In reality, it is only 10-15%.

 With the size and shape of the erosion zone, as well as with the radiation pattern and transportation of the sprayed particles, the problem of uniformity of the applied films is associated. For small surfaces, it can be solved either by choosing the geometry of the target, or by scanning with a substrate or a magnetic field.

 When applying films to flat surfaces of a large area, for example, tinting sheet glass, manufacturing mirrors, etc., planar MPCs with targets up to two meters long and up to twenty centimeters wide are used (Danilin B.S., Syrchin V.K. Magnetron sputtering systems. M: Radio and communication, 1982, p. 57). To ensure uniformity of the films, several sputtering zones of the target (or several isolated cathodes) are created, relative to which the processed sample is moved onto which the sputtered material is deposited. Naturally, an increase in the area and number of cathodes requires the application of large powers (up to 100 kW) and the problem of uniformity of coatings in the peripheral regions is not completely solved, new difficulties arise associated with the removal of heat from magnetrons, etc.

 There are opportunities to improve the quality of the coating, primarily its uniformity in the peripheral areas of the treated object, by increasing the intensity of the sputtering of the target in these areas by a local increase in the magnetic field strength (Ananyin P.S., Krivobokov V.P., Kuzmin OS, Legostaev V N. Magnetron Sputtering System, Patent Application No. 96113838, July 9, 1996). However, it also does not solve all the problems. One of the main disadvantages of such a system is the significant heterogeneity of the cathode sputtering along the length. As a result, the life of the cathode is determined by the resource of its peripheral sections, which are somewhat more prone to erosion.

 The devices for applying thin-layer coatings based on the use of a magnetron (or a group of magnetrons), which is permanently installed in a vacuum chamber along which the processed products move (Krivobokov V.P., Kuzmin OS, Legostaev V.N. Magnetron Sputtering System RF Patent Application N 95121032, 12/13/95). In this design, the MPC cathode is a series of independent coaxial targets with their own magnetic systems, standing in parallel at a distance of 100-200 mm from each other, and the substrates for the processed sheet materials are located on both sides of the series of targets along the side walls of the chamber. Moreover, to reduce the influence of the discrete structure of the cathode, the substrates have the ability to scan in the longitudinal direction, which significantly increases the spatial uniformity of the thickness of the applied coatings. Such a system, when used for processing flat sheet materials, is characterized by the main disadvantage of coaxial MPCs - large losses and low energies for sprayed particles flying at small angles to the surface to be treated.

 As the above review showed, the quality of coatings, performance for various samples very much depend on the choice of one or another design of MPC. However, the technical characteristics of the devices as a whole are greatly influenced by other systems and components of the coating plant. In its most general form, such an installation contains a vacuum working chamber (treatment zone) in which the MPC, MPC power system, vacuum system, gas inlet system, i.e. creating a working gas medium in the processing zone, a system for supplying samples to the processing zone in the form of lock chambers at the inlet and outlet of the working chamber and mechanisms for moving substrates, loading devices, etc. (Danilin B.S., Syrchin V.K. Magnetron spray systems. M .: Radio and communication, 1982, p. 56). The MPC power system is usually a stabilized regulated DC source with a voltage not exceeding 1000 V (Danilin B.S., Syrchin V.K. Magnetron Spray Systems. M: Radio and Communication, 1982, p. 13). This installation, according to most of the signs, is chosen as a prototype.

 We indicate the main disadvantages of such a system.

 1. In magnetron diodes of any design, especially of high power, there is the possibility of the transition of a working glow discharge into an arc. If this process has begun, it is necessary to quickly reduce the voltage to a level that excludes the existence of a vacuum arc, otherwise the cathode and structural elements may be destroyed, as well as a violation of coating uniformity.

 2. When using multi-cathode or extended MPCs with geometric parameters comparable with the dimensions of the working chamber, the total and partial pressures of the working gas may be different at different points, which changes the deposition conditions and discharge characteristics, and therefore reduces the quality and worsens coating uniformity .

 3. Such a plant has limited functional capabilities, since it is not suitable for applying multilayer coatings, especially those whose spraying process puts forward various requirements for a working gas environment. So, for example, it is known (Androsova V.G., Bronnikova E.G., Vasiliev A.M. et al. Piezoelectric resonators: a reference book. M: Radio and communications, 1992, p. 102) that when applying metal films adhesion to silicon dioxide (glass) noticeably increases if there is a very thin (1-10 nm) layer of chromium between the film and the substrate. In a typical installation, it is not possible to improve the adhesion of a metal film to glass.

 The proposed installation allows you to solve these technical difficulties, is the most universal and when replacing the materials of the cathodes of the MPC allows you to satisfy a variety of consumer requirements.

 The coating installation, as well as the prototype, contains one or more MPC located in a sealed working chamber, MPC power supply system from a stabilized regulated voltage source, a vacuum system and gas inlet to the working chamber, lock chambers at the input and output of the working chamber, and a moving mechanism substrates.

 In contrast to the prototype, the MPC power system is additionally equipped with a unit for comparing the average value of the discharge power, as well as the rates of voltage and current with specified values of the reference signals. The output of the comparison unit is connected to a current chopper in the diode power supply circuit and, through the delay line, to the starting device for launching a stabilized regulated voltage source. This embodiment of the power supply system of the MPC provides automatic power off in the event of a transition of a glow discharge into an arc and its inclusion with optimal characteristics after extinction of the arc. A signal about a change in discharge power is used to stabilize the selected parameter.

 When spraying multilayer coatings using reverse movement of samples, which is typical for installations with a small number of MPC cathodes, it is advisable to replace the output gateway with a blank pocket, the dimensions of which should correspond to the dimensions of the sprayed sample.

 For multi-cathode MPC with an extended working chamber, the gas inlet system is multi-channel, with a spaced apart system of injection holes, the distance between which does not exceed 100 cm.

 If in such an MPC the working chamber is divided by diffusion diaphragms into separate compartments having differential pumping, and the injection holes in each compartment are connected to a separate gas inlet system, then such an installation allows multilayer coatings to be applied simultaneously in various gaseous media.

 In some cases, it is advisable to subject the samples to sputtering before ion sputtering in a gas-discharge plasma at a relatively high pressure of the working gas. To implement the ion cleaning function, electrodes connected to an additional high voltage source are installed in the entrance lock chamber. The high voltage source can be made pulsed bipolar.

 The invention is illustrated in FIG. 1, 2, 3, 4.

 In FIG. 1 schematically shows the proposed device with MPC planar type, having several cathode nodes 1 with its own magnetic systems. MPC placed in an extended sealed working chamber 2. At the inlet and outlet of the working chamber 2 through the gate locks 3 connected input 4 and output 5 of the lock chamber. All chambers 2, 4 and 5 through vacuum valves (leakage) 6 are connected to a vacuum system (not shown). The actuators 7 of the valves 6 are controlled by a vacuum control system 8, which, in turn, is connected to pressure sensors 9 in each of the chambers 4, 2, 5. The processed material 10 is located on the substrates 11, which are moved by a movement mechanism. Only the live rolls 12 of this mechanism are shown.

 The cathode nodes 1 of the magnetron sputtering system are connected to the MPC 13 power system. A block diagram of one embodiment of this system is shown in FIG. 2. The magnetron diode 1 is connected to a stabilized regulated voltage source 14. The source 14, as in the prototype, is based on a rectifier with feedback control. A current sensor 15 and a voltage sensor 16 are included in the power supply circuit of diode 1. Some of the blocks highlighted by a dashed line in the figure are a block that implements the functions of comparing the average value of the discharge power, as well as the rates of voltage and current changes with reference signals. This unit contains a differentiator 17 and a current integrator 18 connected to a current sensor 15, as well as a differentiator 20 and a voltage integrator 19 connected to a voltage sensor 16. The outputs of the differentiators 17 and 20 are connected to the adder 22, and the outputs of the integrators 18 and 19 to the multiplier 21. The outputs of the multiplier 21 and the adder 22 are connected to the inputs of the comparator 26, the other inputs of which are connected to the outputs of the reference signal source 23. The output of the comparator 26 is connected to a current chopper 27 in the power supply circuit of diode 1 and through the delay line 24 to the starting device oska 25 source of stabilized regulated voltage 14.

 A schematic diagram of a system for introducing gas into the working chamber 2 is shown separately in FIG. 3 so as not to complicate FIG. 1.

 To create uniform gas pressure along the entire working chamber 2, gas is injected through several channels through injection holes 28 located along the chamber 2 at distances from each other no more than 100 cm. This value is limited by two circumstances: the characteristic distances between structural elements in the working chamber, where is the transfer of the working gas, and its pressure, more precisely the mean free path of atoms and molecules.

 The desire to use the volume of the working chamber as tightly as possible (this increases the productivity of the installation) leads to difficulties in transferring the working gas throughout the entire volume of the chamber. Moreover, in the regions farthest from the injection holes, its pressure differs from the pressure near the hole by several percent or more.

 This is sufficient for the deposition rate of the coatings during the operation of the magnetron at different points of the working chamber to be different. Therefore, the problem of spatial uniformity of coatings arises.

 The experience of the developer indicates that positive results in choosing the location of injection holes are achieved in practice if the distance between them is not more than 100 cm, i.e. no more than 10L, where L is the mean free path of gas molecules at pressures characteristic of the magnetron.

 The pressure along the chamber 2 is monitored by the pressure sensors of the working gas 9. The signals from the sensors 9 are fed to the pressure control and inlet control circuit 29.

 The injection holes 28 are connected to the leakage pipes 30, which are controlled by a pressure control system and an inlet control 29.

The spouts 30 are connected to a gas cylinder or to several cylinders 31. For multilayer coatings, the cylinders 31 are filled with various gases. In addition, the working chamber 2 is divided by the diaphragms 32 into separate compartments, the number of which coincides with the number of MPC cathodes. The presence of small gaps between the diaphragms 32 and the processed material 10 at operating pressure levels in the chamber 2 of the order of 10 ^-1 Pa will practically not affect the composition of the gas medium in each of the compartments, and each of the compartments will be filled with its own working gas. So in FIG. 3 illustrates, by way of example, a device for coating metal-metal oxide on glass. In the first compartment of chamber 2, in the atmosphere of an inert gas Ar, a thin layer of chromium is deposited, which improves the adhesion of the metal film to the glass. Then, in the second compartment in argon atmosphere and, possibly, with a small addition of hydrogen, metal deposition occurs. In the third compartment in the atmosphere of oxygen is the deposition of metal oxides.

 To conduct ion cleaning of the processed material in the inlet lock chamber 4 is an electrode 33, which is connected to a high voltage source 34 (see Fig. 1).

 The ion etching mode is carried out at a relatively high pressure of the working gas. That is why the electrode 33 is placed in the lock 4, and not in the working 2 chamber. The source of high (1-10 kV) voltage 34 can be either constant or pulsed. Pulse etching is technically more difficult to implement. However, our studies have shown that in the nanosecond range, high voltage bipolar pulses have some advantages when cleaning a very dirty surface.

 It should be noted that although the accompanying figures depict installation only with a planar MPC, all the basic components and principles of constructing such machines remain the same when replacing the MPC with a multi-cathode coaxial system, described in RF patent application N 95121032 of 12.13.95.

 In FIG. 4 illustrates, by way of example, a coating installation with a small working chamber 2, but capable of processing large-sized products 10. Here, the exit lock chamber 5 is replaced by a storage volume in the form of a blind pocket 35. Part of the large-sized product 10 is placed in this pocket, while how the other part is processed in chamber 2.

 Installation works as follows.

 The unit prepared for operation has a constantly evacuated working chamber.

 In the input gateway 4, a sheet of the processed material 10 is placed on the substrate 11. The first (input) valve 3 of this gateway 4 is closed, the valve 6 of the vacuum system opens and the process of evacuation of the input gateway begins. Using the vacuum control system 8 (via pressure sensor 9), the moment is determined when the pressure in the inlet gateway reaches a predetermined level. After that, a command is issued to open the shutter 3, which separates the input gateway 4 and the working chamber 2.

 In the next phase, a command is given to move the substrate into the working chamber. At the same time, a voltage of 1-10 kV is supplied from the high voltage power supply 34 to the electrode 33 of the ion cleaning system. A glow discharge plasma arises near the surface of the material being processed, which cleans the surface before coating it.

 After the sample 10 enters the working chamber 2, the working gas inlet system is turned on, which is supplied to the zone adjacent to the cathode of the magnetron 1. To do this, after setting the desired gas pressure in the working chamber from the control system 29, a command is issued to open one of the leakages 30 (or all together if necessary), after which the gas through the injection holes 28 enters the working chamber 2.

 Then, the magnetrons 1 are supplied with power from system 13. The MPC 13 power system is designed to stabilize the operation of the magnetron diode when the emission of ions from the cathode of magnetron 1 and the diode current are unstable in time due to various contaminants, geometric inhomogeneities, and the presence of an oxide layer on the surface of the cathode as a result of interaction with air, etc.

 The use of this system in the initial period of operation of the magnetron is especially relevant during training (i.e., after depressurization of the working chamber).

 The magnetron operates in the normal and abnormal glow discharge region. When using magnetrons with a power of 10 kW or more, work in the field of an abnormal glow discharge (especially in the “training” mode) is fraught with the danger of the formation of a cold arc, which leads to overvoltages in high-voltage elements of power sources (large reserves of reliability are needed).

 The proposed device implements the idea of predicting the formation of cold arcs in a magnetron by tracking areas of non-self-sustained discharges preceding the appearance of a cold arc. These regions are characterized (upon perfect examination) by large values of dU / dt at I≈const due to the formation of many cathode spots. The area of the cold arc is with large dI / dt values at relatively small dU / dt values.

 Thus, for the normal operation of the MPC, it is necessary to monitor the average value of power, as well as the rate of change of current and voltage, and when they exceed certain values, generate a signal that turns off the power of the MPC. An example of a device that implements these functions is shown in FIG. 2. It should be noted that such schemes can be both more complex and simpler, but in any case, the efficiency of the entire device for coating the surface of solids depends very much on their use.

 The voltage from a stabilized regulated voltage source 14 is supplied to the magnetron diode 1. The source 14, as a rule, is a stabilized feedback rectifier. The current sensor 15 and the voltage sensor 16 are included in the source circuit 14. The signal from the current sensor 15 is supplied through the differentiator 17 (the function of which is to differentiate the signal in time) to the adder 22. Similarly, a signal from the voltage sensor 16 is supplied to the adder through a voltage differentiator 20. T.O. blocks 17 and 20 form a signal about the rate of change of current and voltage in the power circuit of the diode. These signals are spaced in time, therefore, after the adder 22, separate signals for changing the current velocity and voltage are formed. The signals from the integrators of current 18 and voltage 19 after the multiplier 21 characterize the average discharge power. Comparison of it in the comparator 26 with the level of the reference voltage from the source 23 also allows you to generate a control signal to the current chopper 27, while the average power will be the regulatory parameter. The integrated signal is also used to stabilize the power of the diode. In parallel with the current chopper 27, a signal is sent through the delay line 24 to the starter 25, which, after a certain time necessary for relaxation of the plasma processes associated with breakdown phenomena at the cathode (this time is regulated by the delay line 24), includes a stabilized regulated voltage source 14 and displays the magnetron diode 1 on the operating parameters in accordance with the laid "soft" mode.

 Thus, the time during which the magnetron diode is inoperative is minimized, and its operation modes are optimized (it operates in the most favorable region of the current – voltage characteristic).

 We continue the description of the operation of the installation as a whole.

 Then, using the mechanism for moving the substrates, the sample 10 moves through the working chamber 2 towards the outlet gateway 5, in which at this time there should be a vacuum. As the sample moves, the coating is sprayed.

 After the release of the entrance gateway 4, it is cut off from the camera 2 and depressurized.

If a multilayer coating is needed, then the simultaneous operation of several magnetrons is used. Moreover, in each zone where the magnetron is located, its own working gas is supplied and its own electrical parameters are selected. For example, if we need to spray a three-layer coating of Cr-Ti-TiO ₂ , then argon is fed into the zone of the first magnetron diode with a cathode of chromium, and the second and third, where the cathodes are made of titanium, respectively, argon (or a mixture of argon-hydrogen) and a mixture argon is oxygen. Thus, all magnetrons work simultaneously, with each of them applying a layer corresponding to the composition of its cathode and gas medium.

 After the process is completed, the sample enters the output gateway 5, which is then isolated from the working chamber by the shutter 3, depressurized and the processed sample is removed from the installation.

 And at this time, the next sample is placed in the input gateway 4, which is then subjected to evacuation, etc.

 The process is organized somewhat differently if we used a working chamber with a blind pocket 35 (Fig. 3).

 The input gateway 4 with the sample is evacuated. The shutter 3 opens, the ion cleaning system is turned on, and the sample 10 gradually passes along the working magnetrons 1 into the blind pocket 35. Then, after processing, it returns back through the entrance gateway 4. In this case, the blind pocket 35 and the working chamber 2 remain continuously under vacuum , which largely eliminates the need for the operator to repeat the training of cathodes of magnetrons 1 and reduces the duration of the vacuum installation.

 According to the circuit diagram described here, the applicant has constructed installations of the Amethyst, Emerald, Opal, and Yakhont type, which have undergone production tests and are used at many industrial enterprises. They received a positive assessment of specialists, but work on their improvement continues.

Claims (6)

 1. Installation for applying thin-layer coatings containing a magnetron spraying system (MPC), placed in a sealed working chamber, MPC power supply system, a vacuum system and a gas inlet system of the working chamber, airlock chambers at the inlet and outlet of the working chamber and a mechanism for moving the substrates, different the fact that the MPC power system is equipped with a unit for comparing average power values, as well as current and voltage rates with reference signals, the output of the comparator is connected to a current chopper in the power circuit MPC and, through the delay line, to the starting device for starting the MPC power system.  2. Installation according to claim 1, characterized in that the exit lock chamber is made in the form of a blind pocket.  3. Installation according to any one of paragraphs.1 and 2, characterized in that the gas inlet system into the working chamber is multi-channel, and the distance between the injection holes does not exceed 100 cm  4. Installation according to claim 3, characterized in that the spraying chamber is divided by diaphragms into separate compartments, each of which is equipped with a separate gas inlet system.  5. Installation according to any one of claims 1 to 4, characterized in that the electrodes connected to an additional high voltage source are additionally installed in the entrance lock chamber.  6. Installation according to claim 5, characterized in that the high voltage source is made pulsed.

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