METHOD FOR CONTROLLING THE DEPOSITION RATE OF THIN FILMS IN A VACUUM MULTI-NOZZLE PLASMA SYSTEM AND A DEVICE FOR PERFORMING OF THE METHOD

Abstract

A method of controlling deposition rate of a film deposition in a vacuum multi-plasma-jet system utilizing plasma-chemical reactions in an active discharge zone, wherein the system comprises at least one series of plasma nozzles, the working tubes of which are terminated by a hollow cathode whose mouth is located in the vicinity of the top area of the holding system with the stored substrate, wherein the principle of the solution consists in the deposition of the thin film on the substrate after the individual ignition of the discharges in each plasma nozzle and in the control of their parameters by means of external sources of voltage, the temperature of each hollow cathode is monitored by means of contactless temperature measurement and based on the evaluation of the measured temperature values, the settings of the discharge parameters is provided, with help of an control unit, in particular it is regulated the effective current in each of the plasma nozzles so that the deposition rates of all the hollow cathodes of the plasma nozzles are the same. A device to provide a method for controlling the deposition rate is also provided.

Claims

1. A method of controlling a deposition rate of a film deposition in a vacuum multi-nozzle plasma system utilizing plasma-chemical reactions in an active discharge zone, wherein the system comprises: at least one row of plasma nozzles; working tubes of the nozzles terminated by a hollow cathode; wherein an output of the cathode is located at an upper part of a substrate holder with a stored substrate, wherein, after individual ignition of the discharges in each plasma nozzle and during the controlling of their parameters by means of external voltage sources and during the deposition of the film on the substrate, the method comprises the steps of: temperature monitoring of each hollow cathode by means of contactless temperature measurement; evaluation of the measured temperature values; and based on the evaluation, setting parameters of the discharge using a control unit to regulate the effective current in each of the plasma nozzle so that the deposition rates of all hollow cathodes of plasma nozzles are the same.

2. The method according to claim 1, wherein the discharge is a DC discharge, and an average current is regulated.

3. The method according to claim 1, wherein the discharge is a pulse-modulated discharge, and the duty cycle is regulated.

4. The method according to claim 1, wherein the method comprises testing of a deviation of actual temperature from a required temperature by the control unit.

5. The method according to claim 4, the method comprising the step of lowering or raising the actual temperature if the deviation is higher than the allowed tolerance T.

6. The method according to claim 5, wherein the actual temperature of the hollow cathode is below the critical temperature Tk or below the minimum measurable temperature of the means of contactless temperature measurement, wherein the method interrupts the deposition process via the control unit.

7. The method according to claim 6, wherein the interruption is provided by moving a shutter in between the nozzles and the substrate until the steady deposition conditions are retrieved.

8. A product by process according to claim 1.

9. A device for performing of method of controlling the deposition rate of film deposition in a vacuum multi-plasma-jet system utilizing plasma-chemical reactions in an active discharge zone, wherein the system comprises at least one row of plasma nozzles having working tubes terminated by a hollow cathode, wherein an output of the cathode is located at an upper part of a substrate holder with the stored substrate, the device comprising: a means of contactless temperature measurement directed to an end part of the hollow cathode in order to monitor its surface temperature; and wherein the means of contactless temperature measurement is connected to a control unit and further connected to voltage sources of the individual plasma nozzles and the drive mechanism of the holding system.

10. The device according to claim 9, the device further comprising openings in a housing of the vacuum chamber, the openings are located on the same plane as the hollow cathodes of the plasma nozzles; wherein the openings further comprise transparent apertures equipped with the means of contactless temperature measurement outside the vacuum chamber.

11. A device according to claim 10, the vacuum chamber comprising at least two rows or two pairs of plasma nozzles, wherein the plasma nozzles in each row or pairs are equidistantly positioned so that between each two adjacent plasma nozzles, the same distance is provided.

12. The device according to claim 11, wherein the rows of opposing plasma nozzles are mutually displaced in a direction perpendicular to the moving of the substrate by half of the distance (d/2).

13. The device according to claim 12, wherein the plasma nozzles in the at least two rows are positioned in an oblique direction with respect to the position of the substrate such that the intersection of the planes extending through their longitudinal axes lies in the plane of the deposited substrate.

14. The device according to claim 13, wherein the nozzles comprise a cooler, preferably made of copper, through which a coolant flows, preferably water, connected to the voltage source via a protective resistor.

15. The device according to claim 14, wherein the cooler surrounds the hollow cathode and the output part overlaps a lower edge of the cooler, wherein the output part is connected to the operating tube through which a working gas flows.

16. The device according to claim 14, wherein the cooler is surrounded by an insulating cover, preferably ceramic or quartz, preventing ignition of spurious discharges during the deposition.

17. The device according to claim 9, wherein the means of contactless temperature measurement is an infrared contactless pyrometer.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0019] Specific examples of realization of device according to the invention are shown in the enclosed drawings, where

[0020] FIG. 1 is a general scheme of a basic realization of the device,

[0021] FIG. 2 is a simplified plan view of the device in FIG. 1, showing the reciprocal arrangement of two adjacent rows of plasma nozzles,

[0022] FIG. 3 is an operational algorithm of control unit for each particular nozzle,

[0023] FIG. 4 is a graphical representation of the thickness profile of the formed thin films sputtered by the multi-nozzle system from different distances according to the invention,

[0024] FIG. 5 is a graphical representation of the deposition rate as a function of the absorbed power,

[0025] FIG. 6 is a graphical representation of the deposition rate as a function of the hollow cathode temperature,

[0026] FIG. 7 is a simplified plan view of an alternative realization of the device equipped with a single row of plasma nozzles,

[0027] FIG. 8 is a simplified plan view of an alternative realization of the device equipped with two pairs of plasma nozzle rows, and

[0028] FIG. 9 is a general scheme of an alternative realization of the device equipped with two pairs of plasma nozzle rows.

[0029] Drawings illustrating the present invention and demonstrating its operation, and the following examples of specific realizations do not in any way limit the scope of protection specified in the definition but merely illustrate the principle of the solution.

DESCRIPTION OF EMBODIMENTS

[0030] In a basic realization shown in FIG. 1 and FIG. 2, a device allowing the implementation of the method for controlling the deposition rate of thin films in a vacuum multi-jet plasma system according to the invention is formed by a vacuum chamber 1 in which inner space 101 the support assembly 2 for substrate 3 is installed. The support assembly 2 is formed by a system consisting of a cooled roll 21 provided with a not shown driving mechanism, and the guiding rollers 22 where the substrate 3 (for example an elastic foil) moves.

[0031] Vacuum chamber 1 is normally connected to not shown pumping unit (for example vacuum pump) via connecting neck 102 and also not shown disjunctive control valve. A reactive gas inlet 104 is installed to the inner space 101 of the vacuum chamber 1 from upper side and there are also two rows of plasma nozzles 4 installed in unmarked flanges through the jacket of the vacuum chamber 1 so that the hollow cathodes are located close to the upper side of the support assembly 2 where the substrate 3 is mounted. Plasma nozzles 4 in each row are equidistantly disposed so the distance (d) between each adjacent hollow cathode is the same. Plasma nozzles 4 that are in opposite positions in rows are dislocated by the half distance (d/2) to each other in perpendicular direction to the substrate 3 movement as shown FIG. 2 and both of rows are adjusted against each other in an oblique direction in such way that the intersection of the planes extending through their longitudinal axes lies in the plane of deposited substrate 3. Individual plasma jets 4 are formed by a cooler 41, preferably made of copper, through which a coolant flows, for example water, and which is connected to the voltage source 6 via a protective resistor 5. The cooler 41 tightly surrounds the hollow cathode 44 where the output part overlaps the lower edge of the cooler 41 by around 15 to 20 mm and which is connected to the operating tube 42, through which a working gas flows. The cooler 41 itself is externally surrounded by an insulating cover 43, for example ceramic or quartz, preventing ignition of spurious discharges during the deposition.

[0032] At the same plane of hollow cathodes 44 plasma nozzles 4 there are additional apertures 103 in the jacket of chamber 1 equipped with transparent windows 7, which are made from for example borosilicate glass. Behind every window 7 there is infrared pyrometer 8 installed outside of the vacuum chamber 1 and focused on the output of each hollow cathode 44 in order to measure its surface temperature. The entire device is equipped with control unit 9 where all pyrometers 8 are connected as well as power sources 6 for all plasma nozzles 4 and the drive mechanism of cooled roll 21 of support assembly 2.

[0033] During deposition of the thin film on the substrate 3 a discharge is ignited in each hollow cathode plasma jet independently, the parameters of which are controlled by means of an external voltage source 6. The bottom part of the hollow cathode 44 protruding from the copper cooling block 41 is not being effectively cooled and due to the ion bombardment is being heated to high temperatures exceeding 1000 C. even at low discharge currents. The actual surface temperature of the of the individual hollow cathodes 44 is measured by a contactless infrared pyrometer 8. The data are sent to the control unit 9 where they are processed and according to which the discharge current is regulated. The operation of the control unit 9 follows the algorithm depicted in FIG. 3. The control unit 9 regulates the effective current value depending on the regime of the discharge in each plasma jet 4. In the DC regime the mean current value is regulated. In the case of the pulsed regime the duty cycle of the pulses is regulated, which means that the proportion of the active to the passive period is controlled. The control unit 9 tests the deviation of the actual temperature from the required temperature and if it is higher than the allowed tolerance T, either the mean current or the duty cycle is reduced and vice versa. The only exception is when an arc discharge arises. If during the deposition process an arc discharge is ignited between the exiting part of the hollow cathode 44 and any anode inside the vacuum chamber 1, then it is always accompanied by abrupt drop of the temperature of the respective hollow cathode 44 either below the critical temperature Tk or below the minimum measurable temperature of the respective pyrometer 8. In such a case the control unit 9 interrupts the deposition process, e.g. by moving a shutter, which is not depicted, in between the system of plasma jets 4 and the substrate 3, until the steady deposition conditions are retrieved. The primary task of the control unit is to maintain the temperature of all hollow cathodes 44 during the deposition process at equal values, so that the deposition speeds of the individual plasma jets 4 are equal. For this simple regulation mechanism to be able to work, it is necessary, that all the hollow cathodes 44 are made of the same material, have equal geometrical dimensions (i.e. length, inner and outer diameter), have an equal distance from the substrate 3 and that the flow rates of the working gas through the hollow cathodes are equal. From the experiments performed it follows that when these conditions are fulfilled, the deposition speed is unambiguously given by the temperature, which is graphically illustrated in FIG. 6. The dependence of the deposition rate on the power is depicted in FIG. 5. The FIG. 4. illustrates a comparison of thickness profiles of the thin films deposited by the system with multiple hollow cathodes according to this invention at different substrate to hollow cathodes distances. According to FIG. 4. it can be stated that, e.g. for the titanium hollow cathodes 44 with inner diameter of 6 mm at argon flow rate of cca. 200 sccm, working pressure of 15 Pa and at substrate 3 to hollow cathode 4 distance of 5 cm, the obtained film has a Gaussian profile with the variance of a 1.9 cm. In this case to obtain a film with the maximum inhomogeneity of 10% it is sufficient to place the individual plasma jets 4 with a spacing of 4.4 cm from each other, however, this holds only under the assumption, that the deposition rate of all the plasma jets 4 are equal.

[0034] The described construction of the device is not the only possible implementation according to the invention, yet, as it is apparent from FIG. 3, just one row of the plasma jets 4 can be installed into the inner volume 101 or according to FIG. 8 and FIG. 9, the device can be equipped with two pairs of rows of plasma jets 4. The support assembly 2 for the substrate 3 does not need to be necessarily composed of the cooling cylinder 21 and the alignment cylinders 22, yet it can be comprised of a horizontally movable flat table equipped with means to hold the substrate 3, e.g. a desk or a plate, on which the thin film is being deposited.

INDUSTRIAL APPLICABILITY

[0035] A method of controlling the deposition rate of film in a vacuum multi-nozzle plasma system and device for performing of the method constructed according to the invention are suitable to be applied in all industrial fields dealing with high-speed plasma deposition of thin films. Albeit it can be utilized for deposition of pure metal films, the main application lies especially in the reactive sputtering of oxide compounds such as TiO.sub.2, Al.sub.2O.sub.3, Fe.sub.2O.sub.3, ZrO.sub.2, WO.sub.3, ZnO and more others.