Magnetron sputtering method

Abstract

FIELD: magnetron sputtering.SUBSTANCE: balanced magnetron sputtering system comprising an anode, a cathode unit with a cathode target and a magnetic block, and a substrate holder is placed in a vacuum chamber. A potential difference is created between the anode and the target cathode using a high-voltage power source. The working gas is supplied to the discharge region between the target cathode and the anode through the working gas supply system. Under the influence of potential difference, the working gas is ionized and a glow discharge is maintained. A source of ultrasonic vibrations with a frequency of 0.35-0.65 MHz is placed on the holder between the target-cathode and the substrate. The source of ultrasonic vibrations is located at a distance of (0.65-0.80)L from the target-cathode, where L is the distance between the target and the substrate, as a result of which the plasma discharge cloud scans along the surface of the substrate.EFFECT: increase in the uniformity of the coating thickness and the oscillation of the plasma cloud over the surface of the substrate during the target sputtering process.1 cl, 3 dwg, 1 tbl, 1 ex

Description

[0001] The invention relates to the field of applying coatings by magnetron sputtering.

[0002] One of the most important tasks of magnetron sputtering is to improve the uniformity of the coating, especially on large-area substrates.

[0003] The uniformity of thin film deposition during magnetron sputtering is significantly affected by equipment parameters. These parameters include the size and shape of the target, the distance between the target and the substrate, and the rotation (oscillation) of the target. Each of these factors plays a unique role in determining the consistency and quality of the deposited coating film.

[0004] The size and shape of the target material are fundamental elements in the sputtering process. A larger target can accommodate a wider range of substrate sizes, but it also requires more precise control to ensure uniform deposition. The target's shape, whether flat or cylindrical, can affect the distribution of sputtered atoms. For example, a flat target typically produces a more uniform distribution than a cylindrical one, which may require additional mechanisms to achieve the same uniformity.

[0005] The distance between the target and substrate is another crucial parameter. This distance directly affects the path length of sputtered atoms from the target to the substrate. A shorter distance can increase the deposition rate, but can also lead to uneven distribution due to shadowing. Conversely, a longer distance can improve uniformity but reduce the deposition rate. Therefore, the optimal distance must be carefully calibrated to balance these competing factors.

[0006] To further improve uniformity, the target can be rotated or oscillated during the sputtering process. Rotation ensures uniform use of the entire target surface, preventing localized depletion and extending the target's life. Oscillation, on the other hand, helps more evenly distribute the sputtered atoms across the substrate, especially when the target is not perfectly flat. These mechanical movements are necessary to achieve uniform film thickness across the entire substrate, especially for large or irregularly shaped substrates.

[0007] Thus, when using a flat substrate holder, the unevenness of the coating film thickness reaches 20% [Minaychev, V.E. Application of films in a vacuum / V.E. Minaichev. - Moscow: Higher School, 1989].

[0008] In practice, more complex methods for producing coatings with uniform thickness are used, one of which is giving the substrate holder a spherical shape. The film thickness unevenness is thereby reduced to ± 10%. If this is insufficient, a double-rotation system, the so-called planetary carousel, is used. Planetary carousels are quite expensive; however, when used, the film thickness unevenness is ± (3-4%) [Moryakov, O.S. Design and Adjustment of Semiconductor Production Equipment / O.S. Moryakov. - Moscow: Vysshaya shkola, 1988]. The above-mentioned coating application system using magnetron sputtering is implemented in a semi-continuous vacuum unit, model 01NI-7-006. The unit is a multi-position carousel-type vacuum unit designed for depositing two-layer films using magnetron sputtering.

[0009] In the setup under consideration, despite the substrate holders rotating planetarily, the thickness variation across the substrate reaches 15% according to the specifications, but in practice, it can reach ±20% due to the fact that vapor distribution from the target's annular erosion zone is not taken into account. Furthermore, oblique deposition results in high film roughness, which negatively impacts the electrical and, especially, magnetic properties of the films. This raises the technical problem of uneven thickness of the resulting thin films.

[0010] A device is known [Device for moving a substrate holder: useful. Model RU 97112 294 / N.V. Vasilenko, E.P. Ivashov, E.V. Prusakov, S.V. Stepanchikov. - Published 27.12.1998], capable of eliminating the main above-mentioned disadvantages, for applying thin films in a vacuum with a special substrate holder, described in the patent.

[0011] This device is designed to reduce film thickness unevenness. This is achieved by mounting the substrate holder on an elastic bellows element, rigidly connected to a fixed base and capable of rotation relative to horizontal coordinate axes. Two drive rods are pivotally attached vertically between the substrate holder and the fixed base. The device is also equipped with a second substrate holder, mounted on the first with axial rotation capability. This second substrate holder is connected to a rotational input via an additional elastic bellows element, which is hermetically sealed between the rotational input and the second substrate holder.

[0012] The use of the proposed device for moving the substrate holder makes it possible to reduce the unevenness of the film thickness by varying the position of the substrate holder relative to the source of the sprayed material [Device for moving the substrate holder: useful. Model RU 97112294 / N.V. Vasilenko, E.P. Ivashov, E.V. Prusakov, S.V. Stepanchikov. - Published 27.12.1998]. This device can be used for any vapor source, since it has three degrees of freedom, but is quite complex both in manufacture and in operation. In addition, the reliability of the bellows against bending is limited by their service life [Device for applying coatings to substrates in vacuum: useful. model 2 634 833 / V.K. Gusev, I.E. Kozhin, A.N. Afonina, A.A. Batrakov. - Published on 03.11.2017].

[0013] A magnetron sputtering system is known [Patent for Invention RU 2748443C1, IPC C23C14 / 35, published 05 / 25 / 2021, Bulletin No. 15], consisting of a vacuum chamber, magnetron sputtering sources placed circumferentially in the vacuum chamber, and a carousel in the form of a drum with substrates, consisting of individual vertically standing plates forming substrate holders, characterized in that each of the plates forming the substrate holder is made in the form of two plates fastened in the middle, while the edges of each of the plates are bent towards the magnetron source and form an angle α between themselves equal to 160-170°. This magnetron system is complex to manufacture and operate. Moreover, the unevenness of the coating film thickness reaches 15%.

[0014] A known method of magnetron sputtering [Patent for Invention RU 2135634 C1, IPC C23C14 / 15, H01J25 / 50, Published August 27, 1999] involves the electromagnetic creation of a moving magnetic field above the target surface. The rotating magnetic field is created above the target surface by applying periodic alternating current voltages to electromagnetic coils, phase-shifted relative to each other according to the spatial arrangement of the coils. This method of magnetron sputtering improves the uniformity of target sputtering, but has virtually no effect on the uniformity of the coating film deposited on the substrate.

[0015] A magnetron sputtering system is also known [Russian Federation Patent for Utility Model RU 134932 U1 IPC C23C 14 / 35, published 27.11.2013, Bulletin No. 33]. A balanced-type magnetron sputtering system comprising an anode and a cathode unit located in a vacuum chamber, including a target and a magnetic block. The magnetron system is equipped with an electrode made in the form of a grid made of refractory metal material, the working potential of which is equal to the potential of the cathode and located relative to the anode on the side opposite to the cathode unit, while the distance between the anode and the grid is greater than the distance at which electrical breakdown is possible between the grid and the anode. This magnetron system was chosen as a prototype.

[0016] The objective of the utility model is to increase the uniformity of the coating thickness when sputtering targets based on systems of immiscible components, for example, Cu-Fe.

[0017] The technical result of the invention is aimed at increasing the uniformity of the coating thickness during target sputtering and ensuring the oscillation of the plasma cloud over the surface of the substrate during the target sputtering process.

[0018] The magnetron sputtering method is based on a balanced magnetron sputtering system comprising an anode and cathode assembly located in a vacuum chamber, including a target and magnetic block, as well as a substrate holder. Unlike the prototype, an ultrasonic vibration source with a frequency of 0.35-0.65 MHz is placed between the target and substrate at a distance of (0.65-0.80)L from the target, where L is the distance between the target and substrate.

[0019] The essence of the technical solution, protected as an invention, consists in introducing a source of ultrasonic vibrations, placing between the target and the substrate at a distance of (0.65-0.80)L from the target a source of ultrasonic vibrations with a frequency of 0.35-0.65 MHz, where L is the distance between the target and the substrate, which in turn leads to scanning of the plasma cloud over the surface of the sprayed substrate and leveling the thickness of the sprayed coating over the surface of the substrate from the axis of the magnetron system to its periphery.

[0020] The invention is explained by drawings.

[0021] - Fig. 1 shows the general view of the MRS: 1 - MRS body, 2 - magnetic block base, 3 - peripheral permanent magnets, 4 - central permanent magnet, 5 - cooling water supply nipple, 6 - cooling water drain nipple, 7 - seal, 8 - seal, 9 - sealing ring, 10 - target-cathode, 11 - electric field lines, 12 - magnetic field lines, 13 - sputtering zone, 14 - accelerated ions (sputtered particles), 15 - anode, 16 - substrate, 17 - coating (film), 18 - discharge plasma, 19 - ultrasonic source holder, 20 - ultrasound source, 21 - terminal for supplying voltage to the target; L is the distance between the target and the substrate being sputtered;

[0022] - Fig. 2 shows the distribution of the thickness of the sprayed coating of the Cu-Fe system when using a magnetron system for sputtering according to the prototype and according to the claimed invention with the same parameters of the sputtering mode;

[0023] - Fig. 3 - shows the external appearance of the surface of a titanium substrate made of VT6 alloy after sputtering a Cu-Fe system target using the claimed invention.

[0024] The magnetic sputtering system consists of a magnetic sputtering unit (MSU) housing (1) with a central cavity housing the magnetic block base (2). Peripheral (3) and central (4) permanent magnets are mounted on the magnetic block base (2). Cooling water is supplied and drained into the magnetic block through nozzles (5) and (6). The magnetron sputtering system is secured to the working chamber housing via seals (7) and (8), as well as an O-ring (9).

[0025] The cavity of the magnetic block is hermetically sealed by a cathode target (10). Electric (11) and magnetic (12) fields are formed above the cathode target (10), respectively. When the magnetic (12) and electric (11) fields interact, a sputtering zone (13) is formed on the cathode target (10). Accelerated ions (14) of the sputtered target, under the influence of the potential difference between the cathode target (10) and the anode 15, reach the substrate (16) and condense on it in the form of a coating film (17).

[0026] The magnetron sputtering system operates as follows: a potential difference is created between the anode (15) and the target-cathode (10) using a high-voltage power source. The working gas is supplied directly into the discharge region between the target-cathode (10) and the anode (15) through the working gas inlet system (not shown in the figure). Under the influence of the potential difference between the anode (15) and the target-cathode (10), the working gas is ionized, and a glow discharge is initiated and maintained. The magnetic field (12), created by the central permanent magnet (4), localizes most of the discharge plasma (18) in the immediate vicinity of the target-cathode (10).

[0027] An ultrasonic vibration source (20) with a frequency of 0.35-0.65 MHz is mounted on the holder (19). The ultrasonic vibration source (20) is positioned between the cathode target (10) and the substrate (16) at a distance of (0.65-0.80)L, where L is the distance between the target and the substrate.

[0028] The magnetic fields (12) of the peripheral permanent magnets (3) installed in the housing (1) of the magnetic block reach the surface of the substrate and ensure the localization of the plasma (18) in this area. The sputtered particles (14), having a certain path length, reach the substrate (16) and form a coating (17) on its surface. The electrons, having begun to move along the open lines of force of the magnetic field (12), directed towards the substrate, are slowed down by the grid potential, which is negative relative to the anode (15), and are attracted by the anode (15).

[0029] To improve the uniformity of the coating (17) on the surface of the substrate (16), the ultrasound source (20) initiates oscillations of the discharge plasma (18) along the surface of the substrate (16). To obtain a coating (17) of uniform thickness, it is necessary to place the ultrasound source (20) at a distance of (0.65-0.80)L, where L is the distance between the target and the substrate. In the case when the ultrasound source (2) is located at a distance of less than 0.65L from the target (10), the ultrasound mainly acts on the plasma cloud above the surface of the cathode target (10), contributing to its more uniform erosion. When the ultrasound source (20) is placed at a distance of more than 0.80L from the target (10), the ultrasonic vibrations affect the deposited substrate (16) and the plasma cloud (18) simultaneously. As a result, such an effect of increasing the uniformity of the coating thickness (17) over the surface of the substrate (16) is not observed.

[0030] In the case where the ultrasound source (20) is located at a distance of (0.65-0.80)L from the target-cathode (10), the ultrasound influence occurs only on the plasma cloud (18) near the surface of the substrate (17), leading to scanning of the plasma cloud along the surface of the substrate (16) with the formation of a coating (17) of uniform thickness.

[0031] The unevenness of the coating (17) thickness increases when using ultrasonic frequencies below 0.35 MHz. In this case, the movement of the plasma cloud (18) is insufficient to equalize the thickness of the coating (17) over the substrate surface. At an ultrasonic frequency above 0.65 MHz, the plasma cloud (18) scans so quickly over the surface of the substrate (16) that a decrease in the density of the plasma cloud (18) occurs, and the cloud (18) itself becomes stationary relative to the surface of the substrate (16). This combined effect leads to a decrease in the uniformity of the coating (17) thickness on the surface of the substrate (16). Therefore, the optimal ultrasonic frequency range is 0.35-0.65 MHz.

[0032] As an example of the implementation of the claimed magnetron sputtering method, a variant of applying a magnetron coating based on a 50% Cu-50% Fe target onto the surface of a titanium substrate made of VT6 alloy should be given. The target diameter was 48 mm and the thickness was 5 mm. The coating was deposited on a disk-shaped substrate with a diameter of 70 mm and a thickness of 2 mm. In this case, the magnetron discharge current was equal to 260-280 mA, and the energy of the working gas ions (Ar+) was equal to 380-400 eV. The film growth rate on a polished substrate made of VT6 titanium alloy was 90 nm / min. The distance between the target-cathode (10) and the substrate (16) was 70 mm. At a distance of 46 mm from the target-cathode (10), a source (20) of ultrasonic vibrations with a frequency of 0.35-0.65 MHz was installed.

[0033] Table 1

[0034] The influence of the installation distance of the ultrasonic source and its frequency on the uniformity of the coating thickness on the substrate of titanium alloy VT6

[0035] Frequency of ultrasonic vibrations, MHz Distance from the target to the source of ultrasonic vibrations, mm Distance from the center of the substrate, mm 0 5 10 15 20 25 30 Coating thickness, nm 0,5 35 460 380 400 440 410 390 360 0,5 46 460 455 448 414 409 400 395 0,5 49 450 418 448 414 443 410 380 0,5 56 428 420 411 403 395 388 380 0,5 63 453 380 403 427 403 427 380 0,30 49 460 380 418 414 372 360 410 0,35 49 450 418 448 414 443 410 380 0,5 49 403 398 395 391 387 380 383 0,65 49 444 409 426 427 380 410 395 0,75 49 380 437 371 425 363 418 360

[0036] Thus, based on the data in Table 1, it can be noted that the claimed method of magnetron sputtering provides a more uniform coating thickness when the ultrasound source (20) is located at a distance of (0.65-0.80)L from the target cathode, and the frequencies of the ultrasonic vibrations are set in the range of 0.35-0.65 MHz.

[0037] Measurements of the coating thickness (17) on the surface of the disk substrate (16) made of VT6 titanium alloy (Fig. 2, Table 1) showed that when using the MRS adopted as a prototype, the coating thickness in the central part of the substrate (16) is greater than in its peripheral areas. The use of the claimed magnetron sputtering method made it possible to level the coating thickness (17) at a level of 450-465 nm along the entire surface of the substrate (16).

[0038] The appearance of the coating when using a target of 50%Cu-50%Fe composition, obtained according to the claimed magnetron sputtering method, is shown in Fig. 3.

[0039] Chemical analysis of the resulting coating revealed that after 5 minutes of spraying, it contained 38% iron and 62% copper. Spraying under similar parameters using the prototype resulted in an iron concentration of 9% by weight. However, coating thickness unevenness was 22-24%, compared to 2-3% using the claimed method.

Claims

A method of magnetron sputtering, which includes placing in a vacuum chamber a balanced-type magnetron sputtering system containing an anode, a cathode unit with a cathode target and a magnetic block and a substrate holder, wherein a potential difference is created between the anode and the cathode target using a high-voltage power source, a working gas is supplied through a working gas inlet system into the discharge region between the cathode target and the anode, the working gas is ionized under the action of the potential difference and a glow discharge is maintained, characterized in that a source of ultrasonic vibrations with a frequency of 0.35-0.65 MHz is placed on the holder between the cathode target and the substrate, wherein the source of ultrasonic vibrations is located at a distance of (0.65-0.80)L from the cathode target, where L is the distance between the target and the substrate, as a result of which the plasma cloud of the discharge scans along the surface of the substrate, ensuring uniformity of the coating thickness.

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