RU2451769C2 - Method, and apparatus for multi-layer film production and multi-layer structure produced by their means - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to ion-plasma sputtering of multi-layer films. According to the film production method, ion-plasma sputtering of substrate by target material is done in vacuum with application of magnetic field. Preliminarily dependence of material properties of sputtered layer on pressure rating of sputtering gas is determined. Sputtering is done at pressure rating as well as rating and/or orientation of applied magnetic field required for obtaining specified properties of sputtered layer material. Wherein at least two layers are sputtered from one target at different sputtering gas pressures. Apparatus for film production comprises a shielded cathode target and a substrate holder located in horizontal magnetic field with orientation field configured to be changed. The shield is made with adjustable height and at least two openings for sputtering material. Each opening has an insert with adjustable height, and additional vertical wrapped partition.

EFFECT: multi-layer films with different properties of the layers may be produced and manufacturing capability increases.

6 cl, 5 dwg

Description

A method and apparatus for producing multilayer films relates to the field of ion-plasma spraying of thin films in vacuum, which can be used to create multilayer films, for example, with a magnetoresistive effect for use in magnetic recording, creation of magnetic sensors for counting marks, determining the position of an object, speed object movements, etc.

For these devices, multilayer film structures containing magnetic layers are most often used. The core of such a multilayer structure is some simple cell, consisting of a set of layers, for example, three-layer: two magnetic layers separated by a non-magnetic conductive layer. In the presence of a negative exchange coupling between the magnetic layers, a giant magnetoresistance (HMS) effect is realized in such a structure - the electrical resistance of the structure depends on the relative position of the magnetizations of the magnetic layers: the resistance is maximum when the magnetizations of the layers are antiparallel and minimum when they are parallel. An example of such multilayer structures are iron layers separated by a layer of chromium, or layers of cobalt separated by a layer of copper. In this case, in order to increase the useful signal, in practice, a set of several identical simplest cells is used - the superlattices Fe / Cr and Co / Cu. A factor limiting the practical use of this type of material is the relatively large magnitude of the external magnetic fields necessary to change the mutual arrangement of the magnetizations of the layers, calculated in hundreds of Oersteds. Much more common are devices that use the effect, which is a special case of HMS - the spin-valve effect. The simplest spin valve consists of two magnetic layers having different coercive forces, separated by a non-magnetic conducting layer. A sample of such a structure is presented, for example, in the technical solution set forth in the Grünberg patent (US patent No. 4949039, G01R 33/06, dated 14.06.1989, prototype). In practice, as a rule, magnetic stiffness and the ability to keep the direction of magnetization unchanged under the action of a certain interval of magnetic fields of one of the layers is ensured by exchange coupling with an additional magnetic layer, for example, a layer of antiferromagnetic alloy iron-manganese. In this case, the magnetization of the free magnetic layer can change its orientation under the influence of an external magnetic field (for example, the use of such a structure in patent EP No. 2023354, H01F 10/00, H01F 10/32, from 05.20.2008). Thus, a change in the mutual orientation of the magnetizations of the layers and, consequently, a change in the electrical resistance of the multilayer structure is achieved. The technology for producing such a multilayer structure in a single cycle requires at least the deposition of two different magnetic materials, and the device for producing should have several targets or sources of the sprayed material. That is, it requires rather sophisticated equipment, and this complicates the process. An even greater number of layers with different physical properties is required to create magnetoresistive read heads from hard drives.

Known technical solutions (US No. 5958155, G02B 1/10, C23C 14/06, C23C 14/34, 07/20/1995, US No. 6811662, C23C 14/34, C23C 14/35, C25B 11/00, dated 22.08. 2003), in which to create different layers the material is sequentially sprayed from different targets in one technological cycle. In this case, a magnetron-type device is used for sputtering with supplying both direct voltage and radio frequency voltage (13.56 MHz) to the targets. A definite drawback of these solutions is the need to use for spraying each layer, including magnetic, a separate target and a separate magnetron.

At the same time, to obtain the necessary layers with different magnetic properties, a variation of the technological parameters of the spraying process can be used.

Thus, there is a known method of producing multilayer magnetic films by thermal evaporation, in which the structure of Ni ₈₀ Fe ₂₀ / SiO ₂ / Ni ₈₀ Fe _{20 is} obtained with different layer coercivity by varying the deposition rate of layers of Ni ₈₀ Fe ₂₀ (patent RU No. 2315820, C23C 14 / 06, from 2004.08.30). In this case, upon receipt and annealing in the plane of the substrate, a horizontal magnetic field is superimposed. The thickness of the silicon oxide interlayer is selected so that there is no exchange interaction between the layers and the layers are magnetized separately. The different coercivity of the layers in this case is most likely related to the different temperature of the growing films deposited at different deposition rates, which is achieved by changing the power of the electron beam. Unless a different evaporation rate of the components of the alloy heated to a high temperature is involved here, leading to a change in the composition of permalloy layers. It should be noted that the molecular beam evaporation method, which is used to obtain films with giant magnetoresistance in ultrahigh vacuum, is more widely known in this area.

Closer to the claimed method for producing films, it is proposed to perform portion deposition of the layer, namely, to interrupt the deposition process for some time to prevent crystallization of the film (patent RU No. 21224243, G11B 5/84, from 1996.06.20). In this case, the temperature of the substrate does not rise above a certain level, and this ensures stabilization of the amorphous state of the film. Thereby, soft magnetic (with interruption of the process) and magnetically hard layers (without interruption) are obtained in a single cycle. In this way, films of transition metals Co, Fe, and NiFe were obtained. In this case, additional annealing has a different effect on cobalt and permalloy films: the coercivity of the latter changes several times during annealing, while the former change it by only a few oersteds. Unlike the first method, the intermediate layer was not sprayed here. This method can also be associated with the influence of the crystal structure of the layers on their magnetic properties: to obtain a soft magnetic layer, their deposition conditions are selected.

The device itself used in this case is typical of the method of magnetron ion-plasma sputtering: the target cathode and the substrate holder, which is closed by a shutter (screen). Changing the properties of the film in the device is ensured by periodic overlapping of the substrate for several seconds from the deposited material by a curtain (screen), and thereby make it possible to lower (stabilize) its temperature. Since only one target is used, the device has certain limitations in terms of obtaining multilayer structures.

A more detailed description of the atomization device (magnetron) is given, for example, in the method for producing epitaxial films (patent RU No. 2333300, C30B 23/02, C30B 29/10, dated 2006.04.26). It contains a cooled target cathode with a magnetic system, to which a high-frequency voltage of 13.56 MHz is applied at an argon pressure of 0.3 · 10 ^-3 - 0.8 · 10 ^-3 mm Hg. The screen here is grounded and located under the edge of the cathode. The device is intended for narrow application and does not allow to obtain multilayer films. And when spraying magnetic materials, it requires rather thin targets. Another drawback of these magnetron sputtering systems is the inefficient consumption of the target material due to the large inhomogeneity of the magnetic field on the target.

At the same time, an ion-plasma method for producing multilayer films was previously proposed, according to which the composition and, consequently, the magnetic properties of the subsequent layer are changed by changing the orientation of the magnetic field applied in the substrate region. The orientation of the field was changed by its rotation.

It is assumed that in this method the parameters of the sputtering of the target do not change, and the influence of the field is realized through the influence of the orientation of the field on the sputtered material of the target.

A device is known which consists of a radio frequency target cathode (standard frequency 13.56 MHz) with a grounded shield, a substrate holder above the target (B. S. Danilin, V. Yu. Kireyev. The use of low-temperature plasma for etching and cleaning materials. M. , Energoatomizdat, 1987, p. 164).

Another device is known in which a horizontal magnetic field of coils oriented in the plane of the substrate is superimposed on the discharge zone (Patent RU No. 2046840). There are no other magnetic fields in the target region. The magnitude of the field in the region of the substrate and the target changes by varying the current in the coils. The rotation of the coils, in principle, is possible here. The grounded screen, unlike the previous device, covers the edges of the target (on the side and overhangs from above). An auxiliary discharge was used to increase the working pressure. However, the use of high frequency voltage is provided. Therefore, the device can be taken as the closest solution. The ability to obtain layers with different magnetic properties using a single target by this device is not shown. The technological capabilities of this technique are not disclosed here. In addition, it would be useful to supplement the device with the possibility of changing the composition of the films and, accordingly, the magnetic properties due to additional effects or changes in the spraying parameters, both in the presence of the field and without it. Moreover, it is important in this way to improve the atomization system with a single target cathode, so that it becomes possible to spray at least the simplest spin-valve structure, for example, in the form of two magnetic layers with different coercive forces separated by a nonmagnetic layer.

Therefore, it is necessary to highlight such spraying conditions in order to significantly expand the capabilities of the previously used method for solving the specific problem of creating a layered material, for example, for magnetically sensitive elements of sensors, and in addition, it is necessary to improve the previously used device for implementing the proposed method.

The technical result of the proposed solution is the ability to obtain structures with various parameters on the basis of a single magnetic material, i.e. to expand the technological capabilities of the method when using the improved ion-plasma spraying device to carry out this task.

The technical result is achieved in that in the method for producing multilayer films, which consists in ion-plasma sputtering of the target material on a substrate in vacuum, one of the layers with different properties from the previous one is obtained by changing the pressure of the spraying gas.

In addition, when an external magnetic field is applied in the deposition plane with the possibility of changing its orientation upon receipt of the next layer and / or its size, the layers may differ in the conditions for obtaining possible combinations of the indicated field parameters and working gas pressure.

The technical result is achieved by the fact that the following improvements are additionally introduced into the device for ion-plasma production of films containing a controlled spraying gas inlet system, substrate holder: a) the target cathode screen is height-adjustable with the sprayed surface being covered by at least two screen parts holes above the sprayed materials located on the surface of the target cathode, b) each hole has a height-adjustable insert, with vertical vertically Verstov separated insulated wall (for the case of the height of the inserts, for the avoidance of insufficient mixing sputtered materials on the substrate) so that no overlap of spray material on a substrate, the center of which is movable in rotation from the center of one hole to another sputtering target. In addition, the device may have inserts in the openings of the screen, the height of which is sufficient to prevent overlapping of the sprayed material on a substrate placed on a substrate holder located in a horizontal magnetic field created by a magnetic system above it, having the ability to change the orientation or / and field magnitude relative to the shielded cathode targets and substrates.

Another result is to obtain a multilayer structure (at least three-layer using only two sputtered materials located on the target cathode) with different properties of the layers (for example, magnetic: coercive force, anisotropy field, etc.), which are obtained using the method, namely, a subsequent layer of the same material is obtained under altered conditions by the pressure of the spray gas or under conditions different from the conditions for obtaining the previous magnetic layer or any desired layer, for example er for the pressure of the working gas, and an advanced device that allows at least two different materials to be placed on and on the target cathode. As controlled physical parameters, the magnetic characteristics of the multilayer structure are described here, but this is rather determined by the task and does not limit the use of other properties of the multilayer structures.

In general, the properties of magnetic materials can be due to several factors, including structure and composition. The latter, in turn, can be largely determined by the technology of production. For example, it is known that the coercive force (H _c ) is largely determined by the parameters of the film microstructure, which, in turn, is determined by the technological parameters of production: working gas pressure, voltage on the target, the presence of a magnetic field, etc. The film composition, if it is sprayed using a multicomponent alloy target, is affected by the degree of reproducibility of the target composition by the film, due primarily to the sputtering coefficients of the components of the alloy target and the reevaporation of these components from the growing film. For example, one of the works states that the main constituents of permalloy iron and nickel have “a significant difference in the sputtering coefficients of the components (ZhTF, 2004, v. 74, issue 1, pp. 120-122). In general, there is a significant amount of literature data which indicate the combined effect of sputtering parameters on the magnetic properties of the films.

In particular, as shown (III All-Russia Conference on Nanomaterials “NANO-2009”, 20-23.04.09, pp. 230-233), the magnetic properties of the films are also affected by a change in the working gas pressure during ion-plasma spraying, which can be used to obtain a multilayer structure, in particular including magnetic layers of the same material, but with different magnetic properties.

Possible options for the deposition process with a change in pressure are given as examples of the preparation of films of transition metals and their alloys - cobalt and permalloy. The experiments on the deposition of multilayer magnetic films were carried out using an ion-plasma spraying device, schematically shown in figure 1.

Here, in the housing 1, the main components of the spraying installation are shown — the substrate holder 2 and below it the water-cooled target cathode 3. The latter is installed in an ungrounded screen 4, the upper part of which is located under the substrate holder 2. A working gas is supplied directly to the region bounded by this screen 4 and the substrate holder used for sputtering targets 10 and 11 located on the surface of the target cathode 3. The figure shows only two simultaneously sputtered targets (usually from different materials) lying on the surface of the cat and the target, but their number can be large. The specified cathode target 3 has a grounded screen 5, while, in contrast to the prototype, its parts 6 (side) and 7 (top) are mounted with the possibility of moving vertically.

Two types of inserts were installed in a similar way: 8 (short on the right in the figure) and 9 (conical on the left), used individually (or in another accessible way) in quantity according to the number of targets of the sprayed material. The height of the cone inserts is selected so as to exclude the simultaneous spraying of sprayed materials on a substrate located above one of the materials used as a target. When using only short inserts 8 with the same purpose of eliminating the deposition of material from different targets onto the substrate 12 while simultaneously spraying materials located on the surface of the target cathode over two (or more) sputtered targets, an additional vertical baffle 13 is used. sprayed material of a short insert, and over other materials of a longer insert. In this case, the substrate moves between the centers of the sprayed materials. The horizontal magnetic field, like that of the prototype, is created by the magnetic system 14 and is used to lower the working pressure and plasma concentration in the region bounded by the non-grounded shield 4. In principle, a high-frequency or other independent discharge does not require this condition to be fulfilled: spraying is realized without fields. In this case, it also served to set the direction of the induced magnetic anisotropy in the plane of the sample. The illustration depicts the use of one magnetic clutch 15, but a double magnetic clutch can also be used. One (for example, internal) rotates the substrate holder, and the second (external) moves the magnet vertically and rotates it.

Measurement of magnetic parameters such as H _c (coercive force along the easy direction of magnetization) and H _k (anisotropy field) was carried out on a Kerr loopscope using an external magnetic field H ₀ from 0-150 Oersted. A vibration magnetometer was also used to study the bulk properties of the films and other available research equipment: an X-ray diffractometer and an atomic force microscope to determine the structure and composition.

The application of the above device when implementing the proposed method is carried out, for example, in the following sequence:

a) First set the spraying speed and determine the effect of pressure changes on the magnetic properties, composition, etc. single-layer films of the same thickness. So, for example, for permalloy and cobalt, the dependence of H _c on pressure is shown in Fig.2. Large values in this case relate to cobalt H _c , which, being a more highly anisotropic material, has a large coercive force. The composition of permalloy from the pressure of the atomizing gas is also given there. As can be seen, with decreasing pressure, the iron content decreases, which leads to an increase in the negative magnetostriction constant of the material (R.C. O'Handley. Modern Magnetic Materials: Principles and Application. New York: Wiley, 2000, p.570). An increase in magnetostriction together with the stresses existing in the films can lead to the appearance of a perpendicular component of magnetic anisotropy, which leads to a change in the structure of domain walls and, consequently, to an increase in Hc with an increase in the working gas pressure P _ar . An additional reason for the increase in coercive force can be a change in the surface roughness with an increase in the indicated pressure, as evidenced by the dependence of the root mean square roughness R _rms on pressure, shown in Fig. 3. An increase in Ar pressure also leads to a decrease in the deposition rate V _{dep of the} films, which is caused by an increase in the scattering of atoms of the sputtered material knocked out of the target by argon atoms. Such collisions broaden the distribution of angles at which the deposited atoms reach the substrate. This in turn leads to an increase in the self-shadowing effect during film growth, which contributes to the formation of intergranular voids and the formation of a columnar microstructure, which also initiates the appearance of a perpendicular component of magnetic anisotropy. In addition, the low value of V _dep contributes to an increase in the number of Ar atoms captured by the deposited film. Thus, the high argon pressure during the deposition of films promotes an increase in the imperfection of the structure of samples, thereby increasing the Hc of the films.

b) Then, having the above dependence, it is possible to carry out the next step - to obtain, for example, a three-layer structure of two magnetic layers and one non-magnetic. For this, at the selected deposition parameters (voltage on the target, working gas pressure, deposition time), the first magnetic layer is deposited. Then a non-magnetic layer of the selected thickness is deposited. In the above device, this is accomplished by transferring the substrate from the first position to the second, where the non-magnetic target is located. At the same time, at the end of the deposition, for some predetermined time, the pressure of the working gas is changed to the value at which it is supposed to sputter the second magnetic layer. As a rule, for such a change and stabilization of argon pressure in the working chamber, it takes 10-15 seconds. In this case, it is necessary to take into account the change in the deposition rate of a non-magnetic material with a change in argon pressure so that the final thickness of the non-magnetic layer corresponds to the required value. After this procedure, the substrate is again placed in a position above the magnetic target, and the second magnetic layer is sprayed.

Another variant of the pressure change process is possible, in which the sputtering of the intermediate (non-magnetic) layer is carried out at constant pressure. Then the substrate is closed by a screen, and argon pressure is changed and stabilized. After obtaining a predetermined pressure, the screen is removed, and at a pressure different from the initial one, a second magnetic layer is deposited. Since in the process of forming a three-layer film structure, the deposition parameters are set in accordance with the previously obtained dependence of the properties of the films on argon pressure, the properties of the second magnetic layer will differ from the first.

An example confirming the presence in the obtained three-layer structure of permalloy layers characterized by different (different from each other) magnetic properties is shown in Fig. 4. Here are the hysteresis loops of a three-layer film, the magnetic layers of which were obtained at different argon pressures, and the thickness of the non-magnetic layer was chosen so as to eliminate the exchange interaction between the permalloy layers — magneto-optical loops: (a) from the substrate side, b) from the deposition side; c) is the volume hysteresis loop measured on the vibromagnetometer. As is most clearly seen from the magnetometric hysteresis loop, the magnetic layers have different coercive forces and are magnetically remagnetized separately. In a similar manner, three-layer structures with cobalt as a magnetic material were obtained. First, we obtained the dependence of the magnetic properties on the working pressure of argon in the chamber (curve 2, shown in figure 2)

and then in the same way received a three-layer film.

Figure 5 (upper graph) shows, for example, the magnetometric hysteresis loop of a three-layer film, the Co layers of which have a thickness of 20 nm and are separated by a layer of copper of the same thickness. Here, the separate magnetization reversal of layers is also clearly visible. Below is a magnetoresistive hysteresis loop, also measured in the plane of the sample along the axis of easy magnetization. From the loop it follows that the three-layer Co / Cu / Co structure has a spin-valve effect due to separate layerwise magnetization reversal of cobalt layers. With a parallel arrangement of the magnetizations of Co layers (under the action of an external magnetic field exceeding the coercive forces of both layers), the resistance of the three-layer structure is minimal, with an antiparallel arrangement of the magnetizations of the layers (the loop region where one of the layers has magnetization reversed under the influence of an external field), the sample resistance is maximum.

Thus, in general terms, the preparation of the simplest (main) layered film structure is described, in particular, the production process for the multilayer structure shown here with a magnetoresistive spin-valve effect.

If necessary, the following layers with the required parameters can be sprayed onto this set of layers. Moreover, if previously to obtain a structure containing magnetic layers with different coercive forces, it was necessary to spray layers of different materials, such as cobalt and permalloy (nickel), that is, two different magnetic targets were required, then when applying the proposed solution, one magnetic target is used . This extends the capabilities of existing equipment. It is quite possible to impose a variation of the magnetic field (magnitude and / or orientation) on the method of obtaining structures described in detail above by changing the pressure. Naturally, it is first necessary to determine its effect on magnetic or other parameters. For films of rare earth transition metal, such dependencies were obtained that are described in the prototype. Pressure dependences of the composition of such ferromagnetic films were also established. In this case, the composition was controlled by the dependence of the rotational moment on temperature. Different temperature of magnetic compensation corresponds to a difference in composition (≈40 ° /%). By varying the pressure during the deposition process, layered structures with different compositions were obtained. Different composition is confirmed, for example, by the presence of two compensation temperatures. Therefore, it is possible to apply the above influence of the magnetic field on the properties of the layers of structures both in combination with pressure and directly by changing the characteristics of the field. The procedure in this case does not fundamentally differ from the above. The structure obtained using the described method is also not limited to the given magnetic materials, but allows the use of other substances important for practice.

Thus, the advantage of the proposed method is the ability to obtain structures with different properties on the basis of a single magnetic material, i.e. significantly expand the application of the method and device technological capabilities of the existing methodology.

Claims (6)

1. A method of producing multilayer films, including ion-plasma spraying of the target material on the substrate in vacuum by applying a magnetic field, characterized in that the dependence of the characteristics of the material of the sprayed layer on the pressure of the spraying gas is pre-established, and then spraying is performed at a pressure value, and the magnitude and / or orientation of the applied magnetic field necessary to obtain the specified characteristics of the material of the sprayed layer, and at least two layers are sprayed from hydrochloric target at different pressures of the atomizing gas. 2. The method according to claim 1, characterized in that the spraying is carried out by applying a horizontal magnetic field, taking into account combinations of the characteristics of the applied magnetic field with the pressure of the atomizing gas. 3. A device for producing multilayer films containing a shielded target cathode and a substrate holder located in a horizontal magnetic field with the possibility of changing the field orientation, characterized in that the screen is made adjustable in height with at least two holes for the sprayed material located on the target, each hole has a height-adjustable insert, and the vertical holes are separated by an insulated additional partition so that there is no overlap sprayed material on a substrate, the center of which can move when rotating from the center of one hole with the sprayed material to another. 4. The device according to claim 3, characterized in that the height-adjustable insert is made in the form of an elongated or shortened cone. 5. A multilayer film obtained by ion-plasma spraying of a target material on a substrate in vacuum by applying a magnetic field and containing at least three layers, characterized in that at least two layers of the film are made of one magnetic material and obtained by sputtering one target at different spray gas pressures, the magnitude of which, as well as the magnitude and / or orientation of the applied magnetic field, are selected from the condition for obtaining the specified magnetic characteristics of the material. 6. The multilayer film according to claim 5, characterized in that it consists of two magnetic layers separated from a non-magnetic layer of one material with different magnetic properties.

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