CN102789786B - Bi-layer structure material of CoPt/Ta vertical magnetic film and preparation method thereof - Google Patents

Abstract

The invention discloses a double-layer structure of a CoPt/Ta perpendicular magnetization film and a preparation method thereof. The material sequentially includes a substrate, a CoPt magnetic layer, and a Ta protective layer, wherein the thickness of the CoPt is 10nm-100nm, and the thickness of the Ta protective layer is 1nm-20nm. Ta is used in the protective layer of the CoPt perpendicular magnetization film, and its function is as follows: ① During sputtering deposition and annealing, Ta element diffuses to the CoPt layer and segregates to the CoPt grain boundary, making the grain boundary area a non-magnetic area and changing the CoPt magnetization reversal mechanism to increase the coercive force of thin film media. ②During the heat treatment process, Ta atoms diffuse to the CoPt magnetic layer, which weakens the exchange coupling between adjacent magnetic particles, reduces the noise of medium inversion, and improves the recording bit density.

Description

CoPt/Ta double-layer structure material and preparation method of perpendicular magnetization film

technical field

The invention belongs to the field of information storage, and in particular relates to a CoPt/Ta double-layer structure material which can be used to improve the vertical magnetic properties of CoPt films and a preparation method thereof.

Background technique

In the external memory of the computer, the magnetic storage technology develops rapidly and forms a huge industry. In recent years, the storage density of magnetic storage media has developed rapidly at a rate of 10 times every 5 years. With the further increase of the magnetic recording density, the size of the recording unit decreases, so that the size of the magnetic grains in the unit recording unit decreases rapidly, and the horizontal magnetic recording (the magnetization direction is parallel to the running direction of the recording medium) encounters the superparamagnetic effect limits. The superparamagnetic effect will cause the recorded information to become unstable or even lost under the influence of external thermal disturbance, thus limiting the increase of the recording density of the medium. In order to further increase the storage density, perpendicular magnetic recording technology (the magnetization direction of the recording bit is perpendicular to the surface of the recording medium) has attracted widespread attention. The idea of vertical recording was first proposed by Dr. Iwasaki of Japan in 1975. In perpendicular recording media, the direction of easy magnetization of magnetic particles is perpendicular to the surface of the recording medium film.

Compared with horizontal recording technology, vertical recording technology has the following two advantages:

First, perpendicular recording uses a unipolar head with a soft magnetic underlayer for reading and writing. Compared with the annular magnetic head used in horizontal recording, vertical recording technology can read and write on the recording medium with double the coercive force. This enables the use of higher magnetocrystalline anisotropy materials in perpendicular recording media. Under the same signal-to-noise ratio (SNR) and thermal stability, the volume of magnetic particles in the recording medium can be smaller, so the perpendicular magnetic recording medium can support higher recording density.

Second, the magnetic particles in perpendicular recording have strong uniaxial anisotropy perpendicular to the film surface. This makes the switching field distribution of the magnetic grains smaller and the transition interval between recording units narrower. A narrower transition interval is conducive to improving the signal-to-noise ratio and further improving the recording density.

The world's first commercial hard disk model based on perpendicular recording technology was made by Seagate Corporation of the United States in 2006. In 2007, Western Digital Corporation of the United States reported a demonstration product based on CoCrPt recording medium with a density of 520G/in ² . The simulation results of Wood et al. showed that vertical recording can support a recording density exceeding 1T/in ² .

In the perpendicular magnetic recording hard disk, with the further increase of the recording density, when the magnetic recording bit and its particle size are reduced to a certain extent, the stored information will still become unstable due to the superparamagnetic effect. The anisotropy of the magnetic recording medium must be sufficiently high in order for the magnetic moments of the majority of magnetic grains in the recording bit to maintain their magnetization directions for a sufficiently long period of time. Under normal temperature conditions, in order to stably record information for more than 10 years, the thermal stability factor (Thermal Stability Factor=K _u V/k _BT ) of the recording medium must be greater than 60. Simultaneously meeting the two competing requirements of high signal-to-noise ratio and thermal stability is the key to further improve the magnetic recording density of hard disks.

Due to the good thermal stability and high recording density of perpendicular magnetic recording materials, it provides favorable conditions for realizing ultra-high density information storage. Perpendicular magnetic recording requires that the size of magnetic particles be as small as possible under the premise of thermal stability. In order to improve thermal stability, materials with high magnetic anisotropy (K _u ) must be used as magnetic recording media. The equiatomic ratio CoPt with L1 ₀ structure is an ordered regular tetragonal phase, the Co and Pt atomic layers are arranged alternately along the c-axis direction, the c-axis is slightly shorter than the a-axis, and the c-axis is the easy magnetization direction. The tetragonal structure of the axial compression deformation makes the CoPt alloy have a high (10 ⁶ -10 ⁷ J/m ³ ) perpendicular magnetic anisotropy, high coercive force and good corrosion resistance, which can effectively improve the thermal stability of the bit properties, reduce media noise, and can greatly increase the magnetic recording density, so it has great application potential in ultra-high recording density magnetic recording media, and is very suitable as an ultra-high-density perpendicular magnetic recording material.

In the industrial application of high-density perpendicular recording media, in order to obtain the L1 ₀ phase, a substrate temperature of 300°C or higher or a heat treatment temperature of 500°C or higher is required. High temperature will make it difficult to control the particle size, and it will also prolong the production cycle of the product, which will eventually increase the cost of industrial production. At present, researchers are committed to selecting a suitable bottom layer (such as Ag, C, BN) to induce the magnetic grains of CoPt alloy films to grow in the (001) vertical orientation. Or by doping a third nonmagnetic impurity (such as Ag, Si ₃ N ₄ , Al ₂ O ₃ , SiO ₂ , B ₂ O ₃ , BN, TiO ₂ , B), not only lowering the annealing temperature, but also greatly weakening the crystallinity Magnetic exchange coupling between particles.

Contents of the invention

The invention provides a CoPt/Ta perpendicular magnetization film for the problems of high annealing temperature encountered in the production process, being easily oxidized and corroded by the influence of the external environment, and difficult for magnetic particles to grow to the vertical orientation of L1 ₀ (001). Double-layer structure material and its preparation method. The present invention does not adopt the bottom material and material doping method, but deposits the protective layer material Ta on the CoPt film to solve the problem that the magnetic anisotropy energy of the CoPt magnetic film is easily oxidized during the preparation and production process. , and promote the growth of L1 ₀ (001) vertical orientation.

A double-layer structure material of a CoPt/Ta perpendicular magnetization film provided by the present invention comprises a substrate, a CoPt magnetic layer, and a Ta protection layer in sequence, wherein the thickness of the CoPt is 10 nm to 100 nm, and the thickness of the Ta protection layer is 1 nm to 1 nm. 20nm.

There are two preparation methods for the double-layer structure material of the CoPt/Ta perpendicular magnetization film, a CoPt composite target method and a CoPt alloy target method.

The steps of the CoPt composite target method include:

The first step prepares Co metal target and Ta metal target;

The second step is to attach Pt sheets on the Co target;

In the _third step, Ar is used as the sputtering gas, and the Co target after the Pt sheet is first sputtered, and then a layer of Ta layer is sputtered on the CoPt to prepare a CoPt magnetic thin film material with a Ta protective layer;

Step 4 Place the prepared CoPt single-layer magnetic film and CoPt/Ta double-layer magnetic film in a vacuum annealing furnace for annealing at high temperature.

The steps of the CoPt alloy target method include:

The first step is to prepare CoPt alloy target and Ta metal target;

In the _second step, Ar is used as the sputtering gas, and the CoPt alloy target is sputtered first, and then the Ta target is sputtered on the CoPt to prepare a CoPt magnetic thin film material with a Ta protective layer;

In the third step, the prepared CoPt/Ta double-layer magnetic thin film is placed in a vacuum annealing furnace for annealing at high temperature.

The technical effect of the present invention is reflected in that: compared with the CoPt material without a Ta protective layer, the magnetic material of the CoPt/Ta structure provided by the present invention has high magnetocrystalline anisotropy and large vertical coercive force. Controlling the annealing temperature at 650°C can promote the growth of CoPt magnetic particles along the c magnetization axis. The present invention considers that Ta has very excellent chemical properties and extremely high corrosion resistance, and can play a very good role in protecting magnetic materials from oxidation and corrosion encountered in sputtering, annealing and testing processes. After the CoPt magnetic material is prepared and a Ta protective layer is added on it, the magnetic properties of CoPt/Ta are much improved compared to CoPt without a protective layer. The main reasons are as follows: ① Ta non-magnetic elements segregate to the grain boundary during the sputtering deposition process, making the grain boundary region a non-magnetic region, thereby changing the magnetization reversal mechanism and improving the coercive force of the thin film medium. ②Under the appropriate annealing temperature, due to thermal diffusion, Ta atoms diffuse to the CoPt magnetic layer, which weakens the exchange coupling between adjacent magnetic particles, reduces the noise of medium inversion, and improves the recording bit density.

Description of drawings

FIG. 1 is a schematic diagram of the layer structure of a CoPt/Ta perpendicular magnetization film.

Figure 2 is the vertical hysteresis loop of CoPt film.

Figure 3 is a differential scanning calorimetry diagram of a CoPt perpendicular magnetization film.

Fig. 4 is the hysteresis loop of CoPt film with different thickness and 1nm Ta protection layer.

Figure 5 is the hysteresis loops of CoPt films with different thicknesses and a 10nm Ta protective layer.

Figure 6 is the hysteresis loops of CoPt thin films with different thicknesses and a 20nm Ta protective layer.

Fig. 7 is the hysteresis loop of the CoPt film without Ta protection layer and with Ta protection layer.

Fig. 8 is the XRD pattern of the CoPt thin film without Ta protection layer and with Ta protection layer.

Fig. 9 is an XPS photoelectron spectrum diagram of Co atoms in CoPt thin films without and with a Ta protective layer.

Figure 10 is the hysteresis loops of CoPt/Ta films annealed at 650°C for different times.

Figure 11 is the measured three-dimensional surface topography of the CoPt/Ta thin film annealed at 650°C for 10 minutes.

Fig. 12 is the measured three-dimensional surface topography of the CoPt/Ta thin film annealed at 650°C for 30 minutes.

Figure 13 is the measured three-dimensional surface topography of the CoPt/Ta thin film annealed at 650 °C for 1 h.

Detailed ways

The present invention is described in more detail below by means of examples, but the following examples are only illustrative, and the protection scope of the present invention is not limited by these examples.

A kind of magnetic material of CoPt/Ta double-layer structure with Ta as protective layer described in the present embodiment, as shown in Figure 1, it comprises substrate 3, CoPt magnetic layer 2, Ta protective layer 1 successively, wherein, CoPt The thickness of the Ta protective layer is 10 nm to 100 nm (preferably 50 nm), and the thickness of the Ta protective layer is 1 nm to 20 nm (preferably 10 nm).

The magnetic material of the CoPt/Ta double-layer structure with Ta as the protective layer provided by the invention has high magnetocrystalline anisotropy and large magnetic coercive force. During the sputtering deposition process, Ta, as a nonmagnetic element, segregates to the CoPt and Ta grain boundaries, making the grain boundary region a nonmagnetic region, thereby changing the magnetization reversal mechanism and improving the coercive force of the thin film medium. And in the heat treatment process, due to thermal diffusion, Ta atoms diffuse to the CoPt magnetic layer, which weakens the exchange coupling between adjacent magnetic particles, reduces the noise of the medium, and improves the recording bit density.

The double-layer structure material of the CoPt/Ta perpendicular magnetization film can be prepared by CoPt composite target method and CoPt alloy target method, and can also be prepared by sputtering method, chemical vapor deposition method, evaporation method, atomic layer deposition method, metal organic Any one of the preparation methods such as thermal decomposition method or laser-assisted deposition method.

In the preparation method provided by the invention, following preferred processing parameters can be adopted:

The power of the sputtering Co target and the CoPt alloy target is 15W-200W (a further preferred value is 20W), and the sputtering Ar pressure is 0.45Pa-1.0Pa (a further preferred value is 0.5Pa).

The sputtering Ta target power is 15W-200W (more preferably 25W), and the sputtering Ar gas pressure is 0.45Pa-1.0Pa (more preferably 0.5Pa).

The annealing temperature is 600°C-850°C, and further, the annealing time of CoPt/Ta and CoPt is 10min-1h.

The CoPt/Ta structure of the present invention and the preparation method using Ta as the CoPt protective layer can adopt methods such as sputtering, chemical vapor deposition, evaporation, atomic layer deposition, metal-organic thermal decomposition, or laser-assisted deposition. any one of the preparation methods.

Example 1

In this embodiment, the magnetron sputtering method is used to prepare CoPt/Ta and CoPt magnetic thin films.

The substrate is Si(100), and a CoPt alloy target with a diameter of 100 mm and a thickness of 5 mm (atomic ratio Co:Pt=1:1) is prepared, and the purity of the target is 99.999% (atomic percentage). Using the method of magnetron sputtering, Ar gas with a purity of 99.999% is introduced during sputtering.

The specific process parameters are as follows: CoPt alloy target adopts DC power supply, sputtering power is 120W; sputtering Ar pressure is 1Pa; pre-sputter for 1 hour before each sputtering to ensure that the oxide layer on the surface of CoPt alloy target is completely removed. The thickness of the film was measured by a step meter to prepare a 50nm CoPt magnetic film. The vertical magnetic properties of CoPt (50nm) thin films were tested by VSM. From the vertical magnetization curve of CoPt shown in Figure 2, it can be seen that the vertical coercive force of CoPt film is 2544.6Oe. CoPt films were annealed for 1h at optimized sputtering power and annealing temperature, and the magnetic grains of CoPt tended to grow in the direction of L1 ₀ (001).

Example 2

The phase transition temperature of CoPt thin film was investigated.

The substrate is Si(100), and a Co target with a diameter of 100 mm and a thickness of 5 mm is prepared. The purity of the target is 99.999% (atomic percentage). The Pt sheet with a size of 2*10 mm is evenly pasted on the Co target. The atomic ratio of Co to Pt was adjusted to be 1:1 by changing the number of Pt flakes. Then, the method of magnetron sputtering is used, and Ar gas with a purity of 99.999% is introduced during sputtering.

The specific process parameters are as follows: the Co target adopts a DC power supply, and the sputtering power is 20W; the sputtering Ar pressure is 0.5Pa; each sputtering is pre-sputtered for 1 hour to ensure that the oxide layer on the surface of the Co target is completely removed. CoPt magnetic films with different atomic ratios can be obtained by changing the number of Pt sheets attached to the Co target each time. By analyzing with the energy spectrometer attached to the scanning electron microscope, the atomic percentage of each element in the film can be obtained. The final test results show that the ratio of Co:Pt=1:1 can be achieved by pasting 8 Pt sheets on the Co target. The thickness of the film was obtained by profilometer analysis, and CoPt magnetic films of 10nm, 50nm and 100nm were prepared respectively.

Differential thermal analysis was carried out with DSC (differential scanning calorimeter), and the obtained results are shown in Fig. 3 . An exothermic peak of CoPt appears at 560°C, indicating that CoPt undergoes a phase transition at 560°C. Therefore, only when the annealing temperature is higher than 560 °C, the phase transformation of CoPt will occur. The sputtered CoPt alloy film has an fcc structure, and the film can undergo phase transformation only under high temperature annealing conditions. However, as the annealing temperature increases, the size of the CoPt grains will continue to grow, and the excessive growth of the grains will lead to magnetic exchange coupling, thereby affecting the magnetic properties of the CoPt medium and the magnetic properties of the noise. Therefore, determining the phase transition temperature of CoPt can optimize the annealing process and prevent excessive growth of CoPt grains. Putting the CoPt film in a high-temperature annealing furnace, and setting the annealing temperature to 600°C to 850°C, phase transition can occur. However, when the annealing temperature is 650°C, it can ensure that all particles in the film undergo phase transition and ensure that the magnetic The crystal grains do not grow too much, which leads to the magneto-crystalline coupling effect between the grains and reduces the magnetic properties of the CoPt thin film.

Example 3

A Ta target with a diameter of 100mm and a thickness of 5mm was prepared, and the purity of the target was 99.99% (atomic percentage), and then magnetron sputtering was used to inject Ar gas with a purity of 99.999% during sputtering. In Example 1, a layer of Ta thin film was respectively coated on the CoPt magnetic layers of 10 nm, 50 nm, and 100 nm of the samples, and the thickness of the Ta thin film was 1 nm, 10 nm, and 20 nm.

The specific process parameters are as follows: the Ta target adopts a DC power supply, the sputtering power is 25W, and the sputtering Ar pressure is 0.5Pa; pre-sputter for 1 hour before each sputtering to ensure that the oxide layer on the Ta target surface is completely removed.

The vertical magnetic properties of 1nm, 10nm, 20nm Ta protective layers plated on 10nm, 50nm, 100nm CoPt thin films were respectively tested by VSM. The comparative hysteresis loops of 10nm, 50nm, and 100nm CoPt films with a 1nmTa protective layer are shown in Figure 4. The M-H perpendicular magnetization curves of three CoPt film samples with different thicknesses added with a 10nm Ta protective layer are shown in Fig. 5 . The comparative hysteresis loops of three thicknesses of CoPt samples plus a 20nm Ta protective layer are shown in Figure 6. From the comparison of vertical magnetization curves in Figure 4, Figure 5, and Figure 6, it can be seen that when the thickness of the CoPt film is 50nm and the thickness of the Ta protective layer is 10nm, the measured vertical coercive force is the largest, and its value is 1289.4Oe.

CoPt film and CoPt(50nm)/Ta(10nm) were measured by VSM, XRD and XPS (both samples were annealed at 650°C for 1h in an annealing furnace with a vacuum degree of 1×10 ^-4 ) double-layer structure Vertical magnetic properties, degree of crystallization, and bonding of magnetic thin films. The measured hysteresis loops, crystallization peaks and bonding peaks of the two samples are shown in Figure 7, Figure 8, and Figure 9. It can be seen from Figure 7 that the saturation magnetization of the two samples is not much different, both are about 600emu/cm ³ , the perpendicular magnetic coercive force of the CoPt magnetization film without the Ta protection layer is only 110.5Oe, while the Ta protection layer is added The vertical magnetic coercive force of the CoPt magnetized film of the layer is as high as 1289.4Oe. Figure 8 compares the crystallization degree of CoPt film and CoPt(50nm)/Ta(10nm) magnetic film. After the CoPt film is annealed for a sufficient time, (111), (200), (002) Bragg diffraction peaks appear, while CoPt(50nm)/Ta(10nm) thin film besides the above three basic peaks, the peak of L1 ₀ (001) also appeared. By Scherrer's formula

D＝Kλ/Bcos(θ)

(wherein K is the Scherrer constant, when B is the half maximum width of the diffraction peak, K is 0.9, θ is the Bragg diffraction angle, and λ is the X-ray wavelength used), the calculated L1 ₀ (001) grain size formed (D) = 42nm.

Fig. 9 is the photoelectron spectrum of the Co atom 2p region of the two samples. The photoelectron peaks in the Co2p region show double peaks with binding energies of 780.5 eV and 796.9 eV, respectively. The appearance of the double peaks originates from the 2p energy level orbital spin splitting of Co atoms, and they correspond to Co2p1/2 and Co2p3/2 respectively, and the photoelectron peaks are of Doniach-Sunjic asymmetry. For CoPt/Ta, a symmetrical peak appears at the high binding energy end of the 2p region at 780.5 eV, and a shake-up satellite appears at a distance of 5.3 eV from the Co2p1/2 peak. The appearance of the peak is caused by the transition of electrons in the O2p band to the empty orbitals in the Co2p band.

The comparative analysis of Figure 7, Figure 8, and Figure 9 shows that after annealing at 650 °C for 1 h, grains in the L1 ₀ (001) direction appeared in the CoPt/Ta film, and the diffusion of Ta atoms in the Ta capping layer to the magnetic layer effectively promoted the CoPt The magnetic particles grow toward the c easy magnetization axis. And the Ta capping layer in the CoPt/Ta thin film effectively restrains the adverse effect of O atoms diffusing into the CoPt magnetic layer during the annealing process on its magnetic properties. During thermal annealing at 650 °C, Ta atoms diffuse into the CoPt layer, effectively isolating the interaction between CoPt particles and weakening the exchange coupling effect of CoPt magnetic particles due to excessive grain growth caused by high-temperature annealing, thereby Greatly improved magnetic anisotropy of CoPt films.

Example 4

The sample CoPt(50nm)/Ta(10nm) in Example 3 was annealed at 650° C. for 10 min, 30 min and 1 h respectively, and magnetic property analysis and atomic force microscope test were performed. Test the vertical coercive force of the film at different annealing temperatures, observe the surface morphology and measure the surface roughness. As shown in Figure 10, the M-H⊥ hysteresis loops of CoPt(50nm)/Ta(10nm) annealed at 650°C for 10min, 30min, and 1h. The vertical coercivity of annealing for 10min is only 949.7Oe, the vertical coercivity of annealing for 30min is 737.7Oe, and the coercivity of annealing for 1h is 1289.4Oe. Figure 11, Figure 12, and Figure 13 are three-dimensional topography images of CoPt(50nm)/Ta(10nm) annealed at 650°C for 10min, 30min, and 1h, respectively, by atomic force microscopy (AFM), which directly reflect the surface of the film Flatness, the surface particles of the film sample are denser, the unevenness is smaller, and the particles are arranged more neatly. It can be seen from these three 3D images that the grains are growing continuously as the annealing time increases. From the results of the roughness analysis, it is read that the surface roughness of the CoPt (50nm)/Ta (10nm) film annealed at 650°C for 10min is 1.705nm, the surface roughness of the film annealed for 30min is 3.181nm, and the surface roughness of the film annealed for 1h is The roughness is 5.627nm (the roughness of the silicon wafer surface has not been deducted). The surface roughness of annealing for 1h is much larger than that of annealing for 10min, which indicates that the grain size of the film continues to increase with the prolongation of annealing time. At the same time, the coercive force of the annealed 1h is much larger than the coercive force perpendicular to the film plane annealed for 10min, indicating that although the CoPt thin film has enhanced crystallinity, the crystal grains have been growing, the orientation has been enhanced, and the magnetic moments are aligned. tends to be consistent, however, the size of the CoPt grains does not reach the size of a magnetic monodomain.

The above description is only a preferred embodiment of the present invention, but the present invention should not be limited to the content disclosed in this embodiment and the accompanying drawings. Therefore, all equivalents or modifications that do not deviate from the spirit disclosed in the present invention fall within the protection scope of the present invention.

Claims (4)

1. a double-layer structure material of CoPt/Ta perpendicular magnetization film, it is made of successively stacked substrate, CoPt magnetic layer and Ta protection layer, wherein, the thickness of CoPt is 10nm～100nm, and the thickness of Ta protection layer is 1nm to 20nm, the Ta protective layer is deposited on the CoPt magnetic layer, and the two are in direct contact to solve the problem of the reduction of the magnetic anisotropy caused by the CoPt magnetic layer being easily oxidized during the production process, and to promote L1 ₀ (001) vertically oriented growth. 2. The double-layer structure material of CoPt/Ta perpendicular magnetization film according to claim 1, characterized in that, the thickness of CoPt is 50nm, and the thickness of Ta protective layer is 10nm. 3. a preparation method of the double-layer structure material of CoPt/Ta perpendicular magnetization film as claimed in claim 1, its step comprises: The first step prepares the CoPt layer; The _2nd step uses Ar as the sputtering gas, sputters a layer of Ta on the CoPt layer, and prepares the CoPt magnetic film material with Ta protective layer; Grain boundary segregation makes the grain boundary region a non-magnetic region, thereby changing the magnetization reversal mechanism and improving the coercive force of the thin film medium; The third step is to place the prepared CoPt/Ta double-layer structure magnetic film in a vacuum annealing furnace for annealing at high temperature. Due to thermal diffusion, Ta atoms diffuse to the CoPt magnetic layer to weaken the exchange coupling between adjacent magnetic particles, reduce the noise of the medium, and increase the recording bit density. 4 . The preparation method according to claim 3 , wherein in the third step, the annealing temperature is 650° C. to promote the growth of CoPt magnetic particles along the c-magnetization axis.