JP2011058073A - Thin film deposition method and thin film deposition apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film deposition method and a thin film deposition apparatus which improve the uniformity of the (001) orientation of an MgO film to be deposited using a sputtering process. <P>SOLUTION: The thin film deposition method deposits the MgO film of the (001) orientation on an amorphous magnetic film by the following steps of: feeding a rare gas to the inside of a vacuum tank 11 which stores a disk-shaped substrate S having the amorphous magnetic film on the principal plane, while rotating the substrate S in the circumferential direction thereof in the vacuum tank 11; and sputtering an MgO target T with the rare gas, the MgO target T being arranged in such a form that a target surface Ta made of MgO is exposed to the inside of the vacuum tank 11 and the target surface Ta is tilted to the principal plane of the substrate 3. In the method, a plane including the principal plane of the substrate S is used as a projection plane, the target surface Ta is arranged in such a form that a projection region SP being a region where the target surface Ta is projected to normal direction thereof is separated from the principal plane of the substrate S, and also the angle between the normal with respect to the principal plane of the substrate S and the normal with respect to the target surface Ta is controlled to be 8&deg; to 14&deg;. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a thin film forming method for forming a thin film using a sputtering method, in particular, a thin film forming method for forming a magnesium oxide film on an amorphous magnetic film using a target having magnesium oxide on the surface, and a thin film forming method used therefor It relates to the device.

  One technique for realizing high output of the tunnel magnetoresistive element is to configure the tunnel insulating film with magnesium oxide (MgO). Then, in the method of forming a thin film that forms an extremely thin insulating film made of MgO so as to develop a tunnel effect, a target having MgO on the surface is sputtered and particles emitted from the target are deposited on the main surface of the substrate. The sputtering method is widely adopted. Among such sputtering methods, for example, as described in Patent Document 1, the substrate accommodated in the vacuum chamber is arranged to be inclined with respect to the surface of the substrate while rotating in the circumferential direction thereof. A so-called oblique incidence sputtering method, in which the surface of a target is sputtered, is widely used.

  The distribution of particles emitted from the surface of the target by sputtering is not necessarily uniform in the plane of the surface of the target, but rather is biased in accordance with the distribution of plasma density formed in the vicinity of the surface of the target. Become. For this reason, in a method in which the target is disposed in such a manner that the surface of the target and the surface of the substrate are opposed to each other, or the surface of the target is left stationary with respect to the surface of the substrate, the surface of particles emitted from the surface of the target The in-plane distribution is directly reflected in the in-plane distribution of the MgO film thickness, and it is difficult to obtain sufficient uniformity of the MgO film thickness. In this regard, according to the oblique incident sputtering method, even if the in-plane distribution of particles emitted from the surface of the target is nonuniform on the surface, the surface of the target is inclined with respect to the surface of the substrate. The substrate rotates about the rotation axis with respect to the surface of the target, and thereby the thickness of the MgO film can be made uniform.

By the way, in order for the tunnel magnetoresistive element to exhibit a high magnetoresistance ratio, the MgO film is not simply formed on the magnetic film, but (001) orientation is required in the MgO film. . In order to give this (001) orientation to the MgO film using the above sputtering method,
[Condition 1] The magnetic film serving as the base of the MgO film is amorphous.
[Condition 2] In order to preferentially orient the (001) plane in the polycrystallized energy of the MgO particles that have reached the amorphous magnetic film and the polycrystallized state on the amorphous magnetic film Possessing the energy of them, they are needed.

JP 2009-151891 A

On the other hand, in the process where the surface of the target is sputtered by the sputtering gas,
[A] Magnesium particles and oxygen particles that are particles of the constituent material of the target,
[B] charged particles in which these constituent materials are charged,
[C] Recoil particles made of sputter gas bounced off the surface of the target, and these various particles will be released or recoiled from the surface of the target. Various kinds of particles that reach the amorphous magnetic film repeatedly collide with other particles before reaching the amorphous magnetic film from the target, and reduce the energy of the particles. Therefore, the energy of various particles when reaching the amorphous magnetic film decreases as the number of times the particles collide with other particles during the flight time of the particles, that is, the average number of collisions increases, while the average collision of the particles The lower the number of times, the higher. In the sputtering technique of the MgO film, the average number of collisions of the [a] particles is set so that the [a] particles constituting the MgO film satisfy the above [Condition 2] over the entire amorphous magnetic film. Sputtering is performed under a low pressure of 10 mPa to 20 mPa so as to be lower than the predetermined number of times over the entire surface of the substrate.

  However, even if the pressure at which the MgO film is formed is the same, since the various particles [a] to [c] are generated in different processes, their flight paths are generally different from each other. It is. For this reason, the energy given to the amorphous magnetic film by each of the particles [a] to [c] is also different from each other according to the route and mass of the various particles that flew. An excessively high energy is always supplied to the portion of the amorphous magnetic film where the particles of the particles land. As a result, the high energy of the various particles [a] to [c] described above causes crystallinity to develop in a part of the amorphous magnetic film, and the amorphousness at such sites is lost. It becomes. In other words, when high energy is given to various particles in accordance with the above [Condition 2] in order to improve the (001) orientation of the MgO film, part of the amorphous magnetic film and further the MgO film itself is damaged. The above [Condition 1] is not satisfied, and the (001) orientation itself of the MgO film is lost.

  In the method in which the target is placed so that the surface of the target and the surface of the substrate face each other, or the surface of the target is left stationary with respect to the surface of the substrate, the portion of the amorphous magnetic film that is damaged is always present. The tunnel magnetoresistive element cannot be formed at such a portion. According to the oblique incident sputtering method as described above, it is possible to disperse the damaged portion of the amorphous magnetic film in the circumferential direction of the substrate, but in the end, damage to the center of the substrate or the periphery of the substrate. Therefore, it becomes difficult to obtain (001) orientation uniformity between the center of the substrate and the periphery of the substrate.

  The present invention has been made in view of the above problems, and an object thereof is to provide a thin film forming method and a thin film forming apparatus for improving the uniformity of (001) orientation in an MgO film formed by using a sputtering method. It is.

Means for solving the above-described problems and their effects are described below.
According to the first aspect of the present invention, the inside of the vacuum chamber is rotated while rotating the substrate in the circumferential direction inside the vacuum chamber containing a disk-shaped substrate having an amorphous magnetic film as a main surface. By supplying a rare gas, exposing the target surface made of magnesium oxide inside the vacuum chamber, and sputtering the target disposed in a manner that the target surface is inclined with respect to the main surface of the substrate by the rare gas. A thin film formation method for forming a (001) -oriented magnesium oxide film on the amorphous magnetic film, wherein the target surface is projected in the normal direction thereof with a plane including the main surface of the substrate as a projection plane The target surface is arranged in such a manner that the projection region which is a region is separated from the substrate, and an angle formed between a normal to the main surface of the substrate and a normal to the target surface is 8 ° or more and 14 ° or less. The bottom line is that.

According to a third aspect of the present invention, there is provided a vacuum chamber that contains a substrate stage for rotating a disk-shaped substrate having an amorphous magnetic film as a main surface in a circumferential direction thereof and is supplied with a rare gas therein. A target surface made of magnesium oxide is exposed inside the vacuum chamber, and the target surface is disposed in a shape inclined with respect to the main surface of the substrate, and a high-frequency power is supplied to the target. A thin film forming apparatus for forming a (001) -oriented magnesium oxide film on the amorphous magnetic film by sputtering a target surface with the rare gas, wherein a plane including a main surface of the substrate is used as a projection plane. The target surface is disposed in such a manner that a projection region, which is a region obtained by projecting the target surface in the normal direction thereof, is separated from the substrate, and the normal to the main surface of the substrate and the To below 14 ° angle at 8 ° above the normal to Getto surface and it and gist.

  In the process in which the target surface made of MgO is sputtered by a rare gas, in addition to magnesium (Mg) particles and oxygen (O) particles which are target constituent particles, these constituent materials are charged with charged particles or targets. The recoil particles made of the rare gas bounced back from the surface are also emitted from the target surface or recoiled at their specific emission angle and recoil angle. As described above, in order to give the (001) orientation to the MgO film by using the sputtering method, the energy required for the MgO particles reaching the amorphous magnetic film to be polycrystallized on the amorphous magnetic film is It is necessary to retain energy for preferentially orienting the (001) plane in the polycrystallized state. In other words, in order to improve the (001) orientation of the MgO film, the various particles constituting the MgO film have the above-described energy over the entire amorphous magnetic film, so that the various particles collide with other particles. A low deposition pressure is required so that the number of times is lower than a predetermined number over the entire main surface of the substrate. However, as the deposition pressure decreases, not only magnesium (Mg) particles and oxygen (O) particles but also the charged particles and recoil particles have high energy and reach the amorphous magnetic film. Thus, the high energy of such various particles causes crystallinity to develop in a part of the amorphous magnetic film and inhibits the (001) orientation of the MgO film.

  The present inventor has found that the factor that inhibits the (001) orientation of the MgO film is that the plane including the main surface of the substrate is the projection plane and the target surface is in the normal direction as the deposition pressure decreases. It has been found that it appears prominently in the projected area, which is the area projected onto the screen. According to the first and third aspects of the present invention, since the MgO film is formed in such a manner as to avoid the projection region, the substrate is compared with the thin film formation mode in which the projection region overlaps the substrate. It is possible to reduce damage to the amorphous magnetic film in the whole. Therefore, even if the deposition pressure is lowered, the uniformity of the (001) orientation distribution of the MgO film can be improved as much as such damage is reduced.

  In addition, in forming an extremely thin insulating film that exhibits the tunnel effect with MgO, it is important to ensure the uniformity of the thickness of the MgO film as well as the uniformity of the (001) orientation distribution. The inventor of the present application has studied sharply the arrangement of the target that separates the projection region from the substrate, and the emission angle of Mg particles and O particles emitted from the target is greatly inclined from the normal to the target surface. And found that it is close to the tangential direction of the target surface. According to the first and third aspects of the present invention, the angle formed between the normal to the main surface of the substrate and the normal to the target surface is 14 ° or less in the target arrangement for separating the projection region from the substrate. Therefore, Mg particles and O particles can be uniformly reached over the entire rotating substrate. Further, since the angle formed between the normal line to the main surface of the substrate and the normal line to the target surface is 8 ° or more, it is possible to prevent Mg particles and O particles from reaching the substrate. Therefore, it is possible to improve the uniformity of (001) orientation distribution while ensuring the film thickness uniformity of the MgO film.

  The gist of the invention described in claim 2 is that the target surface is arranged in such a manner that a region obtained by projecting the target surface in the normal direction thereof is in contact with the side surface of the substrate. The gist of the invention described in claim 4 is that the target surface is arranged in such a manner that a region obtained by projecting the target surface in the normal direction thereof is in contact with the side surface of the substrate.

When the projection region is separated from the main surface of the substrate, Mg particles and O particles emitted from the target are difficult to reach the main surface of the substrate, so that the deposition rate of the MgO film is naturally reduced. According to the second and fourth aspects of the present invention, since the target surface is arranged in such a manner that the projection area is in contact with the side surface of the substrate, deterioration of (001) orientation due to the projection area can be suppressed. It is possible to maximize the deposition rate of the MgO film.

The block diagram which shows schematic structure of the thin film forming apparatus which concerns on this invention with the side cross-section of this apparatus. (A) (b) Side sectional view and plan view showing the positional relationship between the target and the substrate. (A) (b) The figure which shows the relationship between arrangement | positioning of the board | substrate with respect to a target, and in-plane distribution of the orientation of magnesium oxide on a board | substrate. (A) (b) (c) The sectional side view and top view which show the relationship of the position of a target and a board | substrate for every oblique incident angle. The graph which shows the relationship between the distance from a substrate edge, and the intensity | strength of the peak which shows (001) orientation for every oblique incident angle. The graph which shows the relationship between the distance from a substrate center, and a sheet resistivity for every oblique incident angle.

Hereinafter, an embodiment embodying the present invention will be described with reference to FIGS. First, a thin film forming apparatus according to the present invention will be described below.
As shown in FIG. 1, the vacuum chamber 11 in the thin film forming apparatus 10 is connected to an exhaust device 12 composed of a cryopump or the like for exhausting the internal space of the vacuum chamber 11, and the exhaust device 12 and the vacuum chamber 11. Is connected to a pressure detection device VG for detecting the internal pressure of the vacuum chamber 11. When the exhaust device 12 performs the exhaust operation, the inside of the vacuum chamber 11 is depressurized, and the internal pressure is detected by the pressure detection device VG. A gas supply device 13 including a mass flow controller or the like for supplying a rare gas such as argon (Ar), xenon (Xe), or krypton (Kr) at a predetermined flow rate is connected to the vacuum chamber 11. When the gas supply device 13 supplies the rare gas to the inside of the vacuum chamber 11 in a state where the exhaust device 12 performs the exhaust process regularly, the internal pressure in the vacuum chamber 11 is reduced. It changes in the range of 1 mPa-300 mPa according to the flow rate.

  A substrate stage 14 for holding a disk-shaped substrate S having a diameter of 8 inches is accommodated at the bottom of the internal space in the vacuum chamber 11 in a form connected to the output shaft of the substrate rotating device 15. The substrate S supported by the substrate stage 14 is a disk-shaped substrate having an amorphous magnetic film on the surface, such as amorphous cobalt iron boron (CoFeB). Examples include an 8-inch Si wafer, an AlTiC wafer, and a glass wafer. Then, the substrate rotating device 15 rotates the substrate stage 14 so that the substrate stage 14 maintains the temperature of the substrate S at room temperature, and the substrate rotation axis As passing through the center of the substrate S among the normals to the substrate S. Is rotated in the circumferential direction of the substrate S. According to the substrate stage 14 having such a configuration, the sputtered particles flying from one direction toward the surface of the substrate S are uniformly dispersed over the entire circumferential direction of the substrate S. It is possible to improve the film thickness uniformity of the deposit.

  In the internal space of the vacuum chamber 11, a bottomed cylindrical lower shielding plate 16 </ b> A is disposed so as to cover the periphery of the substrate stage 14, and sputter particles flying toward the periphery of the substrate stage 14 and the bottom of the vacuum chamber 11. The lower shielding plate 16 </ b> A shields the substrate stage 14 and the vacuum chamber 11 from the bottom. An annular cover ring CR is disposed along the outer periphery of the substrate S inside the lower shielding plate 16A in the radial direction, and sputtered particles flying toward the periphery of the substrate stage 14 are shielded by the cover ring CR. .

A cathode 18 for generating plasma inside the vacuum chamber 11 is mounted on the top of the vacuum chamber 11. A high frequency power source GE that outputs high frequency power of 13.56 MHz so that the power density is 2.85 W / cm ² is electrically connected to the backing plate 19 of the cathode 18. A disk-shaped MgO target T having a diameter of 5 inches that exposes the target surface Ta mainly composed of MgO to the internal space of the vacuum chamber 11 is electrically connected to the substrate S side of the backing plate 19. ing. The MgO target T is mounted on the vacuum chamber 11 such that the target surface Ta is separated from the substrate rotation axis As and is inclined with respect to the surface of the substrate S.

  A magnetic circuit 21 is disposed on the opposite side of the MgO target T across the backing plate 19, and the magnetic circuit 21 is driven in a state in which high-frequency power from the high-frequency power source GE is supplied to the backing plate 19. A magnetron magnetic field is formed on the target surface Ta of the MgO target T. Since the high-density plasma is generated in the vicinity of the target surface Ta of the MgO target T, the target surface Ta of the MgO target T functions as a cathode, and the target surface Ta is sputtered by rare gas ions.

  On the side of the substrate S with respect to the MgO target T, a dome-shaped shutter 22 covering the upper side of the substrate S is disposed immediately above the substrate stage 14 so as to be connected to the output shaft of the shutter rotation device 23. A part of the shutter 22 is provided with an opening 22 </ b> H that is a through hole that allows the entire target surface Ta of the MgO target T to be exposed toward the substrate S. When the shutter rotating device 23 rotates the shutter 22, the shutter 22 rotates about the substrate rotation axis As, and when the high frequency power is supplied to the backing plate 19, the target surface Ta of the MgO target T. And the opening 22H face each other, and sputtering with respect to the MgO target T becomes possible. When high frequency power is not supplied to the backing plate 19, the target surface Ta of the MgO target T is covered with the shutter 22, and sputtering on the MgO target T becomes impossible, and contamination on the target surface Ta is suppressed.

  Hereinafter, the positional relationship between the MgO target T and the substrate S will be described in detail with reference to FIG. 2A and 2B are a side sectional view and a plan view showing the positional relationship between the MgO target T and the substrate S, respectively.

  As shown in FIG. 2, the oblique incident angle θ that is an angle formed between the target normal At that is a normal to the target surface Ta and the substrate rotation axis As that is a normal to the main surface of the substrate S is 8 ° or more and The target surface Ta is inclined with respect to the main surface of the substrate S so as to be 14 ° or less. The target surface Ta is arranged in such a manner that the cylindrical retraction area SP, which is an area extending along the target normal At, does not overlap the main surface of the substrate S, and the cylindrical retraction area SP is formed on the substrate S. Are arranged in contact with the side surface on the MgO target T side. That is, the projection area, which is an area obtained by projecting the target surface Ta in the direction of the target normal At with the plane including the main surface of the substrate S as the projection plane, is separated from the main surface of the substrate S, and the retreat area SP is the most on the substrate S. The target surface Ta is arranged in the vicinity. Note that the distance (target height H) between the center of the target surface Ta and the center of the main surface of the substrate S in the direction of the substrate rotation axis As is 190 mm, and the center of the target surface Ta in the tangential direction of the main surface of the substrate S The target surface Ta is arranged in such a way that the distance from the center of the main surface of the substrate S is 175 mm.

When the film forming process is started in the thin film forming apparatus 10 having such a configuration, first, the exhaust device 12 is depressurized to a pressure value that is a reference value in the vacuum chamber 11 and then by a substrate transfer device (not shown). The substrate S is carried into the vacuum chamber 11. When the substrate S having the amorphous magnetic film on the main surface is set on the substrate stage 14, the shutter rotation device 23 makes the opening 22H of the shutter 22 and the target surface Ta face each other, and the substrate rotation device 15 The rotation of the substrate S is started around the substrate rotation axis As. When the rotation of the substrate S is started in this way, the gas supply device 13 supplies a rare gas having a preset flow rate to the inside of the vacuum chamber 11 to increase the pressure of the vacuum chamber 11 to the film formation pressure, Next, the high frequency power supply GE supplies high frequency power to the MgO target T to start sputtering of the target surface Ta. Then, the MgO target T is sputtered for a preset period on the amorphous magnetic film constituting the main surface of the substrate S, and an MgO film having a desired thickness is formed on the amorphous magnetic film.

  Here, in order to give the (001) orientation to the MgO film by using the sputtering method, as described in [Condition 2] above, the MgO particles that have reached the amorphous magnetic film are converted into the amorphous magnetic film. It is necessary to have the energy for polycrystallization above and the energy for preferentially orienting the (001) plane in the polycrystallization. In other words, in order to improve the (001) orientation of the MgO film, the number of collisions between the various particles and other particles in order to retain the energy over the entire amorphous magnetic film for the various particles constituting the MgO film. However, a low film forming pressure is required so that the entire surface of the substrate S is lower than the predetermined number of times. However, as the deposition pressure decreases, not only Mg particles and O particles, but also these charged particles and recoil particles from the target surface Ta have high energy to reach the amorphous magnetic film. Therefore, the high energy of such various particles causes crystallinity to develop in a part of the amorphous magnetic film and inhibits the (001) orientation of the MgO film.

  The inventor of the present application has found that such a factor that inhibits the (001) orientation of the MgO film appears more prominently in the projection region as the deposition pressure decreases. As shown in FIG. 2, the retreat area SP constituting such a projection area is an area that is biased toward the MgO target T with respect to the main surface of the substrate S as viewed from the substrate rotation axis As. Therefore, when the MgO film is formed in a state where the retreat area SP and the main surface of the substrate S overlap, the projection area is overlapped over the entire outer periphery of the rotating substrate S, and the outer periphery of the substrate S and the substrate S are overlapped. The strength of the (001) orientation of the MgO film differs greatly from the central part. In this regard, according to the thin film forming apparatus 10, since the MgO film is formed in such a manner as to avoid the projection region, the thin film formation apparatus 10 is compared with the thin film formation mode in which the projection region overlaps the substrate S. It is possible to reduce damage to the amorphous magnetic film as a whole. Therefore, even if the deposition pressure is lowered, the uniformity of the (001) orientation distribution of the MgO film can be improved as much as such damage is reduced. However, since the Mg particles and the O particles do not easily reach the main surface of the substrate S as the projected region is farther from the substrate S, the deposition rate of the MgO film is naturally reduced. In this regard, according to the thin film forming apparatus 10, since the target surface Ta is arranged in such a manner that the side surface of the substrate S on the MgO target T side and the retreat area SP are in contact with each other, the (001) orientation resulting from the projection area In this way, it is possible to maximize the deposition rate of the MgO film.

Further, the inventors of the present application have studied the arrangement of the MgO target T that separates the projection region from the substrate S, and in accordance with the cosine law in which the emission angle of Mg particles and O particles emitted from the MgO target T is generally known. It was found that it was largely inclined with respect to the target normal line At and close to the substantially tangential direction of the target surface Ta, unlike the corresponding one. In forming an extremely thin insulating film that exhibits the tunnel effect with MgO, it is important to ensure the uniformity of the thickness of the MgO film as well as the uniformity of the (001) orientation distribution. In this regard, according to the thin film forming apparatus 10, in the arrangement of the MgO target T that separates the projection region from the substrate S, the angle formed by the substrate rotation axis As and the target normal At is 14 ° or less, that is, the substrate S. The MgO target T is arranged so that the main surface is close to the tangential direction of the target surface Ta. Therefore, the Mg particles and the O particles can be uniformly reached over the entire rotating substrate S. In addition, since the angle formed between the substrate rotation axis As and the target normal At is 8 ° or more, it is possible to prevent Mg particles and O particles from reaching the substrate S. Therefore, after ensuring the film thickness uniformity of the MgO film (001
) It is possible to improve the uniformity of orientation.
(Test example)
The crystal orientation tendency observed in the projection region and the (001) orientation of the MgO film formed under various oblique incident angles θ will be described in detail below along with test examples and the like. First, the tendency of the crystal orientation observed in the projection region will be described with reference to FIG.

First, the substrate S / Ta (5 nm) / CoFeB (3 nm) / MgO (20 nm) / CoFeB (3 nm) / Ta (2 nm) was used as a laminated structure for measuring crystal orientation. Then, when forming the MgO film, the rotation of the substrate S was stopped under the following film forming conditions with different film forming pressures to form the MgO film of the test example, and the MgO (200) peak indicating (001) orientation was formed. The intensity of (2θ = 42.9 °) was measured for each test example by the X-ray diffraction method. FIG. 3 is a diagram illustrating the intensity distribution of the MgO (200) peak in the test example, and is a contour map in which positions where the intensity of the MgO (200) peak is equal are connected by a contour line Lar. FIG. 3A illustrates the intensity distribution of a test example formed under conditions where the film forming pressure is 19 mPa, and FIG. 3B illustrates a test example formed under conditions where the film forming pressure is 310 mPa. In any case, the lower the intensity of the MgO (200) peak, the darker the dots.
(Deposition conditions)
・ Substrate S: Silicon substrate (diameter: 8 inches)
・ Target: MgO target (diameter: 5 inches)
Oblique incident angle θ: 22 °
・ Target height H: 190mm
Amorphous magnetic film: (CoFe) _0.8 B _0.2
-Substrate temperature: Room temperature-Shortest flight distance dts: 200mm
-Film formation pressure: 19 mPa, 310 mPa
・ Sputtering gas: Ar
MgO film thickness: 20nm
As illustrated in FIG. 3, when the MgO film is formed in a state where the rotation of the substrate S is stopped, that is, in a state where the relative position between the main surface of the substrate S and the target surface Ta is fixed, It was confirmed that a (001) -oriented intensity distribution appeared in accordance with the relative distance between the main surface and the target surface Ta. In other words, it was recognized that the intensity distribution of (001) orientation appears so that the intensity of the MgO (200) peak becomes equal at the position where the distance from the edge of the MgO target T becomes equal.

  Further, in the projection area Z1, the second area Z2, the third area Z3, and the fourth area Z4, which are areas partitioned by the contour lines Lar, the intensity of the (001) orientation is as follows according to the film forming pressure. A tendency was observed. That is, as shown in FIG. 3 (a), at 310 mPa where the film formation pressure is relatively high, a height relationship of fourth region Z4 <third region Z3 <projection region Z1 <second region Z2 was recognized. On the other hand, at 19 mPa where the film forming pressure is relatively low, a height relationship of projection region Z1 <fourth region Z4 <second region Z2 <third region Z3 was observed.

The tendency of the intensity distribution of the (001) orientation as described above is
[D] The amorphous nature of the amorphous magnetic film is lost due to the high energy of particles reaching the region in the projection region Z1, which is a region relatively close to the MgO target T.
[E] In the fourth region Z4, which is a region relatively far from the MgO target T, it is difficult to promote MgO polycrystallization or preferential orientation of the (001) plane due to the low energy of particles reaching the region. That suggests that they are a factor.

The difference in intensity distribution between FIG. 3 (a) and FIG. 3 (b) is that the above [d] becomes conspicuous as the film forming pressure decreases, that is, the disappearance of the amorphous property in the projection region Z1 becomes conspicuous. It is a suggestion. Specifically, various particles that reach the amorphous magnetic film are generally released from the MgO target T and then repeatedly collide with other particles to reduce their own energy. In other words, as the various particles that reach the amorphous magnetic film fly under a high deposition pressure, the energy of the particles decreases, and conversely, the various particles fly under a low deposition pressure. As a result, the decrease in energy of the particles is suppressed. Therefore, at a relatively low deposition pressure, the energy of the particles reaching the amorphous magnetic film is relatively high, so that the low intensity due to the above [d] appears remarkably in the projection region Z1. .

  Here, when the initial MgO film is formed at a relatively low film formation pressure as described above, as described in [d] above, particles having high energy are formed in the amorphous magnetic film. As a result, the amorphous property is lost at the portion of the amorphous magnetic film where such particles land. Therefore, if the MgO target T is arranged in such a manner that the projection region Z1 is separated from the main surface of the substrate S, the low intensity due to the above [d] is separated from the main surface of the substrate S. Even if the MgO film is formed at a very low deposition pressure, the loss of (001) orientation on the outer periphery of the substrate S can be suppressed. Therefore, it is possible to improve the uniformity of (001) orientation in the MgO film.

Next, the crystal orientation of the MgO film formed at various oblique incident angles θ will be described with reference to FIGS. First, the substrate S / Ta (5 nm) / CoFeB (3 nm) / MgO (20 nm) / CoFeB (3 nm) / Ta (2 nm) was used as a laminated structure for measuring crystal orientation. Then, when forming the MgO film, the rotation of the substrate S is stopped under the following film forming conditions with different oblique incident angles θ, and the MgO film of the test example is formed. The test example was measured by the X-ray diffraction method. 4A, 4B, and 4C are diagrams schematically showing the positional relationship between the substrate S and the MgO target T in each test example. FIG. 5 is a diagram showing the relationship between the intensity of the MgO (200) peak and the distance from the edge (edge) of the substrate S for each oblique incident angle in the test example. Note that the end of the substrate S in FIG. 5 is the end of the substrate S on the MgO target T side, and the distance from the end is the distance in the radial direction from the end.
(Deposition conditions)
・ Substrate S: Silicon substrate (diameter: 8 inches)
・ Target: MgO target (diameter: 5 inches)
-Oblique incidence angle θ: 0 °, 11 °, 22 °
・ Target height H: 190mm
Amorphous magnetic film: (CoFe) _0.8 B _0.2
-Substrate temperature: Room temperature-Shortest flight distance dts: 200mm
-Film formation pressure: 19 mPa
・ Sputtering gas: Ar
MgO film thickness: 20nm
As shown in FIGS. 4A to 4C, when the oblique incident angle θ is 22 °, a part of the retreat area SP overlaps the outer periphery of the substrate S and is projected onto the main surface of the substrate S. Will be formed. On the other hand, when the oblique incident angle θ is 11 °, a part of the retreat area SP comes into contact with the side surface of the substrate S and the projection area is separated from the main surface of the substrate S. When the oblique incident angle θ becomes 0 °, the retreat area SP itself is separated from the substrate S, and the projection area is further separated from the main surface of the substrate S.

As shown in FIG. 5, when the oblique incident angle θ is 22 °, the peak intensity on the side of the MgO target T of the substrate S (the distance from the substrate edge is 0 mm to 50 mm) is remarkably reduced in accordance with the projection region Z1. An area was recognized. Then, a region where the peak intensity is highest in the vicinity of 100 mm from the end of the substrate S, that is, in the central portion of the substrate S is recognized, and the peak intensity tends to decrease again as the region moves from the central portion to the other end of the substrate S. Admitted. On the other hand, when the oblique incident angle θ is 11 °, a significant increase in the peak intensity on the MgO target T side of the substrate S is recognized as compared with the case where the oblique incident angle θ is 22 °, and the central portion of the substrate S, Also, at the other end portion of the substrate S, a peak intensity substantially equal to that in the case where the oblique incident angle θ was 22 ° was recognized. That is, by separating the projection area Z1 from the main surface of the substrate S, a decrease in (001) orientation strength due to the projection area Z1 can be suppressed, and the intensity distribution on the main surface of the substrate S can be made uniform. That was recognized. On the other hand, when the oblique incident angle θ is 0 °, the peak intensity on the MgO target T side of the substrate S is further increased as compared with the case where the oblique incident angle θ is 11 °. At the other end, a peak intensity substantially equal to that in the case where the oblique incident angle θ was 22 ° or 11 ° was recognized. That is, when the projection region Z1 is separated from the main surface of the substrate S, a decrease in (001) orientation strength due to the projection region Z1 can be suppressed, but the other end portion of the substrate S and the central portion of the substrate S Since the difference in peak intensity is also increasing, it was recognized that the intensity distribution on the main surface of the substrate S was not uniform compared to the case where the oblique incident angle θ was 11 °.

Next, the dependency of the oblique incident angle θ on the specific resistance value of the tunnel magnetoresistive element using the MgO film will be described with reference to FIG. First, as the element structure of the tunnel magnetoresistive element, substrate S / Ta (5 nm) / PtMn (15 nm) / Co ₉₀ Fe ₁₀ (2.5 nm) / Ru ( _0.9 nm) / CoFeB (3 nm) / MgO (2.5 nm ) / CoFeB (3 nm) / Ta (5 nm) / Ru (7 nm). Then, when forming MgO, the tunnel magnetoresistive element of the example was formed while rotating the substrate S with the oblique incident angle θ set to 11 ° under the following film forming conditions, and the area resistance of the tunnel magnetoresistive element was RA was measured. Further, under the same film forming conditions, only the oblique incident angle θ was changed to 22 ° to form a tunnel magnetoresistive element of a comparative example, and the sheet resistance RA of the tunnel magnetoresistive element was measured. FIG. 6 is a diagram showing the relationship between the value obtained by normalizing the area resistance RA at each measurement point by the area resistance RAC at the center of the substrate S and the distance from the center of the substrate S for each oblique incident angle.
(Deposition conditions)
・ Substrate S: Silicon substrate (diameter: 8 inches)
・ Target: MgO target (diameter: 5 inches)
-Oblique incident angle θ: 11 °, 22 °
・ Target height H: 190mm
Amorphous magnetic film: (CoFe) _0.8 B _0.2
-Substrate temperature: Room temperature-Shortest flight distance dts: 200mm
-Film formation pressure: 19 mPa
・ Sputtering gas: Ar
MgO film thickness: 2.5 nm
As shown in FIG. 6, when the oblique incident angle θ is 11 °, the outer peripheral portion of the substrate S has a slightly higher area resistivity RA / RAC than the central portion of the substrate S. Compared with the case where the oblique incident angle θ is 22 °, it is very small, and it was recognized that the uniformity of the sheet resistivity RA / RAC in the entire substrate S is greatly improved. That is, when the oblique incident angle θ is 11 °, the MgO film is formed in a manner avoiding the projection region Z1, so that the substrate is compared with the thin film formation mode in which the projection region Z1 overlaps the substrate S. It is possible to reduce damage to the amorphous magnetic film in the entire S, that is, to improve the uniformity of the (001) orientation distribution of the MgO film, and thus the uniformity of the area resistance RA of the tunnel magnetoresistive element. It was found that

In forming an extremely thin insulating film that exhibits the tunnel effect with MgO, it is important to ensure the uniformity of the thickness of the MgO film as well as the uniformity of the (001) orientation distribution. The inventor of the present application has studied the arrangement of the MgO target T that separates the projection region Z1 from the substrate S, and the emission angle of Mg particles and O particles emitted from the MgO target T is larger than the target normal At. It was found that it was tilted and was close to the substantially tangential direction of the target surface Ta from the relationship between the film forming speed and the oblique incident angle θ. Table 1 shows the relationship between the deposition rate of the MgO film and its uniformity and the oblique incident angle θ.

  As shown in Table 1, in the arrangement of the MgO target T that separates the projection region Z1 from the substrate S, if the oblique incident angle θ is 14 ° or less and 8 ° or more, ± 1% in the substrate plane It was recognized that the following film thickness uniformity was obtained, that is, it was possible to uniformly reach Mg particles and O particles throughout the rotating substrate S. That is, since the emission angle of the particles emitted from the target surface Ta is close to the tangential direction of the target surface Ta, if the angle between the target surface Ta and the main surface of the substrate S is less than 8 °, the particles are emitted from the target surface Ta. It was confirmed that the particles to be distributed are biased to the side closer to the MgO target T on the main surface of the substrate S. On the other hand, when the angle formed by the target surface Ta and the main surface of the substrate S exceeds 14 °, particles emitted from the target surface Ta are biased to the side far from the MgO target T on the main surface of the substrate S. It was recognized that If the angle formed between the target surface Ta and the main surface of the substrate S is not less than 8 ° and not more than 14 °, the particles emitted from the target surface Ta are biased with respect to the main surface of the substrate S. It was found that it was possible. In addition, when the oblique incident angle is 8 ° or more, a high film formation rate of 0.40 nm / min or more can be obtained, that is, the film formation rate is excessively decreased because Mg particles and O particles are difficult to reach the substrate S. It was recognized that it could be avoided. Therefore, in the thin film forming apparatus 10 in which the oblique incident angle θ is set to 8 ° or more and 14 ° or less, the uniformity of the (001) orientation distribution is ensured while ensuring the uniformity of the MgO film thickness. It can be improved.

As described above, according to the present embodiment, the following effects can be obtained.

  (1) The target surface Ta is arranged in such a manner that the projection region Z1 that is a region obtained by projecting the target surface Ta in the direction of the target normal At using the plane including the main surface of the substrate S as the projection surface is separated from the substrate S. Therefore, since the MgO film is formed so as to avoid the projection region Z1, compared with the thin film formation mode in which the projection region Z1 overlaps the substrate S, the amorphous magnetic film in the entire substrate S is formed. Damage can be reduced. Therefore, even if the deposition pressure is lowered, the uniformity of the (001) orientation distribution of the MgO film can be improved as much as such damage is reduced.

(2) Of the arrangement of the MgO target T that separates the projection region Z1 from the substrate S, the oblique incident angle θ, which is the angle formed by the substrate rotation axis As and the target normal At, is 14 ° or less. It becomes possible to make Mg particles and O particles reach uniformly over the entire substrate S. In addition, since the angle formed between the substrate rotation axis As and the target normal At is 8 ° or more, it is possible to prevent Mg particles and O particles from reaching the substrate S. Therefore, it is possible to improve the uniformity of (001) orientation distribution while ensuring the film thickness uniformity of the MgO film.

  (3) Since the target surface Ta is arranged so that the projection region Z1 is in contact with the side surface of the substrate S, the deposition rate of the MgO film can be increased while suppressing the deterioration of (001) orientation caused by the projection region Z1. It is possible to maximize.

In addition, the said embodiment can also be changed and implemented as follows.
In the above embodiment, it is assumed that the retreat area SP is in contact with the side surface of the substrate S on the MgO target T side. Instead, the target surface Ta is formed so that the retreat area SP is separated from the side surface of the substrate S. May be arranged. Even with such a configuration, the effects described in (1) and (2) above can be obtained as long as the projection region Z1 is separated from the main surface of the substrate S.

  θ ... oblique incident angle, As ... substrate rotation axis, At ... target normal, S ... substrate, SP ... retraction area, T ... target, Ta ... target surface, Z1 ... projection area, 10 ... thin film forming apparatus, 11 ... vacuum A tank, 12 ... an exhaust device, 13 ... a gas supply device, 14 ... a substrate stage, 16A ... a lower shielding plate, 18 ... a cathode, 19 ... a backing plate, 22 ... a shutter, 22H ... an opening, 23 ... a shutter rotating device.

Claims (4)

A rare gas is supplied to the inside of the vacuum chamber while rotating the substrate in the circumferential direction inside the vacuum chamber containing a disk-shaped substrate having an amorphous magnetic film as a main surface, and the vacuum chamber A (001) oriented magnesium oxide film is formed by sputtering a target having a target surface made of magnesium oxide inside and exposing the target surface to be inclined with respect to the main surface of the substrate with the rare gas. A method of forming a thin film on the amorphous magnetic film,
The target surface is disposed in such a manner that a projection region, which is a region obtained by projecting the target surface in the normal direction thereof with a plane including the main surface of the substrate as a projection surface, is separated from the main surface of the substrate, and A method of forming a thin film, characterized in that an angle formed between a normal to the principal surface of the substrate and a normal to the target surface is 8 ° or more and 14 ° or less. The thin film formation method according to claim 1, wherein the target surface is disposed in a manner that a region obtained by projecting the target surface in a normal direction thereof contacts a side surface of the substrate. A vacuum chamber that contains a substrate stage that rotates a disk-shaped substrate having an amorphous magnetic film on its main surface in the circumferential direction thereof, and is supplied with a rare gas therein;
A target surface made of magnesium oxide is exposed inside the vacuum chamber, and the target surface is arranged in a shape inclined with respect to the main surface of the substrate. A thin film forming apparatus for forming a (001) oriented magnesium oxide film on the amorphous magnetic film by sputtering with the rare gas,
The target surface is arranged in such a manner that a projection region, which is a region obtained by projecting the target surface in the normal direction thereof with a plane including the main surface of the substrate as a projection surface, is separated from the substrate, and the main surface of the substrate The thin film forming apparatus is characterized in that an angle formed by a normal to the target and a normal to the target surface is not less than 8 ° and not more than 14 °. The thin film forming apparatus according to claim 3, wherein the target surface is arranged such that a region obtained by projecting the target surface in a normal direction thereof is in contact with a side surface of the substrate.