JP2010098084A - Method of forming colossal magneto-resistive material thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To deposit a colossal magneto-resistive material thin film having high-qualiyt crystallinity with favorable productivity when forming the colossal magneto-resistive material thin film. <P>SOLUTION: When depositing the colossal magneto-resistive material thin film which has epitaxially grown after crystal orientation on a base electrode by sputtering using facing targets, a sputtering process having at least two steps are used, a deposition rate is relatively slowed down in the sputtering process in a first step, and the deposition rate is relatively accelerated in the sputtering process in later steps to form the thin film. The epitaxial thin film of favorable quality can be deposited in the first step, and the high crystalline thin film of favorable quality can be deposited in the later steps with productivity improved by increasing the deposit rate. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a giant magnetoresistive material thin film that can be applied to the manufacture of a semiconductor element utilizing a pulse electric field induced resistance change in a material having a magnetoresistive effect.

A multi-component oxide material, which is a giant magnetoresistive (CMR) material, undergoes a reversible resistance change when an electrical stimulus is applied.
This phenomenon is described in A. of University of Houston. lnnatiev et al. found that when a perovskite oxide Pr _1-X Ca _X MnO ₃ (hereinafter PCMO) material is thinned and a pulse voltage is applied, a reversible and stable resistance change occurs depending on the pulse polarity. And called the EPIR (electrical pulse induced resistance change) effect. This is a rewrite asymmetry in which a resistance value is high when a positive voltage pulse is first applied and a resistance value is low when a negative voltage pulse is applied next (see Patent Document 1). A nonvolatile memory using this phenomenon is called ReRAM (resistance RAM).

This ReRAM generally has a structure in which PCMO which is a giant magnetoresistance (CMR) material is sandwiched between a lower electrode layer and an upper electrode layer. Examples of the electrode material include Pt, Ir, Ru, Ph, Ag, Au, Al, and Ta, or YBa ₂ Cu ₃ 0 _7-X , RuO ₂ , IrO ₂ , which has higher conductivity than the CMR material. An oxide such as SrRuO ₃ or a nitride compound such as TaSiN, TiN, TiSiN, or MoN is used. A CMR thin film layer is deposited on the surface of the lower electrode at a film forming temperature of 400 to 600 ° C. using a film forming means such as CVD or PVD.

This PCMO thin film is epitaxially grown following the crystal orientation of the surface of the underlying electrode material to be deposited. Since epitaxial growth is affected by the crystal orientation of the underlying surface, the crystallinity of the underlying metal electrode is also reflected in the crystallinity, axial orientation, and EPIR effect of the CMR thin film. For this reason, a method is considered in which the lower metal electrode is formed into metal crystal grains having the (111) plane as the outermost surface. In addition, in order to control the epitaxial growth, there is a case where film parameter control with high accuracy is performed at a relatively low film formation rate in the initial growth process of the CMR thin film (see Patent Document 2).
US Pat. No. 6,204,139 JP 2004-273656 A

In film formation by magnetron sputtering or laser ablation generally known as a thin film formation method, a film formation temperature of 400 to 600 ° C. is required for crystallization of the PCMO material. Actually, when the temperature is 500 ° C. or lower, most of the deposited layer becomes amorphous, and only a part or only the surface layer of the film is crystallized. There is a problem that the increase and the EPIR effect (resistance change rate) become small.
Further, the Al thin film wiring used in the memory also has a problem that it is disconnected due to melting or migration at a temperature higher than 450 ° C.
In addition, when the conventional magnetron sputtering method is used, not only sputtered particles but also negatively charged particles (electrons) collide with the lower electrode and PCMO during film formation, resulting in loss of crystal structure due to the detachment of oxygen molecules. There is also a problem that defects occur in the structure.
In addition, when magnetron sputtering is used for the film formation of PCMO, it is necessary to use RF (alternating current) as a power source because it is a high resistance material, and the film formation speed is extremely slow, which is not practical from the standpoint of mass productivity. There is also.

  The present invention has been made against the background of the above circumstances, and a method for producing a giant magnetoresistive material thin film that makes it possible to produce a high-quality crystalline film with high productivity even at a relatively low deposition temperature. The purpose is to provide.

  That is, of the giant magnetoresistive material thin film manufacturing method of the present invention, the first present invention forms a giant magnetoresistive material thin film epitaxially grown following the crystal orientation on the base electrode by sputtering using an opposing target. In this case, a thin film is formed by using at least two stages of sputtering processes, relatively slowing the film forming speed in the first stage sputtering process, and relatively high in the film forming speed in the subsequent stage sputtering process. It is characterized by that.

  The method for producing a giant magnetoresistive material thin film of the second invention is characterized in that, in the first invention, the giant magnetoresistive material thin film has a perovskite crystal structure.

  The method for producing a giant magnetoresistive thin film of the third aspect of the present invention is characterized in that, in the first or second aspect of the present invention, the deposition temperature of the thin film is set to 450 ° C. or lower.

  A method for producing a giant magnetoresistive material thin film according to a fourth aspect of the present invention is the method of manufacturing a giant magnetoresistive thin film according to any one of the first to third aspects of the present invention, wherein the film formation rate in the first stage sputtering step is 2 nm / min. It is characterized as follows.

  The method for producing a giant magnetoresistive material thin film according to a fifth aspect of the present invention is the method of manufacturing a giant magnetoresistive material thin film according to any one of the first to fourth aspects of the present invention, wherein the film formation rate of the sputtering step in the stage after the first stage is . It is characterized by the above.

  The method for producing a giant magnetoresistive material thin film of the sixth aspect of the present invention is characterized in that, in any of the first to fifth aspects of the present invention, the target material is Pr1-XCaXMnO3.

  The method for producing a giant magnetoresistive material thin film of the seventh invention is characterized in that, in any one of the first to sixth inventions, the crystal orientation of the surface of the base electrode is a (111) plane. .

  According to an eighth aspect of the present invention, there is provided a giant magnetoresistive material thin film manufacturing method according to any one of the first to seventh aspects of the present invention, wherein the power source used for the sputtering is a direct current pulse power source or a direct current pulse power source and a high frequency power source. The two are used simultaneously or alternately.

  The method for producing a giant magnetoresistive material thin film of the ninth aspect of the present invention is characterized in that, in any one of the first to eighth aspects of the present invention, the atmospheric pressure during the sputtering is 0.5 to 0.05 Pa. To do.

  According to a tenth aspect of the present invention, there is provided a method for producing a giant magnetoresistive thin film according to any one of the first to ninth aspects, wherein a bias potential of −200 to 0 V is applied to a substrate on which a base electrode is held during the sputtering. It is characterized by applying.

  That is, in the present invention, in the first stage, a thin film having high crystallinity is formed following the crystal plane of the base electrode by slowing the film formation rate. Since it has started, good crystallinity is maintained.

  In the conventional facing target sputtering method, if the film formation temperature is 470 ° C. or higher, CMR having a uniform crystal orientation is formed on the lower metal electrode regardless of the film formation rate. However, if the film formation rate is high at a temperature lower than 470 ° C., an amorphous CMR film containing amorphous or entirely amorphous is formed on the base electrode. This is because the CMR particles are amorphous and become amorphous because there is less energy to move and align on the surface of the lower metal electrode with respect to the amount of sputtered particles. For this reason, when high crystallinity is required, a film forming temperature of 500 ° C. or higher is required, and a material that breaks at a temperature higher than 450 ° C. such as an Al thin film wiring cannot be used.

  In the present invention, the deposition rate is relatively slow (preferably 2 nm / min. Or less) at the stage of the first sputtering step, thereby enabling the movement of sputtered particles on the surface of the lower metal electrode, and 450 ° C. or less. However, it is possible to obtain a CMR highly crystalline and highly oriented thin film. 2 nm / min. When sputtering is performed at a film formation speed exceeding 1, the movement of sputtered particles is suppressed and the thin film crystallinity is impaired. In the subsequent stage, the film formation rate can be made relatively fast (preferably 2 nm / min. Or more) to sufficiently increase the productivity. However, if the film formation rate is increased too much, the crystallinity is impaired. Hereinafter, for example, 20 nm / min. The following is desirable. Note that a transition stage in which the film formation rate is increased stepwise or continuously may be provided between the first stage and the subsequent stage.

The facing target sputtering method can be sputtered using a DC pulse power source even for a high resistance material target that cannot be sputtered without using a high frequency power source in the case of magnetron sputtering. With only a high-frequency power source, the maximum film formation rate is several nm / min. To the extent, it is not practical to use for mass production. In the case of an opposed target, the film forming rate is set to 1 to several tens of nm / min. Can be controlled. Thereby, the rate of the initial film formation stage is set to 2 nm / min. After deposition at a thickness of 2 to 5 nm as follows, the film formation rate was several tens of nm / min. Can be used for mass production. In addition, by using a DC pulse power source and a high-frequency power source together, initial film formation can be performed at a film formation rate lower than that of the DC pulse power source.
Note that by setting the film thickness at the first sputtering step to 2 to 5 nm, a high-quality crystalline film can be generated even when the film formation rate is increased at a later stage. Here, if the film thickness is less than 2 nm in the first stage, the film is not sufficiently crystallized, and even if the film formation speed is increased in the later stage, amorphous and crystalline are mixed and crystals The film becomes inferior. Even when the film thickness in the first stage exceeds 5 nm, a film excellent in crystal can be obtained by increasing the film formation speed in the later stage, but the film formation time becomes longer. You will lose your sex.

The material of the giant magnetoresistive material thin film is not limited to a specific material in the present invention, but a preferred example is Pr _1-X Ca _X MnO ₃ having a ternary oxide perovskite structure. .

Further, it is desirable that the crystal orientation of the base electrode that is the basis of epitaxial growth is the (111) plane. A giant magnetoresistive thin film having good crystallinity is formed following this crystal plane.
The atmospheric pressure during sputtering is preferably 0.5 to 0.05 Pa.
By maintaining the low-pressure atmosphere, the plasma can be maintained, the scattering of sputtered particles into the space is reduced, and the kinetic energy of the particles reaching the surface of the lower metal electrode is maintained. If it exceeds 0.5 Pa, the kinetic energy of the particles is lost due to collision with an atmospheric gas such as Ar, and a film with poor crystallinity is formed. If it is less than 0.05 Pa, plasma cannot be maintained and film formation cannot be performed.

  Further, it is desirable to apply a bias voltage of −200 to 0 V to the substrate holding the base electrode during sputtering. This promotes crystal growth of the sputtering particles by repeating desorption and deposition of the sputtered particles that have reached the substrate. This varies depending on the deposition pressure and deposition rate. An effect is acquired by providing a voltage in the range of -200-0V.

  According to the method for manufacturing a giant magnetoresistive material thin film of the present invention, when forming a giant magnetoresistive material thin film epitaxially grown following the crystal orientation on the base electrode by sputtering using a counter target, at least two stages of sputtering are performed. In the first stage, the film formation rate is relatively slowed in the first stage sputtering process, and the film formation speed is relatively increased in the subsequent stage sputtering process to form a thin film. Although the productivity is lowered, a high-quality epitaxial thin film can be formed. At a later stage, the sputtered particles are effectively arranged by the epitaxial thin film that is already being formed, and a high-quality high-crystalline thin film can be formed in a state where the film formation rate is increased and the productivity is increased. .

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
The film forming apparatus includes a film forming chamber 1 as an airtight space, and a vacuum exhaust pump 7 (rotary, turbo molecular pump, cryopump, etc.) is used as an exhaust mechanism for exhausting the film forming chamber 1. It is connected.
Further, a gas introduction line 6 capable of introducing atmospheric gas is connected to the film forming chamber 1, and Ar gas can be introduced in this embodiment. In addition, a reactive gas such as O ₂ can be introduced during the film forming process. Moreover, it can be adjusted by providing a pressure regulator for controlling the gas pressure or changing the gas introduction amount by the mass flow controller 6a.

The film forming chamber 1 is provided with a plasma source in which a pair of targets 2a and 2b, which are CMR materials, are arranged to face each other. This plasma source may be incorporated in the film forming chamber 1 or may be attached to the film forming chamber 1 as another independent unit.
As shown in FIG. 2, the target of this plasma source has a structure in which magnets 11... 11 are arranged on the outer periphery and the rear surface. A magnetic field 12 is formed around the opposing targets 2a and 2b, and the target 2a, The plasma 13 formed between 2b is restrained. As a result, high-density plasma is formed, and negatively charged particles (electrons) are also restrained and do not reach the substrate to be deposited. Therefore, sputtered particles with high kinetic energy are formed, and defects in the PCMO thin film during deposition are formed. Since it is not generated, a dense film structure can be obtained. Each of the targets 2a and 2b is connected to a DC pulse power source and a high-frequency power source alone or both as a sputter power source 3, so that power necessary for sputtering (plasma generation) can be input. The plasma source has a structure in which the side surfaces and bottom portions of the opposed targets 2a and 2b are closed and only the upper portion is opened.

  A substrate stage 4 having a substrate heating mechanism is arranged in parallel to the opening, that is, perpendicular to the opposing targets 2a and 2b. A high frequency power supply 5 for back bias is connected to the substrate stage 4 so that a back bias can be applied to the substrate. Thereby, the sputtered particles generated from the plasma source are irradiated to the wafer 8 on the substrate stage 4 from the opening, and the target component is deposited on the wafer 8. The wafer 8 has a configuration in which a base electrode layer is formed on a substrate. Although the substrate stage is disposed above the plasma source in FIG. 1, it may be disposed below or on the side of the plasma source. However, the sputtered particles deposited inside the plasma source may peel off, and when it is installed under the plasma source, it is necessary to take measures so as not to peel off.

The film forming operation is performed by setting a wafer 8 provided with a base electrode layer (surface crystal orientation (111) plane) on the substrate stage 4, and then setting the inside of the film forming chamber 1 to 1 × 10 ⁻⁴ Pa˜ The vacuum exhaust pump 7 evacuates until the pressure reaches 1 × 10 ⁻⁶ Pa, and the flow rate is adjusted by the mass flow controller 6 a through the gas introduction line 6 into the film forming chamber 1 when the wafer temperature reaches 400 to 450 ° C. While introducing Ar gas, the atmospheric pressure is adjusted to be 0.05 Pa to 0.5 Pa.
Further, by a sputtering power source 3 using a DC pulse power source and / or an RF power source, as a first stage, a film forming rate of 2 nm / min. Electric power is applied to the targets 2a and 2b to generate plasma so as to be as follows. Next, a back bias is applied to the substrate at −200 to 0 V using the high frequency power supply 5 for back bias. At this time, the substrate cleaning may be performed by applying a back bias to the substrate using a high frequency power supply before the power is supplied to the targets 2a and 2b. When the film thickness of the epitaxial thin film deposited and formed on the wafer becomes 2 to 5 nm, the film formation rate of 2 nm / min. The power applied to the targets 2a and 2b is changed so as to achieve the above, and the film formation speed is accelerated to the required film thickness. The upper limit of the input power is possible until the number of arc discharges increases or the plasma generation state becomes unstable.
As described above, film formation can be performed at a relatively low film formation rate in the first stage, and film formation can be performed at a relatively high film formation speed in the subsequent stage.

Examples of the present invention will be described below in comparison with comparative examples.
Using an opposed target sputtering apparatus using PCMO as a target, initial film formation is performed on a Si substrate with platinum (111) as a base electrode layer at a substrate temperature of 450 ° C. and a pressure in a film formation chamber of 0.05 Pa. Film formation rate of 1.5 nm / min. Then, a film thickness of 5 nm was formed, and then the film formation speed was increased to 11 nm to form a film thickness of 45 nm, and a 50 nm PCMO film was formed.
The crystallinity of the PCMO film was evaluated by obtaining the peak intensity of PCMO by XRD (concentration method).

For comparison, on a Si substrate with platinum (111) as a base electrode layer,
A PCMO film having a film thickness of 50 nm with a substrate temperature of 450 ° C., a film forming chamber pressure of 0.05 Pa, a film forming speed of 11 nm, and a film forming chamber (Comparative Example 1)
2. A PCMO film having a film thickness of 50 nm with a substrate temperature of 500 ° C., a pressure in the film formation chamber of 0.05 Pa, a film formation speed of 11 nm, and a film formation rate (Comparative Example 2)
3. A film formed by depositing a PCMO film having a film thickness of 50 nm at a film formation speed of 2.5 nm at a substrate temperature of 450 ° C., a film formation chamber pressure of 0.05 Pa during the film formation (Comparative Example 3),
4). A PCMO film having a thickness of 50 nm and a substrate temperature of 500 ° C., a pressure in the film formation chamber of 0.05 Pa, a film formation speed of 2.5 nm, and a film thickness of 50 nm (Comparative Example 4)
5). Initial film formation was performed at a film formation speed of 3 nm / min. The peak intensity of PCMO was also obtained by XRD (concentration method) for the film (Comparative Example 5) having a film thickness of 5 nm and then accelerated to a film formation speed of 11 nm and having a film thickness of 45 nm. The results of Example 1 and Comparative Examples 1 to 5 are shown in FIG.

  As shown in Comparative Example 1, when the film formation rate is high at 450 ° C., the PCMO peak is low and crystallization is insufficient. In Comparative Example 2 in which the film formation temperature is 500 ° C., the film formation rate is the same as that in Comparative Example 1, but crystallization is progressing due to high temperature conditions. Comparative Example 3 had the same film formation temperature of 450 ° C. as Comparative Example 1, but since the film formation rate was slow, crystallization proceeded and the same peak intensity as Comparative Example 2 was obtained. In Comparative Example 4, the film formation rate was reduced at 500 ° C., but since it has the same peak intensity as Comparative Example 2, it can be seen that the temperature is more dominant than the film formation rate. Although the peak intensity of Comparative Example 5 is stronger than that of Comparative Example 1, it is weaker than Comparative Examples 2 to 4, and is not sufficiently crystallized. In the PCMO film of Example 1, the same peak intensity as in Comparative Examples 2 to 4 was obtained. When the film formation time up to 50 nm was compared for Comparative Example 3 in which the same crystallinity was obtained at 450 ° C., the film formation time in Example 1 was shortened to 22% as compared with Comparative Example 3.

It is a figure which shows the film-forming apparatus which enforces the manufacturing method of one Embodiment of this invention. Similarly, it is a schematic plan view for explaining a plasma generation source at an opposed target. It is XRD peak data of PCMO formed into a film in an example and comparative examples 1-5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Deposition chamber 2a, 2b Target 3 Sputtering power supply 4 Substrate stage 5 High frequency power supply for back bias 6 Gas introduction line 8 Wafer 11 Magnet 12 Magnetic field 13 Plasma

Claims (10)

  When forming a giant magnetoresistive thin film epitaxially grown following the crystal orientation on the underlying electrode by sputtering using a counter target, at least two stages of sputtering processes are used, and the film formation speed is increased in the first stage sputtering process. A method for producing a giant magnetoresistive material thin film, wherein the thin film is formed by relatively slowing down and forming a thin film at a relatively high deposition rate in a subsequent sputtering process.   2. The method for producing a giant magnetoresistive thin film according to claim 1, wherein the giant magnetoresistive thin film has a perovskite crystal structure.   The method for producing a giant magnetoresistive material thin film according to claim 1, wherein a film forming temperature of the thin film is 450 ° C. or less.   The film deposition rate in the first stage sputtering process is 2 nm / min. The method for producing a giant magnetoresistive material thin film according to any one of claims 1 to 3, wherein:   The film formation rate of the sputtering process in the stage after the first stage is 2 nm / min. The method for producing a giant magnetoresistive material thin film according to any one of claims 1 to 4, wherein the method is as described above. The target material _{Pr 1-X Ca X MnO 3} ( where, 0 <x <1) characterized in that it is a method of manufacturing a giant magnetoresistive material thin film according to any one of claims 1 to 5.   The method for producing a giant magnetoresistive thin film according to any one of claims 1 to 6, wherein the crystal orientation of the surface of the base electrode is a (111) plane.   The giant magnetism according to any one of claims 1 to 7, wherein the power source used for the sputtering is a direct current pulse power source, or a direct current pulse power source and a high frequency power source are used simultaneously or alternately. A method of manufacturing a resistive material thin film.   The method for producing a giant magnetoresistive thin film according to any one of claims 1 to 8, wherein the atmospheric pressure during the sputtering is 0.5 to 0.05 Pa.   The method for producing a giant magnetoresistive material thin film according to any one of claims 1 to 9, wherein a bias potential of -200 to 0 V is applied to the substrate on which the base electrode is held during the sputtering.

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