JP6569149B2 - Ferroelectric ceramics, ferroelectric memory and manufacturing method thereof - Google Patents

Description

  The present invention relates to a ferroelectric ceramic, a ferroelectric memory, and a manufacturing method thereof.

  Conventional ferroelectric ceramics have a Pt film formed on a Si substrate and a PZT film formed on the Pt film.

  A conventional ferroelectric memory is formed on a Si substrate, a Pt film formed on the Si substrate, a PZT film formed on the Pt film, an electrode formed on the PZT film, and the Si substrate. It has a source region and a drain region.

  The conventional ferroelectric ceramics and the conventional ferroelectric memory use a Pt film, and the film thickness is required to be 100 nm or more. Therefore, a ferroelectric ceramic and a ferroelectric memory using a film having a lower cost than a Pt film are required.

WO2006 / 088777

  An object of one embodiment of the present invention is to provide a ferroelectric ceramic, a ferroelectric memory, or a manufacturing method thereof with reduced cost.

Hereinafter, various aspects of the present invention will be described.
[1] Ag _x Pd _1-x film;
A ferroelectric film formed on the Ag _x Pd _1-x film;
Comprising
The x satisfies the following formula 1 and is a ferroelectric ceramic.
0.3 <x <0.95 Expression 1

[2] In the above [1],
Ferroelectric ceramics characterized in that the Ag _x Pd _1-x film is oriented to (200).

[3] In the above [1] or [2],
The ferroelectric ceramic, wherein the Ag _x Pd _1-x film is formed on a ZrO ₂ film.

[4] In the above [3],
Ferroelectric ceramics characterized in that the ZrO ₂ film is formed on a Si substrate.
[4-1] In any one of the above [1] to [4],
Ferroelectric ceramics characterized in that the ferroelectric film is a PZT film.

[5] a semiconductor layer;
A ZrO ₂ film formed on the semiconductor layer;
An Ag _x Pd _1-x film formed on the ZrO ₂ film;
A ferroelectric film formed on the Ag _x Pd _1-x film;
An electrode formed on the ferroelectric film;
A source region and a drain region formed in the semiconductor layer;
Comprising
The x satisfies the following formula 1;
0.3 <x <0.95 Expression 1
Note that the semiconductor layer is preferably a single crystal substrate (for example, a Si substrate or a Si wafer), a single crystal layer, an epitaxial layer, a polycrystalline layer (for example, a polycrystalline silicon layer), or the like.

[6] In the above [5],
The ferroelectric memory according to claim 1, wherein the ferroelectric film is a PZT film.

[7] forming a ZrO ₂ film on the semiconductor layer;
Forming an Ag _x Pd _1-x film on the ZrO ₂ film;
Forming a ferroelectric film on the Ag _x Pd _1-x film;
Forming an electrode film on the ferroelectric film;
Forming an electrode on the ferroelectric film by processing the electrode film, the ferroelectric film, the Ag _x Pd _1-x film, and the ZrO ₂ film;
Forming a source region and a drain region in the semiconductor layer by implanting impurity ions into the semiconductor layer using the electrode as a mask;
Comprising
The method of manufacturing a ferroelectric memory, wherein x satisfies the following formula 1.
0.3 <x <0.95 Expression 1

[8] In the above [7],
A method of manufacturing a ferroelectric memory, wherein the ferroelectric film is a PZT film.

  By applying one embodiment of the present invention, a ferroelectric ceramic, a ferroelectric memory, or a manufacturing method thereof can be provided with reduced cost.

It is sectional drawing which shows the ferroelectric ceramic which concerns on 1 aspect of this invention. 1 is a cross-sectional view illustrating a ferroelectric memory according to an aspect of the present invention. FIG. 3 is a diagram showing an XRD diffraction result of a sample of Example 1. FIG. 6 is a diagram showing an XRD diffraction result of a sample of Example 2. It is a diagram showing the piezoelectric hysteresis curve and piezoelectric Butterfly characteristic that is the result of piezoelectric evaluation of _PbZr 0.55 _{Ti 0.45} film of Example 2. It is a figure which shows the electrostriction butterfly curve and piezoelectric hysteresis characteristic of the sample of Example 3. FIG. (A) is a figure which shows the result of having evaluated the piezoelectric hysteresis characteristic of the sample of Example 3, (B) is a figure which shows the result of having evaluated the piezoelectric hysteresis characteristic of the sample of a comparative example.

  Hereinafter, embodiments and examples of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that modes and details can be variously changed without departing from the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited to the description of the embodiments and examples below.

[Embodiment 1]
FIG. 1 is a cross-sectional view showing a ferroelectric ceramic according to one embodiment of the present invention. This ferroelectric ceramic has a semiconductor layer 11, which is a single crystal substrate (eg, Si substrate, Si wafer, etc.), single crystal layer, epitaxial layer, polycrystalline layer (eg, polycrystalline silicon layer), or the like. There should be. A ZrO ₂ film 12 is formed on the semiconductor layer 11, and an Ag _x Pd _1-x film 13 is formed on the ZrO ₂ film 12. x satisfies the following formula 1. A PZT film 14 is formed on the Ag _x Pd _1-x film 13.
0.3 <x <0.95 Expression 1

According to the present embodiment, since the Ag _x Pd _1-x film 13 is used instead of the conventional Pt film, the cost of the ferroelectric ceramics can be reduced.

Next, a method for manufacturing the ferroelectric ceramic of FIG. 1 will be described.
A substrate as the semiconductor layer 11 is prepared. As this substrate, various substrates can be used. For example, a single crystal substrate such as a Si single crystal or a sapphire single crystal, a single crystal substrate with a metal oxide film formed on the surface, a polysilicon film or a silicide film on the surface A substrate on which is formed can be used. In the present embodiment, a Si substrate oriented in (100) is used.

Next, the ZrO ₂ film 12 is formed on the Si substrate as the semiconductor layer 11 by vapor deposition at a temperature of 550 ° C. or lower (preferably a temperature of 500 ° C.). The ZrO ₂ film 12 is oriented to (200). The Si substrate is oriented (100).

Thereafter, an Ag _x Pd _1-x film 13 is formed on the ZrO ₂ film 12 by vapor deposition. The Ag _x Pd _1-x film is oriented (200). Next, a PZT film 14 is formed on the Ag _x Pd _1-x film 13 by a sputtering method or a sol-gel method. The PZT film 14 is a Pb (Zr _1-x Ti _x ) O ₃ film, x satisfies the following formula 2, and the element ratio of Pb: (Zr _1-x + Ti _x ) is (1.4 to 1.1). ): 1.
0 <x <1 (preferably 0.1 <x <1) Formula 2

In this specification, the “PZT film” includes those containing impurities in Pb (Zr _1-x Ti _x ) O ₃ , and even if the impurities are contained, the ferroelectric function of the PZT film does not disappear. As long as it is a thing, various things may be contained.

The method for forming the PZT film 14 by sputtering is as follows.
A sputtering target of Pb (Zr _1-x Ti _x ) O ₃ having an element ratio of Pb: (Zr _1-x + Ti _x ) of (1.4 to 1.1): 1 is sputtered. As a result, a PZT film 14 is formed on the Ag _x Pd _1-x film 13.

The method of forming the PZT film 14 by the sol-gel method is as follows.
A precursor solution for forming a PZT film in which Pb is excessively added by 10 to 40 atomic% is applied on the Ag _x Pd _1-x film 13 and crystallized by heat treatment in a pressurized oxygen atmosphere of 10 atm, for example. I do. As a result, a PZT film 14 is formed on the Ag _x Pd _1-x film 13.

In this embodiment, the PZT film 14 is formed on the Ag _x Pd _1-x film 13, but the present invention is not limited to this, and other strong films are formed on the Ag _x Pd _1-x film 13. It is also possible to form a dielectric film.
The ferroelectric film is made of ABO ₃ or (Bi ₂ O ₂ ) ²⁺ (A _m-1 B _m O _{3m + 1} ) ²⁻ (where A is Li, Na, K, Rb, Pb, Ca, Sr, Ba, At least one selected from the group consisting of Bi, La and Hf, B is at least one selected from the group consisting of Ru, Fe, Ti, Zr, Nb, Ta, V, W and Mo, and m is 5 or less It is a film having a perovskite or a bismuth layered structure oxide represented by:

[Embodiment 2]
FIG. 2 is a cross-sectional view illustrating a ferroelectric memory according to an aspect of the present invention. This ferroelectric memory is a one-transistor type FRAM (registered trademark) (Ferroelectric Random Access Memory).

The ferroelectric memory 10 includes a semiconductor layer 11, which is a single crystal substrate (eg, Si substrate, Si wafer), a single crystal layer, an epitaxial layer, a polycrystalline layer (eg, polycrystalline silicon layer), or the like. There should be. A ZrO ₂ film 12 is formed on the semiconductor layer 11, and an Ag _x Pd _1-x film 13 is formed on the ZrO ₂ film 12. x satisfies the following formula 1. A PZT film 14 is formed on the Ag _x Pd _1-x film 13.
0.3 <x <0.95 Expression 1
An Ag _x Pd _1-x film 13 is formed on the ZrO ₂ film 12. x satisfies the following formula 1. A PZT film 14 is formed on the Ag _x Pd _1-x film 13.
0.3 <x <0.95 Expression 1

  An electrode 15 is formed on the PZT film 14. The material of the electrode 15 is, for example, Pt, Au / Ti, Al, Ni or the like. A source region 16 and a drain region 17 are formed in the semiconductor layer 11.

According to the present embodiment, since the Ag _x Pd _1-x film 13 is used instead of the conventional Pt film, the cost of the ferroelectric memory can be reduced.

  Next, a method for manufacturing the ferroelectric memory of FIG. 2 will be described.

  A substrate as the semiconductor layer 11 is prepared. As this substrate, various substrates can be used. For example, a single crystal substrate such as a Si single crystal or a sapphire single crystal, a single crystal substrate with a metal oxide film formed on the surface, a polysilicon film or a silicide film on the surface A substrate on which is formed can be used. In the present embodiment, a Si substrate oriented in (100) is used.

Next, a ZrO ₂ film is formed on the Si substrate as the semiconductor layer 11 by a vapor deposition method at a temperature of 550 ° C. or lower (preferably a temperature of 500 ° C.). This ZrO ₂ film is oriented to (200). The Si substrate is oriented (100). Note that the ZrO ₂ film is processed in a later step to become the ZrO ₂ film 12 shown in FIG.

Thereafter, an Ag _x Pd _1-x film is formed on the ZrO ₂ film by vapor deposition. The Ag _x Pd _1-x film is oriented (200). Note that the Ag _x Pd _1-x film is processed in a later step to become the Ag _x Pd _1-x film 13 shown in FIG. x satisfies the following formula 1.
0.3 <x <0.95 Expression 1

Next, a PZT film is formed on the Ag _x Pd _1-x film by a sputtering method or a sol-gel method in the same manner as in the first embodiment. This PZT film is a Pb (Zr _1-x Ti _x ) O ₃ film, x satisfies the following formula 2, and the element ratio of Pb: (Zr _1-x + Ti _x ) is (1.4 to 1.1). ): 1.
0 <x <1 (preferably 0.1 <x <1) Formula 2
Note that the PZT film is processed in a later process to become the PZT film 14 shown in FIG.

Next, an electrode film is formed on the PZT film, a photoresist film is applied on the electrode film, and exposure and development are performed, whereby a resist pattern (not shown) is formed on the electrode film. Next, the electrode film, the PZT film, the Ag _x Pd _1-x film, and the ZrO ₂ film are etched using this resist pattern as a mask. As a result, the ZrO ₂ film 12 is formed on the Si substrate 11, the Ag _x Pd _1-x film 13 is formed on the ZrO ₂ film 12, and the PZT film 14 is formed on the Ag _x Pd _1-x film 13. The electrode 15 is formed on the PZT film 14.

  Thereafter, impurity ions are implanted into the Si substrate 11 using the resist pattern and the electrode 15 as a mask, and heat treatment is performed to form the source region 16 and the drain region 17 in the Si substrate 11.

In this embodiment, the PZT film 14 is formed on the Ag _x Pd _1-x film 13, but the present invention is not limited to this, and other strong films are formed on the Ag _x Pd _1-x film 13. It is also possible to form a dielectric film.
The ferroelectric film is made of ABO ₃ or (Bi ₂ O ₂ ) ²⁺ (A _m-1 B _m O _{3m + 1} ) ²⁻ (where A is Li, Na, K, Rb, Pb, Ca, Sr, Ba, At least one selected from the group consisting of Bi, La and Hf, B is at least one selected from the group consisting of Ru, Fe, Ti, Zr, Nb, Ta, V, W and Mo, and m is 5 or less It is a film having a perovskite or a bismuth layered structure oxide represented by:

The natural oxide film on the surface of the Si substrate oriented to (100) is removed using buffered hydrofluoric acid. Thereafter, vapor deposition was performed under the conditions shown in Table 1. This will be described in detail below.

A silicon oxide film having a thickness of 0.3 nm is formed on the Si substrate. The conditions at this time are as follows: the pressure is 7.40 × 10 ⁻³ atm, the O ₂ gas flow rate is 5 sccm, the voltage is 7.5 kV, the current is 1.70 mA, the deposition time is 5 sec, and the temperature of the Si substrate is 650 ° C. is there.

Next, a Zr film having a thickness of 0.6 nm is deposited on the silicon oxide film. The conditions at this time are as follows: the deposition source is Zr, the pressure is 4.90 × 10 ⁻⁵ atm, the voltage is 7.5 kV, the current is 1.30 mA, the deposition time is 30 sec, and the temperature of the Si substrate is 650 ° C.

Next, a ZrO ₂ film having a thickness of 19.2 nm is deposited on the Zr film. The conditions at this time are as follows: the deposition source is Zr, the flow rate of O ₂ gas is 5 sccm, the pressure is 7.40 × 10 ⁻³ atm, the voltage is 7.5 kV, the current is 1.70 mA, the deposition time is 1700 sec, The temperature is 500 ° C.

Next, an Ag _0.4 Pd _0.6 film having a thickness of 25 nm is deposited on the ZrO ₂ film. The conditions at this time were as follows: the deposition source was Ag _0.4 Pd _0.6 , the pressure was 7.70 × 10 ⁻⁵ atm, the voltage was 7.5 kV, the current was 0.5 mA, the deposition time was 470 sec, and the temperature of the Si substrate. Is 430 ° C. An XRD (X-Ray Diffraction) pattern at this time is shown in FIG.

FIG. 3 shows the XRD diffraction results of the sample formed up to the Ag _0.4 Pd _0.6 film as described above. From this XRD chart, it was confirmed that the Ag _0.4 Pd _0.6 film had good a-axis orientation and was oriented to (200). Note that the Ag _0.4 Pd _0.6 film functions as an electrode thin film. The ZrO ₂ film is oriented to (200). In FIG. 3, the vertical axis represents intensity, and the horizontal axis represents 2Θ.

The precious metal market price on February 27, 2015 is 4,972yen / g for Pt, 3,095yen / g for Pd, and 72.14yen / g for Ag. Comparing the case where the Pt electrode is used for the PZT film and the case where the Ag _0.4 Pd _0.6 electrode is used for the PZT film, Ag _0.4 Pd _0.6 is 1,886 yen / g, so Ag _0.4 Pd _{The 0.6} electrode can realize a cost reduction of 62% with respect to the Pt electrode.

In this _embodiment, since it is confirmed that the Ag 0.4 _{Pd 0.6} film is oriented in (200) with good a-axis orientation, the ferroelectric of the PZT film or the like on the _Ag 0.4 _{Pd 0.6} film It can be said that a body membrane can be formed.

The natural oxide film on the surface of the Si substrate oriented to (100) is removed using buffered hydrofluoric acid. Thereafter, a silicon oxide film having a thickness of 0.3 nm is formed on the Si substrate. The conditions at this time are the same as in the first embodiment. Next, a Zr film having a thickness of 0.6 nm is deposited on the silicon oxide film. The conditions at this time are the same as in the first embodiment. Next, a ZrO ₂ film having a thickness of 19.2 nm is deposited on the Zr film. The conditions at this time are the same as in the first embodiment.

Next, an Ag _0.9 Pd _0.1 film having a thickness of 25 nm is deposited on the ZrO ₂ film. The conditions at this time are the same as in Example 1 except that the vapor deposition source is Ag _0.9 Pd _0.1 . When the XRD pattern of the sample at this time was acquired, it was confirmed that the Ag _0.9 Pd _0.1 film had a good a-axis orientation and was oriented to (200).

The price of precious metals on February 27, 2015 is as described in Example 1. Comparing the case where the Pt electrode is used for the PZT film and the case where the Ag _0.9 Pd _0.1 electrode is used for the PZT film, Ag _0.9 Pd _0.1 is 374 yen / g, so Ag _0.9 Pd _{0 .1} electrode can realize 92.5% cost reduction compared to Pt electrode.

Next, a PbZr _0.55 Ti _0.45 film having a thickness of 2 μm is formed on the Ag _0.9 Pd _0.1 film by spin coating or the like. The XRD pattern at this time is shown in FIG.

FIG. 4 shows an XRD diffraction result of the sample formed up to the PbZr _0.55 Ti _0.45 film as described above. From this XRD chart, it was confirmed that the PbZr _0.55 Ti _0.45 film was well mono-oriented at (002), and the (200) peak of Ag _0.9 Pd _0.1 was confirmed. In FIG. 4, the vertical axis represents intensity, and the horizontal axis represents 2Θ.

FIG. 5 is a diagram illustrating a piezoelectric hysteresis curve and a piezoelectric butterfly characteristic, which are results of evaluating the piezoelectricity of the PbZr _0.55 Ti _0.45 film of Example 2. As shown in FIG. 5, it was confirmed that the PbZr _0.55 Ti _0.45 film has good piezoelectric hysteresis and piezoelectric butterfly characteristics.

A method for producing the sample of Example 3 (150 nm-Pt / 2 μm-PZT / 150 nm-Ag _0.7 Pd _0.3 / 15 nm-ZrO ₂ / Si) is as follows.
The natural oxide film on the surface of the Si substrate oriented to (100) is removed using buffered hydrofluoric acid. Thereafter, a silicon oxide film is formed on the Si substrate. The conditions at this time are the same as in the first embodiment. Next, a Zr film is deposited on the silicon oxide film. The conditions at this time are the same as in the first embodiment. Next, a ZrO ₂ film having a thickness of 15 nm is deposited on the Zr film. The conditions at this time are the same as in the first embodiment.

Next, an Ag _0.7 Pd _0.3 film having a thickness of 150 nm is deposited on the ZrO ₂ film. The conditions at this time are the same as in Example 1 except that the vapor deposition source is Ag _0.7 Pd _0.3 .

Next, a PbZr _0.55 Ti _0.45 film having a thickness of 2 μm is formed on the Ag _0.7 Pd _0.3 film by spin coating or the like. Next, a Pt film having a thickness of 150 nm is formed on the PbZr _0.55 Ti _0.45 film by sputtering.

  Further, a 2 mm × 15 mm cantilever was produced from the sample of Example 3 described above. The cantilever was subjected to bipolar drive by applying a voltage of ± 5 V at a frequency of 700 Hz, and the piezoelectric butterfly characteristics and piezoelectric hysteresis characteristics by this bipolar drive were evaluated. The evaluation results are shown in FIG. 6 and FIG.

A method for producing a sample of a comparative example (150 nm-Pt / 2 μm-PZT / 150 nm-Ag _0.7 Pd _0.3 / 15 nm-TiO ₂ / Si) is as follows.
A silicon oxide film is formed on the Si substrate, and a TiO ₂ film having a thickness of 15 nm is formed on the silicon oxide film. The TiO ₂ film is formed by forming a Ti film by sputtering and then oxidizing the Ti film. Next, on this TiO ₂ film, an Ag _0.7 Pd _0.3 film having a film thickness of 150 nm, a PbZr _0.55 Ti _0.45 film having a film thickness of 2 μm, and a Pt film having a film thickness of 150 nm are sequentially sampled. It is formed by the same method.

  Further, a 2 mm × 15 mm cantilever was produced from the sample of the above comparative example. The cantilever was subjected to bipolar drive by applying a voltage of ± 5 V at a frequency of 700 Hz, and the piezoelectric butterfly characteristics and piezoelectric hysteresis characteristics by this bipolar drive were evaluated. The evaluation result is shown in FIG.

  As shown in FIGS. 6 and 7A, in the case of the sample of Example 3, good piezoelectric characteristics were obtained. However, in the case of the sample of the comparative example, the leakage current was large and measurement was impossible as shown in FIG. 7B.

  In the case of the sample of the comparative example, it is a columnar PZT, and there are many grain boundaries, and Ag is diffused along the grain boundaries. On the other hand, in the case of the sample of Example 3, since it is a substantially single-crystal PZT film, there are few grain boundaries, and Ag is hardly diffused.

10 Ferroelectric memory 11 Semiconductor layer (Si substrate)
12 ZrO ₂ film 13 Ag _x Pd _1-x film 14 PZT film 15 Electrode 16 Source region 17 Drain region

Claims (7)

A ZrO ₂ film;
An Ag _x Pd _1-x film formed on the ZrO ₂ film;
A ferroelectric film formed on the Ag _x Pd _1-x film;
Comprising
The x satisfies the following formula 1 and is a ferroelectric ceramic.
0.4 ≦ x ≦ 0.9 Formula 1 In claim 1,
Ferroelectric ceramics characterized in that the Ag _x Pd _1-x film is oriented to (200). In claim 1 ,
Ferroelectric ceramics characterized in that the ZrO ₂ film is formed on a Si substrate. A semiconductor layer;
A ZrO ₂ film formed on the semiconductor layer;
An Ag _x Pd _1-x film formed on the ZrO ₂ film;
A ferroelectric film formed on the Ag _x Pd _1-x film;
An electrode formed on the ferroelectric film;
A source region and a drain region formed in the semiconductor layer;
Comprising
The x satisfies the following formula 1;
0.4 ≦ x ≦ 0.9 Formula 1 In claim 4 ,
The ferroelectric memory according to claim 1, wherein the ferroelectric film is a PZT film. Forming a ZrO ₂ film on the semiconductor layer;
Forming an Ag _x Pd _1-x film on the ZrO ₂ film;
Forming a ferroelectric film on the Ag _x Pd _1-x film;
Forming an electrode film on the ferroelectric film;
Forming an electrode on the ferroelectric film by processing the electrode film, the ferroelectric film, the Ag _x Pd _1-x film, and the ZrO ₂ film;
Forming a source region and a drain region in the semiconductor layer by implanting impurity ions into the semiconductor layer using the electrode as a mask;
Comprising
The method of manufacturing a ferroelectric memory, wherein x satisfies the following formula 1.
0.4 ≦ x ≦ 0.9 Formula 1 In claim 6 ,
A method of manufacturing a ferroelectric memory, wherein the ferroelectric film is a PZT film.