JP6973745B2 - Method for manufacturing PZT thin film laminate - Google Patents

Description

The present invention relates to a technique for producing a PZT thin film laminate using lead zirconate titanate (PZT).

A thin film made of lead zirconate titanate (Pb (Zr, Ti) O ₃ ), that is, PZT, which has excellent piezoelectricity and ferroelectricity, is used for non-volatile memory (FeRAM) applications by taking advantage of its ferroelectricity. There is.

Further, in recent years, a MEMS piezoelectric element made of a PZT thin film is being put into practical use by fusion with MEMS technology. Applications such as inkjet heads (actuators), angular velocity sensors, and gyro sensors are expanding as major devices.

It is desired that such a PZT thin film has a large piezoelectric constant and a dielectric strength, but in recent years, when the PZT thin film is formed by sputtering, a perovskite structure is formed between the platinum electrode layer which is the base layer and the PZT thin film. It is known that a PZT thin film can be formed at a temperature lower than 500 ° C. by forming a buffer layer (seed layer) made of, for example, LaNiO _{3, which can improve the piezoelectric constant and the dielectric strength.}

By the way, it is known that the physical constant of the PZT thin film differs depending on the orientation direction. Especially in the tetragonal system, high piezoelectricity and ferroelectricity are obtained by obtaining the c-axis (001) orientation parallel to the polarization axis. Is shown.

_{However, when the buffer layer made of LaNiO 3} is formed between the platinum electrode layer and the PZT thin film and then the PZT thin film is formed by sputtering at a temperature lower than 500 ° C., the plane orientation of the crystal deviates from the original (001) orientation. Therefore, there is a problem that a changing crystal portion is generated.

International Publication No. 2015/137198

The present invention has been made to solve the problems of such conventional techniques, and an object thereof is to form a PZT thin film layer by sputtering on a buffer layer made _{of LaNiO 3 at a temperature of less than 500 ° C.} It is an object of the present invention to provide a technique for preventing the generation of crystal portions having different plane orientations with respect to the original (001) orientation in the PZT thin film layer at the time of formation.

The present invention made to achieve the above object is a method for producing a PZT thin film laminate, in which a platinum electrode layer is provided on a semiconductor substrate via a platinum adhesion layer made of metallic titanium or a titanium oxide. _{And a substrate having a buffer layer made of LaNiO 3} provided on the platinum electrode layer was prepared, and a PZT target doped with a metal containing nickel was used, and the LaNiO _{3 was used at a temperature of less than 500 ° C.} This is a method for manufacturing a PZT thin film laminate, which comprises a step of forming a PZT thin film layer by sputtering on the buffer layer.
The present invention is a method for producing a PZT thin film laminate in which the nickel-containing metal is nickel or a lanthanum-nickel alloy.
The present invention is a method for producing a PZT thin film laminate in which the doping amount of the nickel-containing metal in the PZT target is 0.1 atm% or more and 5 atm% or less with respect to 100 atm% of PZT.

_{According to the present invention, when a PZT thin film layer is formed on a buffer layer made of LaNiO 3} by sputtering at a temperature of less than 500 ° C., PZT grains are used by using a PZT target doped with a metal containing nickel. Since the growth can be suppressed, it is possible to prevent the generation of crystal portions having different plane orientations from the original (001) orientation in the PZT thin film layer.

(A) (b): Cross-sectional view showing a schematic configuration of an example of a PZT thin film laminate produced by the present invention. Transmission electron microscope (TEM) photograph of the PZT thin film of Comparative Example 1

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
1A and 1B are cross-sectional views showing a schematic configuration of an example of a PZT thin film laminate produced by the present invention.

As shown in FIG. 1A, the PZT thin film laminate 1 of this example is made of metallic titanium (Ti) or titanium on a _{silicon oxide (SiO 2) layer 3 formed on a Si substrate 10 which is a semiconductor substrate.} A platinum (Pt) adhesion layer 4 made of an oxide (TiO _X ), a platinum electrode layer 5 made of platinum (Pt), a buffer layer (seed layer) 6, and a PZT thin film layer 7 are formed in this order. Is what you are doing.

The platinum electrode layer 5 functions as a lower electrode layer when the device is configured. In that case, as shown in FIG. 1 (b), the upper electrode layer 8 is placed on the PZT thin film layer 7. It will be provided.

In order to manufacture the PZT thin film laminate 1 of this example, a SiO ₂ layer 3, a platinum adhesion layer 4 made of metallic titanium or a TiO _x layer, and a platinum electrode layer 5 are formed on the Si substrate 10 in this order. Prepare the board.

Then, a buffer layer 6 _{made of LaNiO 3} is formed on the surface of the platinum electrode layer 5 of this substrate by sputtering.
The buffer layer 6 can be formed by the RF sputtering method.

In this case, a LaNiO ₃ target is used as the sputtering target, and high-frequency power (for example, 13.56 MHz) is applied to the sputtering in, for example, argon gas, which is a sputtering gas, to perform sputtering.

The substrate temperature during sputtering is preferably set to a temperature lower than 500 ° C.
For example, it is preferable to set the temperature to 435 ° C or higher and 485 ° C or lower.

The thickness of the buffer layer 6 made of LaNiO _{3 is preferably set to 100 nm or less.}
If _{the thickness of the buffer layer 6 made of LaNiO 3} exceeds 100 nm, it may not be possible to form a film having a perovskite single-phase structure.

Further, the PZT thin film layer 7 can be formed by the RF sputtering method.
In the present invention, a nickel (Ni) -containing metal-doped PZT target is used as the sputtering target.

Here, examples of the metal containing nickel (Ni) include nickel or a lanthanum-nickel alloy (LaNi ₅ ).
That is, in the present invention, a nickel-doped PZT target or a lanthanum-nickel alloy-doped PZT target can be used.

In the case of the present invention, the doping amount of the nickel-containing metal in the PZT target is not particularly limited, but it is preferably set to 0.1 atm% or more and 5 atm% or less with respect to 100 atm% of PZT, and more preferably 100 atm. % Is 0.5 atm% or more and 5 atm% or less, more preferably 0.5 atm% or more and 1 atm% or less with respect to 100 atm% of PZT.

If the doping amount of the nickel-containing metal in the PZT target is less than 0.1 atm% with respect to 100 atm% of PZT, the effect of the present invention cannot be sufficiently exerted, and if it exceeds 5 atm%, the perovskite single-phase structure is formed. It may not be possible to form a film of.

As a film forming condition, sputtering is performed by applying high frequency power (for example, 13.56 MHz) in a sputter gas such as argon gas.

The substrate temperature during sputtering is preferably set to a temperature lower than 500 ° C.
For example, it is preferable to set the temperature to 430 ° C. or higher and 485 ° C. or lower.

Hereinafter, examples of the present invention will be described together with comparative examples.
[Example 1]
<Formation of a buffer layer made of _{LaNiO 3>}
On a Si substrate having a diameter of 8 inches, a SiO _{2 layer having a thickness of 100 nm, a TiO x} layer having a thickness of 35 nm, which is a platinum adhesion layer, and a Pt layer having a thickness of 100 nm, which is a platinum electrode layer, were formed in this order. An evaluation substrate was used.

Using this evaluation substrate, a buffer layer composed of _three LaNiO layers having a film thickness of 100 nm was formed on the surface of the Pt layer by the RF magnetron sputtering method.
In this case, a LaNiO ₃ target was used as the sputtering target, and argon gas was used as the sputtering gas to set the pressure at 0.1 Pa.
Further, the substrate temperature during sputtering was controlled to be 485 ° C.

<Formation of PZT thin film layer>
A PZT thin film layer having a film thickness of 2 μm was formed on the surface of the buffer layer made of _{LaNiO 3 of the} evaluation substrate by the RF magnetron sputtering method.
In this case, as the sputtering target, a PZT target having a nickel doping amount of 0.5 atm% with respect to 100 atm% of PZT was used.
As the film forming conditions, argon gas was used as the sputtering gas, and the pressure was 0.1 Pa.
Further, the substrate temperature during sputtering was controlled to be 485 ° C.

[Example 2]
A PZT thin film layer was formed under the same conditions as in Example 1 except that a PZT target having a doping amount of lanthanum-nickel alloy (LaNi _{5) of 0.5 atm% with respect to 100 atm% of PZT was used as the sputtering target.}

[Comparative Example 1]
A PZT thin film layer was formed under the same conditions as in Example 1 except that a PZT target not doped with metal was used as the sputtering target.

[Comparative Example 2]
A PZT thin film layer was formed under the same conditions as in Example 1 except that a PZT target having a lanthanum (La) doping amount of 0.5 atm% with respect to 100 atm% was used as the sputtering target.

[Evaluation results]
<Crystal orientation of PZT thin film layer>
The orientation of the crystals of the PZT thin film layers formed by Examples 1 and 2 and Comparative Examples 1 and 2 was observed using an optical microscope and a transmission electron microscope (TEM). The results are shown in FIG. 2 and Table 1.

As shown in the TEM image of FIG. 2, in the case of Comparative Example 1 using the PZT target not doped with metal, the plane orientation of the crystal is the original (from the adjacent region A to the region B with a certain boundary plane as a boundary). 001) It can be seen that the orientation is deviated and changed.
On the other hand, in the PZT thin film layers formed by Examples 1 and 2 and Comparative Example 2, such a deviation in the orientation of the crystals was not observed.

<Evaluation of piezoelectric characteristics of PZT thin film layer>
A MIM (metal-insulator-metal) structure using Pt as an upper electrode layer was formed on the PZT thin films formed in Examples 1 and 2 and Comparative Examples 1 and 2, and the piezoelectric characteristics were evaluated. The results are shown in Table 1.

As shown in Table 1, a significant difference in piezoelectric constants between Examples 1 and 2 and Comparative Example 2 using a metal-doped PZT target and Comparative Example 1 using a metal-doped PZT target. Was not seen.

<Evaluation of dielectric strength of PZT thin film layer>
An MIM structure using Pt as an upper electrode layer was formed on the PZT thin film formed by Examples 1 and 2 and Comparative Examples 1 and 2, and an ultra-high resistance / ultra-low current measurement electrometer (6514 type manufactured by Caseley Co., Ltd.). ) Was used to measure the insulation withstand voltage. The results are shown in Table 1.

As shown in Table 1, in Example 1 using a nickel-doped PZT target and Example 2 using a lanthanum-nickel alloy-doped PZT target, Comparative Example 1 using a metal-undipped PZT target. Although the value of the insulation withstand voltage was slightly lower than that of the above, it was within the range where there was no problem in practical use.

On the other hand, in Comparative Example 2 using the PZT target doped with lanthanum, the value of the withstand voltage was significantly lower than that in Comparative Example 1 using the PZT target not doped with metal.

From the above, it can be confirmed that according to the present invention, it is possible to prevent the generation of crystal portions having different plane orientations from the original (001) orientation in the PZT thin film layer while maintaining a good piezoelectric constant and dielectric strength. rice field.

1 ... PZT thin film stack 3 ... SiO ₂ layer 4 ... platinum adhesion layer 5 ... platinum made of the electrode layer 6 ... LaNiO ₃ buffer layer 7 ... PZT thin film layer 10 ... Si substrate (semiconductor substrate)

Claims (2)

A method for manufacturing a PZT thin film laminate,
A substrate having a platinum electrode layer provided on a semiconductor substrate via a platinum adhesion layer made of metallic titanium or titanium oxide and a _{buffer layer made of LaNiO 3} provided on the platinum electrode layer was prepared.
A method for producing a PZT thin film laminate, which comprises a step of forming a PZT thin film layer by sputtering on a buffer layer made of _{LaNiO 3 at} a temperature of less than 500 ° C. using a PZT target doped with a lanthanum-nickel alloy. The PZT doping amount of the metal containing the nickel at the target, the production method of the PZT thin film laminate according to claim 1, wherein at most 0.1 atm% or more 5 atm% relative PZT100atm%.

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