JP2002289606A - Manufacturing method of ferroelectric thin-film device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the intensity of ferroelectric devices utilizing a good step coverage characteristic of a minute droplet material solution deposit method, and to manufacture a ferroelectric thin film with good crystal orientation in a sure and stable manner. SOLUTION: A manufacturing process of the ferroelectric thin-film devices is to deposit a Sol-gel material for ferroelectric in minute droplets on a substrate, including the process of forming the ferroelectric thin film by heating and crystallization and the process of surface cleaning by ozone irradiation to a base electrode prior to the deposit of the Sol-gel material, and to continuously perform the processes without exposure to the atmosphere. Furthermore, a degreasing process and a crystallization annealing process are performed under reduced pressure after the deposit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ceramic thin film used for a ferroelectric thin film device, a piezoelectric device and the like. In particular, the present invention relates to a method for manufacturing a device that requires a high degree of crystal structure control in order to express a high function as a ferroelectric.

[0002]

2. Description of the Related Art Ferroelectric materials typified by PZT (lead zirconate titanate) are insulative capacitors for storage elements such as CMOS because of their high relative permittivity, and non-volatile storage elements because they have spontaneous polarization. It is widely applied to pressure sensors and actuators due to its piezoelectricity. Often, ferroelectric materials are utilized in the form of thin films. As a method for producing a ferroelectric thin film, a solution coating method, a sputtering method, a vapor deposition method, a laser ablation method, or the like is used. In recent years, SBT (Sr, Bi, Ta-based oxide) has attracted attention as a ferroelectric material. More recently, a device for forming a ferroelectric thin film by depositing SBT in a fine mist state on a substrate and heating and crystallizing the SBT (apparatus example: PRIMAXX L
iquid Source Misted Chemical Deposition apparatus (hereinafter referred to as LSMCD apparatus) has been published. Since this apparatus can provide good step coverage, it is considered to be an effective production method for high integration of ferroelectric devices.
Currently being developed into industrial production processes.

[0003]

However, in the above-mentioned apparatus, MOD (Metal Organic Deposit) is used as a solution material.
ion) material is used. The MOD material has a high stability as a material and has a feature that it does not change for a long time even when exposed to the atmosphere. Generally, the raw material set to the LSMCD device is
Since the raw material tank is set in the apparatus after it is once exposed to the atmosphere, a highly stable MOD material is used.
However, in the case of film formation using a MOD material, there is a disadvantage that the crystal orientation of the formed ferroelectric film is less likely to be caused than in the case of film formation using a sol-gel material. In order to obtain good ferroelectricity, it is necessary to obtain a high remanent polarization (Pr).
It is required to obtain a squareness of the hysteresis curve in order to obtain an improvement in N ratio and characteristic stability. Particularly, in order to meet recent severe demands for high integration, the above-mentioned high Pr and squareness are indispensable conditions, and precise alignment control of the ferroelectric film is indispensable to obtain these. Generally, SBT has a preferred orientation in the C-axis direction derived from its crystal structure. However, SBT preferentially oriented in the C-axis direction is inferior in polarizability and has a high Pr
It is difficult to get One method of obtaining a high Pr by SBT is to obtain a random crystal orientation. However, when the MOD material is used as a film forming material, there is a problem in performing the above-described orientation control.

[0004]

According to a first aspect of the present invention, there is provided a method of manufacturing a ferroelectric thin film device, comprising:
The method further comprises a step of forming a ferroelectric thin film by depositing the material on a substrate in a fine mist state and heating and crystallizing the deposited material.

[0005] According to the above characteristics, MO is used as a film forming material.
There is an effect that more precise alignment control can be performed as compared with the conventional case using the D material.

A method of manufacturing a ferroelectric thin film device according to a second aspect of the present invention is characterized in that a lower electrode is irradiated with plasma, ions, and ozone to clean the surface, and then a ferroelectric thin film is formed.

[0007] According to the above feature, by cleaning the surface, it is possible to obtain an effect that a ferroelectric thin film with less foreign matter and excellent crystal orientation can be formed on the upper surface thereof. That is, in the case of claim 2, the effect of claim 1 becomes more remarkable.

According to a third aspect of the present invention, there is provided a method of manufacturing a ferroelectric thin film device, wherein the steps according to the first and second aspects are performed continuously without exposing to the atmosphere.

According to the above-described feature, an effect is obtained that a ferroelectric thin film having a small amount of foreign matter and a stable crystal orientation can be formed at the upper position of the lower electrode. That is, in the case of the third aspect, the effects of the first and second aspects become more remarkable.

[0010] A method of manufacturing a ferroelectric thin film device according to a fourth aspect of the present invention is characterized in that the degreasing step and the crystallization annealing of the deposited ferroelectric film are performed under reduced pressure.

According to the above feature, an effect is obtained that a ferroelectric thin film with less foreign matter and stable crystal orientation can be formed at the upper position of the lower electrode. That is, in the case of the fourth aspect, the effects of the first, second and third aspects become more remarkable.

According to the first to fourth aspects of the present invention, by using the present manufacturing method, high integration is achieved by utilizing the good step coverage of the mist type raw material solution deposition method, and in addition, a good crystal orientation is obtained. Ferroelectric thin films can be produced reliably and stably, and the effect is particularly remarkable in the industrial field of producing highly integrated ferroelectric thin film devices.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

(Example 1) A 4-inch diameter silicon substrate having a platinum electrode layer on the surface was set in an LSMCD apparatus. A MOD type SBT film forming raw material solution having a concentration of 0.2 mol / L was
It was mounted on the SMCD device and supplied to the atomizing mechanism in the treatment to generate a submicron-sized atomized raw material solution. Subsequently, the atomized raw material solution was introduced into the apparatus chamber, and a 120 nm deposition was deposited on the substrate under reduced pressure at room temperature. The substrate is taken out, put into an electric furnace, subjected to a desolvation step at 260 ° C. in an O2 atmosphere for 5 minutes, and then put into a high-speed heat treatment apparatus.
Annealing crystallization was performed at 700 ° C. in an O 2 atmosphere for 1 minute.

As an upper electrode, a circular platinum having a diameter of 1 mm was formed by sputtering.

An SBT thin film device was manufactured as described above. FIG. 1 shows a cross-sectional structure of this device. 10 is a silicon substrate, 20 is a Pt layer, 30 is an SBT layer, and 40 is a circular Pt having a diameter of 1 mm.

Example 2 A 4-inch diameter silicon substrate having a platinum electrode layer on the surface was set in an LSMCD apparatus. A sol-gel type SBT film forming raw material solution having a concentration of 0.5 mol / L is
Attached to the LSMCD device and supplied to the atomization mechanism within the measure,
A submicron sized feedstock solution was generated. Subsequently, the atomized raw material solution was introduced into the apparatus chamber, and a 120 nm deposition was deposited on the substrate under reduced pressure at room temperature.

After the desolvation step, the upper Pt
The device fabrication process leading to film formation was performed under the same conditions as in Example 1, and an SBT thin film device was fabricated.

Example 3 A 4-inch diameter silicon substrate having a platinum electrode layer on the surface was prepared and set in an LSMCD apparatus. O2 is supplied to the ozone generator installed in the device.
Introduce gas and gas coming out of it (including 10% concentration O3
O2 gas) was sprayed onto the substrate at a flow rate of 5 L / min, and the surface was cleaned under reduced pressure at a substrate temperature of 200 ° C.

The subsequent device fabrication steps from atomization of the MOD type SBT film forming raw material solution, deposition on the substrate, and upper Pt film formation were performed under the same conditions as in Example 2.
A thin film device was fabricated.

Example 4 The steps from atomization of the MOD type SBT film forming raw material solution to deposition on the substrate were performed under the same conditions as in Example 1. Subsequently, the substrates were sequentially moved to an electric furnace and a high-speed heat treatment apparatus installed in the same LSMCD apparatus, and a desolvation step was performed at 260 ° C. and an O 2 atmosphere for 5 minutes, respectively, and at 700 ° C. and an O 2 atmosphere for 1 minute. Was annealed and crystallized.

The subsequent upper Pt film formation was carried out under the same conditions as in Example 2 to produce an SBT thin film device.

(Example 5) The desolvation step was performed in a 600 Torr O2 atmosphere at 260 ° C. for 5 minutes, and the annealing crystallization was performed at 600 Torr.
An O2 atmosphere was performed at 700 ° C. for 1 minute.

The other steps were carried out under the same conditions as in Example 4 to produce an SBT thin film device.

With respect to the SBT thin film devices manufactured according to the above examples, a ferroelectric hysteresis curve as shown in FIG. 2 was obtained for all samples, and it was confirmed that a ferroelectric device was formed. Next, the crystallinity and hysteresis characteristics were measured and evaluated. The results are shown below.

First, the crystallinity was investigated. FIG. 3 shows an X-ray diffraction result of the SBT thin film device of Example 1, and similar X-ray diffraction results were obtained for the SBT thin film devices of Examples 2, 3, 4, and 5. The surface indices (1 1 5), (0
Focusing on (0 4) and (0 0 10), the peak count and (0 0
Table 1 summarizes the peak count ratio based on 4).
Shown in

[0027]

[Table 1] According to FIG. 3 and Table 1, the thin film produced was (1) only SBT, no heterophase, and (2) (0 0 C), (a 0
(0), (1 1 C), (a 0 c), (aa 0) and peaks corresponding to various surface indices are detected, and (3) (0 0 4) (1 15), (0 0 10) Since the peak count ratio is smaller than the bulk material, that the crystallinity is good,
It was found that the crystal orientation was random and the preferred orientation in the C-axis direction was weak, indicating that the crystal orientation was desirable. further,
(1 1 5), (0 0 10)
The peak count ratio was small, indicating that the randomness of the crystal orientation was improved.

Next, the hysteresis characteristics were evaluated.
+3 V to -3 was applied to the upper and lower electrodes of all the samples of Examples 1 to 6.
The amount of polarization between the electrodes was measured by applying an electric field of V, and the residual polarization value (2Pr; the amount of polarization between points A and B shown in FIG. 4) was examined for the obtained hysteresis curve. Table 2 shows the 2Pr values thus obtained.

[0029]

[Table 2] The values of 2Pr increased as Examples 2, 3, 4, and 5 were obtained, and it was found that the ferroelectric characteristics were improved.

As described above, the SBT for ferroelectrics
When a material is deposited on a substrate in a fine mist state and heated and crystallized to form a ferroelectric thin film, when a Sol-gel material is used as an SBT material, more preferably (1)
After irradiating the surface of the lower electrode with ozone and washing the surface, an SBT thin film is formed. (2) The SBT thin film forming process using a Sol-gel material including (1) is continuously performed without exposing to the atmosphere. Performing at least one of the degreasing step and the crystallization annealing step under reduced pressure, using SB with the Sol-gel material.
When combined with the formation of a T thin film, the SBT material for ferroelectric material is deposited in a fine mist state on a substrate, and heated and crystallized to form a ferroelectric thin film.
It is possible to form a ferroelectric thin film in which the randomness of the crystal orientation is improved and the ferroelectric characteristics represented by the remanent polarization value are excellent as compared with the case where the MOD material is used as the T material. I understand.

Although the SBT material has been described above, the present invention has the same effect with other Sol-gel materials for ferroelectrics. Although Pt has been described as the upper and lower electrode materials, the present invention has the same effect for other electrode materials.

[0032]

According to the present invention, when a liquid material for a ferroelectric is deposited in a fine mist state on a substrate and heated and crystallized to form a ferroelectric thin film, a Sol-gel material is used as the liquid material. Furthermore, the lower electrode is cleaned by irradiating it with ozone before the deposition of the Sol-gel material, and the degreasing and crystallization annealing steps are continuously performed without exposing to the atmosphere throughout the entire ferroelectric thin film formation process. In the ferroelectric thin film device manufactured by the manufacturing method of the present invention in which any one or more of the following is combined with the formation of a ferroelectric thin film using the Sol-gel material, a conventional MOD material is used as a liquid material. It is possible to improve the crystal orientation randomness of the ferroelectric, and to form a ferroelectric thin film having good ferroelectric characteristics typified by the remanent polarization value. Since the ferroelectric thin film device can be produced stably and reliably, the effect in the industrial production field is remarkable.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross-sectional structure of an SBT thin film device manufactured in Example 1.

FIG. 2 is a schematic diagram showing the results of measuring the hysteresis characteristics of the SBT thin film devices manufactured in Examples 1 to 5.

FIG. 3 is a schematic view showing the result of measuring X-ray diffraction of the SBT thin film device manufactured in Example 1.

FIG. 4 is a diagram showing a remanent polarization value (2Pr) of the SBT thin film device manufactured in Examples 1 to 5.

[Explanation of symbols]

 10. Silicon substrate, 20. Pt layer 30. SBT layer 40. 1mm diameter circular Pt

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F058 BA05 BA09 BA11 BC03 BD05 BE04 BF41 BH01 BJ01 5F083 FR01 JA14 JA38 PR00 PR23 PR34

Claims (4)

[Claims] 1. A ferroelectric material comprising a step of depositing a Sol-gel material for a ferroelectric material in a fine mist state on a substrate and heating and crystallizing the same to form a ferroelectric thin film. A method for manufacturing a thin film device. 2. The method for manufacturing a ferroelectric thin film device according to claim 1, wherein a ferroelectric thin film is formed after irradiating the lower electrode with plasma, ions and ozone to clean the surface. 3. A method for manufacturing a ferroelectric thin film device, wherein the steps according to claim 1 and 2 are continuously performed without exposing to the atmosphere. 4. The method according to claim 1, wherein the degreasing step and the crystallization annealing of the deposited ferroelectric film are performed under reduced pressure.
4. The method for producing a ferroelectric thin film device according to 2 or 3.