JPH065946A - Method of manufacturing ferroelectric thin film - Google Patents

Abstract

(57) [Summary] [Object] To provide a method for manufacturing a ferroelectric thin film in which oxygen vacancies do not occur in a perovskite structure. In a method of manufacturing a PZT thin film 9 provided on an upper surface of a platinum film 7 by using a sol-gel method, a sol solution is applied and dried in the last two film forming steps, and then R
Sintering is performed in an ozone atmosphere at 700 ° C. for 20 seconds using a TA device. Therefore, it is possible to prevent oxygen vacancies from being generated in the perovskite structure of the PZT thin film 9 by inducing radical oxygen ions. [Effect] It is possible to suppress deterioration of the PZT thin film 9 due to repeated polarization inversion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a ferroelectric thin film using a sol-gel method, and to the durability of the thin film.

[0002]

2. Description of the Related Art In recent years, many semiconductor devices, mainly memory cells and capacitors, using a ferroelectric thin film having remanent polarization and polarization inversion have been reported.

As a method of manufacturing a ferroelectric thin film, a method of manufacturing a ferroelectric thin film formed on the gate of a memory cell will be described below in accordance with the manufacturing process of the memory cell 2. 3A and 3B and FIGS. 4A and 4B are cross-sectional configuration diagrams showing the manufacturing process of the memory cell 2.

As shown in FIG. 3A, a P-type silicon substrate 1
7, a silicon oxide thin film 19 is formed by thermal oxidation, and then CVD (Chemical Vapor Deposition) is performed on the upper surface thereof.
The <111> -oriented platinum film 21 is deposited by the method.

The platinum crystal has a preferred orientation. The preferential orientation refers to the property that crystals having orientation grow regardless of the crystallinity of the underlying layer. Therefore, the platinum film 2
No. 1 also has a crystal structure with excellent orientation.

Next, as shown in FIG. 3B, a PZT thin film 23 which is a ferroelectric thin film is formed on the upper surface of the platinum film 21 by the sol-gel method. Since the platinum film 21 has the preferential orientation as described above, it has a crystal structure excellent in orientation. Therefore, the platinum film 21 acts as a base having excellent orientation, and PZT crystals having excellent orientation can be grown on the upper surface thereof.

Here, the sol-gel method will be briefly described. Generally, as a film forming technique, a vacuum vapor deposition method and a sputtering method are generally well known, but it is said that it is difficult to control the composition of these methods in a complicated system such as a ferroelectric substance or a piezoelectric substance. Against such a background, the sol-gel method, which is a chemical method, has recently been applied as a new film forming technique.

In forming a thin film by the sol-gel method, a film can be formed by performing a series of steps of coating, drying and baking a sol solution. Further, by repeating this series of steps, a thin film having a desired film thickness is obtained.

Next, a method of manufacturing a PZT thin film using the sol-gel method will be described in detail. First, the sol solution is prepared as follows. Pb (CH ₃ CO ₂ ) .3H ₂ O (lead acetate trihydrate) was added to methoxyethanol at a molar ratio of 1:70.
After melting at ℃, it is dehydrated by heating to 120 ℃. After cooling the solution to 90 ° C., PbTiO ₃ : Pb
A predetermined amount of titanium isopropoxide and zirconium propoxide are added with stirring so that the molar ratio of TiO ₃ = 47: 53. The solution is continuously heated to 125 ° C. to remove reaction byproducts. Furthermore, methoxyethanol was added to this solution so that the PZT concentration became 0.5 mol / l,
Thereafter, distilled water in an amount of 2 times the molar amount of the PZT sol solution is added, and the partially hydrolyzed solution is used as a coating solution.

Next, spin coating is performed at 5000 rpm for 20 seconds.
After applying the adjusted sol solution under the condition of ec, and drying it on a hot plate at 200 to 300 ° C., in an oxygen atmosphere 6
Bake at 50 ° C. A desired film thickness is obtained by repeating this series of firing steps a plurality of times. In this way, the PZT thin film 23 of perovskite type crystal can be formed.

As shown in FIG. 4A, the PZT
After depositing a platinum film 25 on the upper surface of the thin film 23 by a sputtering method, the silicon oxide thin film 19, platinum film 21, P
The ZT thin film 23 and the platinum film 25 are formed. Next, as shown in FIG. 4B, using the molded platinum film 25 as a mask, arsenic or phosphorus is ion-implanted and thermally diffused to form an n ⁺ -type drain layer 27 and an n ^{+ -type} source layer 29.

In the memory cell 2 thus formed, the PZT thin film 2 is formed by applying the electric field VP between the silicon substrate 17 and the platinum film 25 which is the control electrode.
3 is polarized in the direction of the electric field VP, and the polarization remains even if the electric field VP is removed. On the other hand, the electric field VQ in the opposite direction to the electric field VP
Is applied between the silicon substrate 17 and the control electrode 25, the polarization of the PZT thin film 23 is inverted in the direction of the electric field VQ, and the polarization remains even if the electric field VQ is removed. Therefore,
The memory cell 2 can store information by utilizing the properties of the above-mentioned remanent polarization and polarization inversion of the ferroelectric thin film.

[0013]

[Problems to be Solved by the Invention]
The conventional method for manufacturing a ferroelectric thin film using the gel method has the following problems.

Generally, an insulator exhibiting ferroelectricity has a perovskite type (AB0 ₃ ) crystal structure. In the PZT thin film 23 produced in the manner described above, the perovskite (AB0 ₃₎ there is an empty lattice oxygen in the crystal structure results. The perovskite structure can be drawn as the simple cubic unit cell shown in FIG. As shown in FIG. 5, cations (A ⁺ ) are at the apex, cations (B ⁺ ) are at the body center, and oxygen ions (O ²⁻ ) are at the center. The vacancy of oxygen ions is called oxygen vacancies.

When this vacancy exists in the vicinity of the interface with the platinum film 21, the PZT thin film 23 accompanies repeated polarization inversion.
Will be deteriorated. As described above, when the ferroelectric thin film is used as a memory element, the deterioration of the polarization inversion property and the increase of the coercive voltage due to the deterioration of the PZT thin film 23 have been problems.

Therefore, the present invention solves the above problems and provides a method of manufacturing a ferroelectric thin film in which oxygen vacancies do not occur in the perovskite structure.

[0017]

The method of manufacturing a ferroelectric thin film according to claim 1 is a method of manufacturing a ferroelectric thin film using a sol-gel method in which a sol solution is applied and then baked to form a film. It is characterized in that the first-stage firing is performed in an ozone atmosphere.

[0018]

In the ferroelectric thin film manufacturing method according to the first aspect of the present invention, the firing is performed in an ozone atmosphere.

Therefore, the generation of oxygen vacancies in the perovskite type crystal is prevented by inducing radical oxygen ions.

[0020]

EXAMPLES As an example of a method for manufacturing a ferroelectric thin film according to the present invention, a method for manufacturing a ferroelectric thin film formed on a gate of a memory cell will be described below in accordance with the manufacturing process of the memory cell 1. Explained. 1A and 1B and FIGS. 2A and 2B are cross-sectional views showing the manufacturing process of the memory cell.

First, as shown in FIG. 1A, a silicon wafer 3 is prepared. Next, after the silicon oxide thin film 5 is formed by thermal oxidation, <11 is formed on the upper surface by the CVD method.
A platinum film 7 having a 1> orientation is deposited.

Next, as shown in FIG. 1B, a PZT thin film 9 which is a ferroelectric thin film is formed on the upper surface of the platinum film 7 by the sol-gel method. The PZT thin film is formed by this sol-gel method as follows.

First, three kinds of sol solutions Q, R and T are prepared. The sol solution Q is adjusted to have a molar ratio of Pb: Zr: Ti = 1: 0.58: 0.48. Further, the sol solution R is adjusted so that only the Pb concentration of the sol solution T increases by 5 mol%. In the sol solution T, only the Pb concentration of the sol solution R is 5
Adjusted to increase mol%.

In this embodiment, three kinds of sol solutions Q, R, and T having different Pb concentrations are prepared as described above, and the sol solution T having a high Pb concentration is prepared in the latter film forming process where Pb is easily lost. By using it, we try to make up for the loss of Pb.

Next, the adjusted sol solution Q was applied under the condition of 3000 rpm by the spin coating method, dried at 100 ° C. for 15 minutes, and then RTA (Rapid Thermal Anneelin).
g) Using an apparatus, sintering is performed in an oxygen atmosphere at 750 ° C. for 20 seconds. By this film forming process, it is possible to form the PZT film 9a (film thickness of about 50 nm) which inherits the excellent orientation of the platinum film 7. Further, by repeating this film forming process once again, the PZT film 9b (film thickness of about 50 nm) which inherits the excellent orientation of the platinum film 7 is formed. As described above, in the film forming steps from the beginning to the second, the firing temperature (750 ° C.) is set so that the orientation of the platinum film can be inherited.

Next, the sol solution R which has been adjusted under the condition of 3000 rpm by the spin coating method is applied and dried under the condition of 100 ° C. for 15 minutes, and then the RTA apparatus is used to 700 ° C. in an oxygen atmosphere at 20 ° C. Sinter under the condition of seconds. By performing this film formation process twice, PZT film formations 9c (about 50 nm) and 9d (about 50 nm) are formed. In these film forming steps, the firing temperature (700 ° C.) and time (2 ° C.) that can inherit the excellent orientation of the platinum film 7 and the PZT film 9b without losing necessary components as much as possible.
0 seconds) is set.

Next, the sol solution T which has been adjusted under the condition of 3000 rpm by the spin coating method is applied and dried under the condition of 100 ° C. for 15 minutes, and then the RTA apparatus is used and the temperature is 650 ° C. in the ozone atmosphere at 30 ° C. Sinter under the condition of seconds. By performing this step twice, PZT film formation 9e (about 50 nm)
And 9f (about 50 nm) are formed.

The above-mentioned two film forming steps are used as the final film forming steps to obtain a desired film thickness, and the baking is performed in the ozone atmosphere as described above. Therefore, in the film formations 9e and 9f corresponding to the upper part of the PZT thin film 9, it is possible to prevent oxygen vacancies from being generated in the perovskite structure.

Further, in the two film forming steps, the baking temperature (650) lower than the baking temperature (750 ° C.) in the first film forming step is used.
It is baked at (° C). Therefore, the PZT films 9e and 9f can be formed with almost no loss of necessary components. Moreover, since the baking is performed for a baking time (30 seconds) longer than the baking time (20 seconds) in the first film forming step, it is possible to compensate for the incomplete crystallization due to the decrease in the baking temperature.

Next, as shown in FIG. 2A, after the upper electrode 11 is formed by the lift-off method, the silicon oxide thin film 5, the platinum film 7, the PZT thin film 9 are etched by etching using the resist pattern as a mask. The upper electrode 11 is molded. Next, using the upper electrode 11 formed as shown in FIG. 2B as a mask, arsenic or phosphorus is ion-implanted and thermally diffused to form the n ⁺ -type drain layer 13 and the n ^{+ -type} source layer 15. To do.

Memory cell 1 formed as described above
In the above, the PZT thin film 9 has good composition controllability in the depth direction of the film, and suppresses the generation of oxygen vacancies near the boundary with the upper electrode 11, so that
It was possible to mitigate the decrease in the polarization inversion of the thin film and the increase in the coercive voltage due to repeated polarization inversion.

In the above embodiment, the firing is performed in the ozone atmosphere in the last two film forming steps, but the firing may be performed in the ozone atmosphere in all the film forming steps.

[0033]

According to the ferroelectric thin film manufacturing method of the first aspect of the present invention, the firing is performed in an ozone atmosphere. Therefore, it is possible to prevent generation of oxygen vacancies in the perovskite structure of the ferroelectric thin film due to the induction of radical oxygen ions.

Therefore, deterioration of the ferroelectric thin film due to repeated polarization inversion can be suppressed.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram illustrating a method of manufacturing a crystalline thin film according to an embodiment of the present invention.

FIG. 2 is a manufacturing process diagram illustrating a method of manufacturing a crystalline thin film according to an embodiment of the present invention.

FIG. 3 is a manufacturing process diagram for showing a conventional crystalline thin film.

FIG. 4 is a manufacturing process diagram for showing a conventional crystalline thin film.

FIG. 5 is a diagram for explaining a perovskite structure.

[Explanation of symbols]

 9 ... PZT thin film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location H01L 27/04 C 8427-4M 27/108

Claims (1)

[Claims] 1. A method of manufacturing a ferroelectric thin film using a sol-gel method, in which a sol solution is applied and then baked to form a film, wherein the baking is performed in an ozone atmosphere. Thin film manufacturing method.