JPH065947A - Manufacture of ferroelectric thin film - Google Patents

Abstract

PURPOSE:To provide a method for manufacturing a ferroelectric thin film in which ideal sol solution can be sintered in a state inherited with excellent orientation of a platinum film. CONSTITUTION:A method for manufacturing a ferroelectric thin film has the step of forming a PZT thin film 9 provided on an upper surface of a platinum film 7 by a sol-gel method, and comprises the steps of adjusting compositions of ideal sol solution Q and sol solution T, and sintering the solution T on the film 7 thereby to form a PZT film 9d inherited with orientation of the film 7. Since an interstitial distance of the film 9d is similar to that of the ideal sol solution of a sintered state, the ideal sol solution can be sintered in a state inherited with excellent orientation (orientation of the film 7) of the film 9d.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a ferroelectric thin film using a sol-gel method, and more particularly to sintering an ideal sol solution.

[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, PZT was added to this solution.
Methoxyethanol was added to a concentration of 0.5 mol / l, and then distilled water was added in an amount twice that of the PZT sol solution, and the partially hydrolyzed solution was used as a coating solution.

Next, spin coating is performed at 5000 rpm for 20 seconds.
The adjusted sol solution is applied under the condition of ec, dried at 200 to 300 ° C. on a hot plate, and then baked at 650 ° 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.

Further, as shown in A of FIG.
After the platinum film 25 is deposited on the upper surface of the T thin film 23 by the sputtering method, the silicon oxide thin film 19, the platinum film 21, and the platinum film 21 are etched by etching using the resist pattern as a mask.
The PZT thin film 23 and the platinum film 25 are formed. Next, as shown in FIG. 4B, arsenic or phosphorus is ion-implanted and thermally diffused using the formed platinum film 25 as a mask,
An n ^{+ type} drain layer 27 and an n ^{+ type} source layer 29 are formed.

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]

Recently, in the perovskite type crystal of PZT obtained by sintering a sol solution, the composition of an ideal sol solution capable of obtaining a film having the highest ferroelectricity has been reported. ing.

Therefore, in order to obtain a PZT thin film exhibiting better ferroelectricity, this ideal sol solution was added to the platinum film 2 as described above.
It is conceivable to sinter in a state where the excellent orientation of No. 1 is inherited. However, according to the conventional method, the platinum film 2
When the PZT thin film was formed on the upper surface of the No. 1, there were the following problems.

When the ideal sol solution is baked and crystallized,
The crystal could not inherit the orientation of the platinum film 21. This is because there is a gap between the interstitial distance of the crystal when the ideal sol solution is sintered and the interstitial distance of the platinum film 21 having the <111> orientation, and the relationship between the interstitials is the inheritance of orientation. Because it was not suitable. That is, it was not possible to form a PZT thin film exhibiting better ferroelectricity.

Therefore, the present invention solves the above-mentioned problems and provides a method for producing a ferroelectric thin film capable of sintering an ideal sol solution in a state where the excellent orientation of the platinum film is inherited. That is.

[0017]

A method of manufacturing a ferroelectric thin film according to claim 1 is a method of forming a ferroelectric thin film on the upper surface of a <111> oriented platinum film by using a sol-gel method. Then, the ferroelectric thin film is divided into a plurality of ferroelectric films, and at least one intermediate layer is provided between the uppermost ferroelectric film and the platinum film. As the layer progresses, the interstitial distance is sequentially changed within a range where the crystal orientation of the underlying layer can be inherited, and an ideal sol solution having a composition exhibiting excellent ferroelectricity by firing is used to form the uppermost ferroelectric substance. The feature is that a film is formed.

[0018]

The method of manufacturing a ferroelectric thin film according to claim 1 is a method of forming a ferroelectric thin film on the upper surface of a platinum film having a <111> orientation by using a sol-gel method. Is formed by dividing into a plurality of ferroelectric film formation, at least one intermediate layer is provided between the uppermost ferroelectric film formation and the platinum film, and as the platinum film is advanced to the upper layer,
The inter-lattice distance is sequentially changed within a range where the crystal orientation of the underlayer can be inherited, and the uppermost ferroelectric film is formed by firing using an ideal sol solution having a composition exhibiting excellent ferroelectricity. It is characterized by that.

Therefore, it is possible to sinter the ideal sol solution in the previous period while inheriting the orientation of the platinum film.

[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, four kinds of sol solutions Q, R, S and T are prepared. The sol solution Q is an ideal sol solution, Pb: Z
Adjust so that the molar ratio is r: Ti = 1.05: 0.52: 0.48. Further, the sol solution R is adjusted to have a molar ratio of Pb: Zr: Ti = 1.05: 0: 1. Also, the sol solution S is P
Adjust so that the molar ratio is b: Zr: Ti = 1.05: 0.2: 0.8. Further, the sol solution T is Pb: Zr: Ti = 1.05: 0.4:
Adjust so that the molar ratio is 0.6.

Next, the adjusted sol solution R is applied to the upper surface of the platinum film 7 by spin coating under the condition of 3000 rpm.
After drying at 00 ℃ for 15 minutes, RTA (Rapid Therma
l Anneeling) device, 700 ℃ in oxygen atmosphere,
PZT film 9a, which is an intermediate layer, is sintered under the condition of 20 seconds.
(Film thickness of about 50 nm) is formed. At this time, the sol solution R
The composition is adjusted so that the interstitial distance Dr during sintering approximates the interstitial distance D21 of the platinum film 21 (Dr> D21). Therefore, the excellent orientation of the platinum film 7 can be inherited by the PZT film 9a. Further, this film forming process is repeated once more to form the PZT film 9b (film thickness 5
0 nm) is formed. At this time, the PZT thin film 9b can similarly inherit the excellent orientation of the platinum film 7.

Next, the adjusted sol solution S is formed into a PZT film 9
It was coated on the upper surface of b by spin coating under the condition of 3000 rpm, dried at 100 ° C. for 15 minutes, and then sintered using an RTA device in an oxygen atmosphere at 700 ° C. for 20 seconds to form an intermediate layer of PZT. A film 9c (film thickness of about 50 nm) is formed. At this time, the composition of the sol solution S is adjusted so that the interstitial distance Ds during sintering approximates the interstitial distance Dr of the PZT film 9b (Ds> Dr). Therefore, the excellent orientation of the PZT film 9b can be inherited by the PZT film 9c.

Next, the adjusted sol solution T is formed into a PZT film 9
It is coated on the upper surface of c by spin coating at 3000 rpm, dried at 100 ° C. for 15 minutes, and then sintered using an RTA apparatus in an oxygen atmosphere at 700 ° C. for 20 seconds to form PZT as an intermediate layer. A film 9d (film thickness of about 50 nm) is formed. At this time, the composition of the sol solution T is adjusted so that the interstitial distance Dt during sintering approximates the interstitial distance Ds of the PZT film 9c (Dt> Ds). Therefore, the excellent orientation of the PZT film 9c can be inherited by the PZT film 9d. The above is the PZT film 9d which is the intermediate layer.
Means that the orientation of the platinum film 7 is inherited.

Next, the adjusted ideal sol solution Q was applied on the upper surface of the PZT film 9d by spin coating under the condition of 3000 rpm and dried at 100 ° C. for 15 minutes, and then, using an RTA apparatus, in an oxygen atmosphere. PZT film 9e (about 50 nm) is formed by sintering at 750 ° C. for 20 seconds. At this time, the composition of the sol solution R is adjusted so that the interstitial distance of the PZT film 9d approximates to the interstitial distance Dq of the ideal sol solution Q in the sintered state (Dq> Dt). Therefore,
The ideal sol solution Q can be sintered in a state where the excellent orientation of the PZT film 9d is inherited. Further, by repeating this film forming process, a PZT film 9f is formed.
At this time, similarly, the PZT film 9f can inherit the excellent orientation of the PZT film 9e. In this example, the PZT films 9e and 9f are used as the uppermost layers and are formed using an ideal sol solution.

As described above, the orientation of the platinum film 7 is set to P
The ideal sol solution Q is inherited by the ZT films 9a, 9b, 9c and 9d, and the ideal sol solution Q is sintered on the upper surface of the PZT film 9d so that the orientation of the platinum film 7 is inherited.
It is possible to form the PZT films 9e and 9f that have been fired.

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 and the upper electrode are etched by etching using the resist pattern as a mask. Mold 11. 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.

The PZT thin film of the ferroelectric memory cell 1 formed as described above had a good film orientation, and the remanent polarizability was not significantly reduced by repeated polarization inversion.

[0031]

The method of manufacturing a ferroelectric thin film according to claim 1 is a method of forming a ferroelectric thin film on the upper surface of a platinum film having a <111> orientation by using a sol-gel method. The body thin film is formed by dividing it into a plurality of ferroelectric films, and at least one intermediate layer is provided between the uppermost ferroelectric film and the platinum film. , The inter-lattice distance is sequentially changed within a range where the crystal orientation of the base can be inherited, and the uppermost ferroelectric film is formed by firing using an ideal sol solution having a composition showing excellent ferroelectricity. It is characterized by doing.

Therefore, it is possible to form a ferroelectric thin film exhibiting better ferroelectricity.

[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.

[Explanation of symbols]

 7 ... Platinum film 9 ... PZT thin film 9a, 9b, 9c, 9d ... PZT film formation (intermediate layer) 9e, 9f ... PZT film formation (uppermost layer)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication H01L 27/108

Claims (1)

[Claims] 1. A method of forming a ferroelectric thin film on a top surface of a <111> oriented platinum film by using a sol-gel method, wherein the ferroelectric thin film is divided into a plurality of ferroelectric film formations. At the same time, an intermediate layer of at least one layer is provided between the uppermost ferroelectric film and the platinum film, and as the platinum film is advanced to the upper layer, a lattice is formed within a range where the crystal orientation of the underlayer can be inherited. A method for producing a ferroelectric thin film, comprising forming an uppermost ferroelectric film by using an ideal sol solution having a composition exhibiting excellent ferroelectricity by sequentially changing the distance.