JPH065948A - Manufacture of ferroelectric thin film - Google Patents

Abstract

PURPOSE:To provide a method for manufacturing a ferroelectric thin film in which necessary components are not lost while growing a crystal inherited with excellent orientation of a base. 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 a step of forming films divided into six substeps in such a manner that the initial two steps sinter at a sintering temperature (750 deg.C) capable of inheriting excellent orientation of the film 7 for 20 sec of a sintering time and that the last two steps sinter at the sintering temperature (650 deg.C) lower than that of the initial two steps for longer time (30sec) than that of the initial two steps. The last two steps prevent failure of necessary components by lowering the sintering temperature, and supplement incompleteness of crystallization due to a drop of the sintering temperature by extending the sintering time.

Description

Detailed Description of the Invention

[0001]

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

[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 silicon oxide thin film 19 is formed by thermal oxidation on a P-type silicon substrate 17 with element isolation, and then a CVD (Chemical Vap) is formed on the upper surface thereof.
The platinum film 21 is deposited by the our Deposition 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 21 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. At this time, the platinum film 21 serves as a base having excellent orientation as described above, and PZT crystals having excellent orientation can be grown.

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.
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.

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 formed as described above, the ferroelectric thin film is polarized in the electric field VP direction by applying the electric field VP between the silicon substrate 17 and the platinum film 25 which is the control electrode. , The polarization remains even after the electric field VP is removed. On the other hand, by applying an electric field VQ opposite to the electric field VP between the silicon substrate 17 and the control electrode 25, the polarization of the ferroelectric thin film is reversed in the direction of the electric field VQ, and the polarization remains even if the electric field VQ is removed. To do. Therefore, the memory cell 2 can store information by utilizing the properties of the remanent polarization and polarization inversion of the ferroelectric thin film as described above.

[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, in order for the ferroelectric thin film to exhibit the remanent polarization and the polarization reversal as described above, it is necessary to have a perovskite type crystal structure excellent in orientation.

Therefore, the PZT thin film 2 which is a ferroelectric thin film
In the production by the sol-gel method of No. 3, since the applied sol solution is in an amorphous state, it is necessary to bake at about 500 to 750 ° C. in order to acquire the property of the ferroelectric substance. It was Furthermore, the platinum film 2 that is the base
In order to inherit the excellent orientation of No. 1, firing at a high temperature (about 750 ° C.) was required. However, when firing is performed at such a high temperature (750 ° C.), there is a problem that some components having a composition with a relatively low melting point are lost.

When the lost component is necessary for the crystal structure, a defective perovskite type crystal structure may be obtained, and the properties of the ferroelectric thin film 23 may be impaired.

Therefore, the present invention solves the above-mentioned problems and provides a method for manufacturing a ferroelectric thin film in which necessary crystals are not lost while growing a crystal that inherits the excellent orientation of the underlayer. is there.

[0018]

A method of manufacturing a ferroelectric thin film according to claim 1, wherein the ferroelectric thin film is formed on the upper surface of the crystalline first film by using a sol-gel method. The film forming step of applying the solution and then baking is performed a plurality of times, and in the initial film forming step of the plurality of film forming steps, baking is performed so that the orientation of the crystalline first film can be inherited. Firing is performed at a temperature, and in the film forming step in the latter half of the plurality of film forming steps, baking is performed at a temperature lower than the baking temperature in the initial film forming step.

In the method of manufacturing a ferroelectric thin film according to a second aspect, the film-forming step in the latter half of the first half is characterized by baking for a longer baking time than the baking time in the initial film-forming step.

[0020]

In the method of manufacturing a ferroelectric thin film according to claim 1, the first thin film is formed by baking at a baking temperature that can inherit the orientation of the crystalline first film in the initial film forming step. It is possible to form a film that inherits the orientation of the film.

Further, by firing at a temperature lower than the firing temperature in the initial film forming step in the latter film forming step, necessary components are less likely to be lost.

In the ferroelectric thin film manufacturing method according to the second aspect, the firing temperature is lowered in the latter manufacturing process by firing in the latter manufacturing process for a firing time longer than the firing time in the initial film forming process. It is possible to compensate for the imperfections of crystallization that accompany it.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As an embodiment 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 ferroelectric memory cell will be described with reference to the manufacturing process of the memory cell 1. And will be described below. 1A, B and FIG.
A and B are cross-sectional views showing the manufacturing process of the memory cell.

As shown in FIG. 1A, first, a silicon wafer 3 is prepared. Next, after the silicon oxide thin film 5 is formed by thermal oxidation, the platinum film 7 is deposited as the crystalline first film on the upper surface of the silicon oxide thin film 5 by the CVD method.

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 method for forming the PZT thin film by the sol-gel method is performed 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 a sol solution T having a high Pb concentration is prepared in a later film forming process where Pb is easily lost. By using it, we try to make up for the loss of Pb.

Next, the sol solution Q 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 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, the firing temperature (750 ° C.) is set so that the orientation of the platinum film can be inherited in the first to second film forming steps as the initial film forming step.

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 device 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 this film forming process, the platinum film 7 and the PZT film 9b are formed without losing necessary components as much as possible.
The firing temperature (70
(0 ° C.) and time (20 seconds) are 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 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.

By performing the above-described two film forming steps as the latter film forming step at a baking temperature (650 ° C.) lower than the baking temperature (750 ° C.) of the former film forming step, most of the necessary components are lost. The PZT films 9e and 9f can be formed without using them.

Further, in this latter film forming process, a baking time (3 seconds) longer than the baking time (20 seconds) in the initial film forming process is used.
Since the baking is performed for 0 second), it is possible to compensate for the incomplete crystallization due to the decrease in the baking temperature in the later film forming step.

In the firing process, particularly in the latter firing process, oxygen atom deficiency (called oxygen bay messenger) may occur in the perovskite type crystal structure of the PZT thin film due to insufficient oxygen atom concentration. However, in the latter film forming process, in order to prevent the generation of the oxygen bay spacers, baking is performed in an ozone atmosphere instead of the oxygen atmosphere.

As described above, the production of the PZT thin film 9 is divided into a plurality of (6) film forming steps in the sol-gel method, and at the same time, a crystal that inherits the excellent orientation of the platinum film 7 is grown. By setting the firing temperature and the firing time at which necessary components were not lost, the formed PZT thin film 9 had good composition controllability in the depth direction of the film, and a perovskite type crystal was obtained.

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 formed by etching using the resist pattern as a mask. Mold 11. Next, the upper electrode 1 formed as shown in FIG. 2B.
Using 1 as a mask, arsenic or phosphorus is ion-implanted and thermally diffused to form an n ⁺ -type drain layer 13 and an n ^{+ -type} source layer 15. The ferroelectric memory cell 1 is formed as described above.

[0038]

According to the method of manufacturing a ferroelectric thin film according to the first aspect of the present invention, the firing is performed at a firing temperature that can inherit the orientation of the crystalline first film in the initial film forming step. There is. Therefore, it is possible to form a film that inherits the orientation of the crystalline first film.

Further, in the latter film forming step, the baking is performed at a temperature lower than the baking temperature in the initial film forming step.

Therefore, it is possible to obtain a ferroelectric thin film having a perovskite type crystal structure having no defects, since the necessary components are hardly lost during firing.

In the ferroelectric thin film manufacturing method according to the second aspect of the present invention, in the latter manufacturing process, the baking time is longer than the baking time in the initial film forming process.

Therefore, by compensating for the incompleteness of crystallization that accompanies the lowering of the firing temperature in the later manufacturing process,
A ferroelectric thin film having a perovskite type crystal structure without defects can be obtained in the latter manufacturing process.

[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

─────────────────────────────────────────────────── ─── 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 (2)

[Claims] 1. A method of forming a ferroelectric thin film on the upper surface of a crystalline first layer by using a sol-gel method, wherein a film forming step of applying a sol solution and baking the same is performed a plurality of times. In the initial film forming step of the multiple film forming steps, baking is performed at a baking temperature that allows the orientation of the crystalline first film to be inherited, and the latter film forming step of the plurality of film forming steps is performed. In the step, the method for producing a ferroelectric thin film is characterized by firing at a temperature lower than the firing temperature in the initial film forming step. 2. The ferroelectric thin film manufacturing method according to claim 1, wherein in the film forming process in the first and second semesters, the baking is performed for a baking time longer than the baking time in the initial film forming process. Thin film manufacturing method.