JP3127849B2 - Method for producing oxide thin film by coating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an oxide thin film by a coating method.

[0002]

2. Description of the Related Art As a method for producing an oxide thin film, a coating method,
CVD, sputtering, laser ablation and the like are widely known. In the coating method, a solution in which an organic metal material is dissolved in an appropriate solvent is applied on a substrate, and heat treatment is performed in an oxidizing atmosphere to form an oxide thin film. Suitable for forming multi-component composite oxide thin films with small ratio deviation and easy composition change.Furthermore, thin films can be uniformly formed over a large area. And so on.

[0003] The solution to be applied is, for example, a Journal of Applied Physics (Journal of A).
Applied Physics, Vol. 72 (19
92), pp. 1566-1576) "Proces
sing and electrical prop
rties of Pb (Zr _x Ti _1-x ) O ₃ (x =
0.2-0.75) films: Composition
no of metallo-organic deco
composition and sol-gelproc
esess ", a metal alkoxide and a metal organic acid salt as an organic metal raw material,
Methoxyethanol is often used.

Further, Japanese Journal of Applied Physics (Japanese Journal of Applied Physics)
f Applied Physics, Vol. 34
(1995); 5683-5688) "Pre
parity and properties of
sol-gel derived La-doped
As shown in “PbTiO ₃ thin films”, 2-ethoxyethanol having a similar molecular structure may be used as a solvent. This is because the feature that these solvents have high solubility and relatively low viscosity effectively acts at the time of solution preparation and application.

[0005]

However, the conventional method has the following disadvantages.

That is, it has been reported that these solvents are harmful substances which are teratogenic and adversely affect reproductive functions. Therefore, these solvents can be used not only in large quantities in factories and the like but also in small quantities at the laboratory level. With danger. From the viewpoint of safety and health, it is not the most suitable solvent, and there may be some restrictions on its use in the future.

[0007] To ensure safety, there is no solution to the above-mentioned problems, such as the use of protective equipment for workers when using solvents and the installation of local exhaust equipment. It is necessary to.

An object of the present invention is to provide a method for producing by that oxides thin film coating method using a solvent having a high safety by radically.

[0009]

In the present invention, there is provided a means for solving], dissolved at least one of the organic metal as the constituent element of the thin film 1-methoxy-2-propanol or 1-ethoxy-2-propanol solvent mainly The used solution is used as a coating solution.

[0010] 1-methoxy-2-used in the present invention
Propanol and 1-ethoxy-2-propanol have a structure in which the -C2H4-OH group of 2-methoxyethanol and 2-ethoxyethanol is replaced by a -C3H6-OH group, respectively. The harm is due to the -C2 H4-OH group of 2-methoxyethanol and 2-ethoxyethanol, and if this portion is a -C3 H6-OH group, the harm is eliminated. 1-methoxy-2-propanol and 1-ethoxy-2-propanol are easily dissolved by reacting with a metal alkoxide raw material to form metal methoxypropoxide or metal ethoxypropoxide,
In addition, the metal organic acid salt forms a metal and a metal alkoxide in the organic acid salt when it is combined with the organic acid to form an ester, which is easily dissolved. As a result, the metal organic acid salt is also easily formed. Dissolve in Since a reaction with such a solute can be expected, even if 1-methoxy-2-propanol or 1-ethoxy-2-propanol, which is highly safe, is used as a solvent, compared to 2-methoxyethanol and 2-ethoxyethanol solvents. Ease of application during spin coating,
There is no inferior point regarding the crystal structure and electrical characteristics of the thin film after the heat treatment. It should be noted that even if it is about 1% of the total amount of this solvent
If a small amount of acid such as H2O or HNO3 is added,
Condensation polymerization reaction caused by partial hydrolysis between lucoxides
In this way, the film formation temperature can be reduced. vice versa
Add a chelating compound such as acetylacetone to the solvent.
To suppress the polymerization reaction more than necessary to produce a stable solution.
It is also possible.

Further , according to the present invention, in the coating solution
Use a solution containing ethyl lactate as a coating solution
Is desired. 1-methoxy-2-propanol also
Alternatively, 1-ethoxy-2-propanol has a low evaporation rate.
When the concentration of the solution is high, unevenness in film thickness occurs during coating.
Adds ethyl lactate, which is easy to produce but has a relatively low evaporation rate
This will cause unevenness in film thickness even if the solution concentration is high.
A piling solution can be made. This is ethyl lactate
By adding to the solvent, the film thickness obtained by one coating
Means that it can be raised
That a uniform thin film can be obtained while reducing
Has the effect. Ethyl lactate itself is an ester compound.
Low reactivity with other solutes and solvents,
Ethyl lactate is not added as the body is almost unchanged
An oxide thin film of the same quality as the thin film obtained from the solution can be obtained. This
At the time, ethyl lactate contains about 50% of the total amount of the solvent at the maximum
It is possible to do.

[0012]

Embodiments of the present invention will be described below with reference to the drawings, together with comparative examples. In Examples 1 to 5 and Example 7, Pb (Zr _0.53 T
i _0.47 ) An example in which an O ₃ (hereinafter referred to as PZT) thin film is produced has been described. In the sixth embodiment, SrBi ₂ Ta, which is also a ferroelectric, is used.
An example of producing a ₂ O ₉ (hereinafter, SBT) thin film has been described. PZ
T and SBT are materials expected to be applied to a nonvolatile memory using a ferroelectric thin film. However, since the vapor pressure of Pb or Bi contained in the constituent elements is high, it is known that a composition deviation easily occurs when a film forming process in a vacuum such as a sputtering method or a CVD method is used. Film formation by a good coating method is a particularly effective material.

[0013]

EXAMPLES Comparative Example 1 Anhydrous lead acetate Pb (CH ₃ COO) ₂ (hereinafter Pb (OAc) ₂ ) in a dry nitrogen atmosphere
Tetraethoxyzirconium Zr (OC ₂ H ₅ )
₄ (hereinafter Zr (OEt) ₄ ), tetraisopropoxytitanium Ti (OCH (CH ₃ ) ₂ ) ₄ (hereinafter Ti
(O-iPr) ₄ ) and 1-methoxy-2-propanol were weighed to form a 0.15 mol / Kg PZT solution. At this time, the Pb material is 10 m in order to promote crystallization.
It was weighed so that there was an ol% excess. After mixing these, the mixture was refluxed at 120 ° C. for 3 hours while stirring under a dry nitrogen atmosphere. As a result, the organic metal was completely dissolved, and a yellow-brown transparent solution was obtained. After filtering this solution through a 0.2 μm filter, Pt (200 nm) / Ti (50 n
m) / SiO ₂ (500 nm) / 150 on Si substrate
Spin coating was performed under the conditions of 0 rpm and 45 seconds. A series of processes of spin coating, heat treatment in oxygen at 250 ° C. for 10 minutes, and oxygen in oxygen at 600 ° C. for 10 minutes was repeated six times, followed by baking in oxygen at 600 ° C. for 60 minutes. No cracks or the like were observed in the thin film after firing. When the film thickness distribution was measured with an ellipsometer, the center film thickness was 185 nm and was within ± 5% over the entire surface of the 6-inch substrate. Pt / PZT produced by depositing Pt (200 nm) by sputtering as an upper electrode and processing it into a 100 μm square by ion milling
The electrical characteristics of the / Pt capacitor were evaluated. FIG. 1 shows the results of hysteresis characteristics and leak current characteristics. The difference (2Pr) between the two points at which the hysteresis curve intersects the y-axis when 5V is applied is 20.2 μC / cm ² , and the leak current density (J) when 5V is applied is 2.4 × 10 ⁻⁷ A / cm ² A conventional example using the 2-methoxyethanol solvent shown in FIG. 7 (2Pr = 21.0 μC / cm ² when 5 V is applied, J
= 2.6 × 10 ⁻⁷ A / cm ² ). 1-methoxy-2 with high safety
-A good ferroelectric PZT thin film comparable to the conventional method can be produced using a propanol solvent.

(Example 1 ) P in a dry nitrogen atmosphere
b (OAc) ₂ , Zr (OEt) ₄ , Ti (O-iP
_r) 4, 1-methoxy-2-propanol 0.6m
ol / Kg of PZT solution was weighed. At this time, the Pb raw material was weighed so as to be in excess of 10 mol% in order to promote crystallization. After mixing these, the mixture was refluxed at 120 ° C. for 3 hours while stirring under a dry nitrogen atmosphere. As a result, the organic metal was completely dissolved, and a yellow-brown transparent solution was obtained. Ethyl lactate was added to this solution and stirred well to prepare a 0.3 mol / Kg PZT solution. After filtering this solution through a 0.2 μm filter,
Pt (200 nm) / Ti (50 nm) / SiO ₂
(500 nm) / Si substrate was spin-coated at 1500 rpm for 45 seconds. After repeating a series of processes of spin coating → heat treatment in oxygen at 250 ° C. for 10 minutes → 600 ° C. in oxygen for 10 minutes, the process was repeated three times.
Baking at 60 ° C. for 60 minutes. No cracks or the like were observed in the thin film after firing. When the film thickness distribution was measured with an ellipsometer, the center film thickness was 203 nm and ±
Within 5%. FIG. 2 shows the result of evaluating the electrical characteristics of the capacitor structure similar to that of Comparative Example 1 . When 5 V is applied, 2Pr = 21.2 μC / cm ² , J = 6.3 × 1
^0-8 A / cm ² was obtained, and characteristics comparable to those of the conventional method were confirmed.

(Example 2 ) In Example 1 , 1-
PZT thin films were prepared under exactly the same process conditions except that methoxy-2-propanol was replaced with 1-ethoxy-2-propanol. Again, no cracks or the like were observed, and the central film thickness was 192 nm and was within ± 5% over the entire surface of the 6-inch substrate. FIG. 3 shows the result of evaluating the electrical characteristics of the same capacitor structure as in Comparative Example 1 . 2Pr = 1 when 5V is applied
8.8 μC / cm ² , J = 2.7 × 10 −7 A / cm ²
Was obtained, and characteristics that were comparable to those of the conventional method were also confirmed.

Example 3 P under dry nitrogen atmosphere
b (OAc) ₂ , Zr (OEt) ₄ , Ti (O-iP
r) A solvent obtained by mixing ₄ , 1-methoxy-2-propanol and ethyl lactate at a weight ratio of 1: 1 was added to 0.3 m
ol / Kg of the PZT solution was weighed. At this time, the Pb raw material is 10 mol to promote crystallization.
Weighed to 1% excess. After mixing these,
When the mixture was refluxed at 120 ° C. for 3 hours while stirring under a dry nitrogen atmosphere, the organic metal was completely dissolved, and a yellow-brown transparent solution was obtained. After filtering this solution through a 0.2 μm filter, Pt (200 nm) / Ti (50 nm)
/ SiO ₂ (500nm) / 1500r on Si substrate
Spin coating was performed under the conditions of pm and 45 seconds. Spin coating → 10 minutes at 250 ° C in oxygen → 10 minutes at 600 ° C in oxygen
After repeating a series of heat treatments for three minutes,
It was baked at 600 ° C. for 60 minutes in oxygen. No cracks or the like were observed in the thin film after firing. When the film thickness distribution was measured by an ellipsometer, the film thickness was 200 nm and was within ± 5% over the entire surface of the 6-inch substrate. FIG. 4 shows the result of evaluating the electrical characteristics of the same capacitor structure as in Comparative Example 1 .
When 5 V is applied, 2Pr = 23.1 μC / cm ² , J =
8.3 × 10 ⁻⁸ A / cm ² was obtained, and characteristics that were comparable to those of the conventional method were also confirmed.

(Example 4 ) P in a dry nitrogen atmosphere
b (OAc) ₂ , Zr (OEt) ₄ , Ti (O-iP
_r) 4, and 1-ethoxy-2-propanol and ethyl lactate in a weight ratio of 1: mixed solvent at a ratio of 1, 0.3
Each PZT solution was weighed to obtain a mol / Kg PZT solution. At this time, the Pb raw material is 10 mol to promote crystallization.
Weighed to 1% excess. After mixing these,
When the mixture was refluxed at 120 ° C. for 3 hours while stirring under a dry nitrogen atmosphere, the organic metal was completely dissolved, and a yellow-brown transparent solution was obtained. After filtering this solution through a 0.2 μm filter, Pt (200 nm) / Ti (50 nm)
/ SiO ₂ (500nm) / 1500r on Si substrate
Spin coating was performed under the conditions of pm and 45 seconds. Spin coating → 10 minutes at 250 ° C in oxygen → 10 minutes at 600 ° C in oxygen
After repeating a series of heat treatments for three minutes,
It was baked at 600 ° C. for 60 minutes in oxygen. No cracks or the like were observed in the thin film after firing. When the film thickness distribution was measured by an ellipsometer, the film thickness was 191 nm and was within ± 5% over the entire surface of the 6-inch substrate. FIG. 5 shows the result of evaluating the electrical characteristics of the same capacitor structure as in Comparative Example 1 .
When 5V is applied, 2Pr = 20.3 μC / cm ² , J =
4.0 × 10 ⁻⁷ A / cm ² was obtained, and characteristics that were comparable to those of the conventional method were also confirmed.

Example 5 A case in which a ferroelectric SrBi ₂ Ta ₂ O ₉ (hereinafter, SBT) thin film is formed as an oxide thin film will be described. Diisopropoxystrontium Sr (OCH (CH ₃ )) as an organic metal raw material
₂ ) ₂ , triisopropoxybismuth Bi (OCH
(CH ₃ ) ₂ ) ₃ , pentaethoxy tantalum Ta
(OC ₂ H ₅ ) ₅ and 1-methoxy- as a solvent
2-propanol was used. Each organometallic raw material and the solvent were weighed to be 0.24 mol / Kg. At this time, the Bi composition ratio was weighed in excess of 10 mol% in consideration of evaporation during the heat treatment. After mixing these, the mixture was refluxed at 85 ° C. for 3 hours while stirring under a dry nitrogen atmosphere. As a result, the organic metal was completely dissolved, and a yellow-brown transparent solution was obtained.
Add ethyl lactate to this solution and add 0.12mol / Kg
Was prepared. The reason why the concentration of the coating solution is lower than that in the case of PZT is that if the concentration is 0.3 mol / Kg, the concentration is too high and cracks occur after firing. After the solution was filtered through a 0.2 μm filter, Pt (2
00 nm) / Ti (20 nm) / SiO ₂ (500 n
m) / Si substrate was spin-coated at 1500 rpm for 45 seconds. After repeating a series of processes of spin coating → heat treatment in oxygen at 250 ° C. for 10 minutes → oxygen in 600 ° C. for 10 minutes three times, baking was performed in oxygen at 800 ° C. for 60 minutes. No cracks or the like were observed in the thin film after firing. When the film thickness distribution was measured by an ellipsometer, the center film thickness was 255 nm and was within ± 8% over the entire surface of the 6-inch substrate. Pt (200 nm) was deposited by sputtering as an upper electrode, processed into a 100 μm square by ion milling, and then annealed in oxygen at 800 ° C. for 30 minutes.
The electrical characteristics of the / SBT / Pt capacitor were evaluated.
FIG. 6 shows the results of the hysteresis characteristics and the leak current characteristics.
When 5 V is applied, 2Pr = 18.5 μC / cm ² , J =
7.3 × 10 ⁻⁸ A / cm ² was obtained. It was confirmed that a thin film exhibiting good ferroelectricity can be produced not only with PZT but also with SBT.

( Comparative Example 2 ) Here, an example in which 2-methoxyethanol conventionally used is used will be described as a comparative example. Pb under dry nitrogen atmosphere
(OAc) ₂ , Zr (OEt) ₄ , Ti (O-iP
r) 0.3 mol / Kg of ₄ , 2-methoxyethanol
The PZT solution was weighed. At this time, the Pb raw material was weighed so as to be in excess of 10 mol% in order to promote crystallization. After mixing these, the mixture was refluxed at 120 ° C. for 3 hours while stirring under a dry nitrogen atmosphere. As a result, the organic metal was completely dissolved, and a yellow-brown transparent solution was obtained. After filtering this solution through a 0.2 μm filter, Pt
(200 nm) / Ti (50 nm) / SiO ₂ (50
0 nm) / Si substrate was spin-coated at 1500 rpm for 45 seconds. Spin coating → 250 in oxygen
After repeating a series of processes of a heat treatment at 600 ° C. for 10 minutes → 600 ° C. for 10 minutes in oxygen three times,
Bake for 0 minutes. No cracks or the like were observed in the thin film after firing. When the film thickness distribution was measured with an ellipsometer, the center film thickness was 230 nm and ± 5% over the entire surface of the 6-inch substrate.
Was within. FIG. 7 shows the result of measuring the electrical characteristics with the same capacitor structure as in the first embodiment. When 5 V is applied, 2Pr = 21.0 μC / cm ² , J = 2.6 × 10 −
7 A / cm ² was obtained.

In the above embodiments, only the case where PZT and SBT are used as the oxide thin film has been described. However, the solvent used in the present invention can be replaced with other metal alkoxides and metal organic acid salts by selecting conditions such as reflux temperature. It also shows good solubility, so that it is possible to add other elements to PZT or SBT, for example lanthanum. Also for the same reason PZ
This method can be sufficiently applied to the production of ferroelectric thin films having different compositions from T and SBT, other perovskite-type oxide thin films, and widely, other many oxide thin films.

[0021]

The present invention provides a method for producing an oxide thin film, for example, a ferroelectric thin film typified by PZT or SBT by a coating method having higher safety than the conventional method. The present invention mainly uses highly safe 1-methoxy-2-propanol or 1-ethoxy-2-propanol instead of the harmful 2-methoxyethanol and 2-ethoxyethanol conventionally used as a solvent for the coating solution. characterized by using a solvent as a component, thereby Ku oxides thin films, such deteriorating the properties Ru can be manufactured. Sa
Furthermore, ethyl lactate having a relatively low evaporation rate is added to the above solution.
The addition makes it possible to increase the oxide film thickness that can be formed by one application.

[Brief description of the drawings]

FIG. 1 shows a hysteresis characteristic and a leak current characteristic of a PZT thin film by a coating solution using a 1-methoxy-2-propanol solvent.

FIG. 2 shows a hysteresis characteristic and a leak current characteristic of a PZT thin film by a coating solution obtained by adding ethyl lactate to a solution using a 1-methoxy-2-propanol solvent.

FIG. 3 shows a hysteresis characteristic and a leak current characteristic of a PZT thin film by a coating solution obtained by adding ethyl lactate to a solution using a 1-ethoxy-2-propanol solvent.

FIG. 4 shows P by a coating solution using a solvent obtained by mixing 1-methoxy-2-propanol and ethyl lactate at a ratio of 1: 1.
It is a hysteresis characteristic and a leak current characteristic of a ZT thin film.

FIG. 5 shows P by a coating solution using a solvent in which 1-ethoxy-2-propanol and ethyl lactate are mixed at a ratio of 1: 1.
It is a hysteresis characteristic and a leak current characteristic of a ZT thin film.

FIG. 6 shows a hysteresis characteristic and a leak current characteristic of an SBT thin film by a coating solution obtained by adding ethyl lactate to a solution using a 1-methoxy-2-propanol solvent.

FIG. 7 shows a hysteresis characteristic and a leak current characteristic of a PZT thin film by a coating solution using a 2-methoxyethanol solvent, which is a conventional method.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C01G 23/00 C01G 35/00 C23C 26/00 H01G 7/06 CA (STN)

Claims (3)

(57) [Claims] 1. A method for producing an oxide thin film by a coating method in which a solution in which an organic metal is dissolved is applied on a substrate and heat-treated to form an oxide thin film, the method comprising the steps of: The metal compound is 1-methoxy-2
A solution in which at least one of -propanol or 1-ethoxy-2-propanol is used as a main component, and a solvent in which ethyl lactate having a lower evaporation rate than the main component is added is used as a coating solution. A method for producing an oxide thin film by a coating method. 2. The organic metals dissolved in the coating solution are mainly organic metals of lead, zirconium and titanium, respectively, and Pb (Zr, T
claim, characterized in that i) O3 or PbTiO3 and their forming a thin film by adding a very small amount of additive 1
A method for producing an oxide thin film according to the coating method described above . 3. The organic metal dissolved in the coating solution is mainly each of strontium, bismuth and tantalum, and SrB is formed by a coating method using this solution.
2. The method for producing an oxide thin film by a coating method according to claim 1, wherein the thin film is formed by adding i2Ta2O9 and a trace amount of an additive thereto.