JP2000327311A - Production of substrate having thin film of metal oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thin film containing a readily volatile component by forming a precursor coating film from a sol gel film made on a substrate, laminating a photoresist layer to the precursor coating film, exposing and developing the photoresist layer to form a pattern opening part, removing a precursor film exposed part to substantially remove the photoresist layer and heat-treating the precursor coating film. SOLUTION: A PT sol gel solution is applied to a Si substrate 1 and heat- treated at 100-400 deg.C to prepare a PT precursor coating film 2. Then a positive type resist is applied to the PT precursor coating film and heat-treated at about 80 deg.C for about 30 minutes to form a photoresist layer 3. A photomask 4 having a fixed pattern is set on the precursor coating film 2, irradiated with ultraviolet rays, etched and the photoresist layer 3 of irradiated part is dissolved and removed. Then the photomask is immersed in a solution of nitric acid and the exposed precursor coating film 2 is removed. The photoresist layer 3 is subjected to O2 dry etching to form a photoresist layer having about 0.1-15 μm thickness. The precursor coating film 2 is baked about 600 deg.C for about one hour to give a Si substrate 1 having a PT thin film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a substrate having a metal oxide thin film. More specifically, the present invention relates to a method for manufacturing a substrate having a metal oxide thin film containing a volatile component such as lead. The substrate having such a metal oxide thin film includes a piezoelectric thin film resonator, a ferroelectric memory, a piezoelectric actuator,
It is suitable for applications such as sensors.

[0002]

2. Description of the Related Art PZT (PbZrTiO _x ), PT (P
Metal oxide thin films containing lead such as bTiO ₃ ) have been applied to semiconductor memory devices, piezoelectric devices, and the like. As a forming method, a film is generally formed on a substrate by a sol-gel method using a sol-gel solution that generates a metal oxide thin film by a sputtering method, an MOCVD method, or a heat treatment, and is then subjected to an etching process using photolithography to form a pattern. It is a target. The following method is mentioned as a method of forming a pattern of such a metal oxide thin film.

For example, Japanese Patent Application Laid-Open No. 5-116454 discloses a method in which a sol obtained by adding a photoacid generator to an alkoxide of a metal element or the like is formed into a film, exposed to light, developed to form a pattern, and then fired. In this method, there is a possibility that the lower electrode is oxidized by excess acid generated at the time of exposure or that the firing furnace is damaged.

Japanese Patent Application Laid-Open No. Hei 7-246705 discloses a method in which a PZT film formed by a sputtering method is photo-etched with hot hydrochloric acid to form a pattern and then baked. In this method, since hot hydrochloric acid is used as the etching solution, there is a problem that the working environment becomes severe.

Japanese Patent Application Laid-Open No. 9-12305 discloses a method in which a precursor film formed by a spin casting method using an ultraviolet curable sol is exposed and developed by photolithography, and then fired at 650 ° C. to form a pattern. No. 6,086,045. In this method, 1.10 to 1.2
In order to obtain a film thickness of μm, it is necessary to repeat the process about 10 times in total, so that repeated firing causes a composition shift due to volatilization of a lead component.

Japanese Patent Application Laid-Open No. 10-102294 discloses a method of depositing and firing raw material powder on a patterned electrode by electrophoretic deposition. In order to obtain a film without pores by this method, it is necessary to repeat the process about three times to increase the film thickness to 45 μm, and thus there is a problem of peeling of the film due to a difference in thermal expansion.

[0007]

In view of the above-mentioned problems of the prior art, in order to facilitate the pattern forming process, a method of patterning and firing a sol-gel film formed by a sol-gel method using a photoresist before firing is used. Is simple and desirable. Although a method of patterning by a lift-off method using a positive photoresist is conceivable, the sol-gel method is not applicable because the sol-gel solution dissolves the resist film.

There is also a method of patterning using a negative type photoresist. However, when the resist is dissolved and removed, the sol-gel film is dissolved, or when the drying is caused by the developer penetrated into the multilayered sol-gel film, the sol-gel film is fired. There are problems such as cracks at the time. Further, there is a method of burning off the sol-gel film together without dissolving and removing the negative resist after development. However, there is a problem that the lead component in the sol-gel film is reduced and precipitated by carbon in the resist.

The present invention provides a method of manufacturing a substrate having a metal oxide thin film, which has solved the problems caused by the above-described pattern forming step. In particular, it is useful as a method for manufacturing a substrate having a metal oxide thin film containing a volatile component such as lead.

[0010]

The gist of the present invention is to provide a method of manufacturing a substrate having a metal oxide thin film including the following steps (a) to (e).

(A) A step of forming a metal oxide precursor film by forming a sol-gel film to be a metal oxide on a substrate and then performing a heat treatment at 100 ° C. to 400 ° C. Temperature range where the sol-gel film is not completely sintered
(0 ° C. or less) to form a precursor film of a metal oxide. Such a precursor film can be easily formed into a pattern by etching or the like, unlike a film after sintering is completed. In addition, if the heat treatment is performed in the above temperature range, a volatile film such as lead is not volatilized, so that a metal oxide precursor film having substantially no composition deviation can be formed. Note that wiring may be formed on the substrate on which the precursor film is formed. For example, a noble metal layer such as Pt, C
A lower electrode composed of a multilayer body in which a rutile type such as IrO ₂ or another metal oxide is laminated on a base metal layer such as u or these conductor layers may be formed.

Taking PZT as an example, the precursor film is in a state before PZT starts crystallization.
In addition, since the lead component is not volatilized, a good composition ratio of P
It is a ZT precursor thin film.

The reason why the above heat treatment temperature is specified to be 100 ° C. or more and 400 ° C. or less is as follows. If the heat treatment temperature is lower than 100 ° C., a precursor film containing an excessive amount of an organic component may be formed, and the precursor film may be dissolved and swelled at the time of forming a photoresist layer.

On the other hand, if the heat treatment temperature exceeds 400 ° C., the firing of the precursor film proceeds, and the conditions (etching conditions, etc.) of the pattern forming step cannot be moderated, or the volatile components such as lead are used. This is because volatilization of the precursor film begins to cause a composition deviation of the precursor film. It is presumed that the organic component contained in the precursor film that has undergone such heat treatment starts to be decomposed or is almost completely decomposed.

The more preferable range of the above heat treatment is from 120 to
300 ° C. More preferably, it is 150 to 250 ° C. The optimal heat treatment conditions are determined depending on the decomposition characteristics of the organic components contained in the sol-gel film and various characteristics of the obtained metal oxide film (whether or not volatile components are contained, the state of the obtained precursor film, etc.). Determined individually. Usually, within such a temperature range, the amount of residual organic components in the precursor film can be adjusted well, and a precursor film with extremely good etching properties can be obtained.

(B) forming a photoresist layer on the precursor film, and exposing and developing to form a pattern opening on the photoresist layer; The photoresist layer can be formed using a known varnish-like or film-like resist material, but it is preferable to use a material that does not affect the precursor film. Specifically, it is preferable that the precursor film does not dissolve and swell when the resist material is applied, and does not cause defects such as peeling and cracks in the precursor film when the resist material is dried. In particular, it is necessary to carefully select organic components such as a solvent.

When a varnish-like resist material is used, a photoresist layer can be formed by a known method such as a spin coating method, a roll coating method, and a curtain coating method. When a film-like resist material is used, a photoresist layer can be formed using a known method such as a lamination method.
The thickness of the photoresist layer is preferably from 0.1 to 10 μm. More preferably, it is 0.5 to 3 μm. This is because the control of the film thickness is easy.

For the exposure and development of the photoresist layer, known methods can be used, but it is preferable to use a method that does not affect the precursor film. Specifically, when removing the resist, the precursor film is dissolved together, peeled,
Those that do not generate defects such as cracks and swelling are preferred. In particular, it is necessary to carefully select the components of the developing solution and the developing conditions.

(C) a step of etching away the exposed portion of the precursor film. The precursor film exposed at the opening of the photoresist layer formed by exposure and development is removed by etching, and the precursor film is patterned into a desired shape.
Since such a precursor film does not form a perfect sintered body, it can be patterned under extremely mild conditions as compared with the conventional case.

Taking PT (PbTiO ₃ ) as an example, PT
If the precursor film is immersed in a 10% nitric acid solution for about 15 to 30 seconds, unnecessary portions can be removed by etching.
Since harsh conditions such as hot hydrochloric acid are not required, there is an advantage that the influence on parts other than the etching part is small and the working environment can be improved.

(D) a step of substantially removing the photoresist layer by a dry etching method. Usually, the photoresist layer is removed using a solvent (such as acetone), but the present invention is characterized in that the photoresist layer is substantially removed by a dry etching method. The reason for using the dry etching method is that in wet etching, a solvent (such as acetone) causes the precursor film to dissolve and swell, and causes defects such as peeling and cracking. As a dry etching method, a plasma etching method, an RIE (reactive ion etching) method,
A known method such as a sand blast method can be used.

"Substantially removing" as used herein means that
When the precursor film is baked with the photoresist layer in the “substantially removed” state, the “remove” is performed so that the carbon component due to the resist residue does not remain in the obtained metal oxide thin film. And "removed" to such an extent that the resulting metal oxide thin film does not prevent the carbon component resulting from the resist residue from exhibiting the desired properties.
To do.

The thickness of the photoresist layer after dry etching is preferably 3 μm or less. When the photoresist layer is baked together with the precursor film while leaving the remaining thickness of the photoresist layer to be 3 μm or more, when carbon due to the photoresist layer remains in the selected metal oxide thin film or when carbon is decomposed, the metal oxide This is because the thin film may be reduced.

If the thickness of the photoresist layer is 10 μm or more, the thickness is reduced by polishing with a belt sander or the like.
It is preferable to use the above-mentioned dry etching method after the thickness is set to not more than μm in order to shorten the dry etching processing time.
The remaining thickness of the photoresist layer after the dry etching is more preferably 1 μm or less, further preferably 0.5 μm or less. This is because a metal oxide thin film can be formed in an extremely good state.

When an easily reducible component such as lead is contained, the remaining thickness of the photoresist layer after dry etching is set to 0.1.
It is more preferably 25 μm or less. This is because it is possible to effectively prevent the easily reducible component such as lead from being reduced and precipitated.

In order to form a thin film having a crystal structure having characteristics such as a perovskite thin film with a good crystal structure, the remaining thickness of the photoresist layer after dry etching is 0.1 μm.
The thickness is preferably not more than 0.3 μm in accordance with the required characteristics of the thin film.

(E) a step of heat-treating the precursor film to form a metal oxide thin film. The precursor film is baked with the photoresist layer “substantially removed” in the above step (d) attached. Since the photoresist layer has been “substantially removed” as described above, no carbon component due to the resist residue remains in the obtained metal oxide thin film, and the obtained metal oxide thin film remains in the resist residue. The resulting carbon component does not prevent the desired properties from being exhibited. Therefore, a substrate having a metal oxide thin film with few defects and good characteristics can be manufactured with high yield.

According to a second aspect of the present invention, a metal component constituting the metal oxide thin film according to the first aspect is specifically exemplified. By combining such metal components, metal oxide thin films having various compositions can be formed. As the crystal structure of the metal oxide thin film, for example, various thin films represented by a perovskite type, a layered perovskite type, a rutile type and the like are obtained.

Specifically, PZT, PT, BTO (Ba
TiO_Three), BST (BaSrTiO)_x), PLZT
(PbLaZrTiO_x), STO (SrTiO_x),
Ta_TwoO_Five, WN, SiWN, TaSiN, CoSi_Two,
TaSi_Two, SiOF, BSG (SiO_Two-B_TwoO_Three), I
rO_Two, RuO_Two, V_TwoO_Three, Cr added V_TwoO_Three, VO_Two, T
i_TwoO_Three, K_0.3MoO_Three, EuO, Sr_ThreeTi_TwoO₇, Sr_Two
Ta_TwoO₇, KLaNb_TwoO₇, RbNdNb_TwoO₇, RbB
iNb_TwoO₇, KCa_TwoNb_ThreeO_Ten, Na_TwoGd_TwoTi
_ThreeO_Ten, K_TwoLa_TwoTi_ThreeO_Ten, K_FourNb₆O₁₇, KTiNb
O_Five, Na_TwoTi_ThreeO₇, LaCoO_Three, Fe_ThreeO_Four, Ni
O, La_1.85Sr_0.15CuO_Four, EuBa_TwoCu_ThreeO _7-x,
Eu_TwoBaCuO_Five, Ca_ThreeTi_TwoO₇, Sr_TwoNb_TwoO₇, C
a_TwoNb_TwoO₇, K_FourNb₆O₁₇, KCa_TwoNaNb_FourO₁₃,
And the like.

According to the present invention utilizing the sol-gel method, the firing temperature can be greatly reduced as compared with the case where powder is used, so that a good thin film having a small composition deviation can be obtained even with the above-mentioned complicated composition. Can be

The gist of the invention of claim 3 is that the obtained metal oxide thin film is at least one selected from a perovskite structure, a layered perovskite structure and a rutile structure. According to the present invention utilizing the sol-gel method, even with a complex composition having a perovskite structure, a layered perovskite structure, or a rutile structure, which is included in the compounds exemplified above, a good thin film with less composition deviation can be obtained.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the method for manufacturing a substrate having a metal oxide thin film according to the present invention will be described below.

(Example 1) External shape 100 mm, thickness 0.52
A 5 mm Si substrate 1 is prepared (FIG. 1). PT sol-gel solution (Dip coat material PT-2 manufactured by Kojundo Chemical Laboratory)
5) is applied onto the Si substrate 1 by spin coating (not shown). The application condition is 2000 rpm × 20 seconds. The coated Si substrate is heat-treated on a hot plate to produce a PT precursor film 2 (FIG. 2). The thickness of the PT precursor film is 0.6 μm. The temperature conditions are in the range of 80 to 450 ° C. as shown in Table 1. Retention time is 1
0 minutes.

The quality of the obtained PT precursor film is inspected with a 20-fold magnifying microscope. If there is no defect on the surface of the film, it is evaluated as ○: acceptable, and if there is any defect, x (defective mode); Table 1 shows the results.

Next, a positive resist (manufactured by Hoechst)
AZ 1500) is applied by a spin coating method (not shown). The coated Si substrate is heat-treated at 80 ° C. for 30 minutes on a hot plate to form a photoresist layer 3 (FIG. 3). The dry thickness of the photoresist layer is equal to the target value of the remaining thickness of the photoresist layer after O ₂ dry etching + 0.6, except for Sample No. 11 and Sample No. 12.
Adjust to be μm.

A photomask 4 having a predetermined pattern is set on the precursor film, and the main wavelength is the GHI wavelength (365).
/ 405/425 nm) (irradiation energy: 400 mJ) (FIG. 4). The photoresist is immersed in a developing solution for 30 seconds to perform an etching process, and the photoresist layer in the ultraviolet irradiation part is dissolved and removed (FIG. 5).

Then, the exposed PT precursor film is removed by etching by dipping in a 10% nitric acid solution for 15 to 30 seconds (FIG. 6). After cleaning and drying, the photoresist layer was removed by about 0.6 μm in the thickness direction by O ₂ dry etching (O ₂ flow rate 200 sccm × output 700 W × 5 minutes), and the remaining thickness was 0.1% as shown in Table 1. Adjust to １５15 μm (FIG. 7).

The remaining thickness of the photoresist layer 31 (FIG. 7) after O ₂ dry etching is measured and confirmed using a surface roughness meter (DEKTAK8000 manufactured by Nihon Vacuum Corporation). Thereafter, firing is performed in a firing furnace at 600 ° C. × 1 hour (heating rate is 2 ° C./min) to obtain a Si substrate having the PT thin film 21 (FIG. 8).

The appearance of the obtained substrate is inspected using a 20 × magnifier. At this time, the quality of the patterning property of the metal oxide thin film and the quality of the metal oxide thin film are checked.

Regarding the quality of the patterning property, ◎ (extremely good) when the pattern edge or line is extremely sharp; 合格 (excellent) when passing or sharp; Passed, those not at a practical level were evaluated as x (defective mode);

As for the quality of the metal oxide thin film,
Very good without any defect on the thin film surface: ◎; good when there is no defect on the thin film surface; good; good if there is no problem with the appearance problem; X (defective mode); rejected. Table 1 shows the results.

[0042]

[Table 1]

From the results shown in Table 1, all of the evaluation items of Sample Nos. 2 to 15, which are examples of the present invention, are acceptable. On the other hand, in Sample No. 1, which is a comparative example in which the heat treatment temperature of the sol-gel film was 80 ° C., the pattern was so thin that precise patterning was not possible. In sample No. 2 in which the heat treatment temperature of the sol-gel film was 100 ° C., although the film formation was at a level where there was no practical problem, the pattern was slightly narrowed.

The heat treatment temperature of the sol-gel film is 450 ° C.
In sample No. 16 which is a comparative example of Example 1, baking relatively progresses at the stage of the precursor film, and the pattern remains under the mild etching conditions of the present example. Sample No. 15, which is an example in which the heat treatment temperature of the sol-gel film is 400 ° C., is a level having no problem in evaluation, but lacks sharpness of the pattern. From this result, it is understood that the heat treatment condition of the sol-gel film is preferably 100 ° C. or more and 400 ° C. or less.

In the sample Nos. 11 and 12, which are examples in which the remaining thickness of the photoresist layer after the dry etching was intentionally set to be thick, a good thin film due to defects such as color unevenness, discoloration, and resist residue during firing. Cannot be obtained.
From this result, the remaining thickness of the photoresist layer after dry etching is 3 μm or less, more preferably 1 μm or less,
Further, it is understood that it is preferable to set the thickness to 0.5 μm or less.

[0046]

According to the present invention, it is possible to provide a method of manufacturing a substrate having a metal oxide thin film which has solved various problems caused by a step of forming a metal oxide thin film pattern using a sol-gel method. In particular, it is useful as a method for manufacturing a substrate having a metal oxide thin film containing a volatile component such as lead.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a cross section of a Si substrate.

FIG. 2 is an explanatory diagram showing a state where a PT precursor film is formed on a Si substrate.

FIG. 3 is an explanatory view showing a state where a positive photoresist layer is formed on a PT precursor film.

FIG. 4 is an explanatory view showing an exposure step.

FIG. 5 is an explanatory diagram showing a state in which a positive photoresist layer has been developed.

FIG. 6 is an explanatory view showing a state where an exposed portion of a PT precursor film is removed by etching.

FIG. 7 is an explanatory view showing a state where a positive photoresist layer is substantially removed.

FIG. 8 is an explanatory view showing a Si substrate on which a metal oxide thin film made of PT is formed.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Si substrate 2 PT precursor film 20 PT precursor film after patterning 21 Metal oxide thin film made of PT 3 Positive photoresist layer 30 Positive photoresist layer after patterning 31 Positive photoresist substantially removed Layer 4 Positive photomask

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G042 DA01 DA02 DB08 DC03 DD02 DD08 DD10 DE09 DE14 4G047 CA02 CA05 CB05 CB06 CC03 CD02 CD07 CD08 4K022 BA02 BA04 BA06 BA07 BA08 BA09 BA10 BA11 BA12 BA14 BA15 BA17 BA18 BA20 BA22 BA23 BA24 BA25 BA26 BA27 BA28 BA33 BA35 CA08 DA06

Claims (3)

[Claims] 1. A method for manufacturing a substrate having a metal oxide thin film, comprising the following steps (a) to (e). (A) After forming a sol-gel film to be a metal oxide on a substrate,
A step of heat-treating at a temperature of 100 ° C. or more and 400 ° C. or less to form a metal oxide precursor film. (B) forming a photoresist layer on the precursor film, exposing and developing to form a pattern opening on the photoresist layer; (C) a step of etching away the exposed portion of the precursor film. (D) a step of substantially removing the photoresist layer by a dry etching method; (E) a step of heat-treating the precursor film to form a metal oxide thin film. 2. The metal component constituting the metal oxide thin film is Pb, Ti, Zr, Ba, Sr, Zn, Mg, M
n, Ca, Li, Na, K, Al, Si, V, Ni, F
e, Cr, Co, Ga, Cu, As, Nb, Nd, S
m, La, Ce, Pr, Er, Yb, Y, Hf, Ta,
Bi, In, Ru, Pd, Pt, Ir, Rh, W, M
The method of claim 1, wherein the substrate is at least one selected from the group consisting of o, B, Rb, Gd, and Eu. 3. The method for manufacturing a substrate having a metal oxide thin film according to claim 1 or 2, wherein the metal oxide thin film is at least one selected from a perovskite structure, a layered perovskite structure, and a rutile structure. A method for manufacturing a substrate having a metal oxide thin film, characterized in that: