JP4998337B2 - Dielectric element manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a dielectric element.

  An oxide known as a ferroelectric such as barium titanate is used to form a dielectric film included in a dielectric element such as a capacitor or a nonvolatile memory.

  In general, a dielectric element is manufactured through a step of etching a dielectric film formed on a noble metal film as a lower electrode to expose a part of the lower electrode. As a method for etching a dielectric film formed from an oxide such as barium titanate, a method by wet etching using concentrated hydrochloric acid is known (for example, Non-Patent Document 1).

On the other hand, Patent Document 1 includes a fluorine-containing compound as a composition for selectively etching an oxide residue remaining after plasma etching and / or chemical mechanical polishing of a metal substrate including a low-k intermediate layer. Compositions have been proposed.
Japanese translation of PCT publication No. 2003-512741 Ferroelectrics, 2003, Vol. 288, p. 303-313

  However, when the dielectric film formed on the base metal film is etched with concentrated hydrochloric acid, not only the dielectric film but also the base metal film is etched. In addition, when a fluorine-containing compound is used, etching of the base metal film is suppressed, but there is a problem in that an unnecessary fluoride adheres to the surface of the base metal film and the base metal film is not exposed in a desired pattern. Became clear.

  The present invention has been made in view of these circumstances. The purpose of the present invention is to manufacture a base metal film and a dielectric element having a dielectric film formed on the base metal film. It is an object of the present invention to provide a method capable of etching a dielectric film with an appropriate etching rate and good contrast while suppressing adhesion of unnecessary substances to the substrate.

  The dielectric element manufacturing method according to the present invention includes an oxide having at least one element selected from the group A consisting of Ba, Sr and Ca and at least one element selected from the group B consisting of Ti and Zr. And a step of removing a part of the dielectric film by bringing the dielectric film formed on the base metal film into contact with an etching solution. The etching solution contains 0.01 to 3.0 mol / L of at least one fluorine compound of ammonium fluoride and hydrogen fluoride, and at least one acid selected from the group consisting of hydrochloric acid, nitric acid, phosphoric acid, and acetic acid. An aqueous solution containing 1 to 5.0 mol / L.

  According to the manufacturing method according to the present invention, by using a fluorine compound and an acid such as hydrochloric acid in combination, and by setting the concentration of the acid within the specified range, damage to the base metal film and adhesion of unnecessary substances to the surface of the base metal film are achieved. It was possible to etch the dielectric film with an appropriate etching rate and good contrast while suppressing it. When an etching solution containing a fluorine compound is used, a white film may be formed on the base metal film where the dielectric film has been removed, but this film is mainly deposited with a salt such as barium fluoride. It is considered that precipitation of such salts is suppressed by using an acid such as hydrochloric acid in combination. The acid combined with the fluorine compound does not react with Ba in the dielectric film to form an insoluble salt in the etching solution, such as sulfuric acid, but is selected from hydrochloric acid, nitric acid, phosphoric acid and acetic acid. By using this, precipitation of such a salt is also prevented.

  In the step of removing a part of the dielectric film, the dielectric film is preferably brought into contact with the etching solution for 10 seconds to 20 minutes. This makes it easy to obtain process reproducibility and enables etching with better contrast.

  The base metal film preferably contains at least one of stainless steel, Cu and Ni. The oxide having one or more elements selected from Group A consisting of Ba, Sr and Ca and one or more elements selected from Group B consisting of Ti and Zr is barium titanate or barium strontium titanate. It is preferable that In the conventional method, when manufacturing a dielectric element composed of these materials, the base metal film is easily damaged, and unnecessary substances adhere to the surface of the base metal film. Therefore, the manufacturing method according to the present invention is applied. It is particularly useful.

  According to the present invention, in the manufacture of a dielectric element having a base metal film and a dielectric film formed on the base metal film, it is possible to suppress dielectric damage while suppressing damage to the base metal film and adhesion of unnecessary substances to the surface of the base metal film. It is possible to etch the body film with an appropriate etching rate and good contrast. In addition, the use of a base metal film is advantageous in terms of cost reduction.

  Hereinafter, a preferred embodiment of the present invention will be described in detail by taking as an example a method of manufacturing a thin film capacitor which is a dielectric element. However, the present invention is not limited to the following embodiments.

  1 and 2 are cross-sectional views showing an embodiment of a method for manufacturing a thin film capacitor. The manufacturing method according to this embodiment includes a step of forming a dielectric film 3 on a base metal film 1 as a lower electrode, and a step of forming a resist pattern 5 covering a part of the dielectric film 3 (FIG. 1A). ), And the dielectric film 3 formed on the base metal film 1 is brought into contact with the etching solution, so that the portion of the dielectric film 3 not covered with the resist pattern 5 is removed, and the dielectric film 3 is patterned. 1 (b), a step of removing the resist pattern 5 (FIG. 1c), and a dielectric film of a laminate composed of the base metal film 1 and the patterned dielectric film 3 A step of forming the metal film 7 on the surface on the third side (FIG. 2A), and a resist pattern 10 covering a part of the metal film 7 formed on the patterned dielectric film 3 Step of forming (FIG. 2B) and the resist pattern of the metal film 7 The step of removing the portion not covered with the pattern 10 to form the patterned metal film 7 as the upper electrode (FIG. 2C) and the step of removing the resist pattern 10 (FIG. 2D) The base metal film 1 as the lower electrode, the metal film 7 as the upper electrode disposed opposite to the base metal film 1, and the base metal film 1 and the metal film 7 are formed by the method according to this embodiment. The thin film capacitor 100 having the dielectric film 3 thus obtained is obtained.

  The base metal film 1 is a metal film made of one or more base metals and functions as a lower electrode in the capacitor 100. The base metal film 1 preferably contains at least one of stainless steel, Cu and Ni. The base metal film 1 may be a metal foil such as a nickel foil.

  The dielectric film 3 is formed, for example, by sputtering an oxide having one or more elements selected from the group A consisting of Ba, Sr and Ca and one or more elements selected from the group B consisting of Ti and Zr. It is formed on the base metal film 1 by a film forming method. More specifically, for example, barium titanate or barium strontium titanate is formed on the base metal film 1.

  The resist pattern 5 can be formed by a photolithography technique using a photosensitive resin. The resist pattern 5 forms an opening through which a portion of the dielectric film 3 that is removed by etching is exposed, and functions as a mask during etching.

  By immersing the laminated body composed of the base metal film 1, the dielectric film 3, and the resist pattern 5 in an etching solution, a portion of the dielectric film 3 that is not covered with the resist pattern 5 is removed.

  The etching solution is an aqueous solution containing at least one fluorine compound of ammonium fluoride and hydrogen fluoride, at least one acid selected from the group consisting of hydrochloric acid, nitric acid, phosphoric acid and acetic acid, and water.

  The concentration of the fluorine compound is 0.01 to 3.0 mol / L with respect to the etching solution. When ammonium fluoride and hydrogen fluoride are used in combination, the total concentration thereof may be 0.01 to 3.0 mol / L. If the concentration of the fluorine compound is less than 0.01 mol / L, the etching rate tends to decrease, and if it exceeds 3.0 mol / L, the etching rate tends to be excessively increased and control in the process tends to be difficult. . From the same viewpoint, the concentration of the fluorine compound is more preferably 0.02 to 1.0 mol / L.

  The concentration of at least one acid selected from the group consisting of hydrochloric acid, nitric acid, phosphoric acid and acetic acid is 0.1 to 5.0 mol / L with respect to the etching solution. When two or more kinds of acids are used, the total concentration may be 0.1 to 5.0 mol / L. If the concentration is less than 0.1 mol / L, the effect of suppressing adhesion of insoluble matter to the base metal film 1 tends to be small, and if it exceeds 5.0 mol / L, the effect of preventing damage to the base metal film 1 is small. Tend to be. From the same viewpoint, the acid concentration is preferably 1.0 to 5.0 mol / L for hydrochloric acid, 1.3 to 5.0 mol / L for nitric acid, 1.0 to 5.0 mol / L for phosphoric acid, In acetic acid, it is 1.0-5.0 mol / L. Of these acids, hydrochloric acid is particularly preferred from the viewpoint that the etching rate adjustment by concentration is particularly easy.

  By using the etching solution, the dielectric film 3 can be etched at an appropriate etching rate. From the viewpoint of production efficiency and process control, the etching rate (thickness removed per unit time) is 40 to 500 nm / min. It is preferable that it is a grade. The etching solution preferably contains a lower alcohol such as isopropyl alcohol, ethyl alcohol, or methyl alcohol. When a lower alcohol is added to the etching solution, the wettability of the etching solution to the resist pattern is improved, and a fine pattern can be formed. A preferred concentration of the lower alcohol is about 1% by mass.

  The time of immersion in the etching solution, in other words, the time for bringing the dielectric film 3 into contact with the etching solution is preferably 10 seconds to 20 minutes. If the immersion time is less than 10 seconds, the reproducibility of the process tends to decrease. The etching pattern tends to be unclear.

  After the etching, the resist pattern 5 is removed (FIG. 1C).

  Thereafter, a metal film 7 is formed on the surface on the dielectric film 3 side of the laminate composed of the base metal film 1 and the dielectric film 3. The metal film 7 is made of, for example, platinum.

  A resist pattern 10 is formed so as to cover a predetermined portion of the metal film 7. The metal layer 7 is patterned by etching using the resist pattern 10 as a mask. Etching of the metal layer 7 can be suitably performed by a method such as an ion milling method or a reactive ion etching method.

  After the metal layer 7 is etched, the resist pattern 10 is removed to obtain the thin film capacitor 100.

  The present invention is not limited to the embodiment as described above, and various modifications can be made without departing from the spirit of the present invention. For example, instead of the resist pattern, an upper electrode that is a metal film formed in a predetermined pattern may be used as an etching mask.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

  A barium titanate film (BT film) having a thickness of 100 nm is formed on a nickel foil by a sputtering method, and BT is formed on the BT film in a predetermined pattern using a photosensitive resin (manufactured by Tokyo Ohka Kogyo Co., Ltd., OFPR-800LB). A resist pattern in which an opening exposing the film was formed was formed.

The test pieces prepared in this way are shown in No. 1 shown in Table 1. It was immersed in each etching liquid which has a composition of 1-26 at 23 degreeC. However, no. In No. 21, a copper foil was used. 24, SUS304 foil was used instead of nickel foil. No. 22 shows a BST (Ba _0.5 Sr _0.5 TiO ₃ ) film (thickness: 100 nm). No. 25, a CaTiO ₃ film (thickness 100 nm) In No. 26, the BaZrO ₃ film was formed in place of the BT film.

  The time for removing all the BT film or BST film by etching was determined as the etching time. The presence or absence of BT film or BST film residue was confirmed using an interference type film thickness measuring device (NanoSpec 6100, manufactured by Nanometrics Japan).

  No. 4 mol / L hydrochloric acid was used as an etching solution. In 1, the BT film could be etched, but the nickel foil was also etched. No. 1 using 1 mol / L hydrochloric acid. In No. 2, the etching rate was very low, and nickel foil etching was also observed. No. 1 using an etching solution containing only a fluorine compound and no hydrochloric acid. In 5 and 10, the BT film was etched at a relatively high etching rate, but a white film that appeared to be barium fluoride was formed on the nickel foil. No. using sulfuric acid as an acid combined with a fluorine compound. In the case of No. 8, a white film that appears to be barium sulfate was formed on the nickel foil.

On the other hand, No. 1 using an etching solution containing 0.01 to 3 mol / L of a fluorine compound and 0.1 to 5 mol / L of hydrochloric acid, phosphoric acid, nitric acid or acetic acid. In the case of 3, 4, 6, 7, 9, 13, 14, 17, 19, 21-26, the BT film, BST film, CaTiO ₃ film or BaZrO ₃ film is etched with an appropriate etching rate and good contrast, Neither etching of nickel foil or copper foil nor formation of a white film on the nickel foil was substantially observed.

  Even when it contains both a fluorine compound and hydrochloric acid, the concentration of the fluorine compound is less than 0.01 mol / L. In No. 15, the BT film was hardly etched and the concentration of the fluorine compound exceeded 3 mol / L. In No. 16, the etching rate was too high, and it was difficult to control the production. In addition, hydrochloric acid concentration of less than 0.1 mol / L No. No. 12, a white film was formed on the nickel foil, and No. 12 using an etching solution containing 7 mol / L acetic acid. In No. 20, the etching pattern was not clear and there was a problem in the contrast of the pattern.

  From the above experimental results, according to the method according to the present invention, the dielectric film is etched with an appropriate etching rate and good contrast while suppressing damage to the base metal film and adhesion of unnecessary substances to the surface of the base metal film. It was confirmed that it was possible.

It is sectional drawing which shows one Embodiment of the manufacturing method of a dielectric material element. It is sectional drawing which shows one Embodiment of the manufacturing method of a dielectric material element.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Base metal film (lower electrode), 3 ... Dielectric film, 5 ... Resist pattern, 7 ... Metal film (upper electrode), 10 ... Resist pattern, 100 ... Thin film capacitor

Claims (4)

A dielectric film formed on a base metal film containing an oxide having one or more elements selected from Group A consisting of Ba, Sr and Ca and one or more elements selected from Group B consisting of Ti and Zr A step of removing a part of the dielectric film by contacting the substrate with an etching solution,
The etchant is
And 0.01~3.0mol / L the full Tsu-containing compounds,
Hydrochloride, an aqueous solution containing a 0.1 to 5.0 mol / L of at least one acid selected from nitric acid and phosphoric acid or Ranaru group,
The fluorine compound is ammonium fluoride or ammonium fluoride and hydrogen fluoride;
The base metal film includes at least one of stainless steel, Cu and Ni;
A method for manufacturing a dielectric element.   The manufacturing method according to claim 1, wherein the dielectric film is brought into contact with the etching solution for 10 seconds to 20 minutes. The production method according to claim 1 or 2 , wherein the oxide is barium titanate or barium strontium titanate. The manufacturing method as described in any one of Claims 1-3 whose said base metal film is stainless steel foil, copper foil, or nickel foil.

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