Method for forming patterned oxide film

Abstract

To provide a method for forming oxide films with high precision in sacrificial layer removal, and consisting of fine shapes and patterns.SOLUTION: It is characterized that it has a step for forming a SrCO3 film patterned on the surface of a substrate, a step for forming an oxide film on top of the same, and a step for removing the portion having the SrCO3 film.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for forming a patterned oxide film, and more particularly to a method for forming a patterned oxide film by lift-off. [Background technology]

[0002] Various oxide films are being investigated in the fields of ferroelectrics, piezoelectrics, ferromagnetics, high-temperature superconductors, transparent conductive films, and wide-gap semiconductors. The oxide films used for these applications are required to have electrical conductivity, ferroelectricity, ferromagnetism, high-temperature superconductivity, etc. However, such oxide films generally have high melting points and excellent chemical resistance, making patterning by reactive ion etching, resist lift-off, etc. difficult.

[0003] Therefore, the present applicant has previously proposed a method for forming a finely shaped or patterned oxide film on a substrate, in which an amorphous calcium oxide (a-CaO) layer is used as a sacrificial layer (mask layer) and a patterned oxide film is formed by water lift-off (Patent Document 1).

[0004] However, subsequent research revealed that although the method of removing (lifting off) a sacrificial layer made of a-CaO with water is excellent for fine processing and patterning, there are cases where residues remain that are not completely removed during lift-off, and that there is room for further improvement. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7357903 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a method for forming an oxide film having a fine shape or pattern, which allows for high precision removal of a sacrificial layer. [Means for solving the problem]

[0007] The method for forming a patterned oxide film according to the present invention is characterized by comprising the steps of forming a patterned SrCO3 film on the surface of a substrate, forming an oxide film thereon, and removing the portion having the SrCO3 film.

[0008] Here, the SrCO3 film is preferably an amorphous SrCO3 film, and the step of removing the portion having the SrCO3 film is preferably a step of contacting with carbonated water.

[0009] In the invention described in Patent Document 1, the sacrificial layer made of a-CaO can be removed with water such as pure water, whereas the present invention focuses on the fact that the SrCO3 film does not easily deliquesce in pure water but easily deliquesces in carbonated water, which is pure water containing carbon dioxide.

[0010] In the present invention, the patterned oxide film refers to an oxide film formed into a fine shape or a desired pattern. In particular, materials having any of ferroelectric properties, piezoelectric properties, high-temperature superconducting properties, ferromagnetic properties, and semiconductor properties are preferred. Specifically, for example, SrRuO3, Ga2O3, Pb(Zr,Ti)O3, La 1-x Sr x MnO3, YBa2Cu3O 7-x Examples include: The substrate may be a semiconductor substrate such as a silicon substrate or a gallium arsenide substrate, or a metal substrate such as copper or aluminum.

[0011] In the present invention, the step of forming a patterned SrCO3 film may be a lift-off method of a photoresist layer, dry etching such as reactive ion etching, or wet etching. For example, the following steps can be taken as an example. An example includes the steps of forming a patterned resist layer on the surface of the substrate using a resist material by photolithography, forming an SrCO3 film on the surface, removing the portion with the resist layer by a lift-off method using an acetone solvent or the like, forming an oxide film thereon, and removing the portion with the SrCO3 film with carbonated water. [Effects of the Invention]

[0012] The method for forming a patterned oxide film according to the present invention uses a thin film layer made of SrCO3 as a sacrificial layer, which can be easily lifted off with carbonated water, leaving little residue and enabling the formation of fine shapes and desired patterns. [Brief explanation of the drawings]

[0013] [Figure 1] 1 illustrates a method for forming a patterned oxide film according to the present invention. [Figure 2] An example of an oxide film pattern is shown. [Figure 3] Indicates the concentration of carbonated water. [Figure 4] The evaluation results of the ohmic characteristics are shown below. [Figure 5] The results of comparing surface roughness are shown below. DETAILED DESCRIPTION OF THE INVENTION

[0014] An example of forming a patterned oxide film according to the present invention will be described below with reference to the drawings, but the present invention is not limited thereto.

[0015] FIG. 1 shows an example of a process for forming a pattern on an oxide film. As shown in FIG. 1(A), for example, a photoresist is applied to the entire surface of a strontium titanate (SrTiO3) single crystal substrate (STO substrate), and then formed by photolithography or the like so that a desired fine shape or pattern remains. As a result, a first sacrificial layer made of the resist film 11 is formed.

[0016] Next, as shown in FIG. 1(B), a second sacrificial layer made of a-SrCO3 (amorphous strontium carbonate) 12 is formed at room temperature using, for example, a pulsed laser deposition (PLD) method. The a-SrCO3 film is formed on the resist film and on the area where the resist film has been removed. Next, as shown in FIG. 1(C), the resist film 11 is removed using a solvent such as acetone.

[0017] Next, in this example, as shown in FIG. 1(D), an oxide film of SrRuO3 is formed on the surface of the substrate. This oxide film can be formed, for example, by a PLD method at high temperature under vacuum. Next, when the substrate is immersed in carbonated water, the second sacrificial layer made of a-SrCO3 is removed, and a patterned oxide film 13 is formed on the surface of the substrate, as shown in FIG. 1(E). In the explanation of the process in Figure 1, the thickness of the resist film shown in (B) and (C) and the thickness of the a-SrCO3 film are shown as a schematic representation of the relative relationship. Similarly, the thicknesses of SrRuO3 and a-SrCO3 in (D) and (E) are also relative, and the thickness of a-SrCO3 shown in Figure 1(C) does not match the thickness of a-SrCO3 shown in Figure 1(D). The thickness of the a-SrCO3 film is preferably 10 times or more the thickness of the oxide film 13.

[0018] Here, the a-SrCO3 film has low solubility in pure water, but becomes soluble in carbonated water as shown in Figure 3. The graph in Figure 3 shows the relationship between the solubility of CO2 in pure water [mol / kg] and pressure [atm]. This graph shows that even under pressure of around 1 atm, CO2 in the atmosphere dissolves and turns into carbonated water. The reaction formula (1) is shown below. TIFF2025145955000002.tif13166In addition, the solubility of SrCO3 in pure water is 1.1 x 10-3 g / 100ml. Figure 2 shows a photograph of the substrate surface after forming an oxide film of SrRuO3 (13 nm) on a layer of a-SrCO3 (400 nm) and immersing it in carbonated water. It can be seen that an oxide film made of SrRuO3 has been patterned with high precision on the substrate.

[0019] Figure 5 shows the surface roughness measurement results after forming an oxide film of SrRuO3 13 nm on a-SrCO3 (400 nm) and a-CaO (400 nm), and then removing it using carbonated water for a-SrCO3 and pure water for a-CaO. It can be seen that the a-SrCO3 film has a smaller surface roughness and less residue. Here, [Rq] root mean square height represents the root mean square over the reference length, and corresponds to the standard deviation of the surface roughness. When an a-SrCO3 film was used as the sacrificial layer, Rq was 0.40 nm, while Rq for an a-CaO film was 1.29 nm. This small value means that there was little residue left behind on the sacrificial layer. Furthermore, when the deliquescence rates of the samples with a-SrCO3 film 400 nm and a-CaO film 400 nm were measured, they were comparable at the level of 24 to 31 nm / min.

[0020] In Figure 4, the current-voltage characteristics (JV characteristics) were evaluated using a pattern of SRO:SrRuCO3 film with a thickness of 13 nm and a width of 50 μm. From this graph, it can be seen that the junction surface exhibits ohmic characteristics. [Explanation of symbols]

[0021] 11 Resist film 12 a-SrCO3 membrane 13 SrRuO3(SRO)

Claims

1. SrCO patterned on the surface of the substrate ３ forming a film; forming an oxide film thereon; SrCO ３ and removing the portion having the film.

2. SrCO ３ The film is amorphous SrCO ３ 2. The method for forming a patterned oxide film according to claim 1, wherein the oxide film is a film.

3. SrCO ３ 3. The method for forming a patterned oxide film according to claim 2, wherein the step of removing the film-containing portion is a step of contacting the film with carbonated water.

4. The patterned SrCO ３ The step of forming the film includes forming a patterned resist layer on the surface of the substrate, and applying SrCO ３ 4. The method for forming a patterned oxide film according to claim 1, further comprising the steps of forming a film and removing the portion having the resist layer.

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