Etching method for metal oxide

Abstract

To provide an etching method for a metal oxide which suppresses a load on an environment.SOLUTION: An etching method for a metal oxide includes: turning a mixed gas G (discharge gas), for which a hydrogen gas is added to a nitrogen gas, into atmospheric pressure plasma P; irradiating a heated metal oxide film 51 with the atmospheric pressure plasma P; and etching the metal oxide film 51. A ratio of a flow of the hydrogen gas with respect to a flow of the nitrogen gas in the etching method for the metal oxide is more than 0% and equal to or less than 4.0%.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for etching metal oxides. [Background technology]

[0002] Patent Document 1 discloses a surface treatment device that utilizes atmospheric pressure plasma. This surface treatment device converts a treatment gas introduced into a plasma generating section into plasma, and by bringing this plasma into contact with the surface of a substrate, performs cleaning of the substrate surface, removal of resist, etc. In addition, when etching silicon, it is disclosed that a perfluorinated gas such as CF4, chlorine gas, or a molecular gas containing chlorine element is used as the treatment gas. Here, atmospheric pressure plasma is a plasma having a pressure equivalent to atmospheric pressure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2006-509331 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, when dry etching metal oxides used as semiconductors, perfluorinated gases such as CF4, chlorine gas, or molecular gases containing chlorine element are used. However, perfluorinated gases such as CF4 are known as greenhouse gases, and chlorine gas and molecular gases containing chlorine element are toxic, so it is preferable to refrain from using them. For this reason, an etching method that can etch metal oxides without using perfluorinated gases or molecular gases containing chlorine element is desired.

[0005] The present invention has been made in view of the above-mentioned conventional circumstances, and an object of the present invention is to provide a method for etching metal oxides which reduces the burden on the environment. [Means for solving the problem]

[0006] The method for etching a metal oxide of the present invention comprises the steps of: 1. A method for etching a metal oxide, comprising: generating atmospheric pressure plasma from a discharge gas obtained by adding hydrogen gas to nitrogen gas; and irradiating a heated metal oxide with the atmospheric pressure plasma to etch the metal oxide, the method comprising the steps of: The ratio of the flow rate of the hydrogen gas to the flow rate of the nitrogen gas is greater than 0% and is equal to or less than 4.0%.

[0007] According to the present invention, it is possible to prevent hydrogen gas from igniting, reduce the burden on the environment, and satisfactorily etch metal oxide. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing the procedure of a method for etching a metal oxide film in Example 1. FIG. [Diagram 2] (A) is an SEM image showing the surface of a metal oxide film on a substrate on which the metal oxide film is laminated, and (B) is an SEM image showing the side surface of the substrate. [Diagram 3] 1 is a schematic diagram of an etching apparatus for carrying out the metal oxide film etching method of Example 1. FIG. [Figure 4] (A) is an SEM image showing the surface of the substrate from which the metal oxide film has been removed, and (B) is an SEM image showing the side surface of the substrate. [Diagram 5] 1 is a graph showing the spectrum of light generated from atmospheric pressure plasma. [Figure 6] 6 is an enlarged graph showing the inside of a square frame in FIG. 5. [Figure 7] 1 is a graph plotting the intensity of light at an emission wavelength caused by NH (nitrogen hydrogen radical) when the ratio of the flow rate of hydrogen gas to the flow rate of nitrogen gas is changed. [Figure 8] 1 is a graph showing photoluminescence (PL) spectra before and after an etching process is performed on a substrate. [Figure 9] 11 is a graph showing the amount of change in peaks caused by oxygen defects before and after an etching process is performed when the substrate temperature is changed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] A preferred embodiment of the present invention will now be described.

[0010] In the method for etching a metal oxide, the heating temperature of the metal oxide may be higher than 150° C. In this case, the metal oxide can be etched better.

[0011] Next, a first embodiment of the metal oxide etching method of the present invention will be described with reference to the drawings.

[0012] <Example 1> The metal oxide etching method of Example 1 first performs a cleaning step of cleaning a substrate 50 made of Si (see FIG. 1(A)). For example, in the cleaning step, the substrate 50 is immersed in an organic solvent such as acetone or methanol, cleaned using an ultrasonic cleaner, and then dried. Thereafter, the substrate 50 is immersed in pure water, cleaned using an ultrasonic cleaner, and then dried. This removes foreign matter such as dust adhering to the surface of the substrate 50 from the surface of the substrate 50. In this manner, the cleaning step is performed.

[0013] Next, after the cleaning process, a metal oxide film forming process is performed to form a metal oxide film 51, which is a metal oxide, on the surface of the substrate 50 (see FIG. 1(B)). The metal oxide film 51 is, for example, zinc oxide (ZnO). In the metal oxide film forming process, the metal oxide film can be formed by a known method such as magnetron sputtering, pulsed laser deposition (PLD), and metalorganic chemical vapor deposition (MOCVD). In the first embodiment, the thickness of the metal oxide film 51 was set to about 200 nm. FIG. 2 shows an SEM image of the surface of the metal oxide film 51 and an SEM image of the substrate 50 on which the metal oxide film 51 is laminated, taken from the side. The metal oxide film 51 is formed of dense crystals that are petal-shaped and rise from the surface of the substrate 50.

[0014] Next, an etching process is performed to etch the surface of the metal oxide film 51 thus formed (see FIG. 1(C)). In the etching process, an etching apparatus 30 shown in FIG. 3 is used. The etching apparatus 30 has a reaction chamber 31, a heating device 32, a temperature detection unit 33, a plasma generation unit 34, and a power supply unit 35.

[0015] The reaction vessel 31 is, for example, a cylindrical glass tube arranged with its axis oriented in the left-right direction. The left and right ends of the reaction vessel 31 are closed by closing members 31H. A communication passage 31G is provided at the upper end of the reaction vessel 31, connecting the inside and outside of the reaction vessel 31. A mounting table 31A is provided inside the reaction vessel 31.

[0016] For example, a nitride ceramic heater is used for the heating device 32. The heating device 32 has a flat body 32A and an electric wire 32B for supplying power to the body 32A. The body 32A is placed on the placement table 31A with the plate thickness direction facing the up-down direction. The electric wire 32B is drawn out to the outside through an insertion hole 31B provided at the lower end of the reaction vessel 31. For the heating device 32 in this embodiment, WALN-3H manufactured by Sakaguchi Electric Heating Co., Ltd. is used.

[0017] For example, a known thermocouple is used for the temperature detection unit 33. The temperature detection unit 33 is attached to an edge portion of the main body 32A of the heating device 32. An electric wire 33A connected to the temperature detection unit 33 is drawn to the outside via an insertion hole 31C provided at the lower end portion of the reaction tank 31. The electric wire 33A drawn to the outside is connected to, for example, a display device (not shown), and is configured to be able to display the temperature detected by the temperature detection unit 33 on the display device.

[0018] The plasma generating unit 34 is provided at the upper end of the reaction vessel 31. The plasma generating unit 34 has a gas flow unit 34A, a first electrode 34B, and a second electrode 34C. For example, a cylindrical glass tube that extends vertically is used for the gas flow unit 34A. The gas flow unit 34A is provided penetrating the upper end of the reaction vessel 31 in the vertical direction. A gas inlet passage 34D is provided at the upper part of the gas flow unit 34A.

[0019] The first electrode 34B is made of, for example, copper formed into a rod shape. The first electrode 34B is inserted into the gas flow part 34A so that the upper end part of the first electrode 34B protrudes above the gas flow part 34A. For example, the first electrode 34B is provided by penetrating a plug 34E that closes the upper end of the gas flow part 34A.

[0020] The second electrode 34C is, for example, a laminate of a ceramic part such as alumina formed in a disk shape and a metal electrode formed in a disk shape. An ejection hole 34F is formed in the center of the second electrode 34C, penetrating in the plate thickness direction. The second electrode 34C is attached to the lower end of the gas flow section 34A so as to close the lower end of the gas flow section 34A. There is a predetermined distance between the lower end of the first electrode 34B and the upper end of the second electrode 34C. The second electrode 34C is disposed facing upward from the mounting table 31A of the reaction vessel 31 at a predetermined distance.

[0021] A known inverter type power supply device is used for the power supply unit 35. The power supply unit 35 and the first electrode 34B are connected by an electric wire 35A. The power supply unit 35 and the second electrode 34C are connected by an electric wire 35B. When power is supplied from a commercial power source, the power supply unit 35 is configured to generate a potential difference of 20 kHz and 9 kVp-p between the electric wires 35A and 35B. The etching apparatus 30 is configured in this manner.

[0022] [An example of the operation of an etching device] First, the substrate 50 having the metal oxide film 51 formed thereon is placed on the upper surface of the main body 32A of the heating device 32. At this time, the substrate 50 is placed on the heating device 32 so that the metal oxide film 51 is on the upper side of the substrate 50. The distance between the surface of the metal oxide film 51 and the lower surface of the second electrode 34C is approximately 10 mm. Then, a mixed gas G of nitrogen gas and hydrogen gas is allowed to flow from the gas inlet passage 34D. The inflow rate of the mixed gas G into the gas inlet passage 34D is approximately 5 L / min. The ratio of the flow rate of hydrogen gas to the flow rate of nitrogen gas is greater than 0% and equal to or less than 4%.

[0023] The mixed gas G flowing in from the gas inflow passage 34D fills the reaction tank 31. Then, the surplus mixed gas G in the reaction tank 31 flows out of the reaction tank 31 through the communication passage 31G. Therefore, the pressure inside the reaction tank 31 into which the mixed gas G flows in is atmospheric pressure.

[0024] Next, the power supply unit 35 is operated. Then, a potential difference of 20 kHz and 9 kVp-p is generated between the first electrode 34B and the second electrode 34C via the electric wires 35A and 35B. This causes a discharge between the first electrode 34B and the second electrode 34C, generating atmospheric pressure plasma P. When the mixed gas G is exposed to the atmospheric pressure plasma P, a part of the mixed gas G becomes high energy nitrogen molecules (N2 * ), nitrogen molecular ion (N2 + ), nitrogen ions (N + ), hydrogen ion (H +), nitrogen atoms (N), hydrogen atoms (H), and nitrogen-hydrogen radicals (NH, NH2, etc.). These high-energy nitrogen molecules (N2 * ), nitrogen molecular ion (N2 + ), nitrogen ions (N + ), hydrogen ion (H + ), nitrogen atoms (N), hydrogen atoms (H), nitrogen-hydrogen radicals (NH, NH2, etc.), etc., together with the mixed gas G, are ejected as atmospheric pressure plasma P from the ejection holes 34F of the second electrode 34C toward the metal oxide film 51 of the substrate 50. This atmospheric pressure plasma P generates light. In other words, the mixed gas G acts as a discharge gas. In this way, the discharge gas obtained by adding hydrogen gas to nitrogen gas becomes atmospheric pressure plasma P.

[0025] Next, the heating device 32 is operated. Then, the temperature of the main body 32A of the heating device 32 rises and reaches a predetermined temperature. Then, the temperature of the substrate 50 and the metal oxide film 51 placed on the main body 32A also rises together with the main body 32A and reaches a predetermined temperature. The heating temperature of the metal oxide film 51 is preferably 150°C or higher, more preferably 200°C or higher, and even more preferably 300°C or higher. Then, after the main body 32A reaches the predetermined temperature, it is held for about 15 minutes. In this way, the atmospheric pressure plasma P is irradiated to the heated metal oxide film 51.

[0026] During the 15 minutes, high energy nitrogen molecules (N2 * ), nitrogen molecular ion (N2 + ), nitrogen ions (N + ), hydrogen ion (H + ), nitrogen atoms (N), hydrogen atoms (H), nitrogen-hydrogen radicals (NH, NH2, etc.), etc. are irradiated, which causes the etching of the metal oxide film 51 to proceed (see FIG. 1(C)). After maintaining this for 15 minutes, the operation of the heating device 32 and the power supply unit 35 is stopped. Then, the inflow of the mixed gas G into the gas inflow path 34D is stopped. In this way, the etching process using the etching device 30 is completed.

[0027] FIG. 4 shows an SEM image of the surface of the substrate 50 after performing an etching process with the temperature of the substrate 50 set to 300° C. and the ratio of the flow rate of hydrogen gas to the flow rate of nitrogen gas set to 1%. As shown in FIG. 4, it was found that by performing the etching process, the metal oxide film 51 can be etched and removed from the surface of the substrate 50 to expose the surface of the substrate 50. That is, the metal oxide film 51 is not shown in FIG. 4. It was also found that the metal oxide film 51 can be etched even when the ratio of the flow rate of hydrogen gas to the flow rate of nitrogen gas is greater than 0% and is 4.0% or less (not shown). In contrast, it was found that the metal oxide film 51 is not etched when the temperature of the substrate 50 is set to 300° C. and the etching process is performed by flowing only nitrogen gas (that is, the ratio of the flow rate of hydrogen gas to the flow rate of nitrogen gas is 0%) into the reaction tank 31 (not shown).

[0028] [Etching Considerations] FIG. 5 shows the spectrum of light generated from atmospheric pressure plasma P. Four types of spectra are shown overlapping in FIG. 5: Sample 1 with a ratio of hydrogen gas flow rate to nitrogen gas flow rate of 1.2%, Sample 2 with a ratio of 2.4%, Sample 3 with a ratio of 3.6%, and Sample 4 with a ratio of 0%. As shown in FIG. 5, in all of Samples 1 to 4, multiple peaks protruding in a pulse shape appear at emission wavelengths between approximately 300 nm and 400 nm. These peaks are light with wavelengths caused by nitrogen gas. FIG. 6 shows an enlarged graph of the tip of the peak with the greatest intensity (within the square frame in FIG. 5). As shown in FIG. 6, in Samples 1 to 3, a peak P caused by NH at an emission wavelength position of approximately 336 nm is shown. NH appears, and the emission wavelength is at about 337 nm, where a peak P due to nitrogen appears. N In contrast, in sample 4, the peak P NH The peak P due to nitrogen is not visible. N Only is shown.

[0029] When the etching process is performed by flowing only nitrogen gas into the reaction chamber 31, the metal oxide film 51 is not etched, and the spectrum shows a peak P NH (See Sample 4 in FIG. 6). When the ratio of the flow rate of hydrogen gas to the flow rate of nitrogen gas is greater than 0% and is equal to or less than 4.0%, the metal oxide film 51 is etched. When the ratio of the flow rate of hydrogen gas to the flow rate of nitrogen gas is 1.2%, 2.4%, and 3.6%, the peak P due to NH is not observed in the spectroscopic spectrum. NH (See Samples 1 to 3 in FIG. 6). Considering these findings, it is believed that NH (nitrogen hydrogen radicals) contribute to the etching of the metal oxide film 51.

[0030] FIG. 7 shows a graph plotting the intensity of light at an emission wavelength (approximately 336 nm) caused by NH (nitrogen hydrogen radical) when the ratio of the flow rate of hydrogen gas to the flow rate of nitrogen gas is changed to 10 different values, 0.4%, 0.8%, 1.2%, 1.6%, 2.0%, 2.4%, 2.8%, 3.2%, 3.6%, and 4.0%. As shown in FIG. 7, it was found that the intensity of light at a wavelength caused by NH was 0.2 or more at all ratios of the flow rate of hydrogen gas to the flow rate of nitrogen gas ranging from 0.4% to 4.0%. Therefore, it is considered that the metal oxide film 51 can be etched by setting the ratio of the flow rate of hydrogen gas to the flow rate of nitrogen gas between 0.4% and 4.0%. Note that the metal oxide film 51 can also be etched when the ratio of the flow rate of hydrogen gas to the flow rate of nitrogen gas is smaller than 0.4% and larger than 0. For this reason, even when the ratio of the flow rate of hydrogen gas to the flow rate of nitrogen gas is smaller than 0.4% and larger than 0, the intensity of light with a wavelength caused by NH (nitrogen hydrogen radical) is considered to be at least 0 or more.

[0031] Fig. 8 shows photoluminescence (PL) spectra of the substrate 50 before and after the etching process. This spectrum was measured at the center of the substrate 50. The heating temperature of the substrate 50 was 300°C. As shown in Fig. 8, in the spectrum Sp before the etching process and the spectrum Sa after the etching process, a peak P ZnO appears, and at approximately 2.3 eV, a peak P due to oxygen vacancies appears. O In addition, the peak P due to oxygen defects in the spectrum Sa after the etching process is O is the peak P due to oxygen defects in the spectrum Sp before the etching process is performed. O was found to be significantly larger than

[0032] The temperature of the substrate 50 was changed to six levels: 60° C., 100° C., 150° C., 200° C., 250° C., and 300° C. At each level, the peak P O 9 is a graph plotting the amount of change in the peak P caused by oxygen defects before and after the etching process is performed, when the temperature of the substrate 50 is 60° C., 100° C., and 150° C. As shown in FIG. O In contrast, as the temperature of the substrate 50 increases to 200° C., 250° C., and 300° C., the peak P due to oxygen defects before and after the etching process is increased. O The change was found to be large.

[0033] The surface of the substrate 50, which had been subjected to an etching process at six different temperatures, 60°C, 100°C, 150°C, 200°C, 250°C, and 300°C, was observed using an SEM. As a result, it was found that when the temperature of the substrate 50 was 60°C, 100°C, and 150°C, no change was observed in the metal oxide film 51, but as the temperature of the substrate 50 increased to 200°C, 250°C, and 300°C, the degree to which the metal oxide film 51 was etched increased (not shown). From this, it was found that the peak P caused by oxygen defects before and after the etching process was performed O It is believed that the amount of change in is correlated with the degree of etching of the metal oxide film 51. Therefore, the heating temperature of the metal oxide film 51 (metal oxide) when etching the metal oxide film 51 is preferably higher than 150° C., more preferably higher than 200° C., and further preferably higher than 300° C.

[0034] Next, the effects of the above embodiment will be described.

[0035] In the method for etching metal oxide, mixed gas G (discharge gas) obtained by adding hydrogen gas to nitrogen gas is turned into atmospheric pressure plasma P, and the heated metal oxide film 51 is irradiated with the atmospheric pressure plasma P to etch the metal oxide film 51. The ratio of the flow rate of hydrogen gas to the flow rate of nitrogen gas is greater than 0% and equal to or less than 4.0%. With this configuration, it is possible to prevent the hydrogen gas from igniting, reduce the burden on the environment, and satisfactorily etch the metal oxide film 51 (metal oxide).

[0036] In the method for etching a metal oxide, the heating temperature of the metal oxide film 51 (metal oxide) is higher than 150° C. According to this configuration, the metal oxide film 51 (metal oxide) can be etched more satisfactorily.

[0037] The present invention is not limited to the embodiments described above and illustrated in the drawings, and the following embodiments are also included within the technical scope of the present invention. (1) Unlike the first embodiment, the material of the substrate is not limited to Si. (2) Unlike the first embodiment, the target of etching may not be a metal oxide film but may be a free-standing metal oxide having a certain thickness. (3) Unlike Example 1, the metal oxide is not limited to ZnO. For example, the present invention can be applied to any metal oxide in which a metal is oxidized, such as cobalt oxide (Co3O4), copper oxide (CuO), silver oxide (Ag2O), or indium oxide (In2O3). (4) Unlike Example 1, the etching process may be performed for a time longer than 15 minutes. In this case, etching of the metal oxide proceeds more easily. (5) The pressure inside the reaction vessel while the mixed gas is being introduced may be slightly higher than atmospheric pressure. [Explanation of symbols]

[0038] 51...Metal oxide film (metal oxide) G … Mixed gas (discharge gas) P...atmospheric pressure plasma

Claims

1. 1. A method for etching a metal oxide, comprising: generating atmospheric pressure plasma from a discharge gas obtained by adding hydrogen gas to nitrogen gas; and irradiating a heated metal oxide with the atmospheric pressure plasma to etch the metal oxide, the method comprising the steps of: A method for etching a metal oxide, wherein a ratio of a flow rate of the hydrogen gas to a flow rate of the nitrogen gas is greater than 0% and is not greater than 4.0%.

2. 2. The method of claim 1, wherein the heating temperature of the metal oxide is greater than 150°C.

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