Etching method, method for manufacturing electronic components, and method for using plasma device.

Abstract

To achieve increase in an etching quantity of ruthenium and increase in a selection ratio of ruthenium to a photoresist in a ruthenium-etching technique to pattern ruthenium of a thick film with high precision.SOLUTION: An etching method is arranged to etch metal by use of a mixture gas that includes an oxygen gas serving as a base gas, and an additive gas containing a chlorine-based gas and a fluoromethane-based gas, in which concentration of the additive gas is 5-10% in the total gas.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an etching technique for etching metals such as ruthenium. [Background technology]

[0002] The manufacture of microdevices requires the development of microfabrication technologies such as metal and conductive oxide film deposition and etching, and in recent years, processing technology for ruthenium, which is used in the electrodes of BAW filters used in mobile communication systems, has become important.

[0003] As a known technique for dry etching of ruthenium or ruthenium oxide, Japanese Patent No. 2956485 (Patent Document 1) describes a technique for etching ruthenium using a gas system containing chlorine gas, hydrogen bromide gas, and oxygen gas. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 2956485 Summary of the Invention [Problem to be solved by the invention]

[0005] It is known that ruthenium can be etched using a reaction with oxygen plasma. However, the mask material used in Patent Document 1 is SOG. Using photoresist, a common mask material, reduces the selectivity with ruthenium, making it unsuitable for etching thick ruthenium. In particular, in bulk acoustic wave filters (BAW filters), ruthenium electrodes tend to become thicker as frequencies increase. This makes it difficult to use photoresist, which requires high patterning accuracy, as a mask material, hindering device development. Therefore, there is a need for a ruthenium film etching technology that increases the etching rate and improves the selectivity even when photoresist is used. [Means for solving the problem]

[0006] According to one aspect of the present disclosure, there is provided an etching method for etching metal using a mixed gas containing oxygen gas as a base gas and an additional gas consisting of a chlorine-based gas and a fluoromethane-based gas, the additional gas having a concentration of 5 to 10% of the total gas. In one embodiment of the present disclosure, metal is etched using a mixed gas containing oxygen gas as a base gas and an additional gas consisting of a chlorine-based gas and a fluoromethane-based gas, with the additional gas concentration being 5 to 10% of the total gas, thereby increasing the amount of metal etched compared to when oxygen gas is used alone. Furthermore, the etching rate can be controlled by fixing the amount of fluoromethane-based gas and adjusting the amount of chlorine-based gas.

[0007] According to one aspect of the present disclosure, an etching method can be provided in which a photoresist is used as a mask material. The use of photoresist as the mask material improves patterning accuracy. Furthermore, the selectivity between metal and photoresist is increased compared to when oxygen gas is used alone. Furthermore, the selectivity between metal and photoresist can be controlled by fixing the amount of fluoromethane-based gas and adjusting the amount of chlorine-based gas.

[0008] According to one aspect of the present disclosure, the etching method can be such that the metal is ruthenium, the chlorine-based gas is selected from chlorine, boron chloride, and chlorine fluoride, and the fluoromethane-based gas is selected from tetrafluoromethane, difluoromethane, and monofluoromethane. In one embodiment of the present disclosure, the metal is ruthenium, the chlorine-based gas is selected from chlorine, boron chloride, and chlorine fluoride, and the fluoromethane-based gas is selected from tetrafluoromethane, difluoromethane, and monofluoromethane, so that the fluorine and chlorine promote the reduction of the ruthenium etching product, thereby achieving an increased etching amount of ruthenium and an increased selectivity between ruthenium and photoresist, and thus enabling high-precision patterning of a thick ruthenium film.

[0009] According to one aspect of the present disclosure, there is provided a method for manufacturing an electronic component such as an acoustic wave filter or a MEMS, which comprises performing any one of the above etching methods. In one aspect of the present disclosure, a method for manufacturing electronic components such as acoustic wave filters and MEMS employs any of the above-described etching methods, thereby enabling electronic components such as acoustic wave filters and MEMS having thick electrodes and a three-dimensional configuration to be manufactured easily and accurately.

[0010] According to one aspect of the present disclosure, there is provided a method for using a plasma device to etch metal using a photoresist as a mask material, using a mixed gas containing oxygen gas as a base gas and an additional gas consisting of a chlorine-based gas and a fluoromethane-based gas, the additional gas having a concentration of 5 to 10% of the total gas. In one embodiment of the present disclosure, a mixed gas containing oxygen gas as a base gas and an additional gas consisting of a chlorine-based gas and a fluoromethane-based gas, with the additional gas concentration being 5 to 10% of the total gas, is used to etch metal using a photoresist as a mask material. This increases the amount of metal etched compared to when oxygen gas is used alone. Furthermore, the use of photoresist as a mask material improves patterning accuracy. Additionally, by fixing the amount of fluoromethane-based gas and adjusting the amount of chlorine-based gas, the metal etch rate and the selectivity between the metal and the photoresist can be controlled.

[0011] According to one embodiment of the present disclosure, the metal may be ruthenium, the chlorine-based gas may be selected from chlorine, boron chloride, and chlorine fluoride, and the fluoromethane-based gas may be selected from tetrafluoromethane, difluoromethane, and monofluoromethane. In one embodiment of the present disclosure, the metal is ruthenium, the chlorine-based gas is selected from chlorine, boron chloride, and chlorine fluoride, and the fluoromethane-based gas is selected from tetrafluoromethane, difluoromethane, and monofluoromethane, so that the fluorine and chlorine promote the reduction of the ruthenium etching product, thereby achieving an increased etching amount of ruthenium and an increased selectivity between ruthenium and photoresist, and thus enabling high-precision patterning of a thick ruthenium film.

[0012] According to one aspect of the present disclosure, there is provided a plasma device that uses a mixed gas containing oxygen gas as a base gas and an additional gas consisting of a chlorine-based gas and a fluoromethane-based gas, the additional gas having a concentration of 5 to 10% of the total gas. In one embodiment of the present disclosure, a plasma device uses a mixed gas containing oxygen gas as a base gas and an additional gas consisting of a chlorine-based gas and a fluoromethane-based gas, with the additional gas concentration being 5 to 10% of the total gas. This makes the plasma device more suitable for etching metals where a large etching amount is desired compared to when oxygen gas is used alone. Furthermore, the plasma device can control the etching rate by fixing the amount of fluoromethane-based gas and adjusting the amount of chlorine-based gas.

[0013] According to one aspect of the present disclosure, the plasma device may be one in which the chlorine-based gas is selected from chlorine, boron chloride, and chlorine fluoride, and the fluoromethane-based gas is selected from tetrafluoromethane, difluoromethane, and monofluoromethane. In one embodiment of the present disclosure, the plasma device is one in which the chlorine-based gas is selected from chlorine, boron chloride, and chlorine fluoride, and the fluoromethane-based gas is selected from tetrafluoromethane, difluoromethane, and monofluoromethane, so that the plasma device can be used to etch ruthenium using a photoresist as a mask material, and the fluorine and chlorine promote the reduction of the ruthenium etching product, thereby achieving an increased etching amount of ruthenium and an increased selectivity between ruthenium and the photoresist, and thus enabling high-precision patterning of thick ruthenium films. [Effects of the Invention]

[0014] According to the present disclosure, an etching rate 10 times or more faster than conventional rates can be achieved. Furthermore, according to the present disclosure, a selectivity between metal and photoresist that is 10 times or more higher than conventional levels can be obtained. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram of a plasma device. [Figure 2] 10 is a graph showing the relationship between the concentration of one kind of additional gas mixed into oxygen gas and the amount of Ru etching. [Figure 3] 1 is a graph showing the relationship between the concentration of one kind of additional gas mixed with oxygen gas and the Ru / photoresist selectivity. [Figure 4] 10 is a graph showing the relationship between the concentration of two types of additional gases mixed with oxygen gas and the amount of Ru etching. [Figure 5] 1 is a graph showing the relationship between the concentration of two types of additional gases mixed with oxygen gas and the Ru / photoresist selectivity. DETAILED DESCRIPTION OF THE INVENTION

[0016] One embodiment will be described as an etching technique for metals such as ruthenium (hereinafter simply referred to as "Ru") used in electrodes of electronic components such as BAW filters, and in particular relates to an etching gas used in a plasma device or the like during etching.

[0017] As mentioned above, plasma etching using oxygen gas can etch Ru, but using photoresist as a mask material reduces the selectivity, making it unsuitable for precise etching of thick Ru films. However, by using a mixed gas containing oxygen gas as the base gas but also including 5-10% of additional gases consisting of chlorine-based gas and fluoromethane-based gas—in other words, by making oxygen gas 90-95% of the total gas flow rate and including the remaining 5-10% of additional gases consisting of chlorine-based gas and fluoromethane-based gas—we have achieved improved etching rates and selectivity when using photoresist. Note that in this specification and claims, the percentages indicating the proportion of gas volume are by volume.

[0018] Examples of chlorine-based gases include chlorine gas (Cl2), boron trichloride (BCl3), and chlorine trifluoride (ClF3). Examples of fluoromethane gases include trifluoromethane (CHF3), difluoromethane (CH2F2), and monofluoromethane (CH3F). Examples of the metal include nickel, cobalt, copper, and ruthenium. The mask material may be a photoresist. Of these, the combination of chlorine gas and trifluoromethane is preferred. This is because chlorine and hydrogen are most effective in decomposing the etching-inhibiting products, while also maintaining the resist selectivity. However, too much hydrogen inhibits etching, so the selectivity increases but the etching rate tends to decrease. Therefore, it is preferable to add fluoromethane gas at a concentration of 5% or less.

[0019] When the mixing ratio of fluoromethane gas is increased to 2.5 to 5.0% and chlorine gas is added to the mixture, the ruthenium etching rate and the selectivity with respect to the photoresist increase almost proportionally with the increase in the mixing ratio. Therefore, by fixing the amount of fluoromethane gas and controlling the amount of chlorine gas, the desired ruthenium etching rate and selectivity with respect to the photoresist can be obtained. Therefore, etching of 300 nm or more, which is considered to be the thick film region of Ru, can be performed. For example, ruthenium can be etched to 500 nm or more using a mask formed with a 3 μm thick photoresist having a wavelength sensitive to the general G line. [Example]

[0020] Experimental Example 1: (Relationship between the concentration of one additional gas mixed with oxygen gas and the amount of Ru etching) Various test gases were flowed into the plasma etching equipment, and the Ru film on a 725 μm thick silicon wafer, on which metallic Ru was deposited by vapor deposition to a thickness of approximately 200 nm, was etched, and the difference in the amount of Ru film etched due to the different test gases was measured.

[0021] Figure 1 shows a schematic diagram of the parallel-plate inductively coupled plasma etching apparatus (ICP) 10 used in this experiment. The wafer was placed in a state of being attracted to an electrostatic chuck (ESC) 11 of this plasma etching apparatus 10, and a test gas (described in detail below) was flowed into chamber 12. A turbomolecular pump 14 with a pressure control valve 13 evacuated the chamber 12 and maintained it at a constant pressure (2.0 Pa). RF power (1000 W) was applied to coil 17 on dielectric electrode 16 as power supply 15, and RF power (100 W) was applied to metal plate electrode 19 as bias power supply 18, independently, to generate plasma 20, which was then processed for 60 seconds. The test gases used were mixtures of oxygen gas (O2) as a base gas and one of four additional gases: chlorine gas (Cl2), fluoromethane gas (CHFl3), tetrafluoromethane gas (CF4), or boron trichloride gas (BCl3). The total gas flow rate was 180 sccm for each. The amount of Ru etched was measured by observing the etched cross section using a microscope. The results are shown in Figure 2. In Figure 2, the straight line graph represents the mixture with chlorine gas added, the dashed line graph represents the mixture with fluoromethane gas added, the dashed line graph represents the mixture with tetrafluoromethane gas added, and the dashed line graph represents the mixture with boron trichloride gas added.

[0022] Results and Discussion: The graph in Figure 2 clearly shows that the relationship between the content of additional gas and the amount of Ru etched is such that the amount of Ru etched is greatest for most test gases, regardless of the type of additional gas, when the additional gas concentration is approximately 5-10% of the total gas concentration of 100%. Therefore, it was found that the amount of Ru etched increases with the amount of additional gas added up to approximately 10%, but once the amount exceeds approximately 10%, the amount of Ru etched tends to decrease as the amount of additional gas added increases.

[0023] Based on the results of Experimental Example 1, the mechanism of Ru etching when an additional gas is added to oxygen gas is thought to be as follows. First, when etching is performed using 100% oxygen gas without the addition of an additional gas, RuO2 is generated during the etching of Ru. However, this RuO2 has a low vapor pressure and therefore inhibits further etching. On the other hand, when etching is performed using oxygen gas with the addition of an additional gas, the generated RuO2 is re-dissociated to form RuO4. This RuO4 is easily vaporized and is thought to not inhibit the etching of Ru. Therefore, until the additional gas concentration increases to 10%, the additional gas reacts with the products that inhibit etching, increasing the amount of Ru etched. However, once the additional gas concentration exceeds 10%, the disadvantage of a decrease in the concentration of oxygen gas that functions as an etchant becomes significant, which is thought to result in a decrease in the amount of Ru etched.

[0024] Experimental Example 2: (Relationship between the concentration of one additional gas mixed with oxygen gas and the Ru / photoresist selectivity) A quartz crystal substrate with the Ru film prepared in Experimental Example 1 was coated with a photoresist material with an i-line sensitivity to a thickness of approximately 3 μm, and etched using various test gases under the same conditions as in Experimental Example 1. The etching depth of the photoresist was measured by observing the etched cross section with a microscope. The selectivity ratio of Ru to photoresist was calculated from the etching depth of Ru obtained in Experimental Example 1 and the etching depth of photoresist obtained in Experimental Example 2. The results are shown in Figure 3. In Figure 3, the line graph shown with a straight line represents a mixed gas to which chlorine gas was added, the line graph shown with a dashed line represents a mixed gas to which fluoromethane gas was added, the line graph shown with a dot-dash line represents a mixed gas to which tetrafluoromethane gas was added, and the line graph shown with a two-dot-dash line represents a mixed gas to which boron trichloride gas was added.

[0025] Results and Discussion: The graph in Figure 3 clearly shows that the relationship between the additional gas content and the selectivity is such that when the additional gas concentration is approximately 10% out of a total gas concentration of 100%, the selectivity reaches its maximum for most of the test gases, with the exception of chlorine gas, regardless of the type of additional gas. Therefore, while the selectivity increases with the amount of additional gas added up to approximately 10%, once the amount exceeds approximately 10%, the selectivity tends to decrease as the amount of additional gas added increases. This trend is similar to the amount of Ru etched. Furthermore, for chlorine gas, even when the amount exceeds 10%, the value remains roughly the same as when it is 10%. This is thought to be because carbon tetrachloride (CCl4), a reaction product between chlorine gas and the photoresist, becomes a deposit component and accumulates on the photoresist, maintaining the selectivity.

[0026] Experimental Example 3: (Relationship between the concentration of two additional gases mixed with oxygen gas and the amount of Ru etching) As in Experimental Example 1, various test gases were used to etch Ru on a 5 mm thick quartz substrate with approximately 200 nm of metallic Ru deposited by vapor deposition. The difference from Experimental Example 1 is that in Experimental Example 1 the test gas was oxygen gas with one additional gas added, whereas in this experiment it was a mixed gas of oxygen gas with two additional gases added. More specifically, the test gas used was a mixed gas containing oxygen gas (O2) as a base and two additional gases, chlorine gas (Cl2) and fluoromethane gas (CHFl3). Ru was then etched with these test gases in the same manner as in Experimental Example 1, and the etching amount was measured. The results are shown in Figure 4. In Figure 4, the broken line represents a graph in which the amount of fluoromethane gas was fixed at 2.5% and the amount of chlorine gas was changed, while the straight line represents a graph in which the amount of fluoromethane gas was fixed at 5.0% and the amount of chlorine gas was changed.

[0027] Results and Discussion: When a gas mixture of oxygen gas and two additional gases, fluoromethane and chlorine, was used, the amount of Ru etched exceeded 110 nm in some places. In other words, compared to the amount of Ru etched of 11 nm when using 100% oxygen gas, the amount of Ru etched using this gas mixture was more than 10 times greater. This is thought to be because the addition of fluoromethane gas promotes the reduction of etching products, and the addition of chlorine gas promotes the decomposition of etching products. The key point here is the decomposition of RuO2 due to the reduction of hydrogen caused by fluoromethane gas.

[0028] Experimental Example 4: (Relationship between the concentration of two additional gases mixed with oxygen gas and the Ru / photoresist selectivity) As in Experimental Example 2, various test gases were used to etch the photoresist on a 5 mm-thick quartz substrate coated with photoresist. The difference from Experimental Example 2 is that, whereas in Experimental Example 2 the test gas was a mixture of oxygen gas and one additional gas, in this experiment it was a mixture of oxygen gas and two additional gases. The selectivity between Ru and the photoresist was then determined in the same manner as in Experimental Example 2. The results are shown in Figure 5. In Figure 5, the broken line represents a graph in which the amount of fluoromethane gas was fixed at 2.5% and the amount of chlorine gas was changed, while the straight line represents a graph in which the amount of fluoromethane gas was fixed at 5.0% and the amount of chlorine gas was changed.

[0029] Results and Discussion: When a mixed gas containing oxygen gas plus two additional gases, fluoromethane and chlorine, was used, the selectivity between Ru and photoresist exceeded 0.2 in some areas. In other words, compared to the selectivity between Ru and photoresist of 0.017 when using 100% oxygen gas, the use of this mixed gas increased the selectivity between Ru and photoresist by more than 10 times. As the concentration of fluoromethane gas increases, CH radical products are generated, so it is preferable to keep it to around 5.0%. It can be seen that if the chlorine gas mixture ratio is increased under these conditions, both the etching rate of Ru and the selectivity between Ru and photoresist increase. Therefore, by adjusting the amount of chlorine gas, it is possible to control both the etching rate of Ru and the selectivity between Ru and photoresist.

[0030] The above-described embodiments are examples of the present invention, and modifications of the embodiments or additions or combinations of known technologies may be made without departing from the spirit of the present invention, and such technologies are also included in the scope of the present invention. [Explanation of symbols]

[0031] 10 Plasma equipment 11 Electrostatic chuck 12 chambers 13 Pressure Control Valve 14 Turbomolecular pump 15 Power supply 16 Dielectric electrode 17 coils 18 Bias power supply 19 Metal Plate Electrode 20. Plasma

Claims

1. An etching method for etching ruthenium using a mixed gas containing oxygen gas as a base gas and an additional gas consisting of a chlorine-based gas and hydrofluoromethane gas containing hydrogen, the additional gas having a concentration of 5 to 10% of the total gas, using a photoresist as a mask material.

2. 2. The etching method according to claim 1, wherein the chlorine-based gas is selected from the group consisting of chlorine, boron chloride, and chlorine fluoride.

3. 3. The etching method according to claim 1, wherein the amount of fluoromethane-based gas is fixed and the amount of chlorine-based gas is adjusted to control the etching rate.

4. 4. The etching method according to claim 1, wherein the amount of the fluoromethane-based gas is fixed and the amount of the chlorine-based gas is adjusted to control the selectivity between ruthenium and the photoresist.

5. A method for manufacturing an electronic component, which is an acoustic wave filter or a MEMS, by carrying out the etching method according to any one of claims 1 to 4.

6. A method for using a plasma device to etch ruthenium using a mixed gas containing oxygen gas as a base gas and an additional gas consisting of a chlorine-based gas and hydrofluoromethane gas containing hydrogen, the additional gas having a concentration of 5 to 10% of the total gas, using a photoresist as a mask material.

7. 7. The method for using a plasma device according to claim 6, wherein the chlorine-based gas is selected from the group consisting of chlorine, boron chloride, and chlorine fluoride.

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