JP7809031B2 - Substrate processing method and substrate processing apparatus - Google Patents

Description

The present invention relates to a technique for performing an etching process on a ruthenium-containing layer on a substrate.

Traditionally, in the manufacturing process of semiconductor substrates (hereinafter simply referred to as "substrates"), various processes are performed on the substrate. For example, after a conductive film is formed on the main surface of the substrate, a process is performed to remove the conductive film adhering to the bevel portion of the substrate. In recent years, with the miniaturization of devices on substrates, ruthenium (Ru) has attracted attention as a material for this conductive film. Ruthenium is difficult to remove by simply immersing it in an aqueous solution of an acid or alkali, such as hydrochloric acid or sodium hydroxide.

Patent Document 1 therefore proposes a ruthenium etching solution (Table 1, Example A32) containing orthoperiodic acid and ammonia and having a pH of 4.5 for etching ruthenium. Patent Document 2 also proposes a ruthenium etching solution containing orthoperiodic acid and ammonia and having a pH of 8 or more and 10 or less.

International Publication No. 2019/138814 Japanese Patent Application Laid-Open No. 2021-90040

However, when ruthenium is etched using the etching solution of Patent Document 1, there is a risk of generating toxic gaseous ruthenium tetroxide (RuO ₄ ).On the other hand, when ruthenium is etched using the etching solution of Patent Document 2, which has a relatively high pH, there is a risk of the etching rate being low and the processing efficiency being reduced.

The present invention was developed in consideration of the above-mentioned problems, and aims to increase the etching rate while suppressing the generation of gaseous ruthenium tetroxide.

Aspect 1 of the present invention is a substrate processing method for etching a ruthenium-containing layer on a substrate, comprising: a) preparing a substrate having a ruthenium-containing layer on its surface; b) contacting an alkaline etching solution with the ruthenium-containing layer on the substrate; and c) after step b), applying plasma to the etching solution to lower the pH, and then contacting the etching solution with the ruthenium-containing layer.

Aspect 2 of the present invention is a substrate processing method according to aspect 1, further comprising the step of: d) after step c), bringing the etching solution into contact with the ruthenium-containing layer while stopping the application of plasma to the etching solution.

Aspect 3 of the present invention is a substrate processing method according to aspect 1 or 2, wherein in step b), ruthenium dioxide is produced from the ruthenium in the ruthenium-containing layer, and in step c), soluble ruthenium tetroxide is produced from the ruthenium dioxide.

Aspect 4 of the present invention is a substrate processing method according to aspect 1 or 2 (or any one of aspects 1 to 3), in which the minimum pH value of the etching solution in step c) is 7.0 or more and 7.5 or less.

Aspect 5 of the present invention is a substrate processing method according to aspect 1 or 2 (or any one of aspects 1 to 4), in which the pH of the etching solution in step b) is 8.0 or more and 10.0 or less.

Aspect 6 of the present invention is a substrate processing method according to aspect 1 or 2 (or any one of aspects 1 to 5), in which the plasma is atmospheric plasma.

Aspect 7 of the present invention is a substrate processing method according to aspect 1 or 2 (or any one of aspects 1 to 6), in which the plasma is room temperature plasma.

Aspect 8 of the present invention is a substrate processing method according to aspect 1 or 2 (or any one of aspects 1 to 7), in which in step c), steam is applied to and recovered from gaseous ruthenium tetroxide produced by contact between the ruthenium-containing layer and the etching solution.

Aspect 9 of the present invention is a substrate processing method according to aspect 1 or 2 (or any one of aspects 1 to 8), in which in steps b) and c), the etching solution contacts the ruthenium-containing layer at the peripheral edge of the substrate.

Aspect 10 of the present invention is the substrate processing method of Aspect 1 or 2 (or any one of Aspects 1 to 9), in which the etching solution contains orthoperiodic acid.

Aspect 11 of the present invention is the substrate processing method of aspect 10, wherein the etching solution contains ammonia as an alkaline additive component.

Aspect 12 of the present invention is a substrate processing apparatus that performs an etching process on a ruthenium-containing layer on a substrate, and includes a substrate holding unit that holds a substrate having a ruthenium-containing layer on its surface; a processing liquid supply unit that applies an alkaline etching liquid onto the substrate and brings it into contact with the ruthenium-containing layer; a plasma applying unit that applies plasma to the etching liquid; and a control unit that, after the alkaline etching liquid has come into contact with the ruthenium-containing layer, controls the plasma applying unit to bring the etching liquid, whose pH has been reduced by the application of plasma, into contact with the ruthenium-containing layer.

The present invention makes it possible to increase the etching rate while suppressing the generation of gaseous ruthenium tetroxide.

FIG. 1 is a plan view of a substrate processing system. 1 is a side view of a substrate processing apparatus according to a first embodiment; FIG. 2 is a diagram illustrating a configuration of a control unit. FIG. 2 is an enlarged vertical cross-sectional view showing the vicinity of an etched portion. FIG. 1 is a diagram showing a flow of substrate processing. FIG. 10 is a graph showing changes in pH of an etching solution. FIG. 10 is a diagram showing the state of etching of a ruthenium-containing layer using an etching solution of a comparative example. FIG. 10 is a diagram showing the etching of a ruthenium-containing layer. FIG. 10 is a side view of a substrate processing apparatus according to a second embodiment. FIG. 1 is a diagram showing a part of a substrate processing flow. FIG. 2 is an enlarged vertical cross-sectional view showing the vicinity of an etched portion. FIG. 2 is an enlarged vertical cross-sectional view showing the vicinity of an etched portion. FIG. 2 is a side view of the substrate processing apparatus. FIG. 2 is a side view of the substrate processing apparatus. FIG. 2 is a side view of the substrate processing apparatus.

Figure 1 is a schematic plan view showing the layout of a substrate processing system 10. The substrate processing system 10 is a system for processing semiconductor substrates 9 (hereinafter simply referred to as "substrates 9"). The substrate processing system 10 includes an indexer block 101 and a processing block 102 coupled to the indexer block 101.

The indexer block 101 comprises a carrier holding unit 104, an indexer robot 105, and an IR movement mechanism 106. The carrier holding unit 104 holds multiple carriers 107, each capable of accommodating multiple substrates 9. The multiple carriers 107 (e.g., FOUPs) are held by the carrier holding unit 104 in an arrayed state in a predetermined carrier array direction. The IR movement mechanism 106 moves the indexer robot 105 in the carrier array direction. The indexer robot 105 performs an unloading operation to unload substrates 9 from the carriers 107, and an unloading operation to load substrates 9 into the carriers 107 held by the carrier holding unit 104. The substrates 9 are transported in a horizontal position by the indexer robot 105.

The processing block 102 includes multiple (e.g., four or more) processing units 108 that process substrates 9, and a center robot 109. The multiple processing units 108 are arranged surrounding the center robot 109 in a plan view. The multiple processing units 108 perform various processes on the substrates 9. The substrate processing apparatus described below is one of the multiple processing units 108. The center robot 109 performs a load operation to load the substrate 9 into the processing unit 108 and an unload operation to unload the substrate 9 from the processing unit 108. Furthermore, the center robot 109 transports the substrate 9 between the multiple processing units 108. The substrate 9 is transported in a horizontal position by the center robot 109. The center robot 109 receives the substrate 9 from the indexer robot 105 and passes the substrate 9 to the indexer robot 105.

Figure 2 is a side view showing the configuration of a substrate processing apparatus 1 according to a first embodiment of the present invention. The substrate processing apparatus 1 is a single-wafer processing apparatus that processes substrates 9 one by one. The substrate processing apparatus 1 is an apparatus that performs wet etching on the peripheral portion of the substrate 9 (i.e., the bevel portion and the area near the bevel portion). Figure 2 shows a cross section of part of the configuration of the substrate processing apparatus 1.

The substrate processing apparatus 1 comprises a substrate holding unit 31, a substrate rotation mechanism 33, a cup unit 4, a supply head 5, an etching unit 6, a housing 11, and a control unit 8. The substrate holding unit 31, the substrate rotation mechanism 33, the cup unit 4, etc. are housed in the internal space of the housing 11. An airflow forming unit 12 is provided in the canopy of the housing 11, supplying gas to the internal space to form a downward airflow (so-called downflow). An FFU (fan filter unit), for example, is used as the airflow forming unit 12. The control unit 8 is located outside the housing 11 and controls the substrate holding unit 31, the substrate rotation mechanism 33, the supply head 5, the etching unit 6, etc.

As shown in FIG. 3 , the control unit 8 is, for example, a typical computer system including a processor 81, a memory 82, an input/output unit 83, and a bus 84. The bus 84 is a signal circuit connecting the processor 81, the memory 82, and the input/output unit 83. The memory 82 stores programs and various information. The processor 81 executes various processes (e.g., numerical calculations) using the memory 82 and other components in accordance with the programs stored in the memory 82. The input/output unit 83 includes a keyboard 85 and a mouse 86 for receiving input from an operator, a display 87 for displaying output from the processor 81, and a transmitter for transmitting output from the processor 81. The control unit 8 may also be a programmable logic controller (PLC), a circuit board, or the like. The control unit 8 may include any combination of a computer system, a PLC, a circuit board, or the like.

The substrate holding unit 31 and substrate rotation mechanism 33 shown in Figure 2 are each part of a spin chuck that holds and rotates the approximately disk-shaped substrate 9. The substrate holding unit 31 holds the horizontally positioned substrate 9 from below. The substrate holding unit 31 is, for example, a vacuum chuck that holds the substrate 9 by suction. The substrate holding unit 31 has an approximately disk-shaped base portion 311 that contacts and suctions the center of the lower main surface (hereinafter also referred to as the "lower surface 92") of the substrate 9. The diameter of the base portion 311 is smaller than the diameter of the substrate 9.

A ruthenium-containing layer 93 containing ruthenium (Ru) is present on the substrate 9. In the example shown in FIG. 2, the ruthenium-containing layer 93 is a film-like portion (i.e., a ruthenium-containing film) that covers the entire upper principal surface (hereinafter also referred to as the "upper surface 91") of the substrate 9. In FIG. 2, the ruthenium-containing layer 93 is indicated by a bold line. The ruthenium-containing layer 93 contains, for example, one or more of ruthenium, a ruthenium alloy, a ruthenium oxide, a ruthenium nitride, or a ruthenium oxynitride. The ruthenium-containing layer 93 may be, for example, a film-like portion (i.e., a ruthenium-containing film) that covers the entire upper surface 91 and/or lower surface 92 of the substrate 9, or may be a portion that covers only a portion of the surface of the substrate 9. In this embodiment, the ruthenium-containing layer 93 is a ruthenium-containing film that covers the entire upper surface 91 of the substrate 9, and the peripheral edge of the substrate 9 is also covered by the ruthenium-containing film. In this embodiment, the ruthenium-containing layer 93 is a ruthenium film formed entirely from simple ruthenium. The substrate holder 31 shown in FIG. 2 holds the substrate 9 from below with the upper surface 91, on which the ruthenium-containing film is formed, facing upward.

The substrate rotation mechanism 33 is disposed below the substrate holding unit 31. The substrate rotation mechanism 33 rotates the substrate 9 together with the substrate holding unit 31 around a rotation axis J1 that extends substantially parallel to the vertical direction. In the example shown in FIG. 2, the substrate rotation mechanism 33 rotates the substrate 9 clockwise in a plan view. The substrate rotation mechanism 33 includes a shaft 331 and a motor 332. The shaft 331 is a substantially columnar or cylindrical member centered on the rotation axis J1. The shaft 331 extends vertically and is connected to the center of the underside of the base portion 311 of the substrate holding unit 31. The motor 332 is an electric rotary motor that rotates the shaft 331. The substrate rotation mechanism 33 may be a motor having a different structure (e.g., a hollow motor, etc.). The rotation direction of the substrate 9 may also be counterclockwise.

The supply head 5 is positioned above the center of the substrate 9 in the radial direction (hereinafter simply referred to as the "radial direction") centered on the rotation axis J1. The supply head 5 is spaced above the upper surface 91 of the substrate 9 and faces the upper surface 91 of the substrate 9 in the vertical direction. The supply head 5 includes a lower head portion 51, an upper head portion 52, and a center nozzle 53. The lower head portion 51 is a substantially annular plate-shaped portion centered on the rotation axis J1. The lower surface of the lower head portion 51 is a substantially horizontal plane extending substantially parallel to the upper surface 91 of the substrate 9 and faces the upper surface 91 of the substrate 9 in the vertical direction. The diameter of the outer edge of the lower head portion 51 in a plan view is smaller than the diameter of the substrate 9. The upper head portion 52 is a substantially cylindrical portion centered on the rotation axis J1 and extends upward from the upper surface of the lower head portion 51. The upper head portion 52 also serves as a support portion that supports the lower head portion 51 from above. The head upper part 52 is supported by an arm (not shown) that extends substantially horizontally.

A pipe is provided inside the upper head 52 to supply gas to the lower head 51. The gas in question is, for example, compressed air or an inert gas such as nitrogen ( _N2 ) gas. In the following description, the gas in question is assumed to be an inert gas. The inert gas supplied to the lower head 51 is sprayed from the lower surface and outer surface of the lower head 51 toward the upper surface 91 of the substrate 9. This forms a stream of inert gas along the upper surface 91 of the substrate 9, flowing radially outward from the radial center of the substrate 9 (hereinafter simply referred to as the "center")

The center nozzle 53 is disposed in a through-hole provided in the center of the lower head portion 51. A processing liquid such as a rinse liquid is supplied to the center nozzle 53 via piping provided inside the upper head portion 52. The rinse liquid (e.g., deionized water (DIW)) supplied to the center nozzle 53 is ejected from the center nozzle 53 toward the center of the substrate 9 and spreads radially outward over the upper surface 91 of the substrate 9. Note that the rinse liquid is not limited to DIW and may be variously modified. Furthermore, various types of processing liquid other than a rinse liquid may be ejected from the center nozzle 53.

The cup unit 4 includes a cup 41 and a cup lifting mechanism (not shown). The cup 41 is an annular member centered on the rotation axis J1. The cup 41 is arranged around the entire circumference of the substrate 9 and substrate holding unit 31 in the circumferential direction (hereinafter simply referred to as the "circumferential direction") centered on the rotation axis J1, covering the sides and below the substrate 9 and substrate holding unit 31. The cup 41 is a liquid receiving container that receives liquid such as processing liquid that splashes toward the surrounding area from the rotating substrate 9. The inner surface of the cup 41 is formed, for example, from a water-repellent material. The cup 41 remains stationary in the circumferential direction regardless of whether the substrate 9 is rotating or stationary. A discharge port (not shown) is provided at the bottom of the cup 41 to discharge the processing liquid received in the cup 41 to the outside of the housing 11.

The cup lifting mechanism moves the cup 41 vertically relative to the substrate holder 31. The cup lifting mechanism includes, for example, an electric linear motor, an air cylinder, or a ball screw and an electric rotary motor connected to the cup 41. The cup lifting mechanism allows the cup 41 to move vertically between a processing position around the substrate 9 shown in FIG. 2 and a retracted position below the processing position.

The cup section 4 may include multiple cups 41 stacked radially. When the cup section 4 includes multiple cups 41, each of the multiple cups 41 can be moved independently in the vertical direction, and the multiple cups 41 are switched to receive the processing liquid depending on the type of processing liquid splashed from the substrate 9.

The etching unit 6 is positioned above the peripheral edge of the substrate 9. The etching unit 6 is positioned radially outward from the outer periphery of the head lower part 51 of the supply head 5, and faces the ruthenium-containing layer 93 on the peripheral edge of the substrate 9 in the vertical direction. The etching unit 6 includes a treatment liquid supply unit 61 and a plasma application unit 62.

Figure 4 is an enlarged vertical cross-sectional view of the vicinity of the etching unit 6. In Figure 4, the ruthenium-containing layer 93 (a ruthenium film in this embodiment) is indicated by a thick line. The processing liquid supply unit 61 includes a processing nozzle 611 that faces the upper surface 91 of the substrate 9 in the vertical direction near the peripheral edge of the substrate 9. The processing nozzle 611 is an insulating, approximately cylindrical member made of, for example, resin. The processing nozzle 611 is supported by an arm (not shown) and can be moved vertically and horizontally by an elevating mechanism and a moving mechanism connected to the arm. The elevating mechanism includes, for example, an electric linear motor, an air cylinder, or a ball screw and an electric rotary motor. The moving mechanism includes, for example, an electric rotary motor.

The processing nozzle 611 discharges the processing liquid 71 (i.e., the etching liquid 71) for etching the ruthenium-containing layer 93 toward the peripheral edge of the substrate 9. The processing nozzle 611 discharges the etching liquid 71 obliquely downward and radially outward from a discharge port provided at the lower end, for example. The etching liquid 71 applied from the processing nozzle 611 to the peripheral edge of the substrate 9 contacts the ruthenium-containing layer 93 covering the substrate 9 at the peripheral edge, etching the ruthenium-containing layer 93. The etching liquid 71 supplied from the processing nozzle 611 to the substrate 9 may wrap around from the upper surface 91 to the peripheral edge of the lower surface 92 of the substrate 9. When the etching liquid 71 is supplied from the processing nozzle 611 to the peripheral edge of the substrate 9, the above-mentioned inert gas is supplied from the supply head 5 (see FIG. 2) toward the substrate 9, forming a stream of inert gas flowing radially outward from the center of the substrate 9. This prevents the etching solution 71 from spreading radially inward beyond the peripheral edge of the substrate 9.

The etching solution 71 contains orthoperiodic acid ( _H5IO6 ) as an oxidizing agent. The etching solution 71 also contains ammonia ( _NH3 ) as an alkaline additive. The etching solution 71 is, for example, an alkaline liquid in _which orthoperiodic acid and ammonia are dissolved in water. In other words, the pH of the etching solution 71 is greater than 7.0. This pH is a value measured using a known pH meter under conditions of 23°C and 1 atmosphere. The same applies to the pH value in the following description.

The pH of the etching solution 71 is preferably 7.5 or higher, and more preferably 8.0 or higher. The pH of the etching solution 71 is preferably 10.0 or lower, and more preferably 9.0 or lower. The etching solution 71 may contain, for example, a pH adjuster for adjusting the pH in addition to orthoperiodic acid and ammonia.

The content of orthoperiodic acid in the etching solution 71 is, for example, 0.05% to 8% by mass. The content of ammonia in the etching solution 71 is, for example, 5 parts by mass to 150 parts by mass per 100 parts by mass of orthoperiodic acid. Note that the content of orthoperiodic acid and the content of ammonia in the etching solution 71 are not limited to the above ranges and may be varied in various ways. Furthermore, the etching solution 71 may contain an oxidizing agent other than orthoperiodic acid in addition to or instead of orthoperiodic acid. The etching solution 71 may contain an alkaline additive component other than ammonia in addition to or instead of ammonia.

The plasma applying unit 62 applies plasma to the etching solution 71. In the example shown in FIG. 4, the plasma applying unit 62 includes a plasma nozzle 621, a pair of plasma electrodes 622, and a power supply 623. The plasma nozzle 621 is supported above the peripheral edge of the substrate 9 by an arm (not shown), and can be moved vertically and horizontally by an elevating mechanism and a moving mechanism connected to the arm. The elevating mechanism includes, for example, an electric linear motor, an air cylinder, or a ball screw and an electric rotary motor. The moving mechanism includes, for example, an electric rotary motor.

The plasma nozzle 621 faces the upper surface 91 of the substrate 9 in the vertical direction near the peripheral edge of the substrate 9. The plasma nozzle 621 is an insulating, approximately cylindrical member made of, for example, resin. The plasma nozzle 621 is positioned radially outward of the processing nozzle 611 of the processing liquid supply unit 61. The plasma nozzle 621 is positioned, for example, on an extension of an imaginary straight line from the rotation axis J1 to the processing nozzle 611 in a plan view. The plasma nozzle 621 is supported with an outlet provided at its lower end facing the upper surface 91 of the substrate 9. The outlet of the plasma nozzle 621 is spaced above the upper surface 91 of the substrate 9.

The plasma nozzle 621 is connected to a gas supply source (not shown). Gas supplied from the gas supply source to the plasma nozzle 621 is delivered from the outlet of the plasma nozzle 621 toward the peripheral edge of the substrate 9. The gas is, for example, a nitrogen-containing gas, and in this embodiment, is atmospheric air (i.e., air). The gas may also be various gases other than air (e.g., nitrogen gas).

A pair of plasma electrodes 622 are fixed to the outer surface of the plasma nozzle 621 at the bottom (i.e., near the outlet of the plasma nozzle 621). The pair of plasma electrodes 622 are arranged facing each other with the plasma nozzle 621 in between. The pair of plasma electrodes 622 are connected to a power supply 623, which is an AC power source. The power supply 623 applies an AC voltage between the pair of plasma electrodes 622. This converts the gas flowing through the plasma nozzle 621 into plasma. Note that the power supply 623 is not limited to an AC power source and may be, for example, a DC pulse power source.

As described above, when the gas supplied from the gas supply source to the plasma nozzle 621 is air, atmospheric plasma is generated in the plasma nozzle 621. The plasma generated in the plasma nozzle 621 is, for example, room temperature plasma with a temperature of 40°C or less. The lower limit temperature of this room temperature plasma is not particularly limited, but is, for example, 5°C. Furthermore, this plasma is, for example, atmospheric pressure plasma generated at approximately atmospheric pressure (for example, 0.5 atm to 2.0 atm, preferably 0.75 atm to 1.5 atm).

The plasma generated by the plasma nozzle 621 is discharged from the outlet at the tip of the plasma nozzle 621 and applied to the etching solution 71 supplied onto the substrate 9. The outlet of the plasma nozzle 621 is preferably entirely immersed in the etching solution 71 supplied onto the substrate 9. This prevents the plasma (specifically, the plasma-converted gas) discharged from the outlet of the plasma nozzle 621 from diffusing into the atmosphere surrounding the etching solution 71, allowing it to be efficiently applied to the etching solution 71.

When plasma is applied to the etching solution 71 from the plasma nozzle 621, the pH of the etching solution 71 decreases. The pH of the etching solution 71 gradually decreases as the plasma application time increases. In the substrate processing apparatus 1, for example, the pH of the etching solution 71 decreases to a range of 7.0 or more and 7.5 or less. In other words, in the substrate processing apparatus 1, applying plasma to the alkaline etching solution 71 decreases the pH of the etching solution 71 within the alkaline range, or makes the etching solution 71 neutral. Note that applying plasma to the etching solution 71 may also decrease the pH of the etching solution 71 to less than 7.0. In other words, the etching solution 71 may become acidic when plasma is applied. When application of plasma to the etching solution 71 is stopped, the pH of the etching solution 71 on the peripheral edge of the substrate 9 increases due to the mixing of newly supplied etching solution 71 from the processing nozzle 611.

Next, the processing flow of substrate 9 in substrate processing apparatus 1 will be described with reference to FIG. 5. When substrate 9 is processed, first, substrate 9 is loaded into substrate processing apparatus 1 and held substantially horizontally by substrate holding unit 31 (step S11). This prepares substrate 9 having a ruthenium-containing layer 93 (in this embodiment, a ruthenium film) on its surface. In step S11, the position of substrate holding unit 31 is adjusted so that the center of substrate 9 coincides with rotation axis J1 in a plan view. When substrate 9 is loaded, supply head 5 and etching unit 6 are retracted to retracted positions (e.g., positions spaced radially outward from the outer periphery of substrate 9 in a plan view) that do not interfere with the loading and unloading of substrate 9. Once substrate 9 is held by substrate holding unit 31, control unit 8 controls substrate rotation mechanism 33 to begin rotating substrate 9. Furthermore, supply head 5 and etching unit 6 are moved from the retracted positions to the processing positions shown in FIG. 2.

The control unit 8 then controls the processing liquid supply unit 61, causing an alkaline etching liquid 71 to be ejected from the processing nozzle 611 toward the peripheral edge of the substrate 9, where the etching liquid 71 contacts the ruthenium-containing layer 93 (step S12). This causes etching of the ruthenium-containing layer 93 on the peripheral edge of the substrate 9. The pH of the etching liquid 71 in step S12 is, for example, 8.0 or higher and 10.0 or lower.

In step S12, no plasma is applied to the etching solution 71 supplied to the ruthenium-containing layer 93. In step S12, the control unit 8 controls the supply head 5, supplying an inert gas from the head lower portion 51 toward the substrate 9, forming a flow of inert gas flowing radially outward from the center of the substrate 9. This prevents the etching solution 71 from spreading radially inward beyond the peripheral edge of the substrate 9. The supply of the etching solution 71 from the processing liquid supply unit 61 and the supply of the inert gas from the supply head 5 are continued until step S17, which will be described later.

After a predetermined time has elapsed since the start of the discharge of the etching solution 71, the control unit 8 controls the plasma application unit 62 to supply gas (air in this embodiment) to the plasma nozzle 621 and apply voltage between the pair of plasma electrodes 622. This converts the gas flowing through the plasma nozzle 621 into plasma, and application of plasma to the etching solution 71 on the peripheral edge of the substrate 9 begins (step S13). On the peripheral edge of the substrate 9, the pH of the etching solution 71 gradually decreases due to the application of plasma. Then, by bringing the etching solution 71 with a reduced pH into contact with the ruthenium-containing layer 93, etching of the ruthenium-containing layer 93 further progresses (step S14). The minimum pH of the etching solution 71 in step S14 is, for example, 7.0 or higher and 7.5 or lower.

FIG. 6 is a graph schematically illustrating the change in pH of the etching solution 71 that contacts the ruthenium-containing layer 93 during processing of a substrate 9 in the substrate processing apparatus 1. The horizontal axis in FIG. 6 represents the elapsed time from the start of application of the etching solution 71 to the substrate 9, and the vertical axis represents the pH of the etching solution 71 that contacts the ruthenium-containing layer 93 on the peripheral edge of the substrate 9. In the example shown in FIG. 6, the pH of the etching solution 71 is 8.0 in step S12 (i.e., before plasma application), begins to decrease in step S13, and decreases to 7.0 in step S14. Note that while the example shown in FIG. 6 depicts the change in pH of the etching solution 71 linearly, this is not a limitation. Furthermore, in step S14, the pH of the etching solution 71 is maintained at a minimum value of 7.0 for a certain period of time, but maintaining the pH at this minimum value is not necessarily required. Furthermore, the pH of the etching solution 71 in step S12 and the minimum pH of the etching solution 71 in step S14 may be changed as appropriate.

After a predetermined time has elapsed since the start of plasma application, the control unit 8 controls the plasma application unit 62 to stop the supply of gas to the plasma nozzle 621 and the application of voltage to the pair of plasma electrodes 622, thereby stopping the application of plasma to the etching solution 71 (step S15). As a result, as shown in FIG. 6 , the pH of the etching solution 71 in contact with the ruthenium-containing layer 93 on the peripheral edge of the substrate 9 begins to increase. Then, with the application of plasma to the etching solution 71 stopped, the etching solution 71 is brought into contact with the ruthenium-containing layer 93, thereby further etching the ruthenium-containing layer 93 (step S16). In the example shown in FIG. 6 , in step S16, the pH of the etching solution 71 returns to 8.0, as in step S12, and is maintained at 8.0.

When a predetermined time has elapsed since the application of plasma was stopped, the control unit 8 controls the processing liquid supply unit 61 to stop the supply of etching liquid 71 to the substrate 9 (step S17). The supply of inert gas from the supply head 5 is also stopped. The etching unit 6 moves from the processing position shown in FIG. 4 to the retracted position described above.

Next, rinse liquid is supplied from the center nozzle 53 of the supply head 5 (see Figure 2) to the center of the upper surface 91 of the substrate 9. The rotation speed of the substrate 9 by the substrate rotation mechanism 33 is also increased. This causes the rinse liquid to spread over the entire upper surface 91 of the substrate 9, performing a rinse process that washes away the etching liquid 71 and other substances adhering to the peripheral edge of the substrate 9 (step S18). The rinse liquid is scattered radially outward from the outer edge of the substrate 9 due to the centrifugal force generated by the rotation of the substrate 9, and is received by the cup portion 4.

After the substrate 9 has been rinsed for a predetermined period of time, the supply of rinse liquid from the center nozzle 53 is stopped. The rotation speed of the substrate 9 is then further increased, and the rinse liquid on the substrate 9 is shaken off and removed, thereby drying the substrate 9 (step S19). Once the drying process of the substrate 9 is complete, the rotation of the substrate 9 is stopped, and the substrate 9 is unloaded from the substrate processing apparatus 1. Note that the rinsing and drying processes of the substrate 9 may be performed using methods different from those described above.

In the substrate processing apparatus 1, as described above, the etching rate can be increased and the etching efficiency can be improved by etching the ruthenium-containing layer 93 with the etching solution 71 having a relatively low pH (e.g., 7.0 to 7.5) in step S14. Furthermore, by making the etching solution 71 alkaline (e.g., pH 8.0 to 10.0) at the start of etching, it is possible to suppress the generation of toxic gaseous ruthenium tetroxide (RuO ₄ ) during etching. The principle of suppressing the generation of ruthenium tetroxide will be described below.

If a ruthenium etching solution containing orthoperiodic acid and ammonia and having a pH of 4.5 (hereinafter also referred to as "comparative etching solution 701") is applied to the peripheral edge of a ruthenium-containing layer 93 on a substrate 9, as shown in FIG. 7, the ruthenium contained in the ruthenium-containing layer 93 is oxidized by the comparative etching solution 701, producing highly volatile, water-insoluble ruthenium tetroxide 94. The toxic gaseous ruthenium tetroxide 94 then diffuses into the atmosphere surrounding the comparative etching solution 701.

On the other hand, in the substrate processing apparatus 1, in step S12, the alkaline etching solution 71 before plasma application is applied to the ruthenium-containing layer 93 on the substrate 9, whereby the ruthenium contained in the ruthenium-containing layer 93 (i.e., metallic ruthenium) is oxidized by the etching solution 71 to produce ruthenium dioxide (RuO ₂ ) 95, as shown in Fig. 8. Then, in step S14, the etching solution 71, whose pH has been reduced after plasma application, is applied to the ruthenium dioxide 95, whereby the ruthenium dioxide 95 is oxidized to produce water-soluble ruthenium tetroxide 96. The water-soluble ruthenium tetroxide 96 dissolves in the etching solution 71, thereby preventing the diffusion of toxic gaseous ruthenium tetroxide into the atmosphere surrounding the etching solution 71.

Next, a substrate processing apparatus 1a according to a second embodiment of the present invention will be described. FIG. 9 is a side view of the substrate processing apparatus 1a. In the substrate processing apparatus 1a, the processing nozzle 611 shown in FIG. 2 is omitted, and etching solution 71 is ejected toward the center of the substrate 9 from the center nozzle 53 of the supply head 5. In other words, in the etching section 6a of the substrate processing apparatus 1a, the processing solution supply section 61a includes the center nozzle 53 as a processing nozzle. In the etching section 6a, the plasma application section 62a also includes a plurality of the plasma nozzles 621 described above. The plurality of plasma nozzles 621 are arranged circumferentially along the periphery of the substrate 9 above the upper surface 91 of the substrate 9. The other components of the substrate processing apparatus 1a are substantially the same as those of the substrate processing apparatus 1, and the same reference numerals will be used in the following description.

In the substrate processing apparatus 1a, a protective film 97 is provided on a ruthenium-containing layer 93 that covers the entire upper surface 91 of the substrate 9. The protective film 97 is, for example, a spin-on-glass (SOG) film, and is provided over the entire upper surface 91 of the substrate 9 except for the peripheral edge portion. The protective film 97 has a substantially circular shape in a plan view.

The processing flow for substrate 9 in substrate processing apparatus 1a is substantially the same as that shown in FIG. 5, except that steps S21 and S22 shown in FIG. 10 are performed between the above-mentioned rinsing process (step S18) and drying process (step S19). Specifically, first, substrate 9 having the above-mentioned protective film 97 provided on ruthenium-containing layer 93 is prepared by being held by substrate holder 31 (FIG. 5: step S11). Next, rotation of substrate 9 is initiated by substrate rotation mechanism 33.

Next, the control unit 8 controls the processing liquid supply unit 61a, and alkaline etching liquid 71 is ejected from the center nozzle 53 toward the center of the substrate 9. The alkaline etching liquid 71 spreads radially outward over the protective film 97 due to centrifugal force generated by the rotation of the substrate 9. The etching liquid 71 contacts the ruthenium-containing layer 93 exposed from the protective film 97 at the peripheral edge of the substrate 9 (step S12). This etches the ruthenium-containing layer 93 at the peripheral edge of the substrate 9. The pH of the etching liquid 71 in step S12 is, for example, 8.0 or higher and 10.0 or lower. Note that in step S12 and steps S13 to S16 described below, the region of the ruthenium-containing layer 93 covered by the protective film 97 is not etched. Furthermore, no inert gas is supplied from the supply head 5.

After a predetermined time has elapsed since the start of the discharge of the etching solution 71, the control unit 8 controls the plasma application unit 62 to supply gas (air in this embodiment) to each plasma nozzle 621 and apply a voltage between a pair of plasma electrodes 622 (see FIG. 4) fixed to each plasma nozzle 621. This converts the gas flowing through each plasma nozzle 621 into plasma, and application of plasma to the etching solution 71 on the peripheral edge of the substrate 9 begins (step S13). On the peripheral edge of the substrate 9, the pH of the etching solution 71 gradually decreases due to the application of plasma. Then, by bringing the etching solution 71 with a reduced pH into contact with the ruthenium-containing layer 93, etching of the ruthenium-containing layer 93 further progresses (step S14). The minimum pH of the etching solution 71 in step S14 is, for example, 7.0 or higher and 7.5 or lower.

After a predetermined time has elapsed since the start of plasma application, the control unit 8 controls the plasma application unit 62 to stop the supply of gas to each plasma nozzle 621 and the application of voltage to the pair of plasma electrodes 622 fixed to each plasma nozzle 621, thereby stopping the application of plasma to the etching solution 71 (step S15). As a result, the pH of the etching solution 71 in contact with the ruthenium-containing layer 93 on the peripheral edge of the substrate 9 begins to increase. Then, with the application of plasma to the etching solution 71 stopped, the etching solution 71 is brought into contact with the ruthenium-containing layer 93, thereby further etching the ruthenium-containing layer 93 (step S16). The pH of the etching solution 71 in contact with the ruthenium-containing layer 93 returns to the same value as the pH in step S12.

When a predetermined time has elapsed since the application of plasma was stopped, the control unit 8 controls the processing liquid supply unit 61a to stop the supply of etching liquid 71 to the substrate 9 (step S17). Note that in steps S12 to S16 described above, a puddle process may be performed in which a liquid film of etching liquid 71 is formed and maintained on the upper surface 91 of the substrate 9 while the rotation of the substrate 9 is stopped or while the substrate 9 is rotating at a low speed.

Next, rinse liquid is supplied from the center nozzle 53 of the supply head 5 to the center of the upper surface 91 of the substrate 9. The rotation speed of the substrate 9 by the substrate rotation mechanism 33 is also increased. This causes the rinse liquid to spread over the entire upper surface 91 of the substrate 9, performing a rinse process that washes away the etching liquid 71 and other substances adhering to the peripheral edge of the substrate 9 (step S18). The rinse liquid is scattered radially outward from the outer edge of the substrate 9 due to the centrifugal force generated by the rotation of the substrate 9, and is received by the cup portion 4.

After the substrate 9 has been rinsed for a predetermined time, the supply of the rinse liquid to the substrate 9 is stopped, and the protective film 97 is removed from the substrate 9 ( FIG. 10 : step S21). As described above, if the protective film 97 is an SOG film, in step S21, the protective film 97 is removed, for example, by applying hydrogen fluoride (HF) to the protective film 97. Note that the type of protective film 97 and the method for removing the protective film 97 may be changed in various ways.

Once removal of the protective film 97 is complete, a rinse liquid is supplied from the center nozzle 53 to the center of the upper surface 91 of the substrate 9, and the substrate 9 is rinsed (step S22). The rotation speed of the substrate 9 is then increased, and the rinse liquid on the substrate 9 is shaken off and removed, thereby drying the substrate 9 (step S19). Once drying of the substrate 9 is complete, the rotation of the substrate 9 is stopped, and the substrate 9 is unloaded from the substrate processing apparatus 1a.

As described above, the substrate processing methods according to the first and second embodiments include the steps of preparing a substrate 9 having a ruthenium-containing layer 93 on its surface (step S11), bringing an alkaline etching solution 71 into contact with the ruthenium-containing layer 93 on the substrate 9 (step S12), and, after step S12, applying plasma to the etching solution 71 to lower the pH and then bringing the etching solution 71 into contact with the ruthenium-containing layer 93 (step S14). This increases the etching rate while suppressing the generation of toxic gaseous ruthenium tetroxide, as described above.

The above substrate processing method preferably further includes, after step S14, a step (step S16) of bringing the etching solution 71 into contact with the ruthenium-containing layer 93 while stopping the application of plasma to the etching solution 71. This shortens the time during which the etching solution 71, which has a relatively low pH (e.g., pH 7.0 to 7.5), comes into contact with the ruthenium-containing layer 93, out of the total contact time between the etching solution 71 and the ruthenium-containing layer 93. As a result, the generation of toxic ruthenium tetroxide gas can be effectively suppressed.

In the above substrate processing method, it is preferable that ruthenium dioxide is generated from the ruthenium in the ruthenium-containing layer 93 in step S12, and that soluble ruthenium tetroxide is generated from the ruthenium dioxide in step S14. This makes it possible to effectively suppress the generation of gaseous ruthenium tetroxide, as described above.

In the above substrate processing method, the minimum pH value of the etching solution 71 in step S14 is preferably 7.0 or higher and 7.5 or lower. This makes it possible to effectively suppress the generation of gaseous ruthenium tetroxide while simultaneously increasing the etching rate.

In the above substrate processing method, the pH of the etching solution 71 in step S12 is preferably 8.0 or higher and 10.0 or lower. This makes it possible to effectively suppress the generation of gaseous ruthenium tetroxide while simultaneously increasing the etching rate.

In the above substrate processing method, the plasma is preferably atmospheric plasma. This simplifies the configuration for generating the plasma.

In the above substrate processing method, the plasma is preferably room temperature plasma. This simplifies the configuration for generating the plasma. Furthermore, since ruthenium tetroxide becomes relatively volatile at temperatures above 45°C, setting the plasma temperature to 40°C or below effectively suppresses the generation of gaseous ruthenium tetroxide.

In the above substrate processing method, in steps S12 and S14, the etching solution 71 preferably contacts the ruthenium-containing layer 93 at the peripheral edge of the substrate 9. This allows the ruthenium-containing layer 93 at the peripheral edge of the substrate 9 to be suitably etched.

As mentioned above, the etching solution 71 preferably contains orthoperiodic acid. This allows for efficient etching of the ruthenium contained in the ruthenium-containing layer 93.

As mentioned above, the etching solution 71 preferably contains ammonia as an alkaline additive. This makes it easy to prepare an alkaline etching solution 71 suitable for etching ruthenium.

The substrate processing apparatus 1, 1a described above includes a substrate holding unit 31, a processing liquid supply unit 61, 61a, a plasma applying unit 62, and a control unit 8. The substrate holding unit 31 holds a substrate 9 having a ruthenium-containing layer 93 on its surface. The processing liquid supply unit 61, 61a applies an alkaline etching liquid 71 onto the substrate 9, bringing it into contact with the ruthenium-containing layer 93. The plasma applying unit 62 applies plasma to the etching liquid 71. After the alkaline etching liquid 71 comes into contact with the ruthenium-containing layer 93, the control unit 8 controls the plasma applying unit 62 to bring the etching liquid 71, whose pH has been reduced by the application of plasma, into contact with the ruthenium-containing layer 93. As described above, the substrate processing apparatus 1, 1a can increase the etching rate while suppressing the generation of toxic gaseous ruthenium tetroxide.

In the substrate processing apparatus 1 described above, the structure of the etching unit 6 is not limited to the example shown in FIG. 4 and may be modified in various ways. For example, in the etching unit 6b shown in FIG. 11, the tip of the plasma nozzle 621 of the plasma application unit 62 is connected to a pipe 612 inside the processing nozzle 611 of the processing liquid supply unit 61. Furthermore, the pair of plasma electrodes 622 of the plasma application unit 62 are fixed to the outer surface of the plasma nozzle 621 outside the processing nozzle 611. The pair of plasma electrodes 622 are arranged, for example, near the connection between the plasma nozzle 621 and the processing nozzle 611.

In the etching unit 6b, when a voltage is applied between the pair of plasma electrodes 622 from the power supply 623 in step S13 described above, the gas (e.g., air) flowing through the plasma nozzle 621 is converted into plasma, and the plasma is applied to the etching solution flowing through the piping 612 of the processing nozzle 611. This reduces the pH of the etching solution flowing through the piping 612 of the processing nozzle 611. Note that in the etching unit 6b, a porous member may be provided in the piping 612 of the processing nozzle 611 at the connection point with the plasma nozzle 621. This improves the uniformity of the application of plasma to the etching solution flowing through the piping 612 of the processing nozzle 611.

In the etching unit 6c shown in Figure 12, the tip of the plasma nozzle 621 of the plasma applying unit 62 is connected to the piping 612 inside the processing nozzle 611 of the processing liquid supply unit 61. Furthermore, a pair of plasma electrodes 622 of the plasma applying unit 62 is fixed to the outer surface of the piping 612 inside the processing nozzle 611. The pair of plasma electrodes 622 is arranged, for example, near the connection between the plasma nozzle 621 and the piping 612 of the processing nozzle 611. The pair of plasma electrodes 622 is arranged between the connection and the outlet provided at the lower end of the processing nozzle 611.

In the etching unit 6c, gas (e.g., air) flowing through the plasma nozzle 621 is supplied to the etching liquid flowing through the piping 612 of the processing nozzle 611, and flows as bubbles in the etching liquid toward the outlet of the processing nozzle 611 along with the etching liquid. In step S13 described above, when a voltage is applied between the pair of plasma electrodes 622 from the power source 623, the bubbles in the etching liquid flowing through the piping 612 of the processing nozzle 611 are converted into plasma. In other words, plasma is applied to the etching liquid flowing through the piping 612 of the processing nozzle 611. This lowers the pH of the etching liquid flowing through the piping 612 of the processing nozzle 611.

The structure of the etching units 6b and 6c described above may be applied to the substrate processing apparatus 1a shown in Figure 9. In this case, a plasma nozzle 621 is connected to the center nozzle 53 instead of the processing nozzle 611 in Figures 11 and 12.

As described above, the substrate processing apparatus 1a can prevent gaseous ruthenium tetroxide from diffusing into the atmosphere surrounding the etching solution 71. However, there is still a possibility that a small amount of toxic gaseous ruthenium tetroxide may be generated, for example, in step S14. For this reason, the substrate processing apparatus 1a may be provided with a gas recovery unit 66 for recovering gaseous ruthenium tetroxide, as shown in FIG. 13, in case gaseous ruthenium tetroxide is generated.

The gas recovery unit 66 includes a recovery head 661, a recovery chamber 662, and a steam nozzle 663. The recovery head 661 is disposed above the peripheral edge of the substrate 9 and sucks in the atmosphere above the peripheral edge of the substrate 9. The recovery head 661 has, for example, a substantially circular ring shape in plan view centered on the rotation axis J1 and includes multiple suction ports arranged circumferentially on its underside. The atmosphere sucked in by the recovery head 661 is sent to the internal space of a recovery chamber 662 disposed outside the housing 11. Steam (i.e., moist air containing water vapor) is supplied from the steam nozzle 663 to the internal space of the recovery chamber 662. The temperature of the steam is, for example, 40°C to 90°C. In the recovery chamber 662, if the atmosphere recovered by the recovery head 661 contains gaseous ruthenium tetroxide, the ruthenium tetroxide reacts with _the water vapor in the steam to generate H ₂ RuO _{5 ,} which is then recovered.

As described above, in the substrate processing apparatus 1a illustrated in FIG. 13, in step S14, steam is applied to and recovered from gaseous ruthenium tetroxide generated by contact between the ruthenium-containing layer 93 and the etching solution 71. This prevents the gaseous ruthenium tetroxide from diffusing into the atmosphere within the housing 11. It also prevents the gaseous ruthenium tetroxide from reacting with ruthenium in the ruthenium-containing layer 93 on the substrate 9 and being reduced to ruthenium dioxide. In the gas recovery unit 66, in addition to the atmosphere recovered by the recovery head 661, the atmosphere discharged to the outside of the housing 11 from the discharge port of the cup portion 4 may also be sent to the recovery chamber 662.

The structure of the gas recovery unit 66 is not limited to the example shown in Figure 13 and may be modified in various ways. For example, the gas recovery unit 66d shown in Figure 14 includes a recovery cover 664d and a steam nozzle 663d. The recovery cover 664d is, for example, a covered, approximately cylindrical member. The recovery cover 664d covers the upper and surrounding areas of the substrate 9 inside the housing 11. In the example shown in Figure 14, the base portion 311d of the substrate holder 31 extends around the entire circumference, radially outward from the periphery of the substrate 9, and the lower end of the recovery cover 664d is in airtight contact with the upper surface of the base portion 311d.

The steam nozzle 663d supplies steam to the internal space of the recovery cover 664d (i.e., the space surrounded by the recovery cover 664d and the base portion 311d). As a result, if gaseous ruthenium tetroxide is generated during etching of the ruthenium-containing layer ₉₃ , the ruthenium tetroxide reacts with water vapor in the steam to generate _H2RuO5 . _{The H2RuO5 is} discharged to the outside of the recovery cover 664d through an exhaust port (not shown) provided in the recovery cover 664d, and is sent to the outside of the housing 11 and recovered.

In this case, too, in step S14, steam is applied to and recovered from the gaseous ruthenium tetroxide generated by contact between the ruthenium-containing layer 93 and the etching solution 71, thereby preventing the gaseous ruthenium tetroxide from diffusing into the atmosphere within the housing 11.

15 includes a plurality of steam nozzles 663e. The tip of each steam nozzle 663e is inserted into the liquid film of etching solution 71 supplied onto substrate 9, and steam is supplied into etching solution 71 from the outlet at the tip. As a result, if gaseous ruthenium tetroxide is generated during etching of ruthenium-containing layer 93, the ruthenium tetroxide reacts with water vapor in the steam in the liquid film of etching solution ₇₁ to generate _H2RuO5 . The _H2RuO5 is discharged together with etching solution 71 to the outside of housing ₁₁ via an exhaust port (not shown) of cup portion 4 and recovered.

In this case, too, in step S14, steam is applied to and recovered from the gaseous ruthenium tetroxide generated by contact between the ruthenium-containing layer 93 and the etching solution 71, thereby preventing the gaseous ruthenium tetroxide from diffusing into the atmosphere within the housing 11.

The substrate processing apparatus 1 shown in FIG. 2 may also be provided with the gas recovery units 66, 66d, and 66e described above, similar to the substrate processing apparatus 1a.

Various modifications are possible to the substrate processing apparatus 1, 1a and substrate processing method described above.

For example, in addition to the processing nozzle 611 described above, the processing liquid supply unit 61 of the substrate processing apparatus 1 may further include another processing nozzle that is positioned below the substrate 9 and ejects the etching liquid 71 toward the peripheral portion of the underside 92 of the substrate 9. The same applies to the substrate processing apparatus 1a.

The substrate processing apparatus 1 may be provided with a heater that heats the etching solution 71 supplied to the peripheral edge of the substrate 9. The heater may be, for example, an electric heater that is positioned below the peripheral edge of the substrate 9 and faces the lower surface 92 of the substrate 9. The same applies to the substrate processing apparatus 1a.

In the substrate processing apparatus 1, the plasma applied from the plasma application unit 62 does not necessarily have to be room temperature plasma at 40°C or below; the temperature of the plasma may be higher than 40°C. Furthermore, the plasma does not necessarily have to be atmospheric pressure plasma; for example, it may be low-pressure plasma. The method of applying plasma to the etching solution 71 is not limited to the above example and may be modified in various ways. The same applies to the substrate processing apparatus 1a.

In the above-described substrate processing method, step S16 may be omitted, and the application of plasma to the etching solution 71 (step S15) and the supply of the etching solution 71 to the substrate 9 (step S17) may be stopped substantially simultaneously.

The substrate holder 31 may hold the substrate 9 with the main surface of the substrate 9 on which the ruthenium-containing layer 93 is provided facing downward.

The substrate processing apparatus 1 may be provided with multiple etching units 6, which may be arranged circumferentially along the peripheral edge of the substrate 9.

In the substrate processing apparatus 1a, an arm (not shown) supporting the center nozzle 53 may be swung approximately horizontally above the rotating substrate 9, thereby supplying the etching solution 71 over approximately the entire upper surface 91 of the substrate 9. In other words, the etching solution 71 may be supplied to the upper surface 91 of the substrate 9 from a so-called scan nozzle. In this case, the scan nozzle may be stopped above the peripheral edge of the substrate 9, thereby supplying the etching solution 71 only to the peripheral edge of the rotating substrate 9.

The above-described substrate processing method may be applied to processes other than etching the peripheral edge of the substrate 9. For example, in the substrate processing apparatus 1a, a substrate 9 not provided with a protective film 97 may be processed to form ruthenium-containing wiring in a region radially inward of the peripheral edge of the substrate 9. In this case, the plasma applying unit 62, which applies plasma to the etching solution 71 ejected from the center nozzle 53, is positioned, for example, above the center of the substrate 9.

The above-described substrate processing apparatus 1, 1a may be used to process glass substrates used in flat panel displays such as liquid crystal displays or organic electroluminescence (EL) displays, as well as glass substrates used in other display devices, in addition to semiconductor substrates. The above-described substrate processing apparatus 1, 1a may also be used to process substrates for optical disks, magnetic disks, magneto-optical disks, photomasks, ceramic substrates, and solar cell substrates.

The configurations in the above embodiments and variations may be combined as appropriate as long as they are not mutually inconsistent.

REFERENCE SIGNS LIST 1, 1a Substrate processing apparatus 8 Control unit 9 Substrate 31 Substrate holder 61 Processing liquid supply unit 62 Plasma application unit 71 Etching liquid 93 Ruthenium-containing layer J1 Rotation shaft

Claims (12)

1. A substrate processing method for performing an etching process on a ruthenium-containing layer on a substrate, comprising:
a) providing a substrate having a ruthenium-containing layer thereon;
b) contacting the ruthenium-containing layer on the substrate with an alkaline etching solution;
c) after step b), applying plasma to the etching solution to lower the pH, and then contacting the etching solution with the ruthenium-containing layer;
A substrate processing method comprising: 2. The substrate processing method according to claim 1,
d) after the step c), bringing the etching solution into contact with the ruthenium-containing layer while stopping application of plasma to the etching solution. 3. The substrate processing method according to claim 1, further comprising:
In the step b), ruthenium dioxide is produced from ruthenium in the ruthenium-containing layer,
A substrate processing method, wherein in the step c), soluble ruthenium tetroxide is produced from the ruthenium dioxide. 3. The substrate processing method according to claim 1, further comprising:
The substrate processing method, wherein the minimum pH value of the etching solution in the step c) is 7.0 or more and 7.5 or less. 3. The substrate processing method according to claim 1, further comprising:
The substrate processing method, wherein the pH of the etching solution in the step b) is 8.0 or more and 10.0 or less. 3. The substrate processing method according to claim 1, further comprising:
The substrate processing method, wherein the plasma is atmospheric plasma. 3. The substrate processing method according to claim 1, further comprising:
The substrate processing method is characterized in that the plasma is room temperature plasma. 3. The substrate processing method according to claim 1, further comprising:
a step of applying steam to gaseous ruthenium tetroxide produced by contact of the ruthenium-containing layer with the etching solution, and recovering the gaseous ruthenium tetroxide; 3. The substrate processing method according to claim 1, further comprising:
In the steps b) and c), the etching solution contacts the ruthenium-containing layer at the peripheral edge of the substrate. 3. The substrate processing method according to claim 1, further comprising:
4. A substrate processing method, wherein the etching solution contains orthoperiodic acid. 11. The substrate processing method according to claim 10,
4. A substrate processing method, wherein the etching solution contains ammonia as an alkaline additive component. 1. A substrate processing apparatus for performing an etching process on a ruthenium-containing layer on a substrate, comprising:
a substrate holder for holding a substrate having a ruthenium-containing layer on its surface;
a treatment liquid supply unit that applies an alkaline etching liquid onto the substrate to bring the alkaline etching liquid into contact with the ruthenium-containing layer;
a plasma applying unit that applies plasma to the etching solution;
a control unit that controls the plasma applying unit after the alkaline etching solution has been brought into contact with the ruthenium-containing layer, thereby bringing the etching solution, the pH of which has been reduced by the application of plasma, into contact with the ruthenium-containing layer;
A substrate processing apparatus comprising: