Substrate processing method and substrate processing system

Abstract

To provide a technology that can perform good displacement of the liquid by the processing fluid before it becomes supercritical in a technology for processing substrates in a chamber by a supercritical state processing fluid.SOLUTION: A substrate processing method of the present invention has the following processes: forming a liquid film with a liquid containing ultrafine bubbles on the surface of a substrate held in a horizontal position; introducing a processing fluid in a non-supercritical state into a chamber containing the substrate in which the liquid film is formed, pressurizing the processing fluid to bring it to a supercritical state and replacing the liquid on the substrate surface with the processing fluid; depressurizing the chamber to vaporize the processing fluid in a supercritical state and discharging it outside the chamber.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a technique for processing a substrate with a processing fluid in a supercritical state in a chamber, and more particularly to a process for processing a substrate covered with a liquid film with a supercritical processing fluid. [Background technology]

[0002] Processing processes for various substrates, such as semiconductor substrates and glass substrates for display devices, involve treating the surface of the substrate with various processing fluids. While processing using liquids, such as chemical solutions and rinse solutions, as processing fluids has been widely used for some time, processing using supercritical fluids has also come into practical use in recent years. In particular, when processing substrates having fine patterns formed on their surfaces, supercritical fluids, which have lower surface tension than liquids, can penetrate deep into the gaps in the patterns, enabling efficient processing and reducing the risk of pattern collapse due to surface tension during drying.

[0003] For example, Patent Document 1 describes a substrate processing apparatus that replaces liquid adhering to a substrate with a supercritical fluid and performs a drying process on the substrate. More specifically, Patent Document 1 describes in detail the drying process flow when carbon dioxide is used as the supercritical processing fluid and IPA (isopropyl alcohol) is used as the liquid to be replaced by carbon dioxide. Specifically, the substrate is placed in a chamber with a mound of IPA to prevent the surface from drying. The chamber is then filled with a processing fluid and pressurized. After maintaining the chamber in a state where both the critical pressure and critical temperature of the processing fluid are exceeded for a certain period of time, the chamber is depressurized, completing the process. Patent Document 2 also describes pressure control during depressurization in a similar supercritical drying process. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-191479 [Patent Document 2] Japanese Patent Application Publication No. 2018-152479 Summary of the Invention [Problem to be solved by the invention]

[0005] To improve the efficiency of the supercritical drying process, it is necessary to shorten the processing time for each of the individual steps, i.e., the steps of increasing the pressure, maintaining the supercritical state, and decreasing the pressure. Although Patent Documents 1 and 2 discuss in detail the progress management of the supercritical state and the depressurization steps, they do not provide any detailed description of the pressure increase step from the introduction of the processing fluid to the supercritical state.

[0006] In order to ensure that the pressure increase process proceeds smoothly and efficiently, it is necessary to efficiently replace the liquid adhering to the substrate with a processing fluid. However, Patent Documents 1 and 2 do not disclose any means for achieving this, and simply increasing the pressure increase rate to shorten the processing time may result in insufficient replacement of the liquid, with the liquid remaining on the substrate and potentially affecting subsequent processing.

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a technology for processing a substrate with a processing fluid in a supercritical state in a chamber, which can effectively replace liquid with a processing fluid before it reaches a supercritical state. [Means for solving the problem]

[0008] One aspect of the present invention is a substrate processing method for processing a substrate with a processing fluid in a supercritical state in a chamber, comprising the steps of: forming a liquid film of a liquid containing ultrafine bubbles on the surface of the substrate held in a substantially horizontal position; introducing the processing fluid that is not in a supercritical state into the chamber containing the substrate on which the liquid film has been formed, pressurizing the processing fluid to bring it to a supercritical state, and replacing the liquid on the substrate surface with the processing fluid; and reducing the pressure inside the chamber, vaporizing the processing fluid that has become supercritical, and discharging it outside the chamber.

[0009] Here, the ultrafine bubbles (hereinafter sometimes abbreviated as "UFB") referred to in the present invention are bubbles with a diameter of 1 μm or less, more preferably 0.1 μm or less. The diameter of the bubbles can be typically expressed by the median or maximum value in the diameter distribution. The gas that forms the bubbles can be a gas with the same composition as the components contained in the liquid that forms the liquid film, or a gas with a different composition that is introduced from the outside.

[0010] Liquids to which UFB has been added have the following effects. First, the impact of the tiny bubbles collapsing reduces the intermolecular forces, thereby lowering the surface tension of the liquid. This increases the fluidity of the liquid, improving, for example, its heat transfer properties. Also, because of their small particle size, they can penetrate even the smallest gaps and have the effect of separating substances that are adhered to each other. In this way, adding UFB has the effect of improving the properties of the liquid.

[0011] These effects can also be useful in substrate processing. That is, they can enhance the cleaning effect of the liquid on the substrate, and this effect is particularly noticeable on substrates with fine patterns formed on their surfaces. However, the effect of adding UFB to improve the liquid properties as described above is relatively gradual, and it does not necessarily achieve a high effect in short-term processing.

[0012] In the present invention, the surface of a substrate housed in a chamber for supercritical processing is covered with a liquid film containing UFBs. A non-supercritical processing fluid is then introduced into the chamber and pressurized, ultimately bringing the processing fluid to a supercritical state. At this time, the high pressure exerted on the liquid and the UFBs contained therein is also applied, causing the UFBs to further shrink in the liquid and collapse within a short period of time. In other words, the collapse of the UFBs in the liquid reduces the surface tension of the liquid, improves cleaning performance, and enhances heat transfer, even in a short period of time.

[0013] Therefore, during the pressurization process until the processing fluid reaches a supercritical state, the liquid with increased fluidity easily leaves the substrate surface, facilitating its replacement by the processing fluid. Furthermore, at this time, impurities remaining on the substrate surface or mixed into the processing fluid can be removed. Furthermore, the bubbles contract under pressure and penetrate deep into the pattern, making the above effect effective even on substrates with fine patterns formed thereon.

[0014] As described above, according to the present invention, by forming a liquid film covering a substrate using a UFB-containing liquid and then pressurizing the liquid, it is possible to obtain the effect of improving the liquid properties using the UFB in a short period of time. Therefore, the UFB-containing liquid can also be suitably applied to substrate processing. In supercritical processing, the efficiency of replacing liquid adhering to the substrate with a processing fluid can be improved, the impurity removal effect of the liquid can be enhanced, and the time required for the pressurization step can be shortened.

[0015] Another aspect of the present invention is a substrate processing system for processing a substrate with a processing fluid in a supercritical state, comprising: a liquid film forming unit for forming a liquid film of a liquid containing ultrafine bubbles on the surface of the substrate held in a substantially horizontal position; a chamber for accommodating the substrate on which the liquid film has been formed; and a fluid supply unit for supplying the processing fluid that is not in a supercritical state into the chamber and pressurizing the processing fluid to bring it to a supercritical state.

[0016] In the invention configured as described above, a liquid film containing UFB is formed on the substrate transported to the chamber for processing using the supercritical processing fluid. Therefore, the UFB in the liquid is pressurized by the above-mentioned principle, improving the properties of the liquid, and enabling replacement of the liquid with the processing fluid and subsequent supercritical processing to be performed successfully. [Effects of the Invention]

[0017] As described above, in the present invention, a substrate whose surface is covered with a liquid containing UFB is placed in a chamber, and a processing fluid is introduced into the chamber and pressurized to bring the liquid to a supercritical state. This allows the UFB to improve the liquid's properties in a short time, enabling successful replacement of the liquid with the processing fluid and subsequent supercritical processing. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a diagram showing a schematic configuration of an embodiment of a substrate processing system according to the present invention; [Figure 2] FIG. 1 is a diagram illustrating an example of the configuration of a wet treatment apparatus. [Figure 3] FIG. 1 is a side view showing the configuration of a supercritical processing apparatus. [Figure 4] 1 is a flowchart showing an outline of processing performed by the substrate processing system. [Figure 5] FIG. 10 is a diagram showing pressure changes in a processing chamber. [Figure 6] FIG. 1 is a diagram showing the action of UFB in liquid. DETAILED DESCRIPTION OF THE INVENTION

[0019] 1 is a diagram showing the schematic configuration of one embodiment of a substrate processing system according to the present invention. This substrate processing system 1 is a processing system for wet-processing various substrates, such as semiconductor wafers, by supplying a processing liquid to the upper surface of the substrate and then drying the substrate, and has a system configuration suitable for carrying out a substrate processing method according to the present invention. Specifically, the substrate processing apparatus 1 includes, as its main components, a wet-processing apparatus 2, a transfer mechanism 3, a supercritical processing apparatus 4, and a control unit 9.

[0020] The wet processing apparatus 2 receives the substrate to be processed and performs a predetermined wet processing. The type of processing is not particularly limited. The transport mechanism 3 transports the substrate after the wet processing out of the wet processing apparatus 2 and loads it into the supercritical processing apparatus 4. The supercritical processing apparatus 4 performs a drying process (supercritical drying process) on the loaded substrate using a processing fluid in a supercritical state. These are installed in a clean room. Therefore, the transport mechanism 3 transports the substrate S in the air atmosphere under atmospheric pressure.

[0021] The control unit 9 controls the operation of each of these devices to achieve predetermined processing. For this purpose, the control unit 9 is equipped with a CPU 91, a memory 92, a storage 93, an interface 94, and the like. The CPU 91 executes various control programs. The memory 92 temporarily stores processing data. The storage 93 stores the control programs executed by the CPU 91. The interface 94 exchanges information with users and external devices. The operations of the devices described below are achieved by the CPU 91 executing control programs written in advance in the storage 93 and causing each device to perform a predetermined operation.

[0022] When the CPU 91 executes a predetermined control program, functional blocks such as a wet treatment control unit 95 that controls the operation of the wet treatment device 2, a transport control unit 96 that controls the operation of the transport mechanism 3, and a supercritical treatment control unit 97 that controls the operation of the supercritical treatment device 4 are realized in software in the control unit 9. Note that at least a part of each of these functional blocks may be configured with dedicated hardware.

[0023] The "substrate" in this embodiment can be any of a variety of substrates, including semiconductor wafers, glass substrates for photomasks, glass substrates for liquid crystal displays, glass substrates for plasma displays, substrates for FEDs (Field Emission Displays), substrates for optical disks, substrates for magnetic disks, and substrates for magneto-optical disks. The following description will be given with reference to the drawings, taking as an example a substrate processing apparatus used primarily for processing disc-shaped semiconductor wafers. However, the present invention can be similarly applied to processing the various substrates exemplified above. Various substrate shapes can also be used.

[0024] Fig. 2 is a diagram showing an example of the configuration of a wet-processing apparatus. More specifically, Fig. 2(a) is a side view showing the overall configuration of a wet-processing apparatus 2, and Fig. 2(b) is a diagram for explaining the operation of the wet-processing apparatus 2. This wet-processing apparatus 2 is an apparatus that processes a substrate by supplying a processing liquid to the upper surface of the substrate. The operation of the wet-processing apparatus 2 is controlled by a wet-processing control unit 95 of the control unit 9.

[0025] The wet processing apparatus 2 supplies a processing liquid to the upper surface of the substrate S to perform wet processing such as surface processing and cleaning of the substrate S. For this purpose, the wet processing apparatus 2 includes a substrate holding unit 21, a splash guard 22, and processing liquid supply units 23 and 24 inside a processing chamber 200. The operations of these units are controlled by a wet processing control unit 95 provided in the control unit 9. The substrate holding unit 21 has a disk-shaped spin chuck 211 having approximately the same diameter as the substrate S, and a plurality of chuck pins 212 are provided on the periphery of the spin chuck 211. The chuck pins 212 abut against the periphery of the substrate S to support the substrate S, allowing the spin chuck 211 to hold the substrate S in a horizontal position while spaced apart from the upper surface of the spin chuck 211.

[0026] The spin chuck 211 is supported by a rotation support shaft 213 extending downward from the center of its bottom surface so that its upper surface is horizontal. The rotation support shaft 213 is rotatably supported by a rotation mechanism 214 attached to the bottom of the processing chamber 200. The rotation mechanism 214 has a built-in rotation motor (not shown), and when the rotation motor rotates in response to a control command from the control unit 9, the spin chuck 211 directly connected to the rotation support shaft 213 rotates around a vertical axis indicated by a dashed line. In FIG. 2, the up-down direction is the vertical direction. As a result, the substrate S is rotated around the vertical axis while remaining in a horizontal position.

[0027] A splash guard 22 is provided to surround the substrate holding part 21 from the side. The splash guard 22 has a generally cylindrical cup 221 provided to cover the peripheral part of the spin chuck 211, and a liquid receiving part 222 provided below the outer periphery of the cup 221. The cup 221 moves up and down in response to a control command from the control part 9. As shown in FIG. 2(a), the cup 221 moves up and down between a lower position where the upper end of the cup 221 is lowered below the peripheral part of the substrate S held by the spin chuck 211, and an upper position where the upper end of the cup 221 is positioned above the peripheral part of the substrate S, as shown in FIG. 2(b).

[0028] 2(a), when the cup 221 is in the lower position, the substrate S held by the spin chuck 211 is exposed to the outside of the cup 221. This prevents the cup 221 from becoming an obstacle when, for example, the substrate S is loaded onto or unloaded from the spin chuck 211.

[0029] 2(b), when the cup 221 is in the upper position, it surrounds the peripheral edge of the substrate S held by the spin chuck 211. This prevents the processing liquid shaken off from the peripheral edge of the substrate S during liquid supply, which will be described later, from scattering inside the chamber 200, making it possible to reliably collect the processing liquid. That is, as the substrate S rotates, droplets of the processing liquid shaken off from the peripheral edge of the substrate S adhere to the inner wall of the cup 221 and flow downward, and are collected by the liquid receiving portion 222 arranged below the cup 221. In order to collect multiple processing liquids individually, multiple stages of cups may be provided concentrically.

[0030] The processing liquid supply unit 23 has a structure in which a nozzle 234 is attached to the tip of an arm 233 that extends horizontally from a pivotal support shaft 232 that is rotatably provided on a base 231 fixed to the processing chamber 200. The pivotal support shaft 232 rotates in response to a control command from the control unit 9, causing the arm 233 to swing, and the nozzle 234 at the tip of the arm 233 moves between a retracted position retracted laterally from above the substrate S as shown in Figure 2(a) and a processing position above the substrate S as shown in Figure 2(b).

[0031] The nozzle 234 is connected to a processing liquid supply source 238, and when an appropriate processing liquid is delivered from the processing liquid supply source 238, the processing liquid is ejected from the nozzle 234 toward the substrate S. As shown in FIG. 2(b), the spin chuck 211 rotates at a relatively slow speed to rotate the substrate S, and a processing liquid L1 is supplied from the nozzle 234 positioned above the center of rotation of the substrate S, thereby processing the upper surface Sa of the substrate S with the processing liquid L1. The processing liquid L1 may be a liquid having various functions, such as a developer, an etching liquid, a cleaning liquid, or a rinse liquid, and may have any composition. Furthermore, processing may be performed using a combination of multiple types of processing liquids.

[0032] The other processing liquid supply unit 24 also has a configuration corresponding to the above-described first processing liquid supply unit 23. That is, the second processing liquid supply unit 24 has a base 241, a pivot shaft 242, an arm 243, a nozzle 244, etc., and these configurations are equivalent to those corresponding to those in the first processing liquid supply unit 23. The pivot shaft 242 rotates in response to a control command from the control unit 9, causing the arm 243 to swing. The nozzle 244 at the tip of the arm 243 supplies the processing liquid to the upper surface Sa of the substrate S.

[0033] In this embodiment, the second processing liquid supply unit 24 is used for the purpose of forming a liquid film for preventing drying on the substrate S after wet processing. That is, the substrate S after wet processing is transported to the supercritical processing device 4 and subjected to supercritical drying processing, but in order to prevent the surface of the substrate S from being exposed and oxidized during transportation or the fine pattern formed on the surface from collapsing, the substrate S is transported with its surface covered with a puddle-shaped liquid film.

[0034] The liquid that constitutes the liquid film is a substance having a surface tension lower than that of water, which is the main component of the treatment liquid used in the cleaning treatment, such as an organic solvent such as isopropyl alcohol (IPA) or acetone.

[0035] Furthermore, in various cleaning processes using liquids, a technique of incorporating minute bubbles called ultrafine bubbles (UFB) or nanobubbles into the liquid has come to be used to enhance the cleaning effect. For example, Japanese Patent Application Laid-Open No. 2015-066470 describes a technique of cleaning silicon wafers in a flowing cleaning liquid in which UFB with a particle size of 1 μm or less is mixed into ultrapure water.

[0036] In this embodiment, a liquid film is formed using IPA containing UFB. For this purpose, the second processing liquid supply unit 24 is provided with a processing liquid supply source 248 that supplies IPA and a UFB generator 249 inserted in the piping leading from the processing liquid supply source 248 to the nozzle 244. For example, UFB generators that generate UFB particles with particle sizes of 1 μm or less and mix them into a liquid are commercially available, and such devices can be used in this embodiment as well. The gas that constitutes the bubbles can be the same as the liquid components. Alternatively, as indicated by the dotted arrow in FIG. 2, an inert gas (e.g., nitrogen gas) may be introduced from the outside and bubbles of that gas may be mixed into the liquid.

[0037] Here, two sets of processing liquid supply units are provided in the wet processing apparatus 2, but the number of processing liquid supply units provided, their structures, and functions are not limited to this. For example, only one set of processing liquid supply units may be provided, or three or more sets may be provided. Furthermore, one processing liquid supply unit may be provided with multiple nozzles. For example, multiple nozzles may be provided at the tip of one arm. Furthermore, in addition to the above-mentioned mode in which the processing liquid is discharged while the nozzle is positioned at a predetermined position, a mode in which the processing liquid is discharged while the nozzle moves in a scanning motion along the upper surface Sa of the substrate S may also be included. Furthermore, a gas supply unit having a nozzle that discharges gas may also be provided. Furthermore, a mode in which at least one of the multiple nozzles provided in the processing liquid supply unit discharges gas may also be included.

[0038] Returning to FIG. 1, the transfer mechanism 3 is provided with a transfer robot 30 having a hand 31 attached to the tip of an extendable and rotatable arm. The hand 31 can support a substrate by partially contacting the underside of the substrate, and as shown by the dotted lines in FIG. 1, is movable toward and away from both the wet-processing apparatus 2 and the supercritical unit 4. This allows substrates to be loaded into and unloaded from both the wet-processing apparatus 2 and the supercritical unit 4. The operation of the transfer robot 30 is controlled by a transfer control unit 96 of the control unit 9. There are many well-known technologies for this type of transfer robot, and any of these can be appropriately selected and used in this embodiment, so a detailed description will be omitted.

[0039] 3 is a side view showing the configuration of a supercritical processing apparatus. The supercritical processing apparatus 4 is an apparatus that performs a drying process using a processing fluid in a supercritical state on a substrate S after wet processing. More specifically, the supercritical processing apparatus 4 is an apparatus that receives the substrate S after wet processing, replaces the liquid remaining on the substrate S with the processing fluid in a supercritical state, and then discharges the processing fluid, thereby finally bringing the substrate S to a dry state.

[0040] The supercritical processing apparatus 4 includes a processing unit 41, a transfer unit 43, and a supply unit 45. The processing unit 41 is the main unit that performs the supercritical drying process. The transfer unit 43 receives the substrate S after wet processing that is transported by the transport mechanism 3 and transports it into the processing unit 41, and also transfers the processed substrate S from the processing unit 41 to an external transport device. The supply unit 45 supplies chemical substances, power, energy, etc. required for processing to the processing unit 41 and the transfer unit 43. These operations are controlled by the control unit 9, particularly the supercritical processing control unit 97.

[0041] The processing unit 41 has a structure in which a processing chamber 412 is mounted on a base 411. The processing chamber 412 is constructed by combining several metal blocks, and its interior is hollow, constituting a processing space SP. The substrate S to be processed is loaded into the processing space SP and undergoes processing. A slit-shaped opening 421 that is elongated in the X direction is formed on the (-Y) side surface of the processing chamber 412. The processing space SP communicates with the outside space via the opening 421. The cross-sectional shape of the processing space SP is approximately the same as the opening shape of the opening 421. In other words, the processing space SP has a cross-sectional shape that is long in the X direction and short in the Z direction, and is a cavity that extends in the Y direction.

[0042] A lid member 413 is provided on the (-Y) side surface of the processing chamber 412 so as to close the opening 421. By closing the opening 421 of the processing chamber 412 with the lid member 413, an airtight processing container is formed. This makes it possible to process the substrate S under high pressure in the internal processing space SP. A flat support tray 415 is attached in a horizontal position to the (+Y) side surface of the lid member 413. The upper surface of the support tray 415 forms a support surface on which the substrate S can be placed. The lid member 413 is supported by a support mechanism (not shown) so as to be freely movable horizontally in the Y direction.

[0043] The lid member 413 can be moved toward and away from the processing chamber 412 by an advancing / retracting mechanism 453 provided in the supply unit 45. Specifically, the advancing / retracting mechanism 453 has a linear motion mechanism such as a linear motor, a linear motion guide, a ball screw mechanism, a solenoid, or an air cylinder. Such a linear motion mechanism moves the lid member 413 in the Y direction. The advancing / retracting mechanism 453 operates in response to a control command from the control unit 9.

[0044] When the cover member 413 moves in the (-Y) direction to move away from the processing chamber 412 and the support tray 415 is pulled out from the processing space SP through the opening 421 as shown by the dotted line, access to the support tray 415 becomes possible. That is, it becomes possible to place the substrate S on the support tray 415 and to remove the substrate S placed on the support tray 415. On the other hand, when the cover member 413 moves in the (+Y) direction, the support tray 415 is accommodated in the processing space SP. When a substrate S is placed on the support tray 415, the substrate S is carried into the processing space SP together with the support tray 415.

[0045] The lid member 413 moves in the (+Y) direction to close the opening 421, thereby sealing the processing space SP. A seal member 422 is provided between the (+Y) side surface of the lid member 413 and the (-Y) side surface of the processing chamber 412, thereby maintaining the processing space SP in an airtight state. The seal member 422 is made of, for example, rubber. In addition, the lid member 413 is fixed to the processing chamber 412 by a locking mechanism (not shown). As described above, in this embodiment, the lid member 413 can be switched between a closed state (solid line) in which the lid member 413 closes the opening 421 to seal the processing space SP, and a separated state (dotted line) in which the lid member 413 is separated significantly from the opening 421 to allow the substrate S to be inserted or removed.

[0046] The processing space SP is kept airtight while the substrate S is processed within the processing space SP. In this embodiment, the fluid supply unit 457 in the supply unit 45 delivers a processing fluid, such as carbon dioxide, that is a substance suitable for supercritical processing. The processing fluid is then pressurized within the processing chamber 412 to bring it to a supercritical state. The processing fluid is supplied to the processing unit 41 in a gaseous or liquid state. Carbon dioxide is a chemical suitable for supercritical drying because it reaches a supercritical state at relatively low temperatures and pressures and has the property of dissolving organic solvents commonly used in substrate processing. The critical point at which carbon dioxide reaches a supercritical state is an atmospheric pressure (critical pressure) of 7.38 MPa and a temperature (critical temperature) of 31.1°C.

[0047] When the processing space SP is filled with the processing fluid and the processing space SP reaches an appropriate temperature and pressure, the processing space SP is filled with the processing fluid in a supercritical state. In this manner, the substrate S is processed by the supercritical fluid in the processing chamber 412. The supply unit 45 is provided with a fluid recovery part 455, and the processed fluid is recovered by the fluid recovery part 455. The fluid supply part 457 and the fluid recovery part 455 are controlled by the supercritical processing control part 97.

[0048] The processing space SP has a shape and volume that can accommodate the support tray 415 and the substrate S supported thereon. That is, the processing space SP has a roughly rectangular cross-sectional shape that is wider than the width of the support tray 415 in the horizontal direction and greater than the combined height of the support tray 415 and the substrate S in the vertical direction, and a depth that can accommodate the support tray 415. In this way, the processing space SP has a shape and volume that can accommodate the support tray 415 and the substrate S. However, there is only a small gap between the support tray 415 and the substrate S and the inner wall surface of the processing space SP. Therefore, a relatively small amount of processing fluid is required to fill the processing space SP.

[0049] The fluid supply unit 457 supplies the processing fluid to the processing space SP further to the (+Y) side than the (+Y) side end of the substrate S. Meanwhile, the fluid recovery unit 55 discharges the processing fluid that flows through the space above the substrate S and the space below the support tray 415 in the processing space SP further to the (-Y) side than the (-Y) side end of the substrate S. As a result, laminar flows of the processing fluid from the (+Y) side to the (-Y) side are formed above the substrate S and below the support tray 415 in the processing space SP.

[0050] The supercritical processing control unit 97 of the control unit 9 determines the pressure and temperature in the processing space SP based on the detection results from a detection unit (not shown), and controls the fluid supply unit 457 and the fluid recovery unit 455 based on the results. This appropriately manages the supply of the processing fluid to the processing space SP and the discharge of the processing fluid from the processing space SP, and adjusts the pressure and temperature in the processing space SP in accordance with a predetermined processing recipe.

[0051] The transfer unit 43 is responsible for transferring the substrate S between the transport mechanism 3 and the support tray 415. For this purpose, the transfer unit 43 includes a main body 431, a lifting member 433, a base member 435, and multiple lift pins 437. The lifting member 433 is a columnar member extending in the Z direction and is supported by a support mechanism (not shown) so as to be movable in the Z direction relative to the main body 431. A base member 435 having a substantially horizontal upper surface is attached to the upper part of the lifting member 433. Multiple lift pins 437 are erected upward from the upper surface of the base member 435. Each of the lift pins 437 supports the substrate S in a horizontal position from below by abutting its upper end with the lower surface of the substrate S. In order to stably support the substrate S in a horizontal position, it is desirable to provide three or more lift pins 437 whose upper ends have the same height.

[0052] The lifting member 433 can be moved up and down by a lifting mechanism 451 provided in the supply unit 45. Specifically, the lifting mechanism 451 has a linear motion mechanism such as a linear motor, a linear motion guide, a ball screw mechanism, a solenoid, or an air cylinder, and this linear motion mechanism moves the lifting member 433 in the Z direction. The lifting mechanism 451 operates in response to a control command from the control unit 9.

[0053] The base member 435 moves up and down as the lifting member 433 moves up and down, and the plurality of lift pins 437 move up and down integrally therewith. This allows the transfer of the substrate S between the transfer unit 43 and the support tray 415. More specifically, as shown by the dotted line in FIG. 3 , the substrate S is transferred with the support tray 415 pulled out to the outside of the chamber. For this purpose, the support tray 415 is provided with through holes 417 for inserting the lift pins 437. When the base member 435 moves up, the upper ends of the lift pins 437 pass through the through holes 417 and reach a position higher than the upper surface of the support tray 415. In this state, the substrate S transferred by the transfer robot 30 is transferred from the hand 31 of the transfer robot 30 to the lift pins 437. When the lift pins 437 move down, the substrate S is transferred from the lift pins 437 to the support tray 415. The substrate S can be removed by reversing the above procedure.

[0054] 4 is a flowchart showing an outline of the processing performed by this substrate processing system. This substrate processing system 1 receives a substrate S to be processed and sequentially performs a wet processing using a processing liquid and a supercritical drying processing using a supercritical processing fluid. Specifically, the processing is as follows. The substrate S to be processed is accommodated in a wet processing device 2 constituting the substrate processing system 1 (step S101). The substrate S may be carried in directly by an external transfer device, or may be carried in from the external transfer device via a transfer robot 30.

[0055] The wet processing apparatus 2 performs wet processing on the substrate S using a predetermined processing liquid (step S102). Then, a liquid film forming process is performed to form a liquid film on the surface using an organic solvent such as IPA (step S103). The IPA used to form the liquid film is supplied to the substrate S from a processing liquid supply source 248 via a UFB generator 249 and contains UFB.

[0056] For example, if a fine pattern is formed on the surface of the substrate S, the surface tension of the liquid remaining on the substrate S may cause the pattern to collapse. Also, incomplete drying may leave watermarks on the surface of the substrate S. Furthermore, exposure of the surface of the substrate S to the outside air may cause deterioration such as oxidation. To prevent such problems from occurring, the surface of the substrate S (the surface on which the pattern is formed) may be transported while covered with a liquid or solid surface layer.

[0057] For example, if the cleaning liquid is primarily water, the substrate S is transported in a state in which a liquid film is formed using a liquid having a lower surface tension and less corrosiveness to the substrate, such as an organic solvent such as IPA or acetone. That is, the substrate S is supported horizontally and transported from the wet processing apparatus 2 to the supercritical processing apparatus 4 by the transport mechanism 3 in a state in which a liquid film is formed on the upper surface of the substrate S (step S104).

[0058] The substrate S transferred to the supercritical processing apparatus 4 is accommodated in the processing chamber 412. Specifically, the substrate S is transferred with the pattern-formed surface facing up, and with the surface covered with a thin liquid film. As shown by the dotted line in FIG. 3, the lid member 413 moves to the (-Y) side, the support tray 415 is pulled out, and the lift pins 437 rise. The transfer device transfers the substrate S to the lift pins 437. The lift pins 437 descend, and the substrate S is placed on the support tray 415. When the support tray 415 and the lid member 413 move together in the (+Y) direction, the support tray 415 supporting the substrate S is accommodated in the processing space SP within the processing chamber 412, and the opening 421 is closed by the lid member 413.

[0059] In this state, carbon dioxide as a processing fluid is introduced into the processing space SP in a gaseous state (step S105). When the substrate S is loaded, outside air enters the processing space SP, but this can be replaced by introducing the gaseous processing fluid. Furthermore, by injecting the gaseous processing fluid, the pressure inside the processing chamber 412 increases.

[0060] During the process of introducing the processing fluid, the processing fluid is continuously discharged from the processing space SP. That is, even while the processing fluid is being introduced by the fluid supply unit 457, the processing fluid is continuously discharged from the processing space SP by the fluid recovery unit 455. This allows the processing fluid used for processing to be discharged without remaining in the processing space SP, and prevents impurities such as residual liquid that have been absorbed in the processing fluid from adhering again to the substrate S.

[0061] If the supply rate of the processing fluid is greater than the discharge rate, the density of the processing fluid in the processing space SP increases, causing an increase in the pressure inside the chamber. Conversely, if the supply rate of the processing fluid is less than the discharge rate, the density of the processing fluid in the processing space SP decreases, causing a decrease in the pressure inside the chamber. The supply of the processing fluid to the processing chamber 412 and the discharge of the processing fluid from the processing chamber 412 are performed based on a pre-created supply and discharge recipe. That is, the control unit 9 controls the fluid supply unit 457 and the fluid recovery unit 455 based on the supply and discharge recipe, thereby adjusting the timing of supply and discharge of the processing fluid, its flow rate, etc.

[0062] FIG. 5 shows pressure changes within the processing chamber. When the processing fluid is carbon dioxide, its critical temperature is not significantly different from room temperature, so temperature changes during processing are not significant. Here, we will explain the phenomenon by focusing on the pressure within the chamber, which changes more significantly. The processing space SP is open to the atmosphere and the internal pressure is atmospheric pressure Pa. At time T1 after the processing space SP is sealed, the introduction of the processing fluid begins, and the internal pressure begins to rise.

[0063] Pressurization continues until the pressure of the processing fluid in the processing space SP increases and exceeds the critical pressure Pc (step S106). At time T2 when the chamber reaches the critical pressure Pc, the processing fluid becomes supercritical in the chamber. That is, a phase change occurs in the processing space SP, causing the processing fluid to transition from a gas phase to a supercritical state. As the processing space SP is filled with the supercritical fluid, the organic solvent, such as IPA, that covers the substrate S is replaced by the supercritical fluid. The organic solvent liberated from the surface of the substrate S is dissolved in the processing fluid and discharged from the processing chamber 412 together with the processing fluid, and is removed from the substrate S. That is, the processing fluid in the supercritical state has the function of replacing the organic solvent adhering to the substrate S as the replacement liquid and discharging it out of the processing chamber 412.

[0064] After time T3 when the processing fluid has definitely transitioned to the supercritical state, the processing space SP is kept filled with the processing fluid in the supercritical state for a predetermined time (steps S107 and S108), whereby the liquid to be replaced adhering to the substrate S can be completely replaced and discharged to the outside of the chamber. Note that although the pressure Pm inside the chamber in the supercritical state is shown as being constant, the pressure may fluctuate as long as it does not become equal to or lower than the critical pressure Pc in FIG.

[0065] At time T4, when the replacement of the replacement target liquid with the supercritical fluid in the processing chamber 412 is completed (step S104), the processing fluid in the processing space SP is discharged to dry the substrate S. Specifically, the amount of fluid discharged from the processing space SP is increased to reduce the pressure inside the processing chamber 12 filled with the processing fluid in a supercritical state (step S109).

[0066] During the depressurization process, the supply of the processing fluid may be stopped, or a small amount of processing fluid may be continuously supplied. When the processing space SP is depressurized from a state where it is filled with supercritical fluid, the processing fluid changes phase from the supercritical state to the gas phase. The vaporized processing fluid is discharged to the outside, and the substrate S becomes dry. At this time, the depressurization rate is adjusted so as not to create solid and liquid phases due to a sudden drop in temperature. That is, after depressurization begins at time T4, depressurization is performed at a relatively slow depressurization rate until time T5, when the pressure is reliably below the critical pressure Pc. As a result, the processing fluid in the processing space SP is directly vaporized from the supercritical state and discharged to the outside.

[0067] After time T5 when the processing fluid is completely vaporized, the depressurization rate is increased, thereby enabling the pressure to be reduced to atmospheric pressure Pa in a short time. In this way, the processing fluid is not liquefied throughout the entire period from time T4 when depressurization begins to time T6 when the pressure inside the chamber is reduced to atmospheric pressure Pa, and the formation of a gas-liquid interface on the substrate S with its surface exposed after drying is avoided.

[0068] As described above, in the supercritical drying process of this embodiment, the processing space SP is filled with a processing fluid in a supercritical state, and then the processing fluid is phase-changed to a gas phase and discharged, thereby efficiently replacing the liquid adhering to the substrate S and preventing it from remaining on the substrate S. Moreover, the substrate can be dried while avoiding problems caused by the formation of a gas-liquid interface, such as contamination of the substrate due to the adhesion of impurities and pattern collapse.

[0069] After processing, the substrate S is discharged to the subsequent process (step S110). That is, the cover member 413 moves in the (-Y) direction, whereby the support tray 415 is drawn out from the processing chamber 412, and the substrate S is delivered to an external transport device via the transfer unit 43. At this time, the substrate S is in a dry state. The content of the subsequent process is optional. In this way, the processing for one substrate S is completed. If there is another substrate to be processed, the process returns to step S101, a new substrate S is received, and the above processing is repeated.

[0070] In this embodiment, the substrate S after the wet processing is carried into the supercritical processing apparatus 4 in a state in which a liquid film of the liquid (IPA) containing UFB is formed on the surface. The reason for this will be explained below.

[0071] Figure 6 is a diagram that schematically illustrates the effect of UFBs in liquid. As shown in Figure 6(a), consider a situation in which the surface of a substrate S, on which a trench-shaped pattern P has been formed, is covered with liquid L containing UFB bubbles B. The representative width of the pattern P is represented by the symbol W, and the median value in the particle size distribution is used here as a representative value for the particle size Dm of UFBs with various particle sizes. However, when focusing particularly on the effect within the pattern P, since bubbles with a particle size smaller than the pattern width W are the ones that have an effective effect, it is also possible to represent the particle size Dm by the substantial maximum value in the particle size distribution.

[0072] As shown in the graph on the right of Figure 6(a), for example, if the particle diameter Dm is smaller than the pattern width W, the liquid L contains many bubbles B whose diameter is smaller than the pattern width W. The bubbles B have the following effects near the surface of the substrate S and inside the pattern P.

[0073] UFBs, which are tiny bubbles, are less susceptible to buoyancy and remain in the liquid for a long time. Furthermore, the impact (pressure wave) generated when the bubbles collapse reduces the intermolecular forces of the liquid, lowering the surface tension of the liquid and increasing its fluidity. The liquid L forms a puddle-shaped liquid film on the surface of the substrate S due to its surface tension, but a decrease in surface tension reduces the ability to maintain the liquid film. In other words, excess liquid that cannot be maintained falls from the substrate S, and the liquid film becomes thinner. While the liquid film protects the surface of the substrate S during transportation, in supercritical processing it is also the target for replacement by the processing fluid. By reducing the surface tension of the liquid L, the amount of liquid L that needs to be replaced on the substrate S is reduced, improving the efficiency of the replacement.

[0074] Furthermore, the pressure waves generated when the bubbles B collapse also reduce the adhesive force between the substrate S and impurities adhering to its surface and inside the pattern P. In other words, even if impurities remain on the substrate S, the liquid L containing UFB has the effect of removing them. It also has the effect of preventing impurities contained in the liquid L and the processing fluid from adhering to the substrate S. In this way, adding UFB to the liquid L can enhance the cleaning effect of the liquid L on the substrate.

[0075] In addition, the inclusion of UFB reduces friction between the liquid and the solid it comes into contact with, improving the heat transferability of the liquid. This allows the thermal energy of the processing fluid to be efficiently transferred to the liquid, contributing to improved replacement efficiency. Furthermore, the inclusion of bubbles in the liquid improves cushioning against impacts, preventing pattern collapse.

[0076] Furthermore, if the bubbles B are made of a gas that does not contain oxygen, for example, an inert gas such as nitrogen gas, the liquid L that comes into contact with the substrate S is made into a low-oxygen state, thereby improving the effect of suppressing oxidation of the surface of the substrate S. For example, after the wet processing is completed, the effect of suppressing the liquid film from adsorbing moisture contained in the atmosphere (air) until the substrate is carried into the supercritical processing apparatus 4 can be obtained.

[0077] The preferred value for the particle size Dm of the bubbles B depends on the pattern width W. In other words, the smaller the particle size Dm, the greater the penetration amount into the pattern P, and the greater the effect. Generally, bubbles with a particle size of 1 μm or less are called UFBs, and when the pattern width W is greater than 1 μm, the above-mentioned effect can be obtained by using a liquid containing such UFBs. In particular, when the pattern width W is small, it is preferable to use UFBs with a particle size of, for example, about 0.1 μm.

[0078] All of the above effects improve the properties of the liquid L covering the substrate S, which can be advantageous in maintaining the cleanliness of the substrate S and allowing the processing to proceed smoothly. However, the collapse of the UFBs proceeds relatively slowly. Furthermore, only bubbles B with a particle size sufficiently small relative to the pattern width W are effective, at least within the pattern P. For these reasons, the effectiveness is generally limited in short-term processing. In this embodiment, a liquid film containing UFBs is formed on the surface of the substrate S under atmospheric pressure, and this is transported to the processing chamber 412. During this time, the effect of UFBs in improving the liquid properties is not very significant.

[0079] Meanwhile, in the processing chamber 412 into which the substrate S has been loaded, high pressure is also applied to the liquid film during the process of increasing the pressure of the processing fluid. As a result, the bubbles B in the liquid L are also pressurized and contract, and as shown in Figure 6(b), the particle size distribution shifts to the smaller particle size side. This makes it easier for the bubbles B to penetrate into the interior of the fine pattern P and into the small gaps between the surface of the substrate S and the impurities, making the effect of UFB more pronounced. Furthermore, the sudden application of high pressure to each bubble B increases the temperature of the gas inside the bubble B due to adiabatic expansion and promotes the collapse (crushing) of the bubble B, further enhancing the above effect.

[0080] In this embodiment, the liquid film on the substrate S, to which high pressure is applied in the subsequent supercritical processing, is formed from the liquid L containing UFB. Therefore, the various property-improving effects of the UFB on the liquid are more pronounced under high pressure, and these effects are effectively exerted even in a short period of time. This allows the substrate S to be kept clean and the processing to proceed smoothly.

[0081] 5, the bubble B is rapidly compressed between time T1 when the pressure increase begins and time T2 when the pressure inside the chamber reaches the critical pressure Pc. This reduces the surface tension of the liquid L on the substrate S, making it easier for the liquid L to separate from the substrate S. As a result, the efficiency of replacing the liquid L with the processing fluid is improved. At the same time, the effectiveness of removing impurities such as metals, organic matter, and moisture remaining on the substrate S or contained in the liquid L or processing fluid from the substrate S is also improved, and these are discharged together with the liquid L, thereby keeping the substrate S clean.

[0082] In particular, by forming the UFB using a gas that does not contain oxygen, specifically nitrogen gas, the liquid L covering the substrate S can be maintained in a low-oxygen state, thereby preventing oxidation of the substrate S and suppressing adsorption of moisture from the atmosphere.

[0083] Furthermore, since the property improvement effect on the liquid L is obtained immediately after the start of the pressure increase and the replacement efficiency with the processing fluid is improved, it is possible to shorten the processing time required for the pressure increase process (from time T1 to time T3 in Figure 5), thereby shortening the takt time in supercritical processing.

[0084] As described above, in the substrate processing system 1 of the above embodiment, the wet processing apparatus 2 functions as the "liquid film forming unit" of the present invention, and the UFB generator 249 functions as the "bubble generator" of the present invention. The processing chamber and fluid supply unit 457 of the supercritical processing apparatus 4 function as the "chamber" and "fluid supply unit" of the present invention, respectively. The transfer mechanism 3 functions as the "transfer unit" of the present invention.

[0085] The present invention is not limited to the above-described embodiment, and various modifications other than those described above are possible without departing from the spirit of the present invention. For example, in the substrate processing system 1 of the above embodiment, the wet processing device 2 is a device that processes the substrate S with a processing liquid and then forms a liquid film using IPA. However, as the "liquid film forming unit" of the present invention, it is sufficient that the surface of the substrate S is ultimately unloaded in a state covered with a liquid film containing UFB, and the content of the processing as the pre-process is not limited to this and is arbitrary. Furthermore, as long as the liquid film covers the substrate S while it is contained in the processing chamber 412, it is also arbitrary when the liquid film is formed.

[0086] Furthermore, the various chemical substances used in the treatment of the above-described embodiments are only examples, and various substances can be used instead as long as they are consistent with the technical concept of the present invention described above.

[0087] As explained above with reference to specific embodiments, in the substrate processing method according to the present invention, "ultra-fine bubbles" refer to bubbles with a diameter of 1 μm or less, and more preferably 0.1 μm or less. By using a liquid containing bubbles with such a diameter, it is possible to satisfactorily process substrates having pattern sizes on the order of micrometers or smaller.

[0088] For example, the substrate processing method according to the present invention may further include a step of transporting the substrate, on which a liquid film has been formed outside the chamber, into the chamber. Furthermore, the substrate processing system according to the present invention may further include a transport unit that transports the substrate, on which a liquid film has been formed in the liquid film forming unit, into the chamber. In the transport under atmospheric pressure achieved by these steps, the effect of UFB contained in the liquid is relatively gentle. Therefore, the surface tension of the liquid is also relatively high, and there is little risk that the liquid constituting the liquid film will fall off the substrate during transport. This makes transport easy.

[0089] In the substrate processing system according to the present invention, the liquid film forming unit may include a bubble generator that generates ultrafine bubbles in the liquid. With this configuration, UFB can be mixed into the liquid just before it is supplied to the substrate, making it possible to form a liquid film using a liquid rich in UFB.

[0090] In the present invention, the UFB may be nitrogen gas. By forming a liquid film using a liquid containing nitrogen gas UFB, the substrate surface can be maintained in a low-oxygen state. This can suppress oxidation of the substrate surface. In addition, the liquid is prevented from absorbing oxygen and moisture from the atmosphere during transportation. [Industrial Applicability]

[0091] The present invention can be applied to any process for processing substrates using a processing fluid introduced into a chamber, for example, single-wafer substrate processing in which substrates such as semiconductor substrates are processed one by one in sequence using a supercritical fluid. [Explanation of symbols]

[0092] 1. Substrate Processing System 2. Wet treatment equipment (liquid film forming section) 3. Conveyance mechanism (conveyance section) 4 Supercritical Processing Section 9 Control Unit 248 Processing liquid supply source 249 UFB Generator (Bubble Generator) 412 Processing chamber (chamber) 457 Fluid supply section

Claims

1. 1. A substrate processing method for processing a substrate with a processing fluid in a supercritical state in a chamber, comprising: forming a liquid film of a liquid containing ultra-fine bubbles on the surface of the substrate held in a substantially horizontal position; introducing the processing fluid that is not in a supercritical state into the chamber containing the substrate on which the liquid film is formed, pressurizing the processing fluid to bring it to a supercritical state, and replacing the liquid on the substrate surface with the processing fluid; reducing the pressure inside the chamber, vaporizing the processing fluid in a supercritical state, and discharging the processing fluid outside the chamber; A substrate processing method comprising:

2. 2. The substrate processing method according to claim 1, wherein the liquid contains ultra-fine bubbles having a particle size of 1 [mu]m or less.

3. 2. The substrate processing method according to claim 1, wherein the liquid contains ultra-fine bubbles having a particle size of 0.1 [mu]m or less.

4. 4. The substrate processing method according to claim 1, further comprising the step of transporting the substrate, on which the liquid film has been formed outside the chamber, into the chamber.

5. 5. The substrate processing method according to claim 1, further comprising the step of mixing the ultra-fine bubbles of nitrogen gas with the liquid, and supplying the liquid mixed with the ultra-fine bubbles to the surface of the substrate to form the liquid film.

6. A substrate processing system for processing a substrate with a processing fluid in a supercritical state, a liquid film forming unit that forms a liquid film of a liquid containing ultra-fine bubbles on the surface of the substrate held in a substantially horizontal position; a chamber that accommodates the substrate on which the liquid film is formed; a fluid supply unit that supplies the processing fluid that is not in a supercritical state into the chamber and pressurizes the processing fluid to bring it to a supercritical state; A substrate processing system comprising:

7. The substrate processing system according to claim 6 , further comprising a transfer unit that transfers the substrate on which the liquid film has been formed in the liquid film forming unit to the chamber.

8. 8. The substrate processing system according to claim 6, wherein the liquid film forming unit has a bubble generator that generates the ultra-fine bubbles in the liquid.

9. The substrate processing system according to claim 8 , wherein the liquid film forming unit mixes the ultra-fine bubbles of nitrogen gas with the liquid.

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