Substrate processing method and substrate processing apparatus

Abstract

To reduce an amount of particles generated on a substrate when the substrate is dried by using a processing fluid in a supercritical state.SOLUTION: A substrate processing method comprises: a pressure rise step of rising a pressure in a processing container up to a predetermined processing pressure by supplying a processing fluid into the processing container in a state where a substrate in which a liquid film is formed is housed in to the processing contained so as to be held by a substrate holding part; and a circulation step of exhausting the processing fluid in the processing container from an exhaust part while maintaining the pressure in the processing container and supplying the processing fluid into the processing container from a second discharging part. The pressure rise step comprises: a first pressure rise stage that the pressure in the processing container is risen up to a switching pressure by supplying the processing fluid from a first discharging part into the processing container; and a second pressure rise stage that the pressure in the processing container is risen up to the processing pressure from the switching pressure by supplying the processing fluid from the second discharging part into the processing container after the first pressure rise stage.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a substrate processing method and a substrate processing apparatus. [Background technology]

[0002] In recent years, in the manufacture of semiconductor devices, a supercritical drying process is being performed in which a substrate, the upper surface of which is wetted with a processing liquid, is brought into contact with a processing fluid in a supercritical state, and the processing liquid is replaced with the processing fluid in the supercritical state to dry the substrate. Patent Document 1 describes a supercritical drying method and an apparatus for carrying out the method. Patent Document 1 describes that a supercritical fluid is first supplied into a chamber (processing vessel) from a lower supply port, and after the pressure in the chamber reaches the critical pressure, the supercritical fluid is supplied into the chamber from an upper supply port at a large flow rate. The supercritical fluid discharged from the lower supply port is made to collide with a blocking plate and then spreads in the chamber so that it does not directly reach the substrate. On the other hand, the supercritical fluid discharged from the upper supply port is provided so as to be directed directly toward the surface of the substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication 2013-251550 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure provides techniques that can reduce the amount of particles generated on a substrate when the substrate is dried using a processing fluid in a supercritical state. [Means for solving the problem]

[0005] According to one embodiment, the method is performed using a substrate processing apparatus including: a processing vessel for accommodating a substrate; a substrate holding unit for holding the substrate horizontally in the processing vessel with the surface of the substrate on which a liquid film is formed facing upward; a main supply line connected to a processing fluid supply unit for supplying a processing fluid in a supercritical state; a first branch supply line and a second branch supply line branching off from the main supply line at a first branch point set on the main supply line; a first discharge unit connected to the first branch supply line and discharging the processing fluid sent from the first branch supply line toward a space in the processing vessel below the substrate held by the substrate holding unit; a second discharge unit connected to the second branch supply line and discharging the processing fluid sent from the second branch supply line toward a space in the processing vessel above the surface of the substrate; a discharge unit for discharging the processing fluid from the processing vessel; and a discharge line connected to the discharge unit. A substrate processing method is provided, comprising: a pressurizing step of increasing the pressure in the processing vessel to a predetermined processing pressure by supplying a processing fluid into the processing vessel while the substrate on which the liquid film is formed is held by the substrate holding part and accommodated in the processing vessel; and a circulation step of, after the pressurizing step, supplying a processing fluid from the second discharge part into the processing vessel and discharging the processing fluid in the processing vessel from the discharge part while maintaining the pressure in the processing vessel at the processing pressure, wherein the pressurizing step comprises a first pressurizing stage of increasing the pressure in the processing vessel to a predetermined switching pressure by supplying a processing fluid from the first discharge part into the processing vessel; and a second pressurizing stage of, after the first pressurizing step, supplying a processing fluid from the second discharge part into the processing vessel to increase the pressure in the processing vessel from the switching pressure to the processing pressure. Effect of the Invention

[0006] According to the present disclosure, it is possible to reduce the amount of particles generated on a substrate when the substrate is dried using a processing fluid in a supercritical state. [Brief description of the drawings]

[0007] [Figure 1] FIG. 2 is a piping diagram of a supercritical drying apparatus according to an embodiment. [Figure 2A] FIG. 4 is a schematic diagram showing an example of a specific configuration of a second discharge section as viewed from above. [Figure 2B] FIG. 4 is a schematic diagram showing an example of a specific configuration of a second discharge section as viewed from the side. [Figure 3A] FIG. 2 is a diagram showing a series of steps of a supercritical drying method according to an embodiment of the present invention. [Figure 3B] FIG. 2 is a diagram showing a series of steps of a supercritical drying method according to an embodiment of the present invention. [Figure 3C] FIG. 2 is a diagram showing a series of steps of a supercritical drying method according to an embodiment of the present invention. [Figure 3D] FIG. 2 is a diagram showing a series of steps of a supercritical drying method according to an embodiment of the present invention. [Figure 3E] FIG. 2 is a diagram showing a series of steps of a supercritical drying method according to an embodiment of the present invention. [Figure 3F] FIG. 2 is a diagram showing a series of steps of a supercritical drying method according to an embodiment of the present invention. [Figure 4] FIG. 13 is a schematic diagram of a supercritical drying device according to a modified embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] A supercritical drying apparatus as an embodiment of a substrate processing apparatus will be described with reference to the accompanying drawings. The supercritical drying apparatus can be used to perform a supercritical drying process for drying a substrate W having a liquid film (e.g., IPA (isopropyl alcohol)) attached to its surface, using a processing fluid (e.g., carbon dioxide) in a supercritical state. The substrate W is, for example, a semiconductor wafer, but may be other types of substrates (glass substrate, ceramic substrate) used in the technical field of semiconductor device manufacturing. The supercritical drying technique can be advantageously used to dry a substrate on which a fine and high aspect ratio pattern is formed, since surface tension that can cause the pattern to collapse does not act on the pattern.

[0009] 1, the supercritical drying apparatus includes a processing unit 10 in which a supercritical drying process is performed. The processing unit 10 includes a processing vessel 12 and a substrate holding tray 14 (hereinafter simply referred to as “tray 14”) that holds substrates W in the processing vessel 12.

[0010] In one embodiment, the tray 14 has a lid 16 that closes an opening provided in a side wall of the processing vessel 12, and a horizontally extending substrate support plate (substrate holder) 18 (hereinafter simply referred to as "plate 18") connected to the lid 16. The substrate W is placed horizontally on the plate 18 with its front surface (the surface on which a device or pattern is formed) facing upward. The plate 18 is, for example, rectangular or square. The area of ​​the plate 18 is larger than that of the substrate W, and when the substrate W is placed at a predetermined position on the plate 18 and the plate 18 is viewed from directly below, the substrate W is completely covered by the plate 18.

[0011] The tray 14 can be moved horizontally between a processing position (closed position) and a substrate transfer position (open position) by a tray moving mechanism (not shown). At the processing position, the plate 18 is located in the internal space of the processing vessel 12, and the lid 16 closes the opening in the side wall of the processing vessel 12 (the state shown in FIG. 1). At the substrate transfer position, the plate 18 is outside the processing vessel 12, and the substrate W can be transferred between the plate 18 and a substrate transport arm (not shown). The movement direction of the tray 14 is, for example, the left-right direction in FIG. 1. The movement direction of the tray 14 may be perpendicular to the plane of FIG. 1, in which case the lid 16 can be provided on the rear or front side of the plate 18 in the figure.

[0012] When the tray 14 is in the processing position, the plate 18 divides the internal space of the processing vessel 12 into an upper space 12A above the plate 18 in which the substrate W is present during processing, and a lower space 12B below the plate 18. However, the upper space 12A and the lower space 12B are not completely separated. A gap is formed between the periphery of the tray 14 in the processing position and the inner wall surface of the processing vessel 12, serving as a communication passage connecting the upper space 12A and the lower space 12B. Furthermore, a through hole may be provided in the plate 18 near the lid 16 to connect the upper space 12A and the lower space 12B.

[0013] As described above, if the internal space of processing vessel 12 is divided into upper space 12A and lower space 12B, and a communication passage is provided that connects upper space 12A and lower space 12B, tray 14 (plate 18) may be configured as a substrate mounting table (substrate holder) that is immovably fixed inside processing vessel 12. In this case, with a lid (not shown) provided on processing vessel 12 open, a substrate transport arm (not shown) enters the vessel body, and substrates W are transferred between the substrate mounting table and the substrate transport arm.

[0014] The processing vessel 12 has a first discharge part 21 and a second discharge part 22 for discharging a processing fluid (here, carbon dioxide (for convenience, also written as "CO2")) supplied from a supply source 30 of supercritical fluid (processing fluid in a supercritical state) into the internal space of the processing vessel 12.

[0015] The first discharge unit 21 is provided below the plate 18 of the tray 14 in the processing position. The first discharge unit 21 discharges CO2 into the lower space 12B toward the lower surface of the plate 18. The first discharge unit 21 can be configured by a through hole formed in the bottom wall of the processing vessel 12. The first discharge unit 21 may be a nozzle body attached to the bottom wall of the processing vessel 12.

[0016] The second discharge unit 22 is provided so as to be located to the side of the substrate W placed on the plate 18 of the tray 14 at the processing position. The second discharge unit 22 can be provided, for example, on one side wall (first side wall) of the processing vessel 12 or in its vicinity. The second discharge unit 22 supplies CO2 into the upper space 12A toward a region slightly above the surface of the substrate W. The second discharge unit 22 is preferably configured to flow CO2 along the upper surface (surface) of the substrate W approximately evenly in the region above the substrate W over the entire diameter of the substrate W. A specific configuration example of the second discharge unit 22 will be described later.

[0017] The processing vessel 12 further has a fluid discharge part 24 that discharges the processing fluid from the internal space of the processing vessel 12. The fluid discharge part 24 can be formed as a header made of a horizontally extending pipe-shaped member having a plurality of holes therein, similar to the second discharge part 22. The fluid discharge part 24 can be provided, for example, on the side wall (second side wall) opposite to the first side wall of the processing vessel 12 on which the second discharge part 22 is provided, or in the vicinity thereof.

[0018] The fluid discharge part 24 can be disposed at any position as long as the CO2 supplied from the second discharge part 22 into the processing vessel 12 passes through the region above the substrate W on the plate 18 and is then discharged from the fluid discharge part 24. That is, for example, the fluid discharge part 24 may be provided at the bottom of the processing vessel 12 near the second side wall. In this case, the CO2 passes through the region above the substrate W in the upper space 12A, flows into the lower space 12B through a communication passage provided at the periphery of the plate 18 (or a through hole formed in the plate 18), and is then discharged from the fluid discharge part 24.

[0019] Next, a supply / discharge system for supplying and discharging CO2 to and from the processing vessel 12 in the supercritical drying apparatus will be described. In the piping system diagram shown in FIG. 1, the member indicated by a circled T is a temperature sensor, and the member indicated by a circled P is a pressure sensor. The member indicated by the symbol OLF is an orifice (fixed throttle) that reduces the pressure of CO2 flowing in the downstream piping to a desired value. The member indicated by a squared SV is a safety valve (relief valve) that prevents damage to the piping or components of the supercritical drying apparatus such as the processing vessel 12 due to unexpected overpressure. The member indicated by the symbol F is a filter that removes contaminants such as particles contained in CO2. The member indicated by the symbol CV is a check valve (non-return valve). The member indicated by a circled FV is a flow meter. The member indicated by a squared H is a heater for adjusting the temperature of CO2. When it is necessary to distinguish one of the above various components from another, a number is added to the end of the alphabet (for example, "filter F2"). The components designated by reference symbol VN (N is a natural number) are on-off valves, and ten on-off valves V1 to V10 are depicted in FIG. 1.

[0020] The supercritical drying apparatus has a supercritical fluid supplying apparatus 30 as a supply source (30) of a supercritical fluid (supercritical CO2). The supercritical fluid supplying apparatus 30 has a well-known configuration including, for example, a carbon dioxide gas cylinder, a pressure pump, a heater, etc. The supercritical fluid supplying apparatus 30 has the ability to deliver supercritical CO2 at a pressure exceeding a supercritical state guarantee pressure (specifically, about 16 MPa) described below.

[0021] A main supply line 32 is connected to the supercritical fluid supply device 30. CO2 flows out of the supercritical fluid supply device 30 in a supercritical state into the main supply line 32, but may become gaseous due to subsequent expansion or temperature change. In this specification, a member called a "line" may be composed of a pipe (a piping member).

[0022] The main supply line 32 branches into a first supply line (first branch supply line) 34 and a second supply line (second branch supply line) 36 at a branch point (first branch point) 33. The first supply line 34 is connected to a first discharge part 21 of the processing vessel 12. The second supply line 36 is connected to a second discharge part 22 of the processing vessel 12.

[0023] A discharge line 38 is connected to the fluid discharge section 24 of the processing vessel 12. A pressure regulating valve 40 is provided in the discharge line 38. By adjusting the aperture of the pressure regulating valve 40, the primary pressure of the pressure regulating valve 40 can be adjusted, and therefore the pressure inside the processing vessel 12 can be adjusted. In addition, by adjusting the aperture of the pressure regulating valve 40, the discharge speed of the processing fluid from the processing vessel 12 can also be adjusted.

[0024] A control unit 100, which is shown in FIG. 1, feedback controls the opening degree (specifically, the position of the valve) of the pressure regulating valve 40 based on the deviation between the measured value (PV) of the pressure in the processing vessel 12 and the set value (SV) so that the pressure in the processing vessel 12 is maintained at the set value. As the measured value of the pressure in the processing vessel 12, for example, a detection value of a pressure sensor with reference symbol PS provided between the on-off valve V3 of the exhaust line 38 and the processing vessel 12, as shown in FIG. 1, can be used. That is, the pressure in the processing vessel 12 may be directly measured by a pressure sensor provided in the processing vessel 12, or may be indirectly measured by a pressure sensor (PS) provided outside the processing vessel 12 (exhaust line 38). The pressure regulating valve 40 can be set to a fixed opening degree based on a command value from the control unit 100 (not feedback controlled).

[0025] The control unit 100 is, for example, a computer, and includes an arithmetic unit 101 and a storage unit 102. The storage unit 102 stores programs for controlling various processes executed in the supercritical drying apparatus (or a substrate processing system including the supercritical drying apparatus). The arithmetic unit 101 controls the operation of the supercritical drying apparatus by reading and executing the programs stored in the storage unit 102. The programs may be recorded in a computer-readable storage medium and installed from the storage medium into the storage unit 102 of the control unit 100. Examples of computer-readable storage media include a hard disk (HD), a flexible disk (FD), a compact disk (CD), a magnet optical disk (MO), and a memory card.

[0026] A bypass line 44 branches off from the first supply line 34 at a branch point 42 set on the first supply line 34. The bypass line 44 is connected to the discharge line 38 at a connection point (junction) 46 set on the discharge line 38. The connection point 46 is located upstream of the pressure regulating valve 40.

[0027] A branch discharge line 50 branches off from the discharge line 38 at a branch point 48 set in the discharge line 38 upstream of the pressure regulating valve 40. The downstream end of the branch discharge line 50 is, for example, open to the atmospheric space outside the supercritical drying apparatus or connected to a factory exhaust duct.

[0028] At a branch point 52 set in the discharge line 38, two branch discharge lines 54, 56 branch off from the discharge line 38. The downstream ends of the branch discharge lines 54, 56 merge with the discharge line 38 again. The downstream end of the discharge line 38 is connected to, for example, a fluid recovery device (not shown). Useful components (e.g., IPA (isopropyl alcohol)) contained in the CO2 recovered by the fluid recovery device are appropriately separated and reused. As shown in FIG. 1, the downstream end of the branch discharge line 50 may be merged with the discharge line 38.

[0029] A purge gas supply line 62 is connected to a junction 60 set in the first supply line 34 between the branch point 42 and the processing vessel 12. A purge gas can be supplied to the processing vessel 12 via the purge gas supply line 62.

[0030] A discharge line 66 for discharging the treatment fluid branches off from a branch point (second branch point) 64 set on the main supply line 32 immediately upstream of the branch point (first branch point) 33. This discharge line 66 will hereinafter be referred to as a "depressurization line 66" to distinguish it from the discharge line 38.

[0031] An example of the configuration of the second discharge part 22 will be described with reference to FIGS. 2A and 2B. The second discharge part 22 has a pipe-shaped member 221 connected to the second supply line 36. The pipe-shaped member 221 has a discharge area 222 exposed to the internal space (particularly the upper space 12A) of the processing vessel 12. A plurality of discharge ports 223 are formed in the discharge area 222 of the pipe-shaped member 221. The second supply line 36 branches into two and is connected to both ends of the discharge area 222. CO2 supplied from the second supply line 36 flows as shown by the arrows in the figure, and is supplied into the processing vessel 12 from the discharge port 223. The configuration of the second discharge part 22 is not limited to that shown in FIGS. 2A and 2B.

[0032] Next, an example of a supercritical drying method (substrate processing method) using the above-mentioned supercritical drying apparatus will be described with reference to Figures 3A to 3F. The procedure described below is automatically executed under the control of the control unit 100 based on the processing recipe and control program stored in the storage unit 102. In Figures 3A to 3F, the on-off valves filled in gray indicate that they are in a closed state, and the on-off valves that are not filled in gray indicate that they are in an open state.

[0033] [Delivery process] A substrate W such as a semiconductor wafer, with the recesses of the pattern on its surface filled with IPA and with a puddle (liquid film) of IPA formed on its surface, is placed on the plate 18 of a tray 14 waiting at a substrate transfer position by a substrate transport arm (not shown). Note that this substrate W has been subjected to, for example, (1) chemical processing such as wet etching and chemical cleaning, (2) a rinsing process in which the chemical liquid is washed away with a rinsing liquid, and (3) an IPA replacement process in which the rinsing liquid is replaced with IPA to form a puddle (liquid film) of IPA, in a single-wafer cleaning device (not shown) in sequence. When the tray 14 on which the substrate W is placed is moved to the processing position, a sealed processing space is formed in the processing container 12, and the substrate W is located in the processing space.

[0034] [Pressure increase process] Next, the pressure increase step is performed. The pressure increase step is divided into an initial deceleration pressure increase stage and a subsequent normal pressure increase stage, and the normal thickness increase stage is further divided into a first normal thickness increase stage using the first supply line 34 and a second normal thickness increase stage using the second supply line 36.

[0035] In addition, the on-off valves V6, V7, V8, and V11 are normally closed from the start of the pressurization process to the end of the depressurization process, and these on-off valves will not be mentioned. In addition, the on-off valve V8 may be normally closed in the pressurization and circulation processes and open in the depressurization process. The on-off valve V8 may be normally closed from the start of the pressurization process to the end of the depressurization process, or may be opened at an appropriate timing as necessary. When the on-off valve V8 is opened, exhaust can be performed without passing through the pressure regulating valve 40, so that the exhaust or depressurization time can be shortened. In the following description, the on-off valve V8 is assumed to be normally closed.

[0036] <Deceleration boost stage> First, as shown in Fig. 3A, the on-off valves V2, V3, V6, and V7 are closed, and the on-off valves V1, V4, V9, and V10 are opened. In this deceleration boost stage, the opening degree of the pressure regulating valve 40 is fixed to an appropriate fixed opening degree corresponding to an opening degree command value from the control unit 100, for example, 2.5%. In other words, feedback control of the opening degree of the pressure regulating valve 40 (for example, control for maintaining the primary side pressure of the pressure regulating valve 40 constant) is not performed. Until the end of the second normal boost stage described later, the opening degree of the pressure regulating valve 40 is maintained at the above-mentioned fixed opening degree (however, it may be changed).

[0037] A portion (e.g., about 35%) of the CO2 sent in a supercritical state from the supercritical fluid supply device 30 to the main supply line 32 is discharged from a depressurization line 66 provided with an orifice OLF, and the remainder flows into the first supply line 34. A portion (e.g., about 35%) of the CO2 that flows into the first supply line 34 flows into the processing vessel 12 via the first discharge part 21. The remainder of the CO2 that has flowed through the first supply line 34 flows into the discharge lines 38, 50 through the bypass line 44 without heading toward the processing vessel 12, and is blocked by the on-off valves V5 to V8 that are in a closed state.

[0038] At this time, by changing the opening degree of the pressure regulating valve 40, it is possible to adjust the ratio of the flow rate of CO2 flowing into the processing vessel 12 to the flow rate of CO2 flowing through the bypass line 44.

[0039] Immediately after the start of the deceleration pressure increase stage, the pressure of CO2 discharged in a supercritical state from the supercritical fluid supply device 30 gradually decreases, but the decrease is particularly large when the CO2 flows into the processing vessel 12, which has a relatively large volume and is in a normal pressure state. That is, at the beginning of the introduction of CO2 into the processing vessel 12, the pressure of CO2 in the processing vessel 12 is lower than the critical pressure (e.g., about 8 MPa), so that CO2 is in a gaseous state. Since the difference between the pressure in the first supply line 34 and the pressure in the processing vessel 12, which is in a normal pressure state, is very large, CO2 flows into the processing vessel 12 at a high flow rate immediately after the start of the deceleration pressure increase stage. If CO2 (especially CO2 in a gaseous state at a high speed) collides with the substrate W or flows near the substrate W, the puddle of IPA on the periphery of the substrate W may collapse (local evaporation or fluctuation), causing the pattern to collapse.

[0040] In this embodiment, since the orifice (OLF) is provided in the first supply line 34, the flow rate of CO2 flowing from the first discharge unit 21 into the processing vessel 12 is lower than that in the case where there is no orifice. Therefore, it is possible to suppress the pattern collapse due to the above-mentioned mechanism.

[0041] In this embodiment, the CO2 flowing into the processing vessel 12 from the first discharge unit 21 collides with the plate 18 of the tray 14, and then bypasses the plate 18 and enters the upper space 12A in which the substrate W is present (see the arrow in FIG. 3A). Therefore, when the gaseous CO2 reaches the vicinity of the substrate W, the flow rate of the CO2 is relatively low. This makes it possible to suppress pattern collapse due to the above-mentioned mechanism.

[0042] Even if CO2 collides with the plate 18 and then bypasses the plate 18 to enter the upper space 12A, if the flow rate of CO2 flowing into the processing vessel 12 is high, the flow rate of CO2 may be high enough to cause pattern collapse when it reaches the vicinity of the periphery of the substrate W. However, in this embodiment, in the deceleration and pressure increase stage, i.e., in the early stage of introduction of CO2 into the processing vessel 12, a part of CO2 flowing through the main supply line 32 is released to the depressurization line 66, and further, a part of CO2 flowing through the first supply line 34 is released to the bypass line 44. Therefore, the flow rate of CO2 flowing from the first discharge part 21 into the processing vessel 12 is further reduced, and pattern collapse due to the above mechanism can be more reliably prevented.

[0043] Pattern collapse due to the above mechanism can occur only in the initial stage of introduction of CO2 into the processing vessel 12. This is because as the pressure inside the processing vessel 12 increases, the flow rate of CO2 flowing into the processing vessel 12 via the first discharge unit 21 decreases. Therefore, it is sufficient to perform the deceleration pressure increase stage for a relatively short period of time, for example, about 10 to 20 seconds. As an example, the deceleration pressure increase stage is performed for about 20 seconds, and the internal pressure of the processing vessel 12 increases from normal pressure to 4 MPa.

[0044] Another advantage of providing the deceleration pressure increase stage is that it is not necessary to extremely reduce the diameter of the orifice (OLF) of the first supply line 34. This makes it possible to shorten the pressure increase time when supplying CO2 from the first supply line 34 to the processing vessel 12.

[0045] <First normal boost stage (first boost stage)> 3B, the on-off valve V10 is closed to stop discharging CO2 from the main supply line 32 via the depressurization line 66. The transition from the deceleration pressurization stage to the first normal pressurization stage may be performed after a predetermined time (e.g., the above-mentioned 20 seconds) has elapsed since the start of the deceleration pressurization stage, or when the pressure inside the treatment vessel 12 reaches a predetermined pressure (e.g., the above-mentioned 4 MPa). The pressure inside the treatment vessel 12 can be detected, for example, by a pressure sensor PS (hereinafter also referred to as "pressure sensor PS12") provided in the discharge line 38 near the fluid discharge portion 24 of the treatment vessel 12.

[0046] In the first normal pressurization stage, the pressure in the treatment vessel 12 increases at a higher pressurization rate than in the decelerated pressurization stage, since no CO2 is discharged through the depressurization line 66. At the same time, the pressure in the lines 44, 38, 50, 54, and 56, the downstream ends of which are blocked by the on-off valves V5 to V8, also increases.

[0047] When the pressure inside the processing vessel 12 exceeds the critical pressure of CO2 (approximately 8 MPa), the CO2 (CO2 not mixed with IPA) present inside the processing vessel 12 becomes a supercritical state. When the CO2 inside the processing vessel 12 becomes a supercritical state, the IPA on the substrate W starts to dissolve into the CO2 in the supercritical state.

[0048] <Depressurization stage> When the detection value of the pressure sensor PS12 (i.e., the pressure inside the processing vessel 12) reaches a predetermined switching pressure of 13 MPa, the on-off valve V9 is closed and the on-off valve V10 is opened, as shown in Fig. 3C. This state is continued for a short time, for example, 0.5 seconds. This reduces the pressure inside the second supply line 36 upstream of the on-off valve V2 in the closed state and the main supply line 32 immediately upstream of the branch point 33 to about 15 MPa.

[0049] Immediately before the transition from the first normal pressure increase stage to the second normal pressure increase stage, the internal pressure of the second supply line 36 upstream of the on-off valve V2 in the closed state and the main supply line 32 immediately upstream of the branch point 33 is, for example, about 17 MPa, and the pressure inside the processing vessel 12 is, for example, 13 MPa as described above. In contrast, the withstand differential pressure of the filter F (also called "filter F2") provided in the second supply line 36 is, for example, 3 MPa. If the on-off valve V2 is suddenly opened from this state, a differential pressure of 4 MPa is applied to both sides of the filter F2, which may damage the filter F2 (filter element). In contrast, by performing the above-mentioned depressurization stage, it is possible to prevent the filter F2 from being damaged when the on-off valve V2 is opened. Note that the primary side pressure of the on-off valve V2 must not be lower than the secondary side pressure by depressurization. If this happens, CO2 (which contains IPA containing particle-causing substances) will flow from the inside of the processing vessel 12 into the second discharge part 22 when the on-off valve V2 is opened.

[0050] The reason why it is desirable to prevent CO2 containing IPA from flowing into the second discharge part 22 from the processing vessel 12 is described in detail in the description of the effects of the embodiment at the end of the specification.

[0051] When performing this depressurization step, the on-off valve V1 is kept open, and the supply of CO2 to the processing vessel 12 is not stopped. If the supply of CO2 (which is at a relatively high temperature) to the processing vessel 12 is stopped, the pressure inside the processing vessel 12 may temporarily decrease as the CO2 in the processing vessel 12 loses heat to the tray 14. This is because the tray 14 is exposed to the atmospheric air at room temperature when the substrate W is loaded and unloaded, and therefore has the lowest temperature among the members facing the space inside the processing vessel 12 (the processing vessel inner wall, the nozzle, etc.).

[0052] A similar problem may occur with the filter F (also referred to as "filter F1") provided in the first supply line 34 at the start of the deceleration boost stage. However, for the following reasons, there is no risk of a differential pressure exceeding the differential pressure resistance of the filter F1 being applied to the filter F1. (Reason 1) Just before the start of the deceleration boost stage, the on-off valve V9 is in a closed state, and the main supply line 32 has an orifice OLF. Therefore, just after the on-off valve V9 is opened, the internal pressure of the main supply line 32 downstream of the orifice OLF does not increase suddenly. (Reason 2) The deceleration boost stage is performed with the on-off valve V10 open, and an orifice OLF is provided in the first supply line 34 upstream of the filter F1, so that the primary side pressure of the filter F1 does not increase suddenly.

[0053] <Second normal boost stage (second boost stage)> Immediately after the depressurization step is completed, as shown in Fig. 3D, the on-off valves V1, V4, and V10 are closed, and the on-off valves V2, V3, and V5 are opened. Then, the CO2 that has flowed through the main supply line 32 flows into the processing vessel 12 through the second supply line 36 and the second outlet 22. CO2 no longer flows into the processing vessel 12 through the first supply line 36 and the first outlet 21. By discharging CO2 from the second outlet 22 early in this manner, the amount of CO2 (which contains IPA containing particle-causing substances) that flows from the processing vessel 12 into the second outlet 22 can be at least significantly reduced (described in detail later).

[0054] In the second normal pressure increase stage, since the on-off valves V3 and V5 are open, a part of the CO2 that has flowed into the processing vessel 12 is discharged from the exhaust line 38. The CO2 discharged from the exhaust line 38 contains the IPA that was on the surface of the substrate W. At this time, since the opening degree of the pressure adjustment valve 40 is small, for example, about 2.5%, the flow rate of CO2 discharged from the processing vessel 12 through the exhaust line 38 is relatively small. Therefore, the pressure in the processing vessel 12 continues to rise. In this way, by increasing the pressure while discharging CO2 from the processing vessel 12, it is possible to prevent particles and particle-causing substances present in the processing vessel 12 from remaining in the processing vessel 12 and contaminating the substrate W.

[0055] Just before the start of the second normal pressure increase stage, the pressure in the lines 44, 38, 50, 54, and 56 is approximately equal to the pressure in the processing vessel 12 (because the on-off valves V5 to V8 are closed), so the pressure in the processing vessel 12 does not drop suddenly just after the on-off valves V3 and V5 are switched to the open state. If the pressure in the processing vessel 12 drops suddenly, the pattern may collapse or particles may increase due to a phase change of CO2. In other words, releasing CO2 to the bypass line has two effects: it not only reduces the inflow rate into the processing vessel 12 during the deceleration pressure increase stage, but also prevents the pressure in the processing vessel 12 from dropping suddenly at the start of the second normal pressure increase stage.

[0056] The second normal pressure increase stage is continued until the pressure in the processing vessel 12 reaches a pressure (supercritical state guarantee pressure) that guarantees that the mixed fluid (CO2+IPA) is maintained in a supercritical state, regardless of the IPA concentration in the mixed fluid (CO2+IPA) on the substrate W and the temperature of the mixed fluid. The supercritical state guarantee pressure is approximately 16 MPa. When the pressure in the processing vessel 12 reaches the above-mentioned supercritical state guarantee pressure, pattern collapse due to a local phase change (e.g., vaporization) of the mixed fluid on the surface of the substrate W will no longer occur. Note that such a local phase change occurs due to non-uniformity in the IPA concentration in the mixed fluid on the surface of the substrate W, and may occur particularly in an area exhibiting an IPA concentration that increases the critical temperature.

[0057] <Distribution process> When the pressure sensor PS12 detects that the pressure inside the processing vessel 12 has reached the supercritical state guaranteed pressure (16 MPa), the operation mode of the pressure regulating valve 40 is switched to a feedback control mode. That is, the control unit 100 (or its subordinate controller) executes feedback control to adjust the aperture (operation amount MV) of the pressure regulating valve 40 based on the deviation between the pressure inside the processing vessel 12 detected by the pressure sensor PS12 (measurement value PV) and the set value SV so that the pressure inside the processing vessel 12 is maintained at the set value (set value SV=16 MPa). At this time, the aperture of the pressure regulating valve 40 fluctuates within a range of, for example, 30 to 50%.

[0058] In addition, when performing the feedback control of the pressure regulating valve 40, a command may be sent from the control unit 100 to the pressure regulating valve 40 so that the initial opening, which is the opening at the start of the feedback control of the pressure regulating valve 40, is set to, for example, the average opening of the pressure regulating valve 40 in the distribution stage executed in the past. By doing so, it is possible to suppress fluctuations in the pressure inside the processing vessel 12 at the start of the feedback control, and the control becomes stable.

[0059] The open / close state of each on-off valve in the circulation stage is the same as that in the second normal pressure increase stage shown in FIG. 3D, and only the control mode and opening degree of the pressure regulating valve 40 are different.

[0060] In the circulation process, supercritical CO2 supplied from the second discharge unit 22 into the processing vessel 12 flows in the region above the substrate, and is then discharged from the fluid discharge unit 24. At this time, a laminar flow of supercritical CO2 flowing approximately parallel to the surface of the substrate W is formed in the processing vessel 12. IPA in the mixed fluid (IPA+CO2) on the surface of the substrate W exposed to the laminar flow of supercritical CO2 is gradually replaced with supercritical CO2. Eventually, almost all of the IPA on the surface of the substrate W is replaced with supercritical CO2.

[0061] The mixed fluid consisting of IPA and supercritical CO2 discharged from the fluid discharge part 24 flows through the discharge line 38 (and the branch discharge lines 54, 56) and is then recovered. The IPA contained in the mixed fluid can be separated and reused. In the circulation process, the on-off valves V6, V7 may be opened or closed depending on the desired flow rate, etc.

[0062] [Discharge process] When the replacement of IPA with supercritical CO2 is completed, as shown in FIG. 3E, the on-off valve V2 is closed to stop the supply of CO2 to the processing vessel 12, and the set pressure of the processing vessel 12 is lowered to normal pressure (time t4 in FIG. 3). This causes the pressure regulating valve 40 to open significantly (for example, fully open), and the pressure in the processing vessel 12 drops to normal pressure. As a result, the supercritical CO2 in the pattern of the substrate W becomes gas and leaves the pattern, and the gaseous CO2 is discharged from the processing vessel 12. Finally, as shown in FIG. 3F, the on-off valve V4 of the bypass line 44 is opened to remove the CO2 remaining between the on-off valve V1 and the on-off valve V4. This completes the drying of the substrate W.

[0063] [Export process] The plate 18 of the tray 14 on which the dried substrate W is placed moves to the substrate transfer position out of the processing vessel 12. The substrate W is taken out of the plate 18 by a substrate transport arm (not shown) and is accommodated in, for example, a substrate processing vessel (not shown).

[0064] According to the above embodiment, the following advantageous effects are achieved.

[0065] As a comparative example, the following is assumed. In the entire pressure increasing process in which the pressure in the processing vessel 12 is increased from normal pressure to the supercritical state guarantee pressure (16 MPa), CO2 is supplied to the processing vessel 12 from the first discharge part 21, and when the pressure in the processing vessel 12 reaches the supercritical state guarantee pressure, the supply route of CO2 to the processing vessel 12 is switched from the first supply line 34 (first discharge part 21) to the second supply line 36 (second discharge part 22) to execute the circulation process. (Note that, in the following description, for the sake of simplicity, the above switching is also simply referred to as "switching of the supply route.") In this way, the following phenomenon may occur. That is, most of the IPA puddle on the substrate W is diffused in the CO2 while the pressure in the processing vessel 12 is increasing from 7 MPa to 14 MPa. The diffused IPA contains particle-causing substances (particle-causing substances originally dissolved in the IPA, or particle-causing substances derived from deposits peeled off from the inner wall of the processing vessel 12 or the surface of the tray 14). Thereafter, while the pressure inside the processing vessel 12 is increasing to 16 MPa, the CO2 containing IPA is forced into the second discharge part 22 (e.g., pipe-shaped member 221) and further into the upstream piping (downstream of filter F2). The IPA forced into the second discharge part 22 and its depth is sprayed from the second discharge part 22 when CO2 is supplied from the second discharge part 22 into the processing vessel 12, contaminating the substrate W. In this case, it has been confirmed that particle contamination occurs intensively in a portion of the substrate W close to the second discharge part 22.

[0066] In contrast, according to the above embodiment, before the pressure inside the processing vessel 12 reaches the supercritical state guarantee pressure (at the time when the pressure reaches 13 MPa in the above embodiment), the supply route of CO2 to the processing vessel 12 is switched from the first discharge part 21 to the second discharge part 22. This significantly prevents CO2 containing IPA from being forced into the second discharge part 22.

[0067] In addition, when the pressure inside the processing vessel 12 exceeds the critical pressure of CO2 (about 8 MPa), IPA starts to diffuse into the processing vessel 12, so it is considered preferable to switch the supply route at this point. However, it has been confirmed through experiments that problems occur even if the timing of switching the supply route is too early. Specifically, according to the inventor's experiments, when the supply route was switched when the pressure inside the processing vessel 12 was 8 MPa and 11 MPa, a large amount of particles that could not be quantified adhered to the substrate. The inventor considers the cause of this as follows. When the IPA paddle remains on the substrate surface and CO2 is discharged from the second discharge part 22 to flow along the substrate surface, the IPA paddle is peeled off by the flow of CO2, and peeling electrification occurs at this time. It is considered that the particles floating inside the processing vessel 12 or the particles contained in the CO2 discharged from the second discharge part 22 are adsorbed to the substrate. In addition, since the problem of peeling static electricity is also considered to be related to the discharge conditions (discharge direction, discharge flow rate, etc.) of CO2 from the second discharge part 22, it is considered that there are cases where the switching pressure for switching the supply route does not need to be as high as 13 MPa as in the above embodiment depending on the discharge conditions. Also, if the above-mentioned peeling static electricity problem can be solved by dissipating the charge by some means, it is also possible to set the switching pressure to the critical pressure of CO2 (about 8 MPa). In addition, even in the configuration of Figure 4 described later, since CO2 discharged from the second discharge part 22M flows along the substrate surface after colliding with the substrate surface, peeling static electricity may occur depending on the discharge conditions.

[0068] From the viewpoint of preventing peeling static electricity, the inventor believes that it is most preferable to switch the supply route immediately after the IPA paddle has completely disappeared from the substrate surface. In actually performing supercritical drying on a substrate (semiconductor wafer) with a 12 mL IPA paddle formed on its surface, the supply route was switched when the pressure in the processing vessel 12 reached 12 MPa, 13 MPa, and 14 MPa. In this case, the number of particles with a size of 20 nm or more was 224 at 12 MPa, 144 at 13 MPa, and 189 at 14 MPa, and the number of particles was the smallest when the supply route was switched at 13 MPa. In addition, in another test, when observation was performed using a supercritical monitor (a device that visualizes the situation in the processing vessel 12), the result was also obtained that the IPA paddle disappeared when the pressure in the processing vessel 12 reached 13.4 MPa, which is generally consistent with the inference that it is preferable to switch the supply route immediately after the IPA paddle has completely disappeared from the substrate surface. However, since the above experimental results may vary slightly depending on the specific configuration of the apparatus and the amount of IPA puddle, etc., it should not be assumed that the supply route should be switched exactly when the pressure inside the processing vessel 12 reaches 13 MPa.

[0069] To summarize what has been described so far, it can be said that it is preferable to switch the supply route when the pressure inside the processing vessel 12 is equal to or higher than the critical pressure of CO2 and lower than the supercritical state guarantee pressure (16 MPa) (preferably a pressure close to the pressure at which IPA disappears on the substrate).

[0070] It may be thought that a similar phenomenon (intrusion of CO2 containing particles) occurs in the first discharge part 21 (which may adversely affect the processing of the next substrate). However, as can be understood by comparing and referring to Figures 3C and 3D, the on-off valves V1 and V4 are closed in a state where the internal pressure of the first discharge part 21 and the first supply line 34 and bypass line 44 connected thereto is increased, so that no or almost no IPA intrudes into the first discharge part 21.

[0071] The embodiments disclosed herein should be considered as illustrative and not restrictive in all respects. The above-described embodiments may be omitted, substituted, or modified in various forms without departing from the scope and spirit of the appended claims.

[0072] For example, the configuration of the processing unit 10 is not limited to that shown in FIG. 1, and may be that (10M) as shown in FIG. 4. In FIG. 1 and FIG. 4, the members with the same reference numerals have substantially the same functions. In the modified embodiment of FIG. 5, the substrate W is supported by a substrate support member 14M attached to the ceiling of the processing vessel 12M. A liquid film of, for example, IPA is formed on the upper surface of the substrate W. The main supply line 32M connected to the supercritical fluid supply device 30 branches into a first supply line 34M and a second supply line 36M. The processing fluid (CO2) discharged from the first discharge part 21 connected to the first supply line 34M collides with the shielding plate 70 and then flows toward the substrate W, bypassing the shielding plate 70. The second discharge part 22M connected to the second supply line 36M discharges the processing fluid toward the upper surface of the substrate W. The CO2 in the processing vessel 12M can be discharged from the fluid discharge part 24M to the discharge line 38M. Components not shown in detail in Fig. 4 (various valves, filters, various sensors, etc.) can be arranged in the same manner as in Fig. 1. The processing unit 10M shown in Fig. 4 can be used to perform procedures similar to those in the above-described embodiments. [Explanation of symbols]

[0073] W substrate 12 Processing vessel 14 Substrate holder (tray) 21 1st discharge part 22 2nd discharge part 32 Main Supply Line 34 First branch supply line 36 Second branch supply line

Claims

1. a processing vessel for accommodating a substrate; a substrate holder that holds the substrate horizontally in the processing vessel with the surface of the substrate on which the liquid film is formed facing upward; a main supply line connected to a processing fluid supply unit for supplying a processing fluid in a supercritical state; a first branch supply line and a second branch supply line branching off from the main supply line at a first branch point set on the main supply line; a depressurization line branching off from the main supply line at a second branch point set on the main supply line at a position upstream of the first branch point; a first discharge unit connected to the first branch supply line and configured to discharge the processing fluid sent from the first branch supply line into the processing vessel; a second discharge unit connected to the second branch supply line and configured to discharge the processing fluid sent from the second branch supply line into the processing vessel; an on-off valve provided in the second branch supply line; a filter provided between the on-off valve and the second discharge portion; A substrate processing method performed using a substrate processing apparatus comprising: The substrate processing method includes: a pressure increasing step of increasing a pressure in the processing vessel to a predetermined processing pressure by supplying a processing fluid into the processing vessel while the substrate on which the liquid film is formed is held by the substrate holding part and accommodated in the processing vessel, The pressurization process includes a first pressurization stage in which a pressure in the processing vessel is increased to a predetermined switching pressure by supplying a processing fluid from the first discharge part into the processing vessel, a second pressurization stage in which, after the first pressurization stage, a pressure in the processing vessel is increased from the switching pressure to the processing pressure by supplying a processing fluid from the second discharge part into the processing vessel, and a depressurization stage performed between the first pressurization stage and the second pressurization stage, The on-off valve is closed during the first pressurization stage and the depressurization stage, and the on-off valve is opened during the second pressurization stage; The substrate processing method, wherein the depressurization step is performed by discharging the processing fluid from the second branch supply line upstream of the on-off valve and the main supply line via the depressurization line.

2. The substrate processing method according to claim 1 , wherein the depressurization line is provided with an orifice.

3. 2. The substrate processing method of claim 1, wherein the first discharge unit is configured to supply a processing fluid toward a space below the substrate held by the substrate holding unit in the processing vessel, and the second discharge unit is configured to supply a processing fluid toward a space above a surface of the substrate held by the substrate holding unit in the processing vessel.

4. The substrate processing apparatus further includes a discharge unit configured to discharge a processing fluid from the processing vessel, and a discharge line connected to the discharge unit.

2. The substrate processing method according to claim 1, further comprising a circulation process, after the pressurization process, of supplying a processing fluid from the second discharge part into the processing vessel and discharging the processing fluid from the discharge part in the processing vessel while maintaining the pressure in the processing vessel at the processing pressure.

5. A valve having an opening adjustment function is provided in the discharge line, 5. The substrate processing method of claim 4, wherein the second pressurization stage of the pressurization process is performed while discharging processing fluid from the processing vessel to the exhaust line, and at this time, the opening of the valve having the opening adjustment function is adjusted so that the inflow amount of processing fluid from the second branch supply line to the processing vessel is greater than the discharge amount of processing fluid from the processing vessel to the exhaust line.

6. 6. The substrate processing method according to claim 5, wherein an opening degree of the valve having an opening degree adjustment function in the circulation step is larger than an opening degree of the valve having an opening degree adjustment function in the second pressure increase stage of the pressure increase step.

7. 7. The substrate processing method according to claim 1, wherein the processing pressure is equal to or higher than a supercritical state assurance pressure at which a mixed fluid of the liquid forming the liquid film and the processing fluid is guaranteed to be maintained in a supercritical state regardless of a temperature of the mixed fluid and a mixing ratio of the liquid forming the liquid film and the processing fluid.

8. 8. The substrate processing method according to claim 7, wherein the processing fluid is carbon dioxide, the liquid is IPA, and the supercritical state guarantee pressure is 16 MPa.

9. The substrate processing method according to claim 8 , wherein the switching pressure is 11 MPa or more.

10. a first opening / closing valve is provided in the first branch supply line; The on-off valve provided in the second branch supply line is called a second on-off valve, A third on-off valve is provided in the depressurization line, a fourth on-off valve is provided in the main supply line upstream of the second branch point; In the first pressure increase stage, the first on-off valve and the fourth on-off valve are opened, and the second on-off valve and the third on-off valve are opened, In the second pressure increase stage, the second on-off valve and the fourth on-off valve are opened, and the first on-off valve and the third on-off valve are opened, 7. The substrate processing method according to claim 1, wherein, in the depressurization step, the third on-off valve is open, and the first on-off valve, the second on-off valve and the fourth on-off valve are open.

11. 11. The substrate processing method according to claim 1, wherein during the first pressure increase stage, no processing fluid is supplied from the second discharge part into the processing vessel, and during the second pressure increase stage, no processing fluid is supplied from the first discharge part into the processing vessel.

12. The substrate processing method according to claim 1 , wherein the second discharge portion is formed of a tubular body having a plurality of holes formed therein.

13. A substrate processing apparatus, comprising: a processing vessel for accommodating a substrate; a substrate holder that holds the substrate horizontally in the processing vessel with the surface of the substrate on which the liquid film is formed facing upward; a main supply line connected to a processing fluid supply unit for supplying a processing fluid in a supercritical state; a first branch supply line and a second branch supply line branching off from the main supply line at a first branch point set on the main supply line; a depressurization line branching off from the main supply line at a second branch point set on the main supply line at a position upstream of the first branch point; a first discharge unit connected to the first branch supply line and configured to discharge the processing fluid sent from the first branch supply line into the processing vessel; a second discharge unit connected to the second branch supply line and configured to discharge the processing fluid sent from the second branch supply line into the processing vessel; A control unit for controlling an operation of the substrate processing apparatus; At least The substrate processing apparatus, wherein the control unit is configured to cause the substrate processing apparatus to perform the substrate processing method according to claim 1 .

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