Cooling system

Abstract

[Problem] To provide a cooling system capable of efficiently cooling an electrostatic chuck while saving power and space when processing a semiconductor wafer. [Solution] One end of a gas pipe 15A is attached to a base 11A1, and a chiller 13A is attached to the other end of the gas pipe 15A. Refrigerant gas is supplied from the chiller 13A and passes through a gas passage inside the base 11A1, thereby cooling the base 11A1. As the base 11A1 is cooled, an electrostatic chuck 3 is cooled so that a wafer can be cooled. One end of a gas branch pipe 17A is attached to a base 11A2, and the other end of the gas branch pipe 17A is connected to a chiller 23 serving as a common chiller, via a gas merging pipe 21. A valve 19A is disposed along the gas branch pipe 17A. By lowering the temperature of the electrostatic chuck 3, the temperature of the wafer can be lowered while power consumption is suppressed.

Description

Cooling system

[0001] The present invention relates to a cooling system, and more particularly to a cooling system that can efficiently cool an electrostatic chuck in a power-saving, space-saving manner when processing a semiconductor wafer.

[0002] The recent advancement of an information-driven society has led to demands for increased memory stacking and higher processing accuracy. Against this backdrop, plasma etching is widely used to process semiconductor wafers, such as silicon wafers. Even when plasma etching deeply etched into the wafer surface, the etching rate can be increased by cooling the heated wafer. Recently, cryoetching, a technology for etching insulating films at extremely low temperatures, has been attracting attention. Cryoetching is said to be a groundbreaking technology that dramatically increases etching speed and significantly reduces global warming potential. To achieve this, plasma processing is performed by placing the wafer in close contact with the holding surface of a chuck table equipped with a cooling structure.

[0003] An example of a cooling structure for a cryoetcher will be described with reference to Fig. 6. In Fig. 6, an electrostatic chuck 3 is disposed in a chamber 1, and a wafer (not shown) is placed on the electrostatic chuck 3. The wafer is attracted to the electrostatic chuck 3 by electrical force. The chamber 1 is evacuated by a vacuum pump 5 and a process gas 7 is introduced based on a semiconductor processing schedule. Radio frequency (RF) power 9 is applied to generate plasma in the chamber 1.

[0004] As the wafer temperature increases during plasma processing, the etching rate decreases. Therefore, a base 11 having a gas passage formed therein for passing a refrigerant gas is disposed on the underside of the electrostatic chuck 3, and the refrigerant gas is supplied to the base 11 from a chiller 13 (see, for example, Patent Document 1). The chiller 13 itself is cooled, for example, by water cooling. Furthermore, in order to increase the etching rate, the power consumption of the radio frequency (RF) power 9 also tends to increase. This increase in power also further increases the amount of heat generated, necessitating further heat dissipation and control by the chiller 13. Under these circumstances, the cooling capacity required of chillers is gradually increasing, and larger chillers tend to be in demand.

[0005] Japanese Patent Application Laid-Open No. 2022-36899

[0006] However, while larger chillers are configured for high efficiency when operating near their rated output, the lower the refrigerant gas output, the more rapidly their operating efficiency drops when operated below the rated output. This can result in power losses and a corresponding decrease in utility, such as the need for more cooling water to cool the chiller. Furthermore, larger chillers require a larger capacity of cooling water, which can increase the space required for their installation.

[0007] The present invention has been made in view of the above-mentioned conventional problems, and has an object to provide a cooling system that can efficiently cool an electrostatic chuck in a power-saving, space-saving manner when processing a semiconductor wafer.

[0008] For this reason, the present invention (claim 1) is a cooling system invention comprising electrostatic chucks respectively disposed in a plurality of chambers, dedicated chillers respectively disposed corresponding to the plurality of chambers for cooling the electrostatic chucks, a dual-purpose chiller for cooling the electrostatic chucks in the plurality of chambers, and a control device for controlling the operation of the plurality of chambers, wherein the dedicated chiller and the dual-purpose chiller are operated together based on a control command from the control device, thereby making it possible to cover the maximum output required for cooling the electrostatic chucks.

[0009] If one large chiller is used to cover the maximum output required to cool an electrostatic chuck, there is a risk that cooling efficiency will decrease in areas with low output. However, by operating a dedicated chiller and a dual-purpose chiller together, efficient operation is possible even in areas with low output. If a low cooling power is required from the chamber side, the dedicated chiller can be used while the dual-purpose chiller can be stopped, thereby saving power. One dual-purpose chiller can cool multiple electrostatic chucks. This allows for a space-saving configuration.

[0010] Furthermore, the present invention (claim 2) is an invention of a cooling system, characterized in that, based on a control command for cooling sent from the control device, the dedicated chiller is operated prior to the dual-purpose chiller depending on the amount of output required for cooling contained in the control command, or the dual-purpose chiller is used to make up for any shortfall in output from the dedicated chiller.

[0011] When the cooling output is low, it can be operated only with the dedicated chiller. In this case, a dual-purpose chiller that does not require cooling does not require water cooling of the chiller itself, making it more efficient and saving power consumption. Also, because it is a small chiller, output adjustments can be made efficiently when the cooling output is low. Furthermore, by using the dual-purpose chiller to make up for any shortfall in the output of the dedicated chiller, overall power consumption can be reduced.

[0012] Furthermore, the present invention (claim 3) is a cooling system invention, characterized in that cooling by the dedicated chiller and the dual-purpose chiller is performed via a refrigerant, respectively, the control command of the control device includes a scheduled time for increasing or decreasing the cooling output, and cooling by at least one of the dedicated chiller and the dual-purpose chiller is performed by increasing or decreasing the cooling output prior to the scheduled time by the delay time, taking into account a delay time until the refrigerant reaches the electrostatic chuck.

[0013] Taking into account the delay time until the coolant reaches the electrostatic chuck, the cooling output is increased or decreased by the delay time ahead of the scheduled time, thereby enabling cooling at an appropriate timing without delay for the electrostatic chuck, thereby improving the etching efficiency when etching a wafer in the chamber.

[0014] Furthermore, the present invention (claim 4) is a cooling system invention comprising a first pipe arranged between the dedicated chiller and the plurality of chambers, and branch pipes having one end connected to the dual-purpose chiller and the other end connected to each of the plurality of chambers, and wherein valves are arranged in the branch pipes corresponding to the plurality of chambers.

[0015] When the valve is closed, cooling of the electrostatic chuck in the closed chamber is not required, which reduces the load on the dual-purpose chiller and reduces the loss of water cooling and power for the chiller, improving utility.

[0016] Furthermore, the present invention (claim 5) is an invention of a cooling system, characterized in that it includes an airtight housing that houses the dedicated chiller and the dual-purpose chiller, the refrigerant is a gas, and the housing is equipped with a gas leak detector that detects leakage of the gas.

[0017] Compared to housing a large chiller, housing a small dedicated chiller and a dual-purpose chiller can save space. If the refrigerant is gas, there is a risk of fire or explosion if it leaks, depending on the composition. However, by housing the dedicated chiller and dual-purpose chiller in an airtight housing and equipping them with a gas leak detector, gas leaks can be detected accurately, allowing for quick response, such as preventing combustion in advance. In addition, since only one gas leak detector needs to be installed per housing, it is energy-efficient and inexpensive.

[0018] Furthermore, the present invention (claim 6) is a cooling system invention, which is configured to include at least one set of a first base connected to the dedicated chiller and a second base connected to the dual-purpose chiller, below the electrostatic chuck.

[0019] At least one second base unit connected to a dual-purpose chiller is provided. If the output required for cooling increases, this can be easily accommodated by providing multiple combinations of dual-purpose chillers and second base units.

[0020] As described above, according to the present invention (claim 1), the dedicated chiller and the dual-purpose chiller are operated together based on a control command from the control device, thereby enabling the maximum output required for cooling the electrostatic chuck to be covered, thereby enabling efficient operation even in areas where the cooling output is low. When a low cooling power is required from the chamber side, the dedicated chiller can be used while the dual-purpose chiller is stopped, thereby saving power. One dual-purpose chiller can cool multiple electrostatic chucks. This allows for a space-saving configuration.

[0021] Configuration diagram of a cooling system according to an embodiment of the present invention. Communication control system diagram of the cooling system. Diagram explaining the control method of the cooling system according to this embodiment. Diagram explaining the occurrence of delay time in the arrival of refrigerant gas due to the length of the gas piping. Example of a configuration in which multiple chillers are grouped together in a panel. Example of a cooling structure for Cryo Etch.

[0022] An embodiment of the present invention will now be described. A configuration diagram of this cooling system 10 is shown in Fig. 1. In Fig. 1, n chambers 1 are arranged, namely, chamber 1A, chamber 1B, ..., chamber 1N. An electrostatic chuck 3 (not shown) is arranged in each chamber 1, and a wafer is placed on this electrostatic chuck 3.

[0023] A base 11A1 having a gas passage formed therein is fixed to the lower surface of the electrostatic chuck 3 in the chamber 1A, and a base 11A2 having a similar gas passage formed therein is further fixed to the lower surface of the base 11A1. That is, the base 11 is configured by stacking the bases 11A1 and 11A2 in two stages. However, the bases 11A1 and 11A2 may be combined into one base 11, and two gas passages may be formed inside the base 11.

[0024] One end of a gas pipe 15A is attached to the base 11A1, and the other end of the gas pipe 15A is attached to a chiller 13A. A refrigerant gas is supplied from the chiller 13A and passes through a gas passage inside the base 11A1, thereby cooling the base 11A1. Cooling the base 11A1 cools the electrostatic chuck 3, thereby cooling the wafer.

[0025] Similarly, a base 11B1 is fixed to the underside of the electrostatic chuck 3 in chamber 1B, and a base 11B2 is fixed to the underside of the base 11B1. One end of a gas pipe 15B is attached to the base 11B1, and a chiller 13B is attached to the other end of the gas pipe 15B. Refrigerant gas is supplied from the chiller 13B and passes through a gas passage inside the base 11B1 to cool the base 11B1. Similarly, a base 11N1, a gas pipe 15N, and a chiller 13N are attached to chamber 1N. Chillers 13A to 13N correspond to dedicated chillers, and gas pipes 15A to 15N correspond to first pipes.

[0026] Meanwhile, one end of a gas branch pipe 17A is attached to the base 11A2, and the other end of the gas branch pipe 17A is connected to a chiller 23, which corresponds to a dual-purpose chiller, via a gas junction pipe 21. A valve 19A is disposed midway along the gas branch pipe 17A. Similarly, one end of a gas branch pipe 17B is attached to the base 11B2, and the other end of the gas branch pipe 17B is attached to the chiller 23 via a gas junction pipe 21. A valve 19B is disposed midway along the gas branch pipe 17B. Similarly, a base 11N2, a gas pipe 17N, and a valve 19N are attached to the chamber 1N, and the chamber 1N is connected to the chiller 23 via a gas junction pipe 21.

[0027] Next, the control of the cooling system according to this embodiment will be described with reference to FIG. 2 . FIG. 2 shows a communication control system diagram of the cooling system. In FIG. 2 , signals can be transmitted between the chamber 1, the vacuum pump 5, the chiller 13, the chiller 23, and the radio frequency (RF) power source 9. The signals are transmitted, for example, via EtherCAT (registered trademark). These signals include the temperature near the electrostatic chuck 3 and the magnitude of the radio frequency (RF) power source 9 required for plasma processing. The chiller control device 30 controls the chillers 13A to 13N, the chiller 23, and the valves 19A to 19N during plasma processing based on the temperature near the electrostatic chuck 3 and the magnitude of the radio frequency (RF) power source 9.

[0028] Next, a control method for the cooling system according to this embodiment will be described with reference to Figures 3 and 4. Figure 3A shows a time chart illustrating an example of changes in the magnitude of power required for the radio frequency (RF) power 9 in an etching processing schedule. A first level of power is required from the chamber 1 at time t1, a second level of power is required at time t3, and the power request is released at time t5. Heat is generated near the electrostatic chuck 3 in accordance with this level of power.

[0029] Figure 3(B) shows a time chart of chiller power for the required power, assuming that cooling is performed by a single large chiller. The characteristics of Figure 3(B) basically change the chiller's cooling capacity in accordance with changes in the amount of power required in Figure 3(A). Assume that the maximum power required by the chiller is 10 kW.

[0030] 4, if the gas pipe 15 between the chamber 1 and the chiller 13 is long, it takes time for the cooling gas supplied from the chiller 13 to reach the chamber 1. For example, when the length of the gas pipe 15 is 10 m, the delay time may be about 20 seconds. Under such circumstances, if the cooling gas is supplied after the temperature of the wafer surface has risen, the wafer temperature may rise even further.

[0031] On the other hand, the scheduled time for application of the radio frequency (RF) power 9 is known in the schedule for chamber 1. Therefore, in the characteristics shown in FIG. 3B, control is performed by advancing the delay time (t = 20 seconds). That is, the chiller control device 30 sends a control command to start cooling at time t0, which is earlier than the cooling start command time t1 by the delay time t. Similarly, control commands are sent for times t3 and t5 at times t2 and t4, which are earlier by the delay time t. This enables precise control so that the wafer surface temperature is appropriate when the power supply from the radio frequency (RF) power 9 increases. Note that in FIG. 3B, the chiller supplies standby operation output before time t0 and after time t4. On the other hand, if the gas piping 15 between chamber 1 and chiller 13 is short, the delay time t is approximately 0 seconds, and sufficient cooling accuracy can be achieved without advancing the control by the delay time.

[0032] Figure 3(C) shows, in a time chart, a method for covering the amount of power required for radio frequency (RF) power 9 by operating both the dedicated chiller 13 and the dual-purpose chiller 23. The upper diagram in Figure 3(C) shows the change in cooling capacity when operating a chiller 13 with a maximum cooling capacity of 6 kW. If the chillers 13 continue to operate according to the etching processing schedule, only one chiller 13 needs to be operated until time t2. This allows for efficient, energy-saving operation.

[0033] If only the chiller 13 is operated between time t2 and time t4, a cooling output exceeding 6 kW cannot be supplied. At this time, the chiller control device 30 issues a control command to open the valve 19 and operate the chiller 23 between time t2 and time t4, thereby compensating for the 4 kW shortage in the cooling capacity of the chiller 13. Since the 4 kW shortage in cooling capacity at time t2 can be predicted in advance, operation of the chiller 23 can be started in advance so that the required cooling capacity can be immediately provided before the valve 19 is switched. This improves cooling efficiency. Only the valves 19A-19N corresponding to the chambers 1A-1N with insufficient cooling capacity need to be opened, resulting in power savings.

[0034] Furthermore, a small pump is used to operate the 6 kW chiller 13, which is more efficient and consumes less power when operating in areas with low cooling capacity compared to when a 10 kW pump is operated. Operation of areas with low cooling capacity can be handled by operating only this chiller 13, while chiller 23 is stopped. Since only one chiller 13 is operating, power consumption is small.

[0035] Furthermore, the chiller 13 uses a small pump and has low maximum power consumption, so the amount of cooling water required to cool the chiller is small. Furthermore, only when the cooling capacity is insufficient is the valve 19A-19N opened to start the chiller 23, thereby compensating for the lack of cooling capacity of the chiller 13, thereby saving power. The chiller 13 can be configured compactly, and the chiller 23 can be used for multiple purposes, so it can be configured in a space-saving manner. Furthermore, the chiller 13 requires less time to reach its rated speed than a large chiller, and the cooling output can be increased or decreased quickly. As described above, by lowering the temperature of the electrostatic chuck 3 using the dedicated chiller 13 and the dual-purpose chiller 23, it is possible to reduce power consumption while also lowering the wafer temperature, thereby maintaining a high etching rate.

[0036] Figure 5 shows an example in which the chillers 13 and 23 are integrated into a panel. With global warming advancing and stricter regulations on fluorocarbons as a countermeasure, it is desirable to use environmentally friendly non-fluorocarbon gas as the refrigerant gas for the chillers 13 and 23. Depending on the composition of this non-fluorocarbon gas, it may be flammable and pose a risk if it leaks, so gas leak detection is desirable. While the outer frame of the panel is omitted in Figure 5, it is constructed with a highly airtight housing. Therefore, only one gas leak detector 31 is required, saving space and power. While this embodiment uses a refrigerant gas as the refrigerant, a liquid refrigerant may also be used. Furthermore, cooling using a Peltier element in the cooling section of the electrostatic chuck without using a refrigerant is also possible. Various modifications and combinations of the present invention are possible without departing from the spirit of the present invention, and it goes without saying that the present invention also encompasses such modifications and combinations.

[0037] REFERENCE SIGNS LIST 1 chamber 3 electrostatic chuck 5 vacuum pump 7 process gas 9 radio frequency (RF) power 10 cooling system 11 base 13 chiller (dedicated) 15 gas piping 17 gas branch piping 19 valve 21 gas junction piping 23 chiller (multipurpose) 30 chiller control device 31 gas leak detector

Claims

1. A cooling system comprising: electrostatic chucks respectively disposed in a plurality of chambers; dedicated chillers respectively disposed corresponding to the plurality of chambers for cooling the electrostatic chucks; a dual-purpose chiller for cooling the electrostatic chucks of the plurality of chambers; and a control device for controlling the operation of the plurality of chambers, wherein the dedicated chiller and the dual-purpose chiller are operated together based on control commands from the control device, thereby being capable of covering the maximum output required for cooling the electrostatic chucks.

2. The cooling system described in claim 1, characterized in that, based on a control command for cooling sent from the control device, the dedicated chiller is operated prior to the dual-purpose chiller depending on the amount of output required for cooling contained in the control command, or the dual-purpose chiller is used to make up for any shortfall in output from the dedicated chiller.

3. A cooling system as described in claim 1 or claim 2, characterized in that cooling by the dedicated chiller and the dual-purpose chiller is performed via a refrigerant, the control command of the control device includes a scheduled time for increasing or decreasing the cooling output, and cooling by at least one of the dedicated chiller and the dual-purpose chiller is performed by increasing or decreasing the cooling output prior to the scheduled time by the delay time, taking into account the delay time until the refrigerant reaches the electrostatic chuck.

4. A cooling system as described in claim 1 or 2, characterized in that it comprises: a first pipe arranged between said dedicated chiller and said multiple chambers; and branch pipes having one end connected to said dual-purpose chiller and the other end connected to each of said multiple chambers, said branch pipes being provided with valves corresponding to said multiple chambers.

5. The cooling system according to claim 3, further comprising: an airtight housing for housing said dedicated chiller and said dual-purpose chiller; said refrigerant being a gas; and said housing being provided with a gas leak detector for detecting leakage of said gas.

6. A cooling system as claimed in claim 1 or 2, characterized in that the electrostatic chuck is provided with at least one set of a first base connected to the dedicated chiller and a second base connected to the dual-purpose chiller, below the electrostatic chuck.

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