JP5150584B2 - Filter cleaning method and method of cleaning or drying the object to be processed - Google Patents

Description

  The present invention relates to a method for cleaning a filter and a method for cleaning or drying an electronic component such as a semiconductor device using the method, and particularly to cleaning a filter for filtering supercritical carbon dioxide used for cleaning an electronic component. It relates to the conversion method.

  Application of supercritical carbon dioxide (critical point 31 ° C., 7.4 MPa) is being studied for cleaning semiconductor devices and MEMS (Micro Electro Mechanical Systems) (Patent Documents 1 and 2). Supercritical carbon dioxide can be produced by bringing carbon dioxide to a high temperature and high pressure above the critical point. Supercritical carbon dioxide has an intermediate property between gas and liquid and has excellent osmotic power and diffusivity. For this reason, supercritical carbon dioxide can easily enter a minute recess or the like of the wafer and entrain and remove foreign substances. In particular, supercritical carbon dioxide easily penetrates into small recesses due to the fact that its surface tension is zero, so it exhibits good cleaning performance even when the width of the recesses is reduced due to high integration of semiconductor devices. . From these characteristics, supercritical carbon dioxide is expected as a next-generation cleaning medium.

  Further, the supercritical carbon dioxide adhering to the recess can be easily vaporized by depressurizing the chamber in which the wafer or the like is accommodated. Utilizing this property, the use of supercritical carbon dioxide for drying wafers and the like has also been studied.

Japanese Patent Laid-Open No. 7-284739 Japanese Patent Laid-Open No. 10-50648

  As described above, supercritical carbon dioxide is useful for cleaning and drying of semiconductor devices and the like. However, if the supercritical carbon dioxide contains fine particles, the fine particles adhere and remain on the object to be processed, resulting in a product yield. There is a risk of direct impact. Therefore, in order to increase the product yield, it is necessary to increase the cleanliness of the supercritical carbon dioxide itself.

  In order to increase the cleanliness of supercritical carbon dioxide, it is preferable to filter the supercritical carbon dioxide with a filter. This inventor examined using a sintered metal filter and a ceramic filter as a filter. These filters are used for filtering nitrogen gas and the like used in the manufacturing process of electronic components such as semiconductor devices. These filters have innumerable fine pores and can remove fine particles from the gas. Filters are managed for cleanliness from the manufacturing stage, cleaned as necessary, and shipped as semiconductor grade. In addition, sufficient quality control is performed through shipment through inspection and strict storage at each stage. Even at the manufacturing site of semiconductor devices and the like, sufficient cleanliness management is performed from the installation to the apparatus until the start of use. For this reason, it has been confirmed that a highly clean gas can be obtained immediately after the start of use.

  As described above, supercritical carbon dioxide is produced by making carbon dioxide at a high temperature and high pressure above the critical point, so the state (phase) of carbon dioxide when passing through the filter is that of supercritical carbon dioxide. It can vary depending on the feed process and the location of the filter. For example, when supercritical carbon dioxide is produced using gas phase carbon dioxide as a raw material, gas phase carbon dioxide may be filtered or supercritical carbon dioxide may be filtered depending on the installation location of the filter. When gas phase carbon dioxide is liquefied and liquid phase carbon dioxide is used to produce supercritical carbon dioxide, liquid phase carbon dioxide may be filtered or supercritical carbon dioxide may be filtered. .

  Since the raw material is carbon dioxide in the gas phase even if it is carbon dioxide in a liquid phase or a supercritical state, the inventor of the present application has determined that the state (phase) of carbon dioxide when passing through the filter is the performance of the filter. The effect on behavior was considered to be small. In other words, the inventor of the present application thought that if a semiconductor grade conventional gas filter was used, carbon dioxide with high cleanliness could be obtained immediately after the start of use, regardless of the state (phase) of carbon dioxide. However, in reality, when carbon dioxide in a liquid phase or a supercritical state is filtered using a new (unused) filter, a phenomenon occurs in which fine particles are contaminated on the object to be processed.

  Thus, when using a filter to improve the cleanliness of carbon dioxide in the liquid phase or supercritical state, if the filter is new (unused), the phenomenon that the object to be treated is contaminated with fine particles has been confirmed. ing. When contamination occurs, the product yield deteriorates and greatly affects the manufacturing process of semiconductor devices and the like. On the other hand, when purifying gas phase carbon dioxide with a filter, such a phenomenon is relatively unlikely to occur. However, there is no change in preventing such a phenomenon as much as possible.

  Therefore, an object of the present invention is to provide a method for efficiently cleaning a filter for filtering gas, liquid, or supercritical carbon dioxide used for at least one of cleaning and drying of an object to be processed. And Another object of the present invention is to provide a method for cleaning or drying an object to be processed using such a method.

According to one embodiment of the present invention, there is provided a filter cleaning method for filtering gas, liquid, or supercritical carbon dioxide used for at least one of cleaning and drying of an object to be processed. This method cleans the filter by flowing carbon dioxide through the filter before attaching the filter to a device for cleaning or drying the workpiece and filtering the gas, liquid, or supercritical carbon dioxide. Including doing.

  The filter is sufficiently cleaned as described above, and generally there is no problem even if it is used as it is. However, when the gas, liquid, or supercritical carbon dioxide flows through the filter, the inventor of the present application causes the fine particles present inside the filter to flow out, or peels off and discharges out of the filter together with carbon dioxide. I found that there is a possibility. The cause of the generation of these fine particles is considered to be various, and when the filter material is partially produced as a fine particle at the time of manufacture of the filter, or from the outside due to the particle suction force (Van der Waals force, static electricity, etc.) of the filter itself. The case where particles adhere may be considered. This phenomenon is likely to occur when liquid or supercritical carbon dioxide flows through the filter, but the same phenomenon may occur to some extent when gaseous carbon dioxide flows.

  Based on this analysis, the inventor of the present application came up with the idea of cleaning the filter by circulating carbon dioxide through the filter prior to use of the filter. It is possible that the filter performance will gradually stabilize if the filter is attached to a cleaning device etc. and then run-in as necessary, but efficient cleaning is difficult due to various restrictions on operating conditions. is there. In the present invention, since the conventional idea is changed and the filter itself is cleaned in advance, efficient cleaning becomes possible. Since the cleaned filter removes a considerable amount of particulates that cause contamination, it can be used to filter carbon dioxide in a gas, liquid, or supercritical state to prevent contamination of the workpiece. The desired filtration performance can be exhibited.

According to another embodiment of the present invention, a method for cleaning or drying an object to be processed is provided. In this method, before attaching a filter to an apparatus for cleaning or drying an object to be filtered and filtering carbon dioxide in a gas, liquid, or supercritical state, carbon dioxide is passed through the filter to clean the filter. A filter cleaning step, a filtration step for filtering carbon dioxide in a gas, liquid or supercritical state using a filter that has been cleaned and attached to the apparatus, and pressurizing or filtering the filtered gas or liquid carbon dioxide Using supercritical carbon dioxide obtained by heating, or using supercritical carbon dioxide obtained by pressurizing and heating filtered gas or liquid carbon dioxide, or filtration using an ultra-critical state carbon dioxide, the step of performing at least one of the cleaning or drying of the object to be processed by the device, including That.

  As described above, according to the present invention, it is possible to efficiently clean a filter for filtering gas, liquid, or supercritical carbon dioxide used for at least one of cleaning and drying of an object to be processed. it can. Moreover, according to this invention, a to-be-processed object can be wash | cleaned or dried using such a method.

It is a schematic block diagram of the to-be-processed object washing | cleaning and drying apparatus to which this invention is applied. It is a schematic block diagram of the cleaning apparatus of the filter which concerns on this invention. It is a schematic block diagram of the apparatus used in the Example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, a processing object cleaning / drying apparatus (hereinafter referred to as processing apparatus 1) to which the present invention is applied will be described.

  The processing apparatus 1 includes a pressure vessel 11 that accommodates the workpiece 2, a supply line 20 that supplies carbon dioxide to the pressure vessel 11, and a discharge line 30 that discharges carbon dioxide in the pressure vessel 11. .

The supply line 20 is connected to a high-pressure carbon dioxide source 12 (hereinafter referred to as a high-pressure CO ₂ source 12), and adjusts the flow rate of the filter 13, the heating means 14 for heating the filter 13, and the high-pressure carbon dioxide to be supplied. And a flow rate adjusting means 40. The flow rate adjusting means 40 has a flow meter 41, a flow rate adjusting valve 42, and a control device 43 for controlling the flow rate adjusting valve 42. The high pressure CO ₂ source 12 and the flow meter 41 are connected by a pipe 21, the flow meter 41 and the flow rate adjustment valve 42 are connected by a pipe 22, the flow rate adjustment valve 42 and the filter 13 are connected by a pipe 23, and the filter 13 And the pressure vessel 11 are connected by a pipe 24.

  The discharge line 30 includes a flow rate adjusting unit 50 that adjusts the flow rate of carbon dioxide when the carbon dioxide is discharged from the pressure vessel 11, and the pressure holding valve 15. The flow rate adjusting means 50 includes a flow meter 51, a flow rate adjusting valve 52, and a control device 53 for controlling the flow rate adjusting valve 52. The pressure vessel 11 and the flow rate adjustment valve 52 are connected by a pipe 31, the flow rate adjustment valve 52 and the pressure holding valve 15 are connected by a pipe 32, and the pressure holding valve 15 and the flow meter 51 are connected by a pipe 33. The flow meter 51 is connected to a piping 34 for releasing carbon dioxide outside the system.

  The pressure vessel 11 holds and accommodates an object to be processed 2 such as a semiconductor wafer therein, and is cleaned or dried with supercritical carbon dioxide or cleaned and dried with respect to the object to be processed 2 by carbon dioxide supplied to the inside. Both processes can be performed. The pressure vessel 11 is made of a stainless steel vessel having a pressure resistance of 7.4 MPa (critical pressure of carbon dioxide) or more.

The high-pressure CO ₂ source 12 is not particularly limited as long as it can store high-pressure carbon dioxide. Examples of the high-pressure CO ₂ source 12 include conventionally known ones such as a high-pressure gas cylinder, a cryogenic container, and a liquefaction storage tank. When storing carbon dioxide in a gas phase or a liquid phase, at least a pump (pressurizing means) 16 for raising the carbon dioxide to a critical pressure or higher or a heater (heating means) 17 for heating to a critical temperature or higher on the supply line 20. By providing either of them, the gas phase or liquid phase carbon dioxide can be converted to a supercritical state, and the supercritical carbon dioxide can be supplied to the pressure vessel 11. Alternatively, supercritical carbon dioxide may be accommodated in the high-pressure CO ₂ source 12, and the pressure may be increased by the pump 16 and supplied to the pressure vessel 11 as necessary. In the former case, gas or liquid carbon dioxide is pressurized or heated, and further filtered through a filter 13 to obtain carbon dioxide in a supercritical state, or gas or liquid carbon dioxide is pressurized and heated, Further, carbon dioxide in a supercritical state is obtained by filtering with the filter 13 and used for washing or drying the object 2 to be processed. In the latter case, carbon dioxide in a supercritical state is filtered and used as it is for washing or drying the object 2 to be treated. These pumps 16 and heaters 17 can be provided on the primary side (inlet side or downstream side) of the filter 13 or on the secondary side (outlet side or upstream side). As is clear from the above description, carbon dioxide is supplied to the pressure vessel 11 and cleaning or drying with supercritical carbon dioxide is performed, but the filter 13 can be any of gas phase, liquid phase, and supercritical. Carbon dioxide in the state can also circulate.

  The filter 13 removes the fine particles contained in the high-pressure carbon dioxide and the fine particles generated in the supply line 20 (primary side of the filter 13), and improves the cleanliness of the object to be processed 2 after the cleaning or drying process. The filter 13 can be a known filter used for filtration of high-pressure carbon dioxide, such as a sintered metal filter or a ceramic filter. Examples of the filter 13 include GFT03W (trade name, manufactured by Nippon Seisen Co., Ltd., gas removal performance in gas 0.3 μm), GFD1N (trade name, manufactured by Nippon Seisen Co., Ltd., removal performance in gas 1 μm), UCS-MB-02VR-30HK filter (manufactured by PURERON JAPAN, Inc., particle removal performance in gas 0.01 μm) and the like. The filter 13 may be provided with a heat retaining means (not shown) for the purpose of facilitating the temperature adjustment of the high-pressure carbon dioxide passing through the filter 13 or reducing the energy consumption.

  The heating means 14 heats the main body of the filter 13 or the primary side of the filter 13. Thereby, the removal efficiency of the fine particles contained in the high-pressure carbon dioxide and the fine particles generated in the supply line 20 (primary side of the filter 13) is improved, and it is easy to maintain the cleanness of the workpiece 2 at a high level. Become. The heating means 14 is not particularly limited as long as it can heat the filter 13, and examples thereof include a double tube heat exchanger, an electric furnace, and an electric heater. When the heating means 14 is installed directly on the filter 13, the temperature is kept with the filter 13 by the above-mentioned heat keeping means for the purpose of facilitating the temperature adjustment of the high-pressure carbon dioxide passing through the filter 13 and reducing the energy consumption. May be.

  In order to accurately adjust the temperature of the high-pressure carbon dioxide passing through the filter 13, a temperature measuring device (not shown) may be provided in the filter 13. The temperature measuring device is not particularly limited as long as it can measure the temperature of the high-pressure carbon dioxide passing through the filter 13, and may measure the internal temperature of the filter 13 or measure the external temperature. Alternatively, the temperature of the high-pressure carbon dioxide passing through the filter 13 may be directly measured. Further, the temperature measuring device may measure an internal temperature or an external temperature of a pipe (pipe 23 or pipe 24) in the vicinity of the filter 13. When a temperature measuring device is provided, it is preferable that the temperature measuring device is covered with a heat insulating material in order to avoid the influence of the surrounding environmental temperature.

  The filter 13 is accommodated in a filter container 13a which is a pressure resistant container. A pipe 23 a is branched from the pipe 23 outside the filter container 13 a. The pipe 23 passes through the filter container 13 a and is connected to the filter 13. The pipe 23a is not connected to the filter 13 and opens to the inside of the filter container 13a. A pipe 24a is also opened inside the filter container 13a, and the other end of the pipe 24a is configured to be open to the atmosphere. The filter 13 is configured to be detachable from the filter container 13a by an appropriate member (not shown) such as a joint provided on the pipes 23 and 24 inside the filter container 13a. Valves 25, 26, 27, and 28 are provided on the pipe 23, the pipe 24, the pipe 23a, and the pipe 24a, respectively. The high-pressure carbon dioxide flows into the filter 13 through the pipe 23, flows out through the pipe 24, and is supplied to the pressure vessel 11. The high-pressure carbon dioxide can also flow into the inside of the filter container 13a through the pipe 23a, flow out through the pipe 24a, and be released to the atmosphere.

  With such a configuration, the internal pressure of the filter 13 and the external pressure of the filter 13 (internal pressure of the filter container 13a) can be balanced by appropriately adjusting the opening / closing and opening of the valves 25, 26, 27, and 28. it can. As a result, the net internal pressure applied to the filter 13 itself can be greatly reduced. For this reason, it becomes easy to prevent accidental breakage of the filter 13 due to excessive internal pressure. Furthermore, since it is not necessary to handle the filter 13 as a pressure vessel, it may be easy to comply with laws and regulations. One example of such laws and regulations is the notification under the Japanese High Pressure Gas Safety Law. In this embodiment, since the filter 13 is not subject to the application of the high-pressure gas safety law, the filter 13 can be removed for cleaning described later without being restricted by laws and regulations.

  By providing the flow rate adjusting means 40, it becomes easy to precisely adjust the flow rate of the high-pressure carbon dioxide supplied to the pressure vessel 11. The flow meter 41 of the flow rate adjusting means 40 is preferably capable of measuring the mass flow rate of high pressure carbon dioxide in a liquid or supercritical state. Examples of such a flow meter 41 include a Coriolis mass flow meter (MFM). The flow rate adjustment valve 42 is not particularly limited as long as the flow rate can be adjusted according to the measurement value of the flow meter 41, but it is preferable to use a flow rate adjustment valve having as high a cleanness as possible. Although the control by the control device 43 may be automatic or manual, it is preferable to use an automatic valve that can be adjusted in conjunction with the measured value of MFM as the flow rate adjustment valve 42.

  By providing the flow rate adjusting means 50, it becomes easy to precisely adjust the flow rate of carbon dioxide discharged from the pressure vessel 11. The flow meter 51 of the flow rate adjusting means 50 is the same as the flow meter 41 of the flow rate adjusting means 40, the flow rate adjusting valve 52 is the same as the flow rate adjusting valve 42 of the flow rate adjusting means 40, and the control device 53 is the flow rate adjusting means 40. The same control device 43 can be used.

  The holding valve 15 is provided to hold the internal pressure of the pressure vessel 11. As the pressure-holding valve 15, for example, an existing pressure-holding valve that mechanically holds pressure with a spring can be used. The holding valve 15 is installed between the flow meter 51 and the flow rate adjustment valve 52, but may be installed on the secondary side of the flow meter 51.

  A method for cleaning the workpiece 2 using the processing apparatus 1 of the present embodiment will be described. In the following processing, gas, liquid, or supercritical carbon dioxide is filtered using a filter 13 that has been cleaned by a method described later. Although description about the method of drying the to-be-processed object 2 is abbreviate | omitted, it is the same as the case where it wash | cleans.

First, the high-pressure carbon dioxide stored in the high-pressure CO ₂ source 12 is supplied to the supply line 20, is boosted by the pump 16 as necessary, is heated by the heater 17, and the flow rate is adjusted by the flow rate adjusting means 40 while adjusting the flow rate. Send to.

  The filter 13 is preferably heated to 30 ° C. or higher by heating means 14 and more preferably 50 ° C. or higher. By heating the filter 13 and increasing the temperature of the high-pressure carbon dioxide that passes through the filter 13, the removal performance of the fine particles contained in the high-pressure carbon dioxide that passes through the filter 13 is improved, and the cleanliness of the workpiece 2 is increased. It becomes easy to maintain. On the other hand, if the temperature of the filter 13 is too high, the thickness of the filter 13 and the piping in the vicinity thereof will increase in order to ensure heat resistance, the processing device 1 will be easily increased in size, and the sealing performance of the airtight part will be ensured. It becomes difficult. For this reason, the temperature of the filter 13 is preferably 200 ° C. or lower.

  The high-pressure carbon dioxide is filtered by the filter 13 (filtration process), and then supplied to the pressure vessel 11. The object to be processed 2 in the pressure vessel 11 is washed with supercritical carbon dioxide by the supplied carbon dioxide. This process may be a method (batch type) in which supply of high-pressure carbon dioxide from the supply line 20 is stopped and carbon dioxide is not discharged from the pressure vessel 11 (batch type). A method (continuous type) in which treatment is performed while carbon dioxide is constantly supplied may be used.

  Next, the carbon dioxide in the pressure vessel 11 is discharged from the discharge line 30 while adjusting the flow rate of the carbon dioxide by the flow rate adjusting means 50. The holding valve 15 may be opened continuously or stepwise, or may be opened in one step. However, when the pressure holding valve 15 is opened, the opening of the flow rate adjusting valve 52 of the flow rate adjusting means 50 is not opened too much in advance so that the flow rate does not increase instantaneously.

  Next, an example of the cleaning method (filter cleaning process) of the filter 13 used in the processing apparatus 1 described above will be described. FIG. 2 is a schematic configuration diagram of a filter cleaning device 61 used for cleaning the filter 13. The filter 13 to be cleaned (same as the filter 13 in FIG. 1) is accommodated in the filter container 13b. The use situation of the filter 13 to be processed is not limited, but a particularly great effect is obtained when the filter 13 is unused, that is, a new filter as described in the embodiment. The filter container 13b is a container similar to the filter container 13a in the processing apparatus 1. Similarly to the filter container 13a, pipes 71 and 72 connected to the filter 13, a branch pipe 73 from the pipe 71, and a pipe 74 capable of releasing the atmosphere are connected to the filter container 13b. Further, as in the case of the filter container 13a, valves 75 to 78 are provided on the pipes 71 to 74. Therefore, the internal pressure of the filter 13 and the external pressure of the filter 13 (internal pressure of the filter container 13b) can be balanced by opening / closing and adjusting the opening degree of these valves 75 to 78. Similarly to the case of the filter container 13a, the filter 13 is connected to the pipes 71 and 72 by appropriate means such as a joint, and can be attached to and detached from the filter container 13b. Such a configuration can prevent accidental breakage of the filter 13 and can facilitate legal compliance.

The CO ₂ container 62 stores gas phase or liquid phase high pressure carbon dioxide. Carbon dioxide is supplied from the CO ₂ container 62 as needed, and is temporarily changed into a liquid phase by the condenser 63 together with the recirculated gas phase carbon dioxide and stored in the storage tank 64. The liquid phase carbon dioxide stored in the storage tank 64 is pressurized by the pump 65, filtered by the filter 66, flows into the filter 13 accommodated inside the filter container 13 b, circulates inside the filter 13, and is outside the filter 13. Is discharged. At this time, the carbon dioxide flows out the fine particles present inside the filter 13 and is discharged to the outside of the filter 13. The carbon dioxide discharged from the filter 13 is vaporized by the evaporator 68, filtered by the filter 69, and merged with the carbon dioxide supplied from the CO ₂ container 62 as necessary by the condenser 63. One or both of the filter 66 and the filter 69 may be omitted depending on circumstances.

  The carbon dioxide flowing through the filter 13 may be in a gas phase, a liquid phase, or a supercritical state, but is preferably liquid or supercritical carbon dioxide. Liquid or supercritical carbon dioxide has a higher density than gas-phase carbon dioxide and has a higher filter cleaning effect. This is because the higher density has a higher ability to carry fine particles, and the fine particles inside the filter are effectively discharged. In particular, in the supercritical state, the surface tension of the fluid is zero, and the diffusibility of carbon dioxide is high. Therefore, even if the fine pores of the filter 13 are fine and complex, the carbon dioxide reaches every corner of the fine pores. , The cleaning effect is enhanced. In order to achieve a supercritical state, the pressure of carbon dioxide is increased to 7.4 MPa (critical pressure of carbon dioxide) or higher with a pump 65 and heated to 31 ° C. (critical temperature of carbon dioxide) or higher with a heater (not shown).

  The pressure of carbon dioxide through which the filter 13 is circulated is preferably higher, more specifically 1 MPa or more. Since carbon dioxide of 1 MPa or more has a high density, the effect of flowing out the fine particles adhering to the filter 13 is high, and the filter cleaning effect is enhanced. Moreover, when the pressure of carbon dioxide is high, the differential pressure (ΔP) before and after the filter 13 can be increased. Since the differential pressure and the flow rate are in a proportional relationship, the higher the differential pressure, the higher the flow rate of carbon dioxide can be circulated, and the cleaning efficiency is improved. Further, since the flow rate of carbon dioxide to be circulated increases as the flow rate increases, processing at a high flow rate is possible, and fine particles adhering to the filter 13 can be efficiently removed. Since carbon dioxide having a high flow rate and a high flow rate is circulated, the cleaning time can be shortened.

  In the present embodiment, the entire amount of carbon dioxide that has circulated through the filter 13 is recirculated and circulated through the filter 13 again. The carbon dioxide to be recirculated may be only a part of the carbon dioxide circulated through the filter 13. Recycling and using carbon dioxide can be expected to reduce the cost of cleaning and reduce the amount of carbon dioxide released outside the system.

  When carbon dioxide is recycled, the removal effect of the fine particles is further enhanced by filtering the recycled carbon dioxide with the filter 69. The carbon dioxide filtered by the filter 69 may be the total amount or a part of the carbon dioxide to be recycled.

  Before the recirculated carbon dioxide is filtered by the filter 69, the carbon dioxide having passed through the filter 13 is vaporized by the evaporator 68. In general, the particle removal performance of a filter is higher when filtering gas than when filtering liquid or supercritical materials. The cleanliness of carbon becomes higher and the cleaning effect of the filter 13 becomes higher. Therefore, when the carbon dioxide flowing through the filter 13 is in a liquid or supercritical state, it is preferable that the carbon dioxide once vaporized by the evaporator 68 and then filtered by the filter 69. The carbon dioxide to be vaporized may be the total amount or a part of the recirculated carbon dioxide. Further, the evaporator 68 can capture the fine particles in the liquid phase, and the movement of the fine particles from the liquid phase to the gas phase is small, so that the load on the filter 69 is reduced. By blowing liquid phase carbon dioxide containing fine particles, the fine particles can be discharged out of the system. Note that a cooler for promoting liquefaction of carbon dioxide may be installed in front of the evaporator 68. By cooling the carbon dioxide with a cooler, the carbon dioxide is liquefied more reliably. By supplying the liquefied carbon dioxide to the evaporator 68, a gas-liquid interface is formed in the evaporator 68, and the carbon dioxide can be gently evaporated from the interface.

  In the filter washing step, it is preferable to circulate carbon dioxide at a flow rate higher than the flow rate at the filtration step (actual volume flow rate at the temperature and pressure at the time of washing). In general, a higher flow rate has a higher flow rate, and it is easier to remove fine particles adhering to the filter, but in particular, the flow rate is higher than that of the filter cleaning process by circulating carbon dioxide at a higher volumetric flow rate than the filtration process. The possibility of fine particles being released from the filter in a low filtration step is reduced.

  In the filter washing step, it is preferable to distribute carbon dioxide having a temperature higher than that in the filtration step. This is because, generally, the higher the temperature, the faster the elution rate of the eluate from the filter, and the higher the elution rate. In addition, by allowing carbon dioxide to circulate at a higher temperature than during the filtration step, the possibility that the effluent is released from the filter in the filtration step at a lower temperature than the filter washing step is reduced. As described above, the higher the density of carbon dioxide, the higher the cleaning effect. However, considering that the density of carbon dioxide decreases as the temperature increases under the same pressure, it is possible to circulate high temperature carbon dioxide. There are also disadvantages. However, by maintaining the carbon dioxide at a high pressure as described above, high-density carbon dioxide can be supplied.

  As described above, according to the present embodiment, fine particles adhering to the filter and a minute amount of eluate from the filter itself can be suppressed, and a filter having a markedly improved cleanliness compared to the prior art can be obtained. For this reason, a gas phase, liquid, or supercritical carbon dioxide having a sufficiently high cleanliness can be obtained immediately after the start of use, and products such as semiconductor devices can be immediately produced at a high yield.

A new filter (NASclean GF-T001) manufactured by Nippon Seisen Co., Ltd. was prepared, and the filter was installed in the apparatus shown in FIG. The apparatus used was basically the same as that shown in FIG. 2, but a heater 70 was installed between the pump 65 and the filter 66. A high pressure cylinder was used as the CO ₂ container 62. Carbon dioxide was introduced under the conditions of 20 MPa, 40 ° C., 3 kg-CO ₂ / h, and cleaning was performed for 6 hours. Moreover, what did not clean with the same filter was prepared as a comparative example.

Next, as shown in FIG. 3 (b), carbon dioxide treated with a cleaned filter 13 is placed in a pressure vessel 11 on which a 6-inch clean silicon wafer is set at a mass flow rate of 20 g-CO ₂ / min. Introduced. When the number of fine particles having a particle size of 0.5 μm or more on the wafer was measured, it was 0 for the wafer used in the example and 3 for the wafer used for the comparative example, and both of them were highly clean so as not to affect the experimental results. The degree was secured. The introduction pipe was heated with an electric heater 18a so that the external temperature was 40 ° C. The pressure vessel 11 was heated by a hot water heater 18b having a hot water setting of 60 ° C. When carbon dioxide was introduced in this state, it became supercritical carbon dioxide having a pressure of 10 MPa and a temperature of 50 to 55 ° C. Immediately after the pressure vessel 11 reached this pressure / temperature state, the pressure was reduced to atmospheric pressure, and the wafer was taken out. The pressure was reduced by fully opening the flow regulating valve 19 on the primary side and then slowly opening the pressure holding valve 15 so that the temperature in the pressure vessel 11 did not become 40 ° C. or lower. The wafer was stored in a clean case, and after a few days, the number of fine particles having a particle diameter of 0.5 μm or more was measured on the wafer with a dust inspection apparatus (WM-3, manufactured by Topcon Co., Ltd.). At this time, an area having a width of 10 mm on the outer periphery of the wafer was not measured. A similar test was performed using the filter of the comparative example.

  Table 1 shows the number of fine particles on the wafer after processing under the above conditions. It was confirmed that the number of fine particles on the wafer after cleaning with carbon dioxide was reduced by cleaning the filter. In particular, most of the fine particles having a particle size exceeding 1 μm were removed. In general, it is presumed that the larger fine particles are easier to remove. By extending the cleaning time, it is considered that the cleanliness of the filter is further increased, and adhesion of fine particles having a smaller particle diameter to the wafer can be suppressed.

1 processor 2 workpiece 11 the pressure vessel 12 the high-pressure CO ₂ source 13 filter 13a, 13b filter vessel 14 heating means 15 keeping valve 16 pump 17 heater 20 supply line 30 exhaust line 40 flow rate regulating means 50 flow controller 61 filter cleaning Equipment 62 CO ₂ container 63 Condenser 64 Storage tank 65 Pump 66 Filter 68 Evaporator 69 Filter

Claims (10)

A method of cleaning a filter for filtering gas, liquid, or supercritical carbon dioxide used for at least one of washing and drying of an object,
Prior to filtering the gas, liquid, or supercritical carbon dioxide by attaching the filter to an apparatus for cleaning or drying the object to be processed, the filter is cleaned by circulating carbon dioxide through the filter. A method for cleaning a filter, comprising:   The method for cleaning a filter according to claim 1, wherein the filter is an unused filter.   The method for cleaning a filter according to claim 1 or 2, wherein the carbon dioxide circulated through the filter is liquid or supercritical carbon dioxide. The method for cleaning a filter according to any one of claims 1 to 3 , wherein the cleaning of the filter includes circulating at least a part of carbon dioxide circulated through the filter through the filter again. .   The method for cleaning a filter according to claim 4, comprising filtering at least part of the carbon dioxide circulated through the filter and then circulating it again through the filter.   The method for cleaning a filter according to claim 5, comprising vaporizing at least part of the carbon dioxide circulated through the filter before filtering at least part of the carbon dioxide circulated through the filter.   The method for cleaning a filter according to claim 6, comprising vaporizing at least a part of carbon dioxide circulated through the filter with an evaporator. Filter cleaning in which a filter is attached to an apparatus for cleaning or drying an object to be processed, and before the gas, liquid or supercritical carbon dioxide is filtered , carbon dioxide is circulated through the filter to clean the filter. Conversion process,
A filtration step of filtering gas, liquid or supercritical carbon dioxide using the filter that has been cleaned and attached to the device ;
Using supercritical carbon dioxide obtained by pressurizing or heating the filtered gas or liquid carbon dioxide, or by pressurizing and heating the filtered gas or liquid carbon dioxide Using the obtained supercritical carbon dioxide or using filtered supercritical carbon dioxide to perform at least one of washing or drying of the object to be processed by the apparatus ;
A method for cleaning or drying an object to be treated.   The method for cleaning or drying an object to be processed according to claim 8, wherein the volume flow rate of carbon dioxide circulated through the filter in the filter cleaning step is larger than the volume flow rate of carbon dioxide circulated through the filter in the filtration step.   The method for cleaning or drying an object to be processed according to claim 8 or 9, wherein a temperature of carbon dioxide circulated through the filter in the filter cleaning step is higher than a temperature of carbon dioxide circulated through the filter in the filtration step.

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