TWI896842B - Cleaning Shed - Google Patents

Abstract

A cleanroom is provided that has unidirectional laminar airflow and uniform circulation characteristics, capable of achieving ISO Class 3 to Class 4 or even higher cleanliness, thereby improving productivity and reducing costs. The high-cleanliness cleanroom of the present invention comprises: (A) a blow-out structure for achieving a high-cleanliness environment; (B) a double-wall structure for forming a uniform circulation path on the side walls of the cleanroom; (C) a rectifying structure for reducing turbulence, stagnation, and dust emission in the airflow generated by various devices; and (D) a localized suction mechanism. These are designed using (E) numerical fluid dynamics (CFD) with consideration of actual conditions.

Description

Cleaning Shed

The present invention relates to a clean room that requires high cleanliness in the manufacturing process of semiconductors and displays such as organic EL displays (OLEDs).

In the manufacturing processes of semiconductors and displays such as OLEDs, even trace amounts of dust and other debris can adhere to the products being manufactured, causing product defects. Therefore, cleanrooms (hereinafter referred to as "cleanrooms") are locally installed in areas requiring a high-quality clean environment and are maintained in a clean state to improve product quality, reliability, and productivity.

One way to clean a shed is laminar flow, which pushes the air inside in one direction in a laminar flow state while exhausting dust. To ensure that air flows generally from top to bottom, a ceiling outlet is formed in part of the ceiling, consisting of a fan filter unit (FFU) with a HEPA (High Efficiency Particulate Air) filter or ULPA (Ultra Low Penetration Air) filter as the final filter. Air is drawn into the floor through openings formed by grilles (double-layer floor), and the fluid is connected to an arbitrary duct or circulation shaft. It is exhausted/circulated through the ventilation duct around the outside of the clean room, and the air is temperature-controlled and dust-removed before being blown out of the ceiling as a downward airflow. This allows the cleanroom to be maintained at the desired high cleanliness and temperature by quickly removing dust generated indoors and handling heat generated by equipment and devices.

For example, Patent Document 1 discloses a partial clean room in which a portion of the interior space of a clean room is partially set to a high cleanliness level. According to Patent Document 1, exhaust vents or outlets are formed only on a portion of the floor of the partial clean room, forming a single-layer structure, thereby reducing construction costs.

[Patent Document 1] Japanese Patent No. 5513989

In the present invention, "cleanliness" refers to the cleanliness standards adopted by clean rooms, such as Federal STD-209E, ISO 14644-1, and JIS B9920. For convenience, the cleanliness standards are described based on the ISO standards.

In cleanrooms with unidirectional airflow, ISO Class 3, 4, or even higher cleanliness levels are required. This requires a uniform downward airflow within the cleanroom. Conventionally, this requires a filter occupancy rate (the percentage of the FFU (Flying Fluid Unit) filter area within the ceiling area) of at least 70-80%, and an average airflow velocity of 0.3-0.5 m/s. Based on this, a positive pressure is maintained within the cleanroom, creating a laminar downward flow of clean air. This prevents the influx of contaminants due to leaks from the cleanroom walls and curtains, and rapidly removes dust generated by people and equipment within the cleanroom.

The closer the filter occupancy rate is to 100%, the easier it is to achieve consistent laminar flow, thus helping to achieve high cleanliness. However, in very large cleanrooms, this increases the number of expensive FFUs, which in turn increases costs. On the other hand, attempting to reduce the number of FFUs increases the risk of stagnation between filters or on the side walls due to insufficient filter occupancy in the blow-out area.

Furthermore, as shown in the upper and lower left images (a) of Figure 5, discussed later, the conventional technology results in an uneven circulation path, such as air returning only along one side of the wall, or air drift or stagnation occurs above the floor grille. As described above, filling a cleanroom with a completely uniform airflow based on unidirectional laminar flow is not easy with conventional technology.

Furthermore, when the equipment is installed and operating within the cleanroom, airflow becomes turbulent, creating biased flow, which further deteriorates and increases the number of stagnant areas. Predicting or improving the dust emission behavior during actual operation based on the equipment's configuration is difficult, and estimating the stagnant areas and duration is costly. In many cases, these issues become apparent during field operation, and deteriorating airflow characteristics can become the root cause of the deterioration in cleanliness.

The cleanliness level of the local space within the local cleanroom disclosed in Patent Document 1 is maintained at approximately Class 10 (equivalent to Federal STD-209E, ISO Class 4). However, cleanrooms using unidirectional laminar airflow, as mentioned above, face installation difficulties and cost issues, as well as numerous problems in actual machine operation. Therefore, it is difficult to meet ISO Class 3 to 4 standards, or even achieve higher cleanliness levels.

In view of the above-mentioned practical situation, the main subject of the present invention is to provide a clean room that is suitable for ISO Class 3 to Class 4 or even higher cleanliness, and forms a unidirectional laminar airflow and uniform circulation airflow characteristics. By quickly reducing the dust and stagnation generated by the internal devices and their operation, it helps to improve productivity. Compared with the past, the occupancy rate of FFUs, which is one of the main reasons for cost increases, can be reduced by up to 50%, thereby helping to reduce costs.

To address the above issues, the cleanroom of the present invention has the following configurations (A) to (E). (A) A fully regulated airflow mechanism with a filter occupancy ratio of less than 70% for the FFUs, a filter spacing of less than 500mm (preferably less than 300mm), and a perforated plate (opening ratio of 20-40%) within the lower 200mm (preferably 100mm). (B) To ensure uniform airflow throughout the cleanroom, at least two or more side walls are double-layered (with a gap of 200mm or less). This eliminates the need for a perforated floor and prevents skewed airflow. (C) Installation of a rectifying/air-guiding mechanism attached to the device to reduce airflow turbulence, swirl, separation, vortex generation, and/or stagnation in bypasses (material passages within production line equipment, or at materially significant locations within process areas) generated by the device. (D) Installation of a localized suction mechanism to prevent/reduce dust and airflow turbulence around bypasses generated by the device and its operation. (E) As described above, numerical fluid dynamics (CFD) taking into account actual conditions is used to perform a phased design of the overall space (A)/(B), the space surrounding the device (C), and the local space (D). In the case of ISO requirements, In Level 3 and 4 areas (primarily bypass), the downward velocity is set to approximately 0.3 m/s, the air age (the time required to reach each location in the space when the air is blown out at 0 seconds) is set to less than three times the theoretical value, and the positive pressure within the cleanroom is set to 20-40 Pa. This configuration provides a stable, high-quality cleanroom. [Effects of the Invention]

The high-definition cleanroom of the present invention can suppress the deviation of airflow or velocity within the space that is easily generated by the previous technology. In particular, it can avoid the windless state (≈0m/s) that causes stagnation or the excessive increase of airflow velocity (over 0.5m/s) that causes airflow turbulence and eddy currents, thereby making the airflow near the bypass uniform (average airflow velocity of approximately 0.3m/s).

Furthermore, by utilizing numerical analysis of air age (retention time) (using the passive scalar transport equation), the air age around the device is limited to a value less than three times the ideal downflow. This eliminates and minimizes the presence of device-generated dust in bypass paths, which was previously difficult to account for. Similarly, by limiting the retention time within the entire space, a cleanroom can be provided that exhibits self-cleaning properties, such as rapid recovery from deterioration in cleanliness.

This creates a unidirectional laminar flow and uniformly circulating airflow within the cleanroom, rapidly reducing the risk of dust and stagnation from internal devices and their operation, ensuring stable, high-quality cleanliness within the space (critical areas, primarily near bypasses). It also helps reduce variations in temperature and humidity within the cleanroom.

Hereinafter, the embodiments of the present invention will be described with reference to the accompanying drawings.

Figure 1 is a longitudinal cross-sectional view of the cleanroom of the present invention. Cleanroom 1 is installed, for example, when high cleanliness is required even within a cleanroom. It is formed by partitioning using partitioning members (partitions, vertical walls, etc.). The following describes the components (A) to (E) of the cleanroom of the present invention.

(A) The filter occupancy rate of the FFU is less than 70%, the filter interval is less than 500mm (preferably less than 300mm), and the lower part is within 200mm (preferably 100mm) and is set as a 100% full-surface rectifier with a perforated plate (opening rate 20-40%).

On the ceiling of the cleanroom 1, multiple FFUs equipped with high-density ULPA filters are installed side by side as air cleaning mechanism 2. These FFUs maintain high cleanliness within the cleanroom. By varying the location and number of FFUs, the system can accommodate spaces of varying widths. The specific configuration and number of FFUs are optional; however, the blow-out mechanism of the present invention uses the average airflow velocity as a benchmark. Furthermore, the present invention is not limited to FFUs; other air cleaning mechanisms can be installed.

As mentioned above, in order to achieve ISO Class 3 to 4 or even higher cleanliness, the filter of the FFU must occupy at least 70-80% of the air outlet. The remaining 20-30% becomes the frame of the FFU air outlet or is set as blank.

The airflow velocity of an FFU is generally in the range of 0.1 to 0.7 m/s. Without uniform airflow characteristics, the airflow within the cleanroom becomes turbulent, causing dust to fly. Meanwhile, the average airflow velocity in ISO Class 3 and 4 unidirectional airflow systems requires a uniform airflow of 0.3 to 0.5 m/s. Therefore, to achieve uniform airflow or reduce the filter occupancy rate, a perforated plate is installed at the FFU's air outlet to expand the airflow area and diffuse the purified air blown out from the FFU into the surrounding area.

The perforated plate has an opening ratio of approximately 30%, temporarily blocking the airflow and rectifying the airflow that is blown out from the opening to the surrounding area. In a typical FFU structure, there is no perforated plate, or there is a perforated plate with a blank space for installation on the end face, or the FFU and perforated plate are integrated. In any case, the frame ends or the blank space used to install the FFU itself or the perforated plate in the integrated unit account for the remaining 20-30% of the filter's occupancy.

As mentioned above, in the past, even if the filter occupies 70-80%, regardless of whether the blow-out area has a perforated plate, the remaining 20-30% is used for the frame frame or blank space for juxtaposing multiple FFUs. Therefore, there is no rectification in this area, making it an inadequate blow-out design. Therefore, if a technician who usually works in clean room design considers the reason why the visible frame frame or blank space is limited to 20% when looking at the ceiling from the inside of the clean room,

On the other hand, in the present invention, the filter occupancy rate of the FFU is reduced to below 70%, for example, to 50-60%, and the number of FFUs is reduced by a maximum of 50% compared to conventional technologies. As mentioned above, if the number of FFUs is attempted to be reduced, the insufficient filter occupancy rate of the blow-out section will bring about the risk of stagnation between filters or on the side walls. Therefore, in the present invention, the FFU is only installed on the ceiling first. A perforated plate 3 (with an opening rate of 20-40%) is constructed on the entire surface 100mm below the FFU installed on the ceiling (100mm below the floor surface from the FFU installed on the ceiling). The perforated plate is processed with holes on the entire surface to minimize the width of the installation frame, or even the frame is eliminated to create an almost 100% full-surface rectification mechanism.

Specifically, when installing the FFU, a frame or panel is placed, but 100mm long bolts or nuts are placed between them, securing the FFU with a 100mm gap between the frame and the punched surface. This separates the FFU from the punched surface, preventing the frame from moving on the punched surface, and ensuring a consistent punched surface. As a result, even with a filter occupancy rate of 50-60%, 100% rectification can be achieved.

The installation of the FFU 2 and perforated plate 3 is explained in detail. When installing the FFU 2, it is separated from the perforated plate 3, so cleanliness must be maintained. First, ensure that there are no gaps between the frame on which the FFU 2 is installed and the ceiling. Specifically, use a dust-proof gasket (liner), such as EPDM (ethylene propylene diene monomer), to seal the installation area against the frame, such as aluminum profiles or steel plates. Next, thoroughly clean the bolts and nuts used to install the perforated plate 3, as well as the installed frame and perforated plate 3. The reason is that after the separated FFU2 and punching plate 3 are installed, it is difficult to clean them, which is necessary to ensure the quality of the blowing structure. In addition, the punching plate 3 for rectification is pre-deburred, degreased, and processed with holes on the entire surface, and is bent according to the appropriate size to prevent warping. When these punching plates 3 are assembled into pre-prepared mounting holes, no gaps between the punching plates 3 are allowed, and they are fixedly arranged with a minimum gap of less than 1 mm. A blocking plate is provided for the portion where the gap occurs. In this way, from the inside of the clean shed, the top surface becomes a full-surface punching surface implemented with the same hole processing to complete the rectification mechanism of the blowing part. In addition, if the roof surface is a fully perforated surface, lighting, alarms, sensors, anti-fall mechanisms, doors and windows are sometimes installed at any position on the surface. These installation locations are basically set and arranged at the two ends of the clean room. Doors and windows that cause air turbulence are not installed above the bypass.

The difference between the perforated plate-type FFU used in conventional technology and the present invention is that the gap between the FFU's filter surface and the perforated surface is narrower, slightly increasing the airflow area. Furthermore, the lower portion is set at 100mm, but this is not limited to this and can be set to 150mm or 200mm. A longer gap between the FFU and the perforated surface facilitates flow regulation, but on the other hand, it reduces the space available for equipment inside the cleanroom, so a 200mm upper limit is desirable.

Furthermore, in the present invention, the spacing between filters in the FFUs that fill the ceiling is set to 300mm or less. Although the filter spacing is 300mm or less as a basic rule, in order to keep the filter occupancy rate below 70% in very wide ceiling areas, it is possible to expand the width to 400-500mm in some areas based on design considerations, such as the spacing between the wall and the FFUs, the size of the FFUs themselves, and the spacing between filters. If the filter space is wide, the airflow fluctuation and deviation will become larger. In order to stabilize the temporal and spatial fluctuations of the airflow velocity on the perforated surface, it is difficult to adjust the opening rate of the perforated plate and the uniformity of the downward airflow. Therefore, it is expected that the filters should be installed at intervals of no more than 500mm.

Accordingly, in actual application, for example, when the outlet temperature of the FFU is adjusted to about 23 degrees Celsius (thereafter, the temperature is set to "degrees Celsius"), the high-purity air to be dust-removed passes through the perforated plate and is supplied downward around the device and in the bypass at an average airflow speed of 0.1 to 0.5 m/s, preferably 0.3 to 0.4 m/s.

In addition to the blow-out structure used to achieve the aforementioned cleanliness, the uniform circulation based on the double-wall structure (B) described later creates unidirectional laminar flow and uniform circulation throughout the cleanroom. Furthermore, through the central rectification (C) or local exhaust (D) centered around the equipment and devices described later, even with a filter ratio reduced by up to 50% compared to conventional systems, ISO Class 3 to 4 cleanliness levels, or even higher, can be achieved.

Furthermore, in Figure 1, the gap between the ceiling and the air intake of the FFU is set to 500mm, but it is not limited to this. In order to avoid the gap between the ceiling and the air intake of the FFU being extremely negative, resulting in reduced air volume and insufficient mixing of temperature, it is expected to ensure that it is above 200mm, and more preferably above 300mm.

Furthermore, the FFU filter occupancy rate is set below 70%, for example, to 50-60%. However, if the filter occupancy rate is less than 40%, the airflow velocity in the blow-out section needs to be increased, which easily causes deviations and makes it difficult to achieve a 100% full-surface straightening mechanism. Therefore, in order to avoid excessive airflow velocities exceeding 0.5 m/s as a blow-out structure, the filter occupancy rate is set to at least 40%, preferably at least 50%. As mentioned above, in previous technologies, the filter occupancy rate must be at least 70-80%. When the filter occupancy rate is below 70%, it is difficult to achieve high cleanliness of ISO Class 3 to 4 or even higher. However, by using the technology of the present invention, high cleanliness can be achieved with a filter occupancy rate of at least 40% and below 70%.

(B) In order to make the airflow circulation uniform throughout the clean room, at least two or more side walls should be double-layered (gap ~ 200mm), and a uniform circulation mechanism that does not require a perforated floor and suppresses biased airflow should be used.

Conventionally, the floor of a cleanroom is covered with perforated flooring, such as grating or perforated metal, to create multiple vents, and a base layer is formed through this perforated flooring. This creates a raised floor (double-layer floor). Around the outside of the cleanroom, a duct (return duct) is formed to guide the air flowing out of the multiple vents to the base layer to the FFUs. The airflow from the cleanroom to the base layer flows into the return port formed on the base wall, circulates through the duct surrounding the cleanroom exterior, which is separated from the inside of the cleanroom, and passes through the FFUs. The circulating airflow created by the FFUs creates a downward airflow from the ceiling of the cleanroom toward the floor.

In a typical cleanroom, filters create a pressure difference between the interior and exterior of the cleanroom. Consequently, the airflow velocity of the air passing through the filters is nearly uniform across the entire ceiling. To improve cleanroom cleanliness, it's ideal to circulate air between the interior and exterior, allowing dust and debris inside the cleanroom to be immediately discharged outside. While downward airflow can immediately remove dust and debris inside the cleanroom, in reality, the placement and operation of this device can create areas of low cleanliness (such as stagnation). In particular, in areas of stagnant airflow within a cleanroom, contamination caused by dust increases, and therefore airflow needs to be adjusted to avoid areas of stagnant airflow.

In the present invention, the wall covering the clean shed 1 is constructed as a double-wall structure consisting of an inner wall 4 and an outer wall 5, thereby duplexing at least two or more of the side walls of the clean shed 1. The upper limit of the gap between the walls is 200 mm, preferably 100-200 mm, and a space is formed in the gap between the walls. On the side walls of the clean shed, the inner wall 4 is made of aluminum profiles, generally PVC panels. In explosion-proof areas, SUS panels are installed on the aluminum profiles from the inside of the clean shed to form a clean shed with smooth inner walls. In the lower part near the floor, an air inlet is provided, which is opened by a regulator to a gap of 100-200 mm from the floor. Air from the cleanroom is drawn in through this intake port and forms a return path upward through the gap between the outer wall 5, which is constructed of insulating panels. This allows the air inside the cleanroom to circulate to the FFU 2, thereby filling the gap between the double-walled walls with air that has bypassed the bypass. This creates a uniform circulation path along at least two of the cleanroom's sidewalls. Furthermore, this configuration is achieved with the short side (width) of the inner wall 4 being no greater than 6500 mm (preferably no greater than 5000 mm), and there are no specific requirements for the long side (length).

The doors and windows attached to the double-wall structure are generally installed in locations that do not obstruct the downward airflow. For example, positive pressure dampers, typically installed on the sidewall above the cleanroom in conventional technology, can cause deflection or flow paths toward the dampers immediately after air is blown out. However, in the present invention, these are installed on the outer wall 5 of the double-wall structure, eliminating this deflection. Regarding the doors, the inner and outer walls 4, 5, are generally located in the same position. The outer wall 5 is a sliding door, while the inner wall 4 is a hinged door. Upon entry, both doors are temporarily opened simultaneously. However, due to the sufficient positive pressure within the cleanroom and the uniform circulation structure, cleanliness is quickly restored. The door of the inner wall 4 is not necessary, and the panel constituting the inner wall can be removed for entry.

Furthermore, when the shed is connected to other sheds, both the inner and outer walls 4, 5, are equipped with connection ports at the same location. In this case, the gaps between the double-walled structures are provided with partitions and other channels to separate the circulating air. Flanges connecting windows, maintenance hatches, wiring panels, and air conditioners are mounted on the outer wall 5. Therefore, the presence of doors and windows on the inner wall 4, in the downdraft area, that could disrupt airflow, is minimized. Alarms and various sensors are also avoided as much as possible in bypass paths.

The inner wall 4 is constructed to ensure airtightness, avoiding any gaps or openings that could disrupt airflow. This prevents leakage into the gaps between the inner wall and the outer wall 5, ensuring downward airflow. Regarding the outer wall 5, the floor rails, which are installed using materials such as aluminum, are properly aligned horizontally using inner liners. Then, densely packed with anti-static steel plates, non-combustible panels, are installed on the sides and ceiling. The joints between the panels are sealed using caulking materials such as silicone. The outer wall 5 is sealed airtight by fully caulking the joints with the floor and between the panels to ensure an internal pressure of at least 50 Pa.

The air blown in by FFU2 creates a positive pressure inside cleanroom 1, while the air intake of FFU2 in the ceiling becomes negative. Consequently, the pressure in the interstitial space between the double walls is equal to or lower than that inside the cleanroom. This improves the airtightness within the cleanroom, reliably preventing air from flowing into the cleanroom from outside. Furthermore, by improving compartmentalization and airtightness, increases in both external air volume and internal circulation air volume can be suppressed, thereby reducing operating costs.

Furthermore, the upper limit of the double-wall spacing is set at 200mm, but this is not limited to this. For example, if the gap between the double walls is intended to serve as a guide for people, it can be appropriately increased to 200mm or more depending on design conditions. However, a larger gap increases the overall size of the cleanroom, or the volume within the cleanroom decreases. Furthermore, while the pressure loss is set to 100Pa or less in Figure 1, this is not a limitation. This is related to the air volume of FFU2 and the temperature rise of the fan, and can be determined based on the specifications of FFU2. Furthermore, not only in quadrilateral cleanrooms, but even in polygonal cleanrooms, at least two or more side walls should be double-walled.

Patent Document 1 provides a return path for returning air discharged from an exhaust port or duct formed only on a portion of the floor of the partial clean room to the upper portion of the general space. The return path is formed as a duct at the longitudinal end of the partial clean room, connected to the duct. It passes through the side of the partial clean room and reaches near the ceiling of the general space. Therefore, it is open to the ceiling and does not form a complete double wall like the present invention.

Conventional systems have used perforated floors, such as gratings or perforated metal plates, with the entire floor section formed as a double floor. Air, along with dust from the cleanroom, is drawn through the floor openings into the underfloor space, creating a downward airflow. However, this also limits the application of the underfloor space. In the present invention, by providing a uniformly drawn circulation structure (double wall) below the bypass, perforated floors are no longer necessary, nor is the double floor required in conventional systems. Furthermore, there is no need to form exhaust vents and outlets as part of the floor section, as in Patent Document 1. This further reduces construction costs, saves space, and increases the volume of the cleanroom.

Figure 2 compares the air velocity streamlines of (a) the conventional technology and (b) the present invention, analyzed using resin fluid dynamics (CFD). In Figure 2, the top figure is a longitudinal cross-section of the cleanroom, the lower left figure is a top-down view, and the lower right figure is a perspective view. Inclined flow is called biased flow. If surrounded by an ellipse, conventional technology creates biased flow at the return port on the floor, resulting in uneven circulation. However, this is reduced in the present invention, resulting in a uniform downward airflow and uniform circulation through the structures of (A) and (B). This method constitutes a combined mechanism that focuses on minimizing the effects of expansion, rotation, and shear, the three elements of fluid deformation motion, in the entire clean room, and successfully brings advantages to convection and diffusion, which are the basis for transporting the fluid's motion.

For technicians working in the cleanroom business, it is easy to imagine (A) a uniform blowout structure or (B) a double-wall circulation mechanism without a perforated floor. In fact, cleanrooms that use these (A) and (B) combined structures have never been seen before. Regarding this structure, the inventors who have been engaged in construction for many years have conducted in-depth research using numerical fluid dynamics (CFD), including the (C), (D), and (E) described later. The result is the present invention, which is an airtight circulation mechanism that not only requires high cleanliness, but also meets the requirements of temperature, dehumidification, and inert gas environment at a high level.

(C) A flow straightening/air guiding mechanism attached to the device for reducing turbulence, swirling, separation, vortex generation, etc. of the airflow in the bypass generated by the device and/or stagnation

Cleanroom 1 houses equipment 6 requiring high cleanliness. The equipment's configuration, shape, and operation can cause dust to be swept along with the airflow. This can be caused by turbulence in the airflow, swirl generated by the airflow being detached from the equipment's exterior, or by the equipment itself obstructing the downward airflow, resulting in swaying. For example, in inkjet equipment, a key process in OLED manufacturing, the carriage (hereinafter referred to as CA, containing the ink directly beneath it) is the core function of the equipment. This can induce airflow turbulence and make temperature control difficult, necessitating airflow rectification. Therefore, by installing flow guides (air deflectors) around the CA, or by installing curved flow guides to prevent stagnation (low airflow velocity areas) near the CA's peripheral devices, or by using covers to eliminate stagnation-related areas, or by using curtains to block inflow and outflow from these areas, airflow in the bypass can be improved and localized stagnation can be reduced. Furthermore, in the photoresist filling step of semiconductor manufacturing, for example, the bypass contains complex structures and drive sources. Therefore, by installing flow guides to prevent biased flow or stagnation and maintain downward airflow, or by using covers to eliminate stagnation-related areas, airflow can be improved and localized stagnation can be reduced.

The FFU's outlet temperature is precisely controlled to, for example, 23°C ± 0.1°C to ± 0.5°C. However, the internal heat generation behavior of the device is difficult to monitor. Therefore, to reduce the risk of heat transfer from the device, a flow straightening/air guide mechanism 7, such as a fairing, flow guide, or air deflector, is attached to the device to prevent heat stagnation around the device. The material, shape, structure, and installation method of the flow straightening/air guide mechanism 7 are appropriately selected based on the device's size, operating conditions, and installation location.

Figure 3 compares velocity vectors from resin flow dynamics (CFD) analysis using (a) conventional technology and (b) the present invention. Figure 3 shows a longitudinal cross-section of a cleanroom containing device 6, as shown by the rounded quadrilateral. In conventional technology, the presence of device 6 increases airflow velocity, causing slack (the portion surrounded by the ellipse) and eddy currents. However, in the present invention, the use of a straightening/air guide mechanism 7 (the upper portion of device 6 is rounded, itself slack-free by the device cover) reduces turbulence and suppresses slack.

Furthermore, since the flow straightening/air guiding mechanism 7 is often attached to the bypass device 6 itself, the device design requires not only fluid dynamics-based application of the flow straightening/air guiding mechanism 7 but also risk management associated with its material, shape, and mounting. For example, design measures based on numerical fluid dynamics (CFD) are required to address vibrations caused by the installation of the flow straightening guide, dust emission from the mounting area, interference with process operation, performance impacts, and heat generation caused by the device covered by the flow straightening cover.

Furthermore, during the design process based on numerical fluid dynamics (CFD), the straightening/air-guiding mechanism 7 was designed with the goal of reducing delamination and subsequent stagnation caused by the descending airflow generated by the device 6. The goal was to minimize the effects of rotation and shear in localized areas, among the three elements of fluid deformation. Specifically, the design focused on suppressing the generation of eddy currents caused by airflow velocity differences or momentum loss due to obstacles. The structure and placement of the straightening/air-guiding mechanism were determined to ensure that diffusion was not dominant while maintaining the convection effect that is the foundation of fluid momentum transport.

(D) Local extraction mechanism to avoid/reduce dust and airflow turbulence around the bypass generated by the device and its operation

As the device 6 operates, components come into contact with each other and dust is generated around the bypass due to dust being blown up by the drive source. For example, in the coating process of OLED manufacturing, dust is swept up from the drive unit as the conveyor-based workbench moves in the bypass. Therefore, a local suction mechanism 8 composed of an exhaust duct and the like is installed under the floor of the device 6 along the bypass. Suction ports are provided at arbitrary intervals to locally suction and discharge dust, thereby preventing dust from flying. The suction ports of the local suction mechanism 8 can have a maximum suction airflow velocity of approximately 10 m/s, but are designed to gradually decelerate around them. Near the bypass, the downward airflow velocity generated by the local suction mechanism 8 becomes less than 0.5 m/s. The dust generated is discharged by the air flow based on the local suction discharge downwards towards the entire area under the floor without being swept onto the bypass. In this way, stagnation near the bypass is avoided and reduced.

In addition to under the floor, local suction mechanism 8 is appropriately installed on the side of the device or at a location connected to the device using flexible or rigid ducting, a box with a suction port, or the like. To prevent excessive turbulence in the downward airflow, which has an average velocity of 0.3 m/s, the downward airflow generated by the local suction mechanism near the bypass is set to a velocity of 0.5 m/s or less. However, this is not a limitation. The local exhaust method, location, and suction airflow velocity should be appropriately selected.

Figure 4 compares the air age (retention time) (the time required to reach each location within the space when the blowing position is set to 0 seconds) of (a) the prior art and (b) the present invention, analyzed using numerical fluid dynamics (CFD). Figure 4 is a longitudinal cross-section of the cleanroom including device 6. As shown by the rounded rectangle, in the prior art, the air age around device 6 increases, posing a risk of stagnation. However, in the present invention, the installation of a localized suction mechanism 8 under the floor of device 6 reduces air age and mitigates the risk of stagnation.

Furthermore, when introducing and installing a localized suction mechanism 8, whether attached to a bypass device 6 or mounted on the device 6 itself, the device design must not only utilize the suction effect based on fluid dynamics, but also implement risk management on the device side associated with its material and installation location, similar to the flow straightening/air guiding mechanism 7. For example, design measures based on numerical fluid dynamics (CFD) are required to address vibrations caused by the installation of the localized suction mechanism 8, dust emission from the mounting area, interference with process operations, and the impact on performance caused by airflow formation. Furthermore, even when the local suction mechanism 8 is installed at the bottom of the device 6, in order to prevent the generation of an upward airflow at the bypass height, which is opposite to the descending airflow of the same laminar flow, it is important to consider forming an airflow at a uniform airflow speed at the bottom while implementing installation conditions that achieve the effect centered on the dust emission position on the side of the device.

Furthermore, during the design process based on numerical fluid dynamics (CFD), the starting point for the conception of the localized suction mechanism 8 was how to restore the device-dependent airflow characteristics, including turbulence, eddy currents, and stagnation, that deteriorate from the ideal downdraft through the device 6. Similar to the rectifying/air-guiding mechanism 7, the consideration was how to reduce the effects of rotation and shear in localized areas, among the three elements of fluid deformation motion, and thereby re-direct the airflow by generating motion through localized suction. Specifically, with a focus on suppressing the generation of new eddy currents caused by airflow velocity differences, the structure and placement were determined by considering the location and air volume of the localized suction, while simultaneously inducing convection, the fundamental mechanism for transporting fluid motion, while preventing diffusion from dominating.

Numerical fluid dynamics (CFD) that takes devices into consideration is generally divided into those that can be implemented without devices and those that can be implemented with devices. Among these, in the case of devices that are standardly applicable in this invention, shape reproducibility becomes one of the necessary conditions that largely influences the accuracy of numerical predictions. In this invention, for devices that are intended to be installed in a high-purity environment, after obtaining an actual model using general 3D CAD, the model is modified for numerical analysis, taking into account the degree of contribution to airflow characteristics. Specifically, this includes the omission of bolts and nuts that are considered to have little impact on airflow characteristics, the omission of mounting holes, the omission of small gaps (e.g., less than 10 mm) between components or devices, and the omission of slight curvatures caused by the bending of components or device housings. These are corrected and numerical analysis is performed while fully retaining the components and shapes that should be considered to affect the airflow characteristics.

Furthermore, in the numerical fluid dynamics (CFD) of this invention, the finite volume method is used as a discretization technique, and velocity and pressure are obtained from the governing equations of the fluid (the Navier-Stokes equations). Furthermore, temperature and mass fraction are derived from the energy equation and chemical species transport equation, respectively, and a passive scalar transport equation is employed for the air age. For particle motion, the Lagrangian equations of motion are calculated and evaluated by coupling pressure with the fluid equations within the same solver. The turbulence model adopts the RANS (Reynolds-Averaged Navier Stokes equation: Reynolds-averaged equation, time-averaged model) two-equation SSTk-ω model, with corrections for low Reynolds numbers. This is done to take into account the presence of slower airflow in the downflow and faster airflow in the exhaust and circulation areas, and to adopt a model suitable for a wider Reynolds number band. The grid type uses a polyhedral grid based on a tetrahedral grid, but this is determined by the complexity of the device being tested and the total number of grids, so it is not limited to this. When analyzing the operation of the device, hexahedral grids are mostly used in the moving area. The quality of the grid is evaluated based on the skewness, and even in the detailed part of the device, the quality is guaranteed to be below 0.98. Basically, a stable analysis is performed, and an unstable analysis is performed when considering the impact of the movement of the device on the airflow. Taking into account the influence of temperature, the analysis considers heat sources such as heat generated by the equipment, heat generated by the FFU, and heat conduction from the cleanroom walls. The chemical species transport equation is used to account for the convective diffusion of the mixed gas, taking into account humidity and the concentration of the mixed gas. The Lagrangian method is used to calculate particle density, particle size, number (flow rate), ejection location, and ejection velocity, taking into account the behavior of dust. Particle generation is then represented by probabilistic tracking based on velocity fluctuations during turbulent diffusion. Dust particles also exhibit generally observed behavior that follows the airflow, but the behavior of the stagnant region is also calculated using the Brownian motion and spherical drag laws that take into account the properties of aerosols.

In this invention, the air age (SVE3 (Scale for Ventilation Efficiency)) is calculated through numerical analysis (passive scalar transport equations), and the stagnation conditions around the device are evaluated as the air age T[s]. By forming the airflow in the bypass with a finite value of less than three times the ideal downflow (3T), it is possible to minimize the presence of particles caused by the device in the bypass, which was difficult to consider with previous technologies. For example, fluid analysis of the behavior of dust particles with a diameter of 0.1 to 5 μm or less, generated from drive sources such as cable shafts during device operation, revealed that dust of any size can be swirled, with the probability of swirling increasing with smaller particle sizes. However, the probability of dust appearing in the suction area below the bypass remains below 1.5%, indicating that the likelihood of dust being swirled above the bypass is significantly lower. As described above, the present invention's method for controlling dust swirling associated with airflow turbulence primarily creates a downward airflow within the bypass, and by regulating the air age within the bypass, it is expected that the risk of dust generation will be substantially reduced.

In Patent Document 1, air ducts made of perforated metal plates are installed below the partitioning member, at positions corresponding to the positions between the multiple production devices, to prevent dust and other particles from being swirled within the production devices (the airflow velocity is, for example, less than 1 m/s). However, these air ducts are used to introduce high-purity air from a local clean room into the general space, which differs from the purpose of the present invention.

As described above, the cleanroom of the present invention can suppress the presence or absence of deviations in airflow and speed caused by the devices around the bypass or their operation, which are prone to occur in conventional technologies, by using (C) a rectifying structure for reducing airflow turbulence, stagnation, and dust emission generated by various devices, or (D) a local suction mechanism. In particular, it can avoid windless conditions (≈0 m/s) that cause stagnation and excessive increases in airflow speed (exceeding 0.5 m/s) that cause airflow turbulence and eddies, and can make the airflow near the bypass uniform (average airflow speed of approximately 0.3 m/s).

(E) As above, the phased design of the overall space (A)/(B), the space around the device (C), and the local space (D) is carried out by numerical fluid dynamics (CFD) taking into account actual conditions. In the ISO Class 3 to Class 4 requirement area (above the bypass), the downward velocity is set to approximately 0.3m/s, the air age is set to less than 3 times the theoretical value, and the positive pressure in the clean room is set to 20-40Pa.

According to the present invention, as described above, the average airflow velocity from the perforated surface in the bypass is 0.1 to 0.5 m/s, preferably 0.3 to 0.4 m/s, forming a downward downdraft of approximately 0.3 m/s. By maintaining a uniform airflow velocity, it is theoretically possible to calculate the number of seconds it will take for the air to reach each location, i.e., the air age. For example, if the average airflow velocity is set to 0.3 m/s and the distance from the perforated plate outlet to the bypass is set to 1.5 m, the arrival time (air age T) at the bypass is 5 seconds. This is the theoretical value of the air age T for the ideal downdraft. This invention uses numerical fluid dynamics (CFD) to define the air age around the device (above the bypass) as less than three times the theoretical value, or 3T, as a finite value, ensuring that the air age above the bypass remains within this range. In other words, under the condition of an airflow velocity of 0.3 m/s, the required time of 3T means that the airflow velocity must be at least 0.1 m/s. This serves as an indicator to avoid a windless state (≈0 m/s) in the bypass. If the air age is sufficiently large (10T, 20T, etc.), there is a concern about a windless state (≈0 m/s), which directly leads to a deterioration in cleanliness. In fact, since this structure is fully applicable, the present invention specifies and uses the air age as an effective standard. In addition, by setting the air age of the bypass space to a finite value, it is possible to achieve self-cleaning functions such as rapid recovery from deterioration of cleanliness.

Furthermore, the air blown in by the FFU creates a positive pressure inside the cleanroom. This prevents low-purity air from outside the cleanroom from flowing into the cleanroom. Typically, positive pressure (the pressure difference between the inside and outside of the cleanroom) is set at approximately 5 to 20 Pa. However, for applications requiring high cleanliness, a higher pressure is desirable, and in the present invention, it is set at 20 to 40 Pa. If the positive pressure exceeds this, there are problems such as noticeable airflow when the cleanroom door is opened, obstructing the door's opening and closing, and generating wind noise from the openings of the exhaust and return ports.

Figure 5 compares the streamlines and air aging of (a) the prior art and (b) the present invention, analyzed using resin fluid dynamics (CFD). Figure 5 is a longitudinal cross-section of the clean room containing the device, with the upper figure showing streamlines and the lower figure showing air aging. While the prior art creates deflection or stagnation along the sidewall or around the device, the present invention creates a uniform downward flow from the top of the clean room downward, reducing stagnation areas.

By making the airflow uniform, it's theoretically possible to calculate how many seconds it will take to reach the floor below. However, in reality, filling the cleanroom with a completely uniform airflow is difficult with conventional technology. Furthermore, it's difficult to predict the stagnation area and duration during setup and operation. The cleanroom of the present invention manages (A) downflow and (B) circulation throughout the cleanroom, even taking into account airflow turbulence or stagnation areas caused by the actual installation and operating conditions, thereby avoiding and reducing (C) straightening and (D) stagnation.

Next, we will discuss the cleaning, preparation, and conditions required to achieve the cleanliness of the cleanroom of this invention. To achieve the high cleanliness of this invention, cleaning the cleanroom after construction is crucial. When cleaning a double-walled structure, after all units 6 are installed and the FFUs 2 begin operation, clean from the doors and windows near the ceiling or the upper surface of the inner wall 4 downward. Similarly, clean units 6 after the cleanroom is finished. In particular, carefully clean the unit covers and exposed components and wiring. Cleaning tools used include wet wipes, alcohol, cleaning rollers, ULPA vacuum cleaners, and blowers. After cleaning, according to the entry rules, restrictions on entry time, personnel, and work content, and the placement of cleaning mats are implemented to ensure that cleanliness levels do not deteriorate. This will gradually tighten management and improve cleanliness.

Furthermore, to achieve the high cleanliness levels demonstrated by this invention, dust suppression measures on the equipment side are also crucial. Specifically, in addition to (A) the downdraft and (B) the circulation-based airflow characteristics formed within the cleanroom, conditions related to numerical fluid dynamics (CFD) were considered to effectively utilize (C) the flow straighteners/air guides and (D) the localized suction mechanism. For example, avoidance items are identified using numerical fluid dynamics (CFD) and design guidelines, including the use of dust-producing materials/components, structures that may obstruct downward airflow, structures that induce turbulence, interference between components, the movement/movement of contacting components, vibrating structures, air-driven machinery, hollow pipes such as those used for wiring, and the flow lines, work content, and frequency of pipe or maintenance, as well as the tools/machines/materials used. For example, in the configurations (C) and (D) of the present invention, various devices are implemented to ensure adequate cleaning by ensuring that wiring routes and wiring, etc., are routed in a manner that avoids bypasses or is contained within a cover.

With the above configuration, it can be said that by being used in industrial applications as an integrated clean room with the device, it can provide a more stable environment that maintains high cleanliness not only when the device is stopped, but also when it is running.

While the above describes the embodiments of the clean room according to the present invention, the present invention is not limited to the above embodiments and can be modified appropriately without departing from the spirit and scope of the present invention. [Industrial Applicability]

Regardless of the size of the space, the cleanroom of this invention, with its generally stable airflow characteristics, can provide a high-cleanliness environment for upstream processes in semiconductor manufacturing (such as photoresist filling) and organic EL coating, sealing, and lamination, where high cleanliness requirements have been increasing in recent years. Furthermore, the structure of this invention can be selectively applied not only when adding new cleanrooms, but also when modifying existing manufacturing processes.

This invention provides a shed structure that is particularly beneficial for reducing the significant costs associated with introducing mass production lines. Compared to conventional systems, the number of FFUs required for a high-quality clean shed can be reduced by up to 50% as initial cost. This energy-saving design also promises to reduce electricity consumption, which contributes to operating costs. While costs associated with additional components such as the double wall increase, the robust airflow characteristics with a strong self-cleaning effect can be expected to reduce the risk of yield degradation. Furthermore, the cost of post-operation equipment shutdowns due to shed environmental degradation and improved yields is lower than with conventional technologies.

Furthermore, the present invention provides a flow field that not only uniforms airflow, but also uniforms temperature distribution and mixed gas concentration distribution. For example, it can also be applied as a basic strategy for uniforming blown-out temperature and concentration and preventing the stagnation of hot or high-concentration gases in the greenhouse. This is effective when it is necessary to quickly reach a target temperature or concentration.

This is also a feature of the present invention that allows for its application as an airtight circulation shed structure. For example, it can be said that this technology not only meets ISO Class 3 cleanliness standards but also fully enables the creation of an atmosphere with a moisture and oxygen concentration of 1 ppm. For example, when this mechanism is used in a precise temperature environment, a dehumidified environment, or an inert gas environment, the outer wall 5, formed of insulating panels, is sealed by caulking to further enhance its airtightness and withstand an internal pressure of approximately 200 Pa. Furthermore, a gas (SG, Supply Gas) that controls the temperature and concentration of the top area flows in through an optionally installed conduit or piping. The inflow location and flow rate are determined using CFD. The air is thoroughly mixed within the ceiling area where the FFU2 is installed. After passing through the FFU2, it achieves a clean, uniform downward flow with a uniform temperature, moisture concentration, and inert gas concentration. A portion of the gas is circulated as RG (Return Gas) to the air conditioner, dehumidifier, and refiner. This duct or piping is installed on the side of the outer wall 5 and performs the same gas exchange within the cleanroom. The (A) full-surface blowout and (B) double-wall circulation mechanisms of the present invention possess a basic structure that can be expanded to these applications. Based on the actual performance requirements, numerical fluid dynamics (CFD) is used to predict flow deviations or stagnation within the cleanroom caused by turbulent mixing and circulation positions of the fluid in the ceiling. As described above, in addition to cleanliness, the present invention provides a basic cleanroom structure that meets even more stringent environmental maintenance requirements, such as temperature, dehumidification, and inert gas environments.

1: Cleanroom 2: Air purifier 3: Perforated plate 4: Inner wall 5: Outer wall 6: Device 7: Airflow/air guide mechanism 8: Localized suction mechanism

Figure 1 shows the configuration of the cleanroom of the present invention. Figure 2 compares the air velocity streamlines of (a) the prior art and (b) the present invention. Figure 3 compares the velocity vectors of (a) the prior art and (b) the present invention. Figure 4 compares the air age of (a) the prior art and (b) the present invention. Figure 5 compares the streamlines and air age of (a) the prior art and (b) the present invention.

1: Cleanroom 2: Air cleaning mechanism (coverage: ≤70%) 3: Perforated plate 4: Inner wall 5: Outer wall 6: Device 7: Rectification/air guide mechanism 8: Local suction mechanism (A): Blowing structure for achieving a high-quality clean environment (B): Double-wall structure for creating a uniform circulation path along the side of the shed (C): Rectification structure for reducing airflow turbulence, stagnation, and dust generation generated by various devices (D): Local suction mechanism

Claims (13)

A clean room, characterized in that a partitioning member is used to divide an area that meets ISO level 3 to 4 standards or even requires a higher cleanliness environment to partially form a clean room, an air cleaning mechanism is installed on the roof of the clean room, the filter occupancy rate of the air cleaning mechanism is set to be greater than 40% and less than 70%, a perforated plate is installed under the filter of the air cleaning mechanism, and the outer wall and the inner wall are covered to form a clean room. At least two or more side walls of the clean shed are double-walled. The outer wall is sealed to withstand an internal pressure of at least 50 Pa. A suction port is provided at the lower portion of the inner wall. Air within the clean shed is drawn in through the suction port, passed through the gap between the double walls, and circulated to the air cleaning mechanism. The clean room as described in claim 1, wherein the air cleaning mechanism is an FFU. The clean room as described in claim 1 or claim 2, wherein the perforated plate is provided within 200 mm below the filter of the air cleaning mechanism. A clean shed as described in claim 1 or claim 2, wherein the perforated plate is provided on the entire surface. A clean room as described in claim 1 or claim 2, wherein air is supplied through the perforated plate at an average airflow velocity of 0.1 to 0.5 m/s. The cleaning shed as described in claim 1 or claim 2, wherein the floor portion does not require a perforated floor. The clean shed as described in claim 1, wherein the gap between the outer wall and the inner wall is less than 200 mm. A clean room, characterized in that a partitioning member is used to divide an area that meets ISO Class 3 to Class 4 standards or even requires a higher cleanliness environment to partially form a clean room, an air cleaning mechanism is installed on the roof of the clean room, the filter occupancy rate of the air cleaning mechanism is set to be greater than 40% and less than 70%, a perforated plate is installed below the filter of the air cleaning mechanism, and a double wall is formed by covering at least two or more side walls of the clean room with an outer wall and an inner wall, and the outer wall is sealed to form an inner wall. The pressure can be at least 50Pa. An intake port is provided at the lower portion of the inner wall. Air within the clean shed is drawn in through the intake port, passed through the gap between the double walls, and circulated to the air cleaning mechanism. A device is provided within the clean shed, along with a rectifying/air guiding mechanism attached to the device, to set the air age around the device to no more than three times the theoretical value of the air age for an ideal downdraft. A cleaning shed as described in claim 8, wherein a local suction mechanism is provided around the aforementioned device. A clean room, characterized in that a partitioning member is used to divide an area that meets ISO Class 3 to Class 4 standards or even requires a higher cleanliness environment to partially form a clean room, an air cleaning mechanism is installed on the roof of the clean room, the filter occupancy rate of the air cleaning mechanism is set to be greater than 40% and less than 70%, a perforated plate is installed below the filter of the air cleaning mechanism, and a double wall is formed by covering at least two or more side walls of the clean room with an outer wall and an inner wall, and the outer wall is sealed to form a double wall. The internal pressure can withstand at least 50Pa. A suction port is provided at the lower portion of the inner wall. Air within the clean shed is drawn in through the suction port, passed through the gap between the double walls, and circulated to the air cleaning mechanism. A device is provided within the clean shed, and a local suction mechanism is provided around the device to set the air age around the device to no more than three times the theoretical value of the air age of an ideal downdraft. In the clean room as described in claim 9 or claim 10, the speed of the downward airflow generated by the aforementioned local suction mechanism near the bypass is less than 0.5 m/s. A clean shed as described in any one of claims 1 to 2, 7, 8 to 10, wherein the pressure inside the clean shed is positive compared to the pressure outside the clean shed. The clean room as described in claim 12, wherein the positive pressure is 20 to 40 Pa.