A wafer cooling system and method based on a rarefied heat transfer mechanism

Abstract

This invention relates to a wafer cooling system and method based on a rarefied heat transfer mechanism. The cooling system includes a main unit, a sensing device, and a control device. The main unit, housed within a vacuum lock, includes a cooling platform and a support unit for supporting the wafer. The control device controls the local lifting and lowering of the main unit to dynamically adjust the distance between the wafer and the cooling platform. The sensing device, electrically connected to the control device, includes a temperature sensor for real-time monitoring of the wafer surface temperature and cooling efficiency, and feeds the monitoring results back to the control device. The control device, connected to the main unit, includes a mass flow controller for controlling the gas flow rate and temperature of the cooling gas injected into the main unit, the pressure within the vacuum lock, the lifting and lowering of the ejector pins, and the height of the cooling platform. Compared with existing technologies, this invention offers advantages such as high efficiency, uniform cooling effect, safety, and high compatibility.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a wafer cooling system and method based on a rarefaction heat transfer mechanism. Background Technology

[0002] In many semiconductor manufacturing processes, reactions occur at high temperatures, such as in chemical vapor deposition (CVD) and resist stripping equipment. Therefore, when the substrate is removed from the reaction chamber, it is often at a considerably high temperature, such as 200-600°C. A common practice is to place a cooling chamber at a location on the transfer chamber, but this location is usually used to house the reaction chamber to further increase throughput. Some solutions opt for cooling bays on the Equipment Front End Modules (EFEM) that can hold multiple wafers. However, this method requires encroaching on the space of a loadport on the EFEM, increasing the lateral width of the equipment. Furthermore, during the high-temperature transfer of the wafer from the loadlock to the cooling chamber within the EFEM, exposure to the atmosphere can lead to over-oxidation or other reactions, defeating the purpose of cooling. Therefore, designing an effective cooling mechanism within the loadlock to allow the wafer to complete the cooling process before exposure to the atmosphere is the most reasonable choice.

[0003] Cooling bottlenecks using vacuum locks primarily occur in small vacuum locks known as single-wafer vacuum locks. In such systems, the reaction chamber typically has a very short per-wafer processing time, and the loadlock needs to transfer a large number of substrates. The time required for vacuum lock de-vacuuming, evacuation, and transfer of 25 wafers becomes the bottleneck (in multi-chamber systems with very short per-wafer processing times, the processing time for 25 wafers is shorter than the time it takes for the vacuum lock to complete one loading cycle). Therefore, the most common approach in this setup is to use small, single-wafer or a few-wafer (e.g., 5 or less) vacuum locks for transfer. Because the vacuum lock evacuation time is very short, a wafer in / out cycle can be completed in <20 seconds, further increasing system throughput (wafers per hour). A common configuration for this method is to use a double-layer vacuum lock; when the upper vacuum lock is opened for transfer, the lower layer simultaneously performs evacuation or de-vacuuming. This alternating cycle achieves high-speed transfer. In this configuration, because the waiting time within the vacuum lock is compressed to the extreme, natural cooling within the vacuum lock is not possible. An effective cooling mechanism needs to be designed so that the wafer can complete the entire cooling process within the vacuum lock.

[0004] In summary, wafer cooling is a critical step in the semiconductor manufacturing industry, especially after high-temperature processes (such as chemical vapor deposition (CVD) and resist stripping). Existing cooling methods typically take place in the transfer cavity or front-end module, but these methods have several problems: firstly, low equipment space utilization, especially when multiple wafer cooling cavities need to be set up in the front-end module; secondly, wafer exposure at high temperatures can lead to excessive oxidation or other adverse reactions, which defeats the purpose of cooling. In existing technologies, wafer cooling during transfer is often not fast or uniform enough, especially in monolithic wafer loadlock systems. These systems often face the dual challenges of efficiency and wafer safety when handling multi-cavity or high-temperature wafers that require rapid transfer. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide a wafer cooling system and method based on a rarefied heat transfer mechanism.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] According to one aspect of the present invention, a wafer cooling system based on a rarefied heat transfer mechanism is provided, comprising a main device, a sensing device, and a control device;

[0008] The main unit is housed within a vacuum lock and includes a cooling platform and a support unit for supporting the wafer. The control device controls the partial lifting and lowering of the main unit to dynamically adjust the distance between the wafer and the cooling platform. The cooling platform is equipped with nozzles for injecting or expelling cooling gas. The wafer is placed on top of the support unit and connected to the cooling platform below.

[0009] The sensing device is electrically connected to the control device, including a temperature sensor, which is used to monitor the wafer surface temperature and cooling efficiency in real time and feed the monitoring results back to the control device.

[0010] The control device is connected to the main unit and includes a mass flow controller, which is used to control the gas flow rate, gas temperature, vacuum lock pressure, and lifting and lowering of the main unit.

[0011] As a preferred technical solution, the cooling platform is provided with channels.

[0012] As a preferred technical solution, the cooling platform is a constant-temperature cooling wall surface, maintained by cooling water or coolant, and its materials specifically include stainless steel, light alloy, high-temperature alloy, high-entropy alloy or ceramic.

[0013] As a preferred technical solution, the nozzle includes a distributed nozzle or a central nozzle, and the nozzle is configured to be adjustable and telescopic.

[0014] As a preferred technical solution, the support unit includes a lifting pin, a floating pin, or a diverter plate, wherein the diverter plate is arranged in a multi-level interlaced manner.

[0015] According to another aspect of the present invention, a wafer cooling method based on a rarefied heat transfer mechanism is provided. This method is applied to a wafer cooling system based on a rarefied heat transfer mechanism as described above. In this method, the wafer is first brought into a vacuum lock and positioned on a support unit. During the cooling process, cooling gas is injected into the vacuum lock through a nozzle. The cooling gas acts as an intermediate heat storage medium, transferring heat from the wafer to the cooling platform. A sensing device monitors the wafer surface temperature and cooling efficiency in real time and feeds the monitoring results back to a control device. The control device uses the dynamic range of Knudsen number to adjust the gas flow rate of the cooling gas, the pressure inside the vacuum lock, and the height of the main device to control the wafer to be in a rarefied heat transfer state in the preset initial stage of vacuum breaking.

[0016] As a preferred technical solution, the mechanism for injecting cooling gas includes continuous gas injection or pulsed gas injection; the cooling gas is an inert gas, including nitrogen or argon.

[0017] As a preferred technical solution, after the preset initial stage of vacuum breaking, the control device adjusts the cooling gas flow rate mechanism to smoothly transition the wafer from a rarefied heat exchange state to a continuous flow heat exchange state.

[0018] As a preferred technical solution, the specific method for adjusting the cooling gas flow rate by the control device is to adopt a slow start strategy in flow control.

[0019] As a preferred technical solution, the specific formula for calculating the Knudsen number is as follows:

[0020] Kn=λ / L

[0021]

[0022] Where Kn is the Knudsen number, λ is the mean free path of gas molecules, L is the characteristic length in the fluid flow, and k B Here, is the Boltzmann constant, T is the absolute temperature of the gas, d is the effective diameter of the gas molecule, and P is the gas pressure.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. This invention first introduces a wafer into a vacuum lock and positions it on a support unit. During cooling, cooling gas is injected into the vacuum lock through nozzles. This cooling gas acts as an intermediate heat storage medium, transferring heat from the wafer to the cooling platform. Sensors monitor the wafer surface temperature and cooling efficiency in real time, feeding the results back to a control device. The control device utilizes the dynamic range of Knudsen number to adjust the cooling gas flow rate, the pressure within the vacuum lock, and the height of the main unit to ensure the wafer is in a rarefied heat transfer state during the initial stage of vacuum breaking. For different wafer surface temperatures, the system can switch between rarefied and Bernoulli heat transfer mechanisms to achieve optimal cooling. The rarefied heat transfer mechanism significantly shortens the wafer cooling time, allowing it to complete the main cooling process before vacuum breaking, demonstrating high efficiency.

[0025] 2. The cooling system of this invention includes a main unit, a sensing device, and a control device. The main unit, housed within a vacuum lock, includes a cooling platform and a support unit for supporting the wafer. The control device controls its local lifting and lowering to dynamically adjust the distance between the wafer and the cooling platform. The sensing device, electrically connected to the control device, includes a temperature sensor for real-time monitoring of the wafer surface temperature and cooling efficiency, and feeds the monitoring results back to the control device. The control device, connected to the main unit, includes a mass flow controller for controlling the gas flow rate, gas temperature, vacuum lock pressure, pin lifting and lowering, and the height of the cooling platform of the cooling gas injected into the main unit. This structural design helps stabilize the wafer's position while allowing necessary minor movements during cooling to optimize heat transfer. It also avoids the impact of micro-deformation of the wafer at high temperatures on the uniformity of the distance between the wafer and the cooling base. With the established feedback mechanism, the support device can be dynamically configured based on the temperature difference at each location, ensuring that Bernoulli flow rate, velocity, and compressive stress are all optimal.

[0026] 3. In this invention, the control device is connected to the main device. The cooling platform is a constant-temperature cooling wall surface, maintained by cooling water or coolant. Its materials specifically include stainless steel, light alloys, high-temperature alloys, high-entropy alloys, or ceramics. It includes a mass flow controller for controlling the gas flow rate, gas temperature, vacuum lock pressure, pin lifting, and cooling platform height of the cooling gas injected into the main device. Dynamic adjustment of the distance between the wafer and the cooling platform ensures uniform cooling effect and reduces wafer stress.

[0027] 4. In this invention, the main device is housed within a vacuum lock, and the injected cooling gas is an inert gas, including nitrogen or argon. This prevents the wafer from being exposed to the atmospheric environment at high temperatures, thus preventing adverse reactions such as oxidation and ensuring safety.

[0028] 5. The cooling system of this invention includes a main unit, a sensing device, and a control device. The main unit is housed within a vacuum lock and includes a cooling platform and a support unit. The support unit includes a rising ejector pin, a floating ejector pin, or a flow divider plate to ensure the stability and heat transfer efficiency of the wafer during the cooling process. These structures can dynamically adjust the distance between the wafer and the cooling surface, eliminating the adverse effects of wafer deformation caused by high temperatures on the heat transfer effect. The cooling platform is equipped with channels and nozzles. The nozzles include distributed nozzles or central nozzles, and the nozzles are configured as adjustable and retractable. The modular design facilitates integration with existing multi-cavity systems and ensures compatibility.

[0029] 6. In this invention, a channel is provided on the cooling platform. The channel is combined with a liftable ejector pin to maintain the wafer in a rarefied heat transfer state and ensure that the gas flow rate, velocity and compressive stress are all in the optimal state.

[0030] 7. In this invention, the flow dividers are arranged in a multi-stage interlaced manner to ensure the uniformity of gas flow rate.

[0031] 8. In this invention, after the preset initial stage of vacuum breaking, the control device adjusts the cooling gas flow rate mechanism to smoothly transition the wafer from a rarefied heat transfer state to a continuous flow heat transfer state. During the vacuum breaking process, a slow-start strategy extends the rarefied heat transfer stage, further optimizing cooling efficiency.

[0032] 9. In this invention, the nozzle includes a distributed nozzle or a central nozzle, combined with multi-stage flow channels to ensure uniform distribution of cooling gas and improve the heat transfer uniformity of the wafer surface. The nozzle is configured as an adjustable telescopic type to accommodate wafers of different sizes and materials. Attached Figure Description

[0033] Figure 1 This is a flowchart of a wafer cooling method based on a rarefaction heat transfer mechanism in an embodiment.

[0034] Figure 2 This example illustrates the relationship between slit distance and heat transfer coefficient under different air pressures.

[0035] Figure 3 This is a side view of the distributed air intake wafer cooling system in the embodiment;

[0036] Figure 4 This is a top view of the distributed air intake wafer cooling system in the embodiment;

[0037] Figure 5 This is a side view of the center-inlet wafer cooling system in the embodiment;

[0038] Figure 6 This is a top view of the center-inlet wafer cooling system in the embodiment. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0040] In many semiconductor manufacturing processes, reactions occur at high temperatures, such as in chemical vapor deposition (CVD) and resist stripping equipment. Therefore, when the substrate is removed from the reaction chamber, it is often at a considerably high temperature, such as 200-600°C. A common practice is to place a cooling chamber at a location on the transfer chamber, but this location is usually used for the reaction chamber to further increase throughput. Therefore, it is not a preferred solution in most cases. Some solutions opt for cooling bays on the front-end module that can hold multiple wafers. However, this method requires encroaching on the space of a loading device on the EFEM, increasing the lateral width of the equipment. Furthermore, during the high-temperature transfer of the wafer from the vacuum lock to the cooling chamber in the EFEM, exposure to the atmosphere can lead to over-oxidation or other reactions, defeating the purpose of cooling. Therefore, designing an effective cooling mechanism within the vacuum lock, allowing the wafer to complete the cooling process before exposure to the atmosphere, is the most reasonable choice.

[0041] In multi-chamber systems, batch vacuum locks typically do not require additional cooling systems. A standard batch vacuum lock can hold 25 wafers at a time. By the time the last wafer finishes its operation, the first 24 wafers have already waited a considerable amount of time. This time is sufficient for the first 20 to 23 wafers to cool down. When the vacuum lock opens and connects to the outside, the robotic arm on the EFEM side begins transporting wafers. As long as the EFEM-side robotic arm prioritizes the substrates that entered the vacuum lock earliest according to the first-in, first-out principle, the last 2-3 wafers with the highest temperatures also have ample time for further cooling. A 25-wafer batch vacuum lock does not require additional cooling design for wafers operating at 300°C or higher.

[0042] In fact, for substrates with higher temperatures, waiting a few extra minutes for the last wafer in a batch of vacuum locks will not have a significant impact on the overall throughput of the equipment, and the impact is negligible. This is because, typically, another vacuum lock has already started working by this time, occupying the vacuum-side robotic arm. The atmospheric robotic arm on the EFEM side has sufficient time to wait.

[0043] In fact, the cooling bottleneck when using vacuum locks for cooling mainly occurs in small vacuum locks called single-wafer vacuum locks. In such systems, the reaction chamber typically has a very short working time per wafer, and the vacuum lock needs to transport a large number of substrates. At this point, the time required for vacuum lock de-vacuuming, vacuum pumping, and transporting 25 wafers becomes the bottleneck (in multi-cavity systems with very short process times per wafer, the time to complete the process for 25 wafers is shorter than the time it takes for the vacuum lock to complete one loading cycle). Therefore, the most common method in this equipment setup is to use small single-wafer or a few-wafer (e.g., 5 or less) vacuum locks for transport. Because the vacuum lock evacuation time is very short, a wafer in / out cycle can be completed in <20 seconds, further increasing system throughput (wafers per hour). A common configuration for this method is to use upper and lower double-layer vacuum locks. When the upper vacuum lock is opened for transport, the lower layer simultaneously performs evacuation or vacuum de-vacuuming. This alternating cycle achieves high-speed transport. In this configuration, because the waiting time within the vacuum lock is compressed to the extreme, natural cooling within the vacuum lock is not possible. An effective cooling mechanism needs to be designed so that the wafer can complete the entire cooling process within the vacuum lock.

[0044] In summary, wafer cooling is a critical step in the semiconductor manufacturing industry, especially after high-temperature processes such as chemical vapor deposition (CVD) and resist stripping. Existing cooling methods typically take place in the transfer cavity or front-end module, but these methods have several drawbacks: firstly, low equipment space utilization, particularly when multiple wafer cooling cavities need to be housed within the EFEM front-end module; secondly, wafer exposure at high temperatures can lead to excessive oxidation or other adverse reactions, defeating the purpose of cooling. In existing technologies, wafer cooling during transfer is often not fast or uniform enough, especially in single-wafer vacuum lock systems. These systems often face the dual challenges of efficiency and wafer safety when handling multi-cavity or high-temperature wafers requiring rapid transfer.

[0045] To address these issues, this application proposes an innovative cooling solution that integrates a cooling mechanism based on the rarefaction heat transfer principle within a vacuum lock. Through mechanical design, a rarefaction heat transfer phase is created during the vacuum breaking stage of the completed wafer within the vacuum lock. This design aims to achieve efficient, uniform cooling with proper wafer stress control, while avoiding additional space requirements and the risks associated with wafer exposure. In this way, the invention not only improves the efficiency and safety of wafer processing but also provides the semiconductor manufacturing industry with a more advanced and reliable cooling solution.

[0046] In rarefied heat transfer, the number of gas molecules is very small in narrow gaps, and continuum mechanics can no longer explain the gas flow. In this case, the interaction between the gas and the rigid body plays a crucial role. For this rarefied gas, the heat transfer efficiency is greatly improved due to the reduced collisions between gas particles. In microscale environments, the Knudsen number (comparing the mean free path of gas molecules to their characteristic length) is usually high, indicating that the gas flow is in a rarefied state. In this state, the number of collisions between gas molecules is reduced, resulting in gas heat transfer mainly occurring through direct molecular-to-surface interactions. In small-scale systems, surface effects become more significant. Due to the increased surface area to volume ratio, the interaction between gas molecules and the wall plays a crucial role in the heat transfer process. In this environment, by precisely controlling the distance between the wafer and the cooling surface and the ambient pressure, heat can be effectively removed from the wafer using the rarefied heat transfer principle, achieving rapid and uniform cooling.

[0047] This application addresses numerous shortcomings of existing technologies in semiconductor device wafer cooling processes by proposing a wafer cooling system based on a rarefied heat transfer mechanism. This system combines mechanical design with gas dynamics characteristics to create a rarefied heat transfer environment within a vacuum lock, achieving rapid and efficient cooling of high-temperature wafers. It includes dynamic control of the rarefied heat transfer environment, mechanical structure optimization, a multi-stage cooling mechanism, gas flow field optimization, and dynamic feedback regulation.

[0048] Specifically, the dynamic control of the rarefied heat transfer environment involves precisely adjusting the distance between the wafer and the cooling platform (e.g., 50 μm) and combining this with real-time pressure monitoring. Utilizing the dynamic range of the Knudsen number, the wafer cooling is ensured to remain in the optimal rarefied heat transfer state. In the initial stage of vacuum breaking (0–47.63 Torr for 50 μm), the rarefied heat transfer efficiency is significantly higher than that of conventional continuous medium cooling.

[0049] The mechanical structure optimization specifically involves designing various mechanical support structures, such as liftable ejector pins and multi-stage flow dividers, to ensure the stability and heat transfer efficiency of the wafer during the cooling process. These structures can dynamically adjust the distance between the wafer and the cooling surface, eliminating the adverse effects of wafer warping caused by high temperatures on the heat transfer effect.

[0050] The multi-stage cooling mechanism is as follows: In this application, rarefied heat transfer and continuous medium heat transfer are combined. As the pressure range gradually increases (>47.63 Torr), the airflow smoothly transitions from rarefied heat transfer to continuous flow heat transfer. In addition, a slow-start strategy is used during the vacuum breaking process to extend the rarefied heat transfer stage, further optimizing the cooling efficiency.

[0051] The gas flow field optimization is as follows: This application integrates a distributed or central nozzle design, combined with the airflow guidance of multi-stage flow channels, to ensure uniform distribution of cooling gas and improve the heat transfer uniformity of the wafer surface.

[0052] The dynamic feedback control is specifically implemented by introducing temperature sensors and flow control components, such as a mass flow controller (MFC), in this application. By monitoring the wafer surface temperature and cooling efficiency in real time, the gas flow rate, pressure, and cooling platform height are automatically adjusted to achieve intelligent cooling.

[0053] This solution is applicable to various high-temperature wafer cooling scenarios, including single-wafer vacuum locks and multi-wafer batch vacuum locks. Its modular design facilitates integration with existing semiconductor equipment, significantly improving wafer processing efficiency and equipment capacity.

[0054] Example 1

[0055] In this embodiment, a wafer cooling system based on a rarefaction heat transfer mechanism is applied. The system includes a main device, a sensing device, and a control device.

[0056] The main unit is housed within a vacuum lock and includes a cooling platform and a support unit for supporting the wafer. The control device controls the local lifting and lowering of the wafer to dynamically adjust the distance between the wafer and the cooling platform. The cooling platform is equipped with nozzles for injecting or expelling cooling gas. The wafer is placed above the support unit and connected to the cooling platform below, including lifting pins, floating pins, or flow dividers.

[0057] The sensing device is electrically connected to the control device, including a temperature sensor, which is used to monitor the wafer surface temperature and cooling efficiency in real time and feed the monitoring results back to the control device.

[0058] The control device is connected to the main unit and includes a mass flow controller, which is used to control the gas flow rate, gas temperature, vacuum lock pressure, ejector pin lifting and lowering, and cooling platform height of the cooling gas injected into the main unit.

[0059] The cooling platform is equipped with channels and features a constant-temperature cooling wall surface maintained by cooling water or coolant. The materials used include stainless steel, light alloys, high-temperature alloys, high-entropy alloys, or ceramics. The nozzles can be distributed or centrally located, and are configured for adjustable telescopic movement. The flow dividers in the support unit are arranged in a multi-stage, interlaced manner.

[0060] In this embodiment, the system structure is as follows: Figure 3 , Figure 4As shown, this includes one or more liftable ejector pins (or other types of floating supports) and a vertically movable supporting sheath. These support points have edge grooves to limit their sliding within a specific range. This design helps stabilize the wafer's position while allowing necessary minor movements during cooling to optimize heat transfer. Alternatively, a structure combining a supporting sheath and a liftable base can be used. This structural design avoids the impact of micro-deformation of the wafer at high temperatures on the uniformity of the spacing between the wafer and the cooling base. With a feedback mechanism in place, the ejector pin height can be dynamically configured based on the temperature difference at each location.

[0061] In this embodiment, multi-nozzle technology is applied, and the system is equipped with distributed nozzles for air intake. The nozzles can be designed in a distributed manner to generate a negative pressure that is uniformly distributed along the wafer surface. In addition to facilitating the creation of a rarefied heat exchange environment, this air intake method, with the help of the weak downward pressure it generates, can also make the wafer more stably drawn downward, promoting heat exchange between the wafer and the cooling surface, while reducing the internal stress that may be generated in the wafer during the cooling process.

[0062] In this embodiment, rarefied heat transfer and flow heat transfer are combined. In a vacuum environment, a rarefied space is created using floating pins or supports, forming a rarefied heat transfer environment between the wafer and the cooling surface, thereby greatly improving heat transfer efficiency. When the vacuum is broken to above the rarefied heat transfer pressure threshold, the system switches to a continuous medium model cooling mechanism, that is, at the nozzle where the vacuum is broken, it enters the flow heat transfer stage.

[0063] In this embodiment, the cooling platform is designed with specially designed channels, combined with liftable pins, to maintain the wafer in a rarefied heat transfer state and ensure that the Bernoulli flow rate, flow velocity, and compressive stress are all at their optimal levels.

[0064] In this embodiment, the temperature-dependent heat transfer mechanism is controlled. For different wafer surface temperatures, the system can switch between rarefaction heat transfer and Bernoulli heat transfer mechanisms as needed to achieve the best cooling effect.

[0065] In this embodiment, the implementation method of the system is as follows: Figure 1As shown, first, the pressure is balanced, then the vacuum lock door is opened. The wafer is carried into the vacuum lock by the wafer automatic transfer robot and positioned on the support unit. The wafer automatic transfer robot retracts to the atmospheric environment, and the vacuum lock door is closed. During the cooling process, cooling gas is introduced into the vacuum lock through the nozzle. The cooling gas serves as an intermediate heat storage body to transfer heat from the wafer to the cooling platform. The sensing device monitors the wafer surface temperature and cooling efficiency in real time and feeds back the monitoring results to the control device. The control device adjusts the gas flow rate of the cooling gas, the lifting of the pressure thimble in the vacuum lock, and the height of the cooling platform using the dynamic change range of the Knudsen number to control the wafer to be in a state of rarefied heat transfer during the initial stage of preset vacuum breaking. The lifting pin is controlled to lower or the base is raised to vent air into the vacuum lock to break the vacuum, and distributed multi-port jetting is performed. Finally, the wafer automatic transfer robot in the atmosphere takes the wafer out of the vacuum lock.

[0066] In this embodiment, the evaluation of the rarefied heat transfer effect first calculates the pressure boundary of the rarefied gas heat transfer in the vacuum lock with the help of the Knudsen number:

[0067] The Knudsen number (usually denoted as Kn) is a dimensionless number used to describe the ratio of the mean free path of molecules in gas flow to a certain characteristic length (such as the diameter of the flow channel, the size of particles, etc.). It is an important parameter for understanding rarefied gas dynamics and is mainly used in the fields of fluid mechanics and gas dynamics.

[0068] The Knudsen number is defined as:

[0069] Kn = λ / L

[0070] Where, λ is the mean free path of gas molecules, that is, the average travel distance of molecules between two consecutive collisions; L is the characteristic length in fluid flow, such as the pipe diameter or particle size.

[0071] The magnitude of the Knudsen number is used to distinguish different fluid flow regions: Kn < 0.01 is the continuum flow region, and the traditional Navier - Stokes equations can be used to describe it; 0.01 < Kn < 0.1 is the slip flow region, and the slip effect between molecules and the boundary needs to be considered; 0.1 < Kn < 10 is the transitional flow region, where molecular motion begins to dominate and the continuum model is no longer applicable; Kn > 10 is the free molecular flow region, where the interaction between molecules is much smaller than the interaction with the container boundary.

[0072] For the designed vacuum lock cavity, assuming the height of the floating pin / lift pin is set at 50um, that is, the gap size between the wafer and the base at this time, the characteristic length is 50um, the gas is nitrogen, and the temperature is 25°C. The pressure is used to distinguish different fluid flow regions, and the mean free path of the gas can be estimated by the following formula:

[0073]

[0074] where λ is the mean free path of the gas, in meters; k B is the Boltzmann constant, which is 1.38×10 -23 J / K; T is the absolute temperature of the gas, in Kelvin; d is the effective diameter of the gas molecule, in meters. In this embodiment, the effective diameter of the nitrogen gas molecule is 3.6×10 -10 m; P is the pressure of the gas, in Pascal, Pa.

[0075] When the characteristic dimension is 50 μm, the corresponding gas pressure boundary value (unit: Torr) is:

[0076] Continuous flow region (Kn < 0.01): the upper limit gas pressure is about 476.25 Torr;

[0077] Slip flow region (0.01 < Kn < 0.1): the upper and lower limits are 476.25 Torr and 47.63 Torr respectively;

[0078] Transition flow region (0.1 < Kn < 10): the upper and lower limits are 47.63 Torr and 0.48 Torr respectively;

[0079] Free molecular flow region (Kn > 10): the lower limit gas pressure is about 0.48 Torr.

[0080] Therefore, from the start of vacuum break to 47.63 Torr, it is considered to be in the thin heat transfer. In addition, for thin heat transfer, there is a relationship between the slit distance and the heat transfer coefficient at different gas pressures, based on the self-built heat transfer model and the DSMC Monte Carlo model. In this embodiment, as Figure 2 shown, within the low-pressure range within 100 Torr, the heat transfer coefficients under two slit gaps are generally similar, and the slit size does not show an obvious influence on the heat transfer coefficient. This is mainly because the molecular mean free path is much larger than the slit distance. Under certain pressure conditions, even if the slit distance becomes larger, the influence on the heat conduction effect is small. However, considering the analytical heat transfer model, the slit size d usually affects the heat transfer coefficient h in the form of the denominator. For example, in the comprehensive heat transfer formula:

[0081]

[0082] Therefore, referring to the heat transfer coefficients at different pressures, the boundary pressure corresponding to the thin condition is 47.63 torr, and the corresponding heat transfer coefficient is about h = 7000 W / m 2*K, considering the linear variation in logarithmic coordinates and the actual influence of the slit size, h = 3500 is chosen for the purging process from 0 to 47.63 torr. This is based on the application of Newton's law of cooling and the law of conservation of energy. Newton's law of cooling describes the heat exchange between an object and its surrounding environment, and its formula is:

[0083] Q=hAΔT

[0084] Where Q is the heat transfer rate, measured in W; and h is the heat transfer coefficient, measured in W / m³. 2 K; A is the heat exchange surface area, in m². 2 ΔT is the temperature difference between an object and its environment, measured in Kelvin (K).

[0085] For cooling silicon wafers, this formula can be combined with the energy conservation equation to calculate the temperature change of the silicon wafer over time. The energy conservation equation is:

[0086] mc*dT / dt=-hAΔT

[0087] Where m is the mass of the silicon wafer in kg, calculated to be 132g; c is the specific heat capacity of the silicon wafer in J / kg·K; dT / dt is the rate of temperature change over time; and -hAΔT represents the heat lost by the silicon wafer.

[0088] Therefore, for a 12-inch wafer at 250℃, with a thickness of 775µm, the density is 2330kg / m³. 3 With a specific heat capacity of 700 J / (kg·K), its heat transfer to a cold wall surface maintained at 18°C ​​can be calculated. The silicon wafer cooling temperatures at 0.1-second intervals from 0 to 0.5 seconds are as follows: 250.0°C at 0.0 seconds; approximately 193.89°C at 0.1 seconds; approximately 151.35°C at 0.2 seconds; approximately 119.09°C at 0.3 seconds; approximately 94.64°C at 0.4 seconds; and approximately 76.11°C at 0.5 seconds.

[0089] In this embodiment, under normal circumstances, the vacuum lock breaking process is completed within 5 to 10 seconds, so the time to reach 47.63 torr is 0.1 to 0.2 seconds, meaning the rarefaction heat transfer time is 0.1 to 0.2 seconds. Within this extremely short time, the contribution of rarefaction heat transfer to wafer cooling is significant. If a slow-then-fast approach is adopted during vacuum breaking, the rarefaction heat transfer time can be increased, further enhancing its contribution to cooling.

[0090] Example 2

[0091] In this embodiment, a wafer cooling method based on a rarefied heat transfer mechanism is applied. In this method, the wafer is first brought into a vacuum lock and positioned on a support unit. During the cooling process, cooling gas is injected into the vacuum lock through a nozzle. The cooling gas acts as an intermediate heat storage medium, transferring heat from the wafer to the cooling platform. A sensing device monitors the wafer surface temperature and cooling efficiency in real time and feeds the monitoring results back to the control device. The control device uses the dynamic range of Knudsen number to adjust the gas flow rate of the cooling gas, the lifting and lowering of the pressure pin in the vacuum lock, and the height of the cooling platform to control the wafer to be in a rarefied heat transfer state in the preset initial stage of vacuum breaking.

[0092] The cooling gas injection mechanism includes continuous injection or pulsed injection; the cooling gas is an inert gas, including nitrogen or argon. After the preset initial vacuum breaking stage, the control device adjusts the cooling gas flow rate mechanism to smoothly transition the wafer from a rarefied heat transfer state to a continuous flow heat transfer state. The specific method for adjusting the cooling gas flow rate mechanism by the control device is to adopt a slow start strategy in flow control.

[0093] Once vacuum breaking begins, the vacuum breaking orifice can also function as a nozzle. The system can adjust the gas flow rate during vacuum breaking, thereby extending the time the wafer remains in a rarefied heat transfer state.

[0094] Raised heat transfer can be dynamically adjusted based on the spacing (feature dimension) between the wafer and the cooling surface, combined with the vacuum breaking time, while meeting the Knudsen number boundary conditions. In other words, the ratio of rarefied to continuous flow heat transfer can be optimized according to the actual process requirements. The specific formula for calculating the Knudsen number is:

[0095] Kn=λ / L

[0096]

[0097] Where Kn is the Knudsen number, λ is the mean free path of gas molecules, L is the characteristic length in the fluid flow, and k B Here, is the Boltzmann constant, T is the absolute temperature of the gas, d is the effective diameter of the gas molecule, and P is the gas pressure.

[0098] In this embodiment, the method is applied to a wafer cooling system, which includes a main device, a sensing device, and a control device.

[0099] The main unit, housed within a vacuum lock, includes a cooling platform and a support unit for supporting the wafer. Its localized lifting and lowering is controlled by a control device to dynamically adjust the distance between the wafer and the cooling platform. The cooling platform is equipped with nozzles for injecting or expelling cooling gas. These nozzles are adjustable and retractable to accommodate wafers of different sizes and materials. The gas inlet method can be parallel or perpendicular to the wafer, depending on the design of the cooling platform, particularly the configuration of the flow channels. The cooling gas injection mechanism can be continuous or pulsed, designed to maintain a consistent temperature difference (ΔT) generated by heat transfer on the wafer surface.

[0100] A wafer is placed above a support unit, and a cooling platform is connected below it. This platform includes rising ejector pins, floating ejector pins, or flow dividers, creating a space between the wafer and the cooling surface that allows for efficient heat transfer of the rarefied gas. Multiple ejector pin units and air inlet nozzles are mounted on the cooling platform to generate a stable adsorption force between the wafer and the platform. The cooling platform features specially designed channels, combined with rising ejector pins, to maintain the wafer in a rarefied heat transfer state and ensure optimal gas flow rate, velocity, and compressive stress. The support device for the cooling platform has a rising structure, allowing for dynamic adjustment of the distance between it and the lower surface of the wafer.

[0101] The cooling platform can be made of stainless steel, light alloys, high-temperature alloys, high-entropy alloys, ceramics, or other easily machinable metals or non-metals with good heat transfer properties, or composite materials. The cooling platform has a constant-temperature cooling wall surface, which can be maintained using cooling water or other coolants. The cooling platform or base can move vertically.

[0102] The sensing device is electrically connected to the control device, including a temperature sensor, which is used to monitor the wafer surface temperature and cooling efficiency in real time and feed the monitoring results back to the control device.

[0103] The control device is connected to the main unit and includes a mass flow controller, which is used to control the gas flow rate, gas temperature, vacuum lock pressure, ejector pin lifting and lowering, and cooling platform height of the cooling gas injected into the main unit.

[0104] In this embodiment, the lifting and lowering of the ejector pin is controlled by a control device, and a mechanism for injecting cooling gas is configured to configure rarefied heat exchange cooling conditions and adjust the gas flow rate and temperature through the nozzle to achieve effective cooling of the wafer.

[0105] The control unit may include an MFC mass flow controller, temperature sensors, etc., to monitor the wafer surface temperature and adjust the gas flow rate and temperature based on the monitoring results.

[0106] In this embodiment, as Figure 4 , Figure 5As shown, the support unit employs a miniature multi-stage flow divider. The system includes three or more miniature flow dividers (or other types of floating supports), which function as wafer supports. This design helps stabilize the wafer's position and precisely control the airflow distribution, ensuring that the flow velocity at each location is essentially consistent. The miniature flow dividers can be interleaved in multiple stages to ensure the uniformity of gas flow velocity.

[0107] In this embodiment, the cooling platform is equipped with nozzles, specifically a central air inlet located at the bottom of the system. This guides the cooling gas to flow uniformly into the system, creating a low-pressure zone that causes the wafer to adhere downwards to the cooling surface. Simultaneously, the high-speed airflow promotes heat exchange between the wafer and the cooling surface. The cooling platform features specially designed flow dividers to guide the airflow distribution. The distribution of the flow dividers can also be adjusted based on flow rate differences to prevent wafer stress or damage caused by temperature gradients. In a vacuum environment, multiple stages of micro-flow dividers are configured between the wafer and the substrate, creating a rarefied heat exchange environment between the wafer and the cooling surface, thereby significantly improving heat transfer efficiency. By rationally controlling the gas flow rate and optimizing the distribution of the flow dividers, contactless cooling between the wafer and the cooling pad can be achieved, forming a thin air cushion within the space. Furthermore, the system can switch between rarefied heat exchange and flow heat exchange as needed to achieve optimal cooling performance for different wafer surface temperatures.

[0108] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A wafer cooling system based on a rarefied heat transfer mechanism, characterized in that, It includes the main unit, sensing device, and control device; The main unit is housed within a vacuum lock and includes a cooling platform and a support unit for supporting the wafer. The control device controls the partial lifting and lowering of the main unit to dynamically adjust the distance between the wafer and the cooling platform. The cooling platform is equipped with nozzles for injecting or expelling cooling gas. The wafer is placed on top of the support unit and connected to the cooling platform below. The sensing device is electrically connected to the control device, including a temperature sensor, which is used to monitor the wafer surface temperature and cooling efficiency in real time and feed the monitoring results back to the control device. The control device is connected to the main unit and includes a mass flow controller for controlling the gas flow rate, gas temperature, vacuum lock pressure, and lifting / lowering of the main unit.

2. The wafer cooling system based on a rarefaction heat transfer mechanism according to claim 1, characterized in that, The cooling platform is provided with channels.

3. A wafer cooling system based on a rarefaction heat transfer mechanism according to claim 1, characterized in that, The cooling platform is a constant-temperature cooling wall surface, maintained by cooling water or coolant, and its materials specifically include stainless steel, light alloy, high-temperature alloy, high-entropy alloy or ceramic.

4. A wafer cooling system based on a rarefaction heat transfer mechanism according to claim 1, characterized in that, The nozzles include distributed nozzles or central nozzles, and the nozzles are configured to be adjustable and telescopic.

5. A wafer cooling system based on a rarefaction heat transfer mechanism according to claim 1, characterized in that, The support unit includes a lifting pin, a floating pin, or a diverter plate, wherein the diverter plate is arranged in a multi-level interlaced manner.

6. A wafer cooling method based on a rarefaction heat transfer mechanism, characterized in that, This method is applied to a wafer cooling system based on a rarefied heat transfer mechanism as described in any one of claims 1-5. In this method, the wafer is first brought into a vacuum lock and positioned on a support unit. During the cooling process, cooling gas is injected into the vacuum lock through nozzles. The cooling gas acts as an intermediate heat storage medium, transferring heat from the wafer to the cooling platform. The wafer surface temperature and cooling efficiency are monitored in real time by a sensing device, and the monitoring results are fed back to the control device. The control device uses the dynamic range of Knudsen number to adjust the gas flow rate of the cooling gas, the pressure inside the vacuum lock, and the height of the main device to control the wafer to be in a rarefied heat transfer state in the preset initial stage of vacuum breaking.

7. A wafer cooling method based on a rarefaction heat transfer mechanism according to claim 6, characterized in that, The mechanism for injecting cooling gas includes continuous injection or pulsed injection; the cooling gas is an inert gas, including nitrogen or argon.

8. A wafer cooling method based on a rarefaction heat transfer mechanism according to claim 6, characterized in that, After the preset initial stage of vacuum breaking, the control device adjusts the cooling gas flow rate mechanism to smoothly transition the wafer from a rarefied heat exchange state to a continuous flow heat exchange state.

9. A wafer cooling method based on a rarefaction heat transfer mechanism according to claim 8, characterized in that, The specific method for adjusting the cooling gas flow rate by the control device is as follows: a slow start strategy in flow control is adopted.

10. A wafer cooling method based on a rarefaction heat transfer mechanism according to claim 6, characterized in that, The specific formula for calculating the Knudsen number is as follows: Kn=λ / L Where Kn is the Knudsen number, λ is the mean free path of gas molecules, L is the characteristic length in the fluid flow, and k B Here, is the Boltzmann constant, T is the absolute temperature of the gas, d is the effective diameter of the gas molecule, and P is the gas pressure.

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