Wafer cooling system and method based on rarefied heat exchange mechanism

Abstract

The invention relates to a wafer cooling system and method based on a rarefied heat exchange mechanism. The cooling system comprises a main body device, a sensing device and a control device, the main body device is arranged in the vacuum lock, comprises a cooling platform and a supporting unit and is used for supporting a wafer, and the control device controls local lifting of the main body device so as to dynamically adjust the distance between the wafer and the cooling platform; the sensing device is electrically connected with the control device, comprises a temperature sensor and is used for monitoring the surface temperature and the cooling efficiency of the wafer in real time and feeding back a monitoring result to the control device; and the control device is connected with the main body device, comprises a mass flow controller and is used for controlling the gas flow and the gas temperature of the cooling gas injected by the main body device, the pressure in the vacuum lock, the lifting of the ejector pin and the height of the cooling platform. Compared with the prior art, the device has the advantages of high efficiency, uniform cooling effect, safety, high compatibility and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor manufacturing, and particularly to a wafer cooling system and method based on a rarefied heat transfer mechanism. Background Art

[0002] In many semiconductor manufacturing processes, the reaction has a relatively high temperature. Such as chemical vapor deposition (CVD), de-glueing equipment, etc. Therefore, when the substrate is taken out of the reaction chamber, it often has a quite high temperature, such as 200 - 600 °C. The common practice is to set a cooling chamber at a certain position on the transfer chamber, but this position is usually used to set the reaction chamber to further improve production capacity. There are also some solutions that choose to set a cooling tank capable of storing multiple wafers on the Equipment Front End Modules (EFEM). However, this method requires occupying the position of a loading device (Loadport) on an EFEM, expanding the lateral width of the equipment. At the same time, when the wafer is transferred from the vacuum lock (Loadlock) to the cooling chamber in the EFEM at a relatively high temperature, it is exposed to the atmosphere, which may cause excessive oxidation or other reactions. This goes against the original intention of cooling. Therefore, designing an effective cooling mechanism in the vacuum lock so that the wafer can complete the cooling process before being exposed to the atmosphere is the most reasonable choice.

[0003] The cooling bottleneck that occurs when using the vacuum lock for cooling mainly appears in a small vacuum lock called a single-wafer vacuum lock. In such a system, usually, each wafer has a very short working time in the reaction chamber, and the Loadloack needs to transfer a large number of substrates. At this time, the time for the vacuum lock to break vacuum, pump vacuum, and transfer 25 wafers becomes the bottleneck (in the case of multiple chambers and a very short process time per wafer, the process time for 25 wafers is shorter than the time for the vacuum lock to complete one loading). Therefore, the most common method in this equipment setting is to use a small single-piece or a small number of pieces (such as <= 5) of vacuum locks for transfer. At this time, because the vacuum pumping time of the vacuum lock is very short, a wafer in-and-out cycle can be completed in < 20 s, which can further increase the output of the system (number of wafers per hour). A common setting of this method is to use an upper and lower double-layer vacuum lock. When the upper vacuum lock is opened for transfer, the lower layer simultaneously performs actions such as pumping air or breaking vacuum. Alternating in a cycle to complete high-speed transfer. In this setting, since the waiting time in the vacuum lock is compressed to the extreme, it is impossible to complete the cooling process in the vacuum lock through natural cooling. It is necessary to further design an effective cooling mechanism so that the wafer can complete the entire cooling process in the vacuum lock.

[0004] In summary, in the semiconductor manufacturing industry, especially after high-temperature processes (such as chemical vapor deposition CVD and the ashing process), wafer cooling is a crucial step. Existing cooling methods are usually carried out in the transfer chamber or the front-end module, but these methods have several problems: one is the low utilization rate of equipment space, especially when cooling cavities for multiple wafers need to be set in the front-end module; the other is that the exposure of wafers at high temperatures may lead to excessive oxidation or other adverse reactions, which goes against the original intention of cooling. In the prior art, the cooling of wafers during the transfer process is usually not fast or uniform enough, especially in the single-wafer loadlock system. These systems often face the dual challenges of efficiency and wafer safety when dealing with multi-chamber or high-temperature wafers that require rapid transfer. Summary of the Invention

[0005] The object of the present invention is to overcome the defects of the above-mentioned prior art and provide a wafer cooling system and method based on the rarefied heat transfer mechanism.

[0006] The object of the present invention can be achieved by the following technical solutions:

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

[0008] The main body device is arranged in the vacuum lock and includes a cooling platform and a support unit, which is used to support the wafer and the local lifting of the main body device is controlled by the control device to dynamically adjust the distance between the wafer and the cooling platform; wherein, a nozzle is provided on the cooling platform, and the nozzle is used to inject or discharge the cooling gas; the wafer is placed above the support unit and is connected to the cooling platform below;

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

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

[0011] As a preferred technical solution, a channel is provided on the cooling platform.

[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, superalloy, 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 thimble, a floating thimble, or a flow splitter plate, among which the flow splitter plates are arranged in a multi-stage interpenetrating manner.

[0015] According to another aspect of the present invention, there is provided a wafer cooling method based on the rarefied heat transfer mechanism. This method is applied to work in a wafer cooling system based on the rarefied heat transfer mechanism as described above. In this method, first, the wafer is brought into the vacuum lock and positioned on the support unit. During the cooling process, cooling gas is injected 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 the monitoring results back to the control device. The control device adjusts the gas flow rate of the cooling gas, the pressure inside the vacuum lock, and the height of the main device by using the dynamic change range of the Knudsen number to control the wafer to be in the rarefied heat transfer state during the initial stage of the preset vacuum break.

[0016] As a preferred technical solution, the mechanism for injecting the 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 initial stage of the preset vacuum break, the control device adjusts the cooling gas flow rate mechanism to smoothly transition the wafer from the rarefied heat transfer state to the continuous flow heat transfer state.

[0018] As a preferred technical solution, the specific method for the control device to adjust the cooling gas flow rate mechanism is: adopting the slow start strategy in flow control.

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

[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 fluid flow, k B is the Boltzmann constant, T is the absolute temperature of the gas, d is the effective diameter of gas molecules, and P is the gas pressure.

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

[0024] 1. First, the present invention brings the wafer into the vacuum lock and positions it on the support unit. During cooling, cooling gas is injected into the vacuum lock through the nozzle. Using the cooling gas as an intermediate heat accumulator, heat is transferred from the wafer to the cooling platform. The 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 adjusts the gas flow rate of the cooling gas, the pressure inside the vacuum lock, and the height of the main device by utilizing the dynamic change range of the Knudsen number to control the wafer to be in a rarefied heat transfer state at the initial stage of the preset vacuum break. For different wafer surface temperatures, the system can switch between the rarefied heat transfer and Bernoulli heat transfer mechanisms as needed to achieve the best cooling effect. By means of the rarefied heat transfer mechanism, the wafer cooling time is significantly shortened, enabling the main temperature reduction to be completed before the vacuum break, which is highly efficient.

[0025] 2. In the present invention, the cooling system includes a main device, a sensing device, and a control device. The main device is arranged inside the vacuum lock and includes a cooling platform and a support unit for supporting the wafer, and its local lifting is controlled by the control device to dynamically adjust the distance between the wafer and the cooling platform. The sensing device is electrically connected to the control device and includes a temperature sensor for monitoring the wafer surface temperature and cooling efficiency in real time and feeding the monitoring results back to the control device. The control device is connected to the main device and includes a mass flow controller for controlling the gas flow rate, gas temperature, pressure inside the vacuum lock, lifting of the ejector pin, and height of the cooling platform of the cooling gas injected into the main device. This structural design helps to stabilize the position of the wafer and at the same time allows it to make necessary small movements during the cooling process to optimize the heat transfer effect. Also, it can avoid the influence of the micro-deformation of the wafer at high temperature on the uniformity of the distance between the wafer and the cooling base. On the premise of establishing a feedback mechanism, the configuration of the support device can be dynamically completed according to the temperature difference at each position to ensure that the Bernoulli flow rate, flow velocity, and compressive stress all reach the optimal state.

[0026] 3. In the present 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, and its materials specifically include stainless steel, light alloy, superalloy, high-entropy alloy, or ceramic. It includes a mass flow controller for controlling the gas flow rate, gas temperature, pressure inside the vacuum lock, lifting of the ejector pin, and height of the cooling platform of the cooling gas injected into the main device. Dynamically regulate the distance between the wafer and the cooling platform to ensure the uniformity of the cooling effect and reduce the wafer stress.

[0027] 4. In the present invention, the main device is arranged inside the vacuum lock, and the injected cooling gas is an inert gas, including nitrogen or argon. This avoids the wafer being exposed to the atmospheric environment at high temperature and prevents adverse reactions such as oxidation, which is safe.

[0028] 5. The cooling system in the present invention includes a main body device, a sensing device, and a control device; the main body device is disposed within a vacuum lock and includes a cooling platform and a support unit, and the support unit includes a lifting thimble, a floating thimble, or a flow splitter 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 effect of wafer deformation caused by high temperature on the heat transfer effect. The cooling platform is provided with channels and nozzles. The nozzles include distributed nozzles or central nozzles, and the nozzles are configured to be adjustable and telescopic. The modular design facilitates integration with existing multi-chamber systems and has compatibility.

[0029] 6. In the present invention, the cooling platform is provided with channels, and by combining the channels with liftable thimbles, it is used to maintain the wafer in a thin heat transfer state and ensure that the gas flow rate, flow velocity, and compressive stress all reach the optimal state.

[0030] 7. In the present invention, the flow splitter plates are arranged in a multi-stage interlaced manner; to ensure the uniformity of gas flow velocity.

[0031] 8. In the present invention, after the initial stage of preset vacuum break, the control device adjusts the cooling gas flow rate mechanism to enable the wafer to smoothly transition from a thin heat transfer state to a continuous flow heat transfer state. During the vacuum break process, the slow start strategy is adopted to extend the thin heat transfer stage, further optimizing the cooling efficiency.

[0032] 9. The nozzles in the present invention include distributed nozzles or central nozzles. Combining with the gas flow guidance of the multi-stage flow channels, it ensures the uniform distribution of the cooling gas and improves the heat transfer uniformity on the wafer surface. The nozzles are configured to be adjustable and telescopic. To adapt to wafers of different sizes and materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a flowchart of a wafer cooling method based on a thin heat transfer mechanism in an embodiment;

[0034] Figure 2 It is the relationship between the slit distance and the heat transfer coefficient under different air pressures in an embodiment;

[0035] Figure 3 It is a side view of a wafer cooling system with distributed air intake in an embodiment;

[0036] Figure 4 It is a top view of a wafer cooling system with distributed air intake in an embodiment;

[0037] Figure 5 It is a side view of a wafer cooling system with central air intake in an embodiment;

[0038] Figure 6 It is a top view of a wafer cooling system with central air intake in an embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0040] In quite a number of semiconductor process manufacturing processes, the reaction has a relatively high temperature. Such as chemical vapor deposition, de-bonding equipment, etc. Therefore, when the substrate is taken out of the reaction chamber, it often has a relatively high temperature, such as 200 - 600°C. The common practice is to set a cooling chamber at a certain position on the transfer chamber, but this position is usually used to set the reaction chamber to further improve production capacity. Therefore, in most cases, it is not a preferred solution. Some solutions choose to set a cooling groove on the front-end module that can store multiple wafers. However, this method requires occupying the position of a loading device on an EFEM, expanding the lateral width of the equipment. At the same time, when the wafer is transferred from the vacuum lock to the cooling chamber in the EFEM at a relatively high temperature, it is exposed to the atmosphere, which may cause excessive oxidation or other reactions to occur. This goes against the original intention of cooling. Therefore, designing an effective cooling mechanism in the vacuum lock so that the wafer can complete the cooling process before being exposed to the atmosphere is the most reasonable choice.

[0041] In a multi-chamber system, a batch-type vacuum lock usually does not require an additional cooling system. A standard batch vacuum lock can load 25 wafers at a time. When the last wafer completes the operation, the first 24 wafers have waited for a long time. This time is sufficient for the first 20 to 23 wafers to complete cooling. When the vacuum lock is opened and communicates with the outside, the robot on the EFEM side starts to transfer. At this time, as long as the robot on the EFEM side gives priority to transferring the substrate that entered the vacuum lock earliest according to the first-in, first-out principle, the last 2 - 3 wafers with the highest temperature also have enough time to further cool down. For a 25-wafer batch vacuum lock, there is no need for additional cooling design for wafers at 300°C or higher temperatures.

[0042] In fact, for substrates at a relatively high temperature, waiting a few more minutes for the last wafer in the batch vacuum lock will not have much impact on the overall equipment output, and the impact can even be ignored. Because usually at this time, another vacuum lock has already started working, occupying the robot on the vacuum side. The robot on the EFEM side of the atmospheric robot has enough time to wait.

[0043] In fact, the cooling bottleneck that occurs when using a vacuum lock for cooling mainly appears in small vacuum locks called single-wafer vacuum locks. In such a system, the reaction chamber usually has a very short working time per wafer, and the vacuum lock needs to transfer a large number of substrates. At this time, the time for the vacuum lock to break vacuum, evacuate, and transfer 25 wafers becomes the bottleneck (in the case of multiple chambers and a very short process time per wafer, the process time for 25 wafers is shorter than the time for the vacuum lock to complete one loading). Therefore, the most common method in this equipment setting is to use a small single-piece or a small number of pieces (such as <= 5) vacuum locks for transfer. At this time, since the evacuation time of the vacuum lock is very short, a wafer in-and-out cycle can be completed in <20s, which can further increase the throughput (number of wafers per hour) of the system. A common setting of this method is to use an upper and lower double-layer vacuum lock. When the upper vacuum lock opens for transfer, the lower layer simultaneously performs actions such as evacuation or breaking vacuum. Alternating in a cycle to complete high-speed transfer. In this setting, since the waiting time inside the vacuum lock is compressed to the extreme, the cooling process cannot be completed by natural cooling within the vacuum lock. It is necessary to further design an effective cooling mechanism so that the wafer can complete the entire cooling process within the vacuum lock.

[0044] In summary, in the semiconductor manufacturing industry, especially after high-temperature processes (such as chemical vapor deposition CVD and photoresist stripping), wafer cooling is a critical step. Existing cooling methods are usually carried out in the transfer chamber or the front-end module, but these methods have several problems: one is the low utilization rate of equipment space, especially when it is necessary to set up cooling chambers for multiple wafers in the EFEM front-end module; the other is that the exposure of wafers at high temperatures may lead to excessive oxidation or other adverse reactions, which goes against the original intention of cooling. In the prior art, the cooling of wafers during transfer is usually 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 dealing with multiple chambers or high-temperature wafers that require rapid transfer.

[0045] To address these problems, this application proposes an innovative cooling solution that integrates a cooling mechanism based on the principle of rarefied heat transfer in the vacuum lock. With the design of the mechanical structure, a rarefied heat transfer stage is created for the wafers that have completed the operation during the vacuum-breaking stage in the vacuum lock. This design aims to achieve efficient, uniform, and well-controlled cooling of the wafer stress, while avoiding the risks of additional space occupation and wafer exposure. In this way, the invention not only improves the efficiency and safety of the wafer processing process, but also provides a more advanced and reliable cooling solution for the semiconductor manufacturing industry.

[0046] For rarefied heat transfer, in a narrow gap, the number of gas molecules is very small, and continuum mechanics can no longer explain the gas flow. In this case, the interaction between the gas and the rigid body plays an important role. For this rarefied gas, due to the reduced collisions between gas particles, the heat transfer efficiency is greatly improved. In a microscale environment, the Knudsen number (comparing the mean free path of gas molecules with the 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 decreases, resulting in the gas heat transfer mainly occurring through the direct interaction of molecules with the surface. In a small-scale system, the surface effect becomes more significant. Due to the increased ratio of surface area to volume, the interaction between gas molecules and the wall plays an important 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, the principle of rarefied heat transfer can be utilized to effectively remove heat from the wafer and achieve fast and uniform cooling.

[0047] This application addresses the many deficiencies in the prior art during the wafer cooling process in semiconductor equipment and proposes a wafer cooling system based on the rarefied heat transfer mechanism. This system creates a rarefied heat transfer environment within the vacuum lock by combining mechanical design and gas dynamics characteristics to achieve fast and efficient cooling of high-temperature wafers. It includes the dynamic control of the rarefied heat transfer environment, mechanical structure optimization, multi-stage cooling mechanism, gas flow field optimization, and dynamic feedback regulation.

[0048] Among them, the dynamic control of the rarefied heat transfer environment is specifically as follows: By precisely adjusting the distance between the wafer and the cooling platform (such as 50 μm) and combining real-time pressure monitoring, using the dynamic change range of the Knudsen number, it is ensured that the wafer cooling is always in the optimal rarefied heat transfer state. In the initial stage of breaking the vacuum (0 - 47.63 Torr for 50 μm), the rarefied heat transfer efficiency is significantly higher than the conventional continuum cooling mode.

[0049] The mechanical structure optimization is specifically as follows: In this application, a variety of mechanical support structures are designed, such as liftable lift pins and multi-stage flow splitters, 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 temperature on the heat transfer effect.

[0050] The multi-stage cooling mechanism is specifically as follows: In this application, by combining rarefied heat transfer and continuum heat transfer, when the pressure range gradually increases (>47.63 Torr), the air flow smoothly transitions from rarefied heat transfer to continuous flow heat transfer. In addition, during the vacuum breaking process, the rarefied heat transfer stage is extended through a slow start strategy to further optimize the cooling efficiency.

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

[0052] The dynamic feedback control is specifically as follows: In this application, temperature sensors and flow control components are introduced, such as a Mass Flow Controller (MFC). By real-time monitoring of the wafer surface temperature and cooling efficiency, the gas flow rate, pressure, and the height of the cooling platform 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 the wafer processing efficiency and equipment productivity.

[0054] Embodiment 1

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

[0056] The main device is arranged in the vacuum lock and includes a cooling platform and a support unit, which is used to support the wafer and is controlled by the control device for its local lifting to dynamically adjust the distance between the wafer and the cooling platform; among them, nozzles are provided on the cooling platform, and the nozzles are used to inject or discharge cooling gas; the wafer is placed above the support unit and is connected to the cooling platform below, including lifting thimbles, floating thimbles, or a flow splitter plate;

[0057] The sensing device is electrically connected to the control device and includes a temperature sensor, which is used to real-time monitor the wafer surface temperature and cooling efficiency and feedback the monitoring results to the control device;

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

[0059] Channels are provided on the cooling platform. The cooling platform is a constant-temperature cooling wall surface, maintained by cooling water or coolant. Its materials specifically include stainless steel, light alloy, superalloy, high-entropy alloy, or ceramic. The nozzles include distributed nozzles or central nozzles, and the nozzles are configured as adjustable telescopic types. The flow splitter plates in the support unit are arranged in a multi-stage interpenetrating manner.

[0060] In this embodiment, the system structure is as Figure 3 、 Figure 4As shown, it includes one or more liftable lift thimbles (or other types of floating supports), and a supporting sheath that can move up and down. These support points have edge grooves to limit their sliding within a specific range. Such a design helps to stabilize the position of the wafer, while allowing necessary small movements during the cooling process to optimize the heat transfer effect. Or a structure of a supporting sheath plus a liftable base can be adopted. This structural design can avoid the influence of the micro-deformation of the wafer at high temperature on the uniformity of the spacing between the wafer and the cooling base. On the premise of establishing a feedback mechanism, the height configuration of the thimble can also be dynamically completed according to the temperature difference at each position.

[0061] In this embodiment, the multi-nozzle technology is applied, and the system is equipped with distributed nozzles for air intake. The nozzles can be designed to be distributed to generate a negative pressure evenly distributed along the surface of the wafer. In addition to facilitating the creation of a rarefied heat transfer environment, this air intake method can also make the wafer suck down more stably with the help of the weak downward pressure it brings, promote the heat exchange between the wafer and the cooling surface, and at the same time reduce the internal stress that may be generated during the cooling process of the wafer.

[0062] In this embodiment, by combining rarefied heat transfer and convective heat transfer, in a vacuum environment, a rarefied space is constructed by using floating thimbles or supports to form a rarefied heat transfer environment between the wafer and the cooling surface, thereby greatly improving the heat transfer efficiency. When the vacuum is broken to above the rarefied heat transfer pressure threshold, the system switches to using the continuous medium model cooling mechanism, that is, at the nozzle where the vacuum is broken, it enters the convective heat transfer stage.

[0063] In this embodiment, the cooling platform is designed with special channels, combined with liftable thimbles, to maintain the wafer in the rarefied heat transfer state and ensure that the Bernoulli flow rate, flow velocity, and compressive stress all reach the optimal state.

[0064] In this embodiment, for the temperature-related heat transfer mechanism regulation, for different wafer surface temperatures, the system can switch to the rarefied heat transfer and Bernoulli heat transfer mechanisms as needed to achieve the best cooling effect.

[0065] In this embodiment, the implementation method flow of the system is as Figure 1As shown, first, balance the pressure, then open the vacuum lock door. Use the wafer automatic transfer robot to bring the wafer into the vacuum lock and position it on the support unit. The wafer automatic transfer robot retracts to the atmospheric environment and closes the vacuum lock door. During the cooling process, cooling gas is introduced into the vacuum lock through the nozzle. The cooling gas serves as an intermediate heat accumulator 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 the monitoring results back 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 rarefied heat transfer state at the initial stage of the preset vacuum break. Control the lifting pin to lower or the base to rise, ventilate the vacuum lock to break the vacuum, and distribute multi-port jetting. Finally, the wafer automatic transfer robot in the atmosphere takes the wafer out of the vacuum lock.

[0066] In this embodiment, the effect evaluation of rarefied heat transfer first calculates the pressure boundary of 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 gas molecules to a certain characteristic length (such as the diameter of the flow channel, the size of particles, etc.) in gas flow. 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, assume that 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. At this time, the characteristic length is 50um, the gas is nitrogen, and the temperature is 25°C. Use pressure 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 molecules, in meters. In this embodiment, the effective diameter of the nitrogen gas molecules is 3.6×10 -10 m; P is the pressure of the gas, in Pascals, Pa.

[0075] When the characteristic size is 50 μm, the corresponding gas pressure boundary values (unit: Torr) are:

[0076] Continuous flow region (Kn < 0.01): The upper limit of the 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 of the gas pressure is about 0.48 Torr.

[0080] Therefore, from the start of vacuum break to 47.63 Torr is considered to be in the rarefied heat transfer. In addition, for rarefied 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 of less than 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 mean free path of the molecules is much larger than the slit distance. Under certain pressure conditions, even if the slit distance increases, 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 rarefied condition is 47.63 Torr, and the corresponding heat transfer coefficient is about h = 7000 W / m 2*K, considering the linear change in logarithmic coordinates and the actual influence of the slit size, during the purge process from 0 to 47.63 torr, h = 3500 is selected. Based on the use of Newton's law of cooling and the energy conservation equation. 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, with the unit of W; h is the heat transfer coefficient, with the unit of W / m 2 ·K; A is the heat exchange surface area, with the unit of m 2 ; ΔT is the temperature difference between the object and the environment, with the unit of K.

[0085] For the cooling of the silicon wafer, this formula can be combined with the energy conservation equation to calculate the change in the temperature 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, with the unit of kg, and it is calculated to be 132 g; c is the specific heat capacity of the silicon wafer, with the unit of J / kg·K; dT / dt is the rate of change of temperature over time; -hAΔT represents the heat lost by the silicon wafer.

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

[0089] In this embodiment, under normal circumstances, the time for the vacuum lock to break the vacuum will be completed within 5 to 10 s. Then, the time to reach 47.63 torr is 0.1 to 0.2 s, that is, the time for thin-film heat transfer is 0.1 to 0.2 s. The contribution of thin-film heat transfer to the cooling of the wafer is huge during this extremely short time. If the method of first slow and then fast is adopted during the vacuum break, the time for thin-film heat transfer can be increased, further enhancing its contribution to cooling.

[0090] Example 2

[0091] In this embodiment, a wafer cooling method based on the rarefied heat transfer mechanism is applied. In this method, first, the wafer is brought into the vacuum lock and positioned on the support unit. During the cooling process, cooling gas is injected 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 the cooling efficiency in real time and feeds the monitoring results back 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 by using the dynamic change range of the Knudsen number to control the wafer to be in the rarefied heat transfer state at the initial stage of the preset vacuum break.

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

[0093] After the vacuum break starts, the hole for the vacuum break can also serve as the nozzle. The system can adjust the mechanism of the gas flow rate during the vacuum break, thereby extending the time for the wafer to be in the rarefied heat transfer state.

[0094] The rarefied heat transfer can be dynamically adjusted according to the distance (characteristic size) between the wafer and the cooling surface, combined with the time of the vacuum break, on the premise of meeting the Knudsen number boundary. That is, the ratio of rarefied heat transfer to continuous flow heat transfer can be optimized according to the actual process requirements. The specific calculation formula for 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 fluid flow, k B is the Boltzmann constant, T is the absolute temperature of the gas, d is the effective diameter of gas molecules, and P is the gas pressure.

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

[0099] The main device is arranged inside the vacuum lock and includes a cooling platform and a support unit, which is used to support the wafer and is controlled by a control device to lift locally, so as to dynamically adjust the distance between the wafer and the cooling platform. Among them, there is a nozzle on the cooling platform, and the nozzle is used to inject or discharge cooling gas. The nozzle is configured to be adjustable and telescopic to adapt to wafers of different sizes and materials. The air intake mode of the nozzle can be parallel to the wafer or perpendicular to the wafer, depending on the design of the cooling platform, especially the configuration of the flow channel layer. The mechanism of injecting cooling gas can be continuous or pulsed, combined with the design of the cooling platform to keep the temperature difference (ΔT) generated by heat transfer on the wafer surface consistent.

[0100] The wafer is placed above the support unit and connected to the cooling platform below. It includes lifting thimbles, floating thimbles or flow splitters, etc., which can form a space that meets the heat transfer of rarefied gas between the wafer and the cooling surface. The multi-thimble unit and the air intake nozzle are installed on the cooling platform to generate a stable adsorption force between the wafer and the cooling platform. The cooling platform is provided with a special channel, combined with the liftable thimble, to maintain the wafer in a rarefied heat transfer state and ensure that the gas flow rate, flow velocity and compressive stress all reach the optimal state. The support device of the cooling platform adopts a liftable structure, which can dynamically adjust the distance from the lower surface of the wafer.

[0101] The material of the cooling platform can be stainless steel, light alloy, superalloy, high-entropy alloy, ceramic or other metals or non-metals or composite materials with good heat transfer and easy processing. The cooling platform is a constant-temperature cooling wall surface, which can be maintained by using cooling water or other cooling liquids. The cooling platform or the base can move up and down.

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

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

[0104] In this embodiment, the lifting of the thimble is controlled by the control device, and a mechanism for injecting cooling gas is configured, and the rarefied heat transfer cooling condition is configured to adjust the gas flow rate and temperature passing through the nozzle to achieve effective cooling of the wafer.

[0105] The control unit can include an MFC mass flow controller (Mass Flow Controller), a temperature sensor, etc., which is used to monitor the wafer surface temperature and adjust the gas flow rate and temperature according to the monitoring results.

[0106] In this embodiment, as Figure 4 、 Figure 5As shown, the support unit adopts a micro multi-stage flow splitter plate. The system includes three or more micro flow splitter plates (or other types of floating supports), and these flow splitter plates have the function of wafer support. Such a design helps to stabilize the position of the wafer and precisely control the distribution of the air flow to ensure that the flow rate at each position is basically the same. The micro flow splitter plates can be arranged in a multi-stage interlaced manner to ensure the uniformity of the gas flow rate.

[0107] In this embodiment, there are nozzles on the cooling platform, that is, the system is designed with a central air inlet at the bottom of the system to guide the cooling gas to flow into the system evenly. The generated low-pressure area can adsorb the wafer downward on the cooling surface, and at the same time, the generated high-speed air flow promotes the heat exchange between the wafer and the cooling surface. The cooling platform is provided with a special flow splitter plate to guide the distribution of the air flow. It can also combine the differences in the flow rates and appropriately adjust the distribution of the flow splitter plates to prevent the wafer stress or damage caused by the temperature gradient. In a vacuum environment, a multi-stage micro flow splitter plate is configured between the wafer and the base to form a rarefied heat exchange environment between the wafer and the cooling surface, thereby greatly improving the heat transfer efficiency. By reasonably controlling the gas flow rate and optimizing the distribution of the flow splitter plates, it is possible to achieve non-contact between the wafer and the cooling disk and form a thin air cushion in the interval. And for different wafer surface temperatures, the system can switch to rarefied heat exchange and flowing heat exchange according to needs to achieve the best cooling effect.

[0108] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A wafer cooling system based on a rarefied heat exchange mechanism, characterized in that: It includes a main device, a sensor device and a control device; The main device is arranged in the vacuum lock, and includes a cooling platform and a supporting unit, which is used to support the wafer, and the control device controls the partial lifting of the main device to dynamically adjust the distance between the wafer and the cooling platform; wherein, a nozzle is arranged on the cooling platform, and the nozzle is used to inject or discharge cooling gas; the wafer is placed on the upper part of the supporting unit, and the lower part is connected to the cooling platform; The sensing device is electrically connected to the control device, and includes a temperature sensor for real-time monitoring of the wafer surface temperature and cooling efficiency, and feeding back the monitoring results to the control device; The control device is connected to the main device and includes a mass flow controller for controlling the gas flow rate, gas temperature, pressure in the vacuum lock and the lifting and lowering of the main device of the cooling gas injected into the main device.

2. A wafer cooling system based on rarefied heat exchange mechanism according to claim 1, characterized in that: The cooling platform is provided with a groove.

3. A wafer cooling system based on rarefied heat exchange mechanism according to claim 1, characterized in that: The cooling platform is a constant temperature cooling wall surface, which is maintained by cooling water or cooling liquid, and its material specifically includes stainless steel, light alloy, high temperature alloy, high entropy alloy or ceramic.

4. The wafer cooling system based on rarefied heat exchange mechanism according to claim 1, characterized in that: The nozzle includes a distributed nozzle or a central nozzle, and the nozzle is configured to be adjustable and telescopic.

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

6. A wafer cooling method based on rarefied heat exchange mechanism, characterized in that: The method is applied to a wafer cooling system based on a rarefied heat exchange mechanism as described in any one of claims 1-5. In the method, the wafer is first brought into a vacuum lock and positioned on a support unit. During the cooling process, cooling gas is introduced into the vacuum lock through a nozzle. The cooling gas serves as an intermediate heat storage body to transfer heat from the wafer to the cooling platform. The sensor 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 uses the dynamic range of the Knudsen number to adjust the gas flow rate of the cooling gas, the pressure in the vacuum lock and the height of the main device to control the wafer to be in a rarefied heat exchange state in the preset initial stage of breaking the vacuum.

7. The wafer cooling method based on rarefied heat exchange mechanism according to claim 6, characterized in that: The mechanism of injecting cooling gas includes continuous gas injection or pulsed gas injection; the cooling gas is an inert gas, including nitrogen or argon.

8. The wafer cooling method based on rarefied heat exchange mechanism according to claim 6, characterized in that: The control device adjusts the cooling gas flow rate mechanism after the preset vacuum breaking initial stage, so that the wafer smoothly transitions from the rarefied heat exchange state to the continuous flow heat exchange state.

9. The wafer cooling method based on rarefied heat exchange mechanism according to claim 8, characterized in that: The specific method of the mechanism for adjusting the cooling gas flow rate by the control device is: adopting the slow start strategy in flow control.

10. The wafer cooling method based on rarefied heat exchange mechanism according to claim 6, characterized in that: The specific calculation formula of the Knudsen number is: Kn=λ / L Where Kn is the Knudsen number, λ is the mean free path of gas molecules, L is the characteristic length in fluid flow, and k B 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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