Patent Publication Number: US-2023138317-A1

Title: Substrate process system including a cooling station

Description:
PRIORITY CLAIM AND CROSS-REFERENCE 
     The present application claims priority to U.S. Provisional Patent Application No. 63/274,930, filed on Nov. 2, 2021, and entitled “SUBSTRATE PROCESS SYSTEM INCLUDING A COOLING STATION,” the entire disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic devices. Semiconductor devices are fabricated by sequentially depositing insulating or dielectric layers, conductive layers, and semiconductor layers over a substrate, and patterning the various material layers using lithography to form circuit components and elements. 
     One of the important drivers for increased performance in semiconductor devices is the higher levels of integration of circuits. This is accomplishing by shrinking the device geometries or feature sizes. However, the widths of trench structures on the device become so narrow that filling such trench structures become problematic. One approach has been utilizing highly flowable precursor materials that may be applied in a liquid phase to a spinning substrate surface. These flowable precursors can flow into the trench structures. Once these flowable materials are deposited, they have to be cured into solid dielectric materials. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrary increased or reduced for clarity of discussion. 
         FIG.  1 A  is a simplified top plan view of a substrate process system according to an embodiment. 
         FIG.  1 B  is a graph illustrating the number of defects formed on a substrate as a function of idle time according to some embodiments. 
         FIG.  2 A  is a simplified top plan view of a curing chamber according to an embodiment. 
         FIG.  2 B  is a simplified cross-sectional view of the curing chamber of  FIG.  2 A . 
         FIG.  3 A  is a simplified cross-sectional view of a cooling station according to an embodiment. 
         FIG.  3 B  is a simplified top plan view of a cooling system according to an embodiment. 
         FIG.  3 C  is a simplified top plan view of a cooling system according to another embodiment. 
         FIG.  4 A  is a simplified cross-sectional view of a cooling station according to an embodiment. 
         FIG.  4 B  is a simplified cross-sectional view of a showerhead according to an embodiment. 
         FIG.  4 C  is a simplified cross-sectional view of a cooling station according to an embodiment. 
         FIG.  5    is a simplified flowchart of a process that may be utilized in a substrate process system according to an embodiment. 
         FIGS.  6 A to  6 C  are simplified cross-sectional views of a portion of a substrate in various stages of the process illustrated in  FIG.  5   . 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure provides many different embodiments or examples for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. Prepositions, such as “on” and “side” (as in “sidewall”) are defined with respect to the conventional plane or surface being on the top surface of the wafer or substrate, regardless of the orientation of the wafer or substrate. The term “horizontal” is defined as a plane parallel to the conventional plane or surface of a wafer or substrate, regardless of the orientation of the wafer or substrate. The term “vertical” refers to a direction perpendicular to the horizontal as defined above, i.e., perpendicular to the surface of a substrate. The terms “first,” “second,” “third,” and “fourth” may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present disclosure. 
     Embodiments of the present disclosure relate to a cooling station, a system and method for controlling a temperature of a substrate or a batch of substrates (wafers) coming out of a process chamber to prevent vapor condensation from forming on the substrate or the batch of substrates. A substrate can include a single or multiple material layers to be patterned. The multiple material layers can include a silicon layer, a dielectric layer, an electrically conductive layer, and the like. When a flowable material is formed on the substrate by a flowable chemical vapor deposition (FCVD) process, the substrate including the flowable material formed (deposited) thereon is provided to a curing chamber where the formed flowable material is heated to form a cured material. In an exemplary embodiment, the flowable material can include TSA(SiH 3 ) 3 N and NH 3 . The cured material is then provided to a cooling station, where the cured material is cooled. However, it is observed that, in conventional systems, when the cured material is provided to an interface chamber having a room temperature (typically between 15° C. and 30° C.) in the fabrication facility in a transition period , with time passing, the low temperature (compared to the temperature in the curing chamber) in the interface chamber may gradually cause vapor of the cured material to condense, and the condensed vapor may deposit on the surface of the substrate, thus causing defects. In general, the amount of defects increases with the idle time during which the substrate with the cured flowable material remains in a cooling station. 
     For addressing the above-mentioned flowable film condense accumulation problem in the cooling station, embodiments provide a substrate process system including a novel cooling station that can reduce or eliminate defects associated with vapor condensation when transferring the cured substrates from the curing chamber to the cooling station, by setting the temperature of the cooling station to a predetermined or target temperature. In some implementations, the predetermined temperature is higher than the room temperature (typically between 15° C. and 30° C.) in the fabrication facility. In one example, the predetermined temperature is higher than 15° C. In other implementations, the predetermined temperature is close to that of the curing chamber or a process chamber (i.e., a chamber where the semiconductor processing is conducted). In some implementations, the predetermined temperature is between a temperature of the process chamber and a temperature of the curing chamber. As a result, the temperature gap between the cooling station and the curing chamber is narrowed, thus reducing or eliminating defects associated with vapor condensation when transferring the substrates. The novel cooling station can also operate as a temperature controller to bring the substrates to a predetermined temperature prior to placing the substrates to a transfer chamber that places the substrates to one or more process chambers using a robotic arm. 
     In some embodiments, a substrate process system is provided to include a novel cooling station that is configured to bring one or more substrates to a predetermined temperature prior to transferring the one or more substrates to a process chamber for processing and controlling a temperature of the one or more substrates after they have been processed to prevent vapor condensation from forming on the one or more substrates. The novel cooling station has several features that can be utilized individually or in combination, i.e., not all of the features described and illustrated herein are required to achieve the advantages and benefits of the cooling station in accordance with the present disclosure. 
     In some embodiments, the cooling station in accordance with the disclosure includes a housing, a wafer holder in the housing and including a plurality of lateral shelves configured to receive a plurality of substrates, a shelter plate mounted on an upper side of the housing and configured to reduce heat loss of an upper substrate that has been processed. The shelter plate thus serves as a passive heating member. In an embodiment, each lateral shelf of the wafer holder includes a heating element configured to control a temperature of a substrate disposed thereon. The wafer holder thus operates as an active heater for each individual substrate. In an embodiment, the cooling station can include an airflow structure configured to receive air from an inlet and control an air circulation of the cooling station. The airflow structure thus operates as a passive heater. In an embodiment, the housing of the cooling station includes a material having low thermal conductivity to reduce heat loss of the cooling station. These features can operate singly or in combination to control a temperature of a processed substrate to prevent condensed vapor formation. These and other embodiments of the disclosure, along with many of the advantages and features, are described in more detail in conjunction with the text below and corresponding figures. 
     The terms “substrate” and “wafer” are often used interchangeably in this field and are to be understood as including silicon-on-insulator (SOI) or silicon-on-sapphire (SOS) technology, doped and undoped semiconductors, epitaxial layers of silicon supported by a base semiconductor foundation, and other semiconductor structures. Furthermore, when reference is made to a “wafer” or “substrate” in the following description, previous process may have been utilized to form regions or junctions in the base semiconductor structure or foundation. In addition, the semiconductor need not be silicon-based, but could be based on silicon-germanium, germanium, or gallium arsenide, and other. The terms “formed” and “deposited” are also used interchangeably herein. 
       FIG.  1 A  is a simplified top view of a substrate process system  10  according to an embodiment. Referring to  FIG.  1 A , the substrate process system  10  includes a transfer chamber  101 , one or more process chambers  102  connected to the transfer chamber  101  and configured to process substrates, a curing chamber  103  for curing substrates that have been processed, a load lock chamber  104  connected to the transfer chamber  101  and configured to transfer substrates without substantially affecting the air pressure therebetween, an interface chamber  105  connected to the load lock chamber  104 , and a cooling chamber  106  disposed in the interface chamber  105  and in a vicinity of the curing chamber  103 . The substrate process system  10  also includes one or more front opening unified pods (FOUPs)  107 . In some embodiments, substrates are supplied from the FOUPs  107  to the interface chamber  105  by a first set of robotic arms  105   a.  The substrates are then supplied to the load lock chamber  104  by a second set of robotic arms  104   a.  The substrates are further supplied to the transfer chamber  101  by a third set of robotic arms  101   a.  The third set of robotic arms  101   a  are also configured to transport the substrates to the process chambers  102 . The FOUPs  107  and the interface chamber  105  allow substrates to be loaded and unloaded without the load lock chamber  104 , the transfer chamber  101 , and the process chambers  102  to air. The pressure of the FOUPs  107  is usually at about 1 atm, i.e., same as the fab environment, whereas the pressure of the load lock chamber  104  is lower, e.g., less than about 10 Torr. 
     In operation, substrates are transferred into and out of the substrate process system  10 , either individually or in batches via the FOUPs  107 . The substrates are transferred from the FOUPs  107  to the load lock chamber  104  via the interface chamber  105 , where they are isolated from the ambient environment. For example, an inert gas (e.g., nitrogen) is purged through the load lock chamber  104  which is pumped down to a low pressure to remove any air from the ambient environment. The substrates are transferred to the process chambers  102  that are also pumped down to a similar pressure to be in equilibrium of the load lock chamber  104  via the transfer chamber  101 . 
     In an embodiment, the process chambers  102  each are configured to deposit a flowable dielectric material on a substrate. In the exemplary embodiment, three pairs of the process chambers  102  are used to deposit the flowable dielectric material on the substrate. For example, the flowable dielectric material can be formed on the substrate by a spin-on coating process. Flowable dielectric materials may include phospho-silicate glass (PSG), boron-silicate glass (BSG), boron-doped phospho-silicate glass (BPSG), undoped silicate glass (USG), or the like. In an embodiment, the substrates of the process chambers  102 , after being processed, are placed into the curing chamber  103 . The processed substrates each have the deposited flowable dielectric material deposited thereon. The curing chamber  103  can perform a curing process on a plurality of processed substrates. In an embodiment, the curing process includes heating the flowable dielectric material to react with precursors under a relatively high pressure, such that the precursors can react with the deposited flowable dielectric material. In some embodiments, the curing chamber  103  is configured to concurrently perform a curing process on the number of substrates that have been processed by the process chambers  102 . In some other embodiments, the substrate process system  10  may have two individual curing chambers  103  disposed on opposite sides of the interface chamber  105  to accommodate the number of substrates that have been processed by the process chambers  102 . In the embodiment of two curing chambers, the second curing chamber  103  is disposed on the left side of the interface chamber  105  (denoted by a dotted line box). 
     After the curing process, the cured substrates are then placed into the cooling station  106  that keeps the cured substrates to a predetermined temperature to prevent vapor condensation from forming on the surface of the cured substrates. As mentioned above, the vapor condensation typically results from the low temperature of the cooling station in conventional systems, and the condensed vapor may deposit on the surface of the substrates, thus causing defects. In an embodiment, the cooling station  106  is configured to perform a cooling process on the number of substrates that have been cured in the single curing chamber  103  or both the curing chambers  103  disposed on opposite sides of the cooling station  106 . It is noted that the curing chamber  103  is a closed chamber, i.e., it is completely sealed while performing the curing process under a pressure that can be more than the atmosphere pressure, whereas the cooling station is an open system that operates at an ambient pressure or atmosphere pressure. 
     In an embodiment, each of the process chambers  102  can be set to a temperature that is sufficiently elevated to facilitate a flowable chemical vapor deposition (FCVD) process. In an embodiment, flowable dielectric material precursors may be silicon-containing precursors including silane, disilane, methylsilane, dimethylsilane, trimethylsilane, tetraethoxylane (TEOS), or combination thereof. In an embodiment, flowable dielectric material precursors may be silicon nitride containing precursors including sillylamine, trisillylamine (TSA) and disillylamine (DSA), or combination thereof. In an exemplary embodiment, the process chambers  102  can have a temperature in a range between 20° C. and 200° C., in a range between 30° C. and 100° C., in a range between 50° C. and 70° C. After depositing a flowable material layer onto the substrates, the thus processed substrates are provided to a curing chamber  103  that performs a curing process on the processed substrates. In an embodiment, the curing process can be performed at a temperature in a range between 20° C. and 200° C., in a range between 30° C. and 60° C. After the flowable dielectric material on the substrates has been cured, the cured substrates are then placed in the cooling station  106  that can have a predetermined temperature below a dew point temperature to prevent vapor condensation from forming on the surface of the cured substrates. In an embodiment, the predetermined temperature of the cooling station  106  can be controlled within a range between 0° C. and 40° C., in a range between 20° C. and 30° C. 
     In an embodiment, the cooled substrates in the cooling station  106  are then either supplied to the FOUPs  107  by the first set of robotic arms  105   a,  where they can be removed. In an embodiment, the cooled substrates in the cooling station  106  are placed back to the load lock chamber  104  by a second set of robotic arms  104   a,  where they will be provided to the process chambers  102  by the third set of robotic arms  101   a  for further flowable material deposition. 
     In an embodiment, the curing chamber  103  has a load lock atmospheric door that can be open to receive multiple processed substrates having a flowable material deposited thereon that is to be cured. In an embodiment, the cooling station  106  has a first access door that is configured to allow the first set of robotic arms  105   a  to place substrates from the FOUPs  107  to the cooling station  106 . In an embodiment, the cooling station  106  also has a second access door that is configured to allow the second set of robotic arms  104   a  to place cured substrates from the curing chamber  103  to the cooling station  106 . In an embodiment, the cooling station  106  further has a third access door that is configured to allow the third set of robotic arms  101   a  to place the cooled substrates from the cooling station  106  to the transfer chamber  101 . In an embodiment, the cooling station  106  can have a single access door configured to receive substrates to be processed from the FOUPs  107  by the first set of robotic arms  105   a,  the cured substrates from the curing chamber  103  by the second set of robotic arms  104   a,  or place the cooled substrates to the transfer chamber  101  by the third set of robotic arms  101   a.  In this embodiment, the cooling station  106  can be rotated along a vertical axis in a rotational movement so that it faces the first, second, or third set of robotic arms, thereby allowing the reception or placement of the substrates from the FOUPs, the curing chamber or to the transfer chamber  101 . 
     It should be noted that  FIG.  1 A  illustrates a substrate process system  10  including three FOUPs  107 , two load lock chambers  104 , three pairs of process chambers  102 , one curing chamber  103 , and one cooling chamber  106 . It is understood that other embodiments may include fewer or more FOUPs, load lock chambers, process chambers, curing chamber, and cooling chamber. Embodiments of the present disclosure may be utilized in other processing equipment, where it is desirable to control the temperature of a substrate as it is being transferred from a location to another location. 
     In some embodiments, the cooling station  106  is configured to store a total number of substrates that have been processed and cured. For example, when each process chamber  102  can process a batch of 25 substrates, the curing chamber  103  may have an integer number of curing sub-chambers or modules configured to receive and cure the total number of substrates that have been processed by the process chambers, and the cooling station  106  has a capacity of receiving and treating 150 (25×6) substrates concurrently. The present inventors have observed that a long idle time of the substrates in the cooling station  106  may induce defects in the substrates because vapor can be condensed onto particles that are then deposited on the surface of the substrates.  FIG.  1 B  is a graph illustrating the number of defects formed on a substrate as a function of idle time according to some embodiments. Referring to  FIG.  1 B , the x-axis represents the idle time in seconds (sec) of a substrate in the cooling station, and the y-axis represents the number of defects due to vapor that is condensed onto particles that are then deposited on the substrate. The idle time refers to the time the substrate awaits further actions, such as removal from the substrate process system  10  through the interface chamber and the FOUPs, or retransfer back to the process chamber for further processing. As can be seen, the number of defects increases when the substrate idles in the cooling station between 180 seconds and 300 seconds, and between 450 seconds and 500 seconds. The present inventors provide the following technical solutions to reduce or eliminate such defect. 
       FIG.  2 A  is a simplified top plan view of a curing chamber  20  according to an embodiment. The curing chamber  20  may be the curing chamber  103  of  FIG.  1   , i.e., the curing chamber  20  is disposed in the vicinity of the cooling system  106  for transferring a substrate having a cured flowable dielectric material formed thereon. In an embodiment, the curing chamber  20  is configured to cure the flowable dielectric material in an atmosphere including ozone. Referring to  FIG.  2 A , the curing chamber  20  has a plurality of heating wires  201  coupled to a heating gas delivery system  202  and configured to control a curing temperature and atmosphere conditions of the curing chamber  20 . In one implementation, the hearting wires  201  may be ceramic liners. In an embodiment, the heating gas delivery system  202  can control the temperature of the curing chamber from about 25° C. to about 200° C., from about 30° C. to about 60° C., and from about 40° C. to about 50° C. The curing chamber  20  has an access door  203  in communication with the load lock chamber  104  and the cooling station  106 . Once the flowable dielectric material has been cured, the access door  203  is opened, the substrate including the cured flowable dielectric material is transferred to the cooling station  106  by the first set of robotic arms  105   a.    
       FIG.  2 B  is a simplified cross-sectional view of the curing chamber  20  of  FIG.  2 A . Referring to  FIG.  2 B , the curing chamber  20  includes a substrate rack  205  configured to support a plurality of processed substrates  206  that include a flowable dielectric material to be cured. The curing chamber  20  also includes a vacuum pump  207  configured to remove process gases, purge gases, and other components from the curing chamber. It should be noted that the curing chamber  20  is an enclosed chamber when the access door  203  is in a closed position, i.e., the access door  203  in the closed position seals the curing chamber  20  to prevent ambient air from entering the curing chamber  20 , thereby affecting the curing temperature and atmosphere conditions of the curing chamber. In some embodiments, the substrate rack  205  of the curing chamber  20  can have a number of slots sufficiently large for receiving and curing a corresponding number of substrates that have been processed by the process chambers  102 . In an embodiment, the plurality of heating wires  201  can provide a uniform distribution of heated air to each slot for curing all substrates concurrently. In an embodiment, each slot has a heating element configured to control a temperature of that slot, i.e., the temperature of each slot in the curing chamber can be controlled individually by its associated heating element. In an embodiment, the heating element is a resistive heating element formed by a metal or including a metallic material having a defined relationship between temperature and resistivity and controlled by a dc current or ac current with an electrical waveform. 
       FIG.  3 A  is a simplified cross-sectional view of a cooling station  30  according to an embodiment. Referring to  FIG.  3 A , the cooling station  30  includes a housing  301 , a plurality of shelves  302  attached to an inner wall surface  301   a  of the housing  301  and configured to provide support to a plurality of substrates  303 , and a shelter plate  304  disposed on an upper side of the housing  301 . In an embodiment, the housing  301  has an open upper side and an open lower side, so that air may flow from the upper side to the lower side or vice versa. It should be noted that the upper side and lower side of the cooling station are open whereas the curing chamber has a top wall and a bottom wall that enclose the curing chamber, i.e., the cooling station is an open enclosure where air can flow in and out through the upper side and the lower side, so that it has the pressure of the atmosphere. In one example, hot air may enter the cooling station  30  through the lower side and exit the cooling station  30  through the upper side. In contrast, the curing chamber  106  or  20  is a sealed enclosure to have a pressure different from the atmosphere pressure. In an embodiment, the shelter plate  304  is removably mounted to the upper side of the housing  301  through a fastening member  306 . In an embodiment, the fastening member  306  includes threaded nuts and bolts configured to mount the shelter plate  304  to a portion of the housing  301 . In an embodiment, the fastening member  306  includes screws that allows an easy and quick assembly of the shelter plate  304  to the housing  301  and its removal from the housing  301 . It should be noted that the fastening member  306  is attached to a portion of the upper side of the housing  301  so that an air gap  307  extends vertically between the upper side of the housing  301  and the shelter plate  304 . In an embodiment, the shelter plate  304  is a square having a size of 20×20 cm 2  for a 300 mm (i.e., 11.8 inch) substrate. In an embodiment, the shelter plate  304  includes aluminum. In an embodiment, the entire housing  301  includes a material having a thermal conductivity equal to or less than 150 W/mK. In some embodiments, the housing may include lead with a thermal conductivity of about 35 W/mK. In some embodiments, the housing may include iron having a thermal conductivity of about 80 W/mK. In some other embodiments, the housing may include platinum having a thermal conductivity of about 70 W/mK. In some other embodiments, the housing may include stainless steel having a thermal conductivity of about 15 W/mK. In yet some other embodiments, the housing may include glass having a thermal conductivity of about 0.8 W/mK. In various implementation, the shelter  304  is configured to function as a passive heating member for preventing upper slot cooling. 
     In an embodiment, the inner region of the cooling station  30  has a cross-sectional square or rectangular shape. Each side of the inner region of the cooling station is designed to accommodate 300 (i.e., 11.8 inch) mm, 450 mm (i.e., 17.7 inch) substrates or substrates having other dimensions. In an embodiment, the cooling station  30  has a height  310  that is relatively large, such that a large number of shelves  302  can be formed in the cooling station to accommodate a number of substrates that have been cured from the curing station  103 . This is a case where the substrate process system  10  has more than one curing chamber  103  for curing a large quantity of batches of substrates having a flowable dielectric material deposited thereon. In an embodiment, each of the shelves  302  includes a heating element  302   a  configured to control temperature of an associated substrate deposited thereon. In an embodiment, the heating element  302   a  includes a heated plate. In an embodiment, the heating element  302   a  includes an electrically conductive material arranged spirally on a surface of the shelf and electrically isolated from the substrate by a dielectric layer. In an embodiment, the heating element  302   a  includes a polymer film having an electrically conductive circuit disposed on the surface of the polymer film and electrically insulated by the polymer film. In an embodiment, each of the shelves  302  includes a temperature sensor (e.g., a thermistor or thermocouple) disposed on its upper surface and configured to measure a temperature of the substrate disposed thereon and configured to control the heating level of the heating element  302   a.  Each temperature sensor provides measured temperature information of a corresponding substrate to a processing unit (not shown), so that the processing unit can control the temperature of each substrate individually. In one implementation, the individual heating elements  302   a  can be individually controlled at one or more temperatures. In another implementation, the individual heating elements  302   a  can be collectively controlled at one or more temperatures. By providing these controllable heating elements, temperature provided to the substrates  303  can be controlled to address the aforementioned condense accumulation on the substrates  303  with time passing. The heating element  302   a  may be referred to as active heating in accordance with the disclosure such that temperature are actively controlled for the individual substrates. 
     In an embodiment, the cooling station  30  includes an access door  308  that can be slidably open and close for receiving or removing substrates. In an embodiment, the cooling station  30  is rotatable around a vertical axis, so that the access door can be facing the transfer chamber, the curing chamber, or the FOUPs. In an embodiment, the housing  301  of the cooling station  30  has a square-shaped or rectangular-shaped cross section and includes a plurality of access doors each disposed at a side surface of the cooling station  30  for receiving or removing substrates. 
       FIG.  3 B  is a simplified top plan view of a cooling system  30 B according to an embodiment. Referring to  FIG.  3 B , the cooling system  30 B includes a squared-shaped or rectangular-shaped inner chamber having four vertical walls. In an embodiment, each wall has a dimension relatively large to accommodate substrates in the lateral or horizontal direction. In an embodiment, the cooling system  30 B has an access door  312  operable in an open position and in a closed position for loading and unloading substrates. In an embodiment, the cooling system  30 B is rotatable around a vertical axis  314  to be in a first position  315  for loading or unloading substrates from and to the FOUPs, a second position  316  for loading or unloading substrates from and to the transfer chamber, and a third position  317  for receiving the cured substrates from the curing station. 
       FIG.  3 C  is a simplified top plan view of a cooling system  30 C according to another embodiment. Referring to  FIG.  3 C , the cooling system  30 C includes a squared-shaped shaped or rectangular-shaped inner chamber having four vertical walls. In an embodiment, each wall has a dimension relatively large to accommodate substrates in the lateral or horizontal direction. In an embodiment, the cooling system  30 C has a first access door  321  arranged in a first side  3011  of the housing  301  facing the FOUPs and operable in an open position and in a closed position for loading and unloading substrates from and to the FOUPs, a second access door  322  arranged in a second side  3012  of the housing  301  facing the cooling station  106  and operable in an open position and in a closed position for transferring cured substrates to the cooling station, and a third access door  323  arranged in a third side  3013  of the housing  301  facing the transfer chamber  103  and operable in an open position and in a closed position for loading and unloading substrates from and to the load lock chamber  104 . 
       FIG.  4 A  is a simplified cross-sectional view of a cooling station  40  according to an embodiment. The cooling station  40  is substantially similar to the cooling station  30  with the difference that it further includes an airflow structure. Accordingly, description provided in relation to the elements illustrated in  FIG.  3    is applicable to the elements illustrated in  FIG.  4    as appropriate. Referring to  FIG.  4 A , the cooling station  40  includes an airflow structure  401  configured to deliver a temperature-controlled air (i.e., the temperature of the air is controlled) to control temperature inside the cooling station. In an embodiment, the airflow structure  401  includes a conduit  402  coupled to an air source  403  that is configured to supply a temperature-controlled air to the airflow structure. In an embodiment, the temperature-controlled air supplied by the air source  403  is in a range between about 20° C. and 100° C., in a range between 40° C. and 80° C., and in a range between 45° C. and 65° C. The temperature-controlled air may include nitrogen, argon, or XCDA dry air. In an embodiment, the airflow structure  401  includes a temperature sensor (not shown) configured to measure a temperature of the temperature-controlled air exiting the airflow structure  401 . In some embodiments, the airflow structure is disposed below the shelter plate  304  and configured to operate as an air curtain, e.g., an air curtain showerhead or a cylindrical air curtain. It should be noted that in some implementations, each of the shelves  302  may include a heating element like  302   a  shown in  FIG.  3 A , which is configured to control temperature of an associated substrate deposited thereon. 
       FIG.  4 B  is a simplified cross-sectional view of a showerhead  410  according to an embodiment. Referring to  FIG.  4 B , the showerhead  410  is a part of the airflow structure  401  disposed below the shelter plate  304  and configured to supply a temperature-controlled air in a vertical direction (the top-to-bottom direction) to the inside of the housing  301 . The showerhead  410  includes a stem  411  having a first end attached to the conduit  402  and a second end opposite the first end. The showerhead  410  also includes a back plate  413  attached to the second end of the stem  411 , and a face plate  415  attached to the back plate  413 . The face plate  415  includes a plurality of holes  417  that are distributed evenly or in a regular arrangement throughout the face plate in various patterns (e.g., a honey comb or concentric spiral pattern). The showerhead  410  directs a temperature-controlled air  419  from the air source  403  in a vertical direction to the inside of the housing  301 . The showerhead  410  may be referred to as passive heating in that it aids air flow for better temperature control within the cooling station. 
       FIG.  4 C  is a simplified cross-sectional view of a cylindrical air curtain structure  490  according to an embodiment. Referring to  FIG.  4 C , the cylindrical air curtain structure  490  is a part of the airflow structure  401  and coupled to the air source  403  through the conduit  402 . The cylindrical air curtain structure  490  includes a plurality of air pipes  420  arranged along the inner wall surface  301   a  of the housing  301 . Each of the air pipes  420  includes at least one outlet and is configured to supply air in a circulation  421  from left-to-right or from right-to-left to control a temperature of the inside of the housing  301 . 
       FIG.  5    is a simplified flowchart of a method  50  of controlling a temperature of a substrate having a cured dielectric material deposited thereon according to an embodiment. Referring to  FIG.  5   , the method  50  includes, at step  501 , providing a substrate having trenches formed therein, and forming a flowable dielectric material on the substrate filing the trenches. The flowable material layer may be formed by a flowable chemical vapor deposition (FCVD) process. In an embodiment, depositing a flowable dielectric material involves exposing the substrate to gaseous reactants including a dielectric precursor and an oxidant. In some embodiments, the flowable dielectric material is a silicon and nitrogen-containing material, such as silicon nitride or silicon oxynitride deposited by introducing vapor phase reactants to the process chamber. The nitrogen may come from a silicon and nitrogen-containing precursor, e.g., trisilyamine (TSA) or disilylamine (DSA), a nitrogen precursor, e.g., ammonia (NH 3 ), or a nitrogen-containing gas, e.g., N 2 , NH 3 , NO, NO 2 , or N 2 O. At step  503 , the method  50  includes transferring the substrate including the formed flowable dielectric material into a curing chamber where a curing process is performed. In an embodiment, the curing process includes submitting the formed flowable dielectric material to a treatment at a temperature in a range of about 25° C. to about 200° C., in a range of about 35° C. to about 55° C., in range of about 40° C. to about 50° C. under an ozone atmosphere and a pressure in a range of 1 atmosphere to about 20 atmospheres. The method also includes, at step  505 , transferring the substrate including the cured flowable dielectric material into a cooling station. The cooling station has a predetermined temperature. In one implementation, the predetermined temperature is higher than the room temperature (typically between 15° C. and 30° C.) in the fabrication facility. In one example, the predetermined is higher than 15° C. In one implementation, the predetermined temperature is close to the temperature of a process chamber (e.g., one of the process chambers  102  in  FIG.  1 A ) and the temperature of a curing chamber (e.g., one of the curing chambers  103  in  FIG.  1 A ). The cooling station includes a housing having an open upper side and a shelter plate disposed over the open upper side. In an embodiment, the cooling chamber includes an airflow structure coupled to an external air source for controlling a circulation of a temperature-controlled air supplied by the air source. 
       FIGS.  6 A to  6 C  are simplified cross-sectional views of a portion of a substrate in various stages of the process illustrated in  FIG.  5   . Referring to  FIG.  6 A , a substrate  601  having multiple trench structures  602   a,    602   b,  and  602   c  is provided. In the example of  FIG.  6 A , the substrate  601  may be a silicon substrate. In other examples, the substrate  601  may have a plurality of layers including, e.g., silicon oxide, silicon germanium, doped or undoped polysilicon, silicon-on-insulator, silicon nitride, doped silicon, germanium, glass, gallium nitride, gallium arsenide. The substrate  601  can have various sizes, such as 300 mm, 450 mm diameter substrate. The trench structures  602   a,    602   b,  and  602   c  are formed in the substrate  601  by an etching process, e.g., a dry plasma etching process. Three-dimensional (3D) structures  611   a  and  611   b  are interposed between two of the trench structures  602   a,    602   b,  and  602   c.  The 3D structures  611   a  and  611   b  are 3D channel structures of non-planar transistors (i.e., 3D transistors or multi-gate field-effect transistors) that are in contact with gates. In one example, the 3D structures  611   a  and  611   b  are fin structures of fin field-effect transistors (FinFETs). In another example, 3D structures  611   a  and  611   b  are 3D channel structures of gate-all-around field-effect transistors (GAA FETs). It should be understood that these examples are not intended to be limiting. In one implementation, the trench structures  602   a,    602   b,  and  602   c  and the 3D structures  611   a  and  611   b  may be formed by patterning a photoresist layer on the substrate using photolithography processes and selectively etching the substrate. Referring to  FIG.  6 B , a flowable dielectric material  603  is deposited on the substrate filling the trench structures  602   a ,  602   b,  and  602   c.  In an embodiment, the flowable dielectric material  603  may include oxynitride. In an embodiment, a gas mixture including a silicon-containing material and a nitrogen containing precursor is provided into the process chamber  102  at a predetermined flow rate and within a predetermined temperature range to maintain the flowable dielectric material  603  in a flowable state (liquid phase). After the flowable dielectric material  603  is deposited, the substrate is transferred to the curing chamber  103  to remove moisture and other volatile components to form a solid dielectric material. In an embodiment, a batch of substrates are processes in the process chamber, and the curing temperature of each individual processed substrate can be controlled in the curing chamber. After the curing process is complete, the cured substrate is transferred to the cooling station  106  shown in  FIG.  1 A  for cooling before being unloaded to the FOUPs or pre-heated again prior to being transferred back to the process chamber  102  for subsequent processing. In one example, the cured substrate may be submitted to a chemical-mechanical polishing (CMP) process to obtain the structure as shown in  FIG.  6 C . As shown in  FIG.  6 C , the upper surface of the structure has been flattened or smoothed by the CMP process. It should be noted that subsequent processes may be further conducted using the structure shown in  FIG.  6 C  as a basis. It should also be noted that although the example in  FIGS.  6 A- 6 C  is directed to FinFET-related fabrication, the sprits described in the disclosure may be applied to the fabrication of other semiconductor devices such as GAA FETs as needed. 
     Embodiments of the present disclosure provide a cooling station. The cooling station includes a housing comprising a plurality of shelves configured to receive a plurality of substrates, a shelter plate disposed over an upper side of the housing and configured to reduce heat loss of an upper substrate of the plurality of substrates, and an airflow structure in the housing and configured to control an air circulation in the housing. 
     Embodiments of the present disclosure also provide a method. The method includes the following steps: providing a substrate; etching the substrate to form a plurality of 3D structures and a plurality of trench structures; forming, at a process chamber, a flowable material layer over the substrate; curing, at a curing chamber, the substrate including the flowable material layer; and transferring the substrate to a cooling station having a predetermined temperature. 
     Embodiments of the present disclosure also provide a method of cooling a flowable dielectric material. The method includes forming a flowable material layer on a substrate, transferring the substrate including the flowable material layer to a curing chamber for curing the flowable layer, and transferring the substrate after curing the flowable material layer to a cooling station. In an embodiment, the cooling station includes a housing having an open upper side, and an airflow structure disposed in the housing and configured to control a circulation of a temperature-controlled air in the inside of the housing. 
     The foregoing merely outlines features of embodiments of the disclosure. Various modifications and alternatives to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. Those skilled in the art will appreciate that equivalent constructions do not depart from the scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.