Patent Publication Number: US-2021189561-A1

Title: System and method for monitoring and performing thin film deposition

Description:
BACKGROUND 
     Technical Field 
     The present disclosure relates to the field of thin film deposition. 
     Description of the Related Art 
     There has been a continuous demand for increasing computing power in electronic devices including smart phones, tablets, desktop computers, laptop computers and many other kinds of electronic devices. Integrated circuits provide the computing power for these electronic devices. One way to increase computing power in integrated circuits is to increase the number of transistors and other integrated circuit features that can be included for a given area of semiconductor substrate. 
     To continue decreasing the size of features in integrated circuits, various thin film deposition techniques are implemented. These techniques can form very thin films. However, thin film deposition techniques also face serious difficulties in ensuring that the thin films are properly formed. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is an illustration of a thin film deposition system, according to one embodiment. 
         FIGS. 2A-2C  illustrate a substrate during successive steps of an atomic layer deposition process, according to one embodiment. 
         FIG. 3  is a plurality of graphs of fluid flow during an atomic layer deposition process. 
         FIG. 4  is an illustration of an atomic layer deposition system, according to one embodiment. 
         FIG. 5  is an illustration of an atomic layer deposition system, according to one embodiment. 
         FIG. 6  is a graph illustrating the intensity compounds in an exhaust fluid, according to one embodiment. 
         FIG. 7  is a block diagram of a semiconductor process system, according to one embodiment. 
         FIG. 8  is a flow diagram of a method for forming a thin film, according to one embodiment. 
         FIG. 9  is a flow diagram of a method for forming a thin film, according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, many thicknesses and materials are described for various layers and structures within an integrated circuit die. Specific dimensions and materials are given by way of example for various embodiments. Those of skill in the art will recognize, in light of the present disclosure, that other dimensions and materials can be used in many cases without departing from the scope of the present disclosure. 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the described subject matter. Specific examples of components and arrangements are described below to simplify the present description. 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. 
     Further, 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. 
     In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments of the disclosure. However, one skilled in the art will understand that the disclosure may be practiced without these specific details. In other instances, well-known structures associated with electronic components and fabrication techniques have not been described in detail to avoid unnecessarily obscuring the descriptions of the embodiments of the present disclosure. 
     Unless the context requires otherwise, throughout the specification and claims that follow, the word “comprise” and variations thereof, such as “comprises” and “comprising,” are to be construed in an open, inclusive sense, that is, as “including, but not limited to.” 
     The use of ordinals such as first, second and third does not necessarily imply a ranked sense of order, but rather may only distinguish between multiple instances of an act or structure. 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
     As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     Embodiments of the present disclosure provide thin films of reliable thickness and composition. Embodiments of the present disclosure accurately monitor the flow of deposition fluids during thin film deposition processes and adjust the flow of fluids in real time to ensure proper formation of the thin films. Embodiments of the present disclosure monitor the flow of the fluids by detecting byproducts of the deposition fluids in exhaust fluids flowing from the thin film deposition chamber. Embodiments of the present disclosure can also determine whether a deposition fluid source is empty or nearly empty and needs to be refilled or replaced. 
     Accordingly, embodiments of the present disclosure provide many benefits. In case that flow rates are not sufficient or if fluid sources are empty during thin film deposition processes, thin films may not be formed properly. This may result in the scrapping of entire batches of semiconductor wafers at great expense in terms of time and resources. Embodiments of the present disclosure overcome these drawbacks by accurately monitoring the flow of deposition fluids in real time, by adjusting fluid flows in real time, and by detecting if fluid levels are low or entirely depleted in fluid sources and refilling or replacing the fluid sources. 
       FIG. 1  is a block diagram of a thin film deposition system  100 , according to one embodiment. The thin film deposition system  100  includes a thin film deposition chamber  102  including an interior volume  103 . A support  106  is positioned within the interior volume  103  and is configured to support a substrate  104  during a thin film deposition process. The thin film deposition system  100  is configured to deposit a thin film on the substrate  104 . 
     In one embodiment, the thin film deposition system  100  includes a first fluid source  108  and a second fluid source  110 . The first fluid source  108  supplies a first fluid into the interior volume  103 . The second fluid source  110  supplies a second fluid into the interior volume  103 . The first and second fluids both contribute in depositing a thin film on the substrate  104 . 
     In one embodiment, the thin film deposition system  100  is an atomic layer deposition (ALD) system that performs ALD processes. The ALD processes form a seed layer on the substrate  104 . The seed layer is selected to chemically interact with a first precursor gas, such as the first fluid supplied by the first fluid source  108 . The first fluid is supplied into the interior volume  103 . The first fluid reacts with the seed layer to form new compounds with each atom or molecule of the surface of the seed layer. The new compounds include atoms that were previously part of the seed layer and atoms that were previously part of the first fluid. The reaction of the seed layer with the first fluid results in new compounds that were not present before the reaction. This corresponds to the deposition of a first layer, or a first step in deposition of the first layer of the thin film. 
     The reaction between the seed layer and the first fluid may also bring one or more byproduct(s). After flowing the first fluid for a selected amount of time, a purge gas is supplied into the interior volume to purge the byproducts of the first fluid, as well as the unreacted portions of the first fluid, from the interior volume  103  through the exhaust channel  102 . As will be described in more detail below, the purge fluid can flow from either or both of the purge sources  112  and  114 . 
     After the first fluid has been purged, a second precursor gas, such as the second fluid is supplied into the interior volume from the second fluid source  110 . The second fluid reacts with the first layer to form a second layer on top of the first layer of the thin film. Alternatively, the flow of the second fluid can complete the formation of the first layer of the thing film by reacting with the first portion of the first layer. As is described in more detailed below, the thin film is made of several layers. Each layer, or pair of layers, is formed by a cycle of flowing the first fluid, purging, flowing the second fluid, and purging again. The total thickness of the thin film is based on the number of cycles. This reaction also result in byproducts. A purge gas is again supplied into the interior volume  103  to purge the byproducts of the second fluid, as well as the unreacted portions of the second fluid, from the interior volume  103 . This sequence of supplying the first fluid, purging, supplying the second fluid, and purging again is repeated until the thin film has a selected thickness. As will be described in more detail below, the purge gas can be flowed from either or both of the purge sources  112  and  114 . 
     In some cases, the thin film deposition process can be very sensitive to concentrations or flow rates of the first and second fluids at the various stages during the thin film deposition processes. If the concentration or flow rate of the first or second fluid is not sufficiently high at particular stages, then the thin film may not be formed properly on the substrate  104 . For example, the thin film may not have a desired composition or thickness if the concentration or flow rate of the first or second fluid is not sufficiently high. 
     The amount of fluid remaining in the first and second fluid sources  108  and  110  can affect the flow rate or concentration of the first and second fluids in the deposition chamber  102 . For example, if the first fluid source  108  has a low amount of the first fluid remaining, then the flow rate of the first fluid from the first fluid source  108  may be low. If the first fluid source  108  is empty and does not include any more of the first fluid, there will be no flow of the first fluid from the first fluid source  108 . The same considerations apply to the second fluid source  110 . Low or nonexistent flow rates can result in a thin film that is not properly formed. 
     In one embodiment, the thin film deposition system  100  includes an exhaust channel  120  communicatively coupled to the interior volume  103  of the deposition chamber  102 . Exhaust products from the thin film deposition process flow out of the interior volume  103  via the exhaust channel  120 . The exhaust products can include unreacted portions of the first and second fluids, byproducts of the first and second fluids, purge fluids used to purge the interior volume  103 , or other fluids or materials. 
     The thin film deposition system  100  includes a byproduct sensor  122  coupled to the exhaust channel  120 . The byproduct sensor  122  is configured to sense the presence and/or concentration of byproducts from one or both of the first and second fluids in the exhaust fluids flowing through the exhaust channel  120 . The first and second fluids interact together to form the thin film on the substrate  104 . The deposition process also results in byproducts from the first and second fluids. The concentration of these byproducts is indicative of the concentration or flow rate of one or both of the first and second fluids during deposition. The byproduct sensor  122  senses the concentration of the byproducts in the exhaust fluids flowing from the interior volume  103  through the exhaust channel  120 . 
     In one embodiment, the thin film deposition system  100  includes a control system  124 . The control system  124  is coupled to the byproduct sensor  122 . The control system  124  receives the sensor signals from the byproduct sensor  122 . The sensor signals from the byproduct sensor  122  are indicative of the concentration of byproducts of one or both of the first and second fluids in the exhaust fluid. The control system  124  can analyze the sensor signals and determine a flow rate or concentration of one or both of the first and second fluid sources  108 ,  110  during particular stages of the deposition process. The control system  124  can also determine a remaining level of the first fluid in the first fluid source  108  and/or of the second fluid in the second fluid source  110 . 
     The control system  124  can include one or more computer readable memories. The one or more memories can store software instructions for analyzing sensor signals from the byproduct sensor  122  and for controlling various aspects of the thin film deposition system  100  based on the sensor signals. The control system  124  can include one or more processors configured to execute the software instructions. The control system  124  can include communication resources that enable communication with the byproduct sensor  122  and other components of the thin film deposition system  100 . 
     In one embodiment, the control system  124  is communicatively coupled to the first and second fluid sources  108 ,  110  via one or more communication channels  125 . The control system  124  can send signals to the first fluid source  108  and the second fluid source  110  via the communication channels  125 . The control system  124  can control functionality of the first and second fluid sources  108 ,  110  responsive, in part, to the sensor signals from the byproduct sensor  122 . 
     In one embodiment, the byproduct sensor  122  senses a concentration of byproducts in the exhaust fluid. The byproduct sensor  122  cents sensor signals to the control system  124 . The control system  124  analyzes the sensor signals and determines that a recent flow rate of the first fluid from the first fluid source  108  was lower than expected, based on the sensor signals from the byproduct sensor  122 . The control system  124  sends control signals to the first fluid source  108  commanding the first fluid source  108  to increase a flow rate of the first fluid during a subsequent deposition cycle. The first fluid source  108  increases the flow rate of the first fluid into the interior volume  103  of the deposition chamber  102  responsive to the control signals from the control system  124 . The byproduct sensor  122  can again generate sensor signals indicative of the concentration of byproducts of the first fluid during the subsequent deposition cycle. The control system  124  can determine whether the flowrate of the first fluid needs to be adjusted based on the sensor signals from the byproduct sensor  122 . In this way, the byproduct sensor  122 , the control system  124 , and the first fluid source  108  makeup a feedback loop for adjusting the flowrate of the first fluid. The control system  124  can also control the second fluid source  110  in the same manner as the first fluid source  108 . Furthermore, the control system  124  can control both the first fluid source  108  and the second fluid source  110 . 
     In one embodiment, the thin film deposition system  100  can include one or more valves, pumps, or other flow control mechanisms for controlling the flow rate of the first fluid from the first fluid source  108 . These flow control mechanisms may be part of the fluid source  108  or may be separate from the fluid source  108 . The control system  124  can be communicatively coupled to these flow control mechanisms or to systems that control these flow control mechanisms. The control system  124  can control the flowrate of the first fluid by controlling these mechanisms. The control system  100  may include valves, pumps, or other flow control mechanisms that control the flow of the second fluid from the second fluid source  110  in the same manner as described above in reference to the first fluid and the first fluid source  108 . 
     In one embodiment, the control system  124  can determine how much of the first fluid remains in the first fluid source  108  based on the sensor signals from the byproduct sensor  122 . The control system  124  may analyze the sensor signals to determine that the first fluid source  108  is empty or is nearly empty. The control system  124  can provide an indication to technicians or other personnel indicating that the first fluid source  108  is empty or nearly empty and that the first fluid source  108  should be refilled or replaced. These indications can be displayed on a display, can be transmitted via email, instant message, or other communication platforms that enable technicians or other experts or systems to understand that one or both of the first and second fluid sources  108 ,  110  are empty or nearly empty. 
     In one embodiment, the thin film deposition system  100  includes a manifold mixer  116  and a fluid distributor  118 . The manifold mixer  116  receives the first and second fluids, either together or separately, from the first fluid source  108  and the second fluid source  110 . The manifold mixer  116  provides either the first fluid, the second fluid, or a mixture of the first and second fluids to the fluid distributor  118 . The fluid distributor  118  receives one or more fluids from the manifold mixer  116  and distributes the one or more fluids into the interior volume  103  of the thin film deposition chamber  102 . 
     In one embodiment, the first fluid source  108  is coupled to the manifold mixer  116  by a first fluid channel  130 . The first fluid channel  130  carries the first fluid from the fluid source  108  to the manifold mixer  116 . The first fluid channel  130  can be a tube, pipe, or other suitable channel for passing the first fluid from the first fluid source  108  to the manifold mixer  116 . The second fluid source  110  is coupled to the manifold mixer  116  by second fluid channel  132 . The second fluid channel  132  carries the second fluid from the second fluid source  110  to the manifold mixer  116 . 
     In one embodiment, the manifold mixer  134  is coupled to the fluid distributor  118  by a third fluid line  134 . The third fluid line  134  carries fluid from the manifold mixer  116  to the fluid distributor  118 . The third fluid line  134  may carry the first fluid, the second fluid, a mixture of the first and second fluids, or other fluids, as will be described in more detail below. 
     The first and second fluid sources  108 ,  110  can include fluid tanks. The fluid tanks can store the first and second fluids. The fluid tanks can selectively output the first and second fluids. 
     In one embodiment, the thin film deposition system  100  includes a first purge source  112  and the second purge source  114 . The first purge source is coupled to the first fluid line  130  by first purge line  136 . The second purge source is coupled to the fluid line  132  by second purge line  138 . In practice, the first and second purge sources  112  and  114  may be a single purge source. 
     In one embodiment, the first and second purge sources  112 ,  114  supply a purging gas into the interior volume  103  of the deposition chamber  102 . The purge fluid is a fluid selected to purge or carry the first fluid, the second fluid, byproducts of the first or second fluid, or other fluids from the interior volume  103  of the deposition chamber  102 . The purge fluid is selected to not interact with the substrate  104 , the thin film layer deposited on the substrate  104 , the first and second fluids, and byproducts of this person second fluid. Accordingly, the purge fluid may be an inert gas including, but not limited to, Ar or N 2 . In one embodiment, the first and second purge sources include a same purge fluid. Alternatively, the purge sources  112  and  114  can include different purge fluid. 
     After a cycle of flowing one or both of the first or second fluids into the interior volume  103 , the thin film deposition system  100  purges the interior volume  103  by flowing the purge fluid into the interior volume  103  and through the exhaust channel  120 . The control system  124  can be communicatively coupled to the first and second purge sources  112 ,  114 , or flow mechanisms that control the flow of the purge fluid from the first and second purge sources  112 ,  114 . The control system  124  can purge the interior volume  103  after or between deposition cycles, as will be explained in more detail below. 
     In one embodiment, the purge source  112  can supply the purge gas after the fluid source  108  supplies the first fluid. The purge source  114  can supply the purge gas after the fluid source  110  supplies the first fluid. In one embodiment, the purge source  112  and purge source  114  both supply the purge gas after the fluid source  108  supplies the first fluid and after the fluid source  110  supplies the second fluid. 
     In one embodiment, the first and second purge lines  136 ,  138  join the first and second fluid lines  130 ,  132  at selected angles. The angles are selected to ensure that the purge fluid flows toward the manifold mixer  116  and not toward the first or second fluid sources  108 ,  110 . Likewise the angle helps ensure that the and second fluids will flow from the first and second fluid sources  108 ,  110  toward the manifold mixer  116  and not toward the first and second purge sources  112 ,  114 . 
     While  FIG. 1  illustrates a first fluid source  108  and a second fluid source  110 , in practice the thin film deposition system  100  can include other numbers of fluid sources. For example, the thin film deposition system  100  may include only a single fluid source or more than two fluid sources. Accordingly, the thin film deposition system  100  can include a different number than two fluid sources without departing from the scope of the present disclosure. 
     Furthermore, the thin film deposition system  100  has been described, in one embodiment, as an ALD system, the thin film deposition system  100  can include other types of deposition systems without departing from the scope of the present disclosure. For example, the thin film deposition system  100  can include a chemical vapor deposition system, a physical vapor deposition system, a sputtering system, or other types of thin film deposition systems without departing from the scope of the present disclosure. A byproduct sensor  122  can be utilized to determine the flowrate or concentration of deposition fluids as well as how much deposition fluid remains in a deposition fluid source. 
       FIGS. 2A-2C  illustrate a substrate  104  during successive steps of an ALD process, according to one embodiment. The description of  FIGS. 2A-2C  will be made with reference to  FIG. 1 . Accordingly, the ALD process is performed, in one example, by the thin film deposition system  100  of  FIG. 1 . 
     In  FIG. 2A , a substrate  104  is positioned in an interior volume  103  of a thin film deposition chamber  102 . A seed layer  140  is positioned on a top surface of the substrate  104 . As will be described in more detail below, the seed layer  140  is of a composition selected to facilitate the beginning of an ALD process. The material of the seed layer  140  is selected based on the materials or fluids that will be used in the ALD process to produce the thin film. In particular, the seed layer  140  is selected to bond with a material for a first layer of the ALD. 
     In one embodiment, the substrate  104  is a semiconductor wafer. The ALD process is one of a large number of semiconductor processes that will be performed on the semiconductor wafer. These semiconductor processes combined to form and pattern various layers of materials including semiconductor materials, dielectric materials, and conductive materials. After the semiconductor processes have been performed, the semiconductor wafer will be diced into a plurality of individual integrated circuit dies. Accordingly, ALD process described in relation to  FIGS. 2A-2C  results in a thin film layer that will be part of various integrated circuit dies. 
     In  FIG. 2B  a first layer  144  of a thin film  141  is deposited on the seed layer  140 . In particular, a first fluid  142  is flowed into the interior volume  103  of the thin film deposition chamber  102 . The first fluid  144  can be provided via the first fluid source  108  of  FIG. 1 . The first fluid  144  includes a precursor or reactant that reacts with the seed layer  140 . In particular, each surface atom or molecule of the seed layer  140  reacts with the precursor or reactant in the first fluid  144 . The result is that a new molecule or compound is formed at each surface site of the seed layer  140 . Accordingly, a first layer  144  of the thin film  141  is formed on the seed layer  140 . The first layer  144  has a thickness of one molecule or compound. 
     Although  FIG. 2B  illustrates a first layer  144  forming on top of the seed layer  140 , in practice, the first layer  144  may incorporate the seed layer  140 . The first layer  144  may correspond to the surface atoms or molecules of the seed layer  140  reacting with the precursor or reactant in the first fluid  142  in order to form new compounds from the seed layer  140  and the precursor or reactant in the first fluid  142 . Specific examples of materials of the seed layer in the first fluid  142  are given in relation to  FIGS. 4 and 5 . 
     In one embodiment, the reaction of the first fluid  142  with the seed layer  140  results in byproducts  146 . The byproducts  146  are the byproducts of the reaction between the seed layer  140  and the first fluid  142 . When the first fluid  144  reacts with and combines with the seed layer  140 , new compounds or molecules are formed from the reaction of the material of the first fluid  144  and the seed layer  140 . Some of the new compounds make up the first layer  144 . Other of the new compounds are byproducts  146 . Accordingly, the first fluid  142  may include a first type of molecule. The first type of molecule reacts with the seed layer  140  and forms a second type of molecule and the third type of molecule. The second type of molecule makes up the first layer  144  of the thin film  141 . The third type of molecule is the byproducts  146 . 
     In  FIG. 2C  a second layer  150  of the thin film  141  is deposited on the first layer  144 . In particular, a second fluid  148  is flowed into the interior volume  103  of the thin film deposition chamber  102 . The second fluid  148  can be provided via the second fluid source  110  of  FIG. 1 . The second fluid  148  includes a precursor or reactant that reacts with the first layer  144 . In particular, each surface atom or molecule of the first layer  144  reacts with the precursor or reactant in the second fluid  148 . The result is that a new molecule or compound is formed at each surface site of the first layer  144 . Accordingly, a second layer  150  of the thin film  141  is formed on the first layer  144 . The first layer  144  has a thickness of one molecule or compound. 
     Although  FIG. 2C  illustrates deposition of a second layer  150  on top of the first layer  144 , in practice, the second layer  150  may incorporate the first layer  144 . The second layer  150  may correspond to the surface atoms or molecules of the first layer  144  reacting with the precursor or reactant in the second fluid  148  in order to form new compounds from the first layer  144  and the precursor or reactant in the second fluid  148 . Accordingly, the process illustrated in  FIGS. 2A-2C  may result in a single layer of the thin film  141 . The first fluid transforms the seed layer, then the second fluid further transforms the seed layer. Specific examples of materials of the second fluid  148  are given in relation to  FIGS. 4 and 5 . 
     In one embodiment, the reaction of the second fluid  148  with the first layer  144  results in byproducts  152 . The byproducts  152  are the byproducts of the reaction between the first layer  144  and the second fluid  148 . When the second fluid  148  reacts with and combines with the first layer  144 , new compounds or molecules are formed from the material of the second fluid  148  and the first layer  144 . Some of the new compounds make up the second layer  150 . Other of the new compounds are byproducts  152 . Accordingly, the second fluid  148  may include a first type of molecule. The first type of molecule reacts with the first layer  144  and forms a second type of molecule and a third type of molecule. The second type of molecule makes up the second layer  150  of the thin film  141 . The third type of molecule is the byproducts  152 . 
     The process shown in relation to  FIGS. 2A-2C  can be repeated multiple times to fully form the thin film  141  on the substrate  140 . Each deposition cycle results in a new layer of the thin film  141  deposited on the previous layer. The overall thickness of the thin film  141  can be tightly controlled by selecting the number of deposition cycles. Because each deposition cycle results in a new layer (or two new layers), the total number of layers of the thin film  141 , and thus, the total thickness, is based directly on the number of deposition cycles. 
     As described previously in relation to  FIG. 1 , is possible that the flow of either the first fluid  142  or the second fluid  148  could be unduly low. The thin film deposition system  100  utilizes the byproduct sensor  122  senses the concentration of the byproducts  146  and/or  152 . The control system  124  can determine the concentration or flow rate of the first fluid  142  and/or the second fluid  148  based on the concentration of the byproducts  146  and/or  152 . The control system  124  can then take actions to increase the flow rate or alert personnel or other system components that the first or second fluid source  108 ,  110  is low or empty. 
       FIG. 3  illustrates a plurality of fluid flow graphs  160 ,  162 , and  164 , according to one embodiment. The first graph  160  illustrates a flow of a first fluid  142 . The second graph  162  illustrates a flow of the purge fluid. The third draft  164  illustrates the flow of a second fluid  148 . 
     At time T 0 , the first fluid  142  begins to flow into the interior volume  103  of the thin film deposition chamber  102 . At time T 1  the first fluid stops flowing. At time T 2 , the purge fluid begins to flow into the interior volume  103  of the thin film deposition chamber  102 . The purge fluid can flow from the purge source  112  or both the purge source  112  and the purge source  114 . At time T 3 , the purge fluid stops flowing. At time T 4 , the second fluid  148  begins to flow into the interior volume  103  of the thin film deposition chamber  102 . At time T 5 , the second fluid  148  stops flowing. At time T 6  the purge fluid begins flowing again. The purge fluid can flow from the purge source  114  or both the purge source  112  and the purge source  114 . At time T 7 , the purge fluid stops flowing. 
     In one embodiment, the process between times T 0  and T 7  corresponds to a single deposition cycle. This process corresponds to the process illustrated in  FIGS. 2A-2C . The flow of the purge fluid is omitted in  FIGS. 2A-2C , but the purge fluid can flow from the purge source  112 , the purge source  114 , or both the purge source  112  and purge source  114  as illustrated in  FIG. 1 . The purge fluid purges the interior volume  103  of remaining portions of the first and second fluids  142 ,  148  and their byproducts  146 ,  152 . Each cycle of flow of the first and second fluids  142 ,  148  results in a layer of the thin film  141 , or a pair of layers as the case may be. 
     In one embodiment, a second cycle of the deposition process begins at time T 8  and ends at time T 15 . A third cycle of the deposition process begins at time T 16  and ends at time T 23 .  FIG. 3  illustrates three deposition cycles. However, the ALD process can include many more deposition cycles than three. In one example, and ALD process may include 20-25 deposition cycles, though more or few deposition cycles can be used without departing from the scope of the present disclosure. 
       FIG. 4  is an illustration of a thin film deposition system  400 , according to one embodiment. The thin film deposition system  400  is similar in many ways to the thin film deposition system  100  of  FIG. 1 . The thin film deposition system  400  may include components shown and described in relation to the thin film deposition system  100  of  FIG. 1 , but that are not shown in  FIG. 4 . 
     The thin film deposition system  400  includes a thin film deposition chamber  102  including an interior volume  103  and the substrate positioned within the interior volume  103 . The thin film deposition system  400  includes a first fluid source  108  and the second fluid source  110  communicatively coupled to the interior volume  103  by a first fluid line  103  and a second fluid line  132 . The thin film deposition system further includes an exhaust channel  120  communicatively coupled to the interior volume  103  and a pH sensor  162  coupled to the exhaust channel  120 . 
     In one embodiment, the first fluid source  108  includes H 2 0 in gas or liquid form. The second fluid source  110  includes HfCL 4  fluid. The HfCL 4  fluid may be a gas. The first and second fluids can be used to form a hafnium based high K gate dielectric layer for CMOS transistors. 
     An ALD process using the thin film deposition system  400  will be described with reference to  FIG. 3 . Between times T 0  and T 1 , the first fluid (H 2 0) output from the first fluid source  108  into the interior volume  103 . In one example, the first fluid flows for about 10 seconds, though other lengths of time can be used without departing from the scope of the present disclosure. 
     Between times T 2  and T 3 , a purge gas is output from a purge source (not shown in  FIG. 4 ), such as either or both of the purge sources  112  and  114  of  FIG. 1 , into the interior volume  103 . The purge gas may include nitrogen molecules (N 2 ) or another nonreactive gas. In one example, purge gas flows for about three seconds, though other lengths of time can be used without departing from the scope of the present disclosure. 
     Between times T 4  and T 5 , HfCL 4  is output from the second fluid source  110  into the interior volume  103 . In one example, the HfCL 4  flows for about one second, though other lengths of time can be used without departing from the scope of the present disclosure. Between times T 6  and T 7 , the purge gas flows. The purge gas can flow from a purge source, such as either or both of the purge sources  112  and  114  of  FIG. 1 . 
     In one embodiment, the seed layer  141  sown in  FIG. 2B  includes functionalized oxygen atoms. When the first fluid (H 2 O) is provided into the interior volume  103 , the H 2 O molecules react with the functionalized oxygen atoms of the seed layer to form OH from each functionalized oxygen atom. The byproducts of this reaction, as well as any remaining H 2 O molecules, are purged from the interior volume  103  via the exhaust channel  120  by flow of the purge gas. The HfCl 4  is then provided into the interior volume  103 . The HfCl 4  reacts with the OH compounds to form, on the substrate  104 , Hf—O—HfCl 3 . One of the byproducts of this reaction is HCl. The purge gas flows again, followed by H 2 O. The H 2 O reacts with the Hf—O—HfCl 3  to form, on the substrate  104 , Hf—OH 3 . A byproduct of this reaction is HCl. The purge gas then flows again. The cycle can be repeated multiple times, as described above. 
     The pH sensors  162  senses the pH of the exhaust gases being purged via the exhaust channel  120 . The pH of the exhaust gases is indicative of the flow rate, concentration, or remaining supply of HfCl 4  in the second fluid source  110 . 
     In one embodiment, when the purge gas flows after flowing H 2 O, the exhaust gas will include the byproduct HCl, as described above, and unreacted H 2 O. The byproduct HCl disassociates in the presence of the unreacted H 2 O. The result is that H+ and Cl− are present in the exhaust gas. H+ is strongly acidic. 
     In one embodiment, the pH sensor is positioned to sense the pH of the exhaust fluid flowing through the exhaust channel  120 . The pH sensor senses the acidic H+ from the disassociated byproduct HCl. Accordingly, the pH is indicative of the concentration of H+ in the exhaust fluid. The concentration of H+ is indicative of the amount of byproduct HCl produced. The amount of byproduct HCl is indicative of the flow rate or concentration of HfCl 4  during the periods when HfCl 4  is provided to the interior volume  103 . Accordingly, the pH of the exhaust fluid is indicative of the flow rate of HfCl 4 , which can in turn be indicative of the amount of HfCl 4  remaining in the second fluid source  110 . 
     In another embodiment, one of the byproducts can include NH3. The byproduct NH 3  disassociates in the presence of the unreacted H 2 O to form NH 4 + and OH−. OH− is highly alkaline. The pH sensor  162  can sense the alkalinity of the OH− in the exhaust fluid. h 
     The pH sensor  162  can include a portion that protrudes into the exhaust channel  120  in order to sense the pH of exhaust fluids. Alternatively, a portion of the exhaust fluid can be drafted out of the exhaust channel  120  into a separate channel from which the pH sensor  162  can sense the pH of the exhaust fluids. 
     In one embodiment, the pH sensor  162  sends sensor signals to the control system  124 . The control system  124  can estimate, based on the sensor signals, a flow rate of the HfCl 4  or a current remaining supply of HfCl4 in the second fluid source  110 . The control system  124  can then take action to adjust the flow rate or request that the fluid source  110  be refilled with HfCl4. 
       FIG. 5  is an illustration of a thin film deposition system  500 , according to one embodiment. The thin film deposition system  500  is similar in many ways to the thin film deposition system  400  of  FIG. 4 . 
     In one embodiment, the thin film deposition system  500  includes a mass spectrometer  164 . The mass spectrometer receives atoms, molecules and compounds from the exhaust fluid in the exhaust channel. The mass spectrometer  164  can receive the atoms, molecules, and compounds via an aperture in the exhaust channel  120  that enables some of the atoms, molecules, and compounds to flow into the mass spectrometer  164 . 
     In one embodiment, the mass spectrometer  164  generates sensor signals indicative of the types and concentrations of various atoms, molecules, and compounds in the exhaust fluid. The mass spectrometer  164  can output the sensor signals to the control system  124 . The control system  124  can determine or estimate the concentration of various byproducts within the exhaust fluid. Based on this information, the control system  124  can adjust the flow of the first or second fluids or can determine that the first or second fluid sources  108 ,  110  are empty or contain low remaining amounts of the first and second fluids. 
       FIG. 6  is a graph illustrating the intensity or concentration of various molecules or compounds in the exhaust fluid, according to one embodiment. Particular types of ions will have a characteristic mass to charge ratio (m/z). The mass spectrometer  164  generates sensor signals indicating the intensity or concentration of particles having particular mass to charge ratios. The control system  124  can generate a graph  170  of the intensity or concentration of particles having particular mass to charge ratios based on the sensor signals. The control system  124  can compare the graph  172 . The reference graph  172  is an indication of the expected or desired intensity of particles present in the exhaust fluid. The control system  124  can compare the graph  170  to the reference graph  172  in order to determine if the concentration of certain types of compounds in the byproducts are at expected levels. The control system  124  can take action responsive to the comparison. 
     The control system  124  can include graphs or reference data for other types of sensor data. For example, the control system  124  can include graphs or reference data for pH sensors signals in order to compare pH sensor signals to reference data. 
     In one embodiment, the control system  124  can estimate and expected thickness of the thin film  141  based on the concentration of byproducts in the exhaust fluid. For example, the control system  124  can include test data indicating the thickness of thin films versus the concentration of various byproducts. The control system  124  can then make estimates about the thickness of the thin film  141  based on the concentration of byproducts sensed by byproduct sensor  122 . 
       FIG. 7  is a block diagram of a semiconductor process system  700 , according to one embodiment. The semiconductor process system  700  includes a thin film deposition system  100 , a thickness analyzer  702 , and a robot arm  704 . After the thin film deposition system  100  deposits the thin film  141  on the substrate  104 , the robot arm  704  transfers the substrate  104  to the thickness analyzer  702 . The thickness analyzer  702  measures the thickness of the thin film. The semiconductor process system  700  can determine whether the thin film deposition process passes or fails based on the thickness analyzer  702 . 
     In one embodiment, the thickness analyzer  702  may include use of spectrometry to determine thicknesses of layers or coatings, such as an x-ray measurement device. In one example, the x-ray measurement device is an x-ray fluorescence measurement device. The x-ray measurement device bombards the thin film  141  with x-rays and measures the energy of radiation emitted by the thin film  141 . The radiation emitted by the thin film  141  is indicative of the elements and compounds included in the thin film  141 . Furthermore, the energy of the radiation emitted by the thin film  141  after absorption of x-rays is indicative of the thickness of the thin film. 
     In one embodiment, the thickness analyzer  702  is an optical thickness analyzer. The optical thickness analyzer can include an ellipsometer. The ellipsometer measures the polarization change in light reflected, absorbed, scattered, or emitted by the thin film  141 . The change in polarization of the light gives an indication of the thickness of the thin film  141 . Other types of thickness analyzers can be utilized to analyze the thickness of the thin film  141  without departing from the scope of the present disclosure. 
     Analyzing the thickness of the thin film  141  can give an indication of whether the thin film deposition process is functioning properly. If the thickness of the thin film  141  is not within the expected range, the thin film deposition process can be adjusted in order to generate a thin film  141  having desired characteristics. Accordingly, the thickness analyzer  702  can help to assure that the thin film deposition system  100  operates correctly in a timely manner. 
       FIG. 8  is a flow diagram of a method  800  for depositing a thin film. At  802 , the method includes forming a thin film on a substrate within a thin film deposition chamber by flowing a first fluid into the thin film deposition chamber. One example of a thin film is the thin films  141  of  FIGS. 2B and 2C . One example of a thin film deposition chamber is the thin film deposition chamber  102  of  FIG. 1 . At  804 , the method  800  includes passing an exhaust fluid from the thin film deposition chamber. At  806 , the method  800  includes sensing byproducts of the first fluid and one or more materials in the exhaust fluid. At  808 , the method  800  includes adjusting a flow of the first fluid based on the byproducts. 
       FIG. 9  is a flow diagram of a method  900  for depositing a thin film. At  902 , the method  900  includes supporting a semiconductor wafer in a thin film deposition chamber. One example of a thin film deposition chamber is the thin film deposition chamber  102  of  FIG. 1 . At  904 , the method  900  includes forming a thin film on the semiconductor wafer with an atomic layer deposition process by flowing a first fluid and a second fluid into the thin film deposition chamber. At  906 , the method  900  includes passing exhaust fluid from the thin film deposition chamber via an exhaust channel. One example of an exhaust channel is the exhaust channel  120  of  FIG. 1 . At  908 , the method  900  includes sensing a byproduct in the exhaust fluid. At  910 , the method  900  includes estimating, a flow characteristic of the first or second fluid based on the byproduct. 
     In one embodiment, a thin film deposition system including a thin film deposition chamber and a support configured to support a substrate within the thin film deposition chamber. The system includes a first fluid source configured to provide a first fluid into the thin film deposition chamber during a thin film deposition process, an exhaust channel configured to pass an exhaust fluid from the thin film deposition chamber, and a byproduct sensor configured to sense byproducts in the exhaust fluid and to generate sensor signals indicative of the byproducts. The system includes a control system configured to receive the sensor signals and to adjust the thin film deposition process responsive to the sensor signals. 
     In one embodiment, a method includes forming a thin film on a substrate within a thin film deposition chamber by flowing a first fluid into the thin film deposition chamber and passing an exhaust fluid from the thin film deposition chamber. The method includes sensing byproducts of the first fluid and one or more materials in the exhaust fluid and adjusting a flow of the first fluid based on the byproducts. 
     In one embodiment, a method includes supporting a semiconductor wafer in a thin film deposition chamber and forming a thin film on the semiconductor wafer with an atomic layer deposition process by flowing a first fluid and a second fluid into the thin film deposition chamber. The method includes passing exhaust fluid from the thin film deposition chamber via an exhaust channel, sensing a byproduct in the exhaust fluid, and estimating, a flow characteristic of the first or second fluid based on the byproduct. 
     Embodiments of the present disclosure provide thin films of reliable thickness and composition. Embodiments of the present disclosure accurately monitor the flow of deposition fluids during thin film deposition processes and adjust the flow of fluids in real time to ensure proper formation of the thin films. Embodiments of the present disclosure monitor the flow of the fluids by detecting byproducts of the deposition fluids in exhaust fluids flowing from the thin film deposition chamber. Embodiments of the present disclosure can also determine whether a deposition fluid source is empty or nearly empty and needs to be refilled or replaced. 
     The various embodiments described above can be combined to provide further embodiments. All U.S. patent application publications and U.S. patent applications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary, to employ concepts of the various patents, applications and publications to provide yet further embodiments. 
     These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.