Patent Publication Number: US-2022236639-A1

Title: Directed self-assembly

Description:
TECHNICAL FIELD 
     The present invention relates generally to semiconductor processing, and, in particular embodiments, to systems, tools, and methods for directed self-assembly. 
     BACKGROUND 
     Generally, the fabrication of Integrated Circuits (IC&#39;s) requires the formation of numerous device elements onto a semiconductor substrate. Traditionally, IC&#39;s are fabricated using optical lithography. Optical lithography forms device elements by forming a layer of photoresist on a substrate, partially exposing the photoresist to light through a patterned mask, developing the exposed photoresist to define the mask pattern in the photoresist, and then etching the photoresist to form the pattern in substrate. 
     Semiconductor technology is driven by a demand for doubling circuit density every two years. As circuit density increases, critical dimensions and pitches of IC device elements decrease. Critical dimensions and pitches have decreased in size to a point at which optical lithography based processes are using multiple patterning techniques to achieve the needed critical dimensions, which increases the costs of the fabrication process. In addition, future technology nodes may require even more complicated multiple patterning steps. 
     Directed self-assembly (DSA) has been identified as an alternative method to form more densely packed devices. The DSA process is controlled by the molecular weight of the block copolymer mixture, which in theory, can be set to the desired dimension, which may be smaller than the dimensions achievable with optical lithography. 
     This is because directed self-assembly allows forming small device elements using self-assembling block copolymers along with a guide pattern formed using a lithography process. However, the guide pattern is patterned using a coarser lithography process while the subsequent directed self-assembly process has the potential to form features having critical dimensions comparable to that achieved with a multiple patterning process. 
     However, directed self-assembly has its own advantages and disadvantages. As noted above, feature size in a directed self-assembly process is determined by the mixture of the block copolymers used. More specifically, in a typical directed self-assembly process, the molecular weight of the block copolymer mixture controls the critical dimension, pitch, and phase (shape) of the formed device elements. A single block copolymer mixture can only correspond to a single critical dimension, pitch, and shape. While this attribute can be leveraged to develop features that may not be easily formed with lithography, the DSA process brings its own unique set of challenges. 
     SUMMARY 
     In accordance with an embodiment of the present invention, a method for forming a device includes blending, in a mixer within a fabrication facility, a first liquid including a first block copolymer with a second liquid including a second block copolymer to form a first mixture, the first block copolymer including a first homopolymer and a second homopolymer, the first homopolymer having a first mole fraction in the first liquid, the second block copolymer including the first homopolymer and the second homopolymer, the first homopolymer having a second mole fraction in the second liquid, the first mole fraction being different from the second mole fraction; placing a substrate over a substrate holder of a processing chamber within the fabrication facility; and coating the substrate with the first mixture within the processing chamber. 
     In accordance with an embodiment of the present invention, a method for forming a device includes blending, in a mixer within a fabrication facility, a first block copolymer and a solvent to form a first mixture, the first block copolymer including a first homopolymer and a second homopolymer; placing a substrate over a substrate holder of a processing chamber within the fabrication facility; and coating the substrate with the first mixture within the processing chamber. 
     In accordance with an embodiment of the present invention, a method for forming a device includes blending, in a mixer within a fabrication facility, a first liquid including a first block copolymer and a second liquid including essentially a first homopolymer to form a first mixture, the first block copolymer including the first homopolymer and a second homopolymer; placing a substrate over a substrate holder of a processing chamber within the fabrication facility; and coating the substrate with the first mixture within the processing chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates a block copolymer coating tool in accordance with an embodiment of the present application; 
         FIG. 2  is illustrates a block copolymer coating tool in accordance with an embodiment of the present application; 
         FIGS. 3A-3E  illustrates cross-sectional views of a semiconductor device during various stages of fabrication in accordance with an embodiment of the present application, wherein  FIG. 3A  illustrates the device after forming a patterned photoresist layer,  FIG. 3B  illustrates the device after coating a mixture comprising a blended block copolymer,  FIG. 3C  illustrates the device after annealing,  FIG. 3D  illustrates the device after selectively removing a plurality of regions, and  FIG. 3E  illustrates the device after forming a first pattern of device elements; 
         FIG. 4  is a flow chart of a directed self-assembly method for forming a first pattern of device in accordance with an embodiment of the present application; 
         FIG. 5  is a flow chart of the method for tuning a first block copolymer mixture within a fabrication facility in order to meet a target metric in accordance with an embodiment of the present application; 
         FIGS. 6A-6B  illustrates cross-sectional views of a semiconductor device during various stages of fabrication in accordance with an embodiment of the present application, wherein  FIG. 6A  illustrates the device after coating a second patterned photoresist layer with a second block copolymer mixture, and  FIG. 6B  illustrates the device after forming a second patterned layer of device elements; and 
         FIG. 7  is a flow chart of a directed self-assembly method for forming a second pattern of device elements over a first pattern of device elements in accordance with an embodiment of the present application. 
     
    
    
     Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale. 
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     As previously noted, a directed self-assembly process uses block copolymers. Block copolymer mixtures are blended by vendors and shipped pre-packaged to the manufacturing facility in discrete bottles. A disadvantage of such a typical directed self-assembly process is that vendors of pre-packaged block copolymers are generally not aware of the specific process requirements for a given process flow and therefore would not be able to meet the specific composition process window required at the manufacturing facility, e.g., to meet the critical dimension targets for the features. A high volume manufacture of IC&#39;s may require multiple packages of the same block copolymer mixture. However, due to quality control issues, multiple bottles of the same block copolymer mixture, especially from different batches, may have inconsistent molecular weights. Hence, different packages of the same block copolymer mixture from the vendor may have differing compositions of the block copolymers and therefore produce features having different critical dimensions and pitches. As an example, in some technologies, a 10% batch-to-batch variability of the molecular weight of a block copolymer mixture can change the critical dimension of a device element by more than 6%. Such large deviations can potentially cause a process hold, where the production line is stopped until the feature sizes are brought back within the process window. Also, reordering pre-packaged block copolymer mixtures is costly because of the downtime of the fabrication facility for the time taken to receive the new bottle. 
     Another disadvantage of directed self-assembly is that every feature having a different critical dimension uses a separate block copolymer mixture. This is costly and time consuming if multiple levels or features are to be fabricated with a directed self-assembly process in a traditional semiconductor fabrication process. This is because for each feature that has to be patterned at a different feature size, a different composition of the block copolymer is to be used, which has to be delivered to the manufacturing facility. This can cause a significant bottleneck and increase costs associated with managing multiple bottles of pre-packaged block copolymer mixtures. For example, using multiple prepackaged bottles can get expensive due to the complexities associated with purchasing, scheduling, storing, and tool requirements associated with using different bottles. 
     Another disadvantage of directed self-assembly is that a pre-packaged block copolymer mixture has a single film thickness which can result in an uneven fill pattern across the substrate when the mixture is applied. In other words, each pre-packaged block copolymer mixture has a predetermined film thickness that it is able to achieve. Therefore, if a pre-packaged block copolymer mixture has a film thickness less than a target thickness, a pattern of device elements will not be properly filled. Thus, even for features having the same critical dimension, the same bottles may not be used because of the differences in thickness of the base layer being patterned. 
     Embodiments of the present invention advantageously avoid the above issues by forming the block copolymer mixtures within the fabrication facility which allows for consistency between batches, improved control over the feature metrics such as critical dimension, pitch, microphase separation, surface roughness, local critical dimension uniformity, and control of the pattern fill density to ensure a uniform coating across a substrate. This disclosure describes embodiments of methods of blending block copolymer mixtures in an inline mixer within a processing tool such as a coating tool within a fabrication facility that enables cost effective manufacturing of ICs with a directed self-assembly process. 
     A coating tool within a fabrication facility is illustrated in  FIG. 1  and  FIG. 2 , in accordance with an embodiment of the invention. Several example embodiments of methods of forming a semiconductor device with the coating tools are described in greater detail in  FIGS. 3-7 . 
       FIG. 1  illustrates a block copolymer coating tool in accordance with an embodiment of the present application. 
     As illustrated in  FIG. 1 , the block copolymer coating tool includes a first mixer apparatus  100  and a processing tool  124  in which a semiconductor substrate  120  is processed. The processing tool  124  comprises a processing chamber  122  and a substrate holder  121  configured to support the semiconductor substrate  120  during processing. A blended block copolymer mixture is coated onto a major surface of the semiconductor substrate  120  by injecting the blended block copolymer mixture from the first mixer apparatus  100  through a nozzle  118  of the processing tool  124 . For example, the nozzle  118  may be a flat flan nozzle, solid stream nozzle, or any other nozzle known to a person having ordinary skill in the art. 
     The substrate holder  121  may be configured to be rotated during the coating process. The processing chamber  122  includes outlets for any excess fluid and may also be connected to a pressure system to maintain a target pressure within the processing chamber  122  in certain embodiments. The processing chamber  122  may also include gas inlets such as for pumping inert gases into the processing chamber  122  for certain applications. 
     Referring to  FIG. 1 , the first mixer apparatus  100  includes a first supply tank  102  and a second supply tank  104  coupled to a mixer  114  comprising a mixing chamber  112 . Although only two sources are illustrated as being mixed, in various embodiments, more than two sources of fluids may be mixed in the mixer  114 . The first supply tank  102  and the second supply tank  104  each hold a first liquid and a second liquid, respectively. In various embodiments, the first supply tank  102  and the second supply tank  104  are made of ceramics, glass, stainless steel or any other material depending upon the corrosive properties of the first and second liquids being used. 
     In various embodiments, the first liquid comprises a first block copolymer comprising a first homopolymer (-A-A- . . . A-A-) and a second homopolymer (-B-B- . . . B-B-). Accordingly, the first homopolymer is a polymer of a first monomer (A) while the second homopolymer is a polymer of a second monomer (B). A block copolymer ((-A-B-)-(-A-B-)- . . . (-A-B-)-(-A-B-)-) is formed when the first homopolymer is mixed with the second homopolymer (B). Examples of homopolymers include methyl-methacrylate, styrene, dimethylsiloxane, ethylene oxide, butadiene, vinylpyridine, isoprene, lactic acid, and others. 
     In various embodiments, the first homopolymer has a first mole fraction in the first liquid. The second liquid comprises a second block copolymer comprising the first homopolymer and the second homopolymer. The first homopolymer has a second mole fraction in the second liquid. Thus, while both the first liquid and the second liquid have the same polymers, the first mole fraction is different than the second mole fraction. 
     In one or more embodiments, the first homopolymer is a polystyrene block comprising repeating styrene units and the second homopolymer is a poly methyl-methacrylate block comprising repeating methyl-methacrylate units. The first homopolymer together with the second homopolymer form poly(styrene-b-methyl-methacrylate), i.e., repeating styrene-b-methyl-methacrylate units, which is a block copolymer. Therefore the first liquid and the second liquid both comprise of poly(styrene-b-methylmethacrylate) with different molecular weights. The first liquid and the second liquid are described herein for example only. A person having ordinary skill in the art may use other types of liquids as well. 
     In various embodiments, the first mole fraction may range from 10% to 90% in the first liquid and the second mole fraction may range from 10% to 90% in the second liquid so long as the first mole fraction and the second mole fraction are different. 
     In various embodiments, the first mixer apparatus  100  may be gravity driven with few intermediate components or may comprise a system of pumps and valves for control of fluid flow. Accordingly, in certain embodiments, the first mixer apparatus  100  optionally includes a first pump  106   a , a second pump  106   b , and a third pump  106   c , a first shutoff valve  108   a , a second shutoff valve  108   b , and a third shutoff valve  108   c , a first flowmeter  110   a , a second flowmeter  110   b , and a third flowmeter  110   c.    
     The first supply tank  102  and the second supply tank  104  are both connected to a first pump  106   a  and a second pump  106   b . The first pump  106   a  and the second pump  106   b  are respectively connected to a first shutoff valve  108   a  and a second shutoff valve  108   b  that are further coupled to the mixer  114 . The mixer  114  is connected to the processing tool  124  via an optional third pump  106   c  connected to a third shutoff valve  108   c  and a third flowmeter  110   c.    
     As illustrated in  FIG. 1 , the mixer  114  may be disposed within the mixing chamber  112 . As one example, the mixer  114  may be designed as described in Application Ser. No. 62/839,917, filed on Apr. 29, 2019, which is incorporated herein by reference. In certain embodiments, the mixer  114  may be a planetary mixer, a static mixer, or any other mixer known to a person having ordinary skill in the art that can blend liquid mixtures. 
     The first mixer apparatus  100  may further include an electronic flow control system  115 , e.g., to control the various aspects of the fluid flow. The electronic flow control system  115  comprises a controller  116  and various memory, input/output devices, analog to digital converters, and other hardware and software as known to a person with ordinary skill in the art. For example, the controller may comprise a processor, microprocessor, or any other type of controller known in the art. In addition, the electronic flow control system  115  includes sensors such as flow sensors, temperature sensors, and others. 
     The electronic flow control system  115  is connected to the first pump  106   a , the second pump  106   b , the third pump  106   c , the first shutoff valve  108   a , the second shutoff valve  108   b , the third shutoff valve  108   c , the first flowmeter  110   a , the second flowmeter  110   b , the third flowmeter  110   c , the mixer  112  as well as other components such as the processing tool. More specifically, measurement data from the first flowmeter  110   a , the second flowmeter  110   b , the third flowmeter  110   c  may be received at the electronic flow control system  115  while control signals generated at the controller  116  may be sent to the first pump  106   a , the second pump  106   b , the third pump  106   c , the first shutoff valve  108   a , the second shutoff valve  108   b , the third shutoff valve  108   c.    
     The electronic flow control system  115  may receive measurement or metrology data from sensors  103  and process information including process recipe/metrics  105  such as a target process window. Sensors  103  may include various types of sensors including, but not limited to optical sensors (such as cameras, lasers, light, reflectometer, spectrometers, etc.), capacitive sensors, ultrasonic sensors, gas sensors, temperature sensors to monitor liquid temperature, or other sensors that may monitor the blending process as well as the first liquid, the second liquid, and the blended first mixture. The electronic flow control system  115  may receive additional data inputted by the user including, but not limited to, the target volumes of a first liquid in the first supply tank  102 , a second liquid in the second supply tank  104 , a first mixture, and a required mixing time. In one example embodiment, a mass spectrometer may be used to determine the composition of the first liquid and the second liquid periodically. In one example embodiment, one or more optical sensors may be used to determine opacity of the first and second liquids periodically that can help determine the validity of the composition. 
     Based on the data from the various sensors  103  and process recipe/metrics  105 , the controller  116  will generate control signals to activate the first pump  106   a  and the second pump  106   b  and deactivate the first shutoff valve  108   a  and the second shutoff valve  108   b  to dispense the first liquid and the second liquid into the mixer  114 . The first pump  106   a , the second pump  106   b , and the third pump  106   c  may comprise of any centrifugal pump or any positive displacement pumps that are able to pump liquid block copolymers as known to a person having ordinary skill in the art. The first shutoff valve  108   a , the second shutoff valve  108   b , and the third shutoff valve  108   c  may comprise of an electromotive diaphragm valve, an electromotive angle seat valve, or any other valve known to a person having ordinary skill in the art. 
     As the first and second liquids flow from the first supply tank  102  and the second supply tank  104 , the controller  116  constantly or periodically monitors the first flowmeter  110   a  and the second flowmeter  110   b  to track the volume of each liquid dispensed into the mixer  114 . For example, the first flowmeter  110   a , the second flowmeter  110   b , and the third flowmeter  110   c  may comprise of a positive displacement flowmeter that can directly provide the volume of a liquid dispensed with no additional calculation required or any other flowmeter known to a person having ordinary skill in the art. 
     Once the controller  116  determines, based on data provided by the first flowmeter  110   a  and the various sensors  103  and process recipe/metrics  105 , that the target volume of the first liquid has been dispensed, the controller  116  generates control signals to activate the first shutoff valve  108   a  and turn off the first pump  106   a . Similarly, when the controller  116  determines, based on data provided by the second flowmeter  110   b  and the various sensors  103  and process recipe/metrics  105 , that the target volume of the second liquid has been dispensed the controller  116  (CTLR) generates control signals to activate the second shutoff valve  108   b  and turn off the second pump  106   b.    
     After the first and second liquids are dispensed into mixer  114 , controller  116  will generate control signals to turn on mixer  114  for a duration based on the data received, and the mixer  114  blends the first liquid and the second liquid to form a first mixture. 
     In various embodiments, the mixer  114  may include a holding tank in which the blended liquids i.e., first mixture, are stored. However, in certain embodiments, the first mixture may be directly injected into the nozzle  118  of the processing tool without any separate holding tanks. In certain embodiments, the nozzle  118  and the holding tank may be integrated together, for example, in a plenum to the processing chamber  122 . 
     After the mixing, the controller  116  generates control signals to activate the optional third pump  106   c  and deactivate the third shutoff valve  108   c  so as to inject the first mixture into the nozzle  118  and coat the semiconductor substrate  120  with the first mixture within the process chamber  122 . 
     In an alternative embodiment in order to generate a more uniform fill density across the semiconductor substrate, using the method above, the second liquid may comprise of a solvent. In certain embodiments, the solvent may be added to improve metrics such as surface roughness and other features. In various embodiments, the solvent may be propylene glycol monomethyl ether acetate, toluene, or any other solvent known to mix with block copolymer mixtures in the art. In other embodiments, the solvent may be added from a third supply tank in addition to the second liquid comprising the second block copolymer from the second supply tank  104 . 
     In another alternative embodiment, the second liquid may comprise of essentially the first homopolymer or essentially the second homopolymer. In such embodiments, the first homopolymer or the second homopolymer may help to fine tune a parameter such as critical dimension or pitch of the feature to be patterned. 
       FIG. 2  illustrates a block copolymer coating tool in accordance with an embodiment of the present application. 
     As illustrated in  FIG. 2 , the coating tool includes a second mixer apparatus  200  and a processing tool  124  in which a semiconductor substrate  120  is processed. The second mixer apparatus  200  may include any number of supply containers ranging from 1, 2, 3, . . . N poured into a mixer  114  to form a first mixture of block copolymers that is coated onto the semiconductor substrate  120  through a nozzle  118 . The first supply container 1 is configured to hold a first liquid, the second supply container 2 is configured to hold a second liquid, and correspondingly the nth supply container N is configured to hold the nth liquid. For example, the supply containers may be made out of ceramics, glass, stainless steel or any other material known by one with ordinary skill in the art based of the corrosive properties of the liquids. 
     In various embodiments, the first mixture includes a first liquid held in the first supply container 1 and a second liquid held in the second supply container 2. The first liquid held in the first supply container 1 as described above may be a first homopolymer and a second homopolymer with the first homopolymer having a first mole fraction in the first liquid. The second liquid held in the second supply container 2 as described above may be a first homopolymer and a second homopolymer with the first homopolymer having a second mole fraction in the second liquid. 
     The liquid valves from the multiple supply containers 1-N may be opened electronically or by the user so that the multiple liquids are blended in the mixer  114  as described above with respect to  FIG. 1  to form the first mixture. In the same manner illustrated in  FIG. 1 , the mixer  114  is connected to the processing tool  124  via the third pump  106   c  that is connected to the third shutoff valve  108   c , and the third flowmeter  110   c . The blended first mixture may be held in a holding tank either within the second mixer apparatus  200  or the processing tool  124 . 
     At the conclusion of mixing, the user deactivates the third shutoff valve  108   c  and turns on the third pump  106   c  so as to inject the first mixture into the nozzle  118  and coat the semiconductor substrate  120  with first mixture within the processing chamber  122 . As the first mixture exits mixer  114 , it flows through the third flowmeter  110   c  and the user constantly or periodically monitors the volume readout of the third flowmeter  110   c . Then, once the third flowmeter  110   c  displays that the desired volume of the first mixture has been dispensed, the user shuts off the third pump  106   c  and activates the third shutoff valve  108   c.    
     In various embodiments, the semiconductor substrate  120  may undergo a curing process either in the processing tool  124  or in a different tool. 
     In other embodiments the first mixture may include a third liquid comprising essentially the first homopolymer, essentially the second homopolymer, or a solvent added from a third supply tank 3 in addition to the first liquid and the second liquid. The first homopolymer, the second homopolymer, and solvent are not described again and may be similar to the solvent described above, e.g., with respect to  FIG. 1 . 
     In other embodiments the first mixture may include a third liquid comprising essentially the first homopolymer from a third supply tank 3 and a fourth liquid comprising essentially the second homopolymer from a fourth supply tank 4 in addition to the first liquid and the second liquid. 
     As mentioned above, the first mixture is blended in order to form device features of a semiconductor device using a directed self-assembly (DSA) process. 
     Although not explicitly described, this embodiment may also include an electronic control system that is coupled to various sensors and data sources to continuously monitor and control the blending process as described with respect to  FIG. 1  above and using the flow chart of  FIG. 5  below. 
       FIGS. 3A-3E  illustrates cross-sectional views of a semiconductor device during various stages of fabrication in accordance with an embodiment of the present application, where  FIG. 3A  illustrates the device after forming a patterned photoresist layer,  FIG. 3B  illustrates the device after coating a mixture comprising a blended block copolymer,  FIG. 3C  illustrates the device after annealing,  FIG. 3D  illustrates the device after selectively removing a plurality of regions, and  FIG. 3E  illustrates the device after forming a first pattern of device elements. 
     Referring to  FIG. 3A , a first patterned photoresist layer  308  is formed over the semiconductor substrate  120 . This stage of processing may be performed at any stage of the device fabrication such as fin formation, gate formation, metal lines, contact plugs, vias, and so on. 
     The semiconductor substrate  120  includes a semiconductor body  320  supporting a first layer to be patterned  306  on which the first patterned photoresist layer  308  is formed. The semiconductor body  320  may be bulk substrate such as a bulk silicon substrate, a silicon-on-insulator substrate, a silicon carbide substrate, a gallium arsenide substrate, or hybrid substrates such as gallium nitride on silicon and other heteroepitaxial substrates, or any other configuration and material known by one with ordinary skill in the art. 
     The first layer to be patterned  306  may be the layer that forms the device feature or it may be an intervening layer that is used to subsequently form the device feature. An example of such an intervening layer may be a hard mask layer that is used to subsequently pattern a feature in an underlying layer. In various embodiments, the first layer to be patterned  306  may be an insulating layer, a conductive layer, a semiconductor layer depending on the feature being fabricated at this stage of fabrication. 
     As known to a person having ordinary skill in the art, embodiments of the present invention contemplate the presence of other intervening layers. For example, an antireflective coating layer  307  may be formed before forming the first patterned photoresist layer  308 . The antireflection coating (ARC) film may comprise a silicon antireflection coating in one embodiment. In certain embodiments, the antireflective coating layer  307  may comprise an organic ARC layer, a metal ARC layer, a metal oxide ARC layer, or a titanium nitride ARC layer. The antireflective coating layer  307  has to also avoid interaction between material of the directed self-assembly being formed (i.e., the first or second homopolymer chains present in the first mixture being deposited as will be described below) and the underlying first layer to be patterned  306 . 
     In various embodiments, the first patterned photoresist layer  308  serves as a first DSA template in that the underlying features are aligned to the first patterned photoresist layer  308 . The first patterned photoresist layer  308  may comprise a positive, a negative, or a hybrid photoresist. In one embodiment, the first patterned photoresist layer  308  is formed by spin coating a resist material over the first layer to be patterned  306 , baking the resist material to form a photoresist, exposing the photoresist using lithography, and developing the exposed photoresist. 
     The first patterned photoresist layer  308  has an opening thus formed with a specific width  302  and critical dimension  304  defined during the lithographic process. Advantageously, the dimensions of the specific width  302  and critical dimension  304  are much larger than the feature being formed, and therefore a lower resolution (therefore lower cost) lithography process can be used to form these features. 
     Referring to  FIG. 3B , the first mixture  310 , blended in the mixer  114  within the same fabrication facility, is coated within the first patterned photoresist layer  308  via the first mixer apparatus  100  or the second mixer apparatus  200  as discussed in more detail above with respect to  FIG. 1  and  FIG. 2 . For sake of clarity, the filling of the adjacent openings of the first patterned photoresist layer  308  is not shown in  FIGS. 3B-3E . The first mixture  310  is coated over the first patterned photoresist layer  308  and fills the openings between the patterns of the first patterned photoresist layer  308 . 
     In one embodiment, the first mixture  310  has a first ratio of the first liquid comprising a first block copolymer liquid to the second liquid comprising a second block copolymer liquid. In another embodiment, the first mixture  310  is a mixture of a first block copolymer liquid blended with a solvent as described in  FIG. 1 or 2 . In yet another embodiment, the first mixture  310  is a mixture of a first block copolymer liquid blended with a homopolymer as described in  FIG. 1 or 2 . Accordingly, in various embodiments, the first mixture  310  has first block copolymer liquid blended with one or more of a second block copolymer liquid, a solvent, or a homopolymer as described in  FIG. 1 or 2 . 
     Referring to  FIG. 3C , the semiconductor substrate  120  is annealed which causes the first homopolymer and the second homopolymer, present in the first mixture  310 , to separate and form a first plurality of regions  312  and a second plurality of regions  314  that alternate between each homopolymer and are aligned with the first patterned photoresist layer  308 . The first plurality of regions  312  correspond to the first homopolymer and the second plurality of regions  314  correspond to the second homopolymer. In various embodiments, the pitch between neighboring first plurality of regions  312  or between neighboring second plurality of regions  314  may vary between 10 nm to 100 nm, thus enabling forming structures that are lower than the resolution limit of the lithography process used to pattern the first patterned photoresist layer  308 . 
     Annealing may include furnace annealing, lamp based annealing, rapid thermal annealing, or any other annealing method known by one with ordinary skill in the art. In various embodiments, the annealing may be performed between 100° C. to 700° C., and in one embodiment between 200° C. and 400° C. 
     As is known to a person having ordinary skill in the art, the chemical composition of the block copolymer may be tailored by varying the composition and mole fraction of the homopolymers to control the type of phase separation after annealing. During annealing, the homopolymers undergo microphase separation forming repeating patterns or periodic structures. The type of pattern may be spheres of the first homopolymer embedded in a matrix of the second homopolymer (or vice versa), hexagonal close packed cylinders of the first homopolymer embedded in a matrix of the second homopolymer (or vice versa), gyroid, or lamellae of alternating first homopolymer and second homopolymer. Of these possible structures, from a lithography perspective, lines can be formed from alternating lamellae while the hexagonal closed packed cylinders can be used for forming an array of contact holes. In the illustration described herein, the first plurality of regions  312  and the second plurality of regions  314  are selected to form in a lamellar shape. However, in other embodiments, the first plurality of regions  312  and the second plurality of regions  314  may be selected to form cylinders of the first plurality of regions  312  in the second plurality of regions  314  (or vice versa). 
     Further, one of the homopolymers has more affinity towards the first patterned photoresist layer  308  and is formed contacting the sidewalls of the first patterned photoresist layer  308 . In this example illustration, the first plurality of regions  312  preferentially forms on the sidewalls of the first patterned photoresist layer  308 . 
     Referring to  FIG. 3D , one of either the first plurality of regions  312  or the second plurality of regions  314  is selectively removed forming a first etch mask in the first patterned photoresist layer  308 . In various embodiments, the first plurality of regions  312  corresponding to the first homopolymer are removed and the second plurality of regions  314  corresponding to the second homopolymer form a first etch mask in the first patterned photoresist layer  308 . In alternative embodiments, the second plurality of regions  314  corresponding to the second homopolymer may be selectively removed and the first plurality of regions  312  corresponding to the first homopolymer may form the first etch mask. 
     The removal of the first plurality of regions  312  or the second plurality of regions  314  may be performed using either wet or dry chemistry. For example, a dry oxygen plasma may be used to remove a poly methyl-methacrylate. If the selectivity of this etch process is poor, some of the second plurality of regions  314  will be removed while removing the first plurality of regions  312 . In some embodiments, this may be used to advantageously reduce the critical dimension of the remaining second plurality of regions  314 . However, lateral etching of the second plurality of regions  314  may not be preferred in certain embodiments, as it may be difficult to control the vertical nature of the sidewall profile needed for patterning the layer to be patterned  306  in the next step. 
     Referring to  FIG. 3E , using the first etch mask, the first pattern of device elements  316  with a first critical dimension  318  and a first pitch  321  are formed in the layer to be patterned  306 . In this case, the first patterned photoresist layer  308  is removed prior to the etching. Of course if a plurality of trenches is being formed in the layer to be patterned  306 , the first patterned photoresist layer  308  may be removed after the patterning of the layer to be patterned  306 . As known to a person having ordinary skill in the art, an anisotropic reactive ion etching process may be used to pattern the layer to be patterned  306 . Any remaining second plurality of regions  314  is removed as well after patterning the layer to be patterned  306 . 
     As previously described, the first critical dimension  318  and the first pitch  321  formed are based on the first ratio of the liquids being blended in the first mixture, e.g., ratio of first block copolymer and second block copolymer or ratio of first block copolymer and a homopolymer. The first patterned photoresist layer  308  and the etch mask formed by the second plurality of elements are removed. 
       FIG. 4  is a flow chart of a first directed self-assembly method to form a first pattern of device elements in accordance with an embodiment of the present disclosure. 
     In block  402 , a first patterned photoresist layer  308  is formed over a first layer to be patterned  306  that is formed over a semiconductor substrate  120 . This first patterned photoresist layer  308  may be formed as described and illustrated using  FIG. 3A . 
     As next illustrated in block  404  and described with respect to  FIG. 3B , the first patterned photoresist layer  308  is coated with the first mixture  310 . The forming of the first mixture  310  is described with respect to  FIGS. 1 and 2 . In various embodiments, as discussed above, the first mixture  310  is a combination of two or more of a first block copolymer, a second block copolymer, a solvent, and a homopolymer that are blended using the first mixer apparatus  100  or the second mixer apparatus  200 . Advantageously, the blending of the first mixture  310  and the coating of the first mixture  310  over the semiconductor substrate  120  happens in the same fabrication facility. Further, this blending may happen closely spaced in time with the coating process to avoid chemical deterioration due to extended storage. 
     Referring next to block  406  and described with respect to  FIG. 3C , the substrate is annealed to form a first plurality of regions  312  and a second plurality of regions  314 . 
     As next illustrated in block  408  and described with respect to  FIG. 3D , the first plurality of regions  312  is selectively removed to form a first etch mask. 
     As next illustrated in block  410  and described with respect to  FIG. 3E , after removing any remaining first patterned photoresist layer, a first pattern of device elements  316  is formed using the first etch mask. 
     As mentioned above, an advantage of blending block copolymers within a fabrication facility is that if a metric of the first formed pattern does not meet a target metric, the blended block copolymer mixture can be tuned within the fabrication facility in lieu of ordering a new mixture from a vendor. 
       FIG. 5  a flow chart of a method for tuning a first block copolymer mixture within a fabrication facility in order to meet a target metric. 
     As illustrated in block  502 , a block copolymer (BCP) mixture such as the first mixture  310  is blended within the fabrication facility using the first mixer apparatus  100  or the second mixer apparatus  200 , as described above using  FIG. 1  and  FIG. 2 , respectively. In various embodiments, as discussed above, the first mixture  310  is a combination of two or more of a first block copolymer, a second block copolymer, a solvent, and a homopolymer that are blended using the first mixer apparatus  100  or the second mixer apparatus  200 . 
     It is conceivable that during production or during process development, the features of the pattern or the blended mixture may not be within a desired target window. This may eventually cause a loss in product yield and therefore embodiments of the present disclosure envision a process control in which the metrics measured at blocks  503  and  506  are actively or periodically monitored and provided to an electronic flow control system  115  such as described in  FIG. 1 . 
     As next illustrated in block  503 , the blended block copolymer mixture, the first liquid, or the second liquid may be analyzed with various metrology tools including sensors such as sensors  103  described with respect to  FIG. 1 . Alternatively, or in addition, to the above metrology of block  503 , as next illustrated in block  504 , a semiconductor substrate  120  is coated with the first mixture  310  and a pattern of device elements  316  is formed on the semiconductor substrate  120  as described using  FIGS. 3A-3E, 4  above. In this case, a metric of the pattern of device elements  316  is measured. In further embodiments, a pattern of the second plurality of regions  314  is measured prior to forming the device elements  316 . Accordingly, in various embodiments, the measured metric may be the critical dimension of the device elements  316 /second plurality of regions  314 , the width (dimension orthogonal to the critical dimension) of the device elements  316 /second plurality of regions  314 , the height or the depth of the device elements  316 /second plurality of regions  314 , the distance between neighboring elements, i.e., the pitch of the device elements  316 /second plurality of regions  314 , the surface roughness of the device elements  316 /second plurality of regions  314 , the local critical dimension uniformity of the device elements  316 /second plurality of regions  314 , the line width variation of the device elements  316 /second plurality of regions  314 , the sidewall angle of the device elements  316 /second plurality of regions  314 , the microphase structure, or any other metric. These metrology measurements may be made using inline tools such as optical metrology tools such as scatterometry that use non-destructive testing or other metrology tools that may use destructive testing such as using optical or electron microscopy. 
     The measured metric is compared to a target metric or target process window, for example, obtained from process recipe/metrics  105  described in  FIG. 5 . This may be done in the electronic control system described in  FIG. 1 , for example. If the measured metric is the same as the target metric or within the process window, no change to the blended liquid or to the process is made at this time. If the measured metric is different than the target metric or outside the process window, the process continues to step  510  and a new or modified recipe for the block copolymer mixture is generated in accordance with  FIG. 1  or  FIG. 2 . The new mixture may change any of the process parameters such as flow rate and/or pressure of the first liquid or the second liquid, temperature as well as other parameters. 
     In various embodiments, if the target metric is the critical dimension or pitch, and the measured critical dimension or pitch does not meet the target metric, the first mixture can be further blended with a third liquid comprising essentially of the first homopolymer or essentially the second homopolymer to form a tuned second mixture with a new critical dimension or pitch. 
     In alternative embodiments, if the target metric is the critical dimension or pitch, and the measured critical dimension or pitch does not meet the target metric, the first mixture can be further blended with a third liquid comprising essentially of the first homopolymer and a fourth liquid comprising essentially of the second homopolymer to form a tuned second mixture with a new critical dimension or pitch. 
     In alternative embodiments, if the target metric is the surface roughness and the measured surface roughness does not meet the target surface roughness, the first mixture can be further blended with a third liquid comprising a solvent to form a new mixture with an improved film thickness. For example, the solvent may comprise of propylene glycol monomethyl ether acetate, toluene, or any other solvent known to change the film thickness of block copolymers known in the art. 
     In alternative embodiments, the microphase of the first mixture may be improper. For example, the microphase may be hexagonal instead of lamellar. In such cases, the first mixture may be further blended with a third liquid comprising essentially of the first homopolymer or essentially of the second homopolymer in order to change the phase of the blended mixture from hexagonal to lamellae and vice-versa. In various embodiments, as previously described, the phase may be changed between close-packed cylinders, hexagonal, and lamellae by changing the composition of the homopolymers in the block copolymers. 
     The process of blocks  502  through  508  are repeated with the new mixture blended or modified with the new process recipe. 
     As mentioned above, another advantage of the disclosed invention is that it allows for multiple layers of IC device elements with different critical dimensions, pitches, and/or shapes to be fabricated on the same semiconductor substrate by blending multiple block copolymer mixtures corresponding to each successive layer of device elements within the fabrication facility. 
       FIGS. 6A-6B  illustrate cross-sectional views of a semiconductor device during various stages of fabrication in accordance with an embodiment of the present application, wherein  FIG. 6A  illustrates the device after coating a second patterned photoresist layer with a second block copolymer mixture, and  FIG. 6B  illustrates the device after forming a second patterned layer of device elements.  FIG. 7  is a flow chart of a second DSA method used to form a second layer of device elements for the fabrication process illustrated in  FIGS. 6A-6B . 
     In this embodiment, a blended mixture with a different composition is formed using the same supply tanks that were previously used to pattern device elements for a different process step. Advantageously, different critical dimensions can be achieved with the same mixing apparatus without having to change supply bottles. 
     Accordingly, this embodiment continues from  FIG. 3E . Referring now to  FIG. 6A  and block  702 , an interlayer dielectric layer  606  is formed over device elements  316  formed in  FIG. 3E , for example. The interlayer dielectric layer  606  may comprise a plurality of layer and may comprise SiO2, SION, Si3N4, glasses such as borosilicate glass, organo silicate glass, low-k dielectric materials, or any other interlayer dielectric known by one with ordinary skill in the art. 
     Next, a second layer to be patterned  608  is formed over the interlayer dielectric layer  606  (block  704 ) and may also comprise a dielectric layer, a conductive layer, or semiconductor layer depending on the feature being formed. 
     Next, a second patterned photoresist layer is formed over the second layer to be patterned  608  (block  706 ). As illustrated in  FIG. 6A , a second patterned photoresist layer  610  is formed over the second layer to be patterned  608 . The second patterned photoresist layer  610  may comprise the same material and may be formed in the same manner as the first patterned photoresist layer  308 , as illustrated in  FIG. 3A . The second patterned photoresist layer  610  is patterned with a second specific pitch  602  and a second specific critical dimension  604 . The second patterned photoresist layer  610  serves as a second DSA template. 
     The second patterned photoresist layer  610  is coated with the second mixture (block  708 ). The second mixture has a composition that is different from the first mixture used in  FIG. 3B . In one embodiment, the second mixture has a second ratio of the first liquid comprising a first block copolymer liquid to the second liquid comprising a second block copolymer liquid. The second ratio is selected to achieve a target second critical dimension for the features being patterned while the first ratio was selected to achieve a different target first critical dimension for the features being patterned. Similar to the first mixture, in various embodiments, the second mixture has first block copolymer liquid blended with one or more of a second block copolymer liquid, a solvent, or a homopolymer as described in  FIG. 1 or 2 . Similar to the first mixture, the second mixture is then coated onto the second patterned photoresist layer  610  via the first mixer apparatus  100  or the second mixer apparatus. 
     Referring to block  710 , a second etch mask  612  is formed by annealing the substrate to cause microphase separation (e.g., similar to  FIG. 3D ) and then removing one of the phase regions. 
     Referring to  FIG. 6B , using the second etch mask  612 , a second pattern of device elements  616  with a second critical dimension  618  and a second pitch  620  are formed (block  712 ). The second critical dimension  618  and the second pitch  620  formed are based on the second ratio of the first liquid to the second liquid in the second mixture. The second patterned photoresist layer  610  and the second etch mask  612  are removed (block  714 ). 
     In various embodiments, the first DSA process is used to form a first pattern of gate lines and the second DSA process is used to form a second pattern of metal lines over the gate lines. In alternative embodiments the first DSA process is used to form a first pattern of gate lines and the second DSA process is used to form a second pattern of contact holes within the gate lines. 
     Advantageously, as discussed in the embodiments described using  FIGS. 3A-3E  and then  FIGS. 6A-6B , two different patterns with different critical dimensions and pitch may be formed using a common source of supply tanks. This advantage scales quickly if more levels use a directed self-assembly process as additional patterns at other critical dimensions may be fabricated with the same number of supply tanks/liquids. 
     Examples of embodiments are described below. 
     Example 1. A method for forming a device includes blending, in a mixer within a fabrication facility, a first liquid including a first block copolymer with a second liquid including a second block copolymer to form a first mixture, the first block copolymer including a first homopolymer and a second homopolymer, the first homopolymer having a first mole fraction in the first liquid, the second block copolymer including the first homopolymer and the second homopolymer, the first homopolymer having a second mole fraction in the second liquid, the first mole fraction being different from the second mole fraction; placing a substrate over a substrate holder of a processing chamber within the fabrication facility; and coating the substrate with the first mixture within the processing chamber. 
     Example 2. The method of example 1, further including: forming a patterned photoresist layer over a layer to be patterned that is disposed over the substrate, where coating the substrate with the first mixture includes coating the patterned photoresist layer with the first mixture; annealing to form a first plurality of regions including the first homopolymer and a second plurality of regions including the including the second homopolymer; selectively removing the first plurality of regions to form an etch mask aligned with the patterned photoresist layer, the etch mask including the second plurality of regions; and forming a pattern in the layer to be patterned using the etch mask. 
     Example 3. The method of one of examples 1 or 2, further including removing the patterned photoresist layer, and removing the second plurality of regions after forming the pattern. 
     Example 4. The method of one of examples 1 to 3, further including: forming a first pattern from the coating of the first mixture; measuring a first critical dimension of a feature of the first pattern; in response to determining that the first critical dimension is different from a target critical dimension, blending, at the mixer, the first liquid with the second liquid to form a second mixture, the first mixture including a first ratio of the first block copolymer with the second block copolymer, the second mixture including a second ratio of the first block copolymer with the second block copolymer, the second ratio being different than the first ratio; and coating a further substrate with the second mixture; and forming a second pattern from the coating of the second mixture, where a second critical dimension of a feature of the second pattern meets a target critical dimension. 
     Example 5. The method of one of examples 1 to 4, further including: blending, at the mixer, the first liquid with the second liquid to form a second mixture, the first mixture including a first ratio of the first block copolymer with the second block copolymer, the second mixture including a second ratio of the first block copolymer with the second block copolymer, the second ratio being different than the first ratio; and coating the substrate with the second mixture. 
     Example 6. The method of one of examples 1 to 5, further including: forming a first pattern by using a first directed self-assembly process based on the first mixture; and forming a second pattern by using a second directed self-assembly process based on the second mixture, where a first critical dimension of a feature of the first pattern is different from a second critical dimension of a feature of the second pattern. 
     Example 7. The method of one of examples 1 to 6, where the first directed self-assembly process includes: forming a first patterned photoresist layer over a first layer to be patterned disposed over the substrate, where coating the substrate with the first mixture includes coating the first patterned photoresist layer with the first mixture, annealing to form a first plurality of regions including the first homopolymer and a second plurality of regions including the second homopolymer, selectively removing the first plurality of regions to form a first etch mask aligned with the first patterned photoresist layer, the first etch mask including the second plurality of regions, and forming the first pattern in the first layer to be patterned using the first etch mask; and where the second directed self-assembly process includes forming, a second patterned photoresist layer over a second layer to be patterned disposed over the substrate, where coating the substrate with the second mixture includes coating the second patterned photoresist layer with the second mixture, annealing to form a third plurality of regions including the first homopolymer and a fourth plurality of regions including the second homopolymer, selectively removing the third plurality of regions to form a second etch mask aligned with the second patterned photoresist layer, the second etch mask including the fourth plurality of regions, and forming a second pattern in the second layer to be patterned using the second etch mask. 
     Example 8. The method of one of examples 1 to 7, where the first pattern is a pattern for gate lines, and where the second pattern is a pattern for metal lines over the gate lines. 
     Example 9. The method of one of examples 1 to 8, where the first pattern is a pattern for gate lines, and where the second pattern is a pattern to form contact holes in the gate lines. 
     Example 10. The method of one of examples 1 to 9, where coating the substrate includes: spinning the substrate holder with the substrate; and injecting the first mixture through a nozzle connected to the mixer, the nozzle being directed towards the substrate in order to coat the substrate with the first mixture. 
     Example 11. The method of one of examples 1 to 10, where, during the blending, the method further includes adding a third liquid including essentially the first homopolymer to form the first mixture. 
     Example 12. The method of one of examples 1 to 11, where, during the blending, the method further includes adding a fourth liquid including essentially the second homopolymer to form the first mixture. 
     Example 13. A method for forming a device includes blending, in a mixer within a fabrication facility, a first block copolymer and a solvent to form a first mixture, the first block copolymer including a first homopolymer and a second homopolymer; placing a substrate over a substrate holder of a processing chamber within the fabrication facility; and coating the substrate with the first mixture within the processing chamber. 
     Example 14. The method of example 13, further including: forming a first pattern from the coating of the first mixture; measuring a first metric of a feature of the first pattern; in response to determining that the first metric is different from a target metric, blending, at the mixer, the first block copolymer with the solvent to form a second mixture, the first mixture including a first ratio of the first block copolymer with the solvent, the second mixture including a second ratio of the first block copolymer with the solvent, the second ratio being different than the first ratio; and coating a further substrate with the second mixture; and forming a second pattern from the coating of the second mixture, where a second metric of a feature of the second pattern meets a target metric. 
     Example 15. The method of one of examples 13 or 14, where the first metric, second metric, and the target metric are measures of a surface roughness. 
     Example 16. The method of one of examples 13 to 15, further including: forming a patterned photoresist layer over a layer to be patterned that is disposed over the substrate, where coating the substrate with the first mixture includes coating the patterned photoresist layer with the first mixture while delivering a solvent to the first mixture; annealing to form a first plurality of regions including the first homopolymer and a second plurality of regions including the including the second homopolymer; selectively removing the first plurality of regions to form an etch mask aligned with the patterned photoresist layer, the etch mask including the second plurality of regions; and forming a pattern in the layer to be patterned using the etch mask. 
     Example 17. A method for forming a device includes blending, in a mixer within a fabrication facility, a first liquid including a first block copolymer and a second liquid including essentially a first homopolymer to form a first mixture, the first block copolymer including the first homopolymer and a second homopolymer; placing a substrate over a substrate holder of a processing chamber within the fabrication facility; and coating the substrate with the first mixture within the processing chamber. 
     Example 18. The method of example 17, where, during the blending, the method further includes adding a third liquid including essentially the first homopolymer to form the first mixture. 
     Example 19. The method of one of examples 17 or 18, where, during the blending, the method further includes adding a third liquid including essentially a solvent to form the first mixture. 
     Example 20. The method of one of examples 17 to 19, further including: forming a first pattern from the coating of the first mixture; measuring a first critical dimension of a feature of the first pattern; in response to determining that the first critical dimension is different from a target critical dimension, blending, at the mixer, the first liquid with the second liquid to form a second mixture, the first mixture including a first ratio of the first liquid with the second liquid, the second mixture including a second ratio of the first liquid with the second liquid, the second ratio being different than the first ratio; and coating a further substrate with the second mixture; and forming a second pattern from the coating of the second mixture, where a second critical dimension of a feature of the second pattern meets a target critical dimension. 
     While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.