Abstract:
Provided is a method for processing a semiconductor substrate to reduce line roughness, the method comprising: positioning a substrate in a film-forming system, the film-forming system comprising a chuck having a clamping mechanism configured to hold the substrate in a processing chamber and flex the substrate by displacing a center of the substrate relative to a peripheral edge of the substrate so as to create a concave surface during processing; coating the substrate with a layer of material; performing a post apply bake process; flexing the substrate to create the concave surface either during the post apply bake or following the post apply bake process, wherein the concave surface has a degree of concavity measured at the center of the substrate that exceeds a base number of microns; and unflexing the substrate and inducing tensile stress in the layer of material on the substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Pursuant to 37 C.F.R. §1.78(a)(4), this application claims the benefit of and priority to prior filed co-pending Provisional Applications Ser. No. 62/083,585 filed on Nov. 24, 2014, which is expressly incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention is related to methods and systems for substrate processing and more specifically to methods and systems for reducing line roughness. 
     2. Description of Related Art 
     Patterns are used to make structures on a substrate to make a device for use in semiconductor applications. Patterns have stochastic variations that appear as line edge roughness or line width changes. Line edge roughness, as well as line width roughness, limits the quality of the end product semiconductor device. 
     Most film deposition tools or curing tools are typically configured to make the substrate as flat as possible. If the film or layer creates tensile stress as a result of processing, then there are no serious issues with line edge roughness. However, many films or layers create compressive stress on silicon. When those films or layers are etched to make fine patterns for semiconductor devices, these films or layers tend to show “wiggling”, which are variations from the ideal line and space pattern of structures. When the variations or line roughness become substantial, line roughness can affect the performance of the device in the semiconductor application. Thus, there is a need for systems and methods to reduce the line roughness during film or layer patterning or curing processes. 
     SUMMARY OF THE INVENTION 
     Provided is a method for processing a semiconductor substrate to reduce line roughness, the method comprising: positioning a substrate in a film-forming system, the film-forming system comprising a chuck having a clamping mechanism configured to hold the substrate in a processing chamber and flex the substrate by displacing a center of the substrate relative to a peripheral edge of the substrate so as to create a concave surface during processing; coating the substrate with a layer of material; flexing the substrate to create the concave surface either during the coating or following the coating, wherein the concave surface has a degree of concavity measured at the center of the substrate that exceeds a base number of microns; and unflexing the substrate and inducing tensile stress in the layer of material on the substrate. 
     In another embodiment, provided is a method for processing a semiconductor substrate, the semiconductor having a structure, the structure having a line roughness, the method configured to improve line roughness, the method comprising: positioning a substrate in a track system, the track system comprising a concave chuck configured to hold a substrate in a track system chamber; depositing a spacer layer on the substrate; flexing the substrate to create the concave surface either during the deposition or following the deposition, wherein the concave surface has a degree of concavity measured at the center of the substrate that exceeds a base number of microns; and unflexing the substrate and inducing tensile stress in the layer of material on the substrate; the degree of concavity is from a range of 150 to 200 μm or the degree of concavity is less than 1 micron per millimeter of diameter length of the substrate, or the degree of concavity is varied according the diameter of the substrate and historical data acquired for processing the layer of material; and wherein the target reduction in line roughness is 4 to 6 nm of 3 sigma (3σ). 
     Also provided is a film-forming system comprising: a processing chamber for processing a substrate; a chuck coupled to the processing chamber, the chuck having a clamping mechanism, the clamping mechanism configured to: hold the chuck in the processing chamber and flex the substrate to create the concave surface either during the deposition or following the deposition, wherein the concave surface has a degree of concavity measured at the center of the substrate that exceeds a base number of microns; and unflex the substrate and induce tensile stress in the layer of material on the substrate; wherein the film-forming system is one of a spin-on deposition system or a vapor deposition system, wherein the clamping mechanism is one of an electrostatic device or a vacuum device; and wherein the processing chamber is at least one of a spin-on coating chamber, or a vapor deposition chamber, or an etching chamber. A base number of microns can be at least 150 μm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  depicts an exemplary prior art cross-sectional view of material layer(s) on a substrate during deposition or curing while  FIG. 1B  depicts an exemplary prior art cross-sectional view of material layers comprising compressive films and no-stress films after deposition or curing; 
         FIG. 2A  depicts an exemplary cross-sectional view of layers of a substrate during deposition or curing while  FIG. 2B  depicts an exemplary cross-sectional view of layers for compressive films and no-stress films after deposition or curing using line roughness reduction techniques in an embodiment of the present invention; 
         FIG. 3A  depicts an exemplary top-view of structures in a tensile to a neutral stress layer on a substrate while  FIG. 3B  is an exemplary top view of structures in a compressive stress layer on a substrate; 
         FIG. 4A  depicts a schematic of a substrate on a concave chuck and a clamping device illustrating the degree of concavity with the substrate disposed above the chuck whereas  FIG. 4B  depicts a schematic of a substrate on a concave chuck and a clamping device illustrating the degree of concavity with the substrate disposed below the chuck; 
         FIG. 5A  is a flowchart for a method of improving the line roughness of a pattern using flexing techniques in an embodiment of the present invention; 
         FIG. 5B  is a flowchart for a method of improving the line roughness of a pattern using flexing techniques in another embodiment of the present invention; 
         FIG. 6  is a flowchart for a method of improving the line roughness of a pattern using flexing techniques in yet another embodiment of the present invention; 
         FIG. 7A  depicts a schematic for a film-forming system for improving the line roughness utilizing flexing techniques of the present invention using a substrate in the cooling chamber while  FIG. 7B  depicts a schematic for a film-forming system for improving the line roughness utilizing the techniques of the present invention using a substrate in the heating chamber; and 
         FIG. 8A  depicts an integration sequence of process operations including a blanket deposition and a second apply bake (PAB) processes;  FIG. 8B  depicts an integration sequence of processes including an exposure and a second exposure bake (PEB) processes;  FIG. 8C  depicts an integration sequence of process operations including a develop and a second develop bake (PDB) processes, and  FIG. 8D  depicts an integration sequence of process operations including a photoresist patterning, spacer deposition, and etch processes, utilizing the line roughness reduction techniques of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for purposes of explanation and not limitation, specific details are set forth, such as a particular geometry of a processing system, descriptions of various components and processes used therein. However, it should be understood that the invention may be practiced in other embodiments that depart from these specific details. 
     Similarly, for purposes of explanation, specific numbers, materials, and configurations are set forth in order to provide a thorough understanding of the invention. Nevertheless, the invention may be practiced without specific details. Furthermore, it is understood that the various embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale. 
     Various operations will be described as multiple discrete operations in turn, in a manner that is most helpful in understanding the invention. However, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation. Operations described may be performed in a different order than the described embodiment. Various additional operations may be performed and/or described operations may be omitted in additional embodiments. 
     As used herein, the term “radiation sensitive material” means and includes photosensitive materials such as photoresists. In this specification, the terms layer and film shall mean the same. 
     “Substrate” as used herein generically refers to the object being processed in accordance with the invention. The substrate may include any material portion or structure of a device, particularly a semiconductor or other electronics device, and may, for example, be a base substrate structure, such as a semiconductor substrate or a layer on or overlying a base substrate structure such as a thin film. The substrate may be a conventional silicon substrate or other bulk substrate comprising a layer of semiconductive material. As used herein, the term “bulk substrate” means and includes not only silicon wafers, but also silicon-on-insulator (“SOI”) substrates, such as silicon-on-sapphire (“SOS”) substrates and silicon-on-glass (“SOG”) substrates, epitaxial layers of silicon on a base semiconductor foundation, and other semiconductor or optoelectronic materials, such as silicon-germanium, germanium, gallium arsenide, gallium nitride, and indium phosphide. The substrate may be doped or undoped. Thus, substrate is not intended to be limited to any particular base structure, underlying layer or overlying layer, patterned or un-patterned, but rather, is contemplated to include any such layer or base structure, and any combination of layers and/or base structures. The description below may reference particular types of substrates, but this is for illustrative purposes only and not limitation. 
     Line edge roughness can be improved with induced tensile stress of patterning materials. The layer of material on the substrate can be processed during or after deposition, curing, or baking systems to have tensile stress. Inducement of tensile stress in the layer of material requires several steps. The layer of material which is in a compressive stress, no stress, or tensile stress state, must be in a compressive stress state. To do this, the substrate needs to be in concave shape during deposition, curing, or baking process. In an embodiment, the substrate can be converted into a concave shape by flexing the substrate against a chuck or hot plate that has a concave shape. During deposition, curing, or baking, the substrate is kept in a concave shape and the stress in the film deposited or cured will become or remain as a compressive stress film. When the substrate undergoes the unflexing operation, the substrate will go back to a flat shape or near zero degree of concavity. During the unflexing operation, the film is induced to have tensile stress regardless of the type of stress that was present in the film before the flexing and unflexing operations. 
       FIG. 1A  depicts an exemplary prior art cross-sectional view of a film-forming system  104  of a film  108  on a substrate  112  during a deposition or curing. The deposited film  104  on the substrate  108  that is disposed on top of a chuck  116  with the deposited film  108  having no tensile stress. The chuck  116  is substantially flat, i.e. with a degree of concavity of zero. 
       FIG. 1B  depicts exemplary prior art cross-sectional views  120  of layers of compressive films and no-stress films after deposition or curing. In a compressive film-forming system (not shown)  124 , the compressive film layer  128  is formed above the substrate  132 . The chuck (not shown) is substantially flat, i.e. with a degree of concavity of zero; consequently, compressive film  128  has a concave shape but has no tensile stress. In a similar film-forming system  144 , the no-stress film layer  148  is formed above the substrate  152  in a substantially flat shape but without tensile stress after a deposition or curing process is completed. In a similar film-forming system  164 , the compressive film layer  168  is formed above the substrate  172  where the compressive film has a convex shape but has no tensile stress after the deposition or curing process is completed. 
       FIG. 2A  depicts an exemplary cross-sectional view  200  of a film-forming system (not shown)  204  and a layer  208  of a substrate  212  during deposition or curing. The layer  208  of material is formed over the substrate  212  on top of the chuck  216 , the chuck  216  having a concave surface.  FIG. 2B  depicts exemplary cross-sectional views  210  of layers for compressive films and no-stress films after deposition or curing using techniques in an embodiment of the present invention. A compressive film  224  on a substrate  228  in a film-forming system (not shown)  220  is shown where the compressive film  224  and substrate are flexed to maintain compressive stress on the film  224 . A no stress film  244  on a substrate  248  in a film-forming system (not shown)  240  is shown where the no stress film  244  and substrate are flexed to create compressive stress on the film  244  during or after the deposition or curing of the substrate  248 . A tensile stress film  264  on a substrate  268  in film-forming system (not shown)  260  is shown where the tensile film  264  and substrate  268  are flexed to create compressive stress on the film  264  during or after the deposition or curing of the substrate  268 . After the flexing operation, the films  224   244  and  264  are unflexed to induce tensile stress in the films  224 ,  244  and  264 . 
       FIG. 3A  depicts an exemplary top-view  300  of structures  308  in a tensile to a neutral stress layer  304  after using the techniques of reducing line roughness in an embodiment of the present invention.  FIG. 3B  is an exemplary top view  350  in a compressive stress layer  354  on a substrate  362 . Due to the compressive stress on the film  354 , the structures  358  are “wiggly” instead of being straight as in an ideal or close to ideal line-and-space pattern. Using the techniques of the present invention of flexing by causing a degree of concavity on the substrate  362  during or after the deposition or curing of the substrate  362 , and unflexing the substrate  362  to induce a target tensile stress on the substrate, the line roughness can be reduced. The line roughness can be reduced by up to 2 nm of 3σ of the deviation. Unflexing the substrate  362  comprises removal of the cause of concavity on the substrate, reduction in the concavity of the substrate, change to a lower temperature, or change of a variable, for example, from a high vacuum state during the flexing to a lower vacuum state after the flexing is complete. Removal of the cause of concavity on the substrate can include lowering the power used in an electrostatic chuck or as mentioned above, lowering the vacuum state of a vacuum chuck. Other factors such as changes to the density of film or changes of the film material may also cause a change in tensile stress on the film on the substrate. 
       FIG. 4A  depicts a schematic  400  of a substrate  412  on a concave chuck  416  and a clamping device  408  illustrating the degree of concavity  404  with the substrate  412  on top of the chuck  416 .  FIG. 4B  depicts a schematic  450  of a substrate  462  on a concave chuck  466  and a clamping device  458  illustrating the degree of concavity  454  with the substrate  462  below the chuck  466 . The degree of concavity can be a range of up to 300 microns for a 300 mm substrate. In another embodiment, the degree of concavity can be a range of 100 to 300 microns or a range that is greater than a base number of microns, where the base number of microns can be up to 100 microns. Alternatively, the degree of concavity can be up to 1 micron per millimeter of diameter of the substrate. In still another embodiment, the degree of concavity is varied according the diameter of the substrate and historical data for the application. 
       FIG. 5A  is a flowchart  500  for a method of improving the line roughness of a pattern using the techniques in an embodiment of the present invention. In operation  504 , a substrate is positioned in a processing chamber of a film-forming system. The film-forming system can be a track system and the processing chamber can be one of a coating chamber or deposition chamber, a bake chamber, or a developing chamber. In operation  508 , the substrate is coated with a layer of material using a deposition process. The material may be a photoresist or a conformal layer of material deposited on the substrate. In operation  512 , the substrate is optionally flexed to create the concave surface on the substrate either during the coating or following the coating with the layer of material and unflexed to induce tensile stress in the layer of material on the substrate. The option to perform this operation or not depends on the historical data acquired for processing the specific layer of material and other ranges of operating variables such as chamber temperature, pressure, and deposition technique used. 
     In operation  516 , a post apply bake process is performed, which is a process that is known in the art for photoresist or conformal layer depositions. In operation  520  the substrate is flexed to create the concave surface on the substrate either during the post apply bake or following the post apply bake process. The flexing of the substrate causes a degree of concavity measured at the center of the substrate. Flexing of the substrate causes the layer of material above the substrate to have compressive stress. In operation  524 , the substrate is unflexed and tensile stress is induced in the layer of material on the substrate. Flexing and unflexing operations are described in more detail above. In operation  528 , two or more operating variables of one or more operations of the method are concurrently controlled in order to achieve a target reduction in line roughness of the substrate, which can be 4 to 6 nm of 3σ of the line roughness. The two or more operating variables can include chamber temperature, chamber pressure, degree of concavity, duration of flexing operation, and the like. 
       FIG. 5B  is a flowchart  550  for a method of improving the line roughness of a pattern using the techniques in an embodiment of the present invention. In operation  554 , a substrate is positioned in a processing chamber of a film-processing system. The film-processing system can be a track system and the processing chamber can be one of a deposition chamber, a bake chamber, or a developing chamber. In operation  558 , a first film-processing procedure is performed on the substrate where the first film-processing procedure can be an exposure or development procedure. In operation  562 , the substrate is optionally flexed to create the concave surface on the substrate either during the first film-processing procedure or following the first film-processing procedure with the layer of material and unflexed to induce tensile stress in the layer of material on the substrate. The option to perform this operation or not depends on the historical data acquired for processing the specific layer of material and other ranges of operating variables such as chamber temperature, pressure, and deposition technique used. 
     In operation  566 , a second film-processing procedure is performed, which can be a post exposure bake or post develop bake procedure. In operation  570 , the substrate is flexed to create the concave surface on the substrate either during the second film-processing procedure or following the second film-processing procedure. The flexing of the substrate causes a degree of concavity measured at the center of the substrate. Flexing of the substrate causes the layer of material above the substrate to have compressive stress. In operation  574 , the substrate is unflexed and tensile stress is induced in the layer of material on the substrate. Flexing and unflexing operations are described in more detail above. In operation  578 , two or more operating variables of one or more operations of the method are concurrently controlled in order to achieve a target reduction in line roughness of the substrate, which can be 4 to 6 nm of 3σ of the line roughness. The two or more operating variables can include chamber temperature, chamber pressure, degree of concavity, duration of flexing operation, and the like. 
     In order to establish the degree of concavity on the substrate, film stress measurements must be conducted. One film stress measurement technique includes (a) measuring the curvature of the substrate prior to deposition or curing and (b) measuring the substrate along the same trace after a film is applied. In one version of stress measurement analysis, the bending plate method is used to calculate stress in a deposited thin film layer, based upon the change in curvature and material properties of the film and substrate. 
     The difference between stress calculated using the curvature data prior to the deposition or curing and the stress calculated using the curvature data after the deposition or curing is the induced film stress. Negative values of stress are compressive (convex surface); positive values are tensile (concave surface). The units of stress are dynes/cm  2  (1 dyne =10 −5  Newton). As mentioned above, the applications of the present invention includes line roughness reduction for deposition, second application bake, second exposure bake, development, or deposition of spacer layer or photoresist layer processes. Other methods of calculating the radius of curvature or degree of concavity can also be used. For more information on thin film stress measurement using a stylus profiler, refer to Veeco Instruments Inc., 2650 E. Elvira Road, Tucson, Ariz. 85706 USA, or access www.veeco.com or other similar vendors. 
       FIG. 6  is a flowchart  600  for a method of improving the line roughness of a pattern using line roughness reduction techniques in another embodiment of the present invention. In operation  604 , a substrate is positioned in a film-forming system. In operation  608 , a spacer layer is deposited on the substrate. In operation  612 , the substrate is flexed to create the concave surface either during the deposition of the spacer layer or following the deposition of the spacer layer, wherein the concave surface has a degree of concavity measured at the center of the substrate. In operation  616 , the substrate is unflexed and tensile stress is induced in the layer of material on the substrate. In operation  620 , the spacer layer on the substrate undergoes an etching process. In operation  624 , two or more operating variables of one or more operations of the method are concurrently controlled in order to achieve a target reduction in line roughness of the substrate, which can be 4 to 6 nm of 3σ of the line roughness. The two or more operating variables can include chamber temperature, chamber pressure, degree of concavity, duration of flexing operation, and the like. 
       FIG. 7A  depicts a schematic  700  for a film-forming system for improving the line roughness utilizing the techniques of the present invention using a substrate in a cooling chamber  12 .  FIG. 7B  depicts a schematic  750  for a film-forming system for improving the line roughness utilizing the techniques of the present invention using a substrate in a heating chamber  14 . Referring to  FIG. 7A , a processing system  10  suitable for use with embodiments of the present invention is shown. Generally, the system  10  includes a heating chamber  12  and a cooling chamber  14 , each having a substrate support  16 ,  18  therein, configured to support and heat or cool a substrate  30   b  positioned thereon. The substrate support  16  is also referred to as a heating plate  16 , and substrate support  18  is also referred to as a chilling plate. As used herein, the substrate  30 b may refer to any structure providing a “substrate” in the fabrication of one or more semiconductor devices. Each of the heating and cooling chambers  12 ,  14  includes an exhaust chamber  20 ,  22  that is fluidically-coupled to a vacuum pump (not shown) via an exhaust port  24 ,  26 . As shown, the heating and cooling chambers may be physically isolated from one another by a movable door  31  that is operationally coupled with the operation of a transfer mechanism  32 , as discussed below. 
     The system  10  of  FIGS. 7A and 7B  includes a dedicated transfer mechanism  32  positioned within the cooling chamber  14  and having a transfer arm  34  configured to transfer the substrate  30   b  between a home position within the cooling chamber  14 , as shown in  FIG. 7A  and a transfer position above the heating plate  16 , as shown in  FIG. 7B . In this way, the substrate  30   a  may be transferred between the heating plate  16  and the chilling plate  18  as necessary and in accordance with a particular processing method. More specifically, the substrate  30   a  supported by the heating plate  16  may be heated and then lifted, via lift pins  28 , off the heating plate  16 . The movable door  31  may be repositioned, provide an opening between the heating and cooling chambers  12 ,  14  to permit entry of the chilling plate  18  into the heating chamber  12 . The transfer arm  34  moves the chilling plate  18  to the transfer position such that the lift pin  28  may lower the substrate  30   b  onto the chilling plate  18 . Thereafter, the transfer arm  34  withdraws the chilling plate  18  with the substrate  30   b  to the home position so the substrate  30   b  may be cooled. Although the illustrated cooling system  14  is shown with a chilling plate  18 , the cooling chamber  14  may comprise at least one of a substrate chuck configured in fluid communication with a chiller unit, a thermoelectric device, or a gas inlet in fluid communication with a convective gas supply. 
     The system  10  may also include one or more feedback control mechanisms (not shown), such as analyzers, sensors, and controllers that monitor and adjust the atmospheres in the heating chamber, cooling chamber, and/or transfer area. For example, the feedback control mechanisms may be capable of making real-time adjustments with respect to temperature, power input to clamping device, vacuum level, pressure level, or degree of concavity. 
       FIG. 8A  depicts an integration sequence  800  of process operations including a blanket deposition  804  and a post apply bake (PAB) process  808 . The blanket deposition process can include depositing a photosensitive material or a conformal layer over one or more layers on the substrate. The photosensitive material can be a photoresist or other material that is applied over the entire substrate. Flexing of the layer of material on the substrate can be performed during or after blanket deposition or coating of the substrate with the photosensitive or other material. After the flexing operation, an unflexing process is performed and tensile stress is induced on the substrate. A post apply bake  808  can be performed on the substrate after the unflexing process. Flexing of the substrate can be performed during or after the post apply bake  808 . After the flexing operation, an unflexing process is performed on the substrate which induces tensile stress in the layer of material on the substrate. Flexing and unflexing operations are described in more detail above. 
       FIG. 8B  depicts an integration sequence  810  of processes including an exposure and a post exposure bake (PEB) processes. The exposure process  814  can include a traditional photoresist exposure in lithography. Post exposure bake  818  follows the exposure process  814 . Flexing of the layer of material on the substrate can be performed during or after the post exposure bake  818  of the substrate. After the flexing operation, an unflexing process is performed and tensile stress is induced on the film on the substrate. Flexing and unflexing operations are described in more detail above. 
       FIG. 8C  depicts an integration sequence  820  of process operations including a develop  824  and a post develop bake (PDB)  828  processes. The develop process  824  can include a traditional develop process in lithography. Post develop bake  828  follows the exposure process  824 . Flexing of the layer of material on the substrate can be performed during or after the post develop bake  828  of the substrate. After the flexing operation, an unflexing process is performed and tensile stress is induced on the film on the substrate. Flexing and unflexing operations are described above. Another integration sequence can include the integration sequence described in relation to  FIG. 8A , followed by the integration sequence described in relation to  FIG. 8B , and followed by the integration sequence described in relation to  FIG. 8C . Other variations of the aforementioned integration sequence can also be done. 
       FIG. 8D  depicts an integration sequence  850  of process operations including a photoresist patterning  854 , spacer deposition  858 , and etch processes  862 , utilizing the line roughness reduction techniques of the present invention. The photoresist patterning process  854  can include a traditional photoresist patterning process in lithography that is well known in the art. Deposition of the spacer  858  follows the photoresist patterning process  854 . An etch process  862  follows which removes the material around the spacer in processes well known in the art. Flexing of the layer of material on the substrate can be performed during or after the deposition of the spacer  858  of the substrate. After the flexing operation, an unflexing process is performed and tensile stress is induced on the film on the substrate. Flexing and unflexing operations are described above. 
     Although only certain embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.