Patent Publication Number: US-11650506-B2

Title: Film structure for electric field guided photoresist patterning process

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Application Ser. No. 62/794,298 filed Jan. 18, 2019, which is incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Field 
     The present disclosure generally relates to methods and apparatuses for processing a substrate, and more specifically to methods and apparatuses for enhancing photoresist profile control. 
     Description of the Related Art 
     Integrated circuits have evolved into complex devices that can include millions of components (e.g., transistors, capacitors and resistors) on a single chip. Photolithography may be used to form components on a chip. Generally the process of photolithography involves a few basic stages. Initially, a photoresist layer is formed on a substrate. The photoresist layer may be formed by, for example, spin-coating. The photoresist layer may include a resist resin and a photoacid generator. The photoacid generator, upon exposure to electromagnetic radiation in the subsequent exposure stage, alters the solubility of the photoresist in the development process. The electromagnetic radiation may have any suitable wavelength, such as a wavelength in the extreme ultra violet region. The electromagnetic radiation may be from any suitable source, such as, for example, a 193 nm ArF laser, an electron beam, an ion beam, or other source. Excess solvent may then be removed in a pre-exposure bake process. 
     In an exposure stage, a photomask or reticle may be used to selectively expose certain regions of a photoresist layer disposed on the substrate to electromagnetic radiation. Other exposure methods may be maskless exposure methods. Exposure to light may decompose the photoacid generator, which generates acid and results in a latent acid image in the resist resin. After exposure, the substrate may be heated in a post-exposure bake process. During the post-exposure bake process, the acid generated by the photoacid generator reacts with the resist resin in the photoresist layer, changing the solubility of the resist of the photoresist layer during the subsequent development process. 
     After the post-exposure bake, the substrate, and, particularly, the photoresist layer may be developed and rinsed. After development and rinsing, a patterned photoresist layer is then formed on the substrate, as shown in  FIG.  1   .  FIG.  1    depicts an exemplary top sectional view of the substrate  100  having the patterned photoresist layer  104  disposed on a target material  102  to be etched. Openings  106  are defined between the patterned photoresist layer  104 , after the development and rinse processes, exposing the underlying target material  102  for etching to transfer features onto the target material  102 . However, inaccurate control or low resolution of the lithography exposure process may cause in poor critical dimension of the photoresist layer  104 , resulting in unacceptable line width roughness (LWR)  108 . Furthermore, during the exposure process, acid (shown as in  FIG.  1   ) generated from the photoacid generator may randomly diffuse to any regions, including the regions protected under the mask unintended to be diffused, thus creating undesired wigging or roughness profile  150  at the edge or interface of the patterned photoresist layer  104  interfaced with the openings  106 . Large line width roughness (LWR)  108  and undesired wiggling profile  150  of the photoresist layer  104  may result in inaccurate feature transfer to the target material  102 , thus, eventually leading to device failure and yield loss. 
     Therefore, there is a need for a method and an apparatus to control line width roughness (LWR) and enhance resolution as well as dose sensitivity so as to obtain a patterned photoresist layer with desired critical dimensions. 
     SUMMARY 
     Embodiments of the present disclosure include a method for forming a film structure to efficiently control of distribution and diffusion of acid from a photoacid generator in a photoresist layer during an exposure process or a pre- or post-exposure baking process. In one example, a device structure includes a film structure disposed on a substrate, and a plurality of openings formed in the film structure, wherein the openings formed across the substrate has a critical dimension uniformity between about 1 nm and 2 nm. 
     In another embodiment, a method of processing a substrate includes applying a photoresist layer comprising a photoacid generator to on a multi-layer disposed on a substrate, wherein the multi-layer comprises an underlayer formed from an organic material, inorganic material, or a mixture of organic and inorganic materials, exposing a first portion of the photoresist layer unprotected by a photomask to a radiation light in a lithographic exposure process, and applying an electric field or a magnetic field to alter movement of photoacid generated from the photoacid generator substantially in a vertical direction. 
     In yet another embodiment, a method of processing a substrate includes applying a photoresist layer on an underlayer disposed on a substrate, exposing a first portion of the photoresist layer unprotected by a photomask to a radiation light in a lithographic exposure process, performing a baking process on the photoresist layer and the underlayer, and applying an electric field or a magnetic field while performing the baking process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. 
         FIG.  1    depicts a top view of an exemplary structure of a patterned photoresist layer disposed on a substrate conventionally in the art; 
         FIG.  2    is a schematic cross-sectional view of an apparatus for processing a substrate, according to one embodiment; 
         FIG.  3    is a top view of one embodiment of an electrode assembly disposed in the apparatus of  FIG.  2   ; 
         FIG.  4    depict an acid distribution control of a photoresist layer disposed on a film structure during an exposure process; 
         FIG.  5    depicts an acid distribution control of a photoresist layer on a film structure with a desired profile during a post exposure baking process; and 
         FIG.  6    is a flow diagram of one method of control acid distribution of a photoresist layer during an exposure process. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, wherever possible, to designate identical elements that are common to the Figures. Additionally, elements of one embodiment may be advantageously adapted for utilization in other embodiments described herein. 
     DETAILED DESCRIPTION 
     Methods for enhancing profile control of a photoresist layer formed by photolithography are provided. The diffusion of acid generated by a photoacid generator during a post-exposure bake procedure that contributes to line edge/width roughness may be mitigated by utilizing a film structure disposed under the photoresist layer as disclosed herein. The electric field application controls the diffusion and distribution of the acids generated by the photoacid generator in the photoresist layer as well as in an underlayer disposed in a film structure under the photoresist layer, thus preventing the line edge/width roughness that results from random diffusion. Methods for forming a film structure disposed under the photoresist layer utilized to control aforementioned acid distribution and diffusion are disclosed herein. 
       FIG.  2    is a schematic cross-sectional view of an apparatus for processing a substrate, according to one embodiment. As shown in the embodiment of  FIG.  2   , the apparatus may be in the form of a vacuum processing chamber  200 . In other embodiments, the processing chamber  200  may not be coupled to a vacuum source. 
     The processing chamber  200  may be an independent stand alone processing chamber. Alternatively, the processing chamber  200  may be part of a processing system, such as, for example, an in-line processing system, a cluster processing system, or the track processing system as needed. The processing chamber  200  is described in detail below and may be used for a pre-exposure bake, a post-exposure bake, and/or other processing steps. 
     The processing chamber  200  includes chamber walls  202 , an electrode assembly  216 , and a substrate support assembly  238 . The chamber walls  202  include sidewalls  206 , a lid assembly  210 , and a bottom  208 . The chamber walls  202  partially enclose a processing volume  212 . The processing volume  212  is accessed through a substrate transfer port (not shown) configured to facilitate movement of a substrate  240  into and out of the processing chamber  200 . In embodiments where the processing chamber  200  is part of a processing system, the substrate transfer port may allow for the substrate  240  to be transferred to and from an adjoining transfer chamber. 
     A pumping port  214  may optionally be disposed through one of the lid assembly  210 , sidewalls  206  or bottom  208  of the processing chamber  200  to couple the processing volume  212  to an exhaust port. The exhaust port couples the pumping port  214  to various vacuum pumping components, such as a vacuum pump. The pumping components may reduce the pressure of the processing volume  212  and exhaust any gases and/or process by-products out of the processing chamber  200 . The processing chamber  200  may be coupled to one or more supply sources  204  for delivering one or more source compounds into the processing volume  212 . 
     The substrate support assembly  238  is centrally disposed within the processing chamber  200 . The substrate support assembly  238  supports the substrate  240  during processing. The substrate support assembly  238  may comprise a body  224  that encapsulates at least one embedded heater  232 . In some embodiments, the substrate support assembly  238  may be an electrostatic chuck. The heater  232 , such as a resistive element, is disposed in the substrate support assembly  238 . The heater  232  controllably heats the substrate support assembly  238  and the substrate  240  positioned thereon to a predetermined temperature. The heater  232  is configured to quickly ramp the temperature of the substrate  240  and to accurately control the temperature of the substrate  240 . In some embodiments, the heater  232  is connected to and controlled by the power source  274 . The power source  274  may alternatively or additionally apply power to the substrate support assembly  238 . The power source  274  may be configured similarly to the power source  270 , discussed below. Furthermore, it is noted that the heater  232  may be disposed from other locations of the processing chamber  200 , such as from chamber wall, chamber liner, edge ring that circumscribes the substrate, the chamber ceiling and the like, as needed to provide thermal energy to the substrate  240  disposed on the substrate support assembly  238   
     In some embodiments, the substrate support assembly  238  may be configured to rotate. In some embodiments, the substrate support assembly  238  is configured to rotate about the z-axis. The substrate support assembly  238  may be configured to continuously or constantly rotate, or the substrate support assembly  238  may be configured to rotate in a step-wise or indexing manner. For example, the substrate support assembly  238  may rotate a predetermined amount, such as 90°, 180°, or 270°, and then rotation may stop for a predetermined amount of time. 
     Generally, the substrate support assembly  238  has a first surface  234  and a second surface  226 . The first surface  234  is opposite the second surface  226 . The first surface  234  is configured to support the substrate  240 . The second surface  226  has a stem  242  coupled thereto. The substrate  240  may be any type of substrate, such as a dielectric substrate, a glass substrate, a semiconductor substrate, or a conductive substrate. The substrate  240  may have a material layer  245  disposed thereon. The material layer  245  may be any desired layer. In other embodiments, the substrate  240  may have more than one material layer  245 . The substrate  240  also has a photoresist layer  250  disposed over the material layer  245 . The substrate  240  has been previously exposed to electromagnetic radiation in an exposure stage of a photolithography process. The photoresist layer  250  has latent image lines  255  formed therein from the exposure stage. The latent image lines  255  may be substantially parallel. In other embodiments, the latent image lines  255  may not be substantially parallel. Also as shown, the first surface  234  of the substrate support assembly  238  is separated from the electrode assembly  216  by a distance d in the z-direction. The stem  242  is coupled to a lift system (not shown) for moving the substrate support assembly  238  between an elevated processing position (as shown) and a lowered substrate transfer position. The lift system may accurately and precisely control the position of the substrate  240  in the z-direction. In some embodiments, the lift system may also be configured to move the substrate  240  in the x-direction, the y-direction, or the x-direction and the y-direction. The stem  242  additionally provides a conduit for electrical and thermocouple leads between the substrate support assembly  238  and other components of the processing chamber  200 . A bellows  246  is coupled to the substrate support assembly  238  to provide a vacuum seal between the processing volume  212  and the atmosphere outside the processing chamber  200  and facilitate movement of the substrate support assembly  238  in the z-direction. 
     The lid assembly  210  may optionally include an inlet  280  through which gases provided by the supply sources  204  may enter the processing chamber  200 . The supply sources  204  may optionally controllably pressurize the processing volume  212  with a gas, such as nitrogen, argon, helium, other gases, or combinations thereof. The gases from the supply sources  204  may create a controlled environment within the processing chamber  200 . An actuator  290  may be optionally coupled between the lid assembly  210  and the electrode assembly  216 . The actuator  290  is configured to move the electrode assembly  216  in one or more of the x, y, and z directions. The x and y directions are referred to herein as the lateral directions or dimensions. The actuator  290  enables the electrode assembly  216  to scan the surface of the substrate  240 . The actuator  290  also enables the distance d to be adjusted. In some embodiments the electrode assembly  216  is coupled to the lid assembly  210  by a fixed stem (not shown). In other embodiments, the electrode assembly  216  may be coupled to the inside of the bottom  208  of the processing chamber  200 , to the second surface  226  of the substrate support assembly  238 , or to the stem  242 . In still other embodiments, the electrode assembly  216  may be embedded between the first surface  234  and the second surface  226  of the substrate support assembly  238 . 
     The electrode assembly  216  includes at least a first electrode  258  and a second electrode  260 . As shown, the first electrode  258  is coupled to a power source  270 , and the second electrode  260  is coupled to an optional power supply  275 . In other embodiments, one of the first electrode  258  and the second electrode  260  may be coupled to a power supply and the other electrode may be coupled to a ground. In some embodiments, the first electrode  258  and the second electrode  260  are coupled to a ground and the power source  274  that delivers power to the substrate support is a bipolar power supply that switches between a positive and negative bias. In some embodiments, the power source  270  or the power supply  275  may be coupled to both the first electrode  258  and the second electrode  260 . In other embodiments, the power source  270  or the power supply  275  may be coupled to the first electrode  258 , the second electrode  260 , and the substrate support assembly  238 . In such embodiments, the pulse delay to each of the first electrode  258 , the second electrode  260 , and the substrate support assembly  238  may be different. The electrode assembly  216  may be configured to generate an electric field parallel to the x-y plane defined by the first surface of the substrate support assembly  238 . For example, the electrode assembly  216  may be configured to generate an electric field in one of the y direction, x direction or other direction in the x-y plane. 
     The power source  270  and the power supply  275  are configured to supply, for example, between about 500 V and about 100 kV to the electrode assembly  216 , to generate an electric field having a strength between about 0.1 MV/m and about 100 MV/m. In some embodiments, the power source  274  may also be configured to provide power to the electrode assembly  216 . In some embodiments, any or all of the power source  270 , the power source  274 , or the power supply  275  are a pulsed direct current (DC) power supply. The pulsed DC wave may be from a half-wave rectifier or a full-wave rectifier. The DC power may have a frequency of between about 10 Hz and 1 MHz. The duty cycle of the pulsed DC power may be from between about 5% and about 95%, such as between about 20% and about 60%. In some embodiments, the duty cycle of the pulsed DC power may be between about 20% and about 40%. In other embodiments, the duty cycle of the pulsed DC power may be about 60%. The rise and fall time of the pulsed DC power may be between about 1 ns and about 1000 ns, such as between about 10 ns and about 500 ns. In other embodiments, the rise and fall time of the pulsed DC power may be between about 10 ns and about 100 ns. In some embodiments, the rise and fall time of the pulsed DC power may be about 500 ns. In some embodiments, any or all of the power source  270 , the power source  274 , and the power supply  275  are an alternating current power supply. In other embodiments, any or all of the power source  270 , the power source  274 , and the power supply  275  are a direct current power supply. 
     In some embodiments, any or all of the power source  270 , the power source  274 , and the power supply  275  may use a DC offset. The DC offset may be, for example, between about 0% and about 75% of the applied voltage, such as between about 5% and about 60% of the applied voltage. In some embodiments, the first electrode  258  and the second electrode  260  are pulsed negatively while the substrate support assembly  238  is also pulsed negatively. In these embodiments, the first electrode  258  and the second electrode  260  and the substrate support assembly  238  are synchronized but offset in time. For example, the first electrode  258  may be at the “one” state while the substrate support assembly is at the “zero” state,” then the substrate support assembly  238  in the one state while the first electrode  258  is at the zero state. 
     The electrode assembly  216  spans approximately the width of the substrate support assembly  238 . In other embodiments, the width of the electrode assembly  216  may be less than that of the substrate support assembly  238 . For example, the electrode assembly  216  may span between about 10% to about 80%, such as about 20% and about 40%, the width of the substrate support assembly  238 . In embodiments where the electrode assembly  216  is less wide than the substrate support assembly  238 , the actuator  290  may scan the electrode assembly  216  across the surface of the substrate  240  positioned on the first surface  234  of the substrate support assembly  238 . For example, the actuator  290  may scan such that the electrode assembly  216  scans the entire surface of the substrate  240 . In other embodiments, the actuator  290  may scan only certain portions of the substrate  240 . Alternatively, the substrate support assembly  238  may scan underneath the electrode assembly  216 . 
     In some embodiments, one or more magnets  296  may be positioned in the processing chamber  200 . In the embodiment shown in  FIG.  1   , the magnets  296  are coupled to the inside surface of the sidewalls  206 . In other embodiments, the magnets  296  may be positioned in other locations within the processing chamber  200  or outside the processing chamber  200 . The magnets  296  may be, for example, permanent magnets or electromagnets. Representative permanent magnets include ceramic magnets and rare earth magnets. In embodiments where the magnets  296  include electromagnets, the magnets  296  may be coupled to a power source (not shown). The magnets  296  are configured to generate a magnetic field in a direction perpendicular or parallel to the direction of the electric field lines generated by the electrode assembly  216  at the first surface  234  of the substrate support assembly  238 . For example, the magnets  296  may be configured to generate a magnetic field in the x-direction when the electric field generated by the electrode assembly  216  is in the y-direction. The magnetic field drives the charged species  355  (shown in  FIG.  3   ) and polarized species (not shown) generated by the photoacid generators in the photoresist layer  250  in a direction perpendicular to the magnetic field, such as the direction parallel with the latent image lines  255 . By driving the charged species  355  and polarized species in a direction parallel with the latent image lines  255 , line roughness may be reduced. The uniform directional movement of the charged species  355  and polarized species is shown by the double headed arrow  370  in  FIG.  3   . In contrast, when a magnetic field is not applied, the charged species  355  and polarized species may move randomly, as shown by the arrows  370 ′. 
     Continuing to refer to  FIG.  3   , the electrode assembly  216  includes at least the first electrode  258  and the second electrode  260 . The first electrode  258  includes a first terminal  310 , a first support structure  330 , and one or more antennas  320 . The second electrode  260  includes a second terminal  311 , a second support structure  331 , and one or more antennas  321 . The first terminal  310 , the first support structure  330 , and the one or more antennas  320  of the first electrode  258  may form a unitary body. Alternatively, the first electrode  258  may include separate portions that may be coupled together. For example, the one or more antennas  320  may be detachable from the first support structure  330 . The second electrode  260  may similarly be a unitary body or be comprised of separate detachable components. The first electrode  258  and the second electrode  260  may be fabricated by any suitable technique. For example, the first electrode  258  and the second electrode  260  may be fabricated by machining, casting, or additive manufacturing. 
     The first support structure  330  may be made from a conductive material, such as metal. For example, the first support structure  330  may be made of silicon, polysilicon, silicon carbide, molybdenum, aluminum, copper, graphite, silver, platinum, gold, palladium, zinc, other materials, or mixtures thereof. The first support structure  330  may have any desired dimensions. For example, the length L of the first support structure  330  may be between about 25 mm and about 450 mm, for example, between about 100 mm and about 300 mm. In some embodiments, the first support structure  330  has a length L approximately equal to a diameter of a standard semiconductor substrate. In other embodiments, the first support structure  330  has a length L that is larger or smaller than the diameter of a standard semiconductor substrate. For example, in different representative embodiments, the length L of the first support structure  330  may be about 25 mm, about 51 mm, about 76 mm, about 100 mm, about 150 mm, about 200 mm, about 300 mm, or about 450 mm. The width W of the first support structure  330  may be between about 2 mm and about 25 mm. In other embodiments, the width W of the first support structure  330  is less than about 2 mm. In other embodiments, the width W of the first support structure  330  is greater than about 25 mm. The thickness of the first support structure  330  may be between about 1 mm and about 10 mm, such as between about 2 mm and about 8 mm, such as about 5 mm. In some embodiments, the first support structure  330  may be square, cylindrical, rectangular, oval, rods, or other shapes. Embodiments having curved exterior surfaces may avoid arcing. 
     The support structure  330  may be made of the same materials as the second support structure  331 . The range of dimensions suitable for the first support structure  330  is also suitable for the second support structure  331 . In some embodiments, the first support structure  330  and the second support structure  331  are made of the same material. In other embodiments, the first support structure  330  and the second support structure  331  are made of different materials. The lengths L, widths W, and thicknesses of the first support structure  330  and the second support structure  331  may be the same or different. 
     The one or more antennas  320  of the first electrode  258  may also be made from a conductive material. The one or more antennas  320  may be made from the same materials as the first support structure  330 . The one or more antennas  320  of the first electrode  258  may have any desired dimensions. For example, a length L 1  of the one or more antennas  320  may be between about 25 mm and about 450 mm, for example, between about 100 mm and about 300 mm. In some embodiments, the one or more antennas  320  have a length L 1  approximately equal to the diameter of a standard substrate. In other embodiments, the length L 1  of the one or more antennas  320  may be between about 75% and 90% of the diameter of a standard substrate. A width W 1  of the one or more antennas  320  may be between about 2 mm and about 25 mm. In other embodiments, the width W 1  of the one or more antennas  320  is less than about 2 mm. In other embodiments, the width W 1  of the one or more antennas  320  is greater than about 25 mm. The thickness of the one or more antennas  320  may be between about 1 mm and about 10 mm, such as between about 2 mm and about 8 mm. The one or more antennas  320  may have a cross-section that is square, rectangular, oval, circular, cylindrical, or another shape. Embodiments having round exterior surfaces may avoid arcing. 
     Each of the antennas  320  may have the same dimensions. Alternatively, some of the one or more antennas  320  may have different dimensions than one or more of the other antennas  320 . For example, some of the one or more antennas  320  may have different lengths L 1  than one or more of the other antennas  320 . Each of the one or more antennas  320  may be made of the same material. In other embodiments, some of the antennas  320  may be made of a different material than other antennas  320 . 
     The antennas  321  may be made of the same range of materials as the antennas  320 . The range of dimensions suitable for the antennas  320  is also suitable for the antennas  321 . In some embodiments, the antennas  320  and the antennas  321  are made of the same material. In other embodiments, the antennas  320  and the antennas  321  are made of different materials. The lengths L 1 , widths W 1 , and thicknesses of the antennas  320  and the antennas  321  may be the same or different. 
     The antennas  320  may include between 1 and about 40 antennas  320 . For example, the antennas  320  may include between about 4 and about 40 antennas  320 , such as between about 10 and about 20 antennas  320 . In other embodiments, the antennas  320  may include more than 40 antennas  320 . In some embodiments, each of the antennas  320  may be substantially perpendicular to the first support structure  330 . For example, in embodiments where the first support structure  330  is straight, each antenna  320  may be substantially parallel to the first support structure  330 . Each of the antennas  320  may be substantially parallel to each of the other antennas  320 . Each of the antennas  321  may be similarly positioned with respect to the support structure  331  and each other antenna  321 . 
     Each of the antennas  320  has a terminal end  323 . Each of the antennas  321  has a terminal end  325 . A distance C is defined between the first support structure  330  and the terminal end  325 . A distance C′ is defined between the second support structure  331  and the terminal end  323 . Each of the distances C and C′ may be between about 1 mm and about 10 mm. In other embodiments, the distances C and C′ may be less than about 1 mm or greater than about 10 mm. In some embodiments, the distance C and the distance C′ are equal. In other embodiments, the distance C and the distance C′ are different. 
     A distance A is defined between facing surfaces of one of the antennas  321  and an adjacent one of the antennas  321 . The distance A′ is defined between facing surfaces of one antenna  320  and an adjacent one the antennas  320 . The distances A and A′ may be greater than about 6 mm. For example, the distances A and A′ may be between about 6 mm and about 20 mm, such as between about 10 mm and about 15 mm. The distances A and A′ between each adjacent antennas  321 ,  320  may be the same or different. For example, the distances A′ between the first and second, second and third, and third and fourth antennas of the one or more antennas  320  may be different. In other embodiments, the distances A′ may be the same. 
     A distance B is defined between facing surfaces of one of the antennas  320  and an adjacent one of the antennas  321 . The distance B may be, for example, greater than about 1 mm. For example, the distance B may be between about 2 mm and about 10 mm, such as between about 4 mm and about 6 mm. Each distance B may be the same, each distance B may be different, or some distances B may be the same and some distances B may be different. Adjusting the distance B allows for easy control of the electric field strength. 
     The antennas  320 ,  321  may be oriented in an alternating arrangement above the photoresist layer  250 . For example, the antennas  320  of the first electrode  258  and the antennas  321  of the second electrode  260  may be positioned such that at least one of the antennas  320  is positioned between two of the antennas  321 . Additionally, at least one antenna  321  may be positioned between two of the antennas  320 . In some embodiments, all but one of the antennas  320  is positioned between two of the antennas  321 . In those embodiments, all but one of the antennas  321  may be positioned between two of the antennas  320 . In some embodiments, the antennas  320  and the antennas  321  may each have only one antenna. 
     In some embodiments, the first electrode  258  has a first terminal  310 , and the second electrode  260  has a second terminal  311 . The first terminal  310  may be a contact between the first electrode  258  and the power source  270 , the power supply  275 , or a ground. The second terminal  311  may be a contact between the second electrode  260  and the power source  270 , the power supply  275 , or a ground. The first terminal  310  and the second terminal  311  are shown as being at one end of the first electrode  258  and the second electrode  260 , respectively. In other embodiments, the first terminal  310  and the second terminal  311  may be positioned at other locations on the first electrode  258  and the second electrode, respectively. The first terminal  310  and the second terminal  311  have different shapes and sizes than the first support structure  330  and the support structure  331 , respectively. In other embodiments, the first terminal  310  and the second terminal  311  may have generally the same shapes and sizes as the first support structure  330  and the support structure  331 , respectively. 
     In operation, a voltage may be supplied from a power supply, such as the power source  270 , the power source  274 , or the power supply  275 , to the first terminal  310 , the second terminal  311 , and/or the substrate support assembly  238 . The supplied voltage creates an electric field between each antenna of the one or more antennas  320  and each antenna of the one or more antennas  321 . The electric field will be strongest between an antenna of the one or more antennas  320  and an adjacent antenna of the one or more antennas  321 . The interleaved and aligned spatial relationship of the antennas  320 ,  321  produces an electric field in a direction parallel to the plane defined by the first surface  234  of the substrate support assembly  238 . The substrate  240  is positioned on the first surface  234  such that the latent image lines  255  are parallel to the electric field lines generated by the electrode assembly  216 . Since the charged species  355  are charged, the charged species  355  are affected by the electric field. The electric field drives the charged species  355  generated by the photoacid generators in the photoresist layer  250  in the direction of the electric field. By driving the charged species  355  in a direction parallel with the latent image lines  255 , line edge roughness may be reduced. The uniform directional movement is shown by the double headed arrow  370 . In contrast, when a voltage is not applied to the first terminal  310  or the second terminal  311 , an electric field is not created to drive the charged species  355  in any particular direction. As a result, the charged species  355  may move randomly, as shown by the arrows  370 ′, which may result in wariness or line roughness. 
       FIG.  4    depicts a film structure  404  disposed on a substrate  400  during a lithography exposure process. A photoresist layer  407  is disposed on the film structure  404 . The film structure  404  includes an underlayer  405  disposed on a hardmask layer  403  and further on a target layer  402 . The target layer  402  is later patterned for forming the desired device features in the target layer  402 . In one example, the underlayer  405  may be an organic material, an inorganic material, or a mixture of organic or inorganic materials. In the embodiment wherein the underlayer  405  is an organic material, the organic material may be a cross-linkable polymeric material that may be coated onto the substrate  400  through a spin-on process, and then thermally cured so that the photoresist layer  407  may be later applied thereon. In the embodiment wherein the underlayer  405  is an inorganic material, the inorganic material may be a dielectric material formed by any suitable deposition techniques, such as CVD, ALD, PVD, spin-on-coating, spray coating or the like. 
     The underlayer  405  functions as a planarizing layer, an antireflective coat and/or photoacid direction controller, which may provide etch resistance and line edge roughness control when transferring the pattern into the underlying hardmask layer  403  and the target layer  402 . The patterning resistant functionality from the underlayer  405  may work with the underlying hardmask layer  403  during the transfer of the resist process. In one example, the underlayer  405  does not interact with the photoresist layer  407  and does not have interfacial mixing and/or diffusion or cross contamination with the photoresist layer  407 . 
     The underlayer  405  includes one or more additives, such as acid agents, (e.g., photoacid generators (PAGs) or acid catalyst), base agents, adhesion promoters or photo-sensitive components. The one or more additives may be disposed in organic solvent or resin and/or an inorganic matrix material. Suitable examples of the acid agents including photoacid generators (PAGs) and/or acid catalyst selected from a group consisting of sulfonic acids (e.g., p-toluenesulfonic acid, styrene sulfonic acid), sulfonates (e.g., pyridinium p-toluenesulfonate, pyridinium trilluoromethanesulfonate, pyridinium 3-nitrobenzensulfonate), and mixtures thereof. Suitable organic solvent may include homo-polymers or higher polymers containing two or more repeating units and polymeric backbone. Suitable examples of the organic solvent include, but are not limited to, propylene glycol methyl ether acetate (PGMEA), ethyl lactate (EL), propylene glycol methyl ether (PGME), propylene glycol n-propyl ether (PnP), cyclohexanone, acetone, gamma butyrolactone (GBL), and mixtures thereof. 
     In one example, the underlayer  405  provides active acid agents, base agents or ironoic/non-ironic species during the lithographic exposure process, pre- or post-exposure baking process, to assist control the photoacid flowing direction from the upper photoresist layer  407 . 
     The hardmask layer  403  may be an ARC layer fabricated from a group consisting of silicon oxide, silicon nitride, silicon oxynitride, silicon carbide, amorphous carbon, doped amorphous carbon, TEOS oxide, USG, SOG, organic silicon, oxide containing material titanium nitride, titanium oxynitride, combinations thereof and the like. 
     The photoresist layer  407  may be a positive-tone photoresist and/or a negative-tone photoresist that are capable of undergoing a chemically amplified reaction. The photoresist layer  407  is a polymer organic material. 
     As discussed above, an electric field from the electrode  116 , as well as a magnetic field from the magnets  296 , may be applied during a lithography exposure process, pre- or post-exposure baking process, particularly, a post exposure baking process. In the example depicted in  FIG.  4   , the electric field and/or and magnetic field is applied during a lithography exposure process. During the lithographic exposure process, a light radiation  412  is directed to a first region  408  of the photoresist layer  407  while with a second region  406  of the photoresist layer  407  protected by a photomask  410 . Photoacid, shown as e −  in  FIG.  4   , is generated in the exposed first region  408  in the photoresist layer  407  when photoacid generator (PAG) is exposed to the light radiation  412 , such as a UV light radiation. However, oftentimes, movement of photoacid are generally random and photoacid distribution may not be evenly distributed in the first region  408  or may not have a clear boundary set at the interface  430  formed in a plane (interfaced with the second region  406 ) defining between the first region  408  and the second region  406 , resulting in portion of photoacid drifting and diffusing into the second region  406 , as shown in the arrow  422 , unintended to have photoacid generation. As such, lateral photoacid movement (e.g., a direction parallel to a planar surface of the substrate  400 ) drifted into the second region  406 , as shown in the arrow  422 , may result in line edge roughness, resolution loss, photoresist footing, profile deformation, thus causing inaccurate feature transfer to the underlying target layer  402  and/or eventually leading to device failure. 
     Although the example discussed here is shown as the movement of electrons from the photoacid, it is noted that any suitable species, including charges, charged particles, photons, ions, electrons, or reactive species in any forms, may also have similar effects when the electric field is applied to the photoresist layer  407 . 
     By applying an electric field and/or magnetic field to the photoresist layer  407 , distribution of photoacid in the exposed first region  408  may be efficiently controlled and confined. The electric field as applied to the photoresist layer  407  may move photoacid in a vertical direction (e.g., y direction shown by arrows  416  and  420  substantially perpendicular to the planar surface of the substrate  400 ) with minimal lateral motion (e.g., x direction shown by the arrow  422 ) without diffusing into the adjacent second region  406 . Generally, photoacid may have certain polarity that may be effected by the electric field or magnetic field applied thereto, thus orienting photoacid in certain directions, thus creating a desired directional movement of the photoacid in the exposed first region  408  without crossing into the adjacent protected second region  406 . In one example, the photoacid may further be controlled to move directionally at a longitudinal direction (e.g., z direction shown by arrow  428 , defined in a plane interfaced with the second region  406  of the photoresist layer  407  protected by the photomask  410 ) along a lateral plane, as shown by arrow  414 , so as to control the longitudinal distribution of photoacid confined in the exposed first region  408  without crossing at a x direction, as shown by arrow  422 , into the second region  406  of the photoresist layer  407 . The magnetic field generated to the photoresist layer  407  may cause the electrons to orbit along a certain magnetic line, such as the longitudinal direction (e.g., z direction shown by arrow  428 ) so as to further control the photoacid in a desired three-dimensional distribution. The interaction between the magnetic field and the electric field may optimize trajectory of photoacid at a certain path as desired and confined in the exposed first region  408 . Furthermore, vertical photoacid movement is desired to smooth out standing waves that are naturally produced by the light exposure tool, thus enhancing exposure resolution. In one embodiment, an electric field having a strength between about 0.1 MV/m and about 100 MV/m may be applied to the photoresist layer  407 , during a lithographic exposure process, pre- or post baking process, to confine photoacid generated in the photoresist layer  407  in a vertical direction, e.g., at a y direction. In one embodiment, a magnetic field of between 0.1 Tesla (T) and 10 Tesla (T), along with the electric field, may be applied to the photoresist layer  407 , during a lithographic exposure process, pre- or post baking process, to confine photoacid generated in the photoresist layer  407  in both longitudinal direction and vertical direction, e.g., at y and z directions, with minimum lateral direction, e.g., at x direction. While in combination of the magnetic field along with the electric field, the photoacid as generated may be further confined to be distributed in the longitudinal direction, e.g., in the direction shown by the arrow  428 , remaining in the first region  408  of the photoresist layer  407 , parallel along the interface  430  within the exposed first region  408 . 
       FIG.  5    depicts another profile of photoacid distribution that may be controlled by utilizing an electric field, magnetic field, or combinations thereof to specifically control the photoacid located at certain zones during a post exposure baking process. The exposed region  502  of the photoresist layer  407  has chemically altered from the first region  408  as shown in  FIG.  4   , after the lithographic exposure process. After the photoresist layer  407  is lithographically exposed, a post exposure baking process is then performed to cure the photoresist layer  407 , including the exposed region  502  and the remaining regions (e.g., shielded by the photomask during the lithographic exposure process) in the photoresist layer  407 . During the post exposure baking process, the acid agent (e.g., such as photoacid), base agent, or other suitable additive from the underlayer  405  may be controlled in a manner that can assist distribution/movement of the photoacid within the photoresist layer  407  in a desired direction, as shown by the arrow  506  in  FIG.  5   . The additive in the underlayer  405  is diffused to the upper photoresist layer  504  during the post exposure baking process (or even during the lithographic exposure process), which helps to improve the sensitivity of the photoresist layer  407  so as to maintain a vertical profile of the photoresist layer  407 . As a result, after development and rinse, a substantially vertical profile may be obtained in the photoresist layer  407 . 
     In one embodiment, the additives, such as acid agents or photoacid as one example, from the underlayer  405  may be thermally driven upwards, as shown by the arrow  506 , during the post exposure baking process so that the profile of the photoresist layer  407  may be efficiently controlled. Furthermore, as the additives from the underlayer  405  may be driven at a particular direction upward by the electric field, magnetic field, or combinations thereof during the post exposure baking process, the electrons provided from the additives may be controlled at certain moving path, such as predominantly in a vertical direction toward the photoresist layer  407 . By doing so, the desired vertical structure may be defined and confined in the photoresist layer  407  as needed. It is noted that the examples of the photoresist layer  407  depicted in  FIGS.  4 - 5    are formed with a straight edge profile (e.g., a vertical sidewall). However, the profile of the photoresist layer  407  may be formed in any desired shapes, such as a tapered or flare-out opening as needed. 
     After the post exposure baking process, an anisotropic etching process, or other suitable patterning/etching processes, may be performed to transfer features into the underlayer  405 , the hardmask layer  403  and the target layer  402  as needed. 
       FIG.  6    depicts a flow diagram of a method  600  for utilizing an underlayer disposed under a photoresist layer to assist controlling photoacid distribution/diffusion in a photoresist layer during a lithographic exposure process or during a pre- or a post-exposure baking process. The method  600  beings at operation  602  by positioning a substrate, such as the substrate  400  described above, into a processing chamber, such as the processing chamber  200  depicted in  FIGS.  2 - 3   , with an electrode assembly and a magnetic assembly disposed therein. 
     At operation  604 , after the substrate  400  is positioned, an electric field and/or a magnetic field may be individually or collectively applied to the processing chamber (during a lithographic exposure process and/or post exposure baking process) to control photoacid movement within in a photoresist layer having an underlayer disposed thereunder. After the electric field and/or a magnetic field is individually or collectively applied to the photoresist layer and the underlayer disposed on the substrate, photoacid as generated may move primarily in a vertical direction, a longitudinal direction, a circular direction, rather than a lateral direction. As a result of the assistance provided by the underlayer disposed under the photoresist layer, the photoacid movement in the photoresist layer may be efficiently controlled. 
     At operation  606 , after the exposure process, a post exposure baking process is performed to cure the photoresist layer and the underlayer. During the baking process, an energy (e.g., an electric energy, thermal energy or other suitable energy) may also be provided to the underlayer. In one example depicted here, the energy is a thermal energy provided to the substrate during the post exposure baking process. The additives from the underlayer may also assist controlling the flow direction of the photoacid within the photoresist layer. By utilizing directional control of photoacid distribution in a predetermined path having a patterned photoresist layer, a desired edge profile with high resolution, does sensitivity, resistance to line collapse, and stochastics failure, and minimum line edge roughness may be obtained. In one example, by utilizing the underlayer structure, the critical dimension uniformity (CDU) (e.g., critical dimension variation) may be reduced from generally from 3 nm to 6 nm down to 1 nm to 2 nm or less, which is about 50% to 600% uniformity improvement. The line width roughness (LWR) may be reduced from generally from 3 nm to 5 nm down to 1 nm to 2 nm or less, which is about 50% to 600% roughness improvement. Furthermore, a distance between a first tip end of a first trench to a second tip end of a second trench may be reduced from generally from 30 nm to 50 nm down to 10 nm to 20 nm. Furthermore, some types of defects, such as corner rounding, footing, deformed profile, slanted sidewall profile, may also be efficiently eliminated and reduced. 
     The previously described embodiments have many advantages, including the following. For example, the embodiments disclosed herein may reduce or eliminate line edge/width roughness with high resolution and sharp edge profile. The aforementioned advantages are illustrative and not limiting. It is not necessary for all embodiments to have all the advantages. 
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.