Abstract:
A technique for patterning a substrate is disclosed. In accordance with one exemplary embodiment, the technique may be realized as a method for patterning a substrate. The method may comprise: providing a resist on the substrate; introducing one or more species of impurities into the resist; selectively exposing a first portion of the resist to radiation while a second portion of the resist is not exposed to the radiation; exposing the resist to a developer and removing the first portion of the resist exposed to the radiation from the substrate; and exposing the resist at a temperature higher than a room temperature but lower than glass transition temperature of the resist.

Description:
PRIORITY 
       [0001]    This application claims priority to U.S. Provisional Patent Application Ser. No. 61/564,574, filed on Nov. 29, 2011, entitled “Techniques For Patterning A Substrate.” The entire specification of U.S. Provisional Patent Application Ser. No. 61/564,574, is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates generally to techniques for substrate processing, more particularly to techniques for patterning resist formed on a substrate. 
       BACKGROUND 
       [0003]    A patterning process is one of many processes used in manufacturing devices, including integrated circuit (IC) devices. Generally, it is used to define features in the devices. It plays an important role as the devices and the features contained therein continue to become smaller. 
         [0004]    One of the patterning processes used in device manufacturing is a photolithographic process. In this process, a desired pattern is formed on a mask. The pattern is then transferred onto the substrate via a photoresist. For example, a layer of photoresist is deposited on the substrate. Thereafter, a mask with an aperture arranged in a desired pattern is disposed above the photoresist. Radiation from a light source above the mask is then directed toward the substrate, and the pattern of the aperture of the mask is imaged on the photoresist. Thereafter, the photoresist is exposed to a developer solution, such as tetramethyl ammonium hydroxide. As the radiation exposure causes the photoresist to become soluble to the developer solution, a portion of the photoresist exposed to the radiation is dissolved and removed from the substrate. Meanwhile, another portion not exposed to the radiation may remain insoluble and remain on the substrate as the resist structures. The remaining resist structures, which may be arranged in a desired pattern, may be baked and further hardened. These resist structures are used as a mask for subsequent, for example, etching process, where the pattern of the resist structure is transferred onto the substrate. 
         [0005]    As the process is a pattern transferring process, any defect in the mask or the resist structures may ultimately be transferred onto the substrate. In the conventional photolithographic processes, excessive line edge roughness (LER) and line width roughness (LWR) are found. Such defects may be transferred into the substrate resulting in trenches or features with rough edges and/or non-uniform widths. And these defects may ultimately lead to devices with non-uniform performance or to defective devices. 
         [0006]    Accordingly, a new process that limits or reduces the LER and LWR in photolithographic process is needed. 
       SUMMARY 
       [0007]    Techniques for patterning resist are disclosed. In accordance with one exemplary embodiment, the technique may be realized as a method for patterning a substrate. The method may comprise: providing a resist on the substrate; introducing one or more species of impurities into the resist; selectively exposing a first portion of the resist to radiation while a second portion of the resist is not exposed to the radiation; exposing the resist to a developer and removing the first portion of the resist exposed to the radiation from the substrate; and exposing the resist at a temperature higher than a room temperature but lower than glass transition temperature of the resist. 
         [0008]    In accordance with other aspects of this particular exemplary embodiment, the one or more species of impurities may be introduced into the resist prior to the exposing the resist to a developer. 
         [0009]    In accordance with further aspects of this particular exemplary embodiment, the one or more species of impurities may be introduced into the resist prior to the selectively exposing the first portion of the resist to the radiation. 
         [0010]    In accordance with additional aspects of this particular exemplary embodiment, the one or more species of impurities may be introduced into the resist after the selectively exposing the first portion of the resist to the radiation. 
         [0011]    In accordance with further aspects of this particular exemplary embodiment, the impurities may contain one or more species chosen from a group consisting of nitrogen (N), carbon (C), silicon (Si), hydrogen (H), oxygen (O), and fluorine (F). 
         [0012]    In accordance with other aspects of this particular exemplary embodiment, the impurities may be introduced in a form of ions using ion implantation process. 
         [0013]    In accordance with further aspects of this particular exemplary embodiment, the exposing the resist at a temperature higher than a room temperature but lower than glass transition temperature of the resist may occur during the ion implantation process. 
         [0014]    In accordance with additional aspects of this particular exemplary embodiment, the exposing the resist at a temperature higher than a room temperature but lower than glass transition temperature of the resist may occur after the ion implantation process. 
         [0015]    In accordance with other aspects of this particular exemplary embodiment, the exposing the resist at a temperature higher than a room temperature but lower than glass transition temperature of the resist may occurs prior to the ion implantation process. 
         [0016]    In accordance with additional aspects of this particular exemplary embodiment, the exposing the resist at a temperature higher than a room temperature but lower than glass transition temperature of the resist occurs prior to the exposing the resist to a developer. 
         [0017]    In accordance with further aspects of this particular exemplary embodiment, the exposing the resist at a temperature higher than a room temperature but lower than glass transition temperature of the resist occurs prior to the exposing the resist to the radiation. 
         [0018]    In accordance with another exemplary embodiment, the technique may be realized as a method for patterning a substrate. The method may comprise: providing a resist on the substrate; introducing one or more species of impurities into the resist; selectively exposing a first portion of the resist introduced with impurities to radiation while a second portion of the resist introduced with impurities is not exposed to the radiation; exposing the resist to a developer and removing the first portion of the resist exposed to the radiation from the substrate. 
         [0019]    In accordance with other aspects of this particular exemplary embodiment, the impurities may contain one or more species chosen from a group consisting of nitrogen (N), carbon (C), silicon (Si), hydrogen (H), oxygen (O), and fluorine (F). 
         [0020]    In accordance with further aspects of this particular exemplary embodiment, the impurities may be negative ions. 
         [0021]    In accordance with additional aspects of this particular exemplary embodiment, the impurities may be introduced in a form of ions using ion implantation process. 
         [0022]    In accordance with further aspects of this particular exemplary embodiment, the method may further comprise: exposing the resist at a temperature higher than a room temperature but lower than a glass transition temperature of the resist. 
         [0023]    In accordance with additional aspects of this particular exemplary embodiment, the impurities may be introduced in a form of ions using ion implantation process and where the exposing the resist at the temperature higher than the room temperature but lower than the glass transition temperature of the resist may occur during the ion implantation process. 
         [0024]    In accordance with further aspects of this particular exemplary embodiment, the impurities may be introduced in a form of ions using ion implantation process and where the exposing the resist at the temperature higher than a room temperature but lower than the glass transition temperature of the resist occurs after the ion implantation process. 
         [0025]    In accordance with another exemplary embodiment, the technique may be realized as a method for patterning a substrate. The method may comprise: providing a resist on the substrate; introducing one or more species of impurities into the resist, wherein the impurities contains at least one of nitrogen (N), hydrogen (H), oxygen (O), and fluorine (F); selectively exposing a first portion of the resist introduced with impurities to radiation while a second portion of the resist introduced with impurities is not exposed to the radiation; and exposing the resist to a developer and removing the first portion of the resist exposed to the radiation from the substrate. 
         [0026]    The present disclosure will now be described in more detail with reference to exemplary embodiments thereof as shown in the accompanying drawings. While the present disclosure is described below with reference to exemplary embodiments, it should be understood that the present disclosure is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present disclosure as described herein, and with respect to which the present disclosure may be of significant utility. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    In order to facilitate a fuller understanding of the present disclosure, reference is now made to the accompanying drawings, in which like elements are referenced with like numerals. These drawings should not be construed as limiting the present disclosure, but are intended to be exemplary only. 
           [0028]      FIG. 1A-1H  illustrate an exemplary method of patterning a substrate according to one embodiment of the present disclosure. 
           [0029]      FIG. 2A-2H  illustrate another exemplary method of patterning a substrate according to another embodiment of the present disclosure. 
           [0030]      FIG. 3A-3H  illustrate another exemplary method of patterning a substrate according to another embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    The present disclosure will now be described in more detail with reference to particular embodiments thereof as shown in the accompanying drawings. While the present disclosure is described below with reference to particular embodiments, it should be understood that the present disclosure is not limited thereto. For example, the present disclosure includes a step in which impurities are added to photoresist or developed resist structure. For clarity and simplicity, the present disclosure will focus on adding the impurities in a form of ions via ion implantation process. However, those of ordinary skill in the art will recognize that the impurities need not be introduced via ion implantation process. The impurities may be introduced via other processes including thermal diffusion process, gas immersion laser doping (GILD) process, and other doping or impurities introducing processes, all of which are not precluded in the present disclosure. 
         [0032]    Referring to  FIG. 1A-1H , there is shown a method  100  for patterning a substrate according to one embodiment of the present disclosure.  FIG. 1A ,  1 C,  1 E, and  1 G illustrate side views of the substrate  102  and the process performed thereon.  FIGS. 1B ,  1 D,  1 F, and  1 H illustrate top views of the substrate  102  during the steps shown in  FIG. 1A ,  1 C,  1 E, and  1 G, respectively. 
         [0033]    In the present embodiment, a substrate  102  may be coated with a layer of resist  106 , as illustrated in  FIG. 1A . In the present disclosure, a bottom anti-reflective coating (BARC) layer  104  may optionally be provided between the substrate  102  and the resist  106 . The resist  106 , in the present disclosure, is not limited to a particular type of resist  106 . For clarity and simplicity, the present disclosure will focus on using positive polymer based photoresist with pendant acid sensitive group containing, among others, a small amount (e.g. about 5-10 weight percent) of onium salt or photo acid generator (PAG)  106   a.  Because of their ionic character, PAG  106   a  may aggregate in an otherwise hydrophobic resist matrix  106 . 
         [0034]    After depositing the resist  106 , the resist  106  may undergo an exposure step shown in  FIG. 1C . In this exposure step, a mask  112  is positioned between the resist  106  and a light source (not shown), and the radiation  114  from the light source is directed toward the resist  106 . In the present embodiment, the light source may be an ultraviolet (UV) light source emitting UV radiation in the range of about 193 nm. However, those of ordinary skill in the art will recognize that radiation with other wavelengths may also be used. 
         [0035]    The mask  112  may comprise one or more transparent areas  112   a,  such as apertures, defined by one or more opaque areas  112   b.  Such transparent areas  112   a  may be arranged in a desired pattern. As shown in  FIG. 1C , the radiation  114  may pass through the transparent areas  112   a,  but not through the opaque areas  112   b.  In the process, the pattern of the apertures may be imaged on the resist  106 , and one or more regions of the resist  106  are exposed to the radiation  114 . This exposure step is followed by a resist development step, where the resist  106  is exposed to developer or alkaline solution, and portions of the resist  106  exposed to the radiation is removed. After the resist development step, one or more resist structure  106   i  may form on the substrate  102 , as shown in  FIG. 1E . If included, portions of the BARC layer  104  may be exposed through the gap between the resist structures  106   i.    
         [0036]    During the exposure step that precedes the resist development step, PAG  106   a  within the resist  106  may be activated, and a small amount of acid may be generated. This acid may catalyze the deprotection of the pendant carboxylic acid groups in the resist  106  when the resist  106  is subsequently baked. The acid, however, is not consumed during the deprotection reaction. Instead, the acid continues to deprotect additional pendant groups. Through this chemical amplification process, solubility of the portions of the resist  106  exposed to the radiation  114  to the developer solution or alkaline solution may increase. The portions may dissolve and be removed from the substrate  102 . The area of the resist  106  not exposed to the radiation  114 , however, may remain insoluble to the developer or alkaline solution and remain on the substrate  102  after the resist development step. 
         [0037]    In the present embodiment, the resist development step may be followed by impurities introduction step, as shown in  FIG. 3E . In this step, impurities are introduced into the resist structure  106   i  remaining on the substrate  102  and, if included, the exposed portion of the BARC layer  104 . In the present embodiment, the impurities may preferably be introduced in a form of ions  122 . The ions  122  may be directed toward the resist structure  106   i  preferably at one or more angles, as shown in  FIG. 1 , and implanted into the vertically and horizontally extending surfaces of the resist structure  106   i.  In the present embodiment, the energy by which the ions  122  are introduced may be low, preferably ranging between about 50 eV to about 2.0 KeV. However, the present disclosure does not preclude implanting ions at other energies. As a result, the ions  122  may be disposed in the resist structure  106   i,  and, if included, the exposed portion of the BARC layer  104 , as shown in  FIG. 1H . 
         [0038]    In the present disclosure, various species of the impurities may be introduced. The preferred species may include species with high chemical potential. For example, the ions  122  that may be implanted may be those capable of forming sub-molecular interactions such as, for example, hydrogen/dangling bonds, n-n*, sp 3 -sp 3 , through space or hydrophobic interactions with the resist polymer or with other ions. Specific examples may include atomic or molecular species containing nitrogen (N), carbon (C), silicon (Si), hydrogen (H), oxygen (O), and fluorine (F). However, other species are not precluded in the present disclosure. When introduced, only one of the foregoing species may be implanted in the present embodiment. In other embodiments, two or more of the foregoing species may be implanted, simultaneously or at different times. Moreover, the ions  122 , in the present disclosure may be positive or negative ions. 
         [0039]    If the species of the ions  122  is N or N containing species, the ions  122  implanted in to the resist structure  106   i  may move away from the surface as a result of hydrophobic interactions. The introduced N may then undergo sub-molecular interactions (e.g. hydrogen bonds or n-n*) with O and/or H atoms in the resist structure  106   i,  and become embedded in the resist structure  106   i.  In the process, stable N-N interactions may occur, and the density of the resist structure  106   i  may increase. With increased density, the etch resistance and the strength or hardness of the resist structures  106   i  may improve. The resist structure  106   i  may be able to withstand other processes performed subsequently, including subsequently performed plasma-based pattern transferring processes. Accordingly, the edges of the resist structure  106   i  will be less likely to be degraded during the pattern transfer, and reduction in LER and LWR may result. 
         [0040]    If the species introduced into the resist structure  106   i  is C or C containing species, the species may stabilize with the polymer in the resist structure  106   i  by through-space sp 3  interactions. In addition, the species may also increase the strength or hardness and etch resistance of the resist structure  106   i.  If the species introduced into the resist structure  106   i  is Si or Si containing species, the etch resistance and the strength or hardness of the resist structure  106   i  may improve even further. Meanwhile, the species containing F, if introduced, may migrate away from the surface and be embedded in the resist structure  106   i  as a result of hydrophobic interactions. The density of the resist structure  106   i,  in the process, may increase, and additional improvement to LER and LWR may be observed. 
         [0041]    During or after the impurities introduction step, the resist structure  106   i  may undergo a thermal treatment step. During this thermal treatment step, the temperature of the resist structure  106   i  (T rs ) may be maintained at a temperature greater than the room temperature (T rm ), but less than the glass transition temperature (T g ) of the resist structure  106   i.  With the thermal treatment, the polymer chains within the resist structure  106   i  may coalesce around or move away from the impurities, and the density of the resist structure  106   i  may increase. The resist structure  106  may also experience reduced buckling that it may otherwise experience during an annealing or other high temperature thermal treatment steps, thereby strengthening and enhancing the sub-molecular interactions discussed above. This may improve the hardness or strength of the resist of the resist structure  106   i  and, thus, its etch resistance. With this improved etch resistance, the fidelity of pattern may be maintained. In other words, the thermal treatment will help adjust the LER. 
         [0042]    In the present disclosure, the thermal treatment below the T g  is preferred as such a treatment may limit the fluidity of the resist structure  106   i.  More fluid resist structures  106   i  are not preferable, as the fidelity of the pattern may be affected. In the present embodiment, this thermal process step may be performed during the ion implantation step. Alternatively, the resist structure  106   i  may undergo a separate thermal treatment process after the ion implantation step. 
         [0043]    In the present embodiment, implanting ions after forming the resist structure  106   i  may provide additional benefits. In addition to the resist structure  106   i,  the ions  122  may also be implanted and mechanically weaken the BARC layer  104  (see  FIG. 1G ). In the process, the etch rate of the BARC layer  104  may be increased, and less time may be necessary in a subsequent etch step to etch the BARC layer  104 . When the overall etch time is reduced, the degradation of edges of the resist structure  106   i  by the etchant used during the etch step is reduced. As such, the rate by which LER may occur may also be reduced. Referring to  FIG. 2A-2H , there is shown another exemplary method  200  for patterning a substrate according to another embodiment of the present disclosure.  FIG. 2A ,  2 C,  2 E, and  2 G illustrate side views of the substrate  102  and the process performed thereon.  FIG. 2B ,  2 D,  2 F, and  2 H respectively illustrate the plan views of the substrate  102  during the steps shown in  FIG. 2A ,  2 C,  2 E, and  2 G. Those of ordinary skill in the art will recognize that several steps and features included in the in the previous embodiment shown in  FIG. 1A-1H  is also included in the present embodiment. Detailed descriptions of such repeating steps and features may be omitted. As such, the method of the present embodiment should be understood in relation to the method shown in  FIG. 1A-1H . In addition, several specific steps, including the thermal treatment step, disclosed in the prior embodiment may be included in the present embodiment even if detailed descriptions of the repeating steps are missing. 
         [0044]    In the present embodiment, the substrate  102  may be coated with the layer of resist  106 , as illustrated in  FIG. 2A . Optionally, a (BARC) layer  104  may also be provided between the substrate  102  and the resist  106 . As illustrated in  FIG. 2B , the resist  106  may comprise PAG  106 . 
         [0045]    In the present embodiment, the impurities may be introduced into the resist  106 . Much like the prior embodiment, however, the impurities are preferably introduced as the ions  122  via the ion implantation process shown in  FIG. 2C . Unlike the prior embodiment, however, the impurities, in the form of ions  122 , are introduced prior to the resist exposure step, and prior to forming the resist structure  106   i.  Although various species may be contained in the ions  122  and introduced as the impurities, the preferred species may include species with high chemical potential. Specific examples of the species may be those containing C, F, O, H, and Off, or their combination. In addition, the ions  122  may be introduced at one or more angles, at one or more energies ranging between about 50 eV to about 2.0 KeV. 
         [0046]    The exposure step, as shown in  FIG. 2E , may follow the impurities introducing step. Thereafter, the development step, as shown in  FIG. 2G , may be performed to form the resist structure  106   i.  Those of ordinary skill in the art will recognize that the thermal treatment step disclosed in the earlier embodiment may also be performed. If performed, the thermal treatment step may be performed during or after the impurities introducing step. 
         [0047]    In the present embodiment, the impurities introduced as ions  122  may collide with PAG  106   a  in the resist  106  and reduce the mean free path of the activated PAG  106   b  during chemical amplification. This reduction may result in the limiting the activated PAG  106   b  from diffusing into the portions of the resist  106  not exposed to the radiation  114 . Accordingly, chemical amplification may be limited to the portions of the resist  106  exposed to the radiation  114 , as it is more entropically favorable for the acid to act in the exposed than the unexposed areas. The ions  122  may also cause a small reduction in the radius of the polymer chains. This decrease may also reduce the diffusion of the acid and the acid-catalyzed deprotection of pendant groups in the portions of the resist not exposed to the radiation  114 . By limiting the acid-catalyzed deportection of the pendant groups in the portions of the resist not exposed to the radiation  114 , LER may be reduced. The resist structures  106   i  with straight, well defined edges may be obtained during the development stage. Thus, the impurities may induce thermodynamic asymmetry during the chemical amplification step. 
         [0048]    If the ions  122  is C or C containing species, the ions  12  may increase the etch resistance of the resist  106  to reduce LER or LWR. If the ions  122  are F ions or F containing ions, the impurities may be embedded within the resist  106  due to the hydrophobic nature of the impurities, and the density of the resist  106  may increase prior to the exposure step. This increase in the density may improve the structural hardness or strength of the resist  106 . As a result, LER that may otherwise occur during the development step may be reduced. 
         [0049]    If the impurities or the ions  122  contain negative OH − , the impurities will dissipate their charges and may generate infinitesimal charge as they are introduced into the resist  106 . This charge may inhibit the developer anion from being transported into the areas of the resist  106  not exposed to the radiation  114 . The developer anions will however dissolve the carboxylic acids in the portions of the resist  106  exposed to the radiation  114  as deprotonation in those portions are more entropically favored. Thus, negative OH −  may induce thermodynamic asymmetry during the resist development step, and LER or LWR may be reduced. 
         [0050]    Referring to  FIG. 3A-3H , there is shown a method  300  for patterning a substrate according to another embodiment of the present disclosure.  FIG. 3A ,  3 C,  3 E, and  3 G illustrate side views of the substrate  102  and the process performed thereon.  FIG. 3B ,  3 D,  3 F, and  3 H illustrate top views of the substrate  102  during steps shown in  FIG. 3A ,  3 C,  3 E, and  3 G, respectively. Those of ordinary skill in the art will recognize that several steps and features included in the in the previous embodiments shown in  FIG. 1A-1H  and  2 A- 2 H are also included in the present embodiment. Detailed descriptions of such repeating steps and features may be omitted. As such, the method of the present embodiment should be understood in relation to the methods shown in  FIG. 1A-1H  and  2 A- 2 H. In addition, several specific steps, including the thermal treatment step, disclosed in the prior embodiment may be included in the present embodiment even if detailed descriptions of the repeating steps are missing. 
         [0051]    In the present embodiment, the substrate  102  may be coated with the layer of resist  106 , as illustrated in  FIG. 3A . Optionally, a (BARC) layer  104  may also be provided between the substrate  102  and the resist  106 . As illustrated in  FIG. 3B , the resist  106  may comprise PAG  106 . After preparing the substrate  102  with the resist  106  coated thereon, the exposure step shown in  FIG. 3C and 3D  may take place. As illustrated in  FIG. 3D , PAG  106   a  in the portions of the resist  106  exposed to the light are activated to form the activated PAG  106   b,  and the solubility of the resist  106  in such portions may be altered. After the exposure step, impurities are introduced into the resist  106 . Similar to the earlier embodiments, the impurities may be introduced as ions  122 , as shown in  FIG. 3E and 3F . If introduced via ion implantation process, the ions  122  may be introduced at one or more energies ranging between about 50 eV to about 1.5 KeV. Moreover, the ions  122  may be introduced at one or more angles. As noted above, various species may be introduced as the impurities. However, the preferred species in the present embodiment may include species high chemical potential. Specific examples of the species may include Si, C, O, H, and OH −  species, or their combination. 
         [0052]    The impurity introducing step shown in  FIG. 3E  may be followed by the development step shown in  FIG. 3G . Much like the prior embodiment, the resist  106  is exposed to the developer or alkaline solution during the step. The portions of the resist  106  exposed to the radiation  114  may be removed from the substrate  102 . As a result, the resist structures  106   i  may form as shown in  FIG. 3G and 3H . 
         [0053]    As noted above, introducing the impurities containing C may increase the etch resistance of the resist  106  and minimize LER and LWR. Meanwhile, introducing impurities containing Si may increase the etch resistance of the resist  106  to a greater extent. Although not precluded in the present disclosure, Si, if introduced, may preferably be introduced after the exposure step. Introduction of the Si prior to the exposure step may not be preferable due to the species&#39; high optical adsorption. The high optical adsorption of Si may induce the resulting resist  106  to increase its reflectivity and reduce the ability of the radiation  114  to increase the solubility of the resist. If OH negative ions are introduced, the ions may induce thermodynamic asymmetry during the resist development step by inhibiting developer anion transport into the unexposed areas. As such, LER or LWR may be improved. 
         [0054]    Herein, techniques for patterning resist on a substrate are disclosed. The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.