Abstract:
The embodiments of the present invention include decomposing a pattern into dependent patterns. The dependent patterns may then be transferred to a semiconductor wafer surface and the pattern&#39;s features may be shrunk. The shrunk features may be transferred to the substrate. The multiple exposures and shrinks facilitate smaller feature dimensions.

Description:
TECHNICAL FIELD  
       [0001]     The invention relates to methods and apparatus for processing semiconductor wafers. In particular, the present invention relates to photolithographic methods and apparatus for processing semiconductor wafers.  
       BACKGROUND  
       [0002]     In semiconductor wafer processing, patterned elements may be formed on the surface of a semiconductor wafer. Typically, these patterned elements may be formed by photolithography. Photolithography may involve depositing a photoresist material on the semiconductor wafer and selectively exposing the photoresist material to light. Portions of the photoresist exposed to light may react to light and subsequent development so patterned elements may be formed. Semiconductor processing may then transfer the patterned elements to the substrate. Integrated circuits may then be formed using numerous steps of photolithography and other semiconductor processing steps. Manufacture of smaller integrated circuits may generally improve the performance and cost of such devices. The ability to achieve smaller dimensions of patterned elements may be generally understood to be limited more by photolithography than any other semiconductor processing step. Achieving smaller dimensions of patterned elements through photolithography may have numerous difficulties.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0003]     The invention is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which the like references indicate similar elements and in which:  
         [0004]      FIG. 1  illustrates a top-down type view of an apparatus in accordance with one embodiment of the present invention.  
         [0005]      FIGS. 2   a - 2   d  illustrate cross sectional type views of a method in accordance with one embodiment of the present invention.  
         [0006]      FIGS. 3   a - 3   h  illustrate cross sectional type views of a method in accordance with one embodiment of the present invention.  
         [0007]      FIG. 4  illustrates an operational flow of a method of dual exposure and shrink in accordance with an embodiment of the present invention.  
         [0008]      FIG. 5  illustrates an operational flow of a method of dual exposure and shrink, including transfer to the substrate, in accordance with an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0009]     In various embodiments, an apparatus and method relating to transferring a pattern to a semiconductor wafer are described. In the following description, various embodiments will be described. However, one skilled in the relevant art will recognize that the various embodiments may be practiced without one or more of the specific details, or with other methods, materials, or components. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of various embodiments of the invention. 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.  
         [0010]     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.  
         [0011]     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.  
         [0012]      FIG. 1  illustrates a top-down view of a master pattern  100  in accordance with one embodiment of the present invention. The master pattern  100  may be a pattern for layers of integrated circuits desired to be transferred to a semiconductor wafer by photolithography. A process to transfer features from a single pattern to a surface, such as the surface of a semiconductor wafer, may have minimum allowable feature dimensions; the physical limitations of the process prevent features smaller than the minimum allowable feature dimensions from being transferred from the single pattern to the surface. However, the desired pattern on the master pattern may include smaller feature sizes than those allowed by the physical limits for minimum allowable feature dimensions. A method to transfer from a desired pattern feature dimensions smaller than the minimum allowable feature dimensions available using standard transferring methods such as photolithography is discussed herein.  
         [0013]     A process to transfer features from a single pattern to a surface may be characterized by a process window. A process window may be defined generally as the furthest deviation from optimal processing conditions where the desired pattern may still be successfully transferred to the semiconductor wafer. The process window may depend largely on the photolithography process chosen and the feature dimensions in the pattern being transferred. Generally, more advanced and costly photolithography processes may allow for larger process windows at the same feature size in the desired pattern. For smaller feature dimensions, certain photolithography processes may have no associated process window because the process, even at optimal conditions, cannot achieve the feature dimensions. For those patterns, a more advanced photolithography process may need to be chosen. Generally, minimum allowable feature dimensions will be associated with a very small process window in the most advanced photolithography process.  
         [0014]     A pattern with larger feature dimensions may have an associated larger process window (using the same photolithography process) than a pattern with smaller feature dimensions. A larger process window may allow for less difficulty in transferring the pattern to the semiconductor surface. Alternatively, larger dimensions may allow a less costly photolithography process to be used. A method to transfer a desired pattern allowing increased photolithography process window or less costly photolithography process is discussed herein.  
         [0015]     Referring to  FIG. 1 , the master pattern  100  includes features  190  and feature dimensions  170 ,  180 . The feature dimension  170  may be a pitch dimension and feature dimension  180  may be a width dimension. Generally, pitch dimensions may be defined as the distance between the same structural elements on like features and width dimensions may be defined as the distance across a feature on a pattern.  
         [0016]     The master pattern  100  may be decomposed into a first pattern  110  and a second pattern  120 . The first pattern  110  may include a first plurality of features  130  and the second pattern  120  may include a second plurality of features  140 . Both the first pattern  110  and the second pattern  120  may include features  130 ,  140  to be transferred that are as small as the minimum allowable feature dimensions  150 ,  160 . The minimum allowable feature dimensions  150 ,  160  may be based on the physical limitations of the method used for pattern transfer. In the manufacture of integrated circuits, the method used for pattern transfer may be a photolithography process. Other methods may be used. In a photolithography process, the minimum allowable feature dimensions, may be defined by the resolution of the photolithography process. The resolution of the photolithography process may be influenced by the wavelength of light, optical characteristics of a projection system, photoresist thickness, and many other variables.  
         [0017]     In methods described below, the master pattern  100  may have feature dimensions  170 ,  180  less than minimum allowable feature dimensions  150 ,  160  of the pattern transfer method used. For example, if a standard 193 nm photolithography process may transfer a feature pitch of a minimum of 150 nm and a feature width of a minimum of 75 nm, the present method may be capable of providing a feature dimension  170  of 75 nm and a feature dimension  180  of 25 nm. In one embodiment of the present invention, the feature dimension  180  is thus smaller than the minimum allowable feature dimension  160  of the process used to transfer features from a single pattern to a surface. In another embodiment, the feature dimension  170  is smaller than the minimum allowable feature dimension  150 . In yet another embodiment, the feature dimension  170  may be approximately half the minimum allowable feature dimension  160 . Other combinations of feature dimensions  170 ,  180  may be available.  
         [0018]     The master pattern  100  in this example may be decomposed into a first pattern  110  and a second pattern  120 . In this example, a standard 193 nm photolithography process may be capable of providing a feature pitch of 150 nm and a feature width of 75 nm when transferring from a single pattern to a surface. The master pattern  100  may include a feature dimension  170  of 75 nm and a feature dimension  180  of 25 nm that may be unallowable based on the chosen transfer method. The first pattern  110  and the second pattern  120  may include a feature dimension  150  of 150 nm, a feature dimension  160  of 75 nm, and may combine to form the master pattern  100  by methods described herein. Transfer of the first pattern  110  and the second pattern  120  may then be allowable based on a standard 193 nm photolithography process. Thus, the feature dimensions of the master pattern  100 , which are smaller than the minimum allowable feature dimensions, may be transferred to the surface.  
         [0019]     Referring to  FIG. 1 , the first plurality of features  130  and second plurality of features  140  may be larger than the features  190  and may have an accordingly larger photolithography process window. In one embodiment of the present invention, the increased process window may allow for less difficulty in photolithography processing. In another embodiment, the larger feature sizes may allow for a less costly photolithography process to achieve the master pattern  100 . Although not illustrated in  FIG. 1 , the increase in size of the first plurality of features  130  and second plurality of features  140  from the features  190  may cause those features to overlap if the first pattern  110  and the second pattern  120  were overlaid.  
         [0020]     For simplicity,  FIG. 1  and subsequent figures illustrate line and space features and, more specifically, nested line and space features. In other embodiments, the features may be isolated line features, isolated space features, isolated or nested hole features, or others. Further, the figures illustrate a master pattern that is decomposed into two dependent patterns, however, more than two dependent patterns may be used. For example, if the master pattern were decomposed into three dependent patterns each capable of being transferred with a 150 nm pitch and 75 nm width, the master pattern may include features with a 50 nm pitch and 10 nm width. As the master pattern is decomposed into more numerous dependent patterns, smaller feature dimensions, particularly feature pitches may be available.  
         [0021]      FIGS. 2   a - 2   d  illustrate cross sectional type views of a method in accordance with one embodiment of the present invention.  FIG. 4  illustrates an operational flow  400  in accordance with an embodiment of the present invention illustrated in  FIGS. 2   a - 2   d . While reference is made to the operational flow for clarity, the operational flow is not meant to be limiting. Steps may be added, taken away, or performed out of order without deviating from the spirit of the present invention.  
         [0022]     In  FIG. 4 , box  410  illustrates disposing a photosensitive layer on a substrate. The photosensitive layer may be disposed using a spin on technique or other methods. Box  420  illustrates transferring a first plurality of features to the photosensitive layer. Now referencing  FIG. 2   a , a first plurality of features  130  may have been transferred to a photosensitive layer  210 . In one embodiment, the first plurality of features  130  may have been transferred using photolithography. In other embodiments, the first plurality of features  130  may have been transferred using a 248 nm, 193 nm, 157 nm, or extreme ultra-violet (EUV) photolithography. Other methods may be used. For clarity, pattern transfers will hereinafter be referenced generally as photolithography, but other methods may be used. The photosensitive layer  210  may comprise a positive or negative photoresist or other materials. The substrate  200  may comprise any suitable material. Specific examples may include silicon, germanium, gallium arsenide and silicon on insulator.  FIG. 2   a  also illustrates minimum allowable feature dimensions  150 ,  160 . The minimum allowable feature dimensions  150 ,  160  may be defined by the photolithography used to pattern the photosensitive layer and may be at the limit of the photolithography process used.  
         [0023]     In  FIG. 4 , box  430  illustrates shrinking the plurality of first features  130  as illustrated in cross sectional view in  FIG. 2   b . In  FIG. 2   b , the first plurality of features  130  may have gone through a shrink to form a shrunk first plurality of features  230 . In one embodiment, the shrink method may have been a thermal shrink. In a thermal shrink, heat may be applied to the photosensitive layer  210  to reflow it and cause a shrink that forms a shrunk first plurality of features  230 . In another embodiment, the shrink method may be a pattern-coating shrink. A pattern-coating shrink may require coating the photosensitive layer  210  with a skin layer and subsequent thermal steps to form a shrunk first plurality of features  230 . In yet another embodiment, the first plurality of features  130  may have gone through a self-deactivating shrink to form a shrunk first plurality of features  230 . In a self-deactivating shrink, the shrunk first plurality of features  230  may not shrink during subsequent shrink methods. For simplicity of illustration,  FIG. 2   b  does not show additional materials that may be required in some embodiments of the present invention. For simplicity, the term shrink hereinafter generally refers to all available shrink methods.  
         [0024]     In  FIG. 4 , box  440  illustrates transferring a second plurality of features  140  to the photosensitive layer  210  as illustrated in cross sectional view in  FIG. 2   c . In  FIG. 2   c , a second plurality of features  140  may have been transferred to the photosensitive layer  210  by photolithography. In one embodiment, the method for transferring the second plurality of features  140  may be the same as the method used for transferring the first plurality of features  130 . In other embodiments, a different method may be used. For ease of illustration, an embodiment of the present has been illustrated where the second plurality of features  140  may be substantially centered with respect to the first plurality of features  130 . In other embodiments, the second plurality of features may not be centered with respect to the first plurality of features.  
         [0025]     In  FIG. 2   d , the second plurality of features  140  may have gone through a shrink process, as illustrated in box  450  in  FIG. 4 . Together with the shrunk plurality of first features  230 , these features may make up the features  190  of master pattern  100 . As illustrated in  FIG. 2   d , the shrunk plurality of first features  230  may not shrink for a second time when the second plurality of features  140  go through a shrink process. For simplicity of illustration, the features  190  are the same size and feature dimensions  170 ,  180  are shown as typical. In another embodiment, the shrunk plurality of first features  230  may shrink when the second plurality of features  140  go through a shrink process to form a smaller feature dimension. In yet another embodiment, the first plurality of features  130  may have feature dimensions larger than those of the second plurality of features  140  such that after being shrunk twice, the first plurality of features  130  may be of similar dimension to the second plurality of features  140  being shrunk once. The combination illustrated was chosen for simplicity and clarity and is not meant to be limiting. Other combinations and methods may be available to produce desired results in the master pattern  100 .  
         [0026]     The feature dimensions  170 ,  180  illustrated in  FIG. 2   d  may be smaller than those available using standard transferring methods as represented by minimum allowable feature dimensions  150 ,  160  illustrated in  FIG. 2   a . As discussed in reference to  FIG. 1 , many combinations of feature dimensions  170 ,  180  smaller than the minimum allowable feature dimensions  150 ,  160  may be available.  
         [0027]      FIG. 5  illustrates an operational flow  500  in accordance with an embodiment of the present invention illustrated in cross sectional views in  FIGS. 3   a - 3   h . While reference is made to the operational flow for clarity in the following description, the operational flow is not meant to be limiting. Steps may be added, taken away, or performed out of order without deviating from the spirit of the present invention.  
         [0028]     In  FIG. 5 , box  510  illustrates disposing a first photosensitive layer  310  on a substrate  200 . Box  520  illustrates transferring a first plurality of features  130  to the first photosensitive layer  310  as illustrated in cross sectional view in  FIG. 3   a . In  FIG. 3   a , a first plurality of features  130  may have been transferred to a first photosensitive layer  310  using photolithography. The first photosensitive layer  310  may comprise a positive or negative photoresist or other materials. As illustrated in  FIG. 3   b , the first plurality of features  130  may have gone through a shrink process to form a shrunk first plurality of features  230 , in analogy to  FIG. 2   b . Correspondingly, in  FIG. 5 , box  530  illustrates shrinking the first plurality of features.  
         [0029]     As illustrated in  FIG. 5 , box  540 , the shrunk first plurality of features  230  may be transferred to the substrate. Correspondingly, in reference to  FIG. 3   c , the shrunk first plurality of features  230  may have been transferred to the substrate  200  to form a transferred first plurality of features  330 . The transferred first plurality of features  330  may have been transferred using chemical or plasma etch or other methods. In other embodiments, the transferred plurality of features  330  may be transferred onto the substrate  200  (not shown). In such embodiments, the shrunk plurality of features  230  may be filled with a material in a variety of methods including chemical vapor deposition, sputter deposition, and others. The semiconductor surface may then be leveled using a planar semiconductor process. Hereinafter, methods of transferring the shrunk first plurality of features to form a transferred plurality of features  330  will be referenced generally as a transfer, but a variety of methods may be used. As illustrated in  FIG. 3   d  and box  550  of  FIG. 5 , the first photosensitive layer  310  may be removed from the substrate  200 .  
         [0030]     Now in reference to  FIG. 5 , box  560  illustrates a second photosensitive layer  320  may be disposed on the substrate  200 . The second photosensitive layer  320  may be positive or negative photoresist or other material. In one embodiment the first photosensitive layer  310  and the second photosensitive layer  320  may be the same material. In other embodiments, they may be different.  
         [0031]     Box  570  illustrates a second plurality of features  140  may be transferred to the second photosensitive layer  320 .  FIG. 3   e  illustrates a second plurality of features  140  may be transferred to a second photosensitive layer  320  using photolithography. The illustrated embodiment shows the plurality of second features  140  may be substantially centered with respect to the transferred plurality of second features  330 . In other embodiments, the second plurality of features  140  may not be centered with respect to the transferred plurality of second features  330 .  
         [0032]      FIG. 5 , box  580  and  FIG. 3   f  illustrate the second plurality of features  140  going through a shrink to form a shrunk second plurality of features  240 . In one embodiment of the present invention, the shrink illustrated in box  580  and  FIG. 3   f  may not be performed. For simplicity of illustration in  FIG. 3   f , an embodiment of the present invention has been shown where the shrunk second plurality of features  240  may have been shrunk to a size similar to the shrunk plurality of first features  230 . In another embodiment of the present invention, the shrunk plurality of second features  240  may be shrunk to a different size.  
         [0033]     In  FIG. 3   g , the shrunk plurality of shrunk features  240  may have been transferred to the substrate to form a transferred second plurality of features  340 .  FIG. 5 , box  590  illustrates a similar transfer.  
         [0034]     As illustrated in  FIG. 3   h , the photosensitive material  320  may be removed. Together, the transferred first plurality of features  330  and transferred second plurality of features  340  may form features  190  from master pattern  110 . For simplicity of illustration, the features  190  are the same size and feature dimensions  170 ,  180  are shown as typical. As discussed in other embodiments, the features  190  and their corresponding pitches and widths may be of different feature dimensions  170 ,  180  to create the desired master pattern  100 .  
         [0035]     The feature dimensions  170 ,  180  illustrated in  FIG. 3   h  may be smaller than those available using standard transferring methods as represented by minimum allowable feature dimensions  150 ,  160  illustrated in  FIG. 3   a . As discussed in reference to  FIG. 1 , many combinations of feature dimensions  170 ,  180  smaller than the minimum allowable feature dimensions  150 ,  160  may be available.  
         [0036]     It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of ordinary skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.