Abstract:
The invention includes a method of patterning radiation. The radiation is simultaneously passed through a structure and through a sub resolution assist feature that is transmissive of at least a portion of the radiation. The sub resolution assist feature alters a pattern of radiation intensity defined by the structure relative to a pattern of radiation intensity that would be defined in the absence of the sub resolution assist feature. The invention further includes methods of forming radiation-patterning tools, and the radiation-patterning tools themselves.

Description:
RELATED PATENT DATA 
     This patent resulted from a continuation application of U.S. Patent application Ser. No. 09/420,205, now U.S. Pat. No. 6,569,574, which was filed on Oct. 18, 1999. 
    
    
     TECHNICAL FIELD 
     The invention pertains to methods of patterning radiation, methods of forming radiation-patterning tools, and to radiation-patterning tools themselves. 
     BACKGROUND OF THE INVENTION 
     Photolithography is commonly used during formation of integrated circuits on semiconductor wafers. More specifically, a form of radiant energy (such as, for example, ultraviolet light) is passed through a radiation-patterning tool and onto a semiconductor wafer. The radiation-patterning tool can be, for example, a photomask or a reticule, with the term “photomask” being sometimes understood to refer to masks which define a pattern for an entirety of a wafer, and the term “reticule” being sometimes understood to refer to a patterning tool which defines a pattern for only a portion of a wafer. However, the terms “photomask” (or more generally “mask”) and “reticule” are frequently used interchangeably in modern parlance, so that either term can refer to a radiation-patterning tool that encompasses either a portion or an entirety of a wafer. For purposes of interpreting the claims that follow, the terms “photomask” and “reticule” will be given their historical distinction such that the term “photomask” will refer to a patterning tool that defines a pattern for an entirety of a wafer, and the term “reticule” will refer to a patterning tool that defines a pattern for only a portion of a wafer. 
     Radiation-patterning tools contain light restrictive regions (for example, totally opaque or attenuated/half-toned regions) and light transmissive regions (for example, totally transparent regions) formed in a desired pattern. A grating pattern, for example, can be used to define parallel-spaced conductive lines on a semiconductor wafer. The wafer is provided with a layer of photosensitive resist material commonly referred to as photoresist. Radiation passes through the radiation-patterning tool onto the layer of photoresist and transfers the mask pattern to the photoresist. The photoresist is then developed to remove either the exposed portions of photoresist for a positive photoresist or the unexposed portions of the photoresist for a negative photoresist. The remaining patterned photoresist can then be used as a mask on the wafer during a subsequent semiconductor fabrication step, such as, for example, ion implantation or etching relative to materials on the wafer proximate the photoresist. 
     Advances in semiconductor integrated circuit performance have typically been accompanied by a simultaneous decrease in integrated circuit device dimensions and a decrease in the dimensions of conductor elements which connect those integrated circuit devices. The demand for ever smaller integrated circuit devices brings with it demands for ever-decreasing dimensions of structural elements on radiation-patterning tools, and ever-increasing requirements for precision and accuracy in radiation-patterning with the tools. 
     An exemplary prior art radiation-patterning tool  12  is shown in FIG.  1 . Radiation-patterning tool  12  comprises a substrate  14  which is at least partially transparent to radiation which is to be patterned, and a structure  16  joined to substrate  14  and formed of a material which is less transparent to the radiation than is substrate  14 . Substrate  14  typically comprises fused silica (for example, quartz), and structure  16  typically comprises chrome. 
     FIG. 1 further illustrates radiation  18  being directed toward radiation-patterning tool  12 , and shows a plot  20  of radiation intensity exiting from radiation-patterning tool  12 . Plot  20  illustrates that structure  16  has attenuated the radiation intensity. Specifically, plot  20  comprises a region  22  of decreased intensity where radiation  18  has been at least partially blocked by structure  16 , and higher intensity regions  24  where radiation  18  has not been blocked by structure  16 . In particular embodiments of the prior art, structure  16  will comprise a material substantially opaque to radiation  18  (for example, chrome can be opaque relative to ultraviolet light), and substrate  14  will be substantially transparent to the radiation (for example, quartz can be transparent to ultraviolet light). 
     A problem associated with the radiation-patterning described with reference to FIG. 1 can be in accurately and reproducible forming the dip in radiation intensity shown at region  22  of plot  20 . Specifically, if radiation  18  is slightly defaced from an optimal focus position, the depth of region  22  (i.e., the change in intensity between region  22  and regions  24 ) can be altered, which can cause variation in a critical dimension of openings ultimately patterned into photoresist. Also, the shape of the intensity profile in graph  20  can be less precise than is desired. Specifically, it would be ideal if the intensity profile of plot  20  exactly mirrored the pattern defined by structure  16  (i.e., if the intensity profile had sharp corners at transitions between regions  24  and  22 , and if region  22  had a flat bottom with a width corresponding to that of structure  16 ). 
     An improved prior art radiation-patterning tool  12   a  is described with reference to FIG.  2 . In referring to FIG. 2, similar numbering is utilized as was used in referring to FIG. 1, with the suffix “a” used to indicate structures shown in FIG.  2 . Radiation-patterning tool  12   a  is similar to the patterning tool  12  of FIG. 1 in that it comprises a substrate  14   a  which is at least partially transparent to incoming radiation  18   a , and a structure  16   a  which is less transparent to radiation  18   a  than the substrate. However, radiation-patterning tool  12   a  differs from the patterning tool  12  of FIG. 1 in that subresolution assist features  30  are provided adjacent structure  16   a . Subresolution assist features  30  are formed of an identical material as structure  16   a  (which simplifies processing, as a single material can be formed over substrate  14   a  and patterned to form features  30  and structures  16   a ). Features  30  are referred to as subresolution assist features because intensity variations caused by features  30  are not resolved from intensity variations caused by structures  16   a  at the resolution provided by the particular wavelength of incoming radiation  18   a . This is shown in the intensity graph  20   a . Specifically, graph  20   a  shows a dip  22   a  corresponding to a region wherein an intensity variation is caused by structure  16   a , and shoulders  32  corresponding to regions wherein intensity variation is caused primarily by features  30 . Since the intensity variations caused by features  30  are shoulders  32  along region  22   a , rather than distinctly resolved elements, such intensity variations are subresolution variations. 
     Subresolution assist features  30  can alleviate some of the problems described above as being associated with the radiation-patterning tool  12  of FIG.  1 . Specifically, subresolution assist features  30  can stabilize an intensity difference between non-blocked regions  24   a  and blocked region  22   a  relative to subtle variations in focus of radiation  18   a . Further, subresolution assist features  30  can improve the overall shape of blocked region  22   a  in the intensity profile  20   a  relative to the shape of region  22  in intensity profile  20  of FIG.  1 . Specifically, subresolution assist features  30  can flatten a bottom of region  22   a , and sharpen the transition at corners of region  22   a , such that region  22   a  has a width which better approximates a width of structure  16   a  than the width of FIG. 1 region  22  approximates a width of structure  16 . 
     A problem associated with the formation of subresolution assist features is that as the dimension of semiconductor devices becomes smaller the desired dimension of subresolution assist features also becomes smaller. It is therefore becoming increasingly difficult to form satisfactory subresolution assist features as integrated circuit device dimensions decrease. It would accordingly be desirable to develop alternative methods of forming subresolution assist features. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention encompasses a method of patterning radiation. The radiation is simultaneously passed through a structure and at least one subresolution assist feature proximate the structure. The structure defines a pattern of radiation intensity. The at least one subresolution assist feature comprises a material that is transmissive of at least a portion of the radiation. The subresolution assist feature alters the pattern of radiation intensity defined by the structure relative to a pattern of radiation intensity that would be defined in the absence of the subresolution assist feature. 
     In another aspect, the invention encompasses another method of patterning radiation. The radiation is simultaneously passed through a first material structure and at least one second material subresolution assist feature proximate the first material structure. The second material is different than the first material. The subresolution assist feature alters a pattern of radiation intensity defined by the first material structure relative to a pattern that would be defined in the absence of the subresolution assist feature. 
     In other aspects, the invention encompasses methods of forming radiation-patterning tools, and the radiation-patterning tools themselves. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention are described below with reference to the following accompanying drawings. 
     FIG. 1 is a diagrammatic view of a prior art radiation-patterning tool, and an intensity profile of radiation passing through the tool. 
     FIG. 2 is a diagrammatic view of another prior art radiation-patterning tool, and an intensity profile of radiation passing through the tool. 
     FIG. 3 is a diagrammatic view of a radiation-patterning tool encompassed by the present invention. 
     FIG. 4 is a diagrammatic view of a construction shown at a preliminary step of a method of forming a radiation-patterning tool in accordance with the present invention. 
     FIG. 5 is a view of the FIG. 4 construction shown at a processing step subsequent to that of FIG.  4 . 
     FIG. 6 is a view of the FIG. 4 construction shown at a processing step subsequent to that of FIG.  5 . 
     FIG. 7 is a view of the FIG. 6 construction shown with radiation passing through the construction in accordance with a preferred aspect of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8). 
     A radiation-patterning tool  50  encompassed by the present invention is shown in FIG.  3 . Patterning tool  50  comprises a substrate  52  and a structure  54  joined with the substrate (structure  54  is on the substrate in the shown embodiment, but it is to be understood that the invention encompasses other embodiments (not shown), wherein structure  54  is spaced from the substrate by one or more intervening materials). Substrate  52  can comprise constructions identical to those of prior art substrate  14   a  of FIG. 2, and accordingly can comprise, for example, fused silica. Structure  54  can comprise constructions identical to structures  16   a  of FIG. 2, and accordingly can comprise, for example, chromium. 
     Radiation-patterning tool  50  comprises subresolution assist features  56  and  58  proximate structure  54 . In the shown embodiment, two subresolution assist features are provided. It is to be understood, however, that only one subresolution assist feature could be provided, or that more than two subresolution assist features could be provided. In one aspect of the invention, subresolution assist features  56  and  58  preferably comprise a different material than structure  54 . Accordingly, structure  54  comprises a first material, and subresolution assist features  56  and  58  comprise a second material. The material utilized in subresolution assist features  56  and  58  is preferably transmissive for at least some of the radiation patterned by radiation-patterning tool  50 . 
     Similarly to the prior art construction described with reference to FIG. 2, substrate  52  comprises a material which is transmissive to a wavelength of radiation which is to be patterned, and structure  54  comprises a material which is less transmissive to the wavelength of radiation than is substrate  52 . Accordingly, structure  54  defines a pattern of radiation intensity for the wavelength of radiation after the radiation is passed through patterning tool  50 . In an aspect of the invention, subresolution assist features  56  and  58  can be formed of a material which is less transmissive of the wavelength of radiation than substrate  52 , but more transmissive of the wavelength of radiation than the material of structure  54 . Accordingly, subresolution assist features  56  and  58  are partially transmissive to the wavelength of radiation. It is found that such partial transmission of a wavelength of radiation can enable subresolution assist features of a given size to perform comparably to opaque subresolution assist features of a smaller size. Accordingly, whereas the prior art radiation-patterning tool  12   a  of FIG. 2 utilized subresolution assist features ( 30 ) formed of the same material as an interposed structure ( 16   a ), and accordingly utilized subresolution assist features having the same level of opaqueness to an incoming radiation ( 18   a ), such subresolution assist features would ideally be formed to a given maximal dimension for a particular wavelength of radiation, and a particular size of structure  54 . In contrast, since subresolution assist features  56  and  58  of radiation-patterning tool  50  are more transmissive of radiation than structure  54 , subresolution assist features  56  and  58  can be formed to a larger maximal dimension than could prior art subresolution assist features  30 . This can simplify formation of resolution assist features  56  and  58  relative to the formation of prior art subresolution assist features  30 . 
     It is emphasized that subresolution assist features  56  and  58  can be formed of materials which are at least partially transmissive to radiation passed through patterning tool  50  and utilized to pattern photoresist. This is in contrast to the prior art resolution assist features that were formed of materials opaque to radiation passed through a patterning tool. Of course, it is preferred that subresolution assist features  56  and  58  be only partially transmissive to radiation passed through patterning tool  50 , rather than completely transmissive, as subresolution assist features  56  and  58  will preferably modify a pattern of radiation intensity defined by structure  54  relative to a pattern of radiation intensity that would be defined in the absence of the subresolution assist features. A preferred transmissivity of the material utilized in subresolution assist features  56  and  58  is from about 5% to about 20% of the radiation passed through tool  50  that has a suitable wavelength to pattern photoresist. For instance, if the radiation passed through tool  50  having a suitable wavelength to pattern photoresist is ultraviolet light radiation, subresolution assist features  56  and  58  will preferably transmit from about 5% to about 20% of said light. 
     Preferred materials for subresolution assist features  56  and  58  are materials comprising molybdenum and silicon (such as, for example, MoSi x N y O z , wherein x, y and z are greater than zero), and materials comprising or consisting essentially of silicon carbide. It is noted that since subresolution assist features  56  and  58  are preferably at least partially transmissive of radiation passed through tool  50 , the subresolution assist features preferably do not comprise chromium in applications in which ultraviolet light is to be passed through tool  50  and utilized for patterning photoresist. 
     In the shown embodiment, features  56  and  58  have a thickness “x” and structure  54  has a thickness “y” which is different than “x”. It is noted that prior art constructions have subresolution features with thicknesses identical to the thickness of an interposed structure, as the subresolution features and interposed structure are formed from the same materials. In contrast, constructions of the present invention can have subresolution assist features with different thicknesses than an interposed structure. Further, although subresolution assist features  56  and  58  are shown having the same thickness (“x”), it is to be understood that subresolution assist features  56  and  58  can have thicknesses different from one another, and can comprise materials different from one another. 
     FIGS. 4-6 describe a method of forming tool  50 . Referring initially to FIG. 4, tool  50  is shown at a preliminary step of the method. Tool  50  comprises substrate  52 , and materials  70 ,  72  and  74  over substrate  52 . Material  72  will ultimately be patterned to form structure  54 , and materials  70  and  74  will ultimately be patterned to form subresolution assist features  56  and  58 . Accordingly, materials  70  and  74  are preferably different from material  72 , and can be different than one another. 
     Referring to FIG. 5, materials  70 ,  72  and  74  (FIG. 4) are patterned to form subresolution assist feature  56 , structure  54 , and subresolution assist feature  58 , respectively. Such patterning can be accomplished by, for example, conventional reticule patterning (such as, for example, formation of photoresist over materials  70 ,  72  and  74 , followed by electron beam or laser etching to pattern the photoresist, and then etching of materials  70 ,  72  and  74  with subsequent removal of the photoresist). Although in the shown embodiment materials  70 ,  72  and  74  are patterned together (i.e., with a common electron beam or laser etch), it is to be understood that the invention encompasses other embodiments (not shown) wherein the materials are provided and patterned sequentially relative to one another. Common patterning of the materials can, however, be preferred, as such will utilize only one electron beam or laser etch, whereas sequential patterning can utilize multiple electron beam or laser etches. Also, it is noted that in the shown embodiment materials  70 ,  72  and  74  are formed to different thicknesses over substrate  52 . It is to be understood that the invention encompasses other embodiments wherein materials  70 ,  72  and  74  are formed to a common thickness over substrate  52 . Such other embodiments can comprise, for example, chemical-mechanical polishing of materials  70 ,  72  and  74  to form a planarized upper surface of such materials. 
     FIG. 5 shows substrate  52  having a thickness T 1 . Such thickness can influence the effectiveness with which patterning tool  50  patterns radiation. Specifically, a ratio of the substrate thickness (T 1 ) relative to a subresolution assist feature thickness (x) defines a change in phase of radiation passing through both substrate  52  and the subresolution assist feature. Preferably, such change in phase is an integer multiple of 360° relative to a change in phase that occurs in radiation passing through both substrate  52  and structure  54 . Such preferable condition can be accomplished by one or both of adjusting a thickness of a subresolution assist feature and adjusting a thickness of substrate  52 . FIG. 6 illustrates tool  50  after the thickness of substrate  52  has been reduced to a thickness T 2 . Although substantially an entirety of the substrate  14  is shown reduced in thickness in FIG. 6 (actually, an entirety of the shown substrate fragment is reduced in thickness), it is to be understood that the invention encompasses other embodiments (not shown) wherein the portions of the substrate underlying features  56  and  58  are treated selectively relative other portions of the substrate. For instance a thickness of portions of the substrate underlying features  56  and  58  can be reduced relative to a thickness of the portion of the substrate underlying structure  54 . Alternatively, a thickness of the portion of the substrate underlying structure  54  can be reduced relative to a thickness of the portions of the substrate underlying features  56  and  58 . 
     FIG. 7 illustrates a preferred configuration wherein radiation  80  enters substrate  52  in phase and exits subresolution features  56  and  58 , and structure  54 , in phase. 
     In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.