Abstract:
In one embodiment, a semiconductor device processing method, comprising the steps of: (a) using a patterned photoresist to form a structure having at least one edge; (b) prior to removal of the photoresist, forming a conforming layer from an organic compound and patterning the conforming layer to form at least one sidewall spacer which are self-aligned to the at least one edge; (c) performing a processing operation which is at least partially localized by the at least one sidewall spacer; and (d) removing the at least one sidewall spacer and the photoresist, wherein the conforming layer is formed via deposition of at least one organic compound selected from C 1  to C 8  alkanes C 2  to C 8  alkenes, C 3  to C 8  cyclo-alkenes, C 4  to C 8  cyclo-alkenes, C 1  to C 8  fluoro-alkanes, C 2  to C 8  fluoro-alkenes, C 3  to C 8  cyclofluoro-alkanes, C 4  to C 8  cyclofluoro-alkenes, or mixtures thereof.

Description:
FIELD OF THE INVENTION 
     The present invention relates to semiconductor devices and fabrication methods. More particularly, the present invention relates to methods for forming sidewall spacers in photolithography processes in order to decrease the minimum patterned dimension possible via a photolithography process. 
     BACKGROUND OF THE INVENTION 
     A continuing trend in integrated circuit device is the steady shrinkage of device dimensions. This shrinkage has proceeded on a fairly steady exponential curve for many years. The minimum patterned dimension is commonly referred to as the “critical dimension.” With conventional MOS technology, as the critical dimension shrinks, the gate oxide becomes thinner, the diffusions become shallower, and the transistor minimum channel length becomes smaller. 
     As the size of contact and via holes shrink, it has been necessary to use thinner photo-resist. This, in turn, means that a less aggressive oxide etch must be used, so that the photo-resist is not destroyed in the process. Additionally, when using thinner resist, the contact or via etch must have greater selectivity to resist, and this requirement is approaching the limitation of current etches. 
     As the limits of current lithographic techniques are reached, methods of attaining smaller sized structures have been explored. It is known to use sidewall spacers on masking structures as a means to attain sub-lithographic dimensions. However, this technique has been limited by the fact that the available materials for forming sidewalls require high temperature processing, and their use is thus incompatible with the presence of photo-resist. 
     It has also been disclosed to use organic materials such as parylene and plasma deposited polymers such as Teflon®, for disposable spacers. One set of processes uses disposable organic spacers made from such compounds in combination with a shallow-trench-isolation pattern, to promote rounding of the trench edge and protection of this edge during subsequent etches. Another set of processes uses disposable organic spacers made from such compounds to decrease the size of contact holes and vias. Since the lithographic size of the hole in the photo-resist can be increased for a given end result, this allows a thicker photo-resist to be used, with the consequent ability to use a more aggressive oxide etch, white decreasing etch selectivity limits. Another set of processes uses disposable organic sidewall spacers made from the compounds listed above in combination with photo-resist to permit alteration of the line-to-space ratio, and to create sub-lithographic structures. 
     A need exists in the art for a method to form sidewall spacers from a compound which can be deposited using vapor deposition techniques and which can easily be removed during the fabrication process of semiconductor devices. 
     SUMMARY OF THE INVENTION 
     In one embodiment, the present invention relates to a semiconductor device processing method, comprising the steps of: (a) using a patterned photoresist to form a structure having al least one edge; (b) prior to removal of the photoresist, forming a conforming layer from an organic compound and patterning the conforming layer to form at least ore sidewall spacer which is self-aligned to the at least one edge; (c) performing a processing operation which is at least partially localized by the at least one sidewall spacer; and (d) removing the at least one sidewall spacer and the photoresist, wherein the conforming layer is formed via deposition of at least one organic compound selected from C 1  to C 8  alkanes, C 2  to C 8  alkenes, C 3  to C 8  cyclo-alkanes, C 4  to C 8  cyclo-alkenes, C 1  to C 8  fluoro-alkanes, C 2  to C 8  fluoro-alkenes, C 3  to C 8  cyclofluoro-alkanes, C 4  to C 8  cyclofluoro-alkenes, or mixtures thereof. 
     In another embodiment, the present invention relates to a method for forming isolation structures, comprising the steps of: (a) forming a patterned masking layer having at least one edge which overlies a substrate containing a body of semiconductor material; (b) forming a conforming layer from an organic compound and patterning the conforming layer to form at least one spacer on the at least one edge of the masking layer; (c) etching the substrate, in areas exposed by the masking layer and the sidewalls, to form said isolation structures; (d) removing the spacers and the patterned masking layer; (e) oxidizing the exposed portions of the semiconductor material; and (f)filling the isolation structures with a dielectric material, wherein the conforming layer is formed via deposition of at least one organic compound selected from C 1  to C 8  alkanes, C 2  to C 8  alkenes, C 3  to C 8  cyclo-alkanes, C 4  to C 8  cyclo-alkenes, C 1  to C 8  fluoro-alkanes, C 2  to C 8  fluoro-alkenes, C 3  to C 8  cyclofluoro-alkanes, C 4  to C 8  cyclofluoro-alkenes, or mixtures thereof. 
     In another embodiment, the present invention relates to a method for forming contacts or vias in an integrated circuit structure, comprising the steps of: (a) forming transistor structures in a substrate which contains a body of semiconductor material; (b) forming a dielectric over the substrate and the transistor structures; (c) depositing and patterning a resist material to form holes there through which expose portions of the dielectric in which contacts or vies are to be formed; (d) forming a conforming layer from an organic compound and patterning the conforming layer to form sidewall spacers on the interior of the holes, whereby the diameter of the holes is reduced; (e) etching the dielectric, in the areas exposed by said holes, to expose an underlying conductive structure; and (f) removing the resist material and the sidewall spacers, wherein the conforming layer is formed via deposition of at least one organic compound selected from C 1  to C 8  alkanes, C 2  to C 8  alkenes, C 3  to C 8  cyclo-alkanes, C 4  to C 8  cyclo-alkenes, C 1  to C 8  fluoro-alkanes, C 2  to C 8  fluoro-alkenes, C 3  to C 8  cyclofluoro-alkanes, C 4  to C 8  cyclofluoro-alkenes, or mixtures thereof. 
     Thus, the present invention overcomes the problems associated with sidewall spacers formed of organic or polymer material which have to be removed via ashing. The present invention also yield a reduction in the minimum patterned dimension or “critical dimension.” 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow chart detailing a process for forming sub-lithographic features via the use of sidewall spacers according to one embodiment of the present invention. 
         FIGS. 2A  to  2 F are schematic cross-sectional views of a semiconductor device formed in accordance with the process detailed in the flow chart of  FIG. 1 ; 
         FIG. 3  is a flow chart detailing a shallow trench isolation process which utilizes sidewall spacers according to another embodiment of the present invention; 
         FIGS. 4A  to  4 F are schematic cross-sectional views of a semiconductor device formed in accordance with the process detailed in the flow chart of  FIG. 3 ; 
         FIG. 5  is a flow chart detailing a process which utilizes sidewall spacers to form vias and/or contacts according to another embodiment of tie present invention; and 
         FIGS. 6A  to  6 D are schematic cross-section views of a semiconductor device formed in accordance with the process detailed in the flow chart of FIG.  5 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a flowchart detailing a process for forming organic spacers and reducing contact hole dimensions according to the present invention.  FIGS. 2A  to  2 F depict the structure formed v a the process shown in the flowchart of  FIG. 1. A  layer of photoresist  206  is deposited over one or more underlying layers, any one or more of which are to be patterned. The underlying layer  204  over which a photoresist  206  is deposited is formed on substrate  202  during one or more pre-photoresist processing steps (Step S 100 ). Next the photoresist layer  206  is deposited over underlying layer  204  (Step S 102 ) and the photoresist patterned as desired (Step S 104 ), as is known in the art. As shown in  FIG. 2A , only one underlying layer  204  is present on the substrate  202  of semiconductor device  200 . However, in another embodiment, more than one underlying layer  204  could be present. 
     One example of an underlying layer  204  is an oxide layer which is to be patterned via the use of photoresist layer  206 . It should be noted that the present invention is not limited to use solely where an oxide layer is to be patterned. Rather, the present invention can be utilized in any situation where smaller critical dimensions are desired, e.g., where smaller critical dimensions are required. 
     As is shown in  FIG. 2B , the patterned layer of photoresist  206   a  has a pattern formed therein according to processes known to those of skill in the art. In one instance the pattern formed could be for trenches, although any pattern suitable for semiconductor fabrication could be utilized. Thus, the present invention is not applicable to only trench formation. Rather, the present invention can be utilized in a wide variety of situations where sub-lithographic dimensions are desired. 
     The trenches  208  can be formed to have any desired width (e.g., a width in the range of about 0.05 microns to about 5 microns). As is shown in  FIG. 2B , trenches  208  have a width A which typically will be towards the upper resolution limit of the photoresist patterning process. 
     Next, a conforming layer  210  is formed via any suitable process tram an organic material in Step S 106 . In one embodiment, the organic material is a hydrocarbon or fluorocarbon which is conformally deposited in Step S 106  over the patterned photoresist layer  206   a  to yield the semiconductor device depicted in  FIG. 2C  having conforming layer  210 . In another embodiment, the organic material is a hydrocarbon or fluorocarbon which is in either a gaseous or vapor state. In one embodiment, the conforming layer  210  is famed from any suitable deposition process as will be explained in detail below. 
     When the conforming layer  210  is formed from an organic hydrocarbon, compounds such as C 1  to C 8  alkanes, C 2  to C 8  alkenes, C 3  to C 8  cyclo-alkanes, C 4  to C 8  cyclo-alkenes, or mixtures of two or more thereof are utilized. Examples of such compounds include, but are not limited to, methane, ethane, propanes, butanes, pentanes, ethylene, propylene, butylenes and butadienes. 
     In another embodiment, the organic layer is formed from a fluorine substituted hydrocarbon. Examples of such fluorocarbons include, but are not limited to, C 1  to C 8  fluoro-alkanes, C 2  to C 8  fluoro-alkenes, C 3  to C 8  cyclofluoro-alkanes, C 4  to C 8  cyclofluoro-alkenes, or mixtures of two or more thereof. Such compounds have at least one fluorine atom bonded to a carbon atom in place of a hydrogen atom. Some specific examples of such compounds include, but are not limited to, tetrafluoromethane (CF 4 ), trifluoromethane (CHF 3 ), difluoromethane (CH 2 F 2 ), fluoromethane (CH 3 F), hexafluoroethane (C 2 F 6 ), tetrafluoroethylene (C 2 F 4 ), perfluorocyclobutene (C 4 F 6 ), hexafluorobutadiene (C 4 F 6 ), perfluorobutene C 4 F 6 ) and octafluorocyclobutane (C 4 F 8 ). 
     In one embodiment, at least half of the hydrogens in the aforementioned hydrocarbons have been substituted with fluorine to yield the fluorocarbons utilized in the present invention. In yet another embodiment, at least three-quarters of the hydrogens in the aforementioned hydrocarbons have been substituted with fluorine to yield the fluorocarbons utilized in the present invention. In still another embodiment, all of the hydrogens in the aforementioned hydrocarbons have been substituted with fluorine to yield the fluorocarbons utilized in the present invention. 
     In another embodiment, the organic hydrocarbon compound used to form conforming layer  210  is selected from any of the compounds listed above and is in a gaseous or liquid state at room temperature (25° C.). In yet another embodiment, when the organic hydrocarbon compound used to form conforming layer  210  is selected from those compounds listed and is in a liquid state at room temperature, the compound selected must have a boiling point near that of water at room temperature. For example, the boiling point of any compound selected should fall any where within the range of about 80° C. to about 120° C. 
     In one embodiment, the conforming layer  210  is formed to have a thickness of about 10 Angstroms to about 10,000 Angstroms. In another embodiment, the conforming layer  210  is formed so as to have a thickness of about 50 Angstroms to about 5,000 Angstroms. In yet another embodiment, the conforming layer  210  is formed so as to have a thickness of about 100 Angstroms to about 2,000 Angstroms. Additionally, it should be noted that here, as well as elsewhere in the text, ranges may be combined. 
     As is shown in  FIG. 2C , the conforming layer  210  is deposited both on the horizontal and vertical surfaces of the patterned photoresist  206   a . It should be noted that the present invention is not limited to embodiments where only horizontal and vertical surfaces are present. Instead the present invention can be utilized to deposit a conforming layer over a wide variety of patterns, be the patterns trench patterns or other types of semiconductor patterns. 
     The deposition of conforming layer  210  in the trenches  208  of the patterned photoresist  206   a  reduces the width of the trenches to width B yielding trenches  212 . In one embodiment, width B is not only less than width A, but is also less than the lithographic resolution possible via the patterning process used to pattern photoresist layer  206 . In another embodiment, width B is less than width A, but width B is not necessarily less than the lithographic resolution possible via the patterning process used to pattern photoresist layer  206 . 
     In one embodiment, trenches  212  can be formed to have any desired width. For example, the width of trenches  212  can be in the range of about 0.05 microns to about 5 microns. 
     In one embodiment, the conforming layer  210  is formed via any suitable deposition technique. Such techniques include, for example, chemical vapor deposition (CVD), atomic layer deposition (ALD), plasma enhanced CVD (PECVD), low pressure CVD (LPCVD), atmospheric, pressure CVD (APCVD) and rapid-thermal CVD (RTCVD). In one embodiment, conforming layer  210  is formed via plasma deposition. 
     When the organic compound being used to form the conforming layer  210  is a gas the rate at the one or more organic compounds are to the reactor is independently from about 1 standard cubic centimeters per minute (sccm) to about 10,000 sccm, or from about 5 sccm to about 1,000 sccm, or even from about 10 sccm to about 100 sccm. In one embodiment, the temperature at which the conforming layer is formed is formed is from about −40 to about 400° C., or from about 0 to about 300° C., or even about 20 to about 150° C. In one embodiment, the pressure in the reactor is from about 1 mTorr to about 760 Torr, or from about 10 mTorr to about 100 Torr, or even from about 20 mTorr to about 10 Torr. If applicable, the bias power used in depositing the conforming layer  210  is about 10 W to about 5000 W, or from about 50 W to about 2,500 W, or even about 100 W to about 1,000 W. 
     Next in Step S 108  conforming film  210  is etched anisotropically to yield sidewall spacers  210  as shown in FIG.  2 E. Anisotropic etching processes are known to those of skill in the art, and as such as discussion hereof is omitted for brevity. 
     Then in Step S 110  underlying layer  204  is subjected to an etching process to form patterned layer  204   a  as is shown in FIG.  2 E. In one embodiment, the etching process may be a plasma etching process, however the present invention is not limited to embodiments only utilizing plasma etching of the one or more underlying layers. Depending upon the composition of the one or more underlying layers, those of skill in the art would recognize what etching process can be utilized to “transfer” the pattern created by the combination of the photoresist and organic sidewall spacers to any one or more of the underlying layers. 
     Once the etching step S 110  is complete, the patterned photoresist layer  206   a  and the sidewall spacers  210   a  are removed via any suitable technique (Step S 112 ) as is known to those of skill in the art. For example, the photoresist and sidewall spacers can be removed via chemical mechanical polishing (CMP), ashing, etc. 
     This embodiment of disposable organic spacers can be used during metallization, DRAM capacitor fabrication (to use more of the available area for capacitor fabrication), in non-volatile memory floating gate fabrication, and in general anywhere a relatively low temperature sidewall material (e.g., about −40 to about 400° C.) is desired. 
     In another embodiment, the present invention can be utilized to form disposable sidewall spacers to be used in trench isolation processes. The benefits of trench isolation, in particular, shallow trench isolation, are known to those of skill in the art. 
       FIG. 3  is a flow chart of a trench isolation process in which the patterned oxidation barrier (silicon nitride in this case) is non-lithographically modified by a disposable organic sidewall spacer.  FIGS. 4A  to  4 F depict a semiconductor structure  400  formed via the process shown in the flowchart of FIG.  3 . 
     The process of this embodiment begins with growth of a pad oxide  404  on a substrate  402  and deposition (Step S 302 ) of a masking layer  406 , which in this example is silicon nitride. A photoresist  408  is deposited over the nitride  406 , and patterned to expose areas where trench isolation is desired. The nitride layer  406  is then etched through the photoresist layer  406 , with the etch stopping within the oxide layer  404  (Step S 304 ). This yields the semiconductor structure  400  shown in  FIG. 4A. A  conforming layer of an organic compound, as described, is then deposited and anisotropically etched to form sidewall spacers  410  on the edges of the resist and nitride stack (Step S 306 ). This yields the semiconductor structure shown in FIG.  4 B. 
     An etch is then performed (Step S 308 ) to go through the oxide  404  and to form the desired trench structure  412  in the substrate  402 , as shown in FIG.  4 C. The photoresist  408  and spacers  410  are then be removed by any suitable technique (e.g., ashing) in Step S 310 . Next, a short isotropic oxide etch (Step S 312 ) creates a slight undercut of the oxide layer away from the edge of the trench (see FIG.  4 D). An oxidation (Step S 314 ) is performed to grow a thin layer of thermal oxide  414  on the sidewalls of trench  412 . As is shown in  FIG. 4E , this step will also grow oxide on the substrate area exposed by the removed spacers and by the oxide etch. Because the nitride layer  406  is set back from the edge of the trench  412 , a thicker, more rounded thermal oxide  414  is grown at the trench edge, providing greater protection against leakage along this edge. Finally, a layer of oxide  416  is deposited and planarized (Step S 316 ), to fill the trench, followed by stripping the nitride layer (Slop S 318 ) to yield the semiconductor structure  400  of FIG.  4 F. 
     In yet another embodiment of the present invention, a method is disclosed which is used to create contact or via holes to contact various conductive structures present in different levels of a semiconductor device.  FIG. 5  is a flow chart of a process which enables the formation of sub-lithographic contact or via holes, via the use of organic sidewall spacers, for the connection of conductive structures on different levels of a semiconductor structure.  FIGS. 6A  to  6 D depict a semiconductor structure  600  formed via the process shown in the flowchart of FIG.  5 . 
     The process of this embodiment begins with Step S 502 , the deposition of a dielectric layer  604  over one or more conductive structures  602 . The conductive structure  602  depicted in  FIG. 6A  may be part of a transistor, such as a gate or source/drain contact, or may be a metallization layer in the integrated circuit, Photoresist layer  606  is deposited, patterned and developed (Step S 504 ) to expose the dielectric layer  604  at the point of a desired contact or via. As seen in  FIG. 6B , a conforming layer of an organic material is deposited in accordance with the above-described process and anisotropically etched (Step S 506 ) to form sidewall spacers  608  on the interior of the resist pattern, effectively reducing the diameter of the hole to be etched. 
     An etch is then performed (Step S 508 ), masked by the photoresist and spacers, to open a hole through the dielectric layer  604  and expose the underlying conductive structure  602 , as is seen in FIG.  6 C. The photoresist  606  and sidewall spacers  608  are removed via any suitable method (e.g., ashing) in Step S 510  and a layer of metal  610  is deposited via any suitable method to fill the contact/via (Step S 512 ), yielding structure  600  as seen in FIG.  6 D. 
     In light of the above, the present invention can be utilized in several ways. For example, organic spacers formed in accordance with any one of the above methods can be used to create sub-lithographic openings, or they may be used to scale down a hole which was created at a larger size in the photoresist to allow use of a thicker resist. 
     Although the invention has been described and illustrated with reference to specific illustrative embodiments thereof, it is not intended that the invention be limited to those illustrative embodiments. Those skilled in the art will recognize that variations and modifications can be made without departing from the spirit of the invention. It is therefore intended to include within the invention all such variations and modifications that fall within the scope of the appended claims and equivalents thereof.