Abstract:
A method of removing regions of an anti-reflective coating includes etching the anti-reflective coating with a fluorinated hydrocarbon-based plasma etch and etching the anti-reflective coating with an oxygen-based plasma etch. In some implementations, the oxygen-based plasma etch is performed following the fluorinated hydrocarbon-based etch. The technique can be used to remove regions of an anti-reflective coating so that a more uniform and controlled etch of an underlayer can subsequently be performed. The disclosed technique is particularly useful for etching organic or organometallic anti-reflective layers, but can be used to etch other anti-reflective layers as well. In addition, the techniques are particularly advantageous for etching anti-reflective coatings disposed on certain oxide and nitride layers, although the underlayer can be formed of other materials as well.

Description:
BACKGROUND 
     The present invention relates generally to the etching of anti-reflective coatings. 
     The requirements for high density, high performance ultra-large scale integrated semiconductor devices place unique demands on the conductive patterns used in such devices, including, for example, increasingly denser arrays with minimal spacing between conductive lines. The demands for such devices have increased with the advent of sub-half micron manufacturing technology. 
     Photolithography represents one technique which typically is used in the fabrication of such devices. Anti-reflective coatings (ARCs) are sometimes incorporated into a device to reduce notching caused by reflections of the photolithographic light source from previously-formed device features. Thus, for example, in i-line photolithography, an i-line photoresist can be applied over a dielectric layer, such as an oxide or nitride layer, with an organic ARC formed between the photoresist and the dielectric layer. 
     To transfer a pattern from a photolithographic mask to a dielectric or other underlayer disposed beneath an ARC, the ARC layer must be etched or removed selectively. Preferably, etching of the ARC should be completed prior to significant etching of the underlayer. That permits subsequent etching of the underlayer subsequently to be carried out in a uniform and controlled manner. 
     Several techniques have been used to etch the ARC. Those processes, however, have presented various difficulties. For example, some techniques tend to etch the sidewalls of the photoresist pattern as well as the ARC, thereby resulting in a deterioration and widening of critical dimensions formed in the underlayer. Other techniques can etch an oxide or nitride underlayer, as well as the ARC. If the latter techniques are used, the depth of the etch through the ARC and into the oxide or nitride layer will vary depending on variations in pattern density and the dimensions of the device features. The subsequently-etched underlayer exhibits variations in the etch profiles as a result of exposure to different etching chemistries. Such variations in the depth of the etch make the fabrication process more difficult to control and lead to the formation of non-uniform device features. 
     SUMMARY 
     In general, a technique is disclosed for removing regions of an anti-reflective coating so that a more uniform and controlled etch of an underlayer can subsequently be performed. The disclosed technique is particularly useful for etching organic or organometallic anti-reflective layers, but can be used to etch other anti-reflective layers as well. In addition, the techniques are particularly advantageous for etching anti-reflective coatings disposed on certain oxide and nitride layers, although the underlayer can be formed of other materials as well. 
     According to one aspect, a method of removing regions of an anti-reflective coating includes etching the anti-reflective coating with a fluorinated hydrocarbon-based plasma etch and etching the anti-reflective coating with an oxygen-based plasma etch. In some implementations, it is advantageous to perform the fluorinated hydrocarbon-based plasma etch first, and subsequently to perform the oxygen-based plasma etch. 
     In various implementations, the method includes one or more of the following features. If the anti-reflective coating is disposed on an underlayer, the fluorinated hydrocarbon-based plasma etch can be halted prior to any etching of the underlayer. The fluorinated hydrocarbon-based plasma etch can be performed, for example, for a pre-selected duration. The oxygen-based plasma etch then can be performed to expose regions of the underlayer below the anti-reflective coating. 
     Alternatively, if the fluorinated hydrocarbon-based plasma is capable of etching the underlayer, etching of a portion of the underlayer can be detected during performance of the fluorinated hydrocarbon-based plasma etch, and the fluorinated hydrocarbon-based plasma etch can be halted after etching of the underlayer is detected. In yet other implementations, near-completion of the etching of the anti-reflective coating can be detected, and the fluorinated hydrocarbon-based plasma etch then can be halted. Etching of the underlayer and/or the near-completion of etching of the anti-reflective coating can be detected, for example, through optical or residual gas analysis techniques. 
     In some implementations, a photoresist mask pattern can be provided on the anti-reflective coating to define the regions of the anti-reflective coating to be removed. The etching steps can be performed, for example, by reactive ion etch processes. 
     As previously noted, the anti-reflective coating can include an organic or organometallic material. Etching the anti-reflective coating with a fluorinated hydrocarbon can include, for example, providing a gaseous flow of one or more of carbon tetrafluoride (CF 4 ), perfluoro ethane (C 2 F 6 ), and trifluoromethane (CHF 3 ). Other gases also can be used. 
     The techniques described above can be used, for example, to fabricate an integrated electrical device including a first layer. The method can include depositing an anti-reflective coating on the first layer and forming a mask pattern, such as a photoresist mask pattern, on the anti-reflective coating. The anti-reflective coating can be etched with a fluorinated hydrocarbon-based plasma etch and subsequently etched with an oxygen-based plasma etch to expose regions of the first layer. The exposed regions of the first layer then can be etched. 
     Other features and advantages will be readily apparent from the following description, the accompanying drawings, and the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an exemplary structure including an anti-reflective coating. 
     FIG. 2 illustrates etching of the anti-reflective coating with a fluorinated hydrocarbon-based gaseous plasma according to the invention. 
     FIG. 3 illustrates the structure of FIG. 1 after completion of the fluorinated hydrocarbon-based etch according to one embodiment of the invention. 
     FIG. 4 illustrates subsequent etching of the anti-reflective coating with an oxygen-based gaseous plasma according to the invention. 
     FIG. 5 illustrates the structure of FIG. 1 after completion of the oxygen-based etch according to one embodiment of the invention. 
     FIG. 6 is a flow chart showing steps of a method of etching an anti-reflective layer according to the invention. 
    
    
     DETAILED DESCRIPTION 
     As shown in FIG. 1, a layer  12  which is to be etched is disposed on a semiconductor or other substrate  10 . The substrate  10  can include, for example, one or more semiconductor layers or structures and may include active or operable portions of semiconductor devices. The layer  12  can include a dielectric, for example, an oxide such as silicon oxide (SiO 2 ) or a nitride such as silicon nitride (SiN). Alternatively, the layer  12  can be formed of other or different materials, including conductive materials. An ARC  14  is deposited on the layer  12  and can be a conventional organic or organometallic material applied, for example, by a spin-on technique (step  100 ). Such ARC materials are commercially available and include, for example, BARLi from Hoescht Celanese, as well as other ARC materials available from Shipley and Brewer Science. A photoresist mask pattern  16  is formed on the ARC  14  (step  102 ). Known techniques can be used to form the photoresist mask  16 . In one particular implementation, the mask pattern  16  defines holes for conductive contacts through the layer  12 . In some implementations, the mask pattern  16  defines other device features. 
     For many applications, the ARC  14  can be deposited at a thickness of between 600 to 2,000 angstroms (Å). The thickness of the ARC  14 , however, generally will depend on the wavelength used during photolithography as well as the relative indices of refraction of the photoresist and the ARC. Thus, thicker or thinner ARCs may be appropriate in particular applications. 
     To provide a more uniform and predictable etch through the ARC  14 , two plasma etching processes are performed sequentially. The first plasma etch process uses a gaseous plasma that is substantially inert with respect to the photoresist mask  16 . For example, as indicated by FIG. 2, the ARC  14  initially can be etched in a reactive ion etch (RIE) chamber using a gaseous plasma based on fluorinated hydrocarbons, such as carbon-tetrafluoride (CF 4 ), perfluoro ethane (C 2 F 6 ) or trifluoromethane (CHF 3 ), among others (step  104 ). One or more inert background gases such as argon (Ar) or helium (He) also can be provided to the chamber during the first plasma etch process. The first plasma etch process etches the ARC  12  quite rapidly, but does not significantly etch the sidewalls of the photoresist mask pattern  16 . Thus, the first plasma etch process can help achieve a relatively high throughput, but does not adversely affect or significantly deteriorate the critical dimensions defined by the mask pattern  16 . 
     Some materials, such as Sio 2  and SiN, can be etched by the fluorocarbon-based plasma etchants. Accordingly, as illustrated by FIG. 3, the first plasma etch process should be halted before etching of the ARC  14  is completed, in other words, before the material below each of the exposed regions  18  in the photoresist mask  16  has been etched through to the layer  12  (step  106 ). In general, it is desirable to use the first plasma etch to etch as much of the ARC  14  as possible, but to stop the first plasma etch process prior to any etching of the layer  12 . A second plasma etch then can be used to complete the etching of the ARC  14 . 
     In one implementation, for example, the first plasma etch process is stopped after a pre-selected duration has elapsed. The pre-selected duration can be determined experimentally and is chosen so that the first plasma etch process is completed prior to completion of the ARC etch. In one implementation which can be used if the fluorinated hydrocarbon plasma is capable of etching the underlayer  12 , a sample substrate having an underlayer and ARC substantially identical to the underlayer  12  and ARC  14  is processed using the first plasma etch process to determine the pre-selected duration. An optical end-point detection technique or a residual gas analysis end-point detection technique, for example, can be used to determine when the first plasma etchant begins to etch the underlayer below the ARC on the sample substrate. A period of time equal to or somewhat less than the duration from commencement of the first plasma etch process until the onset of etching of the underlayer on the sample substrate can be used as the pre-selected duration. 
     Alternatively, in other embodiments, the first plasma etch process can be halted automatically once etching of any portion of the layer  12  beneath the ARC  14  is detected. An optical end-point detection apparatus, such as an optical emission spectrometer end-point detector, or a residual gas analysis end-point detector, can be coupled to the etch system controller for that purpose. For example, a significant change, such as an increase, in the level of emission of one or more by-products of the layer 12 would indicate that etching of the layer  12  has begun. In yet other implementations, the first plasma etch process can be halted automatically by detecting near-completion of the etching of the ARC  14 . Near-completion of the etching of the ARC  14  can occur, for example, when at least a portion of the underlayer  12  becomes exposed during etching of the fluorinated hydrocarbon-based plasma etch. Near-completion of the etching of the ARC  14  can be detected, for example, by using an optical emission spectrometer to monitor the wavelength(s) of one or more by-products of the ARC  14 . A significant change, such as a decrease, in the detected level(s) of emission for the monitored wavelength(s) indicates that at least a portion of the ARC  14  has been etched to the underlayer  12 . The first etch process then can be halted. 
     Once the first plasma etch process is completed, the second plasma etch process is performed to complete the etching of the ARC  14  and to expose regions of the underlayer  12  defined by the openings  18  in the mask pattern  16  (step  108 ). The second plasma etch process should be substantially inert to the layer  12  so that etching of the ARC  14  can be completed without significant etching of the layer  12 . For example, an oxygen-based RIE etch can serve as the second plasma etch process (see FIG.  4 ). One or more inert background gases such as Ar, He or nitrogen (N 2 ) also can be provided to the chamber during the second plasma etch process. Although the oxygen-based plasma will not generally etch a nitride or oxide layer  12 , it may tend to etch the sidewalls of the photoresist mask pattern  16  somewhat. Accordingly, the second plasma etch process should be halted as soon as the ARC  14  has been completely etched through to the layer  12  (FIG.  5 ). 
     Once the second etch process is completed, the exposed regions of the underlayer  12  can be etched using any one of many known techniques (step  110 ). The particular technique used to etch the underlayer  12  depends, in part, on the material forming the underlayer as well as the overall process in which the foregoing technique is used. Specific processes for etching underlayers of various materials, including SiO 2  and SiN, are well-known and, therefore, are not described further. 
     Exemplary etches were performed on several samples having an organic anti-reflective coating with a thickness of approximately 620 Å and disposed on a layer of SiO 2 . In each case, the ARC and SiO 2  layers were etched through small mask openings having a diameter of about 0.25 microns as well as through large mask openings having a diameter at least as large as about 1. Various samples were etched as described below. 
     The ARC of a first sample was etched using only an oxygen-based plasma for about 28 seconds. Oxygen gas (O 2 ) was flowed at about 15 sccm, and nitrogen gas (N 2 ) was flowed at about 45 sccm. The chamber pressure was approximately 30 milliTorr (mTorr) with about 400 Watts of RF power supplied to the chamber. 
     The ARC of a second sample was etched using only a fluorinated hydrocarbon-based plasma for about 60 seconds. CF 4  gas was flowed at about 60 sccm, and CHF 3  gas was flowed at about 40 sccm. In addition, Ar gas was flowed at about 80 sccm. The chamber pressure was approximately 120 mTorr with about 900 Watts of RF power supplied to the chamber. 
     The ARC of a third sample was etched using a fluorinated hydrocarbon-based plasma etch for about 40 seconds followed by an oxygen-based plasma etch for about 10 seconds. During the fluorinated hydrocarbon-based etch, CF 4  gas was flowed at about 60 sccm, and CHF 3  gas was flowed at about 40 sccm. In addition, Ar gas was flowed at about 80 sccm. The chamber pressure was approximately 120 mTorr with about 900 Watts of RF power supplied to the chamber. During the subsequent oxygen-based etch, O 2  was flowed at about 15 sccm, and nitrogen gas N 2  was flowed at about 45 sccm. The chamber pressure was approximately 30 mTorr with about 400 Watts of RF power supplied to the chamber. 
     In each case, following etching of the ARC, the SiO 2  layer was etched using a fluorocarbon-based etchant with a target average depth of about 5000 Å for the regions defined by the large mask openings having an initial diameter greater than about 1 micron. Following the SiO 2  etch, measurements were made to determine the average change Δ in the diameter of the small mask openings and to determine the effective difference in etch rate between the etch through the large mask openings and the etch through the small mask openings. The effective difference in etch rate, S, was calculated according to the following equation: 
     
       
           S= [( D   L   −D   S )/ D   L ]·100%, 
       
     
     where D L  is the average overall depth of the etch through the large mask openings, and D S  is the average overall depth of the etch through the small mask openings. In general, it is desirable for both Δ and S to be small. The results are summarized in TABLE 1. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 CHANGE IN DIAMETER 
                 EFFECTIVE 
               
               
                   
                 OF SMALL OPENINGS 
                 DIFFERENCE IN ETCH 
               
               
                   
                 (Δ) 
                 RATE (S) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 SAMPLE 1 
                 40 NANOMETERS 
                  8% 
               
               
                 SAMPLE 2 
                 10 NANOMETERS 
                 20% 
               
               
                 SAMPLE 3 
                 10 NANOMETERS 
                 10% 
               
               
                   
               
             
          
         
       
     
     As can be seen from TABLE 1, when only the oxygen-based plasma was used to etch the ARC (sample 1), the depth of the resulting overall etch was relatively uniform, as indicated by the value of 8% for S. The diameter of the small openings, however, changed significantly, thereby making it difficult to control the processing of small critical dimensions. On the other hand, when only the fluorinated hydrocarbon-based plasma was used to etch the ARC (sample 2), the size of the small openings increased by only about 10 nanometers (nm). However, the depth of the overall etch was much less uniform, due, in part, to the fact that the fluorinated hydrocarbon-based plasma tends to etch through regions of the ARC defined by the large mask openings somewhat more quickly than through regions of the ARC defined by the small mask openings. The fluorinated hydrocarbon-based etch subsequently begins to etch exposed regions of SiO 2  dielectric layer at several times the rate at which it continues to etch through the remaining regions of the ARC. 
     In contrast, when the ARC was etched with an initial fluorinated hydrocarbon-based plasma followed by an oxygen-based plasma (sample 3), the depth of the overall etch was relatively uniform, as indicated by the value of 10% for S. In addition, the diameter of the small mask openings changed by only about 10 nm, thereby preserving the size of critical dimensions. The use of the fluorinated hydrocarbon-based plasma allows most of the ARC to be etched with little or no adverse effects on the size of the critical dimensions. Additionally, subsequent etching of the ARC to expose regions of the dielectric underlayer using the oxygen-based plasma prevents etching of the SiO 2  until etching of the ARC is completed. That allows etching of the various regions of the SiO 2  to be commenced at the same time to provide a more uniform final etch. 
     In general, the first and second plasma etch processes can be performed in a single RIE chamber, magnetically-enhanced RIE chamber, inductively-coupled plasma RIE chamber or other suitable plasma etch chamber. Alternatively, the first and second plasma etch processes can be performed in separate chambers. Although the first and second plasma etch processes are performed sequentially, in some implementations, other processes or steps may be performed prior or subsequent to the first and second plasma etches, as well as between the first and second plasma etches. Moreover, although it is often desirable to perform the fluorinated hydrocarbon-based plasma etch prior to the oxygen-based plasma etch, the sequence can be reversed so that the oxygen-based plasma etch is performed first. 
     The techniques described above for etching an ARC can be used in the fabrication of electrical circuit elements and patterned layers within integrated circuits including, for example, dynamic random access memory (DRAM) integrated circuits, static random access memory (SRAM) integrated circuits, application specific integrated circuits (ASICs), and integrated circuits containing field effect transistors (FETs) or bipolar transistors (BPTs), as well as other integrated circuits and devices. 
     Other implementations are within the scope of the following claims.