Abstract:
A method for fabricating a circuit, by defining a first set of resist features on a substrate and corresponding to a first mask layout, followed by defining a second set of resist features on the substrate corresponding to a second mask layout, wherein the second set adds to the first set for rectifying an error in either mask layout. In another aspect, the method is by defining a first set of resist features on a substrate and corresponding to a first mask layout that has an error, etching the substrate while the first set protects selected regions, defining a second set of resist features on the substrate and corresponding to a second mask layout, followed by etching the substrate to selectively remove portions of the selected regions for rectifying the error.

Description:
FIELD 
     Embodiments of the invention relate to a method for fabricating a circuit. 
     BACKGROUND 
     Micro-patterning using lithographic technology is well known, particularly in the semiconductor fabrication industry. Lithographic technology generally involves the steps of: a) providing a radiation-sensitive resist layer on a substrate, b) exposure of the resist layer to a radiation through a mask, where the mask has a predetermined pattern of transparent and opaque regions, and c) development of the resist layer in a developer solution, thereby forming a pattern of resist features in the resist layer, corresponding to the predetermined pattern on the mask. 
     The substrate is then processed further, generally with a step of implantation or etch, while the pattern of resist features protect selected region(s) on the substrate from being implanted or etched respectively. In a positive-tone resist, the portions that are exposed to the radiation through the transparent regions in the mask become soluble in the developer solution, and in a negative-tone resist the portions that are exposed to the radiation through the transparent regions in the mask become insoluble in the developer solution. The radiation used is generally ultra-violet light (UV) or extreme UV light (EUV). The positive-tone and the negative tone resists are generally sensitive to different wavelength regions of the radiation. X-rays, ion beams or electron beams are also used for exposure, generally for direct-write in mask-less lithographic systems and with corresponding resists. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, a method for fabricating a circuit is proposed. A first set of resist feature(s) is defined on a partially processed substrate and with a first tone resist, the first set corresponding to a first mask layout. A layer of a second tone resist is provided on the substrate and partially encapsulating the first set. A second set of resist feature(s) is defined on the substrate and with the second tone resist. The second set corresponds to a second mask layout and adds to the first set for rectifying an error in either mask layout. The substrate is then processed while the first and second sets protect selected region(s) on the substrate. 
     According to an embodiment, said error causes two lines of said circuit on said substrate to be disconnected instead of being connected. 
     According to another embodiment, the method uses one of the following combinations wherein:
     a) the first tone resist is a positive tone resist and the second tone resist is a negative tone resist,   b) the first tone resist is a negative tone resist and the second tone resist is a positive tone resist,   c) both of said first and second tone resists are negative tone resists, and   d) at least either of said first and second tone resists for any one of the preceding combinations at a) to c) is a photoresist.   

     According to another embodiment, the processing with the first and second sets is for at least one of the following steps: 
     a) implantation and 
     b) etch. 
     According to another aspect, a second method for fabricating a circuit is proposed. A first set of resist feature(s) is defined on a partially processed substrate and corresponding to a first mask layout, wherein the first mask layout has an error. The substrate is then etched while the first set protects first selected region(s) on the substrate. The first set is then stripped. A second set of resist feature(s) is defined on the substrate and corresponding to a second mask layout. The substrate is then etched while the second set protects second selected regions on the substrate, the etching being to selectively remove portion(s) of the first selected region(s) on the substrate and to form void(s) therein for rectifying the error. 
     According to an embodiment of the second aspect, the error causes two lines of the circuit on the substrate to be connected instead of being disconnected. 
     According to an embodiment of the second aspect, the first selected region(s) is/are in a metallization layer. 
     According to an embodiment of the second aspect, the method further comprises processing for at least partially filling the void(s) with a dielectric material. 
     According to an embodiment of the second aspect, both of the first and second sets are defined by positive-tone photoresists. 
     According to the embodiments of the two aspects, the substrate originates from one of the following: 
     a) a semiconductor wafer, 
     b) a lithium niobate wafer, and 
     c) a silicon on insulator (SOI) wafer. 
     The embodiments of the first aspect of the invention help in rectifying an error in a main mask by using another mask that rectifies the error, to generate an error free pattern of resist feature on the substrate. The substrate is then processed further, such as with steps of implantation or etch. According to the embodiments of the second aspect of the invention, a substrate that is already processed with the main mask bearing the error can also be rectified by further processing the substrate with the mask for rectifying the error. This mask for rectifying the error can generally be fabricated at a much cheaper cost than the main mask, due to significantly reduced complexity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  show a flowchart of a process of lithography for rectifying an error in a mask layout, in accordance with an embodiment of a first aspect of the invention. 
       FIGS.  2 A and  2 B- 1  show a flowchart of processes of lithography and etch for rectifying an error in a mask layout, in accordance with an embodiment of a second aspect of the invention. 
         FIG. 2B-2  shows a flowchart of processes of lithography and etch for rectifying an error in a mask layout, in accordance with an embodiment that is an alternative to the process shown at  FIG. 2B-1 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these specific details. 
     Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not other embodiments. 
     Broadly, embodiments of the invention disclose a method to use a rectifying mask for rectifying a resist pattern that is generated on a substrate by an erroneous main mask. Advantageously, embodiments of the invention save rejection of the erroneous main mask and remaking of a corrected main mask. Generally, due to significantly reduced complexity, the rectifying mask can be made at a much cheaper cost than the main mask. Embodiments of the invention also disclose a method to rectify a substrate that is already processed with an erroneous main mask. In this method, the substrate is further processed with a rectifying mask and advantageously, saves rejection of both, the erroneous main mask as well as the semi-processed substrate. 
       FIGS. 1A and 1B  show a flowchart of a process of lithography for rectifying an error in a mask layout, in accordance with one embodiment of a first aspect of the invention. As shown in  FIG. 1A , a first mask (FM)  104  is used according to a first mask layout, which includes transparent regions  104   a  and opaque  104   b  regions. As shown at (a), a first tone resist (FTR)  106  is provided on a processed layer (PL)  108  on a substrate (Sub)  110 . The FTR  106  is given an exposure  100   a  to radiation  102  through the transparent regions  104   a  of the FM  104 . In this embodiment, FTR  106  is a positive-tone resist, hence the exposed regions will be removed during the step of development  100   b , to form a first set of resist feature (FSRF)  104   c , as shown at (b). A second mask (SM)  114  is then used according to a second mask layout, bearing transparent  114   a  and opaque  114   b  regions. As shown at (c), a layer of a second tone resist (STR)  116  is provided on the PL  108  and partially encapsulating the FSRF  104   c . The STR  116  is provided with an exposure  100   c  to radiation  112 . After development  100   d , a second set of resist feature (SSRF)  114   c  is defined on the PL  108 , in addition to FSRF  104   c  as shown at (d), for rectifying an error in either mask layout. Sub  110  then proceeds for further processing such as an implant or etch step  100   e , while FSRF  104   c  and SSRF  114   c  protect selected region(s) on PL  108 . In this embodiment, the error causes the two FSRF  104   c  on the PL  108  to be disconnected instead of being connected. The SSRF  114   c  is used to connect the two FSRF  104   c . In other embodiments (not shown), the SSRF  114   c  may be used to extend the FSRF  104   c  or may also be used in isolation from the FSRF  104   c . In this embodiment, the FTR  106  is a positive tone photoresist and the STR  116  is a negative tone photoresist. However, in another embodiment (not shown), the FTR  106  may be a negative tone photoresist and the STR  116  may be a positive tone photoresist, with appropriate corresponding mask layouts. In yet another embodiment (not shown), both of the FTR  106  and the STR  116  may be negative tone photoresists. For defining the SSRF  114   c  after the FSRF  104   c , some extra processing steps may be required, such as an ultraviolet baking step for the FSRF  104   c  before providing the STR  116 . However, such requirements for extra steps would depend on the combination of the two resists and their tones used. The choice of the FTR  106  and the STR  116  would be limited by the geometries of the FSRF  104   c  and the SSRF  114   c.    
     FIGS.  2 A and  2 B- 1  show a flowchart of processes of lithography and etch for rectifying an error in a mask layout, in accordance with one embodiment of a second aspect of the invention. A first mask (FM)  204  is used according to a first mask layout, the FM  204  bearing transparent  204   a  and opaque  204   b  regions. The first mask layout has an error, in that for example, the opaque region  204   b  should have been split into two opaque regions  204   b . As shown at (a), a first tone resist (FTR)  206  is provided on a processed layer (PL)  208  on a substrate (Sub)  210 . The FTR  206  is given an exposure  200   a  to a radiation  202 , through the transparent regions  204   a  of FM  204 . In this embodiment, FTR  206  is a positive-tone resist, hence the exposed regions will be removed during the step of development  200   b  to form a first set of resist feature (FSRF)  204   c , as shown at (b). During the following steps of etch and strip  200   c , the PL  208  is etched while the FSRF  204   c  protects the first selected region (FSR)  204   d  in the PL  208  and the FSRF  204   c  is then stripped as shown at (c). A second mask (SM)  214  is used according to a second mask layout, the SM  214  bearing transparent  214   a  and opaque  214   b  regions. As shown at (d), a second tone resist (STR)  216  is provided on the FSR  204   d  and partially on the Sub  210 . The STR  216  is given an exposure  200   d  to a radiation  212  through the transparent regions  214   a  of SM  214 . In this embodiment, the STR  216  is a positive-tone resist, hence the exposed regions will be removed during the step of development  200   e , as shown at (e). A second set of resist feature (SSRF)  214   c  is formed. By a step of etch and strip  200   f , a portion of the FSR  204   d  is selectively removed to form a void  218  therein for rectifying the error. The SSRF  214   c  is then stripped, as shown at (f). Second selected regions (SSR)  214   d  are retained on the Sub  210 . 
       FIG. 2B-2  shows a flowchart of processes of lithography and etch for rectifying an error in a mask layout, in accordance with an embodiment that is an alternative to the process shown at  FIG. 2B-1 . In  FIG. 2B-2 , a further processed layer (PL- 1 )  218  is deposited over Sub  210  and FSR  204   d  at the step at (d). The steps of exposure  200   d  and development  200   e  follow as in the previous embodiment described in  FIG. 2B-1 , but with the (PL- 1 )  218  remaining over the Sub  210  and FSR  204   d . During the step of etch and strip  200   f , the etching is conducted for the PL- 1  first and then for the FSR  204   d , to form the void  218 . The SSRF  214   c  is then stripped, as shown at (f). The PL- 1   218  may be a single layer or a stack of layers. 
     As described in  FIGS. 2A ,  2 B- 1  and  2 B- 2 , the first selected region  204   d  is formed in any layer during the fabrication process, such as a metallization layer or a polysilicon layer or a dielectric layer or in the Sub  210  itself. According to an embodiment, the method further comprises processing for at least partially filling said void(s)  218  with a dielectric material, for better isolation of the multiple SSR  214   d . In the embodiments described here, both of the FTR  206  and the STR  216  are positive-tone photoresists. The choice of the FTR  206  and the STR  216  would be limited by the geometries of the FSRF  204   c  and SSRF  214   c.    
     In all these embodiments, the Sub  110  or Sub  210  may originate from a semiconductor wafer or a lithium niobate wafer or a silicon on insulator (SOI) wafer or a wafer of any other material. 
     The embodiments of the invention are compatible with any semiconductor technology such as complementary metal-oxide-semiconductor (CMOS), bipolar-junction-transistor and CMOS (BiCMOS), silicon-on-insulator (SOI) and the like. The scope of the invention is also not limited to any particular technology in terms of processing sequence, materials, physical dimensions and the like. 
     Although the present invention has been described with reference to specific exemplary embodiments, it will be evident that the various modification and changes can be made to these embodiments without departing from the broader spirit of the invention. Accordingly, the specification and drawings are to be regarded in an illustrative sense rather than in a restrictive sense.