Patent Publication Number: US-2023161263-A1

Title: Methods of patterning a photoresist, and related patterning systems

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 63/281,986, filed on Nov. 22, 2021, the content of which is incorporated herein by reference. 
    
    
     FIELD 
     The invention relates to lithographic systems, and more particularly, to systems for, and methods of, patterning a photoresist. 
     BACKGROUND 
     In microelectronic processes, where lithographic patterning of a photoresist is used in combination with electroplating, the electroplating tends to yield non-uniform thickness of conductive structures. Specifically, the thickness (or other dimension) of such electroplated conductive structures tend to gradually increase towards the edge of the substrate. As a result, dummy patterns are sometimes created at the edge of the substrate. 
     Thus, it would be desirable to provide improved methods of patterning a photoresist, and related patterning systems. 
     SUMMARY 
     According to an exemplary embodiment of the invention, a method of patterning a photoresist is provided. The method includes selectively illuminating an edge portion of a photoresist using an illumination system to form a patterned portion of the photoresist. 
     According to another exemplary embodiment of the invention, another method of patterning a photoresist is provided. The method includes the steps of: (a) patterning a first portion of a photoresist to form a first patterned portion of the photoresist, the first patterned portion corresponding to an active area of a semiconductor element; and (b) selectively illuminating a second portion of the photoresist using an illumination system to form a second patterned portion of the photoresist, the second patterned portion corresponding to an inactive area of the semiconductor element. 
     According to yet another exemplary embodiment of the invention, yet another method of patterning a photoresist is provided. The method includes the steps of: (a) patterning a first portion of the photoresist to form a first patterned portion of the photoresist, the first patterned portion including first patterned features having a dimension of less than 10 microns; and (b) selectively illuminating a second portion of the photoresist using an illumination system to form a second patterned portion of the photoresist, the second patterned portion including second patterned features having a dimension of greater than 10 microns (or greater than 20 microns, or greater than 50 microns). As will be appreciated by those skilled in the art, these dimensions are in a lateral direction (e.g., a width of the patterned feature, a length of a patterned feature, a length and width of a patterned feature, etc.), as opposed to being in a vertical direction (e.g., a depth of the patterned feature). 
     According to an exemplary embodiment of the invention, a patterning system is provided. The patterning system includes a support structure for supporting a photoresist. The patterning system also includes an illumination system configured to selectively illuminate an edge portion of the photoresist to form an edge patterned portion of the photoresist. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is best understood from the following detailed description when read in connection with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawings are the following figures: 
         FIGS.  1 A- 1 B  each include side and top views of workpiece assemblies useful for explaining various exemplary embodiments of the invention; 
         FIGS.  2 A- 2 D  are a series of block diagram side sectional views of a patterning system illustrating a method of patterning a photoresist in accordance with an exemplary embodiment of the invention; 
         FIG.  2 E  is a block diagram representation of a system for processing a photoresist to form conductive structures in accordance with an exemplary embodiment of the invention; 
         FIGS.  2 F- 2 H  are a series of block diagram side sectional views of portions of the system of  FIG.  2 E ; 
         FIG.  3    is a block diagram side sectional view of a patterning system including a plurality of light sources in accordance with an exemplary embodiment of the invention; 
         FIG.  4    is a block diagram side sectional view of a patterning system including a plurality of patterning subsystems in accordance with an exemplary embodiment of the invention; 
         FIG.  5    is a block diagram side view of a patterning system including an illumination system using a plurality of spot light beams in accordance with an exemplary embodiment of the invention; 
         FIG.  6 A  is a top view of a patterned photoresist, illustrated with exemplary fill factors detailed in  FIGS.  6 B- 6 D , in accordance with various exemplary embodiments of the invention; 
         FIGS.  7 A- 7 C  illustrate illumination patterns in accordance with various exemplary embodiments of the invention; 
         FIG.  8    is a top view of a photoresist patterned in accordance with an exemplary embodiment of the invention; 
         FIG.  9    is a top view of a photoresist patterned in accordance with an exemplary embodiment of the invention; and 
         FIGS.  10 - 12    are flow diagrams illustrating methods of patterning a photoresist in accordance with an exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, the term “spot light beam” is intended to be broadly construed, and shall not be limited to any specific shape or configuration. Thus, a spot light beam is not limited to a “round” configuration. 
     As used herein, a “substrate” may refer to any type of substrate, for example, a semiconductor wafer, a panel, a tray, an insulative substrate, a semiconductor element, a plurality of semiconductor elements, etc. In some embodiments (e.g., when the substrate is an insulative substrate), a “seed layer” (i.e., a conductive layer from which conductive structures will be grown) may be utilized. 
     As used herein, a “a semiconductor element” is intended to refer to any structure including (or configured to include at a later step) a semiconductor chip or die. Exemplary semiconductor elements include a bare semiconductor die, a semiconductor die on a substrate (e.g., a leadframe, a PCB, a carrier, a semiconductor chip, a semiconductor wafer, a panel, a BGA substrate, a semiconductor element, etc.), a semiconductor wafer, a packaged semiconductor device, a flip chip semiconductor device, a die embedded in a substrate, a stack of semiconductor dies, amongst others. 
     As provided above, exemplary semiconductor elements are semiconductor wafers, panels, or other structures including a plurality of semiconductor die. As will be understood by those skilled in the art, an “active area” of a semiconductor element is that portion configured to be later used in the manufacturing of semiconductors devices. For example, in a semiconductor wafer (or panel), the active area may refer to the portion including a plurality of semiconductor die to be used to make semiconductor devices. In contrast, the “inactive area” of a semiconductor element is that portion that will not be used later in the manufacturing of semiconductors devices (e.g., the portion that will be discarded). 
     Throughout this document, like reference numerals refer to like elements unless indicated otherwise. Thus, the description of certain elements is omitted in connection with certain drawings to avoid duplication. 
     According to certain exemplary embodiments of the invention, methods of patterning an edge portion of a photoresist are provided (e.g., fast direct-write patterning). With dedicated methods for fast patterning of edge portions of photoresists, production of electroplated layers is improved in terms of thickness uniformity and processing speed. The fill factor (wherein the fill factor refers to a portion of an area covered by conductors—see  FIGS.  6 B- 6 D ) can be optimized to improve the thickness uniformity for a particular product pattern. Another new feature is tunability of a generic edge pattern; this provides an additional degree of freedom for minimizing thickness variation. Using such methods, a generic pattern with an adjustable fill factor may be provided. 
     Various schemes for patterning the edge portion of the photoresist are described herein, including, for example: a scanning scheme, where illumination from a light source is focused on a single spot; illumination is split into multiple spots to be exposed in parallel; a multi-spot scanning scheme based on an active element (e.g., spatial light modulator) in combination with a projection optical system; among others. Proposed embodiments can be implemented using a standalone edge processing tool or as an additional subsystem in a general-purpose lithography tool. 
     Through various embodiments of the invention, fast exposure processes resulting in improved thickness uniformity of patterned layers (e.g., made by electroplating) are provided. Such exposure processes may be useful in microelectronic production, for example, for making redistribution and contact layers. 
     In accordance with certain exemplary aspects of the invention, a plurality of spot light beams are created for patterning an edge portion of a photoresist. The plurality of spot light beams may be provided using at least one of an active optical assembly (e.g., including a spatial light modulator in combination with a projection optical system) or a passive optical assembly (e.g., including a diffractive optical element) of the illumination system. 
     Referring now to the drawings,  FIG.  1 A  illustrates a side view and a top view of a workpiece assembly  128 . Workpiece assembly  128  includes a workpiece  124  and a substrate  104  (e.g., a semiconductor wafer, etc.). Workpiece  124  includes a seed layer  114  and a photoresist  102  (which is provided on seed layer  114 ). Photoresist  102  includes an edge portion  102   a  and an inner portion  102   b . A delineation mark  130  is illustrated with a dotted line to denote the approximate distinction between edge portion  102   a  and inner portion  102   b . Delineation mark  130  also denotes the approximate distinction between a region  118   a  (i.e., a region corresponding to an inactive area of a semiconductor element) and a region  118   b  (i.e., a region corresponding to an active area of a semiconductor element). That is, at some point in the future (after further processing) region  118   a  will include one or more active semiconductor elements, and region  118   b  will not include active semiconductor elements. 
     Referring now to  FIG.  1 B , a side view and a top view of a workpiece assembly  129  is illustrated. Workpiece assembly  129  is similar in many ways to workpiece assembly  128 , except the workpiece assembly  129  is substantially rectangular (e.g., a panel configuration, a square panel configuration, etc.) whereas workpiece assembly  128  is substantially circular (e.g., a wafer configuration). Workpiece assembly  129  includes a workpiece  125  and a substrate  105 . Workpiece  125  includes a seed layer  115  and a photoresist  103  (which is provided on seed layer  115 ). Photoresist  103  includes an edge portion  103   a  and an inner portion  103   b . A delineation mark  131  is illustrated with a dotted line to denote the approximate distinction between edge portion  103   a  and inner portion  103   b . Delineation mark  131  also denotes the approximate distinction between a region  119   a  (i.e., a region corresponding to an inactive area of a semiconductor element) and a region  119   b  (i.e., a region corresponding to an active area of a semiconductor element). 
     Referring now to  FIGS.  2 A- 2 D , a patterning system  200  is illustrated illuminating a workpiece  124  (e.g., workpiece  124  from  FIG.  1 A ).  FIGS.  2 A- 2 D  illustrate a “projection litho stepper” system; however, it is understood that this aspect of the invention is not limited to such a system, for example, this system could be a “litho scanner” (where both reticle and substrate move), a “litho direct write” (LDI) (which writes high resolution features with one or more focused beams), or another type of system within the scope of the invention. Referring specifically to  FIG.  2 A , patterning system  200  includes a support structure  220  for supporting workpiece assembly  128  (including workpiece  124  and substrate  104 ). Support structure  220  is capable of moving in a horizontal x and/or y direction. Patterning system  200  also includes an illumination system  216   a  that is capable of moving in a horizontal x and/or y direction. Illumination system  216   a  includes a light source  206  and an optical assembly  234 . Optical assembly  234  includes illumination optics system  232 , a photomask  212  (e.g., a reticle), and a projection optics system  210 . Finally, patterning system  200  includes an optical assembly  208  that is provided between support structure  220  and light source  206  and is capable of moving in a horizontal x and/or y direction. 
     Light source  206  is illustrated providing light  206   a  to illumination optics system  232  of optical assembly  234 . Light  206   a  is transmitted through photomask  212  to create a pattern. Light  210   a  (i.e., inner patterning light) is illustrated projected through projection optics system  210 , where light  210   a  is expanded and/or narrowed before illuminating a region of photoresist  102  (e.g., inner portion  102   b ). Optical assembly  234  illuminates an illumination region  210   a ′ with light  210   a , where an inner patterned portion  102   b   1  is thus formed. In  FIG.  2 B , illumination system  216   a  has been moved along a horizontal axis (e.g., x-axis) while illuminating inner region  102   b  to form inner patterned portion  102   b   1 , thus patterning the entire inner region  102   b.    
     In  FIG.  2 C , light source  206  has been moved to a position above optical assembly  208  to form illumination system  216   b . Illumination system  216   b  is positioned above edge portion  102   a  of photoresist  102 . Light source  206  is illustrated transmitting light  206   a  to optical assembly  208 . Illumination system  216   b  is illustrated selectively illuminating edge portion  102   a . Illumination system  216   b  is transmitting a beam  208   a  (e.g., a spot light beam) to edge portion  102   a  of photoresist  102 , thus forming patterned portion  102   a   1 . In  FIG.  2 D , illumination system  216   b  is positioned above another part of edge portion  102   a  of photoresist  102  to selectively illuminate another part of edge portion  102   a . Illumination system  216   b  is illustrated transmitting another beam  208   a  to another edge portion  102   a  of photoresist  102 , thus forming another patterned portion  102   a   1 . Thus, illumination system provides a spot light beam which is selectively turned on and off at different locations of edge portion  102   a  to form the edge patterned portion of photoresist  102 . 
     Although light source  206 , optical assembly  234 , optical assembly  208 , illumination system  216   a , and/or illumination system  216   b  are illustrated moving along a horizontal axis (e.g., x-axis, y-axis, etc.), the invention is not so limited. For example, support structure  220  may be moved to achieve a desired relative movement. Other configurations are contemplated. 
     Referring now to  FIG.  2 E , a block diagram representation of a system  250  for processing a photoresist to form conductive structures is illustrated. System  250  includes a photoresist development stage  250   a , a growth of conductors (e.g., conductive structures) stage  250   b , and a photoresist removal stage  250   c . Referring now to  FIG.  2 F , workpiece  124  is illustrated being developed in the photoresist development stage  250   a . Workpiece assembly  128  is supported by support structure  222   a . For example, a photoresist developer solvent may be used to wash away soluble photoresist of patterned portions  102   a   1  and  102   b   1 , thus creating apertures  102   a   1 ′ and  102   b   1 ′ in the edge portion  102   a  and inner portion  102   b , respectively. 
     In  FIG.  2 G , workpiece  124  is illustrated being processed in a growth of conductors stage  250   b  (e.g., using electroplating or the like). Workpiece assembly  128  is supported by support structure  222   b  (which may be the same support structure  222   a  or a different support structure). As illustrated, electroplating is applied to workpiece assembly  128 , thus growing a plurality of conductive structures  114   a  in an edge portion  102   a  of photoresist  102 . Simultaneously, a plurality of conductive structures  114   b  are grown in an inner portion  102   b  of photoresist  102 . As illustrated, conductive structures  114   a  may be taller than conductive structures  114   b.    
     In  FIG.  2 H , photoresist  102  (from  FIG.  2 G ) is illustrated having been removed in a photoresist removal stage  250   c . Workpiece assembly  128  is supported by support structure  222   c  (which may be the same support structure  222   a , support structure  222   b , or a different support structure). A photoresist removal material (e.g., a liquid resist stripper, etc.) is applied to photoresist  102  (from  FIG.  2 G ) to expose the plurality of conductive structures  114   a  and  114   b . Certain steps may be taken which are omitted from these illustrations for simplicity and clarity (such as etching away undesired portions of seed layer  114 , substrate  104 , etc.). 
     As described above in connection with  FIGS.  2 A- 2 D , two illumination sources  216   a  and  216   b  each include a common light source  206 . However, the respective illumination systems may include separate light sources (e.g., a first illumination system may include a first light source, and a second illumination system may include a second light source). Referring now to  FIG.  3   , patterning system  300  is illustrated having illumination system  316   a  including light source  336   a , and illumination system  316   b  including light source  336   b . Workpiece assembly  128  is supported by support structure  320  (which may be the same support structure  220 , or a different support structure). Other elements in  FIG.  3    are the same as in  FIGS.  2 A- 2 D . 
     Referring now to  FIG.  4   , patterning system  400  is illustrated having two patterning subsystems: patterning subsystem  426   a  and patterning subsystem  426   b . Patterning subsystem  426   a  includes illumination system  416   a  (e.g., including a direct write illumination tool) for selectively illuminating the inner portion; patterning subsystem  426   b  includes illumination system  416   b  (e.g., including a direct write illumination tool) for selectively illuminating the edge portion. Workpiece assembly  128  is illustrated supported by support structure  420 ,  422  (which may be the same support structure  220 ,  320 , or a different support structure). Workpiece assembly is illustrated being transferred from patterning subsystem  426   a  to patterning subsystem  426   b.    
     Referring now to  FIG.  5   , light source  206  is positioned above optical assembly  208  to form illumination system  216   b  (similar to the orientation shown in  FIGS.  2 C- 2 D ). Illumination system  216   b  is positioned above edge portion  102   a  of photoresist  102 . Light source  206  is illustrated transmitting light  206   a  to optical assembly  208 . Illumination system  216   b  is illustrated transmitting a plurality of beams  208   a  (e.g., a plurality of spot light beams) to edge portion  102   a  of photoresist  102 , thus forming patterned portion  102   a   1 . Thus, illumination system provides a plurality of spot light beams which are selectively turned on and off at different locations of edge portion  102   a  to form the edge patterned portion of photoresist  102 . 
     Referring now to  FIG.  6 A , photoresist  102  is illustrated after an illumination step (e.g., selective illumination). In the detail shown in  FIG.  6 B , patterned portion  102   a   1  of edge portion  102   a  is illustrated with a low fill factor (e.g., 5% fill factor) of patterned features  102   a   1   a  having a dimension of greater than (or equal to) 10 microns (but could also be greater than 20 microns, or greater than 50 microns, or other dimensions). In the detail shown in  FIG.  6 C , patterned portion  102   a   1  of edge portion  102   a  is illustrated with a high fill factor (e.g., 95% fill factor) patterned features  102   a   1   b . In the detail shown in  FIG.  6 D , inner patterned portion  102   b   1  is illustrated with patterned features  102   b   1   a  having a dimension of less than (or equal to) 10 microns (it being understood that at least a portion of these features could be larger than 10 microns). As will be appreciated by those skilled in the art, these dimensions are in a lateral direction (e.g., a width of the patterned feature, a length of a patterned feature, a length and width of a patterned feature, etc.), as opposed to being in a vertical direction (e.g., a depth of the patterned feature). 
     Referring now to  FIG.  7   , various illumination patterns are illustrated.  FIG.  7 A  illustrates a linear light pattern (e.g., created on a 2D spatial light modulator) projected to a substrate (e.g., at the wafer level). The pattern includes an illuminated portion  708   a   1  and an unilluminated portion  708   a   2 . The light pattern (e.g., light intensity pattern) may be generated by a spatial light modulator.  FIG.  7 B  illustrates a linear pattern projected on to a substrate.  FIG.  7 C  illustrates an exposure pattern in a photoresist. An unilluminated portion  708   a   3  is created by scanning and pulsing (i.e., turning on and off) the illumination pattern. 
     Referring now to  FIG.  8   , photoresist  102  is illustrated after an illumination step (e.g., selective illumination). The photoresist  102  is indicated having been selectively illuminated azimuthally (i.e., in a clockwise direction). An illumination system (not illustrated) may be moved azimuthally, a support structure (not illustrated) may move the photoresist  102  azimuthally, or a combination of movements. 
     Referring now to  FIG.  9   , photoresist  102  is illustrated after an illumination step (e.g., selective illumination). The photoresist  102  is indicated having been selectively illuminated in a step wise manner and/or by linear scanning of an illumination system (not illustrated) or a support structure (not illustrated). The width of illumination field in the inner portion of photoresist (which can be one-dimensional in case of scanning or two-dimensional in case of stepping) is indicated as  210   a′.    
     Referring now to  FIG.  10   , a method of patterning a photoresist is illustrated. At optional Step  1000 , an inner portion of a photoresist is patterned. For example, the inner portion of the photoresist may be patterned by illuminating the inner portion (e.g., using a photomask, a direct write illumination tool, etc.). At Step  1002 , an edge portion of the photoresist is selectively illuminated using an illumination system to form a patterned portion of the photoresist. For example, the step of selectively illuminating the edge portion of the photoresist may include using a spot light beam of the illumination system (or a plurality of spot light beams) (e.g., selectively turned on and off at different locations of the edge portion) to form the patterned portion of the photoresist. 
     In the various embodiments of the invention disclosed herein (including the embodiments shown in  FIGS.  10 - 12   ), the illumination of the edge portion may be accomplished through a scanning process, for example, by moving the illumination system and/or a substrate supporting the photoresist. For example, the step of selectively illuminating the edge portion of the photoresist may include moving at least one of (i) the illumination system and (ii) a substrate supporting the photoresist to form the patterned portion of the photoresist. In another example, the step of selectively illuminating the edge portion of the photoresist may include using a plurality of spot light beams of the illumination system in a scanning process, wherein the scanning process includes moving at least one of (i) the illumination system and (ii) a substrate supporting the photoresist to form the patterned portion of the photoresist. 
     At optional Step  1004 , conductive structures are formed (e.g., through electroplating or other techniques for forming conductive structures) in the inner portion and the edge portion (e.g., where the edge portion surrounds the inner portion). For example, the conductive structures formed in the inner portion correspond to an active area of a semiconductor element, and the conductive structures formed in the edge portion correspond to an inactive area of a semiconductor element. 
     While not shown in  FIG.  10   , additional steps are contemplated as disclosed within the present document. For example, a step of illuminating an inner portion of the photoresist using another illumination system to form an inner patterned portion is contemplated (where such step of illuminating the inner portion may be done before or after Step  1002 ). As disclosed herein, the illumination systems may share a common light source (e.g., see  FIGS.  2 A- 2 D ), or may have distinct light sources (e.g.,  FIG.  3   ). 
     Referring now to  FIG.  11   , another method of patterning a photoresist is illustrated. At Step  1100 , a first portion of a photoresist (e.g., an inner portion of the photoresist) is patterned (e.g., using a photomask, using an illumination source, and/or other techniques within the scope of the invention) to form a first patterned portion of the photoresist, the first patterned portion corresponding to an active area of a semiconductor element. At Step  1102 , a second portion of the photoresist (e.g., an edge portion of the photoresist surrounding the inner portion) is selectively illuminated using an illumination system to form a second patterned portion of the photoresist, the second patterned portion corresponding to an inactive area of the semiconductor element. For example, the step of selectively illuminating the second portion of the photoresist may include using a spot light beam of the illumination system (or a plurality of spot light beams) (e.g., selectively turned on and off at different locations of the edge portion) to form the second patterned portion of the photoresist. 
     If the first patterned portion of the photoresist is formed at Step  1100  using another illumination system (different from the illumination system used to form the second patterned portion at Step  1102 ), the illumination systems may share a common light source (e.g., see  FIGS.  2 A- 2 D ), or may have distinct light sources (e.g.,  FIG.  3   ). 
     At optional Step  1104 , conductive structures are formed in each of the first patterned portion and the second patterned portion (e.g., through electroplating or other techniques for forming conductive structures). 
     Referring now to  FIG.  12   , yet another method of patterning a photoresist is illustrated. At Step  1200 , a first portion of the photoresist (e.g., an inner portion of the photoresist) is patterned (e.g., using a photomask, using an illumination source, and/or other techniques within the scope of the invention) to form a first patterned portion of the photoresist, the first patterned portion including first patterned features having a dimension of less than 10 microns. At Step  1202 , a second portion of the photoresist (e.g., an edge portion of the photoresist surrounding the first portion of the photoresist) is selectively illuminated using an illumination system to form a second patterned portion of the photoresist, the second patterned portion including second patterned features having a dimension of greater than 10 microns (or greater than 20 microns, or greater than 50 microns, or other dimensions). For example, the step of selectively illuminating the second portion of the photoresist may include using a spot light beam of the illumination system (or a plurality of spot light beams) (e.g., selectively turned on and off at different locations of the edge portion) to form the second patterned portion of the photoresist. 
     If the first patterned portion of the photoresist is formed at Step  1200  using another illumination system (different from the illumination system used to form the second patterned portion at Step  1202 ), the illumination systems may share a common light source (e.g., see  FIGS.  2 A- 2 D ), or may have distinct light sources (e.g.,  FIG.  3   ). 
     At optional Step  1204 , conductive structures are formed (e.g., through electroplating or other techniques for forming conductive structures) in each of the first patterned portion and the second patterned portion. 
     Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.