Patent Publication Number: US-9837310-B2

Title: Method of manufacturing a semiconductor device

Description:
PRIORITY CLAIM AND CROSS-REFERENCE 
     This application is a divisional of U.S. patent application Ser. No. 13/834,448, entitled “Method of Fabricating Copper Damascene,” filed on Mar. 15, 2013, which application claims the benefit of U.S. Provisional Application Ser. No. 61/777,689, filed on Mar. 12, 2013, entitled “Method of Fabricating Copper Damascene,” which applications are hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     In semiconductor technology, an integrated circuit can be formed on a semiconductor substrate according to a particular technology node, which typically indicates a minimum feature size. When the minimum feature size moves to about 100 nm or below, damascene processes are frequently utilized to form multilayer copper interconnections including vertical interconnection vias and horizontal interconnection metal lines. As semiconductor device sizes continue to shrink, the damascene process will see a number of potential problems that may affect the quality of the interconnections. For example, in a 20-namometer (nm) fabrication process, the openings may become too narrow and thus may not be properly filled by conventional damascene processes. The top portion of the opening may be blocked, which may create a void underneath that may degrade the performance of the semiconductor device. This problem is particularly acute in high aspect ratio features of small width. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  is a flowchart of a method of fabricating a semiconductor device according to one embodiment of the present disclosure; 
         FIGS. 2-7  are diagrammatic cross-sectional side views of a portion of a semiconductor device at various stages of fabrication according to one embodiment of the present disclosure; 
         FIG. 8  is a flowchart of a method of fabricating a semiconductor device according to one embodiment of the present disclosure; and 
         FIGS. 9-13  are diagrammatic cross-sectional side views of a portion of a semiconductor device at various stages of fabrication according to another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, specific details are set forth to provide a thorough understanding of embodiments of the present disclosure. However, one having ordinary skill in the art will recognize that embodiments of the disclosure can be practiced without these specific details. In some instances, well-known structures and processes are not described in detail to avoid unnecessarily obscuring embodiments of the present disclosure. 
     Reference throughout 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 present disclosure. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. It should be appreciated that the following figures are not drawn to scale; rather, these figures are intended for illustration. 
       FIG. 1  is a flowchart of a method  2  for fabricating a semiconductor device according to various aspects of the present disclosure. Referring to  FIG. 1 , the method  2  includes block  4 , in which a non-conductive layer is formed over a semiconductor substrate. The method  2  includes block  6 , in which a low-k dielectric layer is formed over the non-conductive layer. The method  2  includes block  8 , in which the low-k dielectric layer is etched and the etching stopping at the non-conductive layer to form an opening. The method  2  includes block  10 , in which a plasma treatment is performed on the semiconductor substrate to convert the non-conductive layer into a conductive layer. The method  2  includes block  12 , in which the opening is filled with a copper-containing material in an electroless copper bottom up fill process to form a copper-containing plug. The method  2  includes block  14 , in which the copper-containing plug is planarized so that the top of the copper-containing plug is co-planar with the top of the low-k dielectric layer. The method  2  includes block  16 , in which the semiconductor substrate is heated to form a self-forming barrier layer on the sidewalls of the copper-containing plug. 
     It is understood that additional processes may be performed before, during, or after the blocks  4 - 16  shown in  FIG. 1  to complete the fabrication of the semiconductor device, but these additional processes are not discussed herein in detail for the sake of simplicity. 
       FIGS. 2-7  are diagrammatic fragmentary cross-sectional side views of a semiconductor device at various fabrication stages according to one embodiment of the method  2  of  FIG. 1 . It is understood that  FIGS. 2-12  have been simplified for a better understanding of the inventive concepts of the present disclosure. It should be appreciated that the materials, geometries, dimensions, structures, and process parameters described herein are exemplary only, and are not intended to be, and should not be construed to be, limiting to the invention claimed herein. Many alternatives and modifications will be apparent to those skilled in the art, once informed by the present disclosure. 
     Referring to  FIG. 2 , a semiconductor device  100  is provided. The semiconductor device  100  may be an integrated circuit (IC) chip, system on chip (SOC), or portion thereof, that may include various passive and active microelectronic devices such as resistors, capacitors, inductors, diodes, metal-oxide semiconductor field effect transistors (MOSFET), complementary metal-oxide semiconductor (CMOS) transistors, bipolar junction transistors (BJT), laterally diffused MOS (LDMOS) transistors, high power MOS transistors, or other types of transistors. The semiconductor device  100  includes a substrate  110 . The substrate  110  may be a portion of a semiconductor wafer. For example, the substrate may include silicon. The substrate  110  may alternatively be made of some other suitable elementary semiconductor, such as diamond or germanium; a suitable compound semiconductor, such as silicon carbide, indium arsenide, or indium phosphide; or a suitable alloy semiconductor, such as silicon germanium carbide, gallium arsenic phosphide, or gallium indium phosphide. In one embodiment, the substrate  110  includes various doped features for various microelectronic components, such as a complementary metal oxide semiconductor field-effect transistor (CMOSFET), imaging sensor, memory cell, and/or capacitive element. 
     In some embodiments, a metallization layer  115  is formed in a dielectric layer (not shown) on the substrate  110 . The metallization layer  115  is a conductive layer and may be a first metal layer in the semiconductor device  100 . In an embodiment, the metallization layer  115  includes a material containing copper. 
     According to an aspect of the present disclosure, a first non-conductive layer  120  is formed on the substrate  110 . The first non-conductive layer  120  may be a barrier layer, and hence is alternatively referred to as first barrier layer  120 . Alternatively, the first non-conductive layer  120  may be an etch stop layer. In damascene applications where the underlying layer is a low-k dielectric layer, the first barrier layer  120  is deposited to prevent diffusion of copper, aluminum or other metal into the underlying low-k dielectric layer(s). The barrier layer also serves as a nucleation layer on which the copper in an electroless bottom up fill process is grown. As the name implies, the first non-conductive layer  120  is non-conductive; however, in a later plasma treatment process, the first non-conductive layer  120  will be converted into a conductive layer for forming copper plugs in an electroless copper bottom up fill process. 
     In an embodiment, the first non-conductive layer  120  is a material selected from the group consisting of TaN, TaSiN, TaC, TiN, TiSiN, AlON, AlN, and AlO. Other suitable materials that are non-conductive may also be used. In an embodiment, the first non-conductive layer  120  is formed on the substrate  110  by a chemical vapor deposition (CVD) process. In another embodiment, the first non-conductive layer  120  is formed by an atomic layer deposition (ALD) process. Other suitable deposition processes may also be used. In an exemplary embodiment, the first non-conductive layer  120  has a thickness from about 10 angstroms and about 100 angstroms. 
     Still referring to  FIG. 2 , a first dielectric layer  130  is formed over the first non-conductive layer  120 . The first dielectric layer  130  may be formed by suitable deposition processes such as, for example CVD, PVD, or spin-on coating. The first dielectric layer  130  includes a low-k material in an embodiment, for example, a compound made of a subset of the following elements: Si, O, C, and H. For example, the compound may be silicon oxide or silicon carbide. In an embodiment, the first dielectric layer  130  has a thickness that is less than about 1,000 angstroms. 
     A second non-conductive layer  132  is formed over the first low-k dielectric layer  130 . The second non-conductive layer  132  may be a barrier layer, and hence is alternatively referred to as second barrier layer  132 . Alternatively, the second non-conductive layer  132  may be an etch stop layer. In damascene applications where the underlying layer is a low-k dielectric layer, the second barrier layer  132  is deposited to prevent diffusion of copper, aluminum or other metal into the underlying low-k dielectric layer, such as first dielectric layer  130 . As the name implies, the second non-conductive layer  132  is non-conductive; however, in a later plasma treatment process, the second non-conductive layer  132  will be converted into a conductive layer for forming copper plugs in an electroless copper bottom up fill process. 
     In an embodiment, the second non-conductive layer  132  is a material selected from the group consisting of TaN, TaSiN, TaC, TiN, TiSiN, AlON, AlN, and AlO. Other suitable materials that are non-conductive may also be used. In an embodiment, the second non-conductive layer  132  is formed on the first dielectric layer  130  by a chemical vapor deposition (CVD) process. In another embodiment, the second non-conductive layer  132  is formed by an atomic layer deposition (ALD) process. Other suitable deposition processes may also be used. In an exemplary embodiment, the second non-conductive layer  132  has a thickness from about 10 angstroms to about 100 angstroms. 
     Still referring to  FIG. 2 , a second dielectric layer  134  is formed over the second non-conductive layer  132 . The second dielectric layer  134  may be formed by suitable processes such as, for example CVD, PVD, or spin-on coating processes. The second dielectric layer  134  includes a low-k material in an embodiment, for example, a compound made of a subset of the following elements: Si, O, C, and H. For example, the compound may be silicon oxide or silicon carbide. In an embodiment, the second dielectric layer  134  has a thickness that is less than about 1,000 angstroms. 
     A deposition process is performed to form a hard mask layer  140  over the second dielectric layer  134 . In one embodiment, the hard mask layer  140  includes a photoresist material. In another embodiment, the hard mask layer  140  includes a dielectric material, for example silicon oxide, which can be patterned by a patterned photoresist layer. The hard mask layer  140  is used in a later process as an etching mask to form openings in the first dielectric layer  130  and the second dielectric layer  134 . 
     Referring now to  FIG. 3 , a damascene formation process  145  is performed on the semiconductor device  100  to form a plurality of openings in the hard mask layer  140 , the second dielectric layer  134 , the second non-conductive layer  132 , and the first dielectric layer  130 . In the embodiment shown in  FIG. 3 , a first opening  143   a  is formed in first dielectric layer  130  and second dielectric layer  134  and a second opening  143   b  is formed in second dielectric layer  134  but not in the first dielectric layer  130 . In other embodiments, a single damascene opening may be formed. The damascene formation process  145  may include using a process such as photolithography, immersion lithography, ion-beam writing, or other suitable processes. For example, the photolithography process may include spin-coating, soft baking, exposure, post-baking, developing, rinsing, drying, and other suitable processes. The damascene formation process  145  includes an etching process in which the patterned hard mask layer  140  is used as a mask to etch the openings in the dielectric layers. For example, both the second dielectric layer  134  and the first dielectric layer  130  are etched, with the etching stopping at the first non-conductive layer  120  to form first opening  143   a , and the second dielectric layer  134  is etched, the etching stopping at the second non-conductive layer  132  to form second opening  143   b.    
     For the sake of simplicity, only first opening  143   a  and second opening  143   b  are illustrated herein, though it is understood that many other openings may be formed. Each of the openings  143   a  and  143   b  is approximately aligned (vertically) with a respective one of a portion of the metallization layer  115 . Those skilled in the art will recognize that although metallization layer  115  is shown as a continuous layer for simplicity, in actual practice, metallization layer  115  will be patterned into numerous individual regions. 
     With reference to  FIG. 4 , a plasma/heat treatment  150  is performed on the semiconductor device  100  to convert the first non-conductive layer  120  within the first opening  143   a  into a first conductive layer  160   a , and to convert the second non-conductive layer  132  within the second opening  143   b  into a second conductive layer  160   b . The heat of the plasma converts the TaN in the first and second non-conductive layers  120  and  132 , respectively from a non-conductive N rich layer to a conductive Ta rich layer. In an exemplary embodiment, the heat treatment is performed with a plasma gas selected from the group consisting of Ar, H2, He, Ne or mixtures thereof. In one embodiment, the heat treatment is performed at a temperature ranging between about 20 Celsius and about 400 Celsius, at a pressure ranging between about 0.01 torr and about 100 torr at a power ranging between about 50 watts and about 500 watts, and a time of between 3 seconds and 30 seconds. Those skilled in the art will recognize that the first non-conductive layer  120  can be converted into first conductive layer  160  by other heat treatments, such as for example, rapid anneal and pulsed beam (e.g., laser). 
     With reference to  FIG. 5 , a damascene deposition process  170  is performed on the semiconductor device  100 . The damascene deposition process  170  deposits a conductive material in openings  143   a  and  143   b . In one embodiment, the damascene deposition process  170  includes an electroless copper bottom-up fill process. With conventional copper deposition processes, the top portion of the opening may be blocked, thereby creating a void underneath the opening that may degrade the performance of the semiconductor device. In an electroless copper bottom up fill process, the void is avoided. 
     In the electroless copper bottom-up fill process, the process includes contacting first opening  143   a  and second opening  143   b  with an electroless plating bath and allowing electroless deposition of a conductive material to proceed for a predetermined time. One skilled in the art understands the composition of the electroless plating bath for copper filling and that it may include, for example a reducing agent, a surfactant, and a source of copper ions. In one embodiment, the electroless plating bath includes metal sources, reducing agents, buffer agents, and additives and the conductive material includes one of CuMn, CuCr, CuV, CuTi, and/or CuNb. According to one embodiment, the openings  143   a  and  143   b  are subject to the electroless plating bath for a period from about 100 seconds to about 5,000 seconds. Thereafter, the substrate is removed from the electroless plating bath. The process of contacting the openings to the electroless plating bath and removing the substrate therefrom is repeated to at least partially fill the openings  143   a  and  143   b  with a conductive material. As a result of the damascene deposition process  170 , copper-containing plugs  180  are formed in the openings  143   a  and  143   b . A planarization step using, for example a chemical mechanical polishing (CMP) process is subsequently performed after the damascene deposition process  170  to planarize the copper-containing plugs  180  so that the top thereof is co-planar with the top of the second low-k dielectric layer  134 . The semiconductor device  100  after the step of planarization is shown in  FIG. 6 . 
       FIG. 7  shows a self-forming barrier layer  200  formed on the sidewalls of the copper-containing plugs  180 . The self-forming barrier layer  200  includes metals and is electrically conductive but does not permit inter-diffusion and reactions between the copper-containing plugs  180  and the surrounding dielectric layer, such as first dielectric layer  130  and second dielectric layer  134 . In one embodiment, an anneal treatment  190  is applied to the substrate to form a self-forming barrier layer  200  wrapping around the copper-containing plugs  180 . The anneal treatment may be a rapid thermal anneal (RTA), a laser anneal, and/or a flash lamp anneal. In one embodiment, the barrier layer  200  is self-formed by applying a temperature from about 200 C to about 400 C to the substrate  110  for a time period of about 1 minute. The anneal process may be conducted in an oxygen ambient, a combination of steam ambient and oxygen ambient combined, or under an inert gas atmosphere. In one embodiment where the alloy element in the copper plug  180  manganese (Mn), with the thermal driving force, Mn segregates from copper and is driven to about the surfaces of the copper plug  180  where Mn reacts with oxygen to form manganese oxide (MnOx). In other embodiments, the barrier layer  200  may include CrOx, VOx, TiOx, and/or NbOx; however, the composition depends on the type of copper alloy used in the copper plug  180 . 
       FIG. 8  is a flowchart of a method  302  of fabricating a semiconductor device according to another embodiment of the present disclosure. Referring to  FIG. 8 , the method  302  includes block  304 , in which a non-conductive layer is formed over a semiconductor substrate. The method  302  includes block  306 , in which a low-k dielectric layer is formed over the non-conductive layer. The method  302  includes block  308 , in which the low-k dielectric layer is etched the etching stopping at the non-conductive layer to form an opening. The method  302  includes block  310 , in which a self-assembled monolayer (SAM) is formed on the non-conductive layer. The method  302  includes block  312 , in which a catalytic layer is formed on the SAM. The method  302  includes block  314 , in which the opening is filled with a copper-containing material in an electroless copper bottom fill process to form a copper-containing plug. The method  302  includes block  316 , in which the copper containing plug is planarized so that the top of the copper containing plug is co-planar with the top of the low-k dielectric layer. The method  302  includes block  318 , in which the substrate is heated to form a self-forming barrier layer on the sidewalls of the copper containing plug. 
       FIGS. 9-13  are diagrammatic cross-sectional side views of a portion of a semiconductor device at various stages of fabrication according to one embodiment of the method  302  of  FIG. 8 .  FIG. 9  shows the semiconductor device  400  (similar to the semiconductor device  100  in  FIG. 3  but with the addition of a self assembled monolayer (SAM) deposited in first opening  143   a  and second opening  143   b ). Specifically, a SAM layer  220   a  is deposited on the first non-conductive layer  120  within the first opening  143   a ; a SAM layer  220   b  is deposited on the second non-conductive layer  132  within the second opening  143   b ; and SAM layers  220   c  are deposited on the second non-conductive layer  132  within the first opening  143   a . The SAM is a short carbon chain structure. In an exemplary embodiment, the SAM structure has around 2 to 10 units carbon and two different functional groups on two sides. One side has, as an example a Si—OH functional group that bonds with the non-conductive layers  120  and  132 , and the other side has, as an example a —NH2 functional group that bonds with catalytic layer elements such as Co, Pd, Ru, and Ni found in later formed catalytic layers  240   a ,  240   b , and  240   c  (see  FIG. 10 ). The SAM may be deposited via spin-on coating from a solution containing solvents such as, for example hexane and SAM monomer. 
     Referring now to  FIG. 10 , a catalytic layer deposition  230  is performed on the semiconductor device  400 . A catalytic layer is deposited on the surfaces of the SAM. In the embodiment shown in  FIG. 10 , a catalytic layer  240   a  is deposited on SAM layer  220   a ; a catalytic layer  240   b  is deposited on SAM layer  220   b ; and catalytic layers  240   c  are deposited on SAM layers  220   c . The catalytic layers  240   a ,  240   b , and  240   c  include a material selected from the group consisting of Co, Pd, Ru, Ni, and combinations thereof and are formed over the respective ones of the SAM by chemical bonding, for example. 
     With reference to  FIG. 11 , a damascene deposition process  170  is performed on the semiconductor device  400 . The damascene deposition process  170  deposits a conductive material on the catalytic layers  240   a ,  240   b , and  240   c  in openings  143   a  and  143   b . In one embodiment, the damascene deposition process  170  includes an electroless copper bottom-up fill process. With conventional copper deposition processes, the top portion of the opening may be blocked, thereby creating a void underneath the opening that may degrade the performance of the semiconductor device. In an electroless copper bottom up fill process, the void is avoided. 
     In the electroless copper bottom-up fill process, the process includes contacting first opening  143   a  and second opening  143   b  with an electroless plating bath and allowing electroless deposition of a conductive material on the catalytic layers to proceed for a predetermined time. One skilled in the art understands the composition of the electroless plating bath for copper filling and that it may include, for example a reducing agent, a surfactant, and a source of copper ions. In one embodiment, the electroless plating bath includes metal sources, reducing agents, complex agents, buffer agents, additives and the conductive material includes one of CuMn, CuCr, CuV, CuTi, and/or CuNb. According to one embodiment, the openings  143   a  and  143   b  are subject to the electroless plating bath for a period from about 10 seconds to about 500 seconds. Thereafter, the substrate is removed from the electroless plating bath. The process of contacting the openings to the electroless plating bath and removing the substrate therefrom is repeated to at least partially fill the openings  143   a  and  143   b  with a conductive material. As a result of the damascene deposition process  170 , copper-containing plugs  250  are formed in the openings  143   a  and  143   b . A planarization step using, for example a chemical mechanical polishing (CMP) process is subsequently performed after the damascene deposition process  170  to planarize the copper-containing plugs  250  so that the top thereof is co-planar with the top of the second low-k dielectric layer  134 . The semiconductor device  400  after the step of planarization is shown in  FIG. 12 . 
       FIG. 13  shows a self-forming barrier layer  260  formed on the sidewalls of the copper-containing plugs  250 . The self-forming barrier layer  260  includes metals and is electrically conductive but does not permit inter-diffusion and reactions between the copper-containing plugs  250  and the surrounding dielectric layer, such as first dielectric layer  130  and second dielectric layer  134 . In one embodiment, an anneal treatment  190  is applied to the substrate to form a self-forming barrier  260  wrapping over the copper-containing plugs  250 . The anneal treatment may be a rapid thermal anneal (RTA), a laser anneal, and/or a flash lamp anneal. The anneal process may be conducted in an oxygen ambient, a combination of steam ambient and oxygen ambient combined, or under an inert gas atmosphere. 
     The semiconductor devices with copper damascene shown in  FIGS. 2-7 and 9-13  are only for illustrative purpose and are not limiting. Additional embodiments can be conceived. 
     The present disclosure has described various exemplary embodiments. According to one embodiment, a method of fabricating a semiconductor device includes forming a non-conductive layer over a semiconductor substrate. A low-k dielectric layer is formed over the non-conductive layer. The low-k dielectric layer is etched and stopped at the non-conductive layer to form an opening. A plasma treatment is performed on the substrate to convert the non-conductive layer within the opening into a conductive layer. The opening is filled with a copper-containing material in an electroless copper bottom up fill process to form a copper-containing plug. The copper-containing plug is planarized so that the top of the copper-containing plug is co-planar with the top of the low-k dielectric layer. The substrate is heated to form a self-forming barrier layer on the sidewalls of the copper-containing plug. 
     According to another embodiment, a method of fabricating a semiconductor device includes forming a non-conductive layer over a semiconductor substrate. A low-k dielectric layer is formed over the non-conductive layer. The low-k dielectric layer is etched and stopped at the non-conductive layer to form an opening. A self-assembled monolayer (SAM) is formed on the non-conductive layer. A catalytic layer is formed on the SAM. The opening is filled with a copper-containing material in an electroless copper bottom up fill process to form a copper-containing plug. The copper-containing plug is planarized so that the top of the copper-containing plug is co-planar with the top of the low-k dielectric layer. The substrate is heated to form a self-forming barrier layer on the sidewalls of the copper-containing plug. 
     According to yet another embodiment, a method of fabricating a damascene layer includes forming a first non-conductive layer over a semiconductor substrate. A first low-k dielectric layer is formed over the first non-conductive layer. A second non-conductive layer is formed over the first low-k dielectric layer. A second low-k dielectric layer is formed over the second non-conductive layer. The first low-k dielectric layer is etched and stopped at the first non-conductive layer to form a first opening and the second low-k dielectric layer is etched and stopped at the second non-conductive layer to form a second opening. A plasma treatment is performed on the substrate to convert the first non-conductive layer within the first opening into a first conductive layer and the second non-conductive layer within the second opening into a second conductive layer. The first and second openings are filled with a copper-containing material in an electroless copper bottom up fill process to form a first copper-containing plug and a second copper-containing plug, respectively. The first and second copper-containing plugs are planarized so that the tops of the plugs are co-planar with the top of the second low-k dielectric layer. The substrate is heated to form a self-forming barrier layer on the sidewalls of the first and second copper-containing plugs. 
     In the preceding detailed description, specific exemplary embodiments have been described. It will, however, be apparent to a person of ordinary skill in the art that various modifications, structures, processes, and changes may be made thereto without departing from the broader spirit and scope of the present disclosure. The specification and drawings are, accordingly, to be regarded as illustrative and not restrictive. It is understood that embodiments of the present disclosure are capable of using various other combinations and environments and are capable of changes or modifications within the scope of the claims.