Patent Publication Number: US-10332837-B2

Title: Enhancing barrier in air gap technology

Description:
BACKGROUND 
     The present invention generally relates to semiconductor device manufacturing, and more particularly to fabricating an air gap with a barrier layer. 
     A semiconductor chip consists of an array of devices whose contacts are interconnected by patterns of metal wiring. In very large scale integration (VLSI) chips, these metal patterns are multilayered and are separated by layers of an insulating material. Typical integrated circuit chip designs utilize one or more wiring levels. Insulating or dielectric materials are employed between the wires in each level (intra-level dielectric) and between the wiring levels (inter-level dielectric). The desire for smaller chips may result in higher device density and tighter space between wires and wire levels. 
     SUMMARY 
     According to one embodiment of the present invention, a structure with a preformed barrier layer is provided. The structure may include a first metal line and a second metal line in a dielectric layer, the first metal line and the second metal line are adjacent and within the same dielectric level; an air gap structure in the dielectric layer and between the first metal line and the second metal line, wherein the air gap structure includes an air gap oxide layer and an air gap; and a barrier layer between the air gap structure and the first metal line, wherein the barrier layer is an oxidized metal layer. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The following detailed description, given by way of example and not intended to limit the invention solely thereto, will best be appreciated in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a cross section view of a semiconductor structure according to an exemplary embodiment. 
         FIG. 2  is a section view of the structure illustrated in  FIG. 1  taken along section view A. 
         FIG. 3  is a cross section view of the semiconductor structure and illustrates the formation of a mask pattern on a top surface according to an exemplary embodiment. 
         FIG. 4  is a cross section view of the semiconductor structure and illustrates the formation of a trench in the structure according to an exemplary embodiment. 
         FIG. 5  is a section view of the structure illustrated in  FIG. 4  taken along section view B and illustrates the formation of the opening above a portion of a metal line according to an exemplary embodiment. 
         FIG. 6  is a section view of the structure illustrated in  FIG. 4  taken along section view B and illustrates the formation of the opening above a portion of the metal line according to another embodiment. 
         FIG. 7  is a section view of the structure illustrated in  FIG. 4  taken along section view B and illustrates the formation of the opening above a portion of the metal line according to another embodiment. 
         FIG. 8  is a section view of the structure illustrated in  FIG. 4  taken along section view C and illustrates the formation of the opening adjacent to the metal line according to another embodiment. 
         FIG. 9  is a cross section view of the semiconductor structure and illustrates the formation of an active component on the structure according to an exemplary embodiment. 
         FIG. 10  is a cross section view of the semiconductor structure and illustrates the formation of an air gap, air gap oxide, and a barrier layer according to an exemplary embodiment. 
         FIG. 11  is a section view of the structure illustrated in  FIG. 10  taken along section view D and illustrates the formation of the barrier layer between the metal line and the air gap oxide according to an exemplary embodiment. 
         FIG. 12  is a section view of the structure illustrated in  FIG. 10  taken along section view D and illustrates the formation of the barrier layer between the metal line and the air gap oxide according to another embodiment. 
         FIG. 13  is a section view of the structure illustrated in  FIG. 10  taken along section view D and illustrates the formation of the barrier layer between the metal line and the air gap oxide according to another embodiment. 
         FIG. 14  is a section view of the structure illustrated in  FIG. 10  taken along section view E and illustrates the formation of the barrier layer and a dielectric layer between the metal line and the air gap oxide according to another embodiment. 
         FIG. 15  is a cross section view of a semiconductor structure according to another embodiment. 
         FIG. 16  is a section view of the structure illustrated in  FIG. 15  taken along section view F. 
         FIG. 17  is a cross section view of the semiconductor structure and illustrates the formation of a mask pattern on a top surface according to another embodiment. 
         FIG. 18  is a cross section view of the semiconductor structure and illustrates the formation of a trench in the structure according to another embodiment. 
         FIG. 19  is a section view of the structure illustrated in  FIG. 18  taken along section view G and illustrates the formation of a trench and a preformed barrier layer according to another embodiment. 
         FIG. 20  is a section view of the structure illustrated in  FIG. 18  taken along section view H and illustrates the formation of the trench and the preformed barrier layer according to another embodiment. 
         FIG. 21  is a cross section view of the semiconductor structure and illustrates the formation of an active component on the structure according to another embodiment. 
         FIG. 22  is a cross section view of the semiconductor structure and illustrates the formation of an air gap, air gap oxide, and a barrier layer according to another embodiment. 
         FIG. 23  is a section view of the structure illustrated in  FIG. 22  taken along section view J and illustrates the formation of the barrier layer and the preformed barrier layer between the metal line and the air gap oxide according to another embodiment. 
         FIG. 24  is a section view of the structure illustrated in  FIG. 22  taken along section view K and illustrates the formation of the barrier layer, the preformed barrier layer, and a dielectric layer between the metal line and the air gap oxide according to another embodiment. 
     
    
    
     The drawings are not necessarily to scale. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. The drawings are intended to depict only typical embodiments of the invention. In the drawings, like numbering represents like elements. 
     DETAILED DESCRIPTION 
     Detailed embodiments of the claimed structures and methods are disclosed herein; however, it can be understood that the disclosed embodiments are merely illustrative of the claimed structures and methods that may be embodied in various forms. This invention may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of this invention to those skilled in the art. In the description, details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the presented embodiments. 
     References in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. 
     For purposes of the description hereinafter, the terms “upper”, “lower”, “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, and derivatives thereof shall relate to the disclosed structures and methods, as oriented in the drawing figures. The terms “overlying”, “atop”, “on top”, “positioned on” or “positioned atop” mean that a first element, such as a first structure, is present on a second element, such as a second structure, wherein intervening elements, such as an interface structure may be present between the first element and the second element. The term “direct contact” means that a first element, such as a first structure, and a second element, such as a second structure, are connected without any intermediary conducting, insulating or semiconductor layers at the interface of the two elements. 
     In the interest of not obscuring the presentation of embodiments of the present invention, in the following detailed description, some processing steps or operations that are known in the art may have been combined together for presentation and for illustration purposes and in some instances may have not been described in detail. In other instances, some processing steps or operations that are known in the art may not be described at all. It should be understood that the following description is rather focused on the distinctive features or elements of various embodiments of the present invention. 
     The present invention generally relates to semiconductor device manufacturing, and more particularly to fabricating an air gap with a barrier layer. Ideally, it may be desirable to fabricate an air gap in the back-end-of-line (BEOL) region of a semiconductor structure without exposing or contacting a metal line to an air gap oxide layer to avoid diffusion or electrical connection. One way to fabricate an air gap without exposing or contacting the metal line is to form a barrier layer between the air gap oxide layer and the metal line. One embodiment by which to form the barrier layer between the air gap oxide layer and the metal line is described in detail below by referring to the accompanying drawings  FIGS. 1-14 . 
       FIGS. 1 and 2  are demonstrative illustrations of a structure  100  during an intermediate step of a method of fabricating an air gap according to an embodiment. More specifically, the method can start with fabricating a cap  110  above a first metal line  102   a  and a second metal line  102   b , where the first and second metal lines  102   a ,  102   b  are in an intra-level dielectric layer  104  (hereinafter “ILD”).  FIG. 2  depicts a section view of the structure  100  illustrated in  FIG. 1  taken along section A. The structure  100  illustrated in section view A may be similar to the structure  100  illustrated in section view AA. 
     The structure  100  may be formed by depositing the ILD  104  on a lower-level BEOL, a middle-end-of-line, or a substrate by any method known in the art, such as, for example, chemical vapor deposition, plasma enhanced chemical vapor deposition, atomic layer deposition, or physical vapor deposition. The ILD  104  may include any materials known in the art, such as, for example, oxides, nitrides, and oxynitrides. The ILD  104  may have a thickness ranging from about 25 nm to about 200 nm. The ILD  104  may be planarized using, for example, a chemical-mechanical polishing technique. Metal openings may be formed in the ILD  104  using any technique known in the art, such as, for example, wet or dry etching. The metal openings may be formed in preparation for forming the first and second metal line  102   a ,  102   b.    
     The first and second metal lines  102   a ,  102   b  may be formed in the metal openings. The first metal line  102   a  may be substantially similar to the second metal line  102   b . The first and second metal lines  102   a ,  102   b  may be conductive materials including, for example, copper (Cu), aluminum (Al), or tungsten (W). The first and second metal lines  102   a ,  102   b  may be fabricated using any technique known in the art, such as, for example, a single or dual damascene technique. There may be a first distance (d 1 ) between the first and second metal lines  102   a ,  102   b  ranging from about 5 nm to about 200 nm. In an embodiment, the first and second metal lines  102   a ,  102   b  may be copper (Cu) and may include a metal barrier  105 . The metal barrier  105  may include a first liner  106  and a second liner  108 . The first liner  106  and the second liner  108  may be formed by any method known in the art. The first liner  106  may be any material known in the art including, for example, cobalt (Co) or ruthenium (Ru). The second liner  108  may be any material known in the art including, for example, tantalum (Ta), tantalum nitride (TaN), or any alloy therein. In an embodiment, the metal barrier  105  may be partially formed around the first and second metal line  102   a ,  102   b  having the first liner  106  cover all sides of the first and second metal lines  102   a ,  102   b  and the second liner  108  cover a sidewall and a bottom of the first and second metal lines  102   a ,  102   b.    
     With continued reference to  FIG. 1 , the cap  110  may be deposited on the structure  100 . The cap  110  may be an electrical insulator and may be used to improve interconnect reliability. The cap  110  may be deposited using typical deposition techniques, such as, for example, chemical vapor deposition. The cap  110  may include any suitable dielectric material, such as, for example, silicon nitride (Si 3 N 4 ), silicon carbide (SiC), silicon carbon nitride (SiCN), hydrogenated silicon carbide (SiCH), or any other material known in the art. The cap  110  may have a thickness ranging from about 10 nm to about 55 nm and ranges there between, although a thickness less than 10 nm and greater than 55 nm may be acceptable. 
       FIG. 3  is a demonstrative illustration of the structure  100  during an intermediate step of a method of fabricating an air gap according to an embodiment. More specifically, the method may include patterning the cap  110  and forming a mask opening  120 . The mask opening may have a mask width (mw). 
     An edge of the mask opening  120  may be aligned to an edge of the metal barrier  105 . However, the edge of the mask opening  120  may be aligned, not aligned, or misaligned, from the edge of the metal barrier  105 . In such case, the mask opening  120  may be misaligned by a second or third distance (d 2 , d 3 ) from an edge of the metal barrier  105 . The misalignment may be intentional or unintentional (possibly generated by lithography error). In an embodiment, an edge of the mask opening  120  may be a distance equal to the second distance (d 2 ) from the edge of the metal barrier  105  and may overlap the first metal line  102   a . Such cases are undesirable and may give rise to an electrical short, or other complications, during subsequent processing. Therefore, subsequent measures may be taken to protect the first metal line  102   a  from diffusion or electrical conduction. In another embodiment, after patterning, the cap  110  may cover the second metal line  102   b  and overlap the ILD  104  by a distance equal to the third distance (d 3 ). 
       FIG. 4  is a demonstrative illustration of the structure  100  during an intermediate step of a method of fabricating an air gap according to an embodiment. More specifically, the method may include removing a portion of the ILD  104  to form a trench  122 . 
     The portion of the ILD  104  may be removed using the cap  110  as a mask. The etching technique may include any technique known in the art, such as, for example, a wet or dry etching technique. In an embodiment, the misalignment of the mask opening  120  (illustrated in  FIG. 3 ) may result in a trench width (tw) that may be less than the mask width (mw), and may result in a portion of the ILD  104  remaining on a trench sidewall. 
       FIGS. 5, 6, and 7  represent alternative embodiments of the structure  100  in situations where the mask opening  120  (illustrated in  FIG. 3 ) is above the first metal line  102   a . More specifically, each embodiment may represent a different resulting structure formed during the etching of the trench  122 .  FIGS. 5, 6, and 7  each depict a section view of the structure  100  illustrated in  FIG. 4  taken along section B according to alternative embodiments. 
     The mask opening  120  (illustrated in  FIG. 3 ) may be above the first metal line  102   a  and may be misaligned, as described above. In an embodiment, as illustrated in  FIG. 5 , the first liner  106  may remain intact and may have some material removed during the etching process but may not expose the first metal line  102   a . In another embodiment, as illustrated in  FIG. 6 , the first liner  106  and the second liner  108  may be etched at a similar rate. The first liner may be severed, exposing and possibly etching a portion of the first metal line  102   a . In another embodiment, as illustrated in  FIG. 7 , the first liner  106  and the second liner  108  may be etched at different rates. The first liner may be severed, exposing and possibly etching a portion of the first metal line  102   a.    
       FIG. 8  represents an alternative embodiment of the structure  100  in a situation where the mask opening  120  (illustrated in  FIG. 3 ) overlaps a portion of the ILD  104 . More specifically, the overlap of the mask opening  120  may leave a portion of the ILD  104  along a sidewall of the metal barrier  105 . A possible benefit to this alternative embodiment is that it may allow for more layers between the trench  122  and the second metal line  102   b , which may result in additional insulation or may prevent possible diffusion with any subsequently deposited material.  FIG. 8  depicts a section view of the structure  100  illustrated in  FIG. 4  taken along section C according to an alternative embodiment. 
       FIG. 9  is a demonstrative illustration of the structure  100  during an intermediate step of a method of fabricating an air gap according to an embodiment. More specifically, the method may include the deposition of an active component  112  on the structure  100 . 
     The active component  112  may be deposited on the structure  100  according to any techniques known in the art. The active component  112  may be deposited on all surfaces including, for example, an upper surface of the cap  110 , a sidewall of the trench  122 , and a bottom of the trench  122 . The active component  112  may be any material known in the art, such as, for example, manganese (Mn), aluminum (Al), and titanium (Ti). 
       FIG. 10  is a demonstrative illustration of the structure  100  during an intermediate step of a method of fabricating an air gap according to an embodiment. More specifically, the method may include the formation of an air gap oxide  116 , an air gap  118 , and a barrier layer  114 . 
     The air gap oxide  116  may be a dielectric material, such as, for example, any oxide, nitride, or oxynitride; low-k dielectric is desired. The air gap  118  and air gap oxide  116  may be formed in the trench  122  (illustrated in  FIG. 9 ) by any method known in the art, including, for example, depositing a porous dielectric layer over a disposable solid layer, where the disposable solid layer may then be removed through the porous dielectric layer forming a cavity in the porous dielectric layer. The active component  112  (illustrated in  FIG. 9 ) may react with the air gap oxide  116  to form the barrier layer  114 . 
     The present embodiment is different from the common method of self-forming barrier layers because the active component  112  is deposited after the trench  122  is formed and before the air gap  118  is formed, instead of self-forming. This method allows the barrier layer  114  to be formed, for example, in-situ or during a subsequent annealing step. In conventional self-forming barrier formation, the barrier relies on a pre-introduced active element in a metal alloy, which later diffuses out of the alloy towards an interface to form a barrier. The conventional method may not allow for sufficient amounts of the active component to be used for a barrier during a subsequent air gap formation. The present embodiment may include a thorough coverage of surfaces of the structure  100  prior to air gap  118  formation. The reliability of thorough coverage may be accomplished by depositing the active component  112  after the forming the trench  122  (illustrated in  FIG. 9 ) to possibly assure that there is a consistent layer of the active component  112 . In an embodiment, the barrier layer  114  may include, for example, Mn x Si y C z N v O w . In a preferred embodiment, the barrier layer  114  may include SiO 2  and may be MnSiO 3 . 
       FIGS. 11, 12, and 13  each represent an alternative embodiment of the structure  100  during the deposition of the air gap oxide  116 . More specifically, each embodiment may represent the resulting barrier layer  114  from the previous embodiments illustrated in  FIGS. 5, 6 , and  7 , respectively.  FIGS. 11, 12, and 13  each depict a section view of the structure  100  illustrated in  FIG. 10  taken along section D. 
     In an embodiment, as illustrated in  FIG. 11 , the barrier layer  114  may contact the cap  110 , the first liner  106 , and the second liner  108 , but may not contact the first metal line  102   a . The barrier layer  114  may provide additional insulation or act as a diffusion barrier for the first metal line  102   a . In another embodiment, as illustrates in  FIG. 12 , the barrier layer  114  may contact the cap  110 , the first liner  106 , the second liner  108 , and the first metal line  102   a . In an embodiment, as illustrated in  FIG. 13 , the first liner  106  may be etched at a different rate than the second liner  108  where the barrier layer  114  may conform around a top and sidewalls of the second liner  108 . 
       FIG. 14  represents an alternative embodiment of the structure  100  where the second metal  102   b  may be completely covered by the cap  110  after patterning. More specifically, the embodiment may result in the barrier layer  114  along the portion of the ILD  104  which may be between the metal barrier  105  and the barrier layer  114 .  FIG. 14  depicts a section view of the structure  100  illustrated in  FIG. 10  taken along section E. In an embodiment, the barrier layer  114  may act as a double barrier (db) with the metal barrier  105 . 
     Another way to fabricate an air gap without exposing or contacting a metal line may include using a preformed barrier layer prior to forming the barrier layer between the oxide layer and the metal line. One embodiment by which to include the preformed barrier layer is described in detail below by referring to the accompanying drawings  FIGS. 14-20 . 
       FIGS. 15 and 16  are demonstrative illustrations of a structure  200  during an intermediate step of a method of fabricating an air gap according to an embodiment. More specifically, the method may include fabricating the cap  110  above the first metal line  102   a  and the second metal line  102   b  with a first preformed barrier layer  214   a  and a second preformed barrier layer  214   b .  FIG. 16  depicts a section view of the structure  200  illustrated in  FIG. 15  taken along section F. The structure  200  illustrated in section view F may be similar to the structure  200  illustrated in section view FF. 
     The first preformed barrier layer  214   a  may be formed on the top of the first and second metal lines  102   a ,  102   b  and may be formed before the deposition of the cap  110 . The second preformed barrier layer  214   b  may be formed on the side of the metal barrier  105 , separating the metal barrier  105  from the ILD  104 . The first and second preformed barrier layers  214   a ,  214   b  may be a similar material, and formed using a similar method, as the barrier layer  114  described above. 
       FIG. 17  is a demonstrative illustration of the structure  200  during an intermediate step of a method of fabricating an air gap according to an embodiment. More specifically, the method may include patterning the cap  110  and forming a mask opening  120 . The mask opening may have a mask width (mw). The structure  200  illustrated in  FIG. 17  may be similar to the structure  100  described in  FIG. 3 . 
       FIG. 18  is a demonstrative illustration of the structure  200  during an intermediate step of a method of fabricating an air gap according to an embodiment. More specifically, the method may include removing a portion of the ILD  104  to form a trench  122 . The structure  200  illustrated in  FIG. 18  may be similar to the structure  100  described in  FIG. 4 . 
       FIG. 19  represents an embodiment of the structure  200  in a situation where the mask opening  120  (illustrated in  FIG. 17 ) is above the first metal line  102   a  and above the first and second preformed barrier layers  214   a ,  214   b . More specifically, a portion of the first and second preformed barrier layers  214   a ,  214   b  may be exposed and may act as an etch stop during the formation of the trench  122 .  FIG. 19  depicts a section view of the structure  200  illustrated in  FIG. 18  taken along section G according to an embodiment. 
     The mask opening  120  (illustrated in  FIG. 17 ) may be above the first metal  102   a  and may be misaligned, as described above. In an embodiment, the first preformed barrier layer  214   a  and the second liner  108  may not be etch or may be slightly etched possibly leaving the first metal line  102   a  insulated from the trench  122 . 
       FIG. 20  represents an alternative embodiment of the structure  200  in a situation where the mask opening  120  (illustrated in  FIG. 17 ) overlaps a portion of the ILD  104 . More specifically, the overlap of the mask opening  120  may form a portion of the ILD  104  along a sidewall of the second preformed barrier layer  214   b  (or the second liner  108  if the second preformed barrier layer  214   b  is not present). The present alternative embodiment may allow for more layers between the trench  122  and the second metal line  102   b , which may result in additional insulation or may prevent possible diffusion with any subsequently deposited material.  FIG. 20  depicts a section view of the structure  200  illustrated in  FIG. 18  taken along section H according to an embodiment. 
       FIG. 21  is a demonstrative illustration of the structure  200  during an intermediate step of a method of fabricating an air gap according to an embodiment. More specifically, the method may include the deposition of an active component  112  on the structure  200 . The structure  200  illustrated in  FIG. 21  may be similar to the structure  100  described in  FIG. 9 . 
       FIG. 22  is a demonstrative illustration of the structure  200  during an intermediate step of a method of fabricating an air gap according to an embodiment. More specifically, the method may include the formation of an air gap oxide  116 , an air gap  118 , and a barrier layer  114 . The structure  200  illustrated in  FIG. 22  may be similar to the structure  100  described in  FIG. 10 . 
       FIGS. 23 and 24  represent alternative embodiments of the structure  200  in situations during the deposition of the air gap oxide  116 . More specifically, each embodiment may represent the resulting barrier layer  114  from the previous embodiments illustrated in  FIGS. 19 and 20 , respectively.  FIGS. 23 and 24  each depict a section view of the structure  200  illustrated in  FIG. 22  taken along section J and K, respectively, according to an embodiment. The barrier layer  114  may form, for example, as a reaction of the active component  112  with the air gap oxide  116 . Another possible embodiment may include the formation of the barrier layer  114  during a thermal annealing process. The resulting structures illustrated in  FIGS. 23 and 24  may be representative of a final structure of the structure  200 . 
     The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The terminology used herein was chosen to best explain the principles of the embodiment, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.