Patent Publication Number: US-2023163029-A1

Title: Selective metal residue and liner cleanse for post-subtractive etch

Description:
BACKGROUND 
     The present disclosure relates in general to semiconductor devices and methods of manufacturing semiconductor devices and, in particular, to selectively remove metal residue and liners of interconnects in a post-subtractive etch stage during fabrication of semiconductor devices. 
     Integrated circuits (IC) include interconnect structures having electrically conductive wires that connect devices in different levels of a semiconductor chip to each other. Fabrication of an IC can include a front-end-of-line (FEOL) portion and a back-end-of-line (BEOL) portion. The FEOL portion can include patterned individual devices such as transistors, capacitors, resistors, etc., and other steps leading up to, but not including, deposition of metal interconnect layers and patterning metal interconnect structures (e.g., metal conducting lines). The BEOL portion can include interconnect structures and vias connected to the metal interconnect structures to connect the individual devices patterned from the FEOL portion with other layers above the FEOL and BEOL portions. 
     SUMMARY 
     In an embodiment, a structure in a semiconductor device is generally described. The structure can include a substrate, a dielectric layer deposited directly on the substrate, and a plurality of interconnect structures deposited directly on the dielectric layer. Each interconnect structure can include a liner deposited between a metal line of the interconnect structure and the dielectric layer, and residues of the liner can be absent on sidewalls of the interconnect structures. 
     In another embodiment, a method for forming interconnect structures on a semiconductor device is generally described. The method can include etching a hard mask layer of a deposition stack to pattern a hard mask. The method can further include etching an interconnect layer of the deposition stack using the hard mask to pattern a plurality of metal lines. The method can further include removing the hard mask. The method can further include etching a liner layer of the deposition stack to remove a portion of the liner layer deposited directly on a dielectric layer of the deposition stack. In response to etching the liner layer, a remaining portion of the liner layer can be deposited between the metal lines and the dielectric layer. 
     In another embodiment, a semiconductor device is generally described. The semiconductor device can include a back end of line (BEOL) portion and a front end of line (FEOL) portion connected to the BEOL portion. The FEOL portion can include a structure that includes a substrate, a dielectric layer deposited directly on the substrate, and a plurality of interconnect structures deposited directly on the dielectric layer. Each interconnect structure can include a liner deposited between a metal line of the interconnect structure and the dielectric layer, and residues of the liner can be absent on sidewalls of the interconnect structures. 
     Further features as well as the structure and operation of various embodiments are described in detail below with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a cross sectional view of an exemplary structure that can be used in selective metal residue and liner cleanse for post-subtractive etch in one embodiment. 
         FIG.  2    is a cross sectional view of the exemplary structure of  FIG.  1    after patterning a hard mask layer in one embodiment. 
         FIG.  3    is a cross sectional view of the exemplary structure of  FIG.  2    after patterning an interconnect layer to form free standing metal lines in one embodiment. 
         FIG.  4    is a cross sectional view of the exemplary structure of  FIG.  3    after removing a hard mask on top of the free standing metal lines in one embodiment. 
         FIG.  5    is a cross sectional view of the exemplary structure of  FIG.  4    after removing portions of a liner between the free standing metal lines in one embodiment. 
         FIG.  6    is a diagram illustrating an example application of the structure of  FIG.  5    in one embodiment. 
         FIG.  7    is a flow diagram illustrating a method of selective metal residue and liner cleanse for post-subtractive etch in one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The present application will now be described in greater detail by referring to the following discussion and drawings that accompany the present application. It is noted that the drawings of the present application are provided for illustrative purposes only and, as such, the drawings are not drawn to scale. It is also noted that like and corresponding elements are referred to by like reference numerals. 
     In the following descriptions, numerous specific details are set forth, such as particular structures, components, materials, dimensions, processing steps and techniques, in order to provide an understanding of the various embodiments of the present application. However, it will be appreciated by one of ordinary skill in the art that the various embodiments of the present application may be practiced without these specific details. In other instances, well-known structures or processing steps have not been described in detail in order to avoid obscuring the present application. 
     It will also be understood that when an element such as a layer, region or substrate is referred to as being “on” or “over” another element, it can be directly on the other element or intervening elements can also be present. In contrast, when an element is referred to as being “directly on” or “directly over” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements can be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
     The metal interconnect structures formed on a top layer (e.g., the last metal layer) of the FEOL portion can be metal interconnects insulated by dielectric materials. A top via scheme can be used for fabricating these metal interconnect structures beyond a specific line pitch (e.g., 28 nanometer (nm) line pitch). Top via schemes can include subtractive etching of metals, such as ruthenium (Ru), Rhodium (Rh), Molybdenum (Mo), Niobium (Nb), Iridium (Ir), and/or other conductive materials that can form the interconnects. In an embodiment, a liner can be used as an adhesion layer to connect these metal interconnect on dielectric layers, and these liners may undergo etching, such as reactive-ion etching (RIE). To be described in more detail below, the methods described herein can provide selective etching on the liners, which can prevent punching through the liners and prevent damages to dielectric layers underneath the liners, where damages to the dielectric layers can increase the dielectric constant. Further, upon the etching, metal residues from the etching can be cleansed or removed to prevent contamination of the IC. 
     Further, the methods described herein can provide a complete post RIE cleanse or cleansing to remove metal oxide from surfaces of the metal interconnects. The methods described here can provide a relatively effective post RIE cleanse process by 1) removing all metallic etch residues, 2) removing any remaining hard mask, 3) removing any thin metal oxidized from the metal trenches (e.g., in spacing between formed metal interconnects), 4) selectively removing TaN liners without undercutting and damaging underlying dielectric layers, and 5) preventing flopover of sub etch metal lines from wet cleansing processes. 
     Patterning processes can include additive and subtractive patterning processes. Additive patterning refers to patterning involving the addition of material to a device (e.g., by selective deposition), while subtractive patterning refers to patterning involving the removal of material from a device (e.g., using an etch process). As metal pitches become smaller and pitch lines become thinner, subtractive patterning schemes can become attractive due to factors such as a lack of conductive liner requirement and resistance benefits. The embodiments described herein can provide a subtractive patterning scheme that can selectively remove metal residue and metal liners from sidewalls of metal interconnect structures during fabrication of semiconductor devices. 
       FIG.  1    is a cross sectional view of an exemplary structure  100  that can be used in selective metal residue and liner cleanse for post-subtractive etch in one embodiment. The structure  100  can be a deposition stack including a substrate  102 , a dielectric region  104 , a liner layer  110 , an interconnect layer  112 , an etch stop layer  114 , a cap layer  116 , and a hard mask layer  118 . The substrate  102  can be, for example, a silicon (Si) wafer. The dielectric region  104  can include one or more layers of dielectric materials such as silicon nitride (SiN), silicon oxide (SiO), silicon dioxide (SiO 2 ), tetraethyl orthosilicate (TEOS), and/or other dielectric materials. The dielectric region  104  can be deposited directly on the substrate  102 . The liner layer  110  can be formed by, for example, depositing material such as tantalum nitride (TaN) directly on the dielectric region  104 . The interconnect layer  112  can be formed by, for example, depositing material such as ruthenium (Ru) directly on the liner layer  110 . The etch stop layer  114  can be formed by, for example, depositing material such as silicon carbide nitride (SiCN) directly on the interconnect layer  112 . The cap layer  116  can be formed by, for example, depositing material such as tetraethyl orthosilicate (TEOS) directly on the etch stop layer  114 . In an embodiment, the etch stop layer  114  can be an adhesion layer between the interconnect layer  112  and the cap layer  116 . The hard mask layer  118  can be formed by, for example, depositing material such as silicon nitride (SiN) directly on the cap layer  116 . In one embodiment, the liner layer  110  can be approximately 3 nanometers (nm) thick, the interconnect layer  112  can be approximately 30 nm thick, the etch stop layer  114  can be approximately 4 nm to 5 nm thick, and the hard mask layer  118  can be approximately 5 nm thick. 
       FIG.  2    is a cross sectional view of the exemplary structure  100  of  FIG.  1    after patterning a hard mask layer in one embodiment. In one embodiment, the structure  100  in  FIG.  1    can undergo a patterning process to form another structure  200 . To form the structure  200 , the structure  100  can undergo a metal patterning process to etch or pattern the hard mask layer  118  into a plurality of hard mask structures  202 . In one embodiment, the hard mask layer  118  can be patterned into the hard mask structures  202  using a photoresist and various etching processes such as different types of dry and/or wet etch processes, such as reactive-ion etching (RIE). The hard mask structures  202  can be located or deposited directly on the cap layer  116 . In another embodiment, if the hard mask layer  118  is not deposited on the cap layer  116 , the hard mask structures  202  can be directly patterned or formed on top of the cap layer  116 . 
       FIG.  3    is a cross sectional view of the exemplary structure of  FIG.  2    after patterning an interconnect layer to form free standing metal lines in one embodiment. In one embodiment, the structure  200  in  FIG.  2    can undergo an etch process to form another structure  300 . To form the structure  300 , the hard mask structures  202  can be used in the etch process to etch and pattern the interconnect layer  112 , the etch stop layer  114 , and the cap layer  116  into a plurality of etched structures  310 . Each one of the etched structures  310  can include a cap layer portion  302  etched from the cap layer  116 , a etch stop layer portion  304  etched from the etch stop layer  114 , and a metal line  306  etched from the interconnect layer  112 . The metal lines  306  can be free standing Ru metal lines directly on the liner layer  110 . In one embodiment, the etch process to etch and pattern the interconnect layer  112 , the etch stop layer  114 , and the cap layer  116  can be a dry etch process and anisotropic, and in a vertical direction (−y), such that the etched structures  310  can have the same size (e.g., a width or diameter (w), or a cross-sectional area (a)) as the mask structures  202 . 
       FIG.  4    is a cross sectional view of the exemplary structure of  FIG.  3    after removing a hard mask on top of the free standing metal lines in one embodiment. In one embodiment, the structure  300  in  FIG.  3    can undergo an etching process to form another structure  400 . To form the structure  400 , the structure  300  can undergo a wet etch process to remove the hard mask structure  202 , the cap layer portion  302 , and the etch stop layer portion  304  from each one of the etched structures  310 . In one embodiment, the wet etch process can be a timed wet cleanse process using diluted hydrofluoric (DHF) that is diluted at a ratio of, for example, 1:300. In response to removing the hard mask structure  202 , the cap layer portion  302 , and the etch stop layer portion  304 , from each one of the etched structures  310 , the metal lines  306  remain directly on the liner layer  110 . 
     In one embodiment, a duration of the wet etch process being applied on the structure  300  can change the amount of the etch stop layer portion  304  being removed from the etched structures  310 . For example, the longer the structure  300  is exposed to the wet etch process, the more materials of the etch stop layer portion  304  disposed directly on the metal lines  306  can be removed. The duration of wet etch process can be controlled or programmed based on a size (e.g., length, width, thickness, surface area, etc.) of the etch stop layer portion  304 . For example, the duration of the wet etch process can be increased for thicker etch stop layer portion  304 . In one embodiment, the duration of the wet etch process, for a 4 nm to 5 nm etch stop layer  114 , can be approximately 3 minutes to 6 minutes. In one embodiment, the duration of the wet etch process can vary with a thickness of a liner adhesive layer, such as the etch stop layer  114 . 
       FIG.  5    is a cross sectional view of the exemplary structure of  FIG.  4    after removing portions of a liner between the free standing metal lines in one embodiment. In one embodiment, the structure  400  in  FIG.  4    can undergo a selective wet etch process to form another structure  500 . To form the structure  500 , the structure  400  can undergo the selective wet etch process to remove portions  502  of the liner layer  110  between the metal lines  306 . In one embodiment, the selective wet etch process can be selective such that the materials of the liner layer  110  (e.g., TaN) can be etched at a faster rate when compared to an etch rate of the metal lines  306 . For example, to selectively etch the liner layer  110 , the etch rate for the materials forming the liner layer  110  (e.g., TaN) can be a non-zero value and the etch rates for the materials forming the other layers and/or structures (e.g., Ru, SiCN, TEOS) can be zero. Further, the selective wet etch process can be isotropic such that the materials of the liner  110  (e.g., TaN) may not remain in the regions indicated by portions  502 . 
     In one embodiment, a duration of the selective wet etch process being applied on the structure  400  can change the amount of the liner layer  110  being removed from the portions  502 . For example, the longer the structure  400  is exposed to the selective wet etch process, the more materials of the liner layer  110  in the portions  502  can be removed. The duration of selective wet etch process can be controlled or programmed based on a size (e.g., length, width, thickness, surface area, etc.) of the liner layer  110 . For example, the duration of the selective wet etch process can be increased for thicker liner layer  110 . In one embodiment, the duration of the selective wet etch process, for a 3 nm liner layer  110 , can be approximately 3 to 6 minutes. In one embodiment, the liner layer  110  can become oxidized in response to etching of the interconnect layer  112  (e.g., etching Ru), and a minimum duration (e.g., 3 minutes) can be set for ensuring removal of oxidized liner materials. 
     In response to removing the portions  502 , a plurality of interconnect structures  504  can be formed. Each one of the interconnect structures  504  can include the metal line  306  and a remaining liner portion  506 . Based on the selective and/or anisotropic wet etch process, the remaining liner portion  506  can have the same width (w) or cross-sectional area (a) as the metal line  306 . The selective wet etch process can provide a thorough cleanse process to remove portions  502  of the liner layer  110 , such that the materials of the liner layer  110  can be removed from the dielectric region  104  without damaging the dielectric region  104  and without undercutting the metal lines  306 . Also, the selective and anisotropic wet etch process can provide a thorough cleanse process to prevent the materials of the liner layer  110  to remain on sidewalls of the metal lines  306  in the interconnect structures  504 . 
     In one embodiment, residual metal oxides from the etching of the interconnect layer  112  (e.g., Ru) can remain on surfaces (e.g., top surface of the metal lines  306 ) of the structure  500 . The structure  500  can undergo a hydrogen anneal process to reduce or remove the residual metal oxide on surfaces of the structure  500 , such as a top surface of the metal lines  306 . In one embodiment, the structure  500  can undergo the hydrogen anneal process for an amount of time that may provide optimum grain growth, such as approximately two hours. The hydrogen anneal process can remove any residual metal oxide on surfaces of the structure  500 , such that metal oxide can be absent from the surfaces of the structure  500 . 
       FIG.  6    is a diagram illustrating an example application of the structure  500  of  FIG.  5    in one embodiment. In one or more embodiments, the structure  500  of  FIG.  5    can be a part of a FEOL portion of a semiconductor device  600 . In response to forming the structure  500 , an organic planarization layer (OPL)  610  can be formed to provide surface planarity for additional layers of material to be deposited directly on the FEOL portion. In one or more embodiments, the OPL  610  can be formed by materials such as photoresist and/or other hard mask materials. A barrier layer  612  can be deposited directly on the OPL  610 , and a dielectric layer  614  can be deposited directly on the barrier layer  610 . The barrier layer  612  and the dielectric layer  614  can be parts of a BEOL portion of the semiconductor device  600 . The BEOL portion of the semiconductor device  600  can include additional layers above the dielectric layer  614 . 
       FIG.  7    is a flow diagram illustrating a method of selective metal residue and liner cleanse for post-subtractive etch in one embodiment. An example process  700  may include one or more operations, actions, or functions as illustrated by one or more of blocks  702 ,  704 ,  706 ,  708 , and/or  710 . Although illustrated as discrete blocks, various blocks can be divided into additional blocks, combined into fewer blocks, eliminated, or performed in parallel, depending on the desired implementation. 
     The process  700  can begin at block  702 . At block  702 , a hard mask layer of a deposition stack can be etched to pattern a hard mask. The process  700  can proceed from block  702  to block  704 . At block  704 , an interconnect layer of the deposition stack can be etched using the hard mask to pattern a plurality of metal lines. In one embodiment, a hydrogen anneal process can be applied to remove metal oxide deposited on the metal lines in response to etching the interconnect layer. In one embodiment, the metal lines can be ruthenium (Ru) metal lines. In one embodiment, an etch stop layer can be deposited directly on the interconnect layer, a cap layer can be deposited directly on the etch stop layer, and the hard mask layer can be deposited directly on the etch stop layer. The hard mask can be used for etching of the interconnect layer, the etch stop layer, and the cap layer. 
     The process  700  can proceed from block  704  to block  706 . At block  706 , the hard mask can be removed. In one embodiment, the hard mask can be removed by removing portions of the etch stop layer and the cap layer remaining on the metal lines. In one embodiment, etching the interconnect layer, the etch stop layer, and the cap layer can include applying a dry and anisotropic etch process. In one embodiment, removing the hard mask can include applying a timed wet etch process. In one embodiment, the timed wet etch process uses diluted hydrofluoric (DHF). 
     The process  700  can proceed from block  706  to block  708 . At block  708 , a liner layer of the deposition stack can be etched to remove a portion of the liner layer deposited directly on a dielectric layer of the deposition stack. In one embodiment, a material of the liner layer can be tantalum nitride (TaN). In one embodiment, the liner layer can be etched by applying a selective wet etch process. In one embodiment, the selective wet etch process can include using an etch rate for the liner layer that is greater than an etch rate of the metal lines. In one embodiment, the selective wet etch process can be a timed wet etch process. 
     The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the blocks may occur out of the order noted in the Figures. For example, two blocks shown in succession may, in fact, be performed substantially concurrently, or the blocks may sometimes be performed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements, if any, in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form 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 embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.