Patent Publication Number: US-2013241070-A1

Title: Overlapping contacts for semiconductor device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 13/171,657, filed on Jun. 29, 2011, which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     This disclosure relates generally to the field of semiconductor device fabrication, and more particularly to formation of overlapping contacts (or interconnects) for a semiconductor device. 
     A semiconductor device may include co-planar adjacent contacts that are formed consecutively, during different processing steps. The subsequently formed contacts may need to be electrically connected with one another.  FIG. 1  shows a cross-section of an example semiconductor device  100  having an adjacent first contact  102   a  and second contact  102   b  according to the prior art. First contact  102   a  and second contact  102   b  are formed during different processing steps, i.e., second contact  102   b  is formed after first contact  102   a . First contact  102   a  and second contact  102   b  are located adjacent to one another in a dielectric layer  101  which may include an oxide or a nitride. Both the first contact  102   a  and the second contact  102   b  include a liner, in this case including a first liner layer  103  and second liner layer  104 , and a contact fill metal  105 . Electrical connection between the first contact  102   a  and the second contact  102   b  only exists at a contact interface  106  at the contact sidewalls. The electrical connection between the first contact  102   a  and the second contact  102   b  at contact interface  106  may be poor, as the contact interface  106  has a relatively small area, and may be resistive, as the electrical connection occurs across the liner barriers. 
     BRIEF SUMMARY 
     In one aspect, a semiconductor device with overlapping contacts includes a dielectric layer; a first contact located in the dielectric layer; and a second contact located in the dielectric layer adjacent to the first contact, wherein a portion of the second contact overlaps a top surface of the first contact. 
     Additional features are realized through the techniques of the present exemplary embodiment. Other embodiments are described in detail herein and are considered a part of what is claimed. For a better understanding of the features of the exemplary embodiment, refer to the description and to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Referring now to the drawings wherein like elements are numbered alike in the several FIGURES: 
         FIG. 1  is a cross sectional view of existing first and second contacts formed in a semiconductor device. 
         FIG. 2  is a flowchart illustrating an embodiment of a method for formation of overlapping first and second contacts. 
         FIGS. 3 through 5  are a series of cross sectional views illustrating an embodiment of the method of  FIG. 3  for formation of overlapping first and second contacts in which: 
         FIG. 3  illustrates the formation of a first contact. 
         FIG. 4  illustrates the device of  FIG. 3  after etching a recess for a second contact and removing a top portion of the first contact. 
         FIG. 5  illustrates the device of  FIG. 4  after formation of the second contact in the recess and over the top surface of the etched first contact. 
         FIG. 6  is a flowchart illustrating another embodiment of a method for formation of overlapping first and second contacts. 
         FIGS. 7 through 10  are a series of cross sectional views illustrating another embodiment of the method of  FIG. 6  for formation of overlapping first and second contacts in which: 
         FIG. 7  illustrates the formation of a first contact. 
         FIG. 8  illustrates the device of  FIG. 7  after etching a recess for a second contact and removing a top portion of the first contact. 
         FIG. 9  illustrates the device of  FIG. 8  after removing an additional top portion of the etched first contact. 
         FIG. 10  illustrates the device of  FIG. 9  after formation of the second contact in the recess and over the top surface of the partially removed first contact. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of overlapping contacts (or interconnects) for a semiconductor device, and methods for forming overlapping contacts, are provided, with exemplary embodiments being discussed below in detail. The overlapping contacts are formed subsequently, during different processing steps. Physical means may be used to remove a top portion of the first contact before formation of the second contact. A portion of the second contact may then be formed on a top surface of the partially removed first contact such that the second contact overlaps the first contact. This results in a relatively large contact interface are between the first and second contacts, and gives a correspondingly improved electrical connection between the first and second contacts. Partial removal of the first contact may be accomplished by etching, or by etching in conjunction with an agitated physical clean in various embodiments. Overlapping contacts may be used in many types of electrical devices, including but not limited to static random access memory (SRAM), and for connections including but not limited to logical cross-couples or power rails. 
     Turning to  FIG. 2 , a flowchart of an embodiment of a method  200  for formation of overlapping first and second contacts is shown. In block  201 , a first contact, as shown in  FIG. 3 , is formed. The first contact  302  is formed in a dielectric layer  301   a - b . The first contact  302  includes a liner, including outer liner layer  303  and inner liner layer  304 , and a contact fill metal  305 . Contact fill metal  305  may be, for example, tungsten. Outer liner layer  303  may be, for example, titanium nitride, and the inner liner layer  304  may be, for example, titanium. The dielectric layer  301   a - b  may include, for example, a nitride or an oxide. In the exemplary embodiment shown in  FIG. 3 , the dielectric layer includes top dielectric layer  301   a  and bottom dielectric layer  301   b  comprising different dielectric materials; in other embodiments, the dielectric layer may include a single dielectric material. 
     In block  202  of  FIG. 2 , a recess is formed in the dielectric layer, and a top portion of first contact  302  is removed. Recess formation and partial removal (or pullback) of first contact  302  may be performed by etching. As shown in  FIG. 4 , the etch process performed in block  202  of  FIG. 2  forms a recess  402  in the dielectric layer  301   a - b , and also removes a top portion of the first contact  302 , resulting in an etched first contact  401 . In an exemplary embodiment, the etch process may include reactive ion etching (RIE) or wet etching. In embodiments in which the dielectric layer  301   a - b  includes top dielectric layer  301   a  and bottom dielectric layer  301   b  comprising different dielectric materials, the recess  402  may be formed in the top dielectric layer  301   a , such that the interface between the top dielectric layer  301   a  and bottom dielectric layer  301   b  serves as an etch stop during the etch that forms the recess  402 , thereby determining the depth of the recess  402  in dielectric layer  301   a - b . In such an embodiment, the bottom of recess  402  is therefore located at the top of the bottom dielectric layer  301   b , as shown in  FIG. 4 . 
     Lastly, in block  203  of  FIG. 2 , a second contact  501  is formed adjacent to and on a top surface of the etched first contact  401 , as shown in  FIG. 5 . Second contact  501  may comprise outer and inner liner layers and a contact fill metal such as are described above with respect to first contact  302  in the section discussing block  201 . At least a portion of the second contact  501  is located directly on top of the etched first contact  401 , such that contacts  401  and  501  overlap, and the outer liner layer of second contact  501  is in contact with the fill metal on the top surface of the first contact  401  along contact interface  502 . Contacts  401  and  501  are electrically connected along a contact interface  502  at the top surface of first contact  401 , which provides a relatively large contact interface area, in turn allowing a good electrical connection between contacts  401  and  501 . After the formation of second contact  501 , the device  500  may be polished using, for example, chemical mechanical polishing (CMP). 
     In a second embodiment of a method for formation of overlapping first and second contacts, which is illustrated in  FIG. 6 , partial removal of the first contact is a two-step process, including an additional partial removal step that is performed in after the etching is completed and the recess is formed. The recess may be formed such that a top portion of the partially removed first contact is completely surrounded by the recess, i.e., is not anchored in the dielectric. The additional partial removal step includes an aggressive agitated physical clean such as megasonics to physically knock down and remove a top portion of the partially removed first contact that is not anchored in the dielectric. Turning to  FIG. 6 , in block  601 , a first contact, as shown in  FIG. 7 , is formed. The first contact  702  is formed in a dielectric layer  701 . The first contact  702  includes contact fill metal  705  and a liner including outer liner layer  703  and inner liner layer  704 . Contact fill metal  705  may be tungsten, for example. Outer liner layer  303  may be titanium nitride, for example, and inner liner layer  704  may be titanium, for example. The dielectric layer  701  may be a nitride or an oxide, and may include top and bottom dielectric layers comprising different dielectric materials in some embodiments (as described above with respect to dielectric layer  301   a - b ), or a single dielectric material in other embodiments. 
     In block  602 , a recess is etched in the dielectric, and a top portion of the first contact is removed during the etch. As shown in  FIG. 8 , the etch performed in block  602  of  FIG. 6  forms a recess  802  in the dielectric  701 , and also removes a top portion of first contact  702 , resulting in etched first contact  801 . The etch may include RIE or wet etching. Recess  802  is formed all around the etched first contact  801 , such that an upper portion of the etched first contact  801  is not anchored in the dielectric  701 . 
     Then, in block  603  of  FIG. 6 , an additional top portion of etched first contact  801  is removed, resulting in partially removed first contact  901  shown in  FIG. 9 . Removal of the additional top portion of the contact may allow for a longer contact interface between the first contact and the second contact (discussed below with respect to block  604  of  FIG. 6 ). Any appropriate amount of the etched first contact  801  may be removed during the additional contact removal step of block  603  of  FIG. 6 ; some or all of the top portion of the first contact  801  that is not anchored in the dielectric  701  may be removed. In some embodiments, the top of partially removed first contact  901  may be approximately even with the surface of dielectric  701  after the additional partial contact removal step of block  603  of  FIG. 6 . The additional partial contact removal may include an aggressive agitated physical clean of the top surface of the etched first contact  801 . The agitated physical clean may include megasonics, ultrasonics, cryogenic aerosol, or a pressurized and atomized liquid in various embodiments. In the ultrasonics and megasonics techniques, energy is applied to a liquid solution that is placed on the surface being cleaned, causing microbubbles to form in the liquid solution (referred to as a cavitation event). When the microbubbles collapse, the energy from the collapse is transferred to the surface, resulting in the removal of surface particles or patterning of damage-sensitive portions of the surface. Cryogenic aerosols are another physical method of creating intentional pattern damage on a surface. In the cryogenic aerosol technique, a surface is bombarded with an aerosol mixture, which may include argon (Ar), nitritrogen gas (N 2 ) and/or carbon dioxide (CO 2 ) mixtures. The aerosol mixture vaporizes when it hits the surface. The combination of physical bombardment by the aerosol mixture coupled with the sublimation phase change of the aerosol mixture that occurs on the surface removes particles from or cause desired pattern damage to the surface. Atomized liquid droplets may also be used to cause pattern damage to a surface, with appropriate droplet size and pressure of the atomized liquid. Any of these approaches may be used to physically knock down and remove the upper portion of the etched first contact  801  that is not anchored in the dielectric  701 . 
     Lastly, in block  604  of  FIG. 6 , a second contact  1001  is formed over the top surface of the partially removed first contact  901 , as shown in  FIG. 10 . Second contact  1001  may comprise outer and inner liner layers and a contact fill metal such as are described above with respect to first contact  702  in the section discussing block  601 . Second contact  1001  completely covers partially removed first contact  901 , such that contacts  901  and  1001  overlap, and the outer liner layer of second contact  1001  is in contact with the fill metal on the top surface of the first contact  901  along contact interface  1002 . Contacts  901  and  1001  are electrically connected along contact interface  1002  at the top of first contact  901 , which provides a relatively large contact surface area, allowing a good electrical connection between contacts  901  and  1001 . After formation of second contact  1001 , the device  1000  may be polished using, for example, CMP. 
     The technical effects and benefits of exemplary embodiments include improvement of an electrical connection between two contacts formed during different processing steps by increasing the area of the interface between the two contacts. 
     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 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.