Abstract:
The present invention relates to a method for fabricating interconnecting lines and vias in a layer of insulating material. A via is formed in the layer of insulating material. A protective material is formed so as to be conformal to at least edges and sidewalls of the via, the protective material facilitating shielding of at least the edges and sidewalls of the via from a trench etch step. The trench etch step is performed to form a trench opening in the insulating material. The via and trench are filled with a conductive metal.

Description:
TECHNICAL FIELD 
     The present invention generally relates to semiconductor processing, and in particular to a method for improving a dual damascene process. 
     BACKGROUND OF THE INVENTION 
     The escalating requirements for density and performance associated with ultra large scale integration (ULSI) circuits require responsive changes in interconnection technology which is considered a very demanding aspect of ULSI technology. High density demands for ULSI integration require planarizing layers with minimal spacing between conductive lines. 
     Single damascene is a technique developed to address disadvantages (e.g., poor metal step coverage, residual metal shorts, low yields, uncertain reliability, and poor ULSI integration extendability) associated with traditional etch back methods. Damascene, an art which has been employed for centuries in the fabrication of jewelry, has been adapted for application in the semiconductor industry. Damascene basically involves the formation of a trench which is filled with a metal. Thus, damascene differs from traditional etch back methods which involve building up a metal wiring layer and filling the interwiring spaces with a dielectric material. 
     Single damascene techniques offer the advantage of improved planarization as compared to etch back methods; however, single damascene is time consuming in that numerous process steps are required. Undesirably, an interface exists between the conductive via and conductive wiring. Moreover, adequate planarization layers containing an interwiring spacing less than 0.35 μm are difficult to achieve. 
     An improvement to single damascene is dual damascene which involves substantially simultaneous formation of a conductive via and conductive wiring. The dual damascene technique requires less manipulative steps than the single damascene technique and eliminates the interface between the conductive via and conductive wiring which is typically formed by the single damascene technique. In very and ultra large scale integration (VLSI and ULSI) circuits, an insulating or dielectric material, such as silicon oxide, of the semiconductor device in the dual damascene process is patterned with several thousand openings for the conductive lines and vias which are filled with metal, such as aluminum, and serve to interconnect active and/or passive elements of the integrated circuit. The dual damascene process also is used for forming multilevel signal lines of metal, such as copper, in the insulating layers, such as polyimide, of multilayer substrate on which semiconductor devices are mounted. 
     A conventional dual damascene process is illustrated in FIGS. 1 a - 1   h  in connection with a semiconductor structure  18 . FIG. 1 a  illustrates an insulative layer  20  formed on a semiconductor substrate (not shown). A photoresist layer  22   a  is formed on the insulative layer  20 . The photoresist layer  22   a  is patterned using conventional techniques to form a first opening  30  (FIG. 1 b ). Anisotropic reactive ion etching (RIE) is performed to form a via  40  (FIG. 1 c ) in the insulative layer  20 . Subsequently, a second layer of photoresist  22   b  (FIG. 1 d ) is formed over the structure  18 . 
     The second photoresist layer  22   b  is patterned to form a second opening  48  (FIG. 1 e ) about the size of the ultimate trench. Anisotropic RIE is again performed to form a trench  50  (FIG. 1 f ) in the insulative layer  20 . Although this standard dual damascene technique offers advantages over other processes for forming interconnections, it has a number of disadvantages, such as the edges of the via openings and the sidewalls of the via  40  in the lower half of the insulating layer  20  are poorly defined because of the two etchings and the via edges and sidewalls being unprotected during the second etching. More particularly, gases from the second etch step leak under photoresist portion  22   c  and damage edges and sidewalls of the via  40  as illustrated in FIGS. 1 g  and  1   h.    
     In view of the above, improvements are needed to mitigate poor edge and sidewall definition of vias associated with conventional dual damascene processes. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a method for mitigating poor edge and sidewall definition in vias common to conventional dual damascene processes by employing a conformal insulating layer to protect edges and sidewalls of a via from exposure to a second etch step (to form trenches). In particular, after a first etch step to define a via, a conformal layer of insulating material is formed to insulate edges and sidewalls of the via. The conformal layer protects the via edges and sidewalls from exposure to reactive gases of the second etch step. After the second etch step is substantially complete, the conformal layer is removed to leave a dual damascene structure (trench and via) which has improved via edge and sidewall definition as compared to many structures formed under conventional dual damascene methodologies. 
     One aspect of the invention relates to a method for fabricating interconnecting lines and vias in a layer of insulating material. A via is formed in the layer of insulating material. A protective material is formed so as to be conformal to at least edges and sidewalls of the via. The protective material facilitates shielding of at least the edges and sidewalls of the via from a trench etch step which is performed to form a trench opening in the insulating material. 
     Another aspect of the present invention relates to a dual damascene structure, including: an insulating material; a via formation in the insulating material; a protective layer covering at least sidewalls of the via formation; and a conductive line trench formation. 
     Still another aspect of the present invention relates to a dual damascene structure, including: an insulating material; a via formation in the insulating material; and means for insulating at least edges and sidewalls of the via formation from an etch step to form a conductive line trench formation. 
     Yet another aspect of the present invention relates to a method for fabricating interconnecting lines and vias in a layer of insulating material. A first photoresist layer is formed on the insulating material. The insulating material includes at least one of: silicon oxide (SiO), silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ), (SiN), silicon oxynitride (SiO x N y ), fluonated silicon oxide (SiO x F y ), and polyimide(s). The first photoresist layer is patterned to define a via The via is formed in the layer of insulating material. A protective material is formed so as to be conformal to at least edges and sidewalls of the via The protective material facilitates shielding of at least the edges and sidewalls of the via from a trench etch step. The protective material includes at least one of: a nitride and a polymer. Excess portions of the first photoresist layer and protective material are removed. A second photoresist layer is formed on the insulating material. The second photoresist layer is patterned to define a trench. The trench etch step is performed to form the trench in the insulating material. The via and trench are filled with a conductive metal. 
     To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  is a schematic illustration of an oxide layer covered with a photoresist layer in accordance with a conventional dual damascene process; 
     FIG. 1 b  is a schematic illustration of the photoresist layer of FIG. 1 a  patterned in accordance with a conventional damascene process; 
     FIG. 1 c  is a schematic illustration of the structure of FIG. 1 b  after the oxide layer has been etched in accordance with a conventional damascene process; 
     FIG. 1 d  is a schematic illustration of the structure of FIG. 1 c  after additional photoresist is applied thereon in accordance with a conventional damascene process; 
     FIG. 1 e  is a schematic illustration of the structure of FIG. 1 d  after the additional photoresist has been patterned in accordance with a conventional damascene process; 
     FIG. 1 f  is a schematic illustration of the structure of FIG. 1 e  after the oxide layer is etched for a second time in accordance with a conventional damascene process; 
     FIG. 1 g  is a schematic illustration of the structure of FIG. 1 e  after etchant gases from the second etch step damaged edges and sidewalls of the via in accordance with a conventional damascene process; 
     FIG. 1 h  is a schematic illustration of the structure of FIG. 1 g  after remaining portions of photoresist are removed in accordance with a conventional damascene process; 
     FIG. 2 is a schematic illustration of an oxide layer covered with a photoresist layer in accordance with the present invention; 
     FIG. 3 is a schematic illustration of the structure of FIG. 2 after the photoresist layer has been patterned in accordance with the present invention; 
     FIG. 4 is a schematic illustration of the structure of FIG. 3 undergoing an etching step in accordance with the present invention; 
     FIG. 5 is a schematic illustration of the structure of FIG. 4 after the etching step is substantially complete in accordance with the present invention; 
     FIG. 6 is a schematic illustration of the structure of FIG. 5 undergoing a stripping step to remove excess photoresist in accordance with the present invention; 
     FIG. 7 is a schematic illustration of the structure of FIG. 6 after the stripping step is substantially complete in accordance with the present invention; 
     FIG. 8 is a schematic illustration of the structure of FIG. 7 undergoing a step to form a conformal insulating layer in accordance with the present invention; 
     FIG. 9 is a schematic illustration of the structure of FIG. 8 after the insulating conformal layer is substantially complete in accordance with the present invention; 
     FIG. 10 is a schematic illustration of the structure of FIG. 9 undergoing a etching step to remove excess portions of the conformal insulating layer in accordance with the present invention; 
     FIG. 11 is a schematic illustration of the structure of FIG. 10 after the etching step is substantially complete in accordance with the present invention; 
     FIG. 12 is a schematic illustration of the structure of FIG. 11 after a second photoresist layer has been formed on the structure in accordance with the present invention; 
     FIG. 13 is a schematic illustration of the structure of FIG. 12 after the second photoresist layer has been patterned in accordance with the present invention; 
     FIG. 14 is a schematic illustration of the structure of FIG. 13 undergoing a second oxide layer etch in accordance with the present invention; 
     FIG. 15 is a schematic illustration of the structure of FIG. 14 after the second oxide layer etch is substantially complete in accordance with the present invention; 
     FIG. 16 is a schematic illustration of the structure of FIG. 15 undergoing a stripping step to remove excess portions of photoresist and insulating material in accordance with the present invention; and 
     FIG. 17 is a schematic illustration of a substantially complete dual damascene structure in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. 
     FIG. 2 illustrates an insulator layer  60  which is formed on a semiconductor substrate (not shown). Any suitable technique (e.g., thermal oxidation, plasma enhanced chemical vapor deposition (CVD), thermal enhanced CVD and spin on techniques) may be employed in forming the insulating layer  60 . Preferably, the insulating layer  60  is silicon dioxide (SiO 2 ) with a thickness of about 0.8 to 1.0 microns. Other usuable insulating materials are silicon nitride (Si 3 N 4 ), (SiN), silicon oxynitride (SiO x N y ), and fluonated silicon oxide (SiO x F y ), and polyimide(s). A photoresist layer  62   a  is formed on the insulating layer  60 . The photoresist layer  62   a  is patterned using conventional techniques to form a first opening  70  (FIG.  3 ). The size of the first opening  70  is about the size of the ultimate via. An etch step  80  (e.g., anisotropic reactive ion etching (RIE)) (FIG. 4) is performed to form a via  90  (FIG. 5) in the insulating layer  60 . For example, the insulating layer  60  at the first opening  70  is anisotripically etched with a plasma gas(es), herein carbon tetrafloride (CF 4 ) containing fluorine ions, in a commercially available etcher, such as a parallel plate RIE apparatus or, alternatively, an electron cyclotron resonance (ECR) plasma reactor to replicate the mask pattern of the patterned photoresist layer  62   a  to thereby create the via  90  in the insulating layer  60 . 
     FIG. 6 illustrates a stripping step  100  (e.g., ashing in an O 2  plasma) to remove remaining portions of the photoresist layer  62   a . FIG. 7 illustrates a partially complete dual damascene structure  110  after the stripping step  100  is substantially complete. Next, a deposition step  120  is performed on the structure  110  to form a protective conformal layer  130  (FIG. 9) over the structure  110 . 
     In one embodiment, the protective conformal layer  130  includes nitride (referenced as  130 ′). The deposition step  120  performed on the structure  110  includes a chemistry suitable to form a nitride layer conformal to the exposed surface of the structure  110 . It is to be appreciated that one skilled in the art could readily tailor without undue experimentation a suitable chemistry to form the conformal nitride coating  130 ′. The chemistry and duration thereof may be suitably tailored to form the conformal nitride coating  130 ′ at substantially any desired thickness (e.g., between about the range of 10-1000 Å). 
     According to alternative embodiments of the present invention, the protective conformal layer  130  is a carbon/oxygen based polymer (referenced by  130 ″) conformal to the exposed surface of the structure  110 . The structure  110  is exposed to at least one of a CHF 3  chemistry, an HBR chemistry, a CH 3 F chemistry, and a CH 2 F 2  chemistry to form the conformal polymer coating  130 ″ on the structure  110 . Oxygen based reactive gases are reduced as compared to a typical etch chemistry so that the conformal polymer coating  130 ″ is formed over the structure  110 . 
     One specific example of a suitable chemistry to form the conformal polymer layer  130 ″ includes using a relatively high pressure of 50-100 mT, relatively low power of less than or equal to 500 W, and a temperature of below 80° C. It is to be appreciated that one skilled in the art could readily tailor without undue experimentation a suitable chemistry to form the conformal polymer coating  130 ″. As discussed in greater detail below, the etch chemistry and duration thereof may be suitably tailored to form the conformal polymer layer  130 ″ at substantially any desired thickness (e.g., between about the range of 10-1000 Å). 
     Below are some specific examples of chemistries that may be employed in forming the conformal polymer layer  130 ″. 
     EXAMPLE 1 
     A MERIE method is used with CHF 3  (50 to 200 sccm) with reactant gases of: Ar (100 to 500 sccm) and O 2 (10 to 50 sccm) at a power level within the range of about 100 to 500 W and pressure within the range of about 60 to 100 mT. 
     EXAMPLE 2 
     A MERIE method is used with HBR (100 to 250 sccm) with reactant gases of: Ar (100 to 500 sccm) at a power level within the range of about 100 to 500 W, and pressure within the range of about 500 to 100 mT. 
     EXAMPLE 3 
     A MERIE method is used with CH 3 F (50 to 250 sccm) with reactant gases of: Ar (50 to 200 sccm) and N 2  (10 to 50 sccm) at a power level within the range of about 100 to 500 W, and pressure within the range of about 50 to 100 mT. 
     EXAMPLE 4 
     A MERIE method is used with CH 2 F 2  (100 to 200 sccm) with reactant gases of: Ar (50 to 200 sccm) and N 2  (10 to 50 sccm) at a power level within the range of about 100 to 500 W, and pressure within the range of about 50 to 100 mT. 
     FIG. 9 illustrates the structure  110  after the deposition step  120  is substantially complete. The protective layer  130  is conformal to the exposed surface of the structure  110  with a substantially uniform thickness. 
     FIG. 10 illustrates a directional etch step  140  being performed to remove a predetermined thickness of the protective layer  130 . An etch chemistry including CHF 3 , O 2 , Ar and CF 4 , for example, is employed to perform a dry directional etch of the protective layer  130 . Preferably, the directional etch  140  is performed to remove an amount of the protective layer  130  equivalent to the conformal thickness of the protective layer  130 . 
     Substantial completion of the etch step  140  results in a structure  150  shown in FIG.  11 . The structure  150  includes protective sidewalls  160  which protect edges  162  (FIG. 15) and sidewalls  164  (FIG. 15) of the via  90  from a second etch step  170  (FIG. 14) to form a conductive line trench  180  (FIG.  15 ). 
     FIG. 12 illustrates a second photoresist layer  190  formed on the structure  150 . The second photoresist layer  190  is patterned to form a second opening  200  (FIG. 13) about the size of the ultimate trench  180 . The second etch step (preferably an anisotropic RIE step)  170  (FIG. 14) is performed to form the trench  180  (FIG. 15) in the insulating layer  60 . 
     Turning now to FIG. 15, the sidewalls  160  resulting (from the conformal protective layer  130 ) protect the edges  162  and sidewalls  164  of the via  90  thus mitigating damage thereto from the second etch step  170 . FIG. 16 illustrates a cleaning step  220  to remove remaining portions of photoresist  190  and the conformal protective sidewalls  160  from the structure  150 . FIG. 17 illustrates the dual damascene structure  150  in relevant part. The structure  150  exhibits well defined edges and sidewalls for the via  90  as compared to the structure  20  (FIG. 1 h ) formed using conventional dual damascene techniques. 
     Thereafter, the dual damascene structure  150  is filled with a metal (e.g., aluminum, aluminum alloy, copper, copper alloy, tungsten, tungsten alloy) so as to form a conductive via and conductive line. 
     What has been described above are preferred embodiments of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims.