Abstract:
A method ( 100 ) of fabricating an electronic device ( 200 ) formed on a semiconductor wafer. The method forms a dielectric layer ( 226 ) in a fixed position relative to the wafer, where the dielectric layer comprises an atomic concentration of each of silicon, carbon, and oxygen. After the forming step, the method exposes ( 118 ) the electronic device to a plasma such that the atomic concentration of carbon in a portion of the dielectric layer is increased and the atomic concentration of oxygen in a portion of the dielectric layer is decreased. After the exposing step, the method forms a barrier layer ( 120 ) adjacent at least a portion of the dielectric layer.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     The present embodiments relate to semiconductor devices and methods and are more particularly directed to improving adhesion to a silicon-carbon-oxygen dielectric layer. 
     Semiconductor devices are prevalent in countless different aspects of contemporary society, and as a result, the marketplace for such devices continues to advance at a fairly rapid pace. This advancement is evident in many respects and relates to semiconductor devices either directly or indirectly as well as the methods for forming such devices. For example, the advancement affects numerous device attributes and increases the need for attention to such attributes during design and manufacturing, where such attributes include device size, reliability, yield, and cost. These aspects as well as others are addressed by the prior art and are further improved upon by the preferred embodiments as detailed below. 
     By way of further background, the preferred embodiments relate to adhesion to dielectric layers in semiconductor devices. More specifically, the preferred embodiments relate to a dielectric layer that includes all of silicon, carbon, and oxygen and the adhesion of such a layer to a barrier layer that is to operate as a barrier between the dielectric layer and a metal such as copper. Turning first to the dielectric layer having silicon, carbon, and oxygen, such materials are sometimes combined in a film known as organo-silicon glass (“OSG”), which is commercially available from Novellus and Applied Materials. OSG layers are attractive for various reasons known in the art, such as a favorable (i.e., relatively low) dielectric constant. Turning next to copper, its use is becoming more preferred in the art, particularly as an interconnect metal, because relative to previously used metals, such as aluminum, copper provides lower resistance and, hence, greater reliability. 
     Given the preceding, when copper is used in a same device as an OSG layer, typically a barrier layer is formed between the copper and OSG. The barrier layer prevents or reduces the undesirable chance of the Copper diffusing into the dielectric. However, in connection with the preferred embodiments, the present inventors have determined that when placing a barrier layer between OSG and copper, the adhesion of the barrier layer to the OSG has been unacceptable. For example, such adhesion has been empirically evaluated using several known testing techniques, and those techniques have demonstrated that the barrier layer will detach from the OSG, thereby failing to serve its underlying purposes as a barrier to a subsequently-formed copper layer/device. For example, tape testing has been used, wherein a semiconductor wafer, on which a barrier layer is formed on an OSG layer, is scribed and then tape is applied to the wafer and removed to determine if the layers remain intact. Under such testing, cracks have been found to form at the interface of the barrier layer and the OSG layer, thereby demonstrating qualitatively that the bond between the two layers is unacceptable. As another example, four point bend testing has been performed, wherein a same type of semiconductor wafer as described above is subjected to flexing forces at its ends, in combination with other forces applied more centrally to the wafer. Using this test, a quantitative measure is made to determine the end-applied force at what there is a failure between the OSG and the barrier layer, where such a failure may occur as a crack or break of the barrier layer, or the barrier layer may delaminate from the OSG layer. As a final test, chemical mechanical polishing (“CMP”) may be applied to the above-described wafer. This test is sometimes preferred in that it represents an actual manufacturing step, since CMP is often used to planarize various layers before subsequent processing steps. In any event, under CMP, the present inventors also have observed failures between an adjacent OSG and barrier layer. 
     In view of the above, the present inventors provide below alternative embodiments for improving upon various drawbacks of the prior art. 
     BRIEF SUMMARY OF THE INVENTION 
     In one preferred embodiment, there is a method of fabricating an electronic device formed on a semiconductor wafer. The method forms a dielectric layer in a fixed position relative to the wafer, where the dielectric layer comprises an atomic concentration of each of silicon, carbon, and oxygen. After the forming step, the method exposes the electronic device to a plasma such that the atomic concentration of carbon in a portion of the dielectric layer is increased and the atomic concentration of oxygen in a portion of the dielectric layer is decreased. After the exposing step, the method forms a barrier layer adjacent at least a portion of the dielectric layer. 
     Other aspects are also disclosed and claimed. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 illustrates a flow chart of one preferred embodiment for forming a device that includes a barrier layer adjacent a dielectric layer that includes silicon, carbon, and oxygen. The embodiment described here is often called dual damascene and can be formed with many variations. The invention also includes structures that are formed by a single damascene process where the trench and via levels are formed separately. 
     FIG. 2 illustrates a cross-sectional view of a portion of a semiconductor device according to the preferred embodiment and including a substrate in which a transistor is formed, and overlying the transistor is a dielectric layer in which a metal conductor is formed. 
     FIG. 3 illustrates a portion of the device of FIG.  2  and including the metal conductor as covered by a first barrier layer, where the first barrier layer is covered by a first silicon-carbon-oxygen containing layer, and the first silicon-carbon-oxygen containing layer is covered by both a second barrier layer and a second silicon-carbon-oxygen containing layer. 
     FIG. 4 illustrates the device of FIG. 3 after additional fabrications steps, including the formation of a photoresist layer and an etch through that photoresist layer down to the second barrier layer to form a trench through the second silicon-carbon-oxygen containing layer. 
     FIG. 5 illustrates the device of FIG. 4 after additional fabrications steps, including the formation of a photoresist. 
     FIG. 6 illustrates the device of FIG. 5 after additional fabrications steps, including an etch to form a via through the first silicon-carbon-oxygen containing layer and down to the metal contact. 
     FIG. 7 illustrates the device of FIG. 6 after a strip of both the photoresist and a dielectric layer. 
     FIG. 8 illustrates the device of FIG. 7 subjected to an argon plasma. 
     FIG. 9 illustrates the device of FIG. 8 subjected to a high energy He—H 2  plasma 
     FIG. 10 illustrates the device of FIG. 9 after the formation of a metal barrier layer and a copper layer. 
     FIG. 11 illustrates the device of FIG. 10 after a planarization step. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a flow chart of one preferred embodiment of a method  100  for forming a device according to the preferred embodiment. To further illustrate method  100  and the device that it forms, the various steps of method  100  are discussed below with additional reference to the cross-sectional views shown in FIGS. 2 through 11, as will further demonstrate the inventive scope. 
     The preferred embodiments relate in part to the treatment of a dielectric layer that includes silicon, carbon, and oxygen, where such materials are sometimes combined in a film known as organo-silicon glass (“OSG”). OSG layers may appear at various levels in a semiconductor device and, thus, by way of introduction, an example for use in subsequent discussion is now provided with reference to FIG. 2 which illustrates a semiconductor device  200 . Further, both the prior art and the inventive embodiments described below may be implemented in connection with a structure such as is shown in FIG. 2, where further elaboration for additional processing steps is provided below according to the preferred embodiments. Additionally, while the methods of the preferred embodiments are described with reference to FIGS. 2 through 11, those methods may be applied to any type of device structure (e.g., metal interconnects, metal lines, metal gates, or other conductive structures) and to any type of device (e.g. memory devices, logic devices, power devices, digital signal processors, or microprocessors) in which an OSG layer benefits from improved adhesion to an adjacent barrier layer. 
     Turning first to device  200  of FIG. 2, it includes various device components that are formed as is known in the art, and which may form various devices such as a transistor as shown by way of example formed in connection with an active area  201  formed in a substrate  202  (e.g., silicon). Substrate  202  is part of, or represents, a semiconductor wafer providing the foundation for device  200 . Further, the wafer may be enclosed within one or more tools as further discussed below to accomplish the various steps described in this document. Active area  201  is generally defined between isolation regions  204   1 and  204   2 . Within active area  201 , source and drain regions  208   1  and  208   2 , a gate dielectric  210 , a conductive gate  212 , and sidewall insulators  214   1  and  214   2  are formed, thereby creating a transistor by way of example. A dielectric layer  216  is formed overlying the transistor shown therein and is planarized, where dielectric layer  216  therefore overlies the portion of the device containing active (and possibly passive) components formed as is known in the art. A second dielectric layer  218  is shown to overlie dielectric layer  216 , although in fact layers  216  and  218  may be one layer. 
     Continuing with FIG.  2  and the additional items therein, note that multiple levels of interconnect structure may be formed and may connect to one another and also to various of the components formed in relation to substrate  202 . Due to the many possibilities of the connections that may be achieved by such interconnect structures and the components to which they may connect, considerable extra detail is not necessary with respect to a specific connection as it may be readily ascertained by one skilled in the art. Thus, only a particular example is provided below merely to demonstrate a context and not by way of limitation for the intended inventive scope. For the specific example, a liner/barrier layer  220  is formed within a trench structure formed in dielectric layer  218 , where liner/barrier layer  220  may be one of various materials including tantalum, tantalum nitride, titanium nitride, tungsten, tungsten nitride, and still others. Further, a conductor  222  is formed to align with liner/barrier  220  and is planarized along the top surface of dielectric layer  218 . By way of example, assume that conductor  222  is copper, although it may be formed from other conducting materials. Thereafter, a barrier layer  224 , often referred to as an etch stop layer and commonly on the order of a few hundred angstroms of silicon nitride or another dielectric barrier material, is formed over dielectric layer  218  and, thus, also over the top of conductor  222 . 
     The remaining illustration of FIG. 2 introduces aspects particularly relevant to the preferred embodiment. Overlying barrier layer  224  is formed a dielectric layer  226 . This dielectric layer  226  could be deposited by Chemical Vapor Deposition (“CVD”), spin on process, or another deposition process. The thickness of dielectric layer  226  is based upon performance requirements Further, dielectric layer  226  preferably has a relatively low dielectric constant and is formed of OSG, that is, it includes some combination of at least silicon, carbon, and oxygen. For sake of simplified reference, therefore, for the remainder of this document dielectric layer  226  is referred to as OSG layer  226 . As detailed below, the preferred embodiments relate to improving adhesion of a subsequent barrier layer to OSG layer  226 . Further in this regard and for the sake of simplifying the remaining Figures, much of the detail from FIG. 2 is removed from the following Figures by illustrating cutaway depictions from layer  218  upward, where the focus therefore is with respect to OSG layer  226 ; however, one skilled in the art should appreciate that the configurations illustrated in the remaining Figures are intended to also include the devices of FIG. 2 (or other devices, as mentioned above). 
     Looking to FIG. 3, it illustrates device  200  of FIG. 2 after additional fabrications steps which are now explored also by returning to method  100  of FIG.  1 . By way of further introduction, as a contemporary example method  100  includes the steps to form a so-called dual damascene structure, where that name typically refers to the formation of a void within device layers, where the void includes two portions. These two portions are sometimes referred to using different names, where by way of example a generally vertical and narrower void is sometimes referred to as a via and a generally horizontal and often wider void is referred to as a trench. The dual damascene process in general is known in the art, and indeed it may be achieved with different steps, or with comparable steps in varying orders, and sometimes with or without certain barrier layers. Thus, method  100  with respect to the dual damascene aspects is only by way of example. Given this background, method  100  commences with a step  102  where a barrier layer  228  is formed overlying OSG layer  226 . Barrier layer  228 , by way of example, may be formed in the same or a similar manner as barrier layer  224  and, thus, forms an etch stop layer typically on the order of a few hundred angstroms of silicon nitride. Following step  102 , step  104  forms an additional dielectric layer  230  on top of barrier layer  228 . In the preferred embodiment, dielectric layer  230  is formed of the same OSG material as was layer  226 . The thickness of dielectric layer  230  may be the same or differ from that of dielectric layer  226 . Also for sake of reference, in the remainder of this document dielectric layer  230  is referred to as OSG layer  230 . 
     FIG. 4 illustrates device  200  of FIG. 3 after additional fabrications steps, and according to techniques known in the art. Continuing with method  100 , in step  106  a photoresist layer  232  is formed, patterned and etched. Thus, in the perspective of FIG. 4, all three steps have been performed with respect to photoresist layer  232 , thereby forming a first void  234 , sometimes referred to as a trench, through OSG layer  230  and stopping on barrier (or etch stop) layer  228 . Lastly, for reasons more clear below, the patterning and etching to form void  234  are preferably such that the void vertically aligns at least in part with conductor  222 . 
     FIG. 5 illustrates device  200  of FIG. 4 after additional fabrications steps, and according to techniques known in the art. Continuing with method  100 , in step  108 , the remainder of photoresist layer  232  from FIG. 4 is stripped (with an appropriate cleaning step, if desired), and an additional dielectric layer  236  is formed over device  200  and so that it fills void  234  which was shown in FIG.  4 . Next, in a step  110 , another photoresist layer  238  is formed and patterned. Photoresist layer  238  is patterned such that is an area  240  will be removed in a subsequent etch, as described below. Further, area  240  is also preferably vertically aligned at least in part with conductor  222 , as well as with the area in which void  234  from FIG. 4 was filled with dielectric layer  236 . 
     FIG. 6 illustrates device  200  of FIG. 5 after additional fabrications steps, and according to techniques known in the art. Continuing with method  100 , in step  112 , photoresist layer  238  is etched such that the material of that layer is removed from area  240  as was shown in FIG. 5, and the etch continues to create a void  242 , sometimes referred to as a via, through all of dielectric layer  236 , barrier layer  228 , OSG layer  226 , and barrier layer  224 ; thus, the etch reaches the upper surface of conductor  222 . Accordingly, and as shown below, electrical contact ultimately can be made in the area of trench  242  to conductor  222 . 
     FIG. 7 illustrates device  200  of FIG. 6 after additional fabrications steps, and according to techniques known in the art. Continuing with method  100 , in step  114 , both photoresist layer  238  and dielectric layer  236 , as were shown in FIG. 5, are stripped from device  200 . Since these two layers are formed from different materials, different stripping techniques may be employed. In any event, once they are removed, a single void  244  remains through OSG layers  230  and  226  to an upper surface of conductor  222 . Note that void  244  effectively includes two portions, one with a narrower width closer to conductor  222  as between the etched portions of OSG layer  226  and another with a wider width as between the etched portions of OSG layer  230  and away from conductor  222 ; this double-tier structure is the result of a typical dual damascene process. 
     FIG. 8 illustrates device  200  of FIG. 7 after additional fabrications steps, but note here that various of the remaining steps provide a departure from the prior art and further provide for improved adhesion to the exposed vertical and horizontal portions of OSG layers  230  and  226 , as between those portions and a later-formed barrier layer. Turning then to FIG.  8  and also continuing with method  100  in FIG. 1, in step  116 , device  200  is exposed to argon, preferably in an argon sputter etch process. Such a process is typically achieved in a sputter etch chamber where the argon ions are accelerated onto the wafer in which device  200  is formed. The argon sputter of step  116  is perceived to have various benefits. First, the argon cleans various contaminants that are likely to remain on the upper surface of conductor  222 , as resulting from preceding method  100  steps. Such contaminants may include etch residue and polymers from previous etches, as well as copper oxide in the case where conductor  222  is copper. Second, the argon sputter will slightly round the inward edges of OSG layer  230 , where such edges are shown as  230 ′ in FIG.  8 . For reasons discussed below, such rounding may be beneficial in certain embodiments. Lastly, note that step  116  in most practical implementations is desirable due to the high probability of the existence of contaminants once void  244  is formed. However, the necessity as well as duration of step  116  may be adjusted based on various parameters, including whether the void is formed by a single or dual damascene process. Indeed, if the previous steps were followed by sufficient cleaning operations such that the contaminants with void  244  were negligible, then in such a case, step  116  could be eliminated in an alternative embodiment. 
     FIG. 9 illustrates device  200  of FIG. 8 after additional fabrications steps, as described in method  100  in FIG. 1 with respect to step  118 . In step  118 , which further departs from the prior art, device  200  is exposed to a plasma containing He and H 2 , where the percentage of each of the two may vary. For example, in the prior art, a plasma including He and H 2 , where the He provides 95% and the H 2  provides 5% of the mixture, has been implemented by Applied Materials at very low pedestal power (on the order of 10 Watts) to reduce copper oxide on the top of conductors such as conductor  222 . Further, the prior art He—H 2  plasma is implemented by ionizing that plasma by applying a power source to the chamber coil in which the plasma is formed, where the power source is on the order of 200 to 500 Watts. Returning to step  118 , this same mixture of 95% He and 5% H 2  may be used in step  118 , or a different percentage of He and H 2  may be used, also in combination with a comparable power configuration and source for ionizing the plasma. Toward this end, FIG. 9 includes a block depiction of a chamber coil  246  with a power source  248  connected to coil  246 , where such a configuration is known in the art. Further, power source  248  is preferably set in the range of 200 to 500 Watts, which is in a comparable range to that used in the prior art. However, step  118  contrasts to the prior art in at least one of two respects in the preferred embodiments. First, in the preferred embodiment, the He—H 2  plasma of step  118  is in addition to the argon treatment of step  116 . Second, the plasma of step  118  is accelerated toward the wafer, in which device  200  is formed, by applying a relatively large power to a pedestal  250  that supports substrate  202 ; to illustrate this aspect, FIG. 9 illustrates pedestal  250  in general, where one skilled in the art should be readily familiar with such an apparatus in an appropriate plasma chamber for accomplishing step  118 . Further in this regard, pedestal  250  is coupled to a power source  252 , and preferably in step  118  power source  252  provides a power level anywhere in the range of 100 to 500 Watts. The duration of step  118  may vary according to the preferred embodiment. Preferably, such duration is timed in order to cause the plasma to affect only a certain depth from each exposed surface of OSG layers  226  and  230 . For example, preferably the effect is realized in approximately 10 Angstroms of these layers, and the present inventors have observed an effect of approximately 1 Angstrom per second; as such, to affect 10 Angstroms, then the plasma acceleration of step  118  is performed over a 10 second interval. Also in this regard, the preferred embodiments also contemplate an upper limit on the duration of step  118 . Specifically, and as shown below, in some locations the area of OSG layer  230 , as affected by the step  118  He—H 2  plasma, is subsequently removed and thus the depth of penetration of the step  118  plasma may be compensated for by this removal. However, in other exposed areas, such removal does not occur and, therefore, attention should be provided to these areas as well as the effects, if any, by permitting the step  118  plasma to reach levels such that a greater depth of OSG is affected. For example, by permitting the step  118  duration to extend too long, there is the possibility of increasing capacitance between conductor  222  and any nearby comparable contact (not explicitly shown). To avoid such effects, therefore, the step  118  duration and its corresponding depth of effect should be monitored. 
     Before proceeding with additional steps, some observations with respect to the results achieved by step  118  are noteworthy. In response to the increased power of step  118  as applied to pedestal  250  versus that of the prior art, the He—H 2  plasma is accelerated downward toward the exposed areas of device  200 , including OSG layers  230  and  226 . With respect to the OSG layers  230  and  226 , the present inventors have observed that step  118  thereby alters the atomic concentration of the silicon, carbon, and oxygen near the exposed surfaces (both vertical and horizontal) of these layers. For example, in one empirical study, where OSG layers  230  and  226  prior to step  118  were originally found to have a relatively large atomic concentration of oxygen, a relatively low concentration of carbon, and a concentration of silicon between that of the carbon and oxygen, following step  118  the concentrations are changed near the exposed surfaces of layers  230  and  226  such that the carbon concentration is increased, the oxygen concentration is decreased, and the silicon is also increased, as compared to their respective concentrations prior to that step. The present inventors believe in connection one or more of these concentration changes that better adhesion is permitted between the surface of both OSG layers  230  and  226  to a subsequent metal layer, as further appreciated below. Additionally, under the preferred embodiments, the argon treatment of step  116  is found to remove copper oxide from the upper surface of metal conductor  222 , but some of that material is found to remain along the vertical sidewalls of OSG layer  226  in the area of void  244 . However, the treatment of step  118  is believed to reduce the oxygen in these sidewall areas as well, thereby providing an improved metal conductor in that area in combination with the additional metals as described below. Lastly, it is noted that the step  118  plasma has only a minimal affect on the metal in the upper surface of conductor  222 , when that conductor is formed of copper. 
     FIG. 10 illustrates device  200  of FIG. 9 after additional fabrications steps, as described in method  100  in FIG. 1 with respect to step  120 . In step  120 , a conductive barrier layer  254  is formed within what is shown as void  244  in the preceding FIG.  9 . Barrier layer  254  may be of various materials, such as tantalum by way of example. In the preferred embodiment, the thickness of barrier layer  254  may be on the order of 250 Angstroms. However, with a continuing trend of reduced device sizes, there is stated in the industry a goal to achieve so-called “zero barrier” status. In the meantime, reducing the thickness of barrier layers is a goal and, indeed, it is believed in connection with the preferred embodiments that the thickness of barrier layer  254  also may be reduced. For example, satisfactory device yields have been found with a thickness of barrier layer  254  as low as 50 Angstroms. More specifically, with the changes in atomic concentration in OSG layers  226  and  230  as described above, even at such a reduced thickness there has been confirmed an adequate adhesion between barrier layer  254  and the materials below that layer, unlike the prior art where such adhesion broke down as described in the Background Of The Invention section of this document. 
     Continuing with FIG. 10, and as shown in method  100  of FIG. 1, a step  122  follows step  120  and in which a metal layer  256  is formed over device  200 , extending into what was shown as void  244  in the preceding FIG.  9 . In the preferred embodiment, metal layer  256  is copper, and it is formed by first providing a copper seed layer (not separately shown) in void  244  and on top of barrier layer  254 , and following the copper seed layer with a copper plating step. In connection with these layers, recall that the argon step  116  above was stated to be favorable in causing rounded edges  230 ′. Without such edges  230 ′, the inclusion of barrier layer  254  as well as a copper seed layer would otherwise tend to converge on or pinch off the vertical opening in void  244  and, as a result, the subsequent metal layer  256  may not fully fill that area—such a result is sometimes referred to as creating a cavity within the metal layer. However, looking to FIG. 10, it is seen that the entire void  244  is filled by metal layer  256  because rounded edges  230 ′ permit a thorough filling of void  244  by metal layer  256 . As another observation, given the status of the formation of device  200  in FIG. 10, it may be further seen that barrier layer  254  provides a barrier between metal layer  256  and the OSG layers  230  and  226 . Thus, in the preferred example where metal layer  256  is copper, then barrier layer  254  prevents copper diffusion of metal layer  256  into OSG layers  230  and  226 . However, recalling that step  118  alters the concentrations of the copper and oxygen in those OSG layers  230  and  226 , it is contemplated that in future embodiments layer  254  may be reduced still further in thickness, while the changed concentrations themselves also may thwart copper diffusion by metal layer  256 ; in this manner, again there is an advancement toward the goal of a zero barrier. 
     FIG. 11 illustrates device  200  of FIG. 10 after additional an fabrication step, as described in method  100  in FIG. 1 with respect to step  124 . In step  124 , device  200  is planarized, such as with a chemical mechanical polishing (“CMP”) operation. For sake of reference, the layers affected by the planarization are shown with a subscript “P” in their reference numbers. Thus, following the planarization, OSG layer  230  becomes an OSG layer  230   P , metal barrier layer  254  becomes metal barrier layer  254   P , and metal layer  256  becomes metal layer  256   P . Accordingly, from the resulting structure of device  200  in FIG. 11, electrical contact may be made to metal layer  256   P , thereby also electrically connecting to metal conductor  222 . Lastly, recall it is stated above in connection with step  118  that the duration of the He—H 0  plasma exposure will control the depth at which the concentration of OSG layer  230  is affected; in the preferred embodiment, that affected depth is either partially or entirely removed by the CMP operation of step  124  and, thus, any effects of that treatment along the upper horizontal surface of OSG layer  230  are effectively removed by the CMP. However, below that surface, there is still improved adhesion between OSG layer  230   P  and metal barrier  254   P , where such improvements have been confirmed through the various manners of testing described earlier in this document. 
     From the above, one skilled in the art should appreciate that the preferred embodiments provide for semiconductor devices and methods with improved adhesion between a metal and a silicon-carbon-oxygen dielectric layer. This improved adhesion provides numerous benefits, including device reliability, yield, and cost, and possibly reducing device size by reducing barrier thickness. Further, while certain preferred materials have been described, one skilled in the art may ascertain various alternatives that also may be implemented within the inventive teachings. Additionally, while the preceding embodiment has been shown as one type of dual damascene structure, other dual damascene structures may be formed with many variations and still fall within the inventive scope and, indeed, that scope also includes structures that are formed by a single damascene process where the trench and via levels are formed separately. Thus, the preceding benefits as well as the various alternative steps described and ascertainable by one skilled in the art demonstrate the flexibility of the inventive scope, and they should also demonstrate that while the present embodiments have been described in detail, various substitutions, modifications or alterations could be made to the descriptions set forth above without departing from the inventive scope which is defined by the following claims.