Abstract:
A method of forming a high aspect ratio via opening through multiple dielectric layers, a high aspect ratio electrically conductive via, methods of forming three-dimension integrated circuits, and three-dimensional integrated circuits. The methods include forming a stack of at least four dielectric layers and etching the first and third dielectric layers with processes selective to the second and fourth dielectric layers, etching the second and third dielectric layers with processes selective to the first and second dielectric layers. Advantageously the process used to etch the third dielectric layer is not substantially selective to the first dielectric layer.

Description:
RELATED APPLICATIONS 
     This Application is related to application Ser. No. 11/853,139 filed on Sep. 11, 2007. This Application is a division of copending U.S. patent application Ser. No. 11/853, 118 filed on Sep. 11, 2007. This application is related to application Ser. No. 12/540,457 filed on Aug. 13, 2009. 
    
    
     This invention was made with Government support under contract number N66001-04-C-8032 awarded by the Defense Advanced Research Projects Agency (DARPA). The government has certain rights in this invention. 
    
    
     FILED OF THE INVENTION 
     The present invention relates to the field of integrated circuits; more specifically, it relates to structures of and methods for fabricating ultra-deep vias in integrated circuits and structures of and methods for fabricating three-dimensional integrated circuits. 
     BACKGROUND OF THE INVENTION 
     In order to reduce the footprint and improve the speed of integrated circuits various three-dimensional integrated circuit structures have been proposed. Traditional integrated circuit structures have been two dimensional, in that all the active devices have been formed in a same plane in a same semiconductor layer. Three-dimensional integrated circuits utilize vertically stacked semiconductor layers with active devices formed in each of the stacked semiconductor layers. 
     The fabrication of three-dimensional integrated circuits poses many challenges particularly in the methodology for interconnecting devices in the different semiconductor layers together. The total depth of these interconnects can exceed 1.5 um with diameters in the sub 0.2 um range. It is difficult to fill vias having such large depth to width aspect ratios with high quality, defect free metal. In particular, the metal fill of large aspect ratio and very deep vias often contain voids which can increase the resistance of the via and result in yield loss as well as reduce the reliability of the device. Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove. 
     SUMMARY OF THE INVENTION 
     A first aspect of the present invention is structure, comprising: a substrate; a first dielectric layer on a top surface of the substrate; a second dielectric layer on a top surface of the first dielectric layer; a third dielectric layer on a top surface of the second dielectric layer; a fourth dielectric layer on a top surface of the third dielectric layer; an opening extending from a top surface of the fourth dielectric layer to the top surface of the substrate; a first width of the opening measured in first direction parallel to the top surface of the fourth dielectric layer at the top surface of the fourth dielectric layer is greater than a second width of the opening measured in the first direction at the top surface of the third dielectric layer and greater than a third width of the opening measured in the first direction at a top surface of the substrate, the second width greater than or equal to the third width; a ratio of a depth of the opening measured in a second direction perpendicular to the first direction from the top surface of the fourth dielectric layer to the top surface of the substrate to the third width is equal to or greater than five; and an electrical conductor filling the opening. 
     A second aspect of the present invention is the first aspect, wherein: the first and third dielectric layers comprise silicon nitride; and the second and fourth dielectric layers comprise a silicon oxide. 
     A third aspect of the present invention is the first aspect, wherein: the first dielectric layer and the third dielectric layer each independently have respective thicknesses at least five times less than either a thickness of the second dielectric layer or a thickness of the fourth dielectric layer; and a total thickness of the first, second, third and fourth dielectric layers is greater than or equal to about 1 micron. 
     A fourth aspect of the present invention is the first aspect, further including: a first silicon layer embedded in the fourth dielectric layer, a first transistor in the first silicon layer, an electrically conductive contact in the fourth dielectric layer, the contact electrically contacting the first transistor; a first set of wiring levels on a top surface of fourth dielectric layer, a wire or wires in the first set of wiring levels electrically connecting the contact to the electrical conductor in the opening; and the substrate including a second set of wiring levels contacting a bottom surface of the first dielectric layer, a wire or wires in the second set of wiring levels electrically connecting the electrical conductor in the opening to a second transistor formed in a second silicon layer in contact with a bottom surface of the second set of wiring levels. 
     A fifth aspect of the present invention is the first aspect, wherein: the first and third dielectric layers independently comprise a material selected from the group consisting of low temperature oxide, high density plasma oxide, with plasma enhanced chemical vapor deposition oxide, ultrahigh density plasma oxide, tetraethoxysilane oxide, spin-on-oxide and layers thereof. 
     A sixth aspect of the present invention is the first aspect, wherein: the second and fourth dielectric layers independently comprise a material selected from the group consisting of silicon nitride, silicon carbide, silicon oxy nitride, silicon oxy carbide and Nblock (SiCNH). 
     A seventh aspect of the present invention is the first aspect, wherein the electrical conductor comprises: a tantalum nitride layer over sidewalls and a bottom of the opening; a tantalum layer on the tantalum nitride layer; a seed copper layer the tantalum layer; and an electroplated copper layer on the seed copper layer, the electroplated copper layer completely filling remaining spaces in the opening. 
     An eighth aspect of the present invention is the first aspect, wherein the third dielectric layer comprises multiple dielectric layers. 
     A ninth aspect of the present invention is the first aspect, wherein the third dielectric layers comprises fifth, sixth and seventh dielectric layers, the fifth dielectric layer in abutting the second dielectric layer, the sixth dielectric layer between the fifth and seventh dielectric layers. 
     A tenth aspect of the present invention is the ninth aspect, wherein: the fifth dielectric layer extends through regions of a silicon layer between a bottom surface of second dielectric layer and a top surface of the sixth dielectric layer. 
     An eleventh aspect of the present invention is a structure, comprising: a first substrate, the first substrate including: first transistors electrically connected to a set of wiring levels, each wiring level including electrically conductive wires in a respective dielectric layer; an etch stop layer on a top surface of an uppermost wiring level of the set of wiring levels that is furthest from the substrate, the etch stop layer in contact with a wire of the uppermost wiring level; a first dielectric bonding layer on a top surface of the etch stop layer; and a bottom surface of the first dielectric bonding layer in contact with a top surface of the etch stop layer; a second substrate, the second substrate including: a second dielectric bonding layer; a buried oxide layer on a top surface of the second dielectric bonding layer; a silicon layer on a top surface of the buried oxide layer, the silicon layer including second transistors electrically isolated from each other by dielectric isolation in the silicon layer; a profile modulation layer on a top of the silicon layer and on a top surface of the dielectric isolation; and a dielectric layer on a top surface of the profile modulation layer; a top surface of the first dielectric bonding layer bonded to a bottom surface of the buried oxide; an opening extending from the top surface of the dielectric layer, through the profile modulation layer, through the dielectric isolation, through the buried oxide layer through the first and second dielectric bonding layer and through the etch stop layer to a top surface of the wire; and an electrical conductor filling the opening, the electrical conductor in electrical contact with the wire. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
         FIGS. 1A through 1J  are cross-sections of the fabrication of an exemplary electrically conductive via according to embodiments of the present invention; 
         FIGS. 2A through 2C  are cross-sections of the fabrication of a first exemplary three dimensional integrated circuit according to embodiments of the present invention; and 
         FIG. 3  is a cross-section of additional fabrication steps in the fabrication of three-dimensional integrated circuit according to embodiments of the present. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1A through 1J  are cross-sections of the fabrication of an exemplary electrically conductive via according to embodiments of the present invention. In  FIG. 1A , formed in a semiconductor substrate  100  is a metal wire  105 . Formed on a top surface  110  of substrate  100  is a dielectric etch stop layer  115 . Formed on top of etch stop layer  115  is a first dielectric layer  120 . Formed on first dielectric layer  120  is a second dielectric layer  125 . Formed on second dielectric layer  125  is a third dielectric layer  130 . Formed on top of third dielectric layer  130  is a profile modulation layer  135 . Formed on profile modulation layer  135  is a fourth dielectric layer  140 . Semiconductor substrate  100  may comprise, for example, Si, SiGe, Ge, GaAs or InP. 
     The stack of dielectric materials consisting of dielectric etch stop layer  115 , first dielectric layer  120 , second dielectric layer  125 , third dielectric layer  130 , profile modulation layer  135  and fourth dielectric layer  140  simulates a structure that conductive vias are formed through in fabrication of a three-dimensional integrated circuit according to embodiments of the present invention described infra. Therefore in one example, etch stop layer  115  and first dielectric layer  120  represent layers on a lower semiconductor substrate and second dielectric layer  125 , third dielectric layer  130 , profile modulation layer  135  and fourth dielectric layer  140  represent layers on an upper semiconductor layers with first and second dielectric layers  120  and  125  representing oxide bonding layers that bond the two substrates together. Third dielectric layer  130  represents a dielectric trench isolation (TI) or dielectric shallow trench isolation (STI) on a buried oxide layer (BOX) of a silicon-on-insulator (SOI) substrate. 
     In accordance with the simulation of a three-dimensional integrated circuit according to embodiments of the present invention, etch stop layer  115  is silicon nitride and in one example is about 500 Å thick, first dielectric layer  120  is low temperature silicon oxide (LTO) and in one example is between about 2500 Å and about 3500 Å thick, second dielectric layer  125  is LTO and in one example is between about 2500 Å and about 3500 Å thick, third dielectric layer  130  is high density plasma silicon (HDP) oxide thermal oxide and in one example is about 3600 Å thick, profile modulation layer  135  is silicon nitride and in one example is about 500 Å thick and fourth dielectric layer  140  is HDP oxide and in one example is about 4700 Å thick. In one example, metal wire  105  comprises copper. The HDP oxide of third dielectric layer  130  and fourth dielectric layer  140  may be independently replaced with plasma enhanced chemical vapor deposition (PECVD) oxide, ultrahigh density plasma (UHP) oxide, tetraethoxysilane (TEOS) oxide or spin-on-oxide. The silicon nitride of etch stop layer  115  and profile modulation layer  135  may be independently replaced with silicon carbide, silicon oxy nitride, silicon oxy carbide or Nblock (SiCNH). In oxide fusion bonding applications, first and second dielectric layer are LTO, but in other application may be independently thermal oxide, HDP oxide, PECVD oxide, UDP oxide, TEOS oxide or spin-on-oxide. In one example, thicknesses of etch stop layer  115  and profile modulation layer  135  are independently about 5 times less than a thickness of either fourth dielectric layer  140  or a combined thickness of first, second and third dielectric layers  120 ,  125  and  130 . 
     An LTO oxide is a silicon oxide that is formed at temperatures below about 350° C. In one example, LTO oxides are formed using N 2 O in a plasma enhanced chemical vapor deposition (PECVD) process. An HDP oxide are specifically prepared to be fusion bonded to each other. 
     First second, third and fourth dielectric layers  120 ,  125 ,  130  and  140  are advantageously first similar materials (e.g., silicon oxides) and etch stop layer  115  and profile modulation layer  135  are advantageously second similar materials (e.g. silicon nitrides), where the second materials may be selectively plasma etched relative to the first materials. 
     In  FIG. 1B , an optional antireflective coating (ARC)  145  is formed on fourth dielectric layer and a photoresist layer  150  formed on top of the ARC. An opening  155  is formed in photoresist layer  150  photolithographically by exposing photoresist layer  150  to actinic radiation through a patterned photomask and then developing the photoresist layer to transfer the pattern of the photomask into the photoresist layer. A region of ARC  145  is exposed in the bottom of opening  155 . ARC  145  is a bottom ARC or BARC since it is formed under photoresist layer  150 . A top ARC (TARC) formed over the photoresist may be substituted or both a TARC and BARC may be used. The combination of a photoresist layer and an ARC (i.e., BARC, TARC or both BARC and TARC) is defined as a photo-imaging layer. 
     In  FIG. 1C , the region of ARC  145  exposed in opening  155  of  FIG. 1B  is removed using a reactive ion etch (RIB) that etches ARC  145  faster than photoresist layer  150  (i.e., ARC  145  is RIE&#39;d selective to photoresist layer  150 ) to expose a region of fourth dielectric layer  140  in the bottom of an opening  155 A. An example RIE process for etching ARC  145  includes etching with a mixed CF 4 /CHF 3 /Ar/O 2  gas derived plasma. 
     In  FIG. 1D , the region of fourth dielectric layer  140  exposed in opening  155 A of  FIG. 1C  is removed using an RIB that etches fourth dielectric layer  140  faster than profile modulation layer  135  (i.e., fourth dielectric layer  140  is RIE&#39;d selective to profile modulation layer  135 ) to expose a region of the profile modulation layer in the bottom of an opening  155 B. Note, photoresist layer  150  and ARC  145  are eroded by the fourth dielectric layer  140  RIE etch. The opening in the top surface of photoresist layer  150  is larger than the opening in the bottom surface of the photoresist layer. An example RIE process for etching fourth dielectric layer includes etching with a mixed CO/C 4 F 8 /Ar gas derived plasma. This chemistry (at the proper bias, forward and reverse power, pressure and gas flows) etches silicon oxide about 25 times faster than silicon nitride. 
     In  FIG. 1E , the region of profile modulation layer  135  exposed in opening  155 B of  FIG. 1D  is removed using an RIE that etches profile modulation layer  135  faster than third dielectric layer  130  (i.e., profile modulation layer  135  is RIE&#39;d selective to third dielectric layer  130 ) to expose a region of the third dielectric layer in the bottom of an opening  155 C. An example RIE process for etching profile modulation layer includes etching with a mixed CHF 3 /CF 4 /Ar gas derived plasma. This chemistry (at the proper bias, forward and reverse power, pressure and gas flows) etches silicon nitride about 4 times faster than silicon oxide. It is advantageous to keep profile modulation layer  135  (and etch stop layer  115 ) as thin as possible. 
     In  FIG. 1F , the region of third dielectric layer  130  exposed in opening  155 C of  FIG. 1E  is removed along with regions of second and first dielectric layers  125  and  120  aligned under opening  155 C of  FIG. 1E  using an RIE that etches third, second and first dielectric layers  130 ,  125  and  120  faster than etch stop layer  115  and profile modulation layer  135  (i.e., third dielectric layer  130  is RIE&#39;d selective to etch stop layer  115  and profile modulation layer  135 ) to expose a region of the etch stop layer in the bottom of an opening  155 D. An example RIE process for etching third, second and first dielectric layers  130 ,  125  and  120  includes etching with a mixed CO/C 4 F 8 /Ar gas derived plasma. Note, photoresist layer  150  and ARC  145  are further eroded by the third dielectric layer  130 , second dielectric layer  125  and first dielectric  120  RIE etches. This etch is not selective to fourth dielectric layer  140  and in combination with the further erosion of photoresist layer  150  and ARC  145 , a tapered upper region  160  of opening  155 D is formed in the region of opening  155 D formed through fourth dielectric layer  140 . The sidewall of opening  155 D in region  160  taper at an angle “a” measured between the sidewall and a plane parallel to top surface  110  of substrate  100 . A lower region  165  of opening  155 D is formed through profile modulation layer  135  and third, second and first dielectric layers  130 ,  125  and  120 . The sidewall of opening  155 D in region  165  is at an angle “b” measured between the sidewall and a plane parallel to top surface  110  of substrate  100 . Opening  155 D has width W 1  measured at the top surface of fourth dielectric layer  140 , a width W 2  measured at a top surface of profile modulation layer  135  and a width W 3 , measured at a top surface of etch stop layer  115 . W 1  is greater than W 2 . In one example W 1  is about 0.28 microns and W 3  is about 0.16 microns. 
     In one example, W 2  is equal to W 3  and angle “b” is between about 87° and no greater than 90°. In one example W 2  is greater than W 3 , however angle “b” is less than angle “a.” Again, the presence of profile modulation layer  135  allows the widening of opening  155 D at the top surface of fourth dielectric layer  140  in upper region  160  due to the controlled erosion of photoresist layer  150  while facilitating formation of a straight or sidewall in lower region  165 . Without profile modulation layer  135 , either opening  155 D would be to narrow at the top to be filled with metal without incorporating large voids in the metal fill, or the value of W 1  would need to be much greater to maintain the same value of W 3  obtained with the presence of the profile modulation layer. 
     In  FIG. 1G , photoresist layer  150  and arc  145  (See  FIG. 1F ) are removed using an oxygen ash process (i.e., O 2  plasma etch). Alternatively, this step may be performed after the process illustrated in  FIG. 1H . It is advantageous to perform the photoresist removal step with etch stop layer  115  intact to prevent the photoresist removal process from oxidizing wire  105  particularly when wire  105  comprises copper. 
     In  FIG. 1H , the region of etch stop layer  115  exposed in opening  155 D of  FIG. 1G  is removed using an RIE that etches stop layer  115  faster than first, second, third dielectric layers  120 ,  125  and  130  (i.e., etch stop layer  115  is RIE&#39;d selective to first, second and third dielectric layers  120 ,  125  and  130 , metal wire  105  and optionally fourth dielectric layer  140 ) to expose a region of metal wire  105  in the bottom of an opening  155 E. An example RIE process for etching etch stop layer  115  includes etching with a mixed CF 4 /CHF 3 /Ar/O 2  gas derived plasma. Region  160  has a height H 1  measured from the top surface of fourth dielectric layer  140  to the top surface of profile modulation layer  135  in a direction perpendicular to the top surface of wire  105  in substrate  100 . Region  165  has a height H 2  measured from the top surface of profile modulation layer  134  to the top surface of wire  105  in substrate  100  in a direction perpendicular to the top surface of wire  105  in substrate  100 . In one example H 1  is about 0.4 microns and H 2  is between about 1 micron an and about 1.6 microns for total opening depth (i.e., H 1 +H 2 ) of between about 1.4 microns and about 2.0 microns. With a value of W 3  (see  FIG. 1F ) of about 0.16 microns the depth to width ratio of opening  155 E is between about 1.4/0.16=about 8.75 and about 2.0/0.16=about 12.5. In one example, H 1 +H 2  is equal to or greater than about 1 micron. In one example, H 1 +H 2  is equal to or greater than about 2 microns. In one example (H 1 +H 2 )/W 1  is greater than or equal to 5. In one example (H 1 +H 2 )/W 1  is greater than or equal to 8. 
     In  FIG. 1I , an optional direct current (DC) clean (e.g., sputter cleaning with an inert gas) is performed followed by formation of an electrically conductive liner  170  on the sidewall of opening  155 E and top surface of fourth dielectric layer  140  followed by overfilling the opening  155 E with an electrically conductive core conductor  175 . In one example, conductive liner  170  comprises, in the order of deposition, a layer of TaN, a layer of Ta and a layer of Cu and core conductor  175  comprises electroplated copper. 
     In  FIG. 1J , a chemical-mechanical-polish (CMP) is performed to remove liner  170  and core conductor  175  from over fourth dielectric layer  140  to form an electrically conductive via  180  extending from a top surface  185  of the fourth dielectric layer to a top surface of wire  105  (making electrical contact with wire  105 ). After the CMP, a top surface  190  of via  180  is coplanar with top surface  185  of fourth dielectric layer  140 . 
     It should be understood in the simplest form, embodiments of the present invention may be practiced on a dielectric stack where first, second and third dielectric layers  120 ,  125  and  130  of  FIG. 1  are replaced with a single dielectric layer. In other embodiments, their may be more than three dielectric layers in the stack represented by first, second and third dielectric layers  120 ,  125  and  130  of  FIG. 1 , though they should all be similar materials (e.g., silicon oxides) or have similar selectivity&#39;s to the RIE used to etch stop and profile modulation layers. 
       FIGS. 2A through 2C  are cross-sections of the fabrication of a first exemplary three-dimensional integrated circuit according to embodiments of the present invention. In  FIG. 2A , an upper semiconductor substrate  200  includes a silicon oxide bonding layer  205 , a BOX layer  210  on the bonding layer, a semiconductor layer  215  including semiconductor regions  220  and STI  225  formed in the semiconductor layer, a profile modulation layer  230  on top of semiconductor layer  215  and a dielectric layer  235  on the passivation layer. Exemplary, field effect transistors (FETs)  240  comprising source/drains (S/D) formed in semiconductor regions  220  and gates formed over the silicon regions between the S/Ds are formed in substrate  200 . Semiconductor layer  215  may comprise, for example, Si, SiGe, Ge, GaAs or InP. 
     Etch stop layer may also serve as a diffusion barrier layer for copper and/or as a passivation layer. 
     A substrate  300  includes a semiconductor base later  305 , a BOX layer  310  on the base silicon layer, a semiconductor layer  315  including semiconductor regions  320  and STI  325  formed in the silicon layer, an interlevel dielectric (ILD) wiring set  330  including contacts  335  and wires  340  and  350  formed in respective dielectric layers of dielectric layers  355  of ILD wiring set  330 . Semiconductor base layer  305  may comprise, for example, Si, SiGe, Ge, GaAs or InP. Semiconductor layer  315  may comprise, for example, Si, SiGe, Ge, GaAs or InP. 
     An ILD wiring level comprises a dielectric layer and one or more wires, vias or contacts embedded therein. ILD wiring set  330  is illustrated having three ILD wiring levels. ILD wiring set  330  may include more or less ILD levels (down to one level containing contacts  335 ) or as many levels as required by the integrated circuit design. The ILD wiring levels of ILD wiring set  330  are, by way of example, damascene and dual-damascene ILD levels formed by damascene and dual-damascene processes. 
     A damascene process is one in which wire trenches or via openings are formed in a dielectric layer, an electrical conductor of sufficient thickness to fill the trenches is deposited on a top surface of the dielectric, and a chemical-mechanical-polish (CMP) process is performed to remove excess conductor and make the surface of the conductor co-planar with the surface of the dielectric layer to form damascene wires (or damascene vias). When only a trench and a wire (or a via opening and a via) is formed the process is called single-damascene. 
     A dual-damascene process is one in which via openings are formed through the entire thickness of a dielectric layer followed by formation of trenches part of the way through the dielectric layer in any given cross-sectional view. All via openings are intersected by integral wire trenches above and by a wire trench below, but not all trenches need intersect a via opening. An electrical conductor of sufficient thickness to fill the trenches and via opening is deposited on a top surface of the dielectric and a CMP process is performed to make the surface of the conductor in the trench co-planar with the surface the dielectric layer to form dual-damascene wires and dual-damascene wires having integral dual-damascene vias. 
     Returning to  FIG. 2A , exemplary, field effect transistors (FETs)  345  comprising source/drains (S/D) formed in semiconductor regions  320  and gates formed over the silicon regions between the S/Ds are formed in substrate  300 . Contacts  335  and wires  340  electrically connect FETs  345  into circuits or portions of circuits. Substrate  300  further includes an etch stop layer  360  on top of ILD wiring set  355  and a silicon oxide bonding layer  365  on the etch stop layer. Bonding layers  205  and  365  bond substrates  200  and  300  into a single structure. The bonding process includes placing the bonding layers  205  and  365  in contact at a temperature above room temperature but below, for example, 350° C. 
     In one example, dielectric layers  235 ,  355  and STI  225  are independently selected from the group consisting of thermal oxide, HDP oxide, PECVD oxide, UDP oxide, TEOS oxide and spin-on-oxide, and bonding layers  205  and  365  are LTO. In one example profile modulation layer  230  and etch stop layer  360  are independently selected from the group consisting of silicon nitride, silicon carbide, silicon oxy nitride or silicon oxy carbide. In a second example, dielectric layers  235 ,  355  and STI  225  and bonding layers  205  and  365  are advantageously first similar materials (e.g., silicon oxides) and etch stop layer  360  and profile modulation layer  230  are advantageously second similar materials (e.g. silicon nitrides), where the first and second materials may be selectively plasma etched relative to each other. In one example, dielectric layer  235  is between about 2500 Å and about 7500 Å thick. In one example, profile modulation layer  230  is between about 250 Å and about 1000 Å thick. In one example, STI  225  is between about 1500 Å and about 2500 Å thick. In one example, BOX layer  210  is between about 1500 Å and about 2500 Å thick. In one example, bonding layer  210  is between about 2500 Å and about 3500 Å thick. In one example, bonding layer  365  is between about 2500 Å and about 3500 Å thick. In one example, etch stop layer  360  is between about 250 Å and about 1000 Å thick. 
     Substrate  200  may be formed from an SOI substrate by removal of the semiconductor (e.g., silicon) base layer under BOX layer  210  after formation of FETs  240  followed by a deposition of a layer of LTO to form bonding layer  205  on BOX layer  225 . Substrate  300  may be formed from an SOI substrate complete with ILD wiring set  330  followed by deposition of etch stop layer  360  and a deposition of a layer of LTO to form bonding layer  365 . 
     In  FIG. 2A , a photoresist layer  400  is formed on dielectric layer and patterned to form an opening  405  in the photoresist layer in a manner similar to that described supra for opening  155  in photoresist  150  of  FIG. 1B . While no ARC (TARC or BARC) is illustrated in  FIG. 2A , an ARC (TARC and/or BARC) may be used. 
     In  FIG. 2B , an opening  410  is formed through dielectric layer  235 , profile modulation layer  230 , STI layer  225 , BOX layer  210 , bonding layers  205  and  365  and etch stop layer  360  to expose a top surface of wire  350 . Then photoresist layer  400  (see  FIG. 2A ) is removed. The methodology is similar to that described supra with respect to the formation of opening  155 E of  FIG. 1H . First dielectric layer  235  is RIE&#39;d selective to profile modulation layer  230  using for example, a mixed CO/C 4 F 8 /Ar gas derived plasma when dielectric layer  235  is silicon oxide and profile modulation layer  230  is silicon nitride. This chemistry (at the proper bias, forward and reverse power, pressure and gas flows) etches silicon oxide about 25 times faster than silicon nitride. Second, profile modulation layer  230  is RIE&#39;d selective to dielectric layer  235  and STI  225 , using, for example; a mixed CHF 3 /CF 4 /Ar gas derived plasma when dielectric layers  235  and STI  225  are silicon dioxide and profile modulation layer is silicon nitride. This chemistry (at the proper bias, forward and reverse power, pressure and gas flows) etches silicon nitride about 4 times faster than silicon oxide. It is advantageous to keep profile modulation layer  230  (and etch stop layer  360 ) as thin as possible. Third, STI  235 , BOX layer  210 , bonding layers  205  and  365  are RIE&#39;d selective profile modulation layer  230  and etch stop layer  360  using, for example, a mixed CO/C 4 F 8 /Ar gas derived plasma when STI  235 , BOX layer  210 , bonding layers  205  and  365  are silicon oxide and profile passivation layer  230  and etch stop layer  360  are silicon nitride. The third RIE process is not selective to dielectric layer  235  so opening  410  has a tapered profile in dielectric layer  235 , a substantially straight or slightly tapered profile in STI  225 , BOX  210 , and bonding layers  205  and  365  (compared to the taper of opening  410  in dielectric layer  235 ) because of the presence of profile modulation layer  230 . Fourth, photoresist layer  400  (see  FIG. 2A ) is removed using an oxygen ash process. Fifth, etch stop layer  360  is RIE&#39;d selective to dielectric layer  235 . STI  225 , BOX layer  210  and bonding layers  205  and  365  using, for example, a mixed CF 4 /CHF 3 /Ar/O 2  gas derived plasma when etch stop layer  360  and profile modulation layer  230  are silicon nitride and dielectric layer  210 , STI  225 , BOX layer  225  and bonding layers  205  and  365  are silicon oxide. Sixth an optional DC clean using N 2  and H 2  (i.e. a mixed N 2 /H 2  gas derived plasma etch) is performed. 
     In  FIG. 2C , opening  410  (see  FIG. 2B ) is filled with an electrical conductor for an electrically conductive via  420  in electrical contact with wire  350 . In one example, via  420  is formed by deposition of an electrically conductive liner on the sidewall of opening  410  (see  FIG. 2B ) and top surface of dielectric layer  235  followed by overfilling the opening with an electrically conductive core conductor. In one example, the conductive liner comprises, in the order of deposition, a layer of TaN, a layer of Ta and a layer of Cu and the core conductor comprises electroplated copper. After filling the opening a CMP is performed to remove the liner and core conductor from over dielectric layer  235  to form the via  420  extending from a top surface  425  of dielectric layer  235  to a top surface of wire  350 . After the CMP, a top surface  430  of via  420  is coplanar with top surface  425  of dielectric layer  235 . Thus via  420  is a damascene via. 
     Electrically conductive contacts (not shown) may be made through dielectric layer  235  to the S/Ds and gates of FETs  240 . Alternatively, the contacts may be formed prior to formation of photoresist layer  400  (see  FIG. 2A ). Additional interlevel dielectric layer containing wires may be formed on top of dielectric layer  235 , the wires therein electrically connecting via  420  to FETs  240  and FETs  345  into circuits. See  FIG. 34 . 
       FIG. 3  is a cross-section of additional fabrication steps in the fabrication of three-dimensional integrated circuit according to embodiments of the present. In  FIG. 3 , an electrically conductive contact  440  is formed to one of FETs  240  and an ILD wiring set  445  is formed on dielectric layer  235 . ILD wiring level set  445  includes wires  450  and a terminal pad  455 . ILD wiring set  445  is illustrated having two ILD wiring levels. ILD wiring level set  445  may include more or less ILD levels (down to one level containing wires/terminal pads  455 ) or as many levels as required by the integrated circuit design. The ILD wiring levels of ILD wiring set  445  are, by way of example, damascene and dual-damascene ILD levels formed by damascene and dual-damascene processes. Contact  440  is illustrated as a damascene contact. One wire  450  connects contact  440  to contact  420 . Thus a three-dimensional integrated circuit is formed comprising FETs  240  and FETs  345 . It should be understood that ILD wiring level set may be formed over dielectric layer  235  of  FIG. 2C  to generate a structure similar to that illustrated in  FIG. 3 , but where the upper substrate is a bulk silicon substrate instead of an SOI substrate. 
     In both the examples of  FIGS. 2A through 2C and 3 , silicon layer  215  and BOX  210  is an SOI substrate and silicon layer  315  and BOX is an SOI substrate. It should be understood that substrate  300  may be replaced with a bulk silicon substrate. 
     Thus the embodiments provide a process methodology for deep vias and semiconductor devices using deep via structures that have profiles that are less susceptible to metal fill problems. 
     The description of the embodiments of the present invention is given above for the understanding of the present invention. It will be understood that the invention is not limited to the particular embodiments described herein, but is capable of various modifications, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, it is intended that the following claims cover all such modifications and changes as fall within the true spirit and scope of the invention.