Abstract:
Disclosed herein is the formation of a ball grid array testing receiver that is scalable for design consideration of miniaturization. A dielectric layer is formed upon a substrate that is substantially conformal to the upper surface of the substrate. A patterned masking layer is formed upon the dielectric layer and a subsequent etch forms a depression within the substrate and forms a ledge on the surface of the substrate that is adjacent to the depression. After formation of the ledge, a metal layer is formed continuously on the ledge and within the depression. Following the formation of the metal layer, a masking layer is formed upon the metal layer. The masking layer is patterned so as to form a desired arrangement of metal lines by etching the underlying metal layer. The formation of the ledge enables the masking layer to resist formation of a breach between the surface of the substrate and the depression. As such, metal lines are formed so as to extend into the depression without a breach that would otherwise leave an open circuit during attempted use.

Description:
RELATED APPLICATIONS 
     This is a divisional application of U.S. patent application Ser. No. 09/110,554, filed on Jul. 6, 1998, titled “METALLIZED RECESS IN A SUBSTRATE AND METHOD OF MAKING”, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. The Field of the Invention 
     The present invention relates to patterning techniques in the microelectronics industry. More particularly, the present invention relates to photolithographic techniques for preserving a substantially uniform layer upon a substrate topology. In particular, the present invention relates to methods of patterning and etching trenches and pits and forming a continuous layer that electrically communicates out of the trench or pit to an upper surface. The method is carried out after a manner that avoids nonuniformities of the continuous layer that communicates out of the trench or pit to an upper surface. 
     2. The Relevant Technology 
     In the microelectronics industry, a substrate refers to one or more semiconductor layers or structures which includes active or operable portions of semiconductor devices. In the context of this document, the term “semiconductive substrate” is defined to mean any construction comprising semiconductive material, including but not limited to bulk semiconductive material such as a semiconductive wafer, either alone or in assemblies comprising other materials thereon, and semiconductive material layers, either alone or in assemblies comprising other materials. The term substrate refers to any supporting structure including but not limited to the semiconductive substrates described above. The term semiconductor substrate is contemplated to include such structures as silicon-on-insulator, silicon-on-sapphire, and the like. 
     In the field of chip packaging, a goal for those skilled in the art is to miniaturize the chip package, such as in chip scale packages (CSP) where the package itself is only about 1-2 times the size of the chip. Various methods have been proposed to eliminate wire bonding and to achieve lead on chip (LOC) wiring as a means of decreasing chip packaging size. Traditionally, connections have been achieved by connecting a bonding wire from a bonding pad on the chip to a lead finger. However, wire bonding is time consuming and costly, particularly as the number of inputs and outputs from a single chip increases. 
     As integrated circuit technology advances, other methods of connecting input and output from a chip to the external world must be explored to facilitate miniaturization. New packages such as CSP, ball grid array (BGA) packages and flip chips have all been developed as methods of miniaturizing chip packages. In a BGA, solder balls, also called solder bumps, or electrically conductive prominences, are generally intended to all be of substantially the same size. For example, the solder balls may be about 0.3 to 0.4 millimeters in diameter and contact the die bond pads through the bottom of the package surface. Generally an array of electrical contacts congruent to the solder ball array is to be found on a circuit board to which the package containing the solder balls is to be mounted. The solder balls individually contact their corresponding pads on a printed circuit board (PCB). In order to assure adequate contact, solder paste is often required to accommodate for variations and discrepancies between solder ball sizes and solder ball locations. After contact, the circuit board and the chip are placed in a solder reflow furnace under conditions sufficient to cause the solder ball to reflow and coalesce within the solder paste in order to form an adequate electrical connection. 
     Conventionally, solder bump reflowing is used to mount a chip or chip package onto a PCB. A degree of dimensional variation occurs with solder bumps in the prior art. Reliability in the mounting and electrical connection of integrated circuit packages to their mounting boards is important because the solder joints between the contacts of the chip and those of the PCB are highly difficult to visually inspect and non-destructively test once the chip is in place on the PCB. Although statistical methods of quality control along with destructive testing methods must be relied upon to provide confidence that reliable electrical connections are being made, more effective methods are being sought. 
     Prior to mounting of integrated circuit packages to their mounting boards, it is important and often indispensable that testing of the chip package is carried out. In particular, testing under adverse conditions, called “burn-in” must be conducted. Testing must be carried out before the final mounting of a chip package to a PCB. Accordingly, testing structures have been made that are electrically conductive and that are configured to match the BGA of the chip package. 
     As design efforts that emphasize miniaturization continue, the making of a testing structure that receives and electrically connects with the bumps of a BGA package become increasingly challenging. Formation of a testing array can be carried out according to standard photolithographic techniques. With miniaturization, however, fabrication problems arise. 
     FIG. 1 is an elevational cross-section view of a semiconductor structure  10 . Semiconductor structure  10  comprises a substrate  12 , a metal layer  14 , and a masking layer  16  according to the prior art. It can be seen that masking layer  16  covers portions of metal layer  14  including coverage of an upper surface  24  of substrate  12 . Masking layer  16  is also over a pit surface  26  of substrate  12  within a pit  20  into which metal layer  14  has been formed. 
     Due to various processing parameters, a breach  18  can be seen in masking layer  16 . Breach  18  may be formed due to the presence of a sharp comer  22  on an upper surface  24  of substrate  12 . Sharp comer  22  causes substantial thinning of masking layer  16  during formation thereof. Additionally, breach  18  may be caused by mechanical action of a process performed upon masking layer  16 , exacerbated because of the thinness of masking layer  16  at sharp corner  22 . 
     Where metal layer  14  is used as an electrical contact for testing a BGA upon a chip package or the like, masking layer  16  is patterned in order to achieve a substantially continuous electrically conductive structure comprising metal layer  14 . During CSP or flip chip testing, through electrical conductivity of a BGA, it is preferable that metal layer  14  within pit  20  be in uninterrupted electrical communication with other portions of metal layer  14  that form metal lines (now shown). Patterning of masking layer  16  is carried out in order to form distinct and separate electrical contacts within pit  20  that also run along upper surface  24  of substrate  12 . 
     FIG. 2 illustrates the prior art result of thinning of masking layer  16  (not shown) due to the presence of sharp corner  22  after a patterning etch of metal layer  14  to form metal lines. Semiconductor structure  10  includes substrate  12  and a broken metal line  28  that was formed from metal layer  14 . Typically, there is a dielectric between substrate  12  and metal layer  14 , particularly where substrate  12  may be electrically conductive or semiconductive. Broken metal line  28  exists both upon upper surface  24  of substrate  12  and upon pit surface  26  of pit  20  within substrate  12 . An individual solder ball, bump, or the like is to be inserted within pit  20  during testing. Problematically, no electrical contact can be made from broken metal line  28  within pit  20  to upper surface  24  of substrate  12 . Consequently, no electrical testing of the chip package can be carried out due to the existence of a breach  30  in broken metal line  28 . Additionally, where breach  30  is not formed during fabrication, breach  30  may form during use, where metal layer  14  may have been thinner near sharp corner  22  due to thinning of masking layer  16  instead of the formation of a breach thereof. 
     What is needed in the art is a method of forming a BGA testing receiver that does not suffer from the problems of the prior art. What is also needed in the art is a method of forming a testing package for a semiconductor chip package that resists formation of broken 
     SUMMARY OF THE INVENTION 
     The present invention relates to the formation of a ball grid array (BGA) testing receiver that is subject to miniaturization for salable design. The BGA testing receiver may be known by such terms as a silicon interconnect or an insert. The present invention overcomes the problems of the prior art caused by thinning of a photoresist at a step caused by sharp comers in a substrate. 
     In a first embodiment of the present invention, a dielectric layer is formed upon a substrate that is substantially conformal to the upper surface of the substrate. A masking layer is formed upon the dielectric layer and patterned in such a way so as to expose a pit and to create a ledge. 
     After formation of the ledge and optional formation of a sealing dielectric layer, formation of a metal layer is carried out. Preferably, the metal layer is formed of a refractory metal. Following the formation of the metal layer, a masking layer is formed upon the metal layer. Formation of the ledge resists the thinning of the metal line-forming masking layer at regions at or near the sharp corner that leads into the pit. 
     These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the manner in which the above-recited and other advantages of the invention are obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
     FIG. 1 is an elevational cross-section view of a semiconductor structure according to the prior art, wherein a metal layer has been formed upon a substrate and a masking layer has been formed upon the metal layer with inning of the masking layer at the areas of sharp corners. 
     FIG. 2 is an elevational cross-section view of the semiconductor structure depicted in FIG. 1 after further processing, wherein it can be seen that the masking layer has been removed subsequent to an etch that used the masking layer as a pattern, and wherein the metal layer has been breached to form a broken metal line due to the thinning of the masking layer at the location of the sharp corners, as illustrated in FIG.  1 . 
     FIG. 3 is a plan view of a BGA testing receiver that includes metallization that runs within each pit in a substrate, and that communicates electrically to a peripheral portion of the BGA testing receiver in order to complete electrical circuits from each pit. External bonding techniques such as wire bonding or tap tape can be used to connect the testing array to the outside. 
     FIG. 4 is an elevational cross-section view of a partially-formed semiconductor structure according to an embodiment of the present invention. 
     FIG. 5 is an elevational cross-section view of the semiconductor structure depicted in FIG. 4 after further processing, wherein a dielectric layer has been patterned upon the upper surface of the substrate and a pit-exposing masking layer has been patterned upon the dielectric layer. Additionally, the pit-exposing masking layer has been used during removal of a portion of the dielectric layer in regions immediately adjacent to the pit. 
     FIG. 6 is an elevational cross-section view of a semiconductor structure formed according to an alternative embodiment of the present invention, wherein a plurality of ledges are to be formed. 
     FIG. 7 an elevational cross-section view of the semiconductor structure depicted in FIG. 6 wherein a first ledge has been formed by an anisotropic etch and a second ledge has been formed by an isotropic etch, the etch recipe of which is selective to the materials forming the substrate, the mask, and the first ledge. 
     FIG. 8 is an elevational cross-section view of the semiconductor structure depicted in FIG. 5 after further processing, wherein an optional sealing dielectric layer has been formed and wherein a metal layer has been substantially conformably deposited upon the optional sealing dielectric layer. It can also be seen that a masking layer has been formed upon the metal layer according to the present invention, such that formation of a breach in the masking layer is avoided despite the presence of sharp corners forming the edge of the pit. 
     FIG. 8A is an elevational cross-section view of the semiconductor structure depicted in FIG. 8 after further processing, wherein the masking layer has been removed after patterning of the metal layer, and wherein at least one electrically conductive prominence has been inserted within the pit to make electrical contact with the metal layer for testing of the device connected to the electrically conductive prominence. 
     FIG. 9 is an elevational cross-section view of a semiconductor structure, whereby the inventive method of forming a masking layer without a breach is begun by formation of a dielectric layer and a spacer. 
     FIG. 10A is an elevational cross-section view of the semiconductor structure depicted in FIG. 9 after further processing, whereby an etch to form the pit has been carried out with an etch recipe such as an anisotropic wet etch that is selective to the oxide layer and to the spacer. FIG. 10B is an elevational cross-section view of the semiconductor structure depicted in FIG. 10A after further processing, whereby the spacer has been removed with an etch to expose a ledge from a portion of the upper surface of the substrate. 
     FIG. 11A is an elevational cross-section view of the semiconductor structure depicted in FIG. 9 after further processing according to an alternative embodiment depicted in FIG. 11B, whereby a dielectric layer is used as a hard mask followed by an anisotropic dry etch to form a ledge that is lower than the upper surface of the substrate. FIG. 11C illustrates the formation of a triple-damascene depression that includes a lower ledge in the semiconductor substrate and a ledge thereupon by the formation of a dielectric layer. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made to the drawings wherein like structures will be provided with like reference designations. It is to be understood that the drawings are diagrammatic and schematic representations of the embodiment of the present invention and are not drawn to scale. 
     The present invention relates to the formation of a BGA testing receiver that is subject to miniaturization. The BGA testing receiver may be known by such terms as a silicon interconnect or an insert. The present invention overcomes the problems of the prior art caused by thinning of a photoresist at a step caused by sharp comers in a substrate. 
     FIG. 3 is a plan view of a BGA testing receiver  52  that includes metallization within each pit in a substrate and that communicates electrically to a peripheral portion of the BGA-testing receiver in order to complete electrical circuits from each pit. FIG. 3 illustrates what is known in the art as a paddle on pit  20  (not shown). In the plan view, the metallization within a depression in a BGA testing receiver is known as the paddle portion  56 . The paddle includes a handle portion that includes a metal line  58  that runs from paddle portion  56  to a peripheral portion  54  of BGA testing receiver  52 . Bond pads can be formed at the end of handle portion as shown in FIG.  3 . Wire bonding, tab tape, or other electrical connections can be used to connect to the outside circuitry. 
     The present invention overcomes the problems of the prior art of mask thinning and circuit interruption between pit  20  in BGA testing receiver  52  and metal line  58  that communicates electrically between pit  20  and peripheral portion  54  of BGA testing receiver  52 . 
     In a first embodiment of the present invention, FIG. 4 illustrates a first step in the inventive method that is used to overcome the problems of the prior art. Substrate  12  may be made from a semiconductive substrate, a dielectric substrate, a layered combination thereof, or the like. Where substrate  12  consists of monocrystalline silicon, the shape of pit  20  may be dictated after a wet etch according to the orientation of the crystal lattice of substrate  12 . In FIG. 4, it can be seen that pit  20  has sloping sides  34  due to the existence and orientation of the crystal lattice of substrate  12  where substrate  12  comprises monocrystalline silicon. The presence of vertical sides (not pictured) is likely where substrate  12  is made from a dielectric with no fixed crystal lattice or with an anisotropic dry etch. Additional wet isotropic etches can also be employed including an anisotropic wet etch such as KOH at about 50° C. By this etch, it can form sloping sides  34  as show in FIG.  4 . 
     FIG. 4 also illustrates processing of semiconductor structure  10  according to the inventive method. In a first embodiment, a dielectric layer  36  is formed upon substrate  12  that is substantially conformal to upper surface  24  of substrate  12 , sharp corner  22 , sloping sides  34 , and pit floor  26  of substrate  12 . Formation of dielectric layer  36  may be carried out, by way of nonlimiting example, by thermal oxidation of substrate  12  where substrate  12  is composed of silicon or the like. Additionally, formation of dielectric layer  36  may be carried out by deposition by either chemical vapor deposition (CVD) or physical vapor deposition (PVD). Additionally, dielectric layer  36  may be made by the formation or deposition of nitrides, silicides, carbides and the like. In a preferred embodiment, dielectric layer  36  is made of silicon dioxide, formed by the thermal decomposition of tetra ethyl ortho silicate (TEOS). 
     FIG. 5 illustrates further processing of semiconductor structure  10  depicted in FIG. 4. A masking layer  16  has been formed upon dielectric layer  36  and patterned in such a way so as to expose pit  20  after a fashion that, following etching of dielectric layer  36  with an etch recipe that may be firstly selective to substrate  12  and secondly selective to masking layer  16 , a ledge  40  forms that exposes a portion of upper surface  24  of substrate  12  adjacent to pit  20 . 
     Dimensions of semiconductor structure  10  according to the present invention depend upon the particular and specific application thereof. In general, the depth of pit  20  from upper surface  24  of substrate  12  down to pit floor  26  of substrate  12  is in the range from about 1 micron to about 300 microns. However, pit  20  may be deeper than 300 microns to accommodate a larger solder ball. Preferably the depth of pit  20  is in the range from about 5 microns to about 200 microns, more preferably about 10 microns to about 150 microns, and most preferably about 25 microns to about 100 microns. 
     The width of ledge  40  from sharp corner  22  to the edge  62  of dielectric layer  36  is in a range from about 0.2 microns to about 25 microns, preferably from about 0.5 to about 20 microns, more preferably from about 0.8 microns to about 10 microns, and most preferably from about 1 micron to about 5 microns. The height of dielectric layer  36 , or of edge  62  is preferably in a range from about 1 to about 20 microns, although it may be greater than 20 microns depending upon the application. Ledge widths greater than 25 microns are used with multiple ledges and/or corners having an angle less than that of sharp corner  22 . Any combination of disclosed pit depth range, a disclosed height of edge  62  of dielectric layer  36 , and a disclosed ledge width is contemplated. 
     An alternative embodiment of the present invention includes forming a plurality of ledges in order to overcome the problems of prior art. FIG. 6 illustrates a first step where dielectric layer  36  and a second dielectric layer  38  have been patterned by masking layer  16  by use of an anisotropic dry etch. Additionally, pit  20  has been formed by an etch that is selective to substrate  12 . 
     FIG. 7 illustrates further processing of semiconductor structure  10  depicted in FIG.  6 . Following the anisotropic dry etch, a second etch is carried out that is isotropic. The second etch could be a wet isotropic etch. The second etch may be selective to masking layer  16 , dielectric layer  36 , and substrate  12  but may not selective to second dielectric layer  38 . Thereby, an undercut may form beneath masking layer  16  and ledge  40  is created both upon a portion of upper surface  24  of substrate  12  and upon a portion of dielectric layer  36  within the undercut. Thereby, ledge  40  comprises two topology steps, using a single masking layer  16 . 
     It can be appreciated that a series of ledges may be created according to this alternative embodiment, wherein dielectric layers are selected and etch recipes are employed in etches that are variously selective to different dielectric layers, beginning with dielectric layer  36 . In general, this method of forming a semiconductor device comprises forming in succession, a plurality of dielectric layers upon an upper surface of a substrate. For this method, each subsequent-formed dielectric layer has a chemical quality that is different from the previous-formed dielectric layer. After the plurality of dielectric layers is formed, a depression may be formed through the plurality of dielectric layers with a first etch. The first etch may include etching into the substrate or the etch can stop at the substrate. Optionally, pit  20  may be formed previous to formation of the plurality of dielectric layers. 
     In order to create ledges, etching of the plurality of dielectric layers is done with at least one subsequent etch, whereby the at least one subsequent etch has an etch recipe that is progressively less selective to any given previously formed dielectric layer than to any given subsequently formed dielectric layer. In this manner, a single subsequent etch or a series of etches will cause a “staircase” shape and a multiple-damascene shape to form out of the plurality of dielectric layers. The “staircase” shape forms due to the progressively decreasing selectivity between the first-formed dielectric layer and the last-formed dielectric layer. The “staircase” shape will terminate at a depression in the substrate. In FIG. 7 the depression is pit  20  that includes first dielectric layer  36  and second dielectric layer  38 . As illustrated in FIG. 7, the staircase shape is formed by ledge  40  upon the exposed portion of second dielectric layer  38  next to an edge  62  of dielectric layer  36 , and by ledge  40  upon the exposed portion of upper surface  24  of substrate  12 . 
     Where an embodiment of the present invention includes two ledges, one above the other, the preferred composite width of the two ledges may be about two-thirds the aforementioned ranges of ledge widths. Where the number of ledges is equal to three, the preferred composite ledge widths may be in a composite width range of about one-half the width range for a single ledge. 
     Dielectric layer  36  may be in a thickness range from about 1 micron to about 30 microns, preferably from about 1.2 microns to about 15 microns, more preferably from about 1.4 microns to about 10 microns, and most preferably from about 1.6 to about 5 microns. Where there will be two of ledges  40 , as illustrated in FIG. 7, the thickness of dielectric layer  36  and second dielectric layer  38  may be about two-thirds the thickness of dielectric layer  36  in the presence of one of ledge  40 . Where there is a third of ledge  40 , the thickness of dielectric layer  36  etc., may be about one-half the aforementioned thickness of dielectric layer  36  for a single occurrence of ledge  40 . 
     FIG. 8 illustrates further processing of semiconductor structure  10  as depicted in FIG. 5 or in FIG. 7 after formation of ledge  40  and removal of masking layer  16 . A metal layer  14  is formed on dielectric layer  36  of FIG. 5 or upon dielectric layer  38  of FIG.  7 . Dielectric layer  36  in FIG. 8 may therefore represent a plurality of dielectric layers as seen in FIG.  7 . As such, FIG. 8 is intended to represent further processing of the structures seen in FIGS. 5 and 7. 
     Where substrate  12  may be electrically conductive or semiconductive, a sealing dielectric layer  64  is used. Preferably, metal layer  14  is formed of a refractory metal, a refractory metal alloy, or other electrically conductive material such as a metal nitride such as TiN or the like or silicides such as TiSi or the like. Preferred refractory metals include metals selected from Group IIIB through VIIIB. More preferred of the refractory metals includes the group consisting of W, Ni, and Ti. Additionally, a preferred composition to form metal layer  14  consists of an intermetallic such as gamma TiAl or the like. 
     Finally, as seen in FIG. 8, metal layer  14  can be a composite of layers upon sealing dielectric layer  64 , such as a titanium layer  71 , where a titanium nitride layer  72  is upon titanium layer  71 , and where a tungsten layer or a titanium aluminide layer  73  is upon titanium nitride layer  72 . 
     Selection of particular materials to form metal layer  14  will be dependent upon the particular application. Where electrical conductivity is important, better electrical conductors will be selected. Where metal wear is important during multiple repeat testing cycles, a refractory metal that resists wear during multiple contact with BGAs is preferred. Where high-temperature burn-in testing is important to testing of chip packages, an intermetallic such as TiAl may be selected whereby destructive metal flow and/or allotropic phase changes are avoided at the higher temperatures. Additionally, stacks of metals which include a refractory metal on a layer can also be used. 
     Additionally, metal layer  14  may be formed upon sealing dielectric layer  64  where substrate  12  acts with sealing dielectric layer  64  as an electrically conductive composite. As set forth above, the dielectric layer can form a portion of substrate  12 . Additionally, sealing dielectric layer  64  may not be etched to form pit  20 , rather it may act as a liner layer within pit  20  upon pit surface  26  and sloping sides  34 . A preferred embodiment of metal layer  14  includes a first layer of Ti upon substrate  12 , followed by a second layer of TiN and finally followed by a third layer of W. As a composite structure, metal layer  14  consists of a Ti-rich first layer of substantially all Ti, a gradation into TiN x , where 0≦x≦1, and a gradation into W that is substantially free of TiN. Alternatively, the third layer may compromise TiAl. 
     Following the formation of metal layer  14 , a masking layer  60  is formed upon metal layer  14 . Masking layer  60  will serve as a mask in the formation of metal lines. As it can be seen in FIG. 8, metal layer  14  also forms a metal layer step  42  above ledge  40 , and consequently the metal line-forming masking layer  60  forms a masking layer step  44  above metal layer step  42 . The formation of ledge  40  and the subsequent formations of metal layer step  42  and masking layer step  44  resists the thinning of metal line-forming masking layer  60  at regions at or above sharp corner  22 . It can be appreciated that formation of ledge  40  may be followed by formation of multiple ledges as described above, depending upon the specific application. Masking layer  60  is removed once the metal lines are patterned out of metal layer  14  and etched according to a selected arrangement, resulting in metal lines  58 , that may result by way of non-limiting example in the arrangement shown in FIG.  3 . 
     FIG. 8A illustrates testing of a CSP  68  that includes a solder ball  70 . It can be seen that solder ball  70  of CSP  68  has been inserted into pit  20  to make electrical contact with metal layer  14 . Were metal layer  14  to be viewed in plan view such as that depicted in FIG. 3, metal layer  14  would include metal line  58  as metal layer  14  leads away from pit  20 . 
     In a further embodiment of the present invention, formation of ledge  40  is carried out by the formation of spacer  46  as illustrated in FIG.  9 . Dielectric layer  36 , which is composed for example of an oxide of silicon, is patterned and etched in order to expose the region of substrate  12  that will correspond to the formation of pit  20  (not shown). A spacer material is deposited upon dielectric layer  36  and conformably upon the region that corresponds to the location of pit  20 . A spacer etch follows, whereby spacer  46  remains. Optionally, the spacer etch will double as a pit-forming etch, whereby etch selectivity will be higher for spacer  46  and dielectric layer  36  than for substrate  12 . It can be appreciated that dielectric layer  36  may be formed from a plurality of dielectric layers, each of which has chemical qualities that are different from the others, as set forth above. 
     FIG. 10A illustrates the result of an etch into substrate  12 , where the etch recipe is selective to spacer  46  and dielectric layer  36 . FIG. 10B illustrates semiconductor structure  10  after further processing of semiconductor structure  10  illustrated in FIG.  10 A. It can be seen that a subsequent etch that is selective to dielectric layer  36  and to substrate  12  has been carried out to remove spacer  46 , thereby exposing ledge  40 . Subsequent to exposure of ledge  40 , the formation of metal layer  14  (not shown) is carried out and of metal line-forming masking layer  60  (not shown) in order to pattern metal lines. 
     Alternatively, formation of spacer  46  can be carried out substantially by beginning as set forth above. Formation of spacer  46  is carried out as illustrated in FIGS. 9 and 10A. Following formation of spacer  46 , a substantially anisotropic etch is carried out that may be selective to dielectric layer  36 . The structure illustrated in FIG. 11A is substantially identical to that in FIG.  10 B. The removal of spacer  46  and an etch that follows causes pit  20 , seen in FIG. 11B, to form at a lower level than pit surface  26  of substrate  12  seen in FIG.  11 A. 
     FIG. 11A is analogous to FIG. 10B, whereby spacer  46  has been removed after a pit-forming etch. FIG. 11B illustrates the effect of the removal of spacer  46  after which a ledge-forming and pit-deepening etch creates a lower ledge  48  and a lower pit surface  66 . By comparing FIGS. 11A and 11B, it can be seen that lower pit surface  66  of substrate  12  in FIG. 11B is lower than pit surface  26  of substrate  12  in FIG. 11A by a distance of H′. Additionally, FIG. 11B illustrates the formation of lower ledge  48 , at a distance of H below the level of ledge  40  as illustrated in FIG.  11 A. Distances H′ and H may be substantially the same. Accordingly, lower ledge  48  has a level that is beneath upper surface  24  of substrate  12 . 
     At this point, dielectric layer  36  may be removed or it may be left upon upper surface  24  of substrate  12  before the formation of optional sealing dielectric layer  64 , metal layer  14 , and masking layer  16 , depending upon the preferred application. 
     Comparison of FIG. 11A to FIG. 11B illustrates this embodiment of the invention. FIG. 11A has a single-depth depression in substrate  12  to form pit  20 . FIG. 11B has a two-level depression formed into substrate  12  that makes up pit  20 . The two-level depression in substrate  12  include a first level comprising lower ledge  48  and a second level comprising lower pit surface  66 . Thus, a dual-damascene pit structure comprising pit  20  is illustrated in both FIG.  11 A and FIG.  11 B. Where dielectric layer  36  may be removed, the depression in substrate  12  that would form pit  20  in FIG. 11B comprises a dual-damascene depression in substrate  12 . 
     It can now be appreciated that a combination of ledge  40  and lower ledge  48  may occur by varying the configuration of semiconductor structure  10  as depicted in FIG.  11 B. Dielectric layer  36  may be entirely removed to form the dual-damascene depression in substrate  12  as illustrated in FIG.  11 B. Additionally, combination of ledge  40  and lower ledge  48  is created by allowing dielectric layer  36  to be sufficiently thick so that an isotropic etch of dielectric layer  36  causes recession thereof away from lower ledge  48  to form ledge  40  as illustrated in FIG.  11 C. Additionally, the formation of ledge  40  may be formed by patterning a masking layer upon dielectric layer  36  sufficient to expose and remove that portion of dielectric layer  36  that forms ledge  40 . Thus, the combination of lower pit surface  66 , lower ledge  48 , and ledge  40  forms a triple-damascene depression that comprises pit  20 . Hence, removal of dielectric layer  36  results in a dual-damascene depression made entirely of substrate  12 . It can now be appreciated that a triple-damascene structure can be made by performing a second anisotropic etch upon semiconductor structure  10 , illustrated in FIG. 11C, wherein dielectric layer  36  is used as a hard mask, and whereby the levels of lower pit surface  66 , lower ledge  48 , and ledge  40  will all result in lower levels, and upper surface  24  of substrate will have a new ledge next to ledge  40 . 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrated and not restrictive. The scope of the invention is, therefore, indicated by the appended claims and their combination in whole or in part rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.