Through substrate vias for back-side interconnections on very thin semiconductor wafers

Through substrate vias for back-side electrical and thermal interconnections on very thin semiconductor wafers without loss of wafer mechanical strength during manufacturing are provided by: forming (101) desired device regions (21) with contacts (22) on the front surface (19) of an initially relatively thick wafer (18′); etching (104) via cavities (29) partly through the wafer (18′) in the desired locations; filling (105) the via cavities (29) with a conductive material (32) coupled to some device region contacts (22); mounting (106) the wafer (18′) with its front side (35) facing a support structure (40); thinning (107) the wafer (18′) from the back side (181) to expose internal ends (3210, 3220, 3230, 3240, etc.) of the conductive material filled vias (321, 322, 323, 324, etc.); applying (108) any desired back-side interconnect region (44) coupled to the exposed ends (3210, 3220, 3230, 3240, etc.) of the filled vias; removing (109) the support structure (40) and separating the individual device or IC assemblies (48) so as to be available for mounting (110) on a further circuit board, tape or larger circuit (50).

FIELD OF THE INVENTION

The present invention generally relates to semiconductor (SC) devices and integrated circuits (ICs) and their methods of manufacture, and more particularly, structures and methods for providing through-semiconductor-vias (TSVs) on very thin semiconductor wafers, die and/or ICs.

BACKGROUND OF THE INVENTION

A need continues to grow for more complex semiconductor (SC) based devices and circuits able to operate at higher and higher frequencies and handle increasing amounts of power and have lower unit cost. Many of these requirements create conflicting demands on the associated semiconductor device and integrated circuit (IC) design and manufacturing technology. For example, and not intended to be limiting, most SC devices and ICs are fabricated in and/or on substrate wafers, usually but not always single crystal SC wafers, which are then cut up (“singulated”) into the individual devices or ICs. The manufacturing cost can be reduced by using larger and larger wafers, since more devices and ICs can be produced at the same time on larger wafers. However, to avoid undue wafer breakage, the wafer thickness must be increased as the wafer diameter is increased. With thicker wafers, the resulting IC or SC die thickness increases, and it becomes more difficult to remove heat from the devices or ICs. A further complication is the desire to be able to provide additional wiring on the SC die or IC and to include further interconnection layers and passive devices such as inductors, capacitors, and interconnections as a part of the SC die or IC. As used herein, the words “interconnection(s)”, “interconnection layers” and “interconnect levels” and the like, singular or plural, are intended to couple different connection points on or above the SC surface and to include any type of passive components.

If only one surface of the SC die or IC is available for fabricating semiconductor devices and interconnections, the desired degree of complexity may not be achievable with present day structures and fabrication techniques. Further, as operating speed and power handling increase, the problems of efficient heat removal from the device die or IC become more and more difficult. Thus, there is a strong desire to be able to provide interconnections on the rear surface as well as the front surface of the devices or ICs, and to facilitate efficient heat transfer from the front surfaces where the active devices are typically located to the rear surface of the die or IC, without compromising mechanical robustness of the wafers during manufacture.

It is known to use conductor filled vias through the SC wafers as a means of providing electrical and thermal connections between the front and rear surfaces of the wafer and resulting individual device and IC die. These conductor filled vias are referred to as “through-substrate-vias” or “through-semiconductor-vias” and abbreviated as “TSV” (singular) or “TSVs” (plural). However, the desire to use larger diameter wafers for cost efficient manufacturing and at the same time provide highly conductive TSVs for electrically and thermally coupling the front and rear faces of the wafer substrate and resulting die are in conflict. The thicker the wafers, the more difficult it is to etch and fill the TSVs with conductors and the larger the amount of wafer area that must be devoted to such vias. Thus, thicker wafers mean larger TSVs and wasted device and IC surface area, thereby lowering the device and IC packing density on the wafer and increasing the cost of the resulting devices and ICs. Conversely, trying to use large diameter thin wafers so as to maintain the device area packing density reduces the mechanical stability of the wafers. It is well known that thin wafers break more easily, thereby reducing the manufacturing yield and increasing the cost of the resulting die and ICs. Thus, a need continues to exist for improved SC device and IC structures and fabrication techniques that facilitate providing minimal area TSVs for back-side interconnections and/or efficient heat removal without compromising mechanical stability of the wafers during manufacturing.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, or the following detailed description.

For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the invention. Additionally, elements in the drawings figures are not necessarily drawn to scale. For example, the dimensions of some of the elements or regions or layers in the figures may be exaggerated relative to other elements or regions or layers to help improve understanding of embodiments of the invention.

The terms “first,” “second,” “third,” “fourth” and the like in the description and the claims, if any, may be used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation or fabrication in sequences other than those illustrated or otherwise described herein. Furthermore, the terms “comprise,” “include,” “have” and any variations thereof, are intended to cover non-exclusive inclusions, such that a process, method, article, or apparatus that comprises a list of elements or steps is not necessarily limited to those elements or steps, but may include other elements or steps not expressly listed or inherent to such process, method, article, or apparatus. The term “coupled,” as used herein, is defined as directly or indirectly connected in an electrical or non-electrical manner.

As used herein, the term “semiconductor” is intended to include any semiconductor whether single crystal, poly-crystalline or amorphous and to include type IV semiconductors, non-type IV semiconductors, compound semiconductors as well as organic and inorganic semiconductors. Further, the terms “substrate” and “semiconductor substrate” are intended to include single crystal structures, polycrystalline and amorphous structures, thin film structures, layered structures as for example and not intended to be limiting semiconductor-on-insulator (SOI) structures, and combinations thereof. The term “semiconductor” is abbreviated as “SC.” The terms “wafer” and “substrate”, singular or plural, are intended refer to supporting structures that are relatively thin compared to their lateral surface area and used in connection with batch fabrication of electronic devices. Non-limiting examples of such wafers and substrates include: semiconductor wafers, SOI wafers, and other types of supporting structures in or on which active and/or passive electronic devices are fabricated or that are used in connection with the fabrication of such devices. The term “oxide” is intended to include any form of insulating dielectric whether organic or inorganic, and the term “metal” is intended to include any type of electrical conductor, whether organic or inorganic. Non-limiting examples of such conductors are doped semiconductors, semi-metals, alloys and mixtures, combinations thereof, and so forth.

For convenience of explanation and not intended to be limiting, semiconductor devices and methods of fabrication may be described herein for silicon semiconductors but persons of skill in the art will understand that other semiconductor materials can also be used.

FIGS. 1-10are simplified schematic cross-sectional views of a generalized SC device or IC wafer during various stages101-110of manufacture, according to the present invention, showing structures201-210that result from each manufacturing stage101-110. The convention is followed of identifying various common regions or dimensions that may change size and/or shape during the manufacturing process by the same reference numbers, wherein the initial regions or values are identified with a prime (′), as for example, regions or thicknesses18′,30′, d′, etc., and the final regions or values are identified by the same reference number or letter, as for example, regions or thicknesses18,30, d, etc., with the prime (′) omitted, it being understood that the reference number or letter with the prime (′) identifies the initial region or value and the same reference number without the prime identifies the final region or value. Referring now to manufacturing stage101, initial substrate18′ of, for example a semiconductor (SC), having upper surface19, rear surface181and thickness20is provided having therein various device regions211,212,213,214, etc., collectively device regions21. Thickness20(also referred to as “D”) can be comparatively large even though TSVs will be provided in later manufacturing stages, since the problem of providing narrow, high aspect ratio vias in thick wafers is avoided by the present invention. The via aspect ratio (AR) is generally defined as the via length (or depth) divided by the via diameter (or width), i.e., via AR=d/w, where d is the via depth perpendicular to the SC surface and w is the via width (or diameter for a circular via). Vias may have any cross-sectional shape, for example, and not intended to be limiting, round, polygonal, rectangular (like a trench), etc. Substrate thickness20generally depends upon the diameter of initial substrate18′ the larger the diameter the greater the desired thickness20so as to preserve favorable mechanical stability during manufacturing. By way of example and not intended to be limiting, for silicon wafers of 200 mm diameter, thickness20can be in the range of about 650 to 750 micrometers and for silicon wafers of 300 mm diameter, thickness20can be in the range of about 735 to 815 micrometers, although other diameters and thicker and thinner wafers can also be used. Embodiments of the present invention allows the via width w and aspect ratio to be selected independent of the initial wafer thickness D, while at the same time preserving robust wafer mechanical stability during manufacturing and making it possible to obtain thin active device substrates when manufacturing is complete so that heat extraction and electrical coupling to the devices therein or both are facilitated.

The exact nature and number of the various devices formed in device regions21are not important to the present invention, and can include any type of active or passive device and associated interconnections. It is presumed that initial substrate18′ has on surface19various electrical contact regions221,222,223,224,225, etc., collectively contacts22, associated with device regions21. In general, contacts22can be referred to as the “first level metallization” or “first level metal”, and can include the electrical contacts to devices21. Methods for forming such device regions and first level metallization are well known in the art and will depend upon the particular device types and IC functions desired by the designer. Structure201results.

Manufacturing stages102-103ofFIGS. 2-3, illustrate by way of example and not intended to be limiting, the formation of several layers of interconnections tying various first and second level metallization contact areas together and to other contacts. Methods for forming multiplayer metal interconnections are well known in the art and comprise, in general, superposing various dielectric and conductor layers that are patterned to implement the desired interconnections, including various passive devices if needed. Referring now to manufacturing stage102ofFIG. 2, dielectric layer23is applied to surface19of initial substrate18′ and vias opened to those portions of first layer metal22desired to be contacted. These vias are then filled with second level metal portion241over device region212, second level metal portion242over device region213, second level metal portion243over device region214, and so forth to provide desired second level metal interconnections24. Second level metal portions242,242,243, etc., are referred to collectively as second level metal24and the particular portions of first level metal22contacted by second level metal24shown inFIG. 2are merely illustrative of what is accomplished generally and not intended to represent a particular circuit. Structure202results.

Referring now to manufacturing stage103ofFIG. 3, dielectric layer25with upper surface26is desirably applied to form interlayer insulation between second level metal24and third level metal27. Vias are opened to the underlying portions of second level metal24desired to be coupled via third level metal27. These vias are filled, for example, with the third layer metal portions271,272,273, etc., to provide the desired third layer metal interconnections, referred to collectively as third level metal27. Persons of skill in the art will understand that various portions of third level metal27can be placed most anywhere above initial substrate18′ depending on the desired interconnections and any passive devices desired to be included. Thus,FIG. 3is intended to be indicative of what can be accomplished and not to represent a particular circuit implementation. Structure203results. WhileFIGS. 2-3illustrate formation of multiple interconnections levels, any number of metal layers (e.g., metal levels 1, 2, 3 . . . N) may be used depending upon the needs of the circuit or device designer. The structures ofFIGS. 2 and 3are intended merely as examples and not by way of limitation. While the present invention facilitates providing multiple layers of interconnections, different embodiments may use only a single metal layer or multiple dielectric and metal layers as desired by the circuit designer. In the manufacturing stages that follow, multi-layer structure203ofFIG. 3is assumed to be present, but this is not intended to be limiting and persons of skill in the art will understand based on the description herein, that structure203is illustrative of the use of any number (e.g., 1, 2, 3 . . . N) of metal layers, associated dielectric layers and other passive components as may be desired.

Referring now to manufacturing stage104ofFIG. 4, in a preferred embodiment mask28is applied and patterned to provide openings281,282,283,284, etc. Photoresist is suitable for mask28but other well known mask materials (hard, soft and/or combinations thereof) may be used. Any number of openings281,282,283,284. . . M may be provided depending upon the number and location of through substrate vias (TSVs) desired by the designer. Openings281,282,283,284. . . M are desirably located in places that are free of underlying metal levels22,24,27, etc., so that as dielectric layers23,25for example and initial substrate18′ are etched through openings281,282,283,284. . . M in mask28, the desired interconnect levels are not interrupted. Cavities291,292,293,294, etc., (collectively29) of width w and depth30′ (also referred to as depth d′) from surface19are etched in initial substrate18′ under openings281,282,283,284. . . M. Cavities29are desirably etched to depth30′ (depth d′) from surface19, less than substrate thickness20. Cavities29can have high aspect ratios, that is, be slender compared to their depth (w<<d′) even with thick wafers since it is not necessary to etch completely through initial substrate18′. This allows the via diameter or width w to be selected so as to optimize the electrical and thermal conductivity of the vias independent of the initial wafer thickness D. For example, when using a silicon wafer as initial substrate18′ having initial thickness20of about D=700-1000 micrometers, via cavities29of width w˜0.5 to 10 micrometers and depth d′˜10 to 200 micrometers can be achieved using means well known in the art. With silicon substrates, cavity etching is preferably performed by deep reactive ion etching (DRIE) using, for example, the well known “Bosch” process (e.g., see U.S. Pat. No. 5,501,893), but other cavity formation methods may also be employed depending on the nature of initial substrate18′. Laser drilling is a non-limiting example of another technique that can be used with various substrates. Laser drilling equipment such as that manufactured, for example, by XSiL Ltd, Silverstone House, Ballymoss Road, Sandyford, Dublin 18, Ireland is suitable. Structure204results, wherein narrow high aspect ratio via cavities29of depth30′ (depth d′) have been formed in initial substrate18′. Aspect ratios (AR=d/w or d′/w) in the range of 10 to 20 or higher are desirable. Since cavity depth d′ is not constrained by the initial wafer thickness D, very small width w cavities can be provided. An advantage of being able to form narrow high aspect ratio cavities in initial substrate18′ is that they occupy much less substrate area than wide low aspect ratio cavities, so that many more vias can be provided within the same overall wafer or die area with less disruption of the circuit layout.

Referring now to manufacturing stage105ofFIG. 5, mask28is removed using, for example a standard photo-resist strip, the exposed surface rinsed clean and regions321,322,323,324, etc., of conductive material (e.g., metal)32used to fill cavities29and contact any regions of third level metal27desired to be coupled to other conductors. By way of example and not intended to be limiting: (i) portion3211of conductive material (e.g., metal)32couples portion2711of third level metal27to conductive material region321in cavity291; (ii) portion3221of conductive material32couples third level metal portion2712to conductive material region322in cavity292; (iii) portion3231of conductive material32couples portions2721and2731of third level metal27to each other and to conductive material region323in via cavity293; (iv) portion3241of conductive material32couples portion2732of third level metal27to conductive material region324in cavity294, and so forth, depending upon the number of via cavities29that have been etched in initial substrate18′. Passivation layer34having upper surface35is desirably provided over conductive material32, but may be omitted in other embodiments. Interconnect region33refers to the combination of the various interconnect metal layers and associated dielectric layers, whether of only one metal level or multiple metal levels, and with or without passivation layer34. Structure205results. In the manufacturing sequence illustrated by stages101-105, various interconnect layers (or none) can be applied prior to etching of via cavities29in initial substrate18′ at any stage and not limited merely to stage104. In the preferred embodiment, cavities29are etched in initial substrate18′ in step104prior to filling the cavities and providing conductive material32in step105. However, in other embodiments, still further dielectric and metal levels may be applied to provide still further interconnects, including various passive devices if desired, after cavities29are etched and filled. Structure205results.

In some circumstances it is desirable prior to introducing conductive material32into cavities29to apply one or more thin liners (preferably of refractory materials) to cavities29, as for example and not intended to be limiting, a dielectric liner if it is desired to have via conductive material32insulated from substrate18′,18, and/or a barrier layer to prevent subsequent diffusion of conductive material32in via cavities29into substrate18′,18, and/or an adhesion layer to promote adhesion of conductive material32to an underlying liner and/or substrate18′,18. Silicon oxide, silicon nitride and combinations thereof are suitable insulating layers, but other well known dielectric materials can also be used. The insulating layer thickness should be chosen so as to withstand the largest voltage difference that would appear between conductive material32in via cavities29and substrate18′,18. This will depend upon the particular circuit being implemented and is within the competence of those of skill in the art. Tantalum, titanium, Ti/TiN combinations and other refractory metals are suitable barrier and/or adhesion layers. Whether or not such barrier and/or adhesion layers are needed depends upon the semiconductor material of substrate18′,18and conductive material32in via cavities29. For example and not intended to be limiting, when substrate18′,18comprises silicon and it is desired to use copper for conductive material32, it is desirable to provide a Ta barrier layer of about 100 nanometers thickness, more or less in cavities29, to prevent subsequent diffusion of copper from conductive material32in via cavities29into silicon substrate18′,18where it could adversely affect the properties of substrate18′,18. Deposition of copper for conductive material32is preferably by electro-plating. A sputtered initial seed layer may be desirable to facilitate plating. Deposition of, for example, tungsten for conductive material32in via cavities29is preferably accomplished by chemical vapor deposition (CVD). Tungsten provides a closer match to the coefficient of expansion of silicon than does copper, but either metal is useful, as are other semiconductor materials. A suitable barrier material for tungsten via metal is titanium and/or Ti/TiN combinations with thicknesses in the range of about 10 to 40 nanometers of Ti plus about 1 to 30 nanometers of Ti/TiN, but thicker and thinner layers can also be used depending upon the post deposition thermal environment to which the filled vias and substrate will be exposed. The choice of via metal depends on the material of substrate18′,18, the number and location of vias, via size, and the tolerable via thermal and/or electrical resistance, depending on the design goals. For via cavities29of width w in the range of about 0.5 to 10 micrometers, as noted above, liner thicknesses in the range of about 100 nanometers or less are suitable. Persons of skill in the art will understand based on the description herein that such liners may be desirably included depending upon the materials and other choices made the designer. Since in general, liner thicknesses are a relatively small percentage (e.g., ≦1-20%) of via width w, such liners are not shown inFIGS. 5-10to avoid unduly cluttering the drawings.

Referring now to manufacturing stage106ofFIG. 6, the combination of initial substrate18′ and interconnect region33is flipped over and mounted on surface41of support structure40, desirably by means of interface layer36. Support structure40has thickness42, chosen so as to provide robust support of initial substrate18′ and thinned substrate18(seeFIG. 7) during subsequent manufacturing stages. Glass and/or other refractory materials with coefficients of expansion not grossly different than that of substrate18′,18are examples of suitable materials for support structure40. The Electronic Markets Materials Division of 3M Company of St. Paul, Minn. provides suitable commercial tools and materials for bonding initial substrate18′ with interconnect region33to support structure40and is preferred, but other tools and techniques well known in the art (e.g., two-sided sticky-tape on glass, ceramic or SC substrates) may also be used. It will be noted that outer surface35of interconnect region33is bonded to support structure40, so that interconnect region33and underlying device regions21are protected during further manufacturing stages. Also, thickness42of support structure40can be chosen independent of the geometry of via cavities29, so as to provide the desired mechanical robustness to minimize wafer breakage during subsequent manufacturing steps. This is a significant advantage. Structure206results.

Referring now to manufacturing stage107ofFIG. 7, portion31(see structure206ofFIG. 6) of initial substrate18′ is removed, thereby leaving thickness30of thinned substrate18with surfaces3240,3230,3220,3210, etc., of regions324,323,322,321, etc., of conductive material (e.g., metal)32exposed on surface182of thinned substrate18. Removal of portion31of initial substrate18′ is preferably accomplished by grinding followed by chemical-mechanical polishing (CMP), but other techniques well known in the art may also be used. Initial substrate18′ is supported during this thinning operation and resulting thinned substrate18is supported during subsequent manufacturing operations by robust support structure40so that the substrate thinning operation does not result in increasingly fragile wafers. Front face interconnect region33and device regions21are protected during this substrate thinning operation. Structure207results. Thickness30of final thinned substrate18and depth d of exposed conductive material filled vias29ofFIG. 7are generally close to thickness30′ and depth d′ of initial substrate18′ and vias cavities29etched in initial substrate18′ ofFIG. 6, differing by the amount of over-thinning used to expose conductive material32filling vias29if, for example, liners are used in via cavities29. To a first order approximation, d˜d′.

Referring now to manufacturing stage108ofFIG. 8, interconnect region44is provided on surface182of thinned substrate18. Similar to what was explained in connection with interconnect region33, interconnect region44may comprise one or more dielectric and metal levels. In other embodiments, interconnect region44may be omitted and one or more of via conductor regions3240,3230,3220,3210, etc., on substrate surface182bonded to a heat sink or circuit board (not shown). By way of example and not intended to be limiting,FIG. 8illustrates the situation, where multi-layer interconnections have been provided, so that interconnect region44comprises for example, first dielectric layer46with openings extending to exposed portions3240,3230,3220,3210, etc., of via conductive material32, first metal level48contacting these exposed via portions, second dielectric layer50with openings extending to first metal level48, second metal level52filling such openings and extending elsewhere as desired by the designer, third dielectric layer54having openings contacting second metal level52, third metal level56filling such openings and providing, in this example, bonding pads on which solder bumps58may be formed. A more specific example by way of illustration and not intended to be limiting is provided at the left ofFIG. 8, wherein dielectric layer46has an opening above portion3240of conductive material32in via cavity294. Portion481of first metal level48fills this opening and extends elsewhere on first dielectric layer46. Second dielectric layer50overlies first metal level portion481and has an opening extending thereto. Portion521of second metal level52fills this opening and extends over second dielectric layer50. Third dielectric layer54covers second metal level portion521and has an opening extending thereto. Portion561of third metal level56fills this opening and provides bonding pad561that can be used, for example, for forming solder bump581. In further embodiments, additional dielectric and metal levels and other external attachment means well known in the art can also be used. Structure208results.

Referring now to manufacturing stage109ofFIG. 9, support structure40is removed by, for example, softening or dissolving binding layer or adhesive36(or the sticky tape if that is being sued). When glass is used for support structure40, infra-red light transmitted though glass support structure40can be used to thermally soften binding layer or adhesive36, permitting support structure40to be lifted away from surface35of interconnect region33of thinned substrate18. Any remaining portions361of adhesive or binding layer36may then be dissolved or pealed away from surface35of interconnect region33so that substantially completed assembly48is free standing as shown by structure209. Thinned substrate18may be singulated to release the desired individual devices or ICs before or after manufacturing stage109. For convenience of explanation it is assumed herein that assembly48shown by structure209is part of a desired IC, many of which have been formed via batch processing at the same time on the same substrate, e.g., substrate18′,18.

Referring now to manufacturing stage110ofFIG. 10, assembly48is attached to circuit board or tape or larger circuit50by means of solder bumps58present in this example on assembly48or by whatever other bonding means is desired. Since during this attachment operation in manufacturing stage110, assemblies48are being handled individually after singulation rather than in wafer form, the risk of breakage due to the very thin nature of substrate18, whose thickness30(other than the interconnection regions33,44) is approximately equal to depth30′ of etched vias29, wherein, unless substrate18′,18has been substantially over-thinned, d˜d′.FIG. 10also illustrates, for example, how heat removal from, for example, device region213can be improved by the invented structure, since heat sink54can be mounted on interconnect region33directly above and in close proximity to device region213. Since even with multiple layers in interconnect region33, their overall thickness is often smaller than thickness30of thinned wafer18, lower thermal impedance can be obtained.

It will be appreciated that the invented structure and method permit much thinner final substrates18than could otherwise be safely handled by themselves and that can include any desired number of interconnect levels in interconnect region33on its front or primary face19and any desired number of interconnect levels on its back-side or rear face182using back-side interconnect region44, any and all of which can be coupled to narrow high aspect ratio via cavities29filled with conductive material32and extending through thickness30(depth d) of substrate18, which has been thinned in a manner that preserves its mechanical integrity during manufacture. Back-side, interconnect region44having one or more metal levels is formed on newly exposed rear face182of substrate18where narrow high aspect ratio vias cavities29filled with conductive material32are exposed and available, and, because of support structure40, without significant risk of substrate breakage from mechanical handling during manufacturing. Further, when final substrate18is very thin, back-side interconnect region44can add significant additional mechanical strength to facilitate handling assemblies48after singulation. For example, and not intended to be limiting, front side AD region21in many cases is only 5-7 micrometers thick, so that the remaining portion of substrate18between AD region21and rear face182is electrically inactive. Under these circumstances, final thickness30of substrate or wafer18can be made as small as 12 to 20 micrometers. In this situation in order to avoid having assemblies48be excessively fragile after singulation, advantage is taken of the mechanical strength that can be added to substrate18by back-side interconnect region44. For example, a four layer interconnect region can add 5-7 micrometers of additional material to surface182of substrate18. Further interconnect layers can easily add 10 micrometers thickness to substrate18. Thus, when substrate18is desired to be very thin (e.g., 10-20 micrometers or less), back-side interconnect region44can comprise approximately 30% to 50% or more of the total thickness of assembly48, thus greatly increasing the mechanical strength and robustness of assemblies48after singulation when they are to be mounted on board, tape or circuit50. Stated another way, it is useful that thickness30of final substrate18be less than 20% of thickness20of initial substrate or wafer18′ (i.e., 80% or more of initial thickness20of substrate18′ has been removed), more generally be less than about 10%, and preferably less than about 5% of thickness20of initial substrate or wafer18′. Such thicknesses are made possible by the above-described method and structure. This is a substantial advance over the prior art. It will also be appreciate based on the explanation herein, that vias cavities29filled with high thermal conductivity material32can be used to provide more efficient heat extraction from device regions21by providing high thermal conductivity paths from the front side (19,35) of assembly48where regions21are located to the back side (182,62) of assembly48where a heat sink (not shown) can also be attached. Thus, the connections included in interconnect regions33and/or44may serve thermal as well as electrical purposes. This is especially valuable when substrate18is very thin and it is desired to extract heat from the rear rather than the front face of assemblies48.

According to a first embodiment, there is provided a method for forming through-substrate conductor filled vias (321,322,323,324, etc.) for back-side electrical or thermal interconnections (44) or both on a thinned substrate (18), comprising, providing (101) desired device regions (21) with contacts (22) on a front surface (19) of an initial substrate (18′) having a back side (181), forming (104) via cavities (29) to depth d′ from the front surface (19) partly through the initial substrate (18) in desired locations, filling (105) the via cavities (29) with a conductive material (32) coupled to some device region contacts (22), mounting (106) the initial substrate (18′) with its front surface (19) coupled to a support structure (40), thinning (107) the initial substrate (18′) from the back side (181) to provide a final substrate (18) that is thinner than the initial substrate (18′) and on whose back surface (182) are exposed internal ends (3210,3220,3230,3240, etc.) of the conductive material filled vias (321,322,323,324, etc.), applying (108) any desired back-side interconnect region (44) coupled to the one or more exposed ends (3210,3220,3230,3240, etc.) of the conductive material filled vias (321,322,323,324, etc.), and removing (109) the support structure (40) and separating individual device or IC assemblies (48) of the final substrate (18) so as to be available for mounting (110) on a further circuit board, tape or larger circuit (50). According to a further embodiment, the method further comprises prior to the filling step (105), providing one or more refractory liners in the via cavities (29). According to a still further embodiment, the one or more refractory liners comprise a dielectric liner. According to a yet further embodiment, the one or more refractory liners comprise a barrier layer for inhibiting diffusion of the conductive material (32) into the final substrate (18). According to a still yet further embodiment, the one or more refractory liners comprise an adhesion layer for attachment of the conductive material (32) to the final substrate (18) in the via cavities (29). According to a yet still further embodiment, the via cavities (29) have a width w and the one or more refractory liners have a thickness less than about 20% of w. According to another embodiment, the final substrate (18) has a thickness (30) of about 20 micrometers or less and the back-side interconnect region (44) has a thickness of at least about 30% to 50% of the final substrate thickness (30). According to a still another embodiment, the initial substrate (18′) has a first thickness (20) and the final substrate (18) has a second thickness (30) and the second thickness (30) is less than or equal about 20% of the first thickness (20). According to a yet another embodiment, the initial substrate (18′) has a first thickness (20) and the final substrate (18) has a second thickness (30) and the second thickness (30) is less than or equal about 10% of the first thickness (20). According to a still yet another embodiment, the initial substrate (18′) has a first thickness (20) and the final substrate (18) has a second thickness (30) and the second thickness (30) is less than or equal about 5% of the first thickness (20).

According to a second embodiment, there is provided a an electronic assembly (48) formed by a process, comprising, providing (101-103) an initial substrate (18′) having an active device region (21) proximate a first surface (19) thereof, forming (104) via cavities (29) extending part-way through the initial substrate (18′) from the first surface (19), filling (105) the via cavities (29) with a conductive material (32) at least partly coupled to some part of the active device region (21), mounting (106) the initial substrate (18′) on a temporary support structure (40) with the first surface (19) facing the temporary support structure (40) and a rear face (181) of the initial substrate (18′) exposed, removing (107) material from the rear face (181) until a new surface (182) is reached of a thinned substrate (18) on which interior ends (3210,3220,3230,3240, etc.) of the via cavities (29) filled with the conductive material (32) are exposed, providing (108) a further interconnect region (44) on the new surface (182) making contact to at least some of the interior ends (3210,3220,3230,3240, etc.) of the via cavities (29) filled with the conductive material (32), and removing (109) the temporary substrate (40). According to a further embodiment, the thinned substrate (18) has a thickness (30) less than or equal to about 20% of a thickness (20) of the initial substrate (18′). According to a still further embodiment, the via cavities (29) have a refractory liner. According to a yet further embodiment, the refractory liner comprises one or more of an insulating material, a barrier material, or an adhesion material. According to a still yet further embodiment, the further interconnect region (44) has a thickness of 30% to 50% of the thickness (30) of the thinned substrate (18).

According to a third embodiment, there is provided a method for forming electronic assemblies (48), comprising, providing (101-103) an initial semiconductor substrate (18′) of a first thickness (20) and having a region (21) of active devices proximate a first surface (19) thereof, forming (104) via cavities (29) extending part-way through the initial semiconductor substrate (18′) from the first surface (19), filling (105) the via cavities (29) with a conductive metal (32) coupled to some of the active devices, mounting (106) the initial semiconductor substrate (18′) on a temporary support structure (40) with the first surface (19) facing the temporary support structure (40) and a rear face (181) of the initial semiconductor substrate (18′) exposed, removing (107) material from the rear face (181) until a new surface (182) is reached on which interior ends (3210,3220,3230,3240, etc.) of the metal filled via cavities (29) are exposed, thereby forming a thinned semiconductor substrate (18) of a second thickness (30) and still having the region (21) active devices proximate the first surface (19), providing (108) a further interconnect region (44) on the new surface (182) making contact to some or all of the interior ends (3210,3220,3230,3240, etc.) of the via cavities (29) filled with the conductive metal (32, and removing (109) the temporary substrate (40). According to a further embodiment, the method further comprises during or after the providing step (101-103), forming (101-103) one or more interconnect levels on the first surface (19) coupling some of the active devices to each other or to locations that can be contacted by part of the conductive metal (32) during the filling step (105) or both. According to a still further embodiment, the removing step (107) removes at least 80% of the first thickness (20). According to a yet further embodiment, the further interconnect region (44) has a third thickness at least equal to 30% to 50% of the second thickness. According to a still yet further embodiment, the removing step (107) comprises chemical-mechanical-polishing.