Patent Publication Number: US-2006003497-A1

Title: Semiconductor device packages including hermetic packaging elements for at least partially encapsulating conductive elements and other package elements for protecting the portions of semiconductor devices not covered by the hermetic package elements, and packaging methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is a continuation of application Ser. No. 10/912,469, filed Aug. 3, 2004, pending, which is a continuation of application Ser. No. 10/353,752, filed Jan. 28, 2003, now U.S. Pat. No. 6,770,514, issued Aug. 3, 2004, which is a continuation of application Ser. No. 10/074,844, filed Feb. 13, 2002, now U.S. Pat. No. 6,514,798, issued Feb. 4, 2003, which is a divisional of application Ser. No. 09/640,801, filed Aug. 17, 2000, now U.S. Pat. No. 6,432,752, issued Aug. 13, 2002. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to hermetically packaged semiconductor devices and, more particularly, to semiconductor devices including stereolithographically fabricated hermetic packages. The present invention also relates to the use of stereolithography to fabricate hermetic packages on semiconductor device assemblies or on semiconductor dice.  
     Semiconductor Device Packages  
      2. Background of Related Art  
      Solid-state electronic devices, such as semiconductor dice, which are also referred to as semiconductor devices, are typically manufactured on substrates of semiconductor material, such as silicon, germanium, gallium arsenide, or indium phosphide. Circuitry is formed on one surface of a substrate with input and output pads being formed on an active surface of the semiconductor dice of the substrate to facilitate electrical connection with other electronic devices.  
      Semiconductor devices are often packaged to protect the semiconductor dice from mechanical damage, external contamination, and moisture. Typical types of semiconductor device packages include plastic encapsulated packages, quasi-hermetic cavity type packages, and fully hermetic cavity type packages.  
      When plastic packages are used, the plastic of the package contacts metal elements of the semiconductor device. Typically, these plastic-metal interfaces do not seal sufficiently to prevent exposure of the die to moisture or to soluble ions. When brought into contact with a semiconductor die, these soluble ions act as electrolytes and, thus, cause corrosive failure of the semiconductor die. In addition, the extensive use of precious metals coupled with base metals in semiconductor dice provides direct current (dc) galvanic potentials for electrochemical corrosion reactions and dendrite growth, thereby affecting the performance and life of the encapsulated semiconductor chip. Thus, while plastic encapsulation of semiconductor devices is the most common form of packaging, semiconductor dice in plastic packages are still vulnerable to electrochemical processes.  
      As a result of the problems associated with the plastic encapsulation of semiconductor devices, it is sometimes desirable to hermetically package semiconductor dice to prevent external moisture and chemicals from contacting the same. Hermetic packages for semiconductor chips are generally formed from metal or ceramic material. Typically, conventional hermetic packages include a lid or a cap to seal a semiconductor device mounted on a suitable substrate. When a semiconductor device includes a die connected to a lead frame, the leads of the lead frame also need to be hermetically sealed. In metal packages, the individual leads are sealed into the metal platform by separated glass seals. In ceramic packages, the leads extend through the ceramic and are sealed thereby.  
      Several types of ceramic packages are used to hermetically seal semiconductor chips. Exemplary ceramic hermetic packages include ceramic dual-in-line packages, hard glass packages, side-brazed dual-in-line packages, bottom-brazed or top-brazed chip carriers, pin-grid arrays, or other multilayer ceramic packages. Some of these types of packages are described in U.S. Pat. Nos. 4,769,345, 4,821,151, 4,866,571, 4,967,260, 5,014,159, and 5,323,051. Typically, these packages include a base with a receptacle formed therein to receive a semiconductor device and a lid that is disposable over the receptacle.  
      In sealing these hermetic packages, the material of one or both of the lid and the base typically must be heated to a temperature that will facilitate sealing of the lid over the receptacle of the base and, thus, hermetic sealing of the semiconductor device within the receptacle. These hermetic packages are, however, somewhat undesirable due to the high temperatures (e.g., at least about 400° C. to about 500° C.) and lengthy sealing times (e.g., as much as about one or two hours) that are required to obtain a hermetic seal as the lid of a hermetic package is sealed over the receptacle of the hermetic package. Such high temperatures for prolonged periods of time can cause oxidation of the leads of a semiconductor device or cracking of the passivation layer over the active surface of a semiconductor device, both of which can cause the semiconductor device to fail.  
      Moreover, as conventional hermetic packages are typically fabricated separately from the semiconductor device assembly disposed therein, conventional hermetic packages are relatively bulky and can occupy undesirably large amounts of the real estate on a carrier substrate to which the packaged semiconductor device is connected.  
      U.S. Pat. No. 5,958,100 (hereinafter “the &#39;100 patent”), which is assigned to the assignee of the present invention, discloses a relatively small, substantially hermetic package that is fabricated on semiconductor dice at the wafer stage. The material of the hermetic package, which is referred to as a thermoplastic glass, is a glass with a lower melting temperature than the glass and ceramic materials typically used as hermetic packages. Nonetheless, the packaged semiconductor devices of the &#39;100 patent are somewhat bulky. Moreover, despite the lower process temperatures of the materials used to fabricate the hermetic packages of the &#39;100 patent, packaging temperatures may be as high as about 350° C.; As the &#39;100 patent teaches a method of molding the hermetic package directly onto a semiconductor device assembly by use of known molding equipment, the semiconductor device may be exposed to these molding temperatures for several minutes, until the thermoplastic glass cools.  
      Less bulky hermetic packages are disclosed in U.S. Pat. Nos. 5,682,065 and 5,903,044, both of which have been assigned to the assignee of the present invention. Each of these patents discloses a method of fully hermetically packaging semiconductor dice at the wafer scale. Thus, the hermetic package disclosed in these patents takes up much less space than that occupied by conventional hermetic packages. The hermetic package of these patents is somewhat undesirable, however, in that the conventional hermetic packaging materials used to form such a package have very high process temperatures (e.g., up to about 600° C.). Thus, the semiconductor dice can be damaged during packaging.  
      Thus, a hermetic packaging method is needed to fabricate a compact, substantially hermetic package wherein the temperature to which a semiconductor device is exposed during the packaging process is reduced, as is the amount of time the semiconductor device is exposed to the increased temperature.  
     Stereolithography  
      In the past decade, a manufacturing technique termed “stereolithography,” also known as “layered manufacturing,” has evolved to a degree where it is employed in many industries.  
      Essentially, stereolithography as conventionally practiced involves utilizing a computer to generate a three-dimensional (3-D) mathematical simulation or model of an object to be fabricated, such generation usually effected with 3-D computer-aided design (CAD) software. The model or simulation is mathematically separated or “sliced” into a large number of relatively thin, parallel, usually vertically superimposed layers, each layer having defined boundaries and other features associated with the model (and thus the actual object to be fabricated) at the level of that layer within the exterior boundaries of the object. A complete assembly or stack of all of the layers defines the entire object, and surface resolution of the object is, in part, dependent upon the thickness of the layers.  
      The mathematical simulation or model is then employed to generate an actual object by building the object, layer by superimposed layer. A wide variety of approaches to stereolithography by different companies has resulted in techniques for fabrication of objects from both metallic and nonmetallic materials. Regardless of the material employed to fabricate an object, stereolithographic techniques usually involve disposition of a layer of unconsolidated or unfixed material corresponding to each layer within the object boundaries, followed by selective consolidation or fixation of the material to at least a partially consolidated, fixed, or semisolid state in those areas of a given layer corresponding to portions of the object, the consolidated or fixed material also at that time being substantially concurrently bonded to a lower layer of the object to be fabricated. The unconsolidated material employed to build an object may be supplied in particulate or liquid form, and the material itself may be consolidated or fixed, or a separate binder material may be employed to bond material particles to one another and to those of a previously formed layer. In some instances, thin sheets of material may be superimposed to build an object, each sheet being fixed to a next lower sheet and unwanted portions of each sheet removed, a stack of such sheets defining the completed object. When particulate materials are employed, resolution of object surfaces is highly dependent upon particle size, whereas when a liquid is employed, surface resolution is highly dependent upon the minimum surface area of the liquid which can be fixed and the minimum thickness of a layer that can be generated. Of course, in either case, resolution and accuracy of object reproduction from the CAD file is also dependent upon the ability of the apparatus used to fix the material to precisely track the mathematical instructions indicating solid areas and boundaries for each layer of material. Toward that end, and depending upon the layer being fixed, various fixation approaches have been employed, including particle bombardment (electron beams), disposing a binder or other fixative (such as by ink-jet printing techniques), or irradiation using heat or specific wavelength ranges.  
      An early application of stereolithography was to enable rapid fabrication of molds and prototypes of objects from CAD files. Thus, either male or female forms on which mold material might be disposed might be rapidly generated. Prototypes of objects might be built to verify the accuracy of the CAD file defining the object and to detect any design deficiencies and possible fabrication problems before a design was committed to large-scale production.  
      In more recent years, stereolithography has been employed to develop and refine object designs in relatively inexpensive materials and has also been used to fabricate small quantities of objects where the cost of conventional fabrication techniques is prohibitive for same, such as in the case of plastic objects conventionally formed by injection molding. It is also known to employ stereolithography in the custom fabrication of products generally built in small quantities or where a product design is rendered only once. Finally, it has been appreciated in some industries that stereolithography provides a capability to fabricate products, such as those including closed interior chambers or convoluted passageways, which cannot be fabricated satisfactorily using conventional manufacturing techniques. It has also been recognized in some industries that a stereolithographic object or component may be formed or built around another, pre-existing object or component to create a larger product.  
      However, to the inventor&#39;s knowledge, stereolithography has yet to be applied to mass production of articles in volumes of thousands or millions, or employed to produce, augment or enhance products including other, pre-existing components in large quantities, where minute component sizes are involved, and where extremely high resolution and a high degree of reproducibility of results is required. In particular, the inventor is not aware of the use of stereolithography to fabricate substantially hermetic packages for semiconductor devices. Furthermore, conventional stereolithography apparatus and methods fail to address the difficulties of precisely locating and orienting a number of pre-existing components fQr stereolithographic application of material thereto without the use of mechanical alignment techniques or to otherwise assure precise, repeatable placement of components.  
     SUMMARY OF THE INVENTION  
      According to one aspect, the present invention includes a packaged semiconductor device. A first embodiment of the packaged semiconductor device includes a semiconductor die operably connected to a carrier substrate and a substantially hermetic package formed over the semiconductor die and in contact with the carrier substrate so as to seal the semiconductor die from the external environment. The semiconductor die may be any type of semiconductor die known in the art and may be connected to the carrier substrate by any type of connection known in the art. The substantially hermetic package includes superimposed, contiguous, mutually adhered layers of a suitable hermetic packaging material, such as a thermoplastic glass.  
      In another embodiment, the hermetically packaged semiconductor device of the present invention includes a semiconductor die operably connected to a lead frame, the die and portions of the lead frame adjacent thereto being sealed in a substantially hermetic package. Again, the semiconductor die and the lead frame may be of any type known in the art, and the semiconductor die may be connected to the lead frame by any known, suitable method. The substantially hermetic package has a plurality of superimposed, contiguous, mutually adhered layers of a suitable hermetic packaging material, such as a thermoplastic glass.  
      In yet another embodiment of the packaged semiconductor device of the present invention, a semiconductor die is substantially hermetically packaged at the wafer scale. The hermetic package includes external circuits that communicate with the bond pads of the semiconductor die so as to facilitate connection of the packaged semiconductor device to a higher level substrate or to a lead frame.  
      Another aspect of the present invention includes the stereolithographic fabrication of a hermetic package over a semiconductor die that is operably connected to a carrier substrate, a lead frame, or another higher level connection element. Preferably, the hermetic package is fabricated by forming layers of unconsolidated hermetic material adjacent to or around the assembly and by consolidating the hermetic material in selected regions adjacent to the semiconductor die or the connection element. Preferably, selective laser sintering (SLS) techniques are employed to fabricate the hermetic package from layers of particulate or powdered hermetic packaging material.  
      As it is important that packages of the present invention protect the semiconductor dice therein from moisture, accompanying ions, and other potentially damaging factors from the environment external to the semiconductor dice, the substantially hermetic packages of the present invention are preferably manufactured from materials that will adhere and seal to the materials of the semiconductor device so as to prevent potentially damaging factors from contacting same. Accordingly, the stereolithography processes that are preferred for fabricating the substantially hermetic packages of the present invention are capable of fabricating structures from materials that have good hermetic qualities when used with semiconductor devices.  
      In one such stereolithography process, known as “selective laser sintering” or “SLS,” structures are fabricated from layers of powdered or particulate material. The particles in selected regions of each of the layers can be bonded together by use of a laser under the control of a computer. The laser either heats the material particles and sinters adjacent particles together, heats a binder material mixed in with the particles to bond the particles, or heats a binder material with which the material particles are coated to secure adjacent particles in the selected regions of a layer to one another.  
      Another exemplary stereolithography process that may be used to fabricate substantially hermetic packages incorporating teachings of the present invention is referred to as “laminated object manufacturing” or “LOM.” Laminated object manufacturing involves the use of a laser or other cutting device to define the peripheries of a layer of an object from a sheet of material. Adjacent layers of the object are secured to one another to form the object.  
      The stereolithographic package fabrication method of the present invention preferably includes the use of a machine vision system to locate the semiconductor device assemblies, individual semiconductor dice, or other substrates over which the substantially hermetic packages are to be fabricated, as well as the features or other components on or associated with the semiconductor device assemblies, dice, or substrates (e.g., bond wires, leads, etc.). The use of a machine vision system directs the alignment of a stereolithography system with each semiconductor device assembly, die, or substrate for material disposition purposes. Accordingly, the semiconductor device assemblies, dice, or other substrates need not be precisely mechanically aligned with any component of the stereolithography system to practice the stereolithographic embodiment of the method of the present invention.  
      In a preferred embodiment, the substantially hermetic package to be fabricated upon a semiconductor device assembly, die, or other substrate in accordance with the invention is fabricated using precisely focused electromagnetic radiation in the form of a laser under control of a computer and responsive to input from a machine vision system, such as a pattern recognition system, to define each layer of the object to be formed from a layer of material disposed on the semiconductor device assembly, die, or substrate.  
      Other features and advantages of the present invention will become apparent to those of skill in the art through a consideration of the ensuing description, the accompanying drawings, and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       FIG. 1  is a schematic cross-sectional representation of a semiconductor device assembly including a semiconductor die wire bonded to a carrier substrate, the semiconductor device assembly being substantially hermetically packaged according to the method of the present invention;  
       FIG. 2  is a schematic cross-sectional representation of a semiconductor device assembly including a semiconductor die flip-chip bonded to a carrier substrate, the semiconductor device assembly being substantially hermetically packaged according to the method of the present invention;  
       FIG. 3  is a schematic cross-sectional representation of a semiconductor device assembly including a semiconductor die and a leads-over-chip (LOC) type lead frame connected thereto, the semiconductor device assembly being substantially hermetically packaged according to the method of the present invention;  
       FIG. 4  is a schematic cross-sectional representation of a semiconductor device assembly including a semiconductor die wire bonded to a conventional lead frame, the semiconductor device assembly being substantially hermetically packaged according to the method of the present invention;  
       FIG. 5  is a schematic, partial cross-sectional representation of a substantially hermetically packaged semiconductor die according to the present invention;  
       FIGS. 1A, 2A ,  3 A,  4 A, and  5 A are schematic representations of exemplary hermetically packaged devices such as those illustrated in  FIGS. 1, 2 ,  3 ,  4 , and  5 , respectively, wherein a metal is used as the hermetic packaging material and conductive structures of the packaged semiconductor device are electrically isolated from the metal hermetic packaging material;  
       FIG. 6  is a schematic, partial cross-sectional representation depicting flip-chip bonding of the packaged semiconductor die of  FIG. 5  to a higher level substrate;  
       FIG. 7  is a schematic, partial cross-sectional representation depicting the wire bond connection of the packaged semiconductor die of  FIG. 5  to a conventional lead frame;  
       FIG. 8  is a schematic representation of a semiconductor wafer with a plurality of semiconductor dice;  
       FIG. 9  is a schematic, partial cross-sectional representation of the wafer of  FIG. 8 , illustrating the application of a first portion of hermetic packages over a surface of the wafer;  
       FIG. 10  is a schematic, partial cross-sectional representation of the wafer of  FIG. 9 , illustrating thinning of the wafer;  
       FIG. 11  is a schematic, partial cross-sectional representation of the Wafer of  FIG. 10 , illustrating the removal of material located in streets between adjacent semiconductor dice of the wafer;  
       FIG. 12  is a schematic, partial cross-sectional representation of the wafer of  FIG. 11 , illustrating the application of a second portion of the hermetic packages over the exposed surface of the semiconductor dice and between adjacent semiconductor dice;  
       FIG. 13  is a schematic, partial cross-sectional representation of the wafer of  FIG. 12 , illustrating exposure of bond pads of the semiconductor dice through the hermetic packages;  
       FIG. 14  is a schematic, partial cross-sectional representation of the wafer of  FIG. 13 , illustrating the fabrication of conductive traces on the hermetic packages and in contact with the exposed bond pads;  
       FIG. 15  is a schematic representation of an exemplary stereolithography apparatus, a selective laser sintering apparatus, that can be employed in the method of the present invention to fabricate hermetic packages on semiconductor devices or other substrates in accordance with the method of the present invention;  
       FIG. 16  is a schematic representation of another exemplary stereolithographic apparatus, a laminated object manufacturing apparatus, that can be employed in the method of the present invention to fabricate hermetic packages in accordance with the method of the present invention;  
       FIG. 17  is a partial cross-sectional side view of a semiconductor device or substrate disposed on a platform of a stereolithographic apparatus and depicting a hermetic package being fabricated on the semiconductor device or substrate; and  
       FIG. 18  is a schematic representation of a variation of the method illustrated in  FIGS. 15 and 17 , wherein the hermetic package has two portions or sections. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring to  FIG. 1 , an embodiment of a substantially hermetically packaged semiconductor device  10  is illustrated. Semiconductor device  10  includes a semiconductor die  12  electrically connected to a higher level carrier substrate  16 . As illustrated, a back side  13  of semiconductor die  12  is secured to carrier substrate  16 , with bond pads  14  on an active surface  15  of semiconductor die  12  being connected to corresponding terminals  17  of carrier substrate  16  by way of wire bonds  18 .  
      Semiconductor device  10  also includes a substantially hermetic package  20  that completely covers semiconductor die  12 , wire bonds  18 , and terminals  17  and substantially seals each of these elements to protect same from the environment external to semiconductor device  10 . As illustrated, hermetic package  20  extends over the surface of carrier substrate  16  just beyond terminals  17 . Accordingly, hermetic package  20  consumes a minimal amount of real estate on carrier substrate  16  and is, therefore, relatively compact.  
      Hermetic package  20  is preferably formed from a suitable hermetic packaging material, such as a metal, ceramic, or glass. Exemplary types of glass that are most preferred for fabricating hermetic package  20  are thermoplastic glasses, such as those disclosed in U.S. Pat. No. 5,089,445 (hereinafter “the &#39;445 patent”), issued to Gaylord L. Francis on Feb. 18, 1992, and in U.S. Pat. No. 5,089,446 (hereinafter “the &#39;446 patent”), issued to Lauren K. Cornelius et al. on Feb. 18, 1992, the disclosures of both of which are hereby incorporated by this reference. The &#39;445 and &#39;446 patents disclose tin-phosphorus oxyfluoride and lead sealing glasses, respectively. These glasses have sealing temperatures of below about 350° C. and coefficients of thermal expansion (CTEs) of below about 110×10 7 /° C.  
       FIG. 2  illustrates another embodiment of a semiconductor device  10 ′ according to the present invention. Semiconductor device  10 ′ includes a semiconductor die  12  flip-chip bonded to a higher level carrier substrate  16 . Accordingly, bond pads  14  of semiconductor die  12  are connected to terminals  17  of carrier substrate  16  by way of solder balls  18 ′ or other similar conductive structures. Semiconductor die  12 , solder balls  18 ′, and terminals  17  are substantially hermetically sealed within a hermetic package  20 ′. As illustrated, hermetic packaging material may fill the space between active surface  15  of semiconductor die  12  and carrier substrate  16 . Alternatively, this space may be filled with an underfill material prior to packaging or the space may remain open.  
      As shown in  FIG. 2 , the amount of real estate on carrier substrate  16  that is occupied by hermetic package  20 ′ is only slightly larger than the amount of real estate occupied by semiconductor die  12 . Accordingly, hermetic package  20 ′ is relatively compact.  
      Referring now to  FIG. 3 , another embodiment of a packaged semiconductor device  10 ″ according to the present invention includes a leads-over-chip (LOC) type semiconductor die  12 ″ and a correspondingly configured lead frame  30 . Bond pads  14 ″ of semiconductor die  12 ″ are electrically connected to corresponding leads  32  of lead frame  30  as known in the art, such as by wire bonds or tape automated bonding (TAB).  
      The hermetic package  20 ″ of semiconductor device  10 ″ substantially hermetically encapsulates semiconductor die  12 ″ in its entirety, as well as the portions of leads  32  that traverse active surface  15 ″ of semiconductor die  12 ″. Accordingly, packaged semiconductor device  10 ″ may have a relatively small hermetic package  20 ″.  
      Yet another embodiment of a substantially hermetically packaged semiconductor device  10 ′″ incorporating teachings of the present invention is depicted in  FIG. 4 . Semiconductor device  10 ′″ includes a semiconductor die  12 , the bond pads  14  of which are operably connected to leads  36  of a conventional (i.e., die paddle type) lead frame  34  by wire bonds  38 . A hermetic package  20 ′″ is disposed over semiconductor die  12  and wire bonds  38 , as well as over portions of lead frame  34  adjacent semiconductor die  12 , including the portions of leads  36  proximate wire bonds  38 .  
       FIG. 5  depicts another embodiment of a substantially hermetically packaged semiconductor device  110  that includes only a semiconductor die  12  and a substantially hermetic package  120 . Semiconductor die  12  includes a passivation layer  130  on active surface  15  thereof to provide protection for the active circuitry of semiconductor die  12 , as is known in the art. While such a passivation layer  130  provides some sealing effect, it does not provide a substantially hermetical seal over semiconductor die  12 .  
      Hermetic package  120  has one or more circuit traces  122  on a surface thereof, each circuit trace  122  communicating with a bond pad  14  of semiconductor die  12  through a cavity or via  123  extending through the packaging material so as to facilitate the connection of semiconductor die  12  to external components. For example, semiconductor device  110  can be operably connected to external components by way of a carrier substrate  16 , as shown in  FIG. 6 , to which semiconductor device  110  is either flip-chip bonded or connected by way of wire bonds or other known connective elements. Alternatively, semiconductor device  110  can be operably connected to external components by way of a lead frame  34 , as illustrated in  FIG. 7 .  
      Turning to  FIGS. 1A, 2A ,  3 A,  4 A, and  5 A, the illustrated hermetically packaged semiconductor devices  10 A,  10 A′,  10 A″,  A′″, and  110 A, respectively, are substantially the same as the hermetically packaged semiconductor device structures illustrated in  FIGS. 1, 2 ,  3 ,  4 , and  5 , respectively. Hermetic packages  20 A,  20 A′,  20 A″,  20 A′″, and  120 A are, however, formed from a metal. In addition, hermetically packaged semiconductor devices  10 A,  10 A′,  10 A″,  10 A′″, and  110 A each include electrically insulative coatings or layers  21 ,  21 ′,  21 ″,  21 ′″, and  121 , respectively, formed over at least the electrically conductive structures of semiconductor devices  12 ,  12 ″ so as to insulate the electrically conductive structures from the metal of hermetic packages  20 A,  20 A′,  20 A″,  20 A′″, and  120 A. These electrically insulative coatings  21 ,  21 ′,  21 ″,  21 ′″, and  121  may also be formed from a hermetic packaging material in accordance with teachings of the present invention, or from a suitable material by other, known methods.  
      Referring now to  FIGS. 8-14 , a method for forming a hermetic package  120  on one or more semiconductor dice  12  is illustrated.  
       FIG. 8  illustrates a wafer  72  with a plurality of semiconductor dice  12  thereon. As shown, semiconductor dice  12  have not been separated, but remain physically connected to one another as part of wafer  72 . When in wafer form, semiconductor dice  12  are electrically isolated from one another by way of streets  74  scribed between adjacent semiconductor dice  12 .  
      As shown in  FIG. 9 , the side of wafer  72  on which active surfaces  15  of semiconductor dice  12  are located is coated with a layer of hermetic packaging material to form a first portion  124  of hermetic package  120 . First portion  124  has a substantially planar surface and a sufficient thickness to entirely cover active surfaces  15  and streets  74  located between adjacent semiconductor dice  12 . Preferably, the hermetic packaging material of first portion  124  can be etched so as to facilitate the subsequent exposure of bond pads  14  therethrough. First portion  124  may be formed by the stereolithography process described hereinafter. Alternatively, first portion  124  may be formed by any other suitable, known technique, such as spin coating, dip coating, or flow coating.  
      While  FIG. 9  illustrates the formation of first portion  124  on the side of wafer  72  on which active surfaces  15  of semiconductor dice  12  are located, first portion  124  may also be formed on back side  76  of wafer  72 .  
      Turning now to  FIG. 10 , the thickness of wafer  72  may be optionally reduced by removing material thereof from back side  76  thereof by any suitable, known method, such as by mechanical abrasion or chemical mechanical planarization (CMP) (e.g., chemical mechanical polishing). Reducing the thickness of wafer  72  may also improve the planarity of back side  76  thereof. If first portion  124  of hermetic package  120  (see  FIG. 5 ) is applied to back side  76  of wafer  72 , such a thinning process may be effected prior to applying first portion  124  to back side  76 .  
      With reference to  FIG. 11 , a layer of a suitable resist material (not shown) may be applied, as known in the art, to the opposite side of wafer  72  from that upon which first portion  124  of hermetic package  120  (see  FIG. 5 ) is disposed. When the layer of resist material is applied to back side  76  of wafer  72 , the layer of resist material is patterned so as to form a photomask through which regions of back side  76  that are located directly beneath streets  74  are exposed. When the layer of resist material is applied over active surfaces  15  of semiconductor dice  12 , the layer of resist material is patterned so that streets  74  are exposed therethrough. The regions of wafer  72  that are exposed through the resist material are then etched with a suitable etchant to remove the material of streets  74 . The orientations and positions of semiconductor dice  12  relative to one another are maintained, however, by first portion  124 . The photomask may then be removed from wafer  72  by known processes.  
      As an alternative to the use of a photomask, a hard mask, such as a silicon oxide or silicon nitride hard mask, may be formed on either back side  76  of wafer  72  or over active surfaces  15  of semiconductor dice  12 . Streets  74  may then be etched through, as known in the art. Such a hard mask need not be removed from wafer  72 .  
      As another alternative, the material of wafer  72  located under and in vertical alignment with streets  74  may be removed by other known processes, such as by the use of wafer saws, so long as the orientations and lateral positions of semiconductor dice  12  are maintained by first portion  124  of hermetic package  120 . Once the semiconductor material lying between adjacent semiconductor dice  12  has been removed, wafer  72  is inverted and hermetic packaging material is applied to the other side of semiconductor dice  12  and between adjacent semiconductor dice  12 , as shown in  FIG. 12 , to form a second portion  126  of hermetic package  120 . As illustrated, second portion  126  is applied to back sides  76  of semiconductor dice  12 .  
      Referring now to  FIG. 13 , a mask (not shown), such as a photomask or hard mask, is disposed on hermetic package  120  over active surfaces  15  of semiconductor dice  12  so that regions  128  of hermetic package  120  located over bond pads  14  are exposed therethrough. These regions  128  are then removed by known processes, such as by use of a suitable, known etchant, such as hydrofluoric acid in wet etch processes or a suitable fluorocarbon in dry etch processes, thereby exposing bond pads  14  through hermetic package  120 . The mask may thereafter be removed from hermetic package  120  by known processes.  
      As shown in  FIG. 14 , an electrically conductive layer (e.g., of metal) is formed on hermetic packages  120  and in contact with bond pads  14  so as to again substantially hermetically seal semiconductor dice  12  within their respective hermetic packages  120 . The electrically conductive layer is then patterned, as known in the art (e.g., by mask and etch techniques) to form conductive circuit traces  122  without disrupting the hermetic seals provided by hermetic package  120 . Each circuit trace  122  communicates with a corresponding bond pad  14  to facilitate connection thereof with a circuit external to semiconductor device  110 .  
      Semiconductor devices  110  may be disconnected from one another by removing hermetic packaging material located between adjacent semiconductor devices  110  without disrupting the substantially hermetic seal provided by hermetic package  120 . Such disconnection of semiconductor devices may be effected by use of a wafer saw, mask and etch processes, or otherwise, as known in the art. Each resulting semiconductor device  110  includes a semiconductor die  12  that is substantially fully hermetically sealed on the top, bottom, and all edges thereof by hermetic package  120  and circuit traces  122  thereof, thereby leaving no portion of semiconductor die  12  exposed to an environmental attack.  
     Methods of Fabricating Substantially Hermetic Packages  
      In another aspect, the present invention includes methods of fabricating hermetic packages according to the present invention, such as those illustrated in and described with reference to  FIGS. 1-5 .  
      While the hermetic package fabrication process of the present invention is preferably performed substantially simultaneously on several semiconductor dice  12  or other substrates, such as prior to singulating semiconductor dice  12  from wafer  72  or on a collection of individual semiconductor devices or other substrates, such as partial wafers, individual semiconductor devices or other substrates can also be provided with hermetic packages in accordance with teachings of the present invention. As another alternative, the method of the present invention can be used to substantially simultaneously fabricate hermetic packages  20  on a collection of different types of semiconductor devices or other substrates.  
      The hermetic packages of the present invention are preferably fabricated from a material with good sealing or hermetic properties when applied to a semiconductor die, lead frame, or substrate. Exemplary materials that may be used in the packages of the present invention include, without limitation, ceramics, metals, and glasses, such as thermoplastic glasses. Of course, if metals are used to form the hermetic packages of the present invention, electrically conductive structures of the packaged semiconductor device should be electrically isolated from the hermetic packaging material to prevent electrical shorting and failure of the semiconductor device. For example, a thin layer of a suitable insulative material, such as glass or ceramic, may be formed over regions of electrically conductive structures of the semiconductor device that will be covered with the hermetic packaging material, as described above with reference to  FIGS. 1A, 2A ,  3 A,  4 A, and  5 A, respectively. These thin insulative layers  21 ,  21 ′,  21 ″,  21 ′″, and  121  may be formed in accordance with methods of the present invention or otherwise, as known in the art. Preferably, the thin insulative layers  21 ,  21 ′,  21 ″,  21 ′″, and  121  that are used when a hermetic package is formed from a metal also provide hermetic protection to the adjacent regions of the semiconductor device, while the metal hermetic package provides both hermetic protection and robustness.  
      By way of example and not to limit the scope of the present invention, the hermetic packages can be manufactured from thermally conductive materials in powdered or particulate form or in the form of thin sheets.  
      For simplicity, the ensuing description is limited to an explanation of a method of stereolithographically fabricating hermetic packages  20  directly on semiconductor dice  12 . As should be appreciated by those of skill in the art, however, the method described herein is also useful for fabricating hermetic packages separately from a semiconductor device or other substrate, as well as for disposing hermetic packages on packaged semiconductor devices or semiconductor devices having one or more layers of protective material on the back sides thereof. However, the effectiveness of heat transfer from a packaged or coated device will naturally be somewhat compromised unless the coating material is thermally conductive or enhanced with thermally conductive materials.  
     Stereolithography Apparatus and Methods  
       FIG. 15  schematically depicts various components, and operation, of an exemplary stereolithography apparatus  80  to facilitate the reader&#39;s understanding of the technology employed in implementation of the method of the present invention, although those of ordinary skill in the art will understand and appreciate that apparatus of other designs and manufacture may be employed in practicing the method of the present invention. Preferred, basic stereolithography apparatus for implementation of the method of the present invention, as well as operation of such apparatus, are described in great detail in United States Patents assigned to DTM Corporation or to Board of Regents, The University of Texas System, both of Austin, Tex., or to The B.F. Goodrich Company of Akron, Ohio, such patents including, without limitation, U.S. Pat. Nos. 4,863,538; 4,944,817; 5,017,753; 5,132,143; 5,155,321; 5,155,324; 5,156,697; 5,182,170; 5,252,264; 5,284,695; 5,304,329; 5,316,580; 5,342,919; 5,352,405; 5,385,780; 5,430,666; 5,527,877; 5,648,450; 5,733,497; 5,749,041; and 5,817,206. The disclosure of each of the foregoing patents is hereby incorporated herein by this reference.  
      With continued reference to  FIG. 15  and as noted above, a 3-D CAD drawing, in the form of a data file, of an object (e.g., hermetic package  20  of  FIG. 1 ) to be fabricated is placed in the memory of a computer  82  controlling the operation of apparatus  80 , if computer  82  is not a CAD computer in which the original object design is effected. In other words, an object design may be effected in a first computer in an engineering or research facility and the data files transferred via wide or local area network, tape, disc, CD-ROM, or otherwise as known in the art to computer  82  of apparatus  80  for object fabrication.  
      The data is preferably formatted in an STL (for STereoLithography) file, STL being a standardized format employed by a majority of manufacturers of stereolithography equipment. Fortunately, the format has been adopted for use in many solid-modeling CAD programs, so translation from another internal geometric database format is often unnecessary. In an STL file, the boundary surfaces of an object are defined as a mesh of interconnected triangles.  
      Data from the STL files resident in computer  82  is manipulated to build an object, such as a hermetic package  20 , illustrated in  FIGS. 1-5 , one layer at a time. Accordingly, the data mathematically representing one or more objects to be fabricated are divided into subsets, each subset representing a slice or layer of the object. The division of data is effected by mathematically sectioning the 3-D CAD model into at least one layer, a single layer or a “stack” of such layers representing the object. Each slice may be from about 0.003 to about 0.020 inch thick. As mentioned previously, a thinner slice promotes higher resolution by enabling better reproduction of fine vertical surface features of the object or objects to be fabricated.  
      Apparatus  80  includes a horizontal platform  90  on which an object is to be fabricated or a substrate disposed for fabrication of an object thereon. Platform  90  is preferably vertically movable in fine, repeatable increments responsive to computer  82 . Material  86  is disposed in a substantially uniform layer of desired thickness by a particulate spreaders that operates under control of computer  82 . The particulate spreader includes two cartridges  104   a  and  104   b  disposed adjacent platform  90  and a roller or scraper bar or blade  102  that is vertically fixed and horizontally movable across platform  90 . As a sufficient quantity of particulate material  86  to form a layer of desired thickness is pushed upward out of each cartridge  104   a ,  104   b  by a vertically movable support  106   a ,  106   b , respectively, roller or scraper  102  spreads that quantity of particulate material  86  in a uniform layer of desired thickness (e.g., 0.003 to 0.020 inches) over platform  90 , a substrate disposed thereon, or an object being fabricated on platform  90  or a substrate thereon. Supports  106   a ,  106   b  of cartridges  104   a ,  104   b  are also preferably vertically movable in fine, repeatable increments under control of computer  82 .  
      By way of example and not limitation, and as noted above, the layer thickness of material  86  to be formed, for purposes of the invention, may be on the order of about 0.003 to 0.020 inch, with a high degree of uniformity. It should be noted that different material layers may have different heights, so as to form a structure of a precise, intended total height or to provide different material thicknesses for different portions of the structure.  
      With continuing reference to  FIG. 15 , in a selective laser sintering embodiment of the hermetic package fabrication process of the present invention, material  86  preferably comprises particles of one or more materials that are useful in hermetic packaging applications, such as thermoplastic glasses, ceramics, metals, or a mixture of any of the foregoing, which material  86  is deposited by cartridges  104   a ,  104   b  and roller or scraper  102  over platform  90  with the latter in its uppermost position. Alternatively, the particles of hermetic packaging material may be coated with a suitable binder resin for use in hermetic packaging applications or mixed with particles of such a binder resin.  
      A fixative head, such as a laser  92 , an ink jet nozzle, or a metal spray gun, is suspended above platform  90 . The type of fixative head employed depends upon the nature of the particulate material  86  employed to fabricate the object, as well as an optional binder employed to consolidate particles of material  86  in selected regions of the layer.  
      When the fixative head includes a laser  92 , apparatus  80  may also include a galvanometer  94  with one or more pivotal mirrors. Before fabrication of a first layer of an object is commenced, the operational parameters for apparatus  80  are set to adjust the size (diameter, if circular) of the laser light beam used to consolidate or fix material  86 . In addition, computer  82  automatically checks and, if necessary, adjusts by means known in the art the surface level  88  of material  86  over platform  90  or a substrate upon which an object is to be fabricated to maintain same at an appropriate focal length for laser beam  98 . Alternatively, the height of the mirror of galvanometer  94  may be adjusted responsive to a detected surface level  88  to cause the focal point of laser beam  98  to be located precisely at the surface of material  86  at surface level  88  if level  88  is permitted to vary, although this approach is more complex.  
      The size of the laser beam “spot” impinging on the surface of material  86  to consolidate or fix same may be on the order of 0.001 inch to 0.008 inch. Resolution is preferably ±0.0003 inch in the X-Y plane (parallel to surface  100 ) over at least a 0.5 inch×0.25 inch field from a center point, permitting a high resolution scan effectively across a 1.0 inch×0.5 inch area. Of course, it is desirable to have substantially this high a resolution across the entirety of surface  100  of platform  90  to be scanned by laser beam  98 , such area being termed the “field of exposure,” such area being substantially coextensive with the vision field of a machine vision system employed in the apparatus of the invention as explained in more detail below. The longer and more effectively vertical the path of laser beam  96 / 98 , the greater the achievable resolution.  
      The sequence of operation and movements of platform  90 , cartridges  104   a ,  104   b  and their supports  106   a ,  106   b , roller or scraper  102 , and laser  92  or another type of fixative head are controlled by computer  82 .  
      Once roller or scraper  102  spreads and smooths material  86  into a first thin layer  108  of substantially uniform thickness (for example, 0.003 to 0.020 inches) over platform  90  or a substrate disposed thereon, laser  92  directs a laser beam  96  toward the mirrors of galvanometer  94 , which reflect a laser beam  98  toward selected regions of layer  108  in order to affix the particles of material  86  in the selected regions by melting or sintering particles of material  86  to secure adjacent particles of the thermally conductive component of material  86  that are exposed to laser beam  98  to one another. Particles of material  86  in these selected regions of layer  108  are preferably affixed in a regular horizontal pattern representative of a first or lowermost transverse layer or slice of the object to be fabricated, as numerically defined and stored in computer  82 . Accordingly, laser beam  98  is directed to impinge on particles of first thin layer  108  in those areas where the corresponding layer of the object to be fabricated is comprised of solid material and avoids those areas outside of a periphery of the corresponding layer of the object to be fabricated, as well as those areas of the corresponding layer where a void or aperture exists. Laser beam  98  is withdrawn upon consolidation of material  86  in regions comprising at least the peripheral outline of the corresponding layer of the object being fabricated.  
      With reference to  FIG. 17 , when material  86  ( FIG. 15 ) in each of the regions of layer  108  ( FIG. 15 ) that correspond to solid areas of the corresponding layer of the object to be fabricated have been exposed to laser beam  98  ( FIG. 15 ), a first particle layer  108   a  ( FIG. 17 ), or first preform layer, is formed. First particle layer  108   a  has at least the peripheral outline of the corresponding layer of the object being fabricated at that vertical or longitudinal level, material  86  within apertures or voids in layer  108  remaining unconsolidated as loose, unfused particles.  
      Next, platform  90  is indexed downwardly a vertical distance which mayor may not be equal to the thickness of the just-fabricated layer  108   a  (i.e., a layer-manufactured structure may have layers of different thicknesses). Another layer  108   b  of unconsolidated particulate material  86  is then formed over layer  108   a  as previously described. Laser beam  98  is then again directed toward selected regions of the new layer  108   b  to follow a horizontal pattern representative of a next, higher layer or slice of the object to be fabricated, as numerically defined and stored in computer  82 . As each successive layer  108  is formed by consolidating material  86  in selected regions, the consolidated material is preferably also secured to the immediately underlying, previously fabricated layer  108 . It will be appreciated that, in  FIG. 17 , the thicknesses of each layer  108  has been exaggerated to clearly illustrate the layered manufacturing process.  
      Of course, since an object to be fabricated by use of a stereolithography apparatus, such as apparatus  80 , may not have uniformly configured and sized cross-sections taken transverse to the length thereof, adjacent layers or slices of the object, while contiguous, may not be identical.  
      The deposition and smoothing of layers  108  of unconsolidated particles of material  86  and the selective fusing of particles of material  86  in selected regions of each successive layer  108  is continued under control of computer  82  for one or more layers until a recognizable three-dimensional structure gradually emerges, and the layering process is further continued until a completed object has been fabricated. At any time during the fabrication process, or thereafter, unconsolidated particulate material  86  is removed and may be recovered. Any recovered material may be subsequently used to form another object.  
      As an alternative to the use of a laser to sinter or otherwise bond particles of material  86  in the selected regions of each unconsolidated material layer  108  together to form at least partially consolidated layers  108   a ,  108   b , an ink jet nozzle or a metal spray gun may be employed as the fixative head. Exemplary apparatus including such fixative heads and exemplary uses thereof are disclosed in the following U.S. Pat. Nos. 5,340,656; 5,387,380; 5,490,882; 5,490,962; 5,518,680; 5,660,621; 5,684,713; 5,775,402; 5,807,437; 5,814,161; 5,851,465; and 5,869,170, each of which have been assigned to the Massachusetts Institute of Technology, Cambridge, Mass. The disclosures of each of the foregoing patents are hereby incorporated by this reference. Such a fixative head deposits a liquid binder (e.g., resin or metal) over the particles of material  86  in selected regions of each layer  108 , penetrating therebetween and solidifying, thus bonding particles in the selected regions of layer  108  to at least partially consolidated regions of the next underlying formed layer  108   a . If an ink jet nozzle is employed as the fixative head, the binder may comprise a nonmetallic binder such as a polymer compound. Alternatively, when a metal spray gun is used as the fixative head, a metallic binder such as a copper or zinc alloy or Kirksite, a proprietary alloy available through Industrial Modern Pattern and Mold Corp., may be employed. In the case of a metal alloy, the binder may be supplied in wire form which is liquified (as by electric arc heating) and sprayed onto the uppermost particulate layer. Another alternative is to liquify the distal end of the binder wire with a laser or other heating means immediately above the unconsolidated powder layer rather than using a metal spray.  
      Referring again to  FIG. 15 , in practicing the present invention, a commercially available stereolithography apparatus operating generally in the manner as that described above with respect to apparatus  80  is preferably employed, but with further additions and modifications as hereinafter described for practicing the method of the present invention. For example, and not by way of limitation, the SINTERSTATION® 2000, SINTERSTATION® 2500, and SINTERSTATION® 2500 plus stereolithography systems, each offered by DTM Corporation of Austin, Tex., are suitable for modification.  
       FIG. 16  illustrates a laminated object manufacturing (LOM) variation of the hermetic package fabrication process of the present invention. LOM employs sheets of material to form an object. As depicted in  FIG. 16 , an apparatus  200  for effecting the LOM method includes a platform  202 , actuating means  204  for moving platform  202  in vertical increments, a sheet feeder  206 , a laser head  208 , and a control computer  210 . Sheet feeder  206  may comprise a photocopier-type feeder and provide individual sheets, or may comprise a roll-type feeder with a feed roller and a take-up roller, as desired. In either case, a sheet  212  of suitable material, such as a thin metal (e.g., copper, aluminum, tungsten, titanium, etc.) or a ceramic or glass sheet, is placed on platform  202 . Laser head  208 , under control of computer  210 , cuts an outline of the periphery of that layer of the object being fabricated. The surrounding sheet material may then be removed, if desired, and a second, uncut sheet  212 ′ placed over sheet  212  is bonded to sheet  212  by suitable means, after which laser head  208  cuts the perimeter outline of the second layer of the object. If desired, the laser may be used to rapidly heat the second sheet  212 ′ and bond it to the first sheet  212  before second sheet  212 ′ is cut at its periphery. Alternatively, a heated roller  214  may be biased against and rolled over the uppermost second sheet  212 ′ to secure the uppermost second sheet  212 ′ and the immediately adjacent, underlying sheet  212  to each other before the uppermost second sheet  212 ′ is cut to define the periphery of the corresponding layer of the object being fabricated. The embodiment of  FIG. 16  is particularly suitable for substantially concurrently forming a large plurality of hermetic packages on the back side of an unsingulated semiconductor wafer or other large-scale substrate.  
      Such bonding can be effected by melting or sintering, or by an adhesive material disposed on the top, bottom, or both surfaces of each sheet. One or both surfaces of the sheets may be precoated with adhesive, or adhesive may be applied thereto, such as by rolling or spraying, during the layered manufacturing process.  
      Referring again to  FIG. 15 , it should be noted that apparatus  80  useful in the method of the present invention may include a camera  140  which is in communication with computer  82  and preferably located, as shown, in close proximity to galvanometer  94  located above surface  100  of support platform  90 . Camera  140  may be any one of a number of commercially available cameras, such as capacitive-coupled discharge (CCD) cameras available from a number of vendors. Suitable circuitry as required for adapting the output of camera  140  for use by computer  82  may be incorporated in a board  142  installed in computer  82 , which is programmed as known in the art to respond to images generated by camera  140  and processed by board  142 . Camera  140  and board  142  may together comprise a so-called “machine vision system” and, specifically, a “pattern recognition system” (PRS), operation of which will be described briefly below for a better understanding of the present invention. Alternatively, a self-contained machine vision system available from a commercial vendor of such equipment may be employed. For example, and without limitation, such systems are available from Cognex Corporation of Natick, Mass. For example, the apparatus of the Cognex BGA Inspection Package™ or the SMD Placement Guidance Package™ may be adapted to the present invention, although it is believed that the MVS-8000 product family and the Checkpoint product line, the latter employed in combination with Cognex PatMax™ software, may be especially suitable for use in the present invention.  
      It is noted that a variety of machine vision systems are in existence, examples of which and their various structures and uses are described, without limitation, in U.S. Pat. Nos. 4,526,646; 4,543,659; 4,736,437; 4,899,921; 5,059,559; 5,113,565; 5,145,099, 5,238,174; 5,463,227; 5,288,698; 5,471,310; 5,506,684; 5,516,023; 5,516,026; and 5,644,245. The disclosure of each of the immediately foregoing patents is hereby incorporated by this reference.  
      Of course, apparatus  200  depicted in  FIG. 16  could also be equipped with such a machine vision system.  
     Stereolithographic Fabrication of the Hermetic Packages  
      Referring again to  FIGS. 15 and 17 , in order to facilitate fabrication of one or more hermetic packages  20  in accordance with the method of the present invention with apparatus  80 , a data file representative of the size, configuration, thickness and surface topography of, for example, a particular type and design of semiconductor die  12  or other substrate on which one or more hermetic packages  20  are to be fabricated is placed in the memory of computer  82 . Also, it may be desirable to place a data file representative of the various features of semiconductor die  12  in memory.  
      One or more semiconductor dice  12 , wafers  72 , or other substrates may be placed on surface  100  of platform  90  to have hermetic packages  20  fabricated thereon. Camera  140  is then activated to locate the position and orientation of each semiconductor die  12 , including those on a wafer  72 , or other substrate. The features of each semiconductor device  10 , wafer  72 , or other substrate are compared with those in the data file residing in memory, the locational and orientational data for each semiconductor device  10 , wafer  72 , or other substrate then also being stored in memory. It should be noted that the data file representing the design size, shape and topography for each semiconductor die  12  or other substrate may be used at this juncture to detect physically defective or damaged semiconductor devices  10  or other substrates prior to fabricating a hermetic package  20  thereon or before conducting further processing or assembly of semiconductor die  12  or other substrates. Accordingly, such damaged or defective semiconductor dice  12  or other substrates can be deleted from the stereolithographic hermetic package fabrication process, from subsequent testing, or from assembly with other components. It should also be noted that data files for more than one type (size, thickness, configuration, surface topography) of semiconductor die  12  or other substrate may be placed in computer memory and computer  82  programmed to recognize not only the locations and orientations of each semiconductor die  12  or other substrate, but also the type of semiconductor device  10  or other substrate at each location upon platform  90  so that material  86  may be at least partially consolidated by laser beam  98  in the correct pattern and to the height required to fabricate hermetic packages  20  in the appropriate, desired locations on each semiconductor device  10  or other substrate.  
      Continuing with reference to  FIGS. 15 and 17 , a substantially uniform layer  108  of material  86  is disposed over wafer  72  or the one or more semiconductor dice  12  or other substrates on platform  90  to a depth substantially equal to the desired thickness of a formed layer  108  of hermetic package  20 .  
      Laser  92  is then activated and scanned to direct laser beam  98 , under control of computer  82 , toward specific locations of surface level  88  relative to each semiconductor device  10  or other substrate to effect the aforementioned partial cure of material  86  to form a first layer  108   a  of each hermetic package  20 . Platform  90  is then lowered and another layer  108  of material  86  of a desired thickness disposed over formed layer  108   a . Laser  92  is again activated to add another layer  108   b  to each hermetic package  20  under construction. This sequence continues, layer by layer, until each of the layers  108  of each hermetic package  20  have been completed. As illustrated, layers  108  are first formed laterally adjacent edges of a semiconductor die  12  or other substrate, then over one of the major surfaces thereof (e.g., active surface  15  or back side  13 ). Each semiconductor die  12  or other substrate is then inverted on platform  90  and the remaining layers  108  of hermetic package  20  are formed. Of course, a portion of hermetic package  20  may be prefabricated and disposed on platform  90  prior to the disposal of one or more semiconductor dice  12  thereon. Other stereolithographic fabrication sequences for hermetic packages  20  are, of course, also within the scope of the present invention.  
      In  FIG. 17 , the first, bottommost layer of hermetic package  20  is identified by numeral  108   a , and the second layer is identified by numeral  108   b . As illustrated, hermetic package  20  has only a few layers  108 . In practice of the invention, however, hermetic packages  20  may have many thin layers  108 . Accordingly, hermetic packages  20  with any number of layers  108  are within the scope of the present invention.  
      Each layer  108  of hermetic package  20  may be built by first defining any internal and external object boundaries of that layer with laser beam  98 , then hatching solid areas of that layer of hermetic package  20  located within the object boundaries with laser beam  98 . An internal boundary of a layer may comprise a portion, a void or a recess in hermetic package  20 , for example. If a particular layer includes a boundary of a void in the object above or below that layer, then laser beam  98  is scanned in a series of closely spaced, parallel vectors so as to develop a continuous surface, or skin, with improved strength and resolution. The time it takes to form each layer  108  depends upon the geometry thereof, the surface tension and viscosity of material  86 , and the thickness of that layer.  
      With reference to  FIG. 18 , in embodiments where it is desirable to form a hermetic package  20  completely around semiconductor die  12  or another substrate, a first portion  24  of hermetic package  20  may be provided on platform  90 . First portion  24  may include a receptacle  25  configured to receive semiconductor die  12  or another substrate prior to the stereolithographic fabrication of the remainder, or a second portion  26 , of hermetic package  20  around the remaining surfaces of semiconductor die  12  or the other substrate. Alternatively, first portion  24  may have a substantially planar surface on which semiconductor device  10  is to be disposed prior to fabricating the remainder of hermetic package  20 . First portion  24  may be fabricated stereolithographically or otherwise, as known in the art.  
      Of course, it is the purpose of every embodiment of a substantially hermetic package incorporating teachings of the present invention to protect the semiconductor device or devices enclosed therein. Accordingly, it may be desirable to drive reactive gases, such as oxygen and hydrogen, out of a package and, thus, away from the semiconductor device or devices therein, prior to sealing the hermetic package. As an example of the manner in which reactive gases may be substantially removed within the confines of a substantially hermetic package, the hermetic packages or at least the final layers thereof may be fabricated in an inert atmosphere, such as an atmosphere containing nitrogen or other inert gases.  
      Referring again to  FIGS. 15 and 17 , once hermetic packages  20  have been fabricated, platform  90  is elevated and removed from apparatus  80 , along with any substrate (e.g., semiconductor die  12 , wafer  72  (see  FIG. 8 ), or other substrate) disposed thereon and any stereolithographically fabricated structures, such as hermetic package  20 . Excess, unconsolidated material  86  (e.g., excess powder or particles) may be manually removed from platform  90 , from any substrate disposed thereon, and from hermetic package  20 . Each hermetically packaged semiconductor device  10  or other substrate is removed from platform  90 .  
      Residual particles of the material that was used to fabricate hermetic package  20  are preferably removed by use of known solvents or other cleaners that will not substantially degrade, deform, or damage hermetic package  20  or the substrate (e.g., semiconductor die  12 ) on which hermetic package  20  was fabricated. Such cleaning is particularly important when electrically conductive materials, such as metals, are used to fabricate hermetic package  20 , as a residue of such electrically conductive materials can cause electrical shorts that may result in failure of semiconductor die  12 .  
      Although  FIGS. 15-18  illustrate the stereolithographic fabrication of hermetic package  20  on a substrate, such as a semiconductor die  12 , a wafer  72 , or another substrate, hermetic package  20  or a portion thereof can be fabricated separately from a substrate, then assembled with the substrate by known processes.  
      The use of a stereolithographic process as exemplified above to fabricate hermetic package  20  is particularly advantageous since a large number of hermetic packages  20  may be fabricated in a short time, the dimensions and positions thereof are computer-controlled to be extremely precise, wastage of packaging material  86  is minimal, and the stereolithography method requires minimal handling of semiconductor dice  12 , wafers  72 , or other substrates.  
      Stereolithography is also an advantageous method of fabricating hermetic packages according to the present invention since, when resinous binders are used to secure adjacent particles of thermally conductive material in selected regions, stereolithography can be conducted at substantially ambient temperature, the small spot size and rapid traverse of laser beam  98  resulting in negligible thermal stress upon semiconductor devices  10 , wafers  72 , or other substrates, as well as on the features thereof.  
      The stereolithography fabrication process may also advantageously be conducted at the wafer level or on multiple substrates, saving fabrication time and expense. As the stereolithography method of the present invention recognizes specific semiconductor devices  10  or other substrates, variations between individual substrates are accommodated. Accordingly, when the stereolithography method of the present invention is employed, hermetic packages  20  can be simultaneously fabricated on different types of semiconductor dice  12  or other substrates, as well as on both semiconductor devices  10  and other substrates.  
      While the present invention has been disclosed in terms of certain preferred embodiments, those of ordinary skill in the art will recognize and appreciate that the invention is not so limited. Additions, deletions and modifications to the disclosed embodiments may be effected without departing from the scope of the invention as claimed herein. Similarly, features from one embodiment may be combined with those of another while remaining within the scope of the invention.