Abstract:
In one embodiment, the present invention includes a method for forming a sacrificial material layer, patterning it to obtain a first patterned sacrificial material layer, embedding the first patterned sacrificial material layer into a dielectric material, treating the first patterned sacrificial material layer to remove it to thus provide a patterned dielectric layer having a plurality of openings in which vias may be formed. Other embodiments are described and claimed.

Description:
BACKGROUND 
   Semiconductor devices are typically formed on a semiconductor die, which is then packaged in a package including a substrate. Substrate capacity and cost is a concern for the microelectronics industry. A substrate can include so-called vias, which are conductive structures to connect different metal layers in the substrate. As advances occur, the cost for laser drilling vias is increasing due to the increasing number of vias and decreasing size of the vias, which forces the innovation of new laser technologies. Due to the increasing number of vias, the throughput time of substrate manufacturing is increased. 
   Substrates can be formed of organic material including a core and multiple layers of patterned copper separated by dielectric polymer and interconnected by vias. The vias can be formed by carbon dioxide (CO 2 ) laser drilling. This process can be time consuming, and limited to via diameters greater than about 50 microns. Further, practical concerns such as laser via to pad alignment and manufacturing throughput time restrict substrate design to a single via diameter per buildup (BU) layer. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-section view of a substrate in accordance with an embodiment of the present invention. 
       FIGS. 2A-2D  are process flow diagrams of a method in accordance with one embodiment of the present invention. 
       FIGS. 3A-3E  are process flow diagrams of a method in accordance with another embodiment of the present invention 
   

   DETAILED DESCRIPTION 
   In various embodiments, microvias may be formed in a substrate such as a package substrate or other such substrate using sacrificial materials. While the scope of the present invention is not limited in this regard, such microvias may have diameters of less than approximately 30 microns and up to greater than approximately 120 microns, in some embodiments. In this way, the need for other methods of forming microvias such as using laser techniques can be avoided. In different implementations, sacrificial material may be patterned into shapes that the microvias will take. Then a process to embed the sacrificial material into a dielectric may be performed. The sacrificial material may then be removed, leaving openings in the dielectric. These openings may then be used to form microvias, e.g., by plating of a conductive material such as a metal, by an electroless or electrolytic plating process. 
   Referring now to  FIG. 1 , shown is a cross-section view of a substrate in accordance with an embodiment of the present invention. As shown in  FIG. 1 , substrate  10  may include a plurality of conductive planes  25 , which in some embodiments may be copper (Cu) planes. Between conductive planes  25 , dielectric layers may be present, such as formed using a polymer. Contacts may be made between conductive plates  25  by a plurality of microvias  30 . In various embodiments, the area for the microvias may be formed using a sacrificial material in accordance with an embodiment of the present invention. 
   In various embodiments, a core material  40  may be a polymer or other dielectric material, which can be reinforced with glass fibers. Connections may be made through core material  40  by a plurality of plated through holes (PTHs)  45 . Above core material  40 , conductive planes may be present with dielectric layers  50  separating them. Microvias  30  and  55  are formed in the BU dielectric layers to make electrical connections between the metal layers in the buildup, and are typically metallized using an electroless or electrolytic deposition technique. Microvias  30  and  55 , which are typically formed by laser drilling may instead be formed in accordance with an embodiment of the present invention. Although shown as a core-type package, the scope of the present invention is not limited in this regard and other embodiments may be used in a coreless substrate. 
   Referring now to  FIGS. 2A-2D , shown is a process flow of a method in accordance with one embodiment of the present invention. As shown in  FIG. 2A , a sacrificial material  110  may be patterned in a desired manner. A number of different sacrificial materials may be used, where a stimulus to later remove the material may either be thermal, light, microwave, or any other method. When using a thermal stimulus, the phase change (sublimation) temperature may range from room temperature to approximately 400° Celsius (C). Examples of such materials may include, but are not limited to, naphthalene and its derivatives (sublimes slowly at room temperature but may be made to sublime faster at higher temperatures, e.g., approximately 50° C.), camphor (or other terpene based systems), polycarbonates (and its derivatives) (sublimation temperature of ˜200° C.), poly(norbornene) and derivatives (sublimation temperature of ˜400° C.). The materials may also be made photosensitive by adding photoinitiators such as, but not limited to Irgacure 819, Irgacure 369 etc. By using such materials, they may be placed on desired regions simply by photopatterning. The sacrificial material may be deposited by spin-coating, printing or other methods. 
   Various photolithography or other processes may be performed to obtain a desired pattern of sacrificial material  110 . Then sacrificial material  110  may be embedded within a dielectric  115 . A wide variety of dielectric polymers may be used. Examples of dielectric polymers include thermoplastics, such as polyimides, polyesters, polyamides, and polyolefins, and thermosets, such as epoxies and bismaleimides. A wide variety of methods may be used to place a uniform dielectric coating, including vacuum lamination, spin coating, and other methods known in the art. In various embodiments, a lamination or solvent casting of dielectric  115  on sacrificial material  110  may be performed to embed sacrificial material  110  within dielectric  115 , as shown in  FIG. 2B . In one embodiment, the sacrificial material is polycarbonate and the dielectric material is a polyimide. The polycarbonate is patterned analogous to a metal pattern on a substrate such that it can be easily removed. The polyimide film is taken slightly above the glass transition temperature (Tg) such that it softens and is pressed onto the patterned polycarbonate, such that it is embedded into the film. The polycarbonate embedded dielectric film is laminated onto the substrate. In another embodiment, the sacrificial material is patterned by photolithography, etching or other methods on a surface, from which it may be easily removed. The dielectric polymer is poured over the patterned sacrificial material and solvent cast to form a film with the sacrificial material embedded in it. Alternatively, the sacrificial material may be patterned directly on the substrate and the dielectric solvent cast on the substrate. 
   To position a sacrificial material where microvias are desired to be located, a deposition process may be performed to apply dielectric  115  including sacrificial material  110  onto a substrate. More specifically, as shown in  FIG. 2C , a substrate  100 , which may be a package substrate or other substrate, may have conductive interconnects  120 , which may be Cu pads or lines to provide interconnections to lower layers (not shown in  FIG. 2C ) of substrate  100 . Accordingly, dielectric layer  115  may be deposited above substrate  100  as shown in  FIG. 2C , e.g., by a lamination process. Then to eliminate sacrificial material  110 , a given treatment process may be performed such as an ultraviolet (UV) treatment or a thermal treatment to release sacrificial material  110 , resulting in the structure shown in  FIG. 2D , which is a cross section view of a substrate including openings for formation of microvias. Of course, the microvias may then be metallized by a plating process. 
     FIGS. 3A-3E  show a similar method for forming microvias using sacrificial materials. However, note that various differences in the processes exist. In the embodiment of  FIG. 3A , a sacrificial material  220  is deposited onto a substrate  200  that includes patterned conductive interconnects  210 , such as patterned Cu pads/lines, although other metals such as aluminum, silver, gold and others may be used. In various embodiments, sacrificial material  220  may be coated onto substrate  200 . In one embodiment, the sacrificial material is modified poly(norbornene) with a photoinitiator. The sacrificial material is coated onto the patterned substrate by spin-coating. Then sacrificial material  220  may be patterned using photolithography in connection with a mask  225 , as shown in  FIG. 3B . After such UV treatment, sacrificial material  220  is patterned as shown in  FIG. 3C . Then deposition of a dielectric material  230  may be performed. For example, a dielectric film is laminated onto the patterned sacrificial material. Finally, another treatment such as a thermal or UV treatment may be performed to eliminate sacrificial material  220 , as shown in  FIG. 3E  in which a plurality of openings are provided within dielectric material  230  to enable formation of microvias. While shown with these particular processes in the embodiments of  FIGS. 2A-2D  and  3 A- 3 E, the scope of the present invention is not limited in this regard. 
   While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.