Self-adhesive die

Abstract

An apparatus for enhancing the thermal performance of semiconductor packages effectively. The concept of this invention is to provide silicon nanowires on the backside of an integrated circuit die to directly attach the die to the substrate, thereby improving the interface between die and substrate, and thus enhancing thermal performance and enhancing reliability by improving adhesion.

Claims

1. A semiconductor package comprising: a semiconductor die, including an active side and an opposite back side, the opposite back side shaped as a plurality of nanowires, a plurality of cavities between the plurality of nanowires; and a substrate having a first side, the opposite back side of the semiconductor die attached to the first side of the substrate.

2. The semiconductor package of claim 1, wherein the plurality of nanowires are of silicon.

3. The semiconductor package of claim 1, wherein the semiconductor die is pressure fit to the first side of the substrate via the plurality of nanowires.

4. The semiconductor package of claim 1, wherein each of the plurality of nanowires is between 10 nanometers and 1 micrometer in diameter.

5. The semiconductor package of claim 1, wherein each of the plurality of nanowires is less than 20 micrometer in length.

6. The semiconductor package of claim 1, wherein the substrate is a laminate.

7. The semiconductor package of claim 1, wherein the plurality of nanowires includes one of an amine based, a sulfur based, and a phosphorous based silane coupling agents.

8. The semiconductor package of claim 1, wherein the substrate is a leadframe.

9. The semiconductor package of claim 8, wherein the leadframe includes a die attach pad, the opposite back side of the semiconductor die being attached to the die attach pad.

10. The semiconductor package of claim 8, wherein the leadframe includes a roughened surface that is in contact with the plurality of nanowires.

11. The semiconductor package of claim 1, wherein the opposite back side of the semiconductor die is shaped as a plurality of nanowires by metal assisted chemical etching.

12. A semiconductor package comprising: a semiconductor die, including an active side and an opposite back side, the opposite back side shaped as a plurality of nanowires, the opposite back side including a plurality of cavities in between the plurality of nanowires; a substrate having a first side, the opposite back side of the semiconductor die attached to the first side of the substrate; and mold compound in the plurality of cavities.

13. The semiconductor package of claim 12, wherein each of the plurality of cavities is less than 20 m deep.

14. The semiconductor package of claim 12, wherein the plurality of nanowires includes one of an amine based, a sulfur based, and a phosphorous based silane coupling agents.

15. The semiconductor package of claim 12, wherein the substrate is a leadframe.

16. The semiconductor package of claim 15, wherein the leadframe includes a die attach pad, the opposite back side of the semiconductor die being attached to the die attach pad.

17. The semiconductor package of claim 12, wherein the substrate is a laminate.

18. The semiconductor package of claim 12, wherein the plurality of nanowires and the plurality of cavities together cover an entire area of the opposite back side.

Description

DESCRIPTION OF THE VIEWS OF THE DRAWING

(1) FIG. 1 is sectional view, including an expanded view of area of interest of a die mounted integrated circuit in according with an embodiment of this invention.

(2) FIG. 2 through FIG. 4 are illustrations of steps in the fabrication of a wafer formed according to an embodiment of this invention.

(3) FIG. 5A is a scanning electron microscope (SEM) photo of Si nanowire arrays on Si.

(4) FIG. 5B is an illustration of the metal-assisted chemical etching of localized regions in a silicon wafer.

(5) FIG. 6 is a flow diagram of the process used to mount a die according to an embodiment of this invention.

(6) In the drawings, like reference numerals are sometimes used to designate like structural elements. It should also be appreciated that the depictions in the figures are diagrammatic and not to scale.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(7) The embodiments of the invention are described with reference to the attached figures. The figures are not drawn to scale and they are provided merely to illustrate the invention. Several aspects of the invention are described below with reference to example applications for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide an understanding of the invention. One skilled in the relevant art, however, will readily recognize that the invention can be practiced without one or more of the specific details or with other methods. In other instances, well-known structures or operations are not shown in detail to avoid obscuring the invention. The embodiments of the invention are not limited by the illustrated ordering of acts or events, as some acts may occur in different orders and/or concurrently with other acts or events. Furthermore, not all illustrated acts or events are required to implement a methodology in accordance with the present invention.

(8) The embodiments of the invention relate generally to the packaging of integrated circuits. As explained in the background section, the testing and operation of an integrated circuit (IC) package may subject the package to temperature extremes and other stresses. Such stresses may cause delamination and degrade the thermal performance of the package. The present invention provides a simple, cost-effective approach for die attached to lead frame surface.

(9) Referring next to FIG. 1, an improved packaging structure design in accordance with one aspect of the invention will be described. FIG. 1 illustrates a cross-sectional view of one embodiment of the present invention where a die 100 is secured to the die attach pad 101 with Silicon nanowires. The nanowires are between the 10 nm and 1 m in diameter and 0.1-20 m long and adhere the bottom of the die to the top surface of the die attach pad. The bottom surface of the die 100 includes a plurality of silicon nanowires.

(10) The bond between the die pad 101 and the back of the die 100 is obtained by applying pressure to the die/die attach pad combination. Pressure is typically in the range of 0.01-1 Megapascal (MPa). In addition, the silicon nanowire can be modified with Amine-based, sulfur-based and phosphorous-based silane coupling agents to substantially enhance the adhesion between silicon nanowire and lead frame surface.

(11) The die mount procedure mentioned above improves adhesion through increasing the bonding area and possibly forming mechanical interlocking using roughened lead frame, thus enabling enhanced package performance and reliability.

(12) Embodiments of the present invention will now be described with reference to FIGS. 2-6. A particular embodiment of the regions pertaining to the die 100, silicon nanowires, die attach pad 101 will be described.

(13) FIG. 2 is an exemplary sample of a semiconductor wafer 200 having top 201 and backside 202 surfaces.

(14) FIG. 3 illustrates application of metal nanoparticles to the backside of the wafer 200. Application can be accomplished in a variety of methods. In this particular embodiment, the particles are applied by printing the backside of the wafer with an ink containing metal nanoparticles. The metal nanoparticles can be Platinum (Pt), Gold (Au) or Silver (Ag). The ink is then dried to evaporate the volatile suspension vehicle.

(15) FIG. 4 shows the backside of the wafer after silicon nanowires, are formed utilizing Metal-assisted Chemical Etching to form the nanowires.

(16) FIG. 5B is a diagrammatic illustration of the Metal-Assisted Chemical Etching process. In this particular embodiment, the etching is accomplished using the chemical reaction:
Si+2H.sub.2O.sub.2+6HF.fwdarw.H.sub.2SiF.sub.6+2H.sub.2O+H.sub.2

(17) As shown in the illustration in FIG. 5B, where a metal catalyst and a semiconductor interface form a cathode and anode, respectively. Through the metal catalyst, charge injection is sustained from a solution to the substrate and charge is balanced by the cathodic and anodic reactions. The presence of a local site for reaction the metal nanoparticle defines the selectivity of the etching mechanism.

(18) FIG. 5A shows a SEM photo of typical arrays of silicon nanowire arrays formed using the Metal-Assisted Chemical Etching process.

(19) Referring next to the flow chart 600 presented in FIG. 6, one suitable approach for forming a package having good electrical and thermal performance and low delamination at the die-die attach pad interface will be described. Unless explicitly indicated otherwise, the operations described below may be performed concurrently or in any order. Operations may be added to or removed from flow chart 600.

(20) Step 601 involves providing a semiconductor wafer containing integrated circuit die, having a top side and a bottom side.

(21) Step 602 involves depositing metal nanoparticles on the backside of the semiconductor wafer utilizing a printing process wherein the printing process prints ink containg metal nanoparticles on the wafer. The ink is then dried to allow the suspension vehicle in the ink to evaporate leaving the metal nanoparticles on the backside of the wafer.

(22) Step 603 involves etching cavities in backside of wafer using metal assisted chemical etching to form nanowires in the backside of wafer. The cavities formed in the backside of the wafer are typically less than 20 m deep.

(23) Step 604 involves separating the integrated circuit die using a method selected from sawing, scribing and breaking or laser cutting.

(24) Step 605 involves providing a substrate for mounting the die. The substrate can be a lead frame, a laminate or a ceramic package.

(25) Step 606 involves adhering the backside of integrated circuit die to the top surface of the substrate with the nanowires therebetween. Adhering the backside of the integrated circuit die to the top surface of the substrate is accomplished by the physical phenomenon called the Van der Waals Force or chemical interaction if coupling agents are used. The Van der Waals Force is the sum of the attractive or repulsive forces between molecules (or between parts of the same molecule) other than those due to covalent bonds, the hydrogen bonds, or the electrostatic interaction of ions with one another or with neutral molecules or charge molecules. Since the backside of the die has a plurality of silicon nanowires, intimate contact is achieved with the substrate, which leads to the Van der Waals interaction. The interaction with each silicon nanowire is small, however, since the total number of silicon nanowires is large, the total Van der Waals force is large enough to cause excellent self adhesion of the die to the substrate. Better adhesion can be further achieved with substrates through chemical modification of silicone nanowire surface with silane coupling agents or having a rough top surface contact area of a substrate such as roughened lead frame. Since there is no interface between die and silicon nanowires, the thermal performance will be effectively improved.

(26) While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only and not limitation. Numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the spirit or scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above described embodiments. Rather, the scope of the invention should be defined in accordance with the following claims and their equivalents.