PACKAGING OF ELECTRONIC CHIPS WITH AIR-BRIDGE STRUCTURES
A circuit assembly for fabricating an air bridge structure and a method of fabricating an integrated circuit package capable of supporting a circuit assembly including an air bridge structure. A circuit assembly comprises an electronic chip and a conductive structure embedded in a plurality of materials having a plurality of vaporization temperatures. The plurality of materials is formed on the electronic chip and the conductive structure is coupled to the electronic chip. To fabricate the circuit assembly, a support structure that may include post structures is formed on an electronic chip. Interstices of the support structure are filled with a material having a vaporization temperature that is less than the vaporization temperature of the support structure. Conductive structures are embedded in the support structure and the material, and a connective structure is mounted on the support structure. Finally, the material is removed from the interstices by heating the circuit assembly.
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This application is a Divisional of U.S. application Ser. No. 10/931,510 filed Sep. 1, 2004, which is a Divisional of U.S. application Ser. No. 09/382,929, filed Aug. 25, 1999, which are incorporated herein by reference.
FIELD OF THE INVENTIONThis invention relates to the packaging of electronic chips, and more particularly to the packaging of electronic chips having air-bridge structures.
BACKGROUND OF THE INVENTIONAs the density of devices, such as resistors, capacitors, and transistors, in an integrated circuit is increased, the distance between the signal carrying conductors is decreased, and the capacitive coupling between the conductors is increased. Several problems result from the increased capacitive coupling. First, the increased capacitive coupling reduces the rate at which information can be transferred along each of the signal carrying conductors. Second, the increased capacitive coupling between the signal carrying conductors reduces the noise margin on the conductors. In the worst case, a signal on one signal carrying conductor is capacitively coupled to an adjacent signal carrying conductor, and the information on the adjacent conductor is destroyed. Since it is desirable to avoid destroying information, it is also desirable to reduce the capacitive coupling between the signal carrying conductors of an integrated circuit.
In an integrated circuit, decreasing the dielectric constant of an insulator that separates two adjacent signal carrying conductors reduces the capacitive coupling between the two adjacent signal carrying conductors. Silicon dioxide is the most commonly used insulator in the fabrication of integrated circuits and has a relatively high dielectric constant of about four. Carbon dioxide has a smaller dielectric constant than silicon dioxide, so replacing silicon dioxide with carbon dioxide reduces the capacitive coupling between the two adjacent conductors. Unfortunately, the thermal conductivity of carbon dioxide is much less than the thermal conductivity of silicon dioxide. This lower thermal conductivity causes a reduction in the rate at which heat is conducted away from an integrated circuit chip that employs a carbon dioxide insulator, which can result in the catastrophic failure of the integrated circuit.
Air has a dielectric constant of one, which is less than the dielectric constant of carbon dioxide and much less than the dielectric constant of silicon dioxide. Replacing silicon dioxide with air in an integrated circuit reduces the capacitive coupling between signal carrying conductors. Air bridge structures, which are structures consisting primarily of signal carrying conductors surrounded by air in an integrated circuit, are fabricated to reduce the dielectric constant in the conductive structures of an integrated circuit. Unfortunately, since, in an air bridge structure, the signal carrying conductors are no longer embedded in a layer of silicon dioxide, the structural integrity of the integrated circuit is decreased. This problem is especially significant when an integrated circuit fabricated using air bridge structures is packaged as a flip chip,
For these an other reasons there is a need for the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The above mentioned problems with air bridge structures, closely spaced conductors, silicon dioxide insulators and other problems are addressed by the various embodiments of the present invention and will be understood by reading and studying the following specification.
In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific preferred embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that logical, mechanical and electrical changes may be made without departing from the spirit and scope of the present inventions. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.
Integrated circuit assembly 100 is not limited to use in connection with a particular type of electronic chip 103. Memory chips, such as a dynamic random access memory (DRAM) chips, static random access memory (SRAM) chips, read-only-memory (ROM) chips, and random access memory (RAM) chips, microprocessor chips, logic chips, digital signal processing chips, analog signal processing chips, and application specific integrated circuit (ASIC) chips can all be used in connection with integrated circuit assembly 100.
Material layer 106 is fabricated on the surface of electronic chip 103, and has a plurality of vaporization temperatures. In one embodiment, material layer 106 is fabricated from a plurality of materials in which each of the plurality of materials has a different vaporization temperature.
Material layer 106 includes a structural component, such as ribbed structure 109, and a non-structural component, such as fill material 112. An advantage of using a structural component in the various embodiments of the present invention is that the structural component is easily modified to support flip-chip mounting or silicon on substrate mounting of electronic chip 103, without interfering with the layout of the air-bridge structures. Ribbed structure 109 is designed to support the entire weight of electronic chip 103, if electronic chip 103 is mounted using a C4 or flip-chip interconnect. If electronic chip 103 is not mounted using as a C4 or flip-chip interconnect, then the design of ribbed structure 109 is only required to support long run air bridge structures. Ribbed structure 109, in one embodiment, is fabricated by forming a layer of inorganic material, such as SiO2, Si3N4, or a low temperature SiO2, on the surface of electronic chip 103. The layer of inorganic material is formed to a depth equal to the distance between the surface of electronic chip 103 and the first wiring layer of electronic chip 103. The surface of the layer of inorganic material is patterned and etched to form ribbed structure 109.
Fill material 112 is a non-structural component, and in one embodiment, is a polymer, such as a photoresist or a polyimide. Preferably, fill material 112 is carbon, which has a vaporization temperature of about 400 degrees centigrade, and is deposited in interstices 116 or the etched areas of ribbed structure 109 by sputtering. Fill material 112 is patterned and etched to form a template for the vertical wiring vias and the horizontal interconnect paths of conductive structure 115. In one embodiment, conductive structure 115 is fabricated using the dual damascene process. (“Process for Fabricating Multi-Level Integrated Circuit Wiring Structure from a Single Metal Deposit”, John E. Cronin and Peiing P. Lee, U.S. Pat. No. 4,962,058, Oct. 9, 1990, is incorporated by reference.) Alternatively, a single damascene or a subtractive etch process sequence is used to produce conductive structure 115. Conductive structure 115 is formed by depositing a conductive material, such as aluminum, gold, silver, or copper, or an alloy of aluminum, gold, silver, or copper, in the vertical wiring vias and conductive interconnect paths of the template formed in fill material 112. The conductive vias couple conductive structure 115 to electronic chip 103. Excess conductive material is removed by a planarizing process, such as chemical mechanical polishing (CMP), applied to the surface of fill material 112 and ribbed structure 109. After CMP, the surface of fill material 112, ribbed structure 109, and conductive structure 115, including the conductive vias and conductive interconnects, are ready for coupling to C4 structure 118.
Variations of the process described above include fabricating material layer 106 from an organic material or a mix of organic materials and inorganic materials, and patterning and etching the surface of material layer 106 to form a post structure. In addition, the process described for forming air bridge structures and support structures can be repeated to form as many wiring levels as required for the design of a particular electronic chip 103.
C4 structure 118, comprising insulation layer 121, vaporization plug 124, and conductive elements 127, is formed above ribbed structure 109 and fill material 112. Insulation layer 121 is the base of C4 structure 118 and is fabricated from an insulator, such as SiO2 or Si3N4. After forming insulation layer 121, vias are patterned and etched at via sites 127 and 130. A conductor, such as aluminum, gold, copper, or silver, or an alloy of aluminum, gold, copper, or silver, is deposited to fill via sites 127 and 130, and the metal is polished back to the surface of ribbed support structure 109 and fill material 112. Finally, a vaporization plug site is etched in insulation layer 121, and a fill material 112, such as carbon, is deposited to form vaporization plug 124. Any excess carbon is removed by polishing back the carbon to the surface of ribbed structure 109 and fill material 112.
Integrated circuit assembly 100 is placed in a furnace to vaporize fill material 112, leaving air bridge-structure 115, C4 structure 118, and electronic chip 103. In one embodiment, the furnace has an O2 atmosphere heated to about 400 degrees centigrade. In an alternate embodiment, integrated circuit assembly 100 is mounted as a flip chip on a substrate prior to vaporizing fill material 112.
Integrated circuit assembly 300 is not limited to use in connection with a particular type of electronic chip 303. The electronic chips described as suitable for use in connection with integrated circuit assembly 100 of
The plurality of post support structures 306, in one embodiment, is formed from an inorganic material, such as SiO2 or Si3N4. The processes described above for fabricating ribbed support structures 109 of
To fabricate the plurality of post support structures 306 from a conductor, a layer of material is formed above electronic chip 303. In one embodiment, the layer of material is an organic material, such as carbon. Alternatively, the layer of material is an organic polymer. The layer of material is patterned and etched to form a template for the first level vertical wiring and the plurality of post support structures 306. The template for the vertical wiring and the plurality of post support structures 306 are filled with a conductive material to form the plurality of support structures 306 and the vertical wiring for conductive structure 312. Excess conductive material on the surface of the layer of material deposited above electronic chip 303 is removed by chemical mechanical polishing or a similar planarizing process. An advantage of forming post support structures 306 from a conductor is that post support structures 306 provide a thermally conductive path to the C4 surface.
To form a first level air-bridge conductive segment, a horizontal pattern is patterned and etched. A conductive material, such as gold, copper, aluminum, or silver, or an alloy of gold, copper, aluminum, or silver, is deposited to fill the etched pattern. Excess conductive material is planarized back to the level of the surface of the organic material. The operations described above for forming an air-bridge level are repeated until the fabrication of the final air-bridge level is completed.
After completion of the fabrication of the final air-bridge level, the support structure for the C4 contacts is formed from a layer of SiO2 or other insulating material. The layer is patterned and etched to leave holes for vertical wiring to the positions of the C4 contacts. A layer of metal is applied to the surface of the SiO2 and the surface is planarized back to the oxide surface leaving the vertical metal conductors flush with the oxide. This vertical wiring level connects the C4 contacts to the last air-bridge level.
Additional openings are etched in the oxide such that all the interior carbon or polymer areas are accessible.
The C4 contacts on the surface of electronic chip 303 are reflowed in an H2 atmosphere. Electronic chip 303 is flipped and the C4 contacts are joined to a substrate in an H2 atmosphere. The assembly is placed in a furnace having an O2 atmosphere at approximately 400 degrees centigrade and the carbon is reduced to gaseous C02. If a polymer is used as the fill material instead of the carbon, the polymer is also removed using an O2 plasma.
If a hermetic packaging is used, the package is back filled with helium to improve the thermal properties of the assembly. If a heat sink is required, it is attached prior to the removal of the carbon support structure.
Conclusion
An integrated circuit assembly having air-bridge structures and a method for manufacturing an integrated circuit assembly having air-bridge structures has been described. An integrated circuit assembly includes structural components that protect the air-bridge structures during flip-chip mounting. A method of fabricating an electronic chip compatible with flip-chip mounting techniques includes the fabrication of ribbed support structures and post support structures. The support structures are fabricated from either insulating or conductive materials.
Various embodiments include a circuit assembly for fabricating an air bridge structure and a method of fabricating an integrated circuit package capable of supporting an air bridge structure is disclosed. A circuit assembly comprises an electronic chip and a conductive structure embedded in a plurality of materials having a plurality of vaporization temperatures. The plurality of materials are formed on the electronic chip and the conductive structure is coupled to the electronic chip.
Various embodiments include a method of forming an air bridge structure comprising a plurality of operations is also disclosed. First, a support structure including interstices is formed on an electronic chip. Next, the interstices of the support structure are filled with a material having a vaporization temperature that is less than the vaporization temperature of the support structure. Conductive structures, including conducive structures formed from copper alloy, are embedded in the support structure and the material, and a connective structure is mounted on the support structure. Finally, the material is removed from the support structure.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the embodiments of the present invention. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof
Claims
1. An integrated circuit assembly comprising:
- an electronic chip; and
- a post structure mounted on the electronic chip and capable of protecting an air-bridge structure and supporting a C4 structure.
2. The integrated circuit assembly of claim 1, wherein the post structure is fabricated from a same material as the air-bridge structure.
3. The integrated circuit assembly of claim 1, wherein the post structure is mounted on an insulating base formed on the electronic chip.
4. The integrated circuit assembly of claim 1, wherein the post structure is fabricated from an insulator.
5. The integrated circuit assembly of claim 4, wherein the insulator is silicon dioxide.
6. The integrated circuit assembly of claim 1, wherein the post structure is fabricated from a polymer.
7. The integrated circuit assembly of claim 6, wherein the polymer is polyimide.
8. An integrated circuit assembly comprising:
- an electronic chip;
- a material layer fabricated on a surface of the electronic chip, the material layer including a fill material;
- a plurality of post structures embedded in the fill material; and
- one or more air-bridge conductive structures embedded in the fill material.
9. The integrated circuit assembly of claim 8, further including a C4 structure including an insulating layer, a vaporization plug, and one or more conductive elements formed in the insulating layer, the C4 structure formed above the fill material.
10. The integrated circuit assembly of claim 8, wherein the plurality of post structures isformed from an inorganic material.
11. The integrated circuit assembly of claim 8, wherein the plurality of post structures is formed from a conductor.
12. The integrated circuit assembly of claim 11, wherein each of the plurality of posts structures is formed on an insulating base on the a surface of the electronic chip.
13. The integrated circuit assembly of claim 8, wherein the plurality of post structures is formed from a same material used to form the air-bridge conductive structure.
14. The integrated circuit assembly of claim 8, wherein the fill material is carbon.
15. The integrated circuit assembly of claim 8, wherein the fill material is foam.
16. The integrated circuit assembly of claim 8, wherein the fill material has a vaporization temperature that is different from a vaporization temperature of the material from which the plurality of post structures is fabricated.
17. The integrated circuit assembly of claim 8, wherein the electronic chip is a memory chip.
18. The integrated circuit assembly of claim 8, wherein the one or more air-bridge conductive structures include copper.
19. The integrated circuit assembly of claim 8, wherein at least one of the one or more air-bridge conductive structures include a plurality of vertical wiring vias and a conductive interconnect path.
20. An integrated circuit assembly comprising:
- an electronic chip;
- an air-bridge conductive structure coupling one or more electronic devices embedded in the electronic chip; and
- a plurality of post structures to support a C4 conductive structure, wherein one or more of the plurality of post structures supports the air-bridge conductive structure.
21. The integrated circuit assembly of claim 20, wherein the air-bridge conductive structure is a long-run air bridge conductive structure.
22. The integrated circuit assembly of claim 20, wherein each of the one or more post structures supporting the air-bridge conductive structure is fabricated from a same material as the air-bridge conductive structure.
23. The integrated circuit assembly of claim 22, wherein each of the one more post structures supporting the air-bridge conductive structure terminates in an insulator at a surface of the electronic chip.
24. The integrated circuit assembly of claim 20, wherein the one or more post structures supporting the air-bridge conductive structure are insulating posts.
25. The integrated circuit assembly of claim 24, wherein the insulating posts are formed from silicon dioxide.
26. The integrated circuit assembly of claim 20, wherein the air-bridge conductive structure includes copper.
27. The integrated circuit assembly of claim 20, wherein the air-bridge conductive structure includes gold.
28. A computer system comprising:
- a processor;
- a memory device having a plurality of circuit devices, the memory device coupled to the processor; and
- an air-bridge structure and a support structure fabricated on the memory device, the air-bridge structure capable of coupling at least two of the plurality of circuit devices and the support structure capable of supporting the memory device mounted as a flip chip, wherein the support structure includes a plurality of post structures.
29. The computer system of claim 28, wherein the plurality of post structures is fabricated from a conductor.
30. The computer system of claim 29, wherein the conductor includes copper.
31. The computer system of claim 29, wherein the conductor includes aluminum.
32. The computer system of claim 29, wherein the conductor includes gold.
33. The computer system of claim 29, wherein the conductor includes silver.
34. The computer system of claim 28, wherein one or more of the plurality of post structures are insulating posts.
35. The computer system of claim 28, wherein one or more of the plurality of post structures is fabricated from silicon dioxide.
36. The computer system of claim 28, wherein one or more of the plurality of post structures supports the air-bridge structure.
37. The computer system of claim 28, wherein one or more of the plurality of post structures supporting the air-bridge structure is formed from a same material as the air-bridge structure.
38. The computer system of claim 28, wherein the memory device is coupled to the processor by an address bus, a data bus, and a control bus.
39. The computer system of claim 28, further including a heat sink coupled to the electronic chip.
Type: Application
Filed: Jul 12, 2006
Publication Date: Nov 2, 2006
Applicant:
Inventor: Paul Farrar (South Burlington, VT)
Application Number: 11/457,110
International Classification: H01L 23/495 (20060101);