INTEGRATED CIRCUIT POWER DISTRIBUTION NETWORK

Abstract: A power distribution network for an integrated circuit is fabricated together with the circuit on a silicon substrate (10). The silicon substrate (10) is fabricated to form diffusion regions (50) as part of the active devices in the integrated circuit. A dielectric separation layer (51) is fabricated over the surface of substrate (10). Above the region (50) there is fabricated a power distribution line (52) comprising a metallization of aluminum or aluminum-alloy material. A passivation layer (54) is formed over the dielectric layer (51) and the conductor (52) but is opened above the central region of the conductor (52). An adhesion and diffusion barrier layer (58) is fabricated over the conductor (52) and passivation layer (54). Above the layer (58) there is fabricated a thick layer of metallization (60) in the form of a conductor strip configured similar to the underlying conductor layer (52). The conductive layers (58, 60) are etched to have essentially the same width as the conductor line (52). The conductive layers (58 and 60) can optionally be made to have a greater width than the underlying layer as is illustrated by the conducting layers (76, 78).

Description: INTEGRATED CIRCUIT POWER DISTRIBUTION NETWORK TECHNICAL FIELD The present invention pertains to integrated circuits and more particularly to the distribution of power to elements within the circuit. OMPI BACKGROUND ART As integrated circuit features become smaller to achieve increased density, the metallization inter¬ connection layers become thinner and narrower. Such metallization is used to provide power to each of the power receiving components in the circuit and for supplying ground connections throughout the circuit. As the dimensions of the metallization become smaller the circuit trace resistance becomes greater thereby increasing the heat dissipation of the integrated circuit and reducing the amplitude of the supply voltage at the circuit elements. The reduction in the metallization dimensions further can have an adverse affect on the inductive and capacitive parameters of the. integrated circuit. Therefore there exists a need for thicker and more massive metallization patterns which overcome the problems of thin patterns but do not interfere with the reduction of integrated circuit dimensions to increase circuit density. DISCLOSURE OF THE INVENTION The present invention comprises a power distribution network for an integrated circuit which includes a first conductor pattern which is fabrica'ted to supply power to the individual elements within the integrated circuit. A passivation layer is fabricated to cover the circuit elements but is open over a substantial area of the first conductor pattern. A second conductor pattern is fabricated on the integrated circuit with a similar pattern to that of the first conductor pattern. The second conductor pattern is positioned to be in contact with the first conductor pattern through the opening in the passivation layer. The second conductive pattern is essentially connected to the first conductor pattern along its entire length. OMPI BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the present invention and the advantages thereof, reference is now made * to the following Description taken in conjunction with the accompanying Drawings in which: FIGURE 1 is a perspective view of a metallization pattern for an integrated circuit; FIGURE 2 is a sectional view of one of the strips of the metallization pattern shown in FIGURE 1; FIGURE 3 is a sectional view of a metallization pattern in accordance with the present invention and; FIGURE 4 is a sectional view of a metallization pattern for a plurality of power distribution lines. DISCLOSURE OF THE INVENTION A power distribution network for an integrated circuit is illustrated in FIGURE 1. A silicon substrate 10 serves as the base for the fabrication of integrated circuit elements on the upper surface thereof. As a part of the circuit fabrication process there is laid down a power distribution network for supplying power to the elements within the circuit. The network includes a first group of parallel strips 12-24 which are connected in common to a perpendicular strip 26. Strip 26 is in turn connected to a bonding pad 28. A second portion of the power distribution network comprises a plurality of parallel strips 30-44. These parallel strips are in turn connected to a perpendicular, common strip 46 which is itself connected to a bonding pad 48. In a typical application a positive voltage is connected through a wire bond to the pad 28 and a negative voltage or ground is connected through a wire bond to pad 48. The power thus supplied is distributed to the elements of the circuit through the strips 12-24 and 30-44. The strips 12-24 and 30-40 are representative of power distribution strips and a substantial number of such strips are used in large scale integration. A cross sectional view of a power distribution strip as illustrated in FIGURE 1 is shown in FIGURE 2. In a typical application the silicon substrate 10 is fabricated to have a diffusion region 50 fabricated therein. The diffusion region 50 forms a part of the circuit elements within the integrated circuit fabricated on the substrate 10. A dielectric separation layer 51 is formed on the surface of the silicon substrate 20. Layer 51 is typically silicon dioxide having a thickness of 6,000- 10,000 Angstroms. Immediately above the diffusion region 50 there is fabricated a conductor 52 which is in oh ic contact with the diffusion region 50. The conductor 52 is fabricated in a pattern which is similar to that shown for the power distribution network strips in FIGURE 1. The conductor 52 is typically aluminum or aluminum alloy with a thickness of 6,000-12,000 Angstroms. A preferred method for fabricating conductor 52 is by sputtering or evaporation techniques followed by photolithographic etching. After the conductor layer 52 has been formed, a passivation layer 54 is laid down over the conductor 52 and the separation layer 51. By means of photolitho¬ graphic etching an opening 56 is formed in the passivation layer 54. The opening 56 extends along the longitudinal dimension of the conductor layer 52 but is slightly narrower than the conductor layer. The opening 56 thus has slightly less area than that of the conductor layer 52. The overlap of the passivation layer 54 over the edges of the conductor 52 forms a sealed junction. The passivation layer 54 is typically glass or silicon dioxide with a thickness of 9,000-12,000 Angstroms. After the opening 56 has been formed in the passivation layer, a layer of adhesion and diffusion barrier metal 58 is formed over the opening 56 and over the adjacent edges of the passivation layer 54. Typical materials for use as the layer 58 include titanium, tungsten, molybdenum and chromium. These metals likewise can be deposited by means of sputtering or evaporation techniques. The material of layer 58 provides electrical contact and adhesion to the conductor 52, passivation layer 54 and an additional conductor layer to be added above the layer 58. Layer 58 also functions as a diffusion barrier. The thickness of layer 58 is typically 2000-2500 Angstroms. Over the adhesion and diffusion barrier layer 58 there is fabricated a metal conductor 60 in a configuration similar to the conductor 52. The conductor 60 is fabricated of aluminum, copper, gold or silver using conventional deposition and photolithographic etching. The typical thickness of layer 60 is 4000-6000 Angstroms. During photolithographic etching cf metal conductor 60, the adhesion and diffusion barrier layer 58 is also photolithographically configured to be similar to the conductor 52. The conductive layer 60 together with the conductor 58 extends longitudinally above the conductive layer 52 to essentially form a single conductive strip having an enhanced thickness. This enhanced thickness reduces the trace resistance of the power conduction lines for the integrated circuit. A cross sectional illustration of the pov-er distribution lines of the present invention is shown in FIGURE 3 wherein the conductor layer 52 is deposited directly on the surface of substrate 10 over separation layer 51 in the absence of a diffused region, such as 50 shown in FIGURE 2. The conductive layers 52 and 60, separation layer 51, adhesion and barrier layer 58 and passivation layer 52 are the same as shown for the embodiment illustrated in FIGURE 2. A further embodiment of the present invention is illustrated in FIGURE 4. A silicon substrate 54 has a dielectric separation layer 65 on the surface thereof. Positive and negative power distribution trace lines 66 and 68 respectively are fabricated over layer 65. These lines are fabricated of materials such as, for example, aluminum or aluminum alloy. The conductive lines 66 and 68 have a thickness on the order of 6000-12,000 Angstroms. After the lines 66 and 68 have been formed on the substrate 64 over layer 65 there is laid down a passivation layer 70 over the upper surface of layer 65 and the conductive lines. By photolithograph and etching techniques there is created an opening 72 in the passiva¬ tion layer 70 over trace 66 and an opening 74 in a passivation layer 70 over conductive line 68. The passivation layer 70 has a thickness of approximately 9000-12,000 Angstroms. Above the passivation layer 70 and the exposed areas of conductor lines 66 and 68 there is fabricated an adhesion and diffusion barrier layer 76. This layer is typically titanium, tungsten, molybdenum or chromium and has a typical thickness of 2000-2500 Angstroms. Over the adhesion and diffusion barrier layer 76 there is fabricated a metal conductor 78 which is typically aluminum, copper, gold or silver. Layers 76 and 78 are etched to produce a plurality of strips, one over each of the conductor lines 66 and 68. Each of the strips of layers 76 and 78 are wider .than the underlying conductive lines 66 and 68. A typical thickness for layer 76 is 2000-2500 Angstroms. A typical thickness for layer 78 is 4000-6000 Angstroms. Layers 76 and 78 are photolithographically etched such that they are formed into strips corresponding to each of the conductor lines 66 and 68. The strips of layer 78, like the strips of layer 76 are wider than the underlying conductive lines. This serves to reduce the resistance of the power distribution lines and to enhance the capacitive coupling between the power distribution lines. In summary, the present invention provides a power distribution network wherein additional layers of metallization are formed over the conductor lines which interconnect the active elements in an integrated circuit. The enhanced power distribution lines have greater thickness and optionally greater width to reduce the resistance in the power lines, reduce inductance and control power line capacitance to enhance the performance of the integrated circuit. Although several embodiments of the invention have been illustrated in the accompanying drawings and described in the foregoing detailed description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention. OMPI

Claims: CLAIMS 1. A power distribution network for an integrated circuit, comprising: a first conductor pattern fabricated to supply power to elements within said circuit, a passivation layer covering said circuit but open over a substantial portion of said first conductor pattern, and a second conductor pattern configured similar to said first conductor pattern and contacting said first conductor pattern through the opening in said passivation layer. 11 2. A power distribution network for an integrated circuit, comprising: a first conductor pattern fabricated in connection with power receiving elements within said circuit, said first pattern comprising a plurality of narrow, elongate strips connected in common, a passivation layer covering said circuit but exposing the central, longitudinal portions of said strips of said first pattern, and a second conductor pattern comprising a plurality of narrow, elongate strips covering the exposed portions of said first conductor pattern and bonded thereto, said second pattern connected to a bonding pad for receiving power for said circuit. 3. The power distribution network recited in Claim 2 wherein said passivation layer overlaps the longitudinal edges of said strips of said first conductor pattern. 4. The power distribution network recited in Claim 2 wherein said strips for said first and said second conductor patterns have essentially the same width. 5. The power distribution network recited in Claim 4 wherein the opening in said passivation layer, which exposes said first conductor pattern, is narrower than the strips for said first and second conductor patterns. 6. A method for producing a power distribution network for an integrated circuit, comprising the steps of: fabricating a first conductor pattern on said integrated circuit to interconnect the power receiving elements in said circuit, applying a passivation layer over said circuit and said first conductor pattern, opening the passivation layer above the first conductor pattern, and applying a second conductor pattern having a similar configuration to said first conductor pattern and connected thereto through the opening in said passivation layer. 7. A method for producing a power distribution network for an integrated circuit, comprising the steps of: fabricating a first conductor pattern on said integrated circuit to interconnect the power receiving elements in said circuit, said first conductor pattern comprising a plurality of narrow metallization strips, applying a passivation layer over said circuit and said first conductor pattern, opening said passivation layer above central, longitudinal portions of each of the strips of said first conductor pattern, and fabricating a second conductor pattern having a similar configuration as said first conductor pattern, said second pattern located on said passivation layer and extending through the opening therein to contact the strips of said first conductor pattern. OMPI

Inventors: MULHOLLAND W
Applicants: MOSTEK CORP, MULHOLLAND W
Application year: 1980
Main classification: H01L23
IPC codes: H01L23