Pad over interconnect pad structure design

Abstract

A design rule checker that performs a maximum pattern density check in a first intermediary metallization layer that underlies a top metallization layer and a pad opening in an integrated circuit. The maximum pattern density check is performed at least under some circumstances if a modulus of the primary metallization material is less than a modulus of a surrounding dielectric material. The maximum pattern density check verifies that the pattern density within the underlying portion is below a maximum pattern density that depends on the thickness of the access pad. A maximum metal width check may also be performed in this portion.

What is claimed is: 
     
         1 . A computer program product comprising one or more computer-storage media having thereon computer-executable instructions that are structured such that, when executed by one or more processors of the computing system, cause the computing system to perform a method for assisting in a design of an electrical circuit, the method comprising:
 an act of identifying a pad opening for at least one of a plurality of access pads that are in and/or above a top metallization layer of the electrical circuit;   an act of identifying 1) a first intermediary metallization layer that is a neighboring metallization layer to the top metallization layer, and 2) a first portion of the first intermediary metallization layer that underlies the pad opening of an access pad;   an act of identifying a primary metallization material of the first intermediary metallization layer;   an act of identifying surrounding dielectric material that intermediates between the top metallization layer and the first intermediary metallization layer,   wherein the computer-executable instructions are further structured such that, when executed by the one or more processors, the computing system is caused to operate a design rule checker that is configured to perform a maximum pattern density check at least under some circumstances when the identified primary metallization material has a modulus less than a modulus of the surrounding dielectric material, the maximum pattern density check verifying whether a pattern density of the first portion is below a maximum pattern density, the pattern density of the first portion being a ratio of metal area in the first portion to a total area of the first portion, the maximum pattern density depending on a thickness of the access pad.   
     
     
         2 . The computer program product in accordance with  claim 1 , wherein the maximum pattern density is higher if the thickness of the overlying access pad is thicker. 
     
     
         3 . The computer program product in accordance with  claim 1 , wherein the primary metallization material is selected from the group consisting of aluminum, silver, copper, gold, or any other conductive material that is softer than the surrounding dielectric material. 
     
     
         4 . The computer program product in accordance with  claim 1 , wherein the computer-executable instructions are further structured such that, when executed by the one or more processors, the computing system is caused to operate the design rule checker to perform a maximum metal width check at least under some circumstances when the identified primary metallization material has a modulus less than a modulus of the surrounding dielectric material, the maximum metal width check verifying whether a metal width within the first portion is below a maximum metal width. 
     
     
         5 . The computer program product in accordance with  claim 4 , wherein the maximum metal width depends on a thickness of the access pad. 
     
     
         6 . The computer program product in accordance with  claim 1 , wherein the computer-executable instructions are further structured such that, when executed by the one or more processors, the computing system is caused to propose one or more identified non-metal spaces in a metallization pattern of the first portion if the maximum metal density check fails. 
     
     
         7 . The computer program product in accordance with  claim 1 , wherein the design rule check is further configured to check the minimum spacing of vias underneath the pad opening between the first intermediary metallization layer and the top metallization layer. 
     
     
         8 . The computer program product in accordance with  claim 1 , wherein the computer-executable instructions are further structured such that, when executed by the one or more processors, the computing system is further caused to make available to a designer a library of pad structures that comply with the maximum pattern density check, wherein the designer may select one of the pad structures to be used and further edit the selected pad structure to thereby form at least the first portion of the first intermediary metallization layer. 
     
     
         9 . A method for designing an electrical circuit, the method comprising:
 an act of identifying a pad opening for at least one of a plurality of access pads that are in and/or above a top metallization layer of the electrical circuit;   an act of identifying a first intermediary metallization layer that is a neighboring metallization layer to the top metallization layer;   an act of identifying a metallization pattern to be inserted into a first portion of the first intermediary metallization layer, the first portion underlying the pad opening, wherein a design rule checker verifies that a pattern density of the metallization pattern is less than a maximum pattern density that depends on a thickness of the overlying access pad, a pattern density of the metallization pattern being a ratio of metal area in the first portion to the total area of the first portion,   wherein a primary portion of the metallization in the metal area in the first portion has a modulus less than a modulus of surrounding dielectric material that intermediates between the top metallization layer and the first intermediary metallization layer.   
     
     
         10 . The method in accordance with  claim 9 , wherein the metallization pattern is a first metallization pattern, the pattern density is a first pattern density, and the maximum pattern density is a first maximum pattern density, the method further comprising:
 an act of identifying a second intermediary metallization layer that is a neighboring metallization layer to the first intermediary metallization layer;   an act of identifying a second metallization pattern to be inserted into a second portion of the second intermediary metallization layer, the second portion underlying the pad opening and the first portion of the first intermediary metallization layer, wherein the design rule checker verifies that a second pattern density of the second metallization pattern is less than a second maximum pattern density that depends on the thickness of the overlying access pad, the second pattern density of the second metallization pattern being a ratio of metal area in the second portion to the total area of the second portion, wherein the second maximum pattern density is larger than the first maximum pattern density.   
     
     
         11 . The method in accordance with  claim 10 , wherein the first pattern density is smaller than the second pattern density. 
     
     
         12 . The method in accordance with  claim 10 , wherein the first pattern density is larger than the second pattern density. 
     
     
         13 . The method in accordance with  claim 10 , further comprising:
 an act of identifying a third intermediary metallization layer that is a neighboring metallization layer to the second intermediary metallization layer;   an act of identifying a third metallization pattern to be inserted into a third portion of the third intermediary metallization layer, the third portion underlying the pad opening and the first portion of the first intermediary metallization layer and the second portion of the second intermediary metallization layer, wherein the design rule checker verifies that a third pattern density of the third metallization pattern is less than a third maximum pattern density that depends on the thickness of the overlying access pad, the third pattern density of the third metallization pattern being a ratio of metal area in the third portion to the total area of the third portion.   
     
     
         14 . The method in accordance with  claim 13 , wherein the third pattern density is larger than the second pattern density. 
     
     
         15 . The method in accordance with  claim 9 , wherein the primary portion of the metallization is aluminum. 
     
     
         16 . An electrical circuit comprising:
 a top metallization layer;   a plurality of access pads in and/or above the top metallization layer;   a substrate; and   a first intermediary metallization layer disposed between the top metallization layer and the substrate and being a neighboring metallization layer to the top metallization layer,   wherein for at least one of the plurality of access pads, the access pad has a pad opening and a pad structure underlying the pad opening, the pad structure comprising:
 a first portion of the first intermediary metallization layer that underlies the pad opening, and 
 wherein a metallization pattern is formed in the first portion after having been subject to a maximum pattern density check in which a pattern density of the metallization pattern within the first portion is verified to be below a maximum pattern density that depends on a thickness of the overlying access pad, wherein the pattern density of the metallization pattern within the first portion is a ratio of metal area in the first portion to the total area of the first portion, 
 wherein a primary portion of the metallization in the metal area in the first portion has a modulus less than a modulus of surrounding dielectric material that intermediates between the top metallization layer and the first intermediary metallization layer. 
   
     
     
         17 . The electrical circuit in accordance with  claim 16 , wherein the primary portion of the metallization is selected from the group consisting of aluminum, silver, copper, gold, or any other conductive material that is softer than the surrounding dielectric material. 
     
     
         18 . The electrical circuit in accordance with  claim 16 , wherein the surrounding dielectric material is silicon dioxide or any other material that is harder than the primary portion of the metallization. 
     
     
         19 . The electrical circuit in accordance with  claim 16 , wherein the substrate is a semiconductor material. 
     
     
         20 . The electrical circuit in accordance with  claim 16 , wherein the semiconductor material has formed therein semiconductor devices that underlie the pad opening.