Patent Publication Number: US-2023160836-A1

Title: Monitoring copper corrosion in an integrated circuit device

Description:
PRIORITY 
     This application claims priority to U.S. Provisional Application No. 62/791,046, filed Jan. 11, 2019, which is hereby incorporated in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to integrated circuit devices and structures, and more particularly to systems and methods for monitoring copper corrosion in an integrated circuit device. 
     BACKGROUND 
     In the context of integrated circuit (IC) manufacturing, copper interconnects have generally replaced aluminum interconnects. In general, copper interconnects (a) have a lower resistivity (about 35% less) than aluminum, (b) have a higher electromigration resistance (typically 2-4 orders of magnitude better than aluminum), (c) are compatible with low k dielectric material, and (d) provide a better yield and reliability than aluminum. 
     On the other hand, unlike aluminum, exposed copper does not form an effective native oxide (CuO 2  is relatively porous, allowing oxygen penetration). Thus, copper is generally more susceptible to corrosion than aluminum, particularly during and immediately after a Cu CMP (chemical mechanical planarization) process. Copper corrosion can have a significant impact on IC device yield and reliability. 
     The standard industry practice for detecting copper corrosion in IC manufacturing is utilization of defect inspection tools, such as (a) laser scattering based inspection or (b) brute force pattern recognition by comparison of digitized images, to detect copper corrosion after a copper CMP process or after deposition of a dielectric barrier (e.g., SiN or SiC), for example. However, with these conventional corrosion detection approaches, the detection sensitivity typically varies significantly from device to device, making it difficult to establish a stable baseline and detect process variations. In addition, copper corrosion may be enhanced when exposed to a light source by the process of light-induced copper redeposition, and the corrosion is often highly dependent on the relevant circuit or structure. 
     Thus, there is a need for effectively monitoring copper corrosion in IC structures, for both (a) in-line defect monitoring during IC manufacturing and (b) end-of-line reliability assessment. There is also a need for a corrosion monitoring system that can be located in a scribe-line, independent of the particular IC structure or device, and highly-sensitive to the relevant corrosion. 
       FIGS.  1    and  FIGS.  2 A- 2 B  illustrate copper corrosion mechanisms that occur in two common IC structures.  FIG.  1    is a cross-sectional side view of an example of a common copper structure  100  in an IC device that is susceptible to corrosion. Structure  100  includes a copper region  102  enclosed by a barrier layer  104  on four sides and bottom, e.g., a tantalum (Ta) layer or tantalum nitride (TaN) layer, or tantalum (Ta)/tantalum nitride (TaN) bi-layer. Copper region  102  may be susceptible to corrosion, including oxidation at the exposed upper surface  106  of copper region  102  and/or electrochemical corrosion due to an electro-chemical potential difference between copper  102  and barrier layer  104  (e.g., Ta or TaN). 
       FIGS.  2 A and  2 B  show an example of another common copper structure  200  in an IC device that is susceptible to corrosion.  FIGS.  2 A and  2 B  are based on images in the Handbook of Semiconductor Manufacturing Technology, 2ed (2008), by Yoshio Nishi &amp; Robert Doering, Chapter 5: Surface Preparation, at pp. 5-25.  FIG.  2 A  is a cross-sectional side view of structure  200  which includes an adjacent pair of copper regions  202 A and  202 B, with copper region  202 A connected to a p-doped active region  204 A by a first conductive contact  206 A and copper region  202 B connected to an n-doped active region  204 B by a second conductive contact  206 B. In addition to oxidation at the exposed surfaces of copper regions  202 A and  202 B, copper regions  202 A and  202 B may be susceptible to corrosion from photo-inducted copper re-deposition, e.g., during Cu CMP process, or during Cu CMP clean process, or right after Cu CMP process, in which the top surface of structure  200  is exposed to slurry or liquid or ambient moisture. Photo-inducted copper re-deposition may result from light incident on the p-n junction “space charge region”  210 , which creates a voltage difference between copper regions  202 A and  202 B due to the photo-voltaic effect (similar to a solar cell), and drives a flow of copper ions between copper regions  202 A and  202 B. The depleted copper in copper region  202 A may form “bat-cave vias” that extend into copper region  202 A under a portion of the via. Further, copper redeposition onto copper region  202 B may form on the side walls of the respective via that may cause copper intrusion into the interlayer dielectric (ILD). 
       FIG.  2 B  is a top view of structure  200 , after corrosion of the copper regions  202 A and  202 B caused by photo-inducted copper re-deposition. As shown, copper regions  202 B have a noticeably different appearance than copper regions  202 A after the redeposition of Cu ions from copper regions  202 A to copper regions  202 B. As discussed above, this corrosion may be detected using defect inspection tools, such as laser scattering based inspection or comparison of digitized images for brute force pattern recognition. 
     SUMMARY 
     Systems and methods for monitoring copper corrosion in an integrated circuit (IC) device are provided. A corrosion-sensitive structure formed in the IC device may include a p-type silicon region adjacent an n-type silicon region to define a p-n junction space charge region. A copper region formed over the silicon may be connected to both the p-region and n-region by respective contacts, to thereby define a short circuit. Light incident on the p-n junction space charge region, e.g., during a CMP process, creates a current flow through the metal region via the short circuit, which drives chemical reactions that cause corrosion in the copper region. Due to the short circuit configuration, the copper region is highly sensitive to corrosion. The corrosion-sensitive structure may be arranged with less corrosion-sensitive copper structures in the IC device, with the corrosion-sensitive structure used as a proxy to monitor for copper corrosion in the IC device. 
     One embodiment provides an IC device including a corrosion monitoring system. The corrosion monitoring system may include a p-type active region adjacent an n-type active region to define a p-n junction space charge region; a first conductive contact connected to the p-type active region, and a second conductive contact connected to the n-type active region; and a metal region connected to both the first conductive contact and the second conductive contact, to thereby define a short circuit. Incident light on the p-n junction space charge region creates a current flow through the metal region via the short circuit, which drives chemical reactions that cause corrosion in the metal region. 
     In one embodiment, the metal region is a copper region, such that the corrosion monitoring system comprises a copper corrosion region. In one embodiment, the IC device includes one or more copper corrosion regions, and a plurality of other copper structures that are less susceptible to corrosion than the copper corrosion region(s). 
     In some embodiments, the IC device includes, in addition to the corrosion monitoring system, a plurality of non-short circuited integrated circuit structures, each comprising: a p-type active region adjacent an n-type active region to define a p-n junction space charge region; a first conductive contact connected to the p-type active region, and a second conductive contact connected to the n-type active region; and a first metal region coupled to the first conductive contact and a second metal region connected to the second conductive contact and physically discrete from the first metal region; wherein incident light on the p-n junction space charge region of the respective integrated circuit structure creates a current flow through the first and second metal regions, which drives chemical reactions that cause corrosion at respective surfaces of the first and second metal regions; and wherein the corrosion at the respective surfaces of the first and second metal regions of the respective integrated circuit structure is less severe than the corrosion in the metal region of the corrosion monitoring system. One example of a non-short circuited integrated circuit structure is shown in  FIG.  2 A , discussed above. Thus, in some embodiments an IC device may include any number of functional integrated circuit structures that are susceptible to corrosion but not directly short circuited, and corrosion monitoring system including at least one integrated circuit structure that is short circuited and thus exhibits more severe/faster corrosion, to thereby provide an indication of the corrosion susceptibility of the overall IC device, including the non-short circuited structures. 
     In one embodiment, the corrosion monitoring system includes at least two n-type active regions and at least two p-type active regions arranged in an alternating manner to define at least two p-n junction space charge regions; and a first conductive contact connected to each p-type active region, and a second conductive contact connected to each n-type active region; wherein the metal region is connected to both the first conductive contacts connected to each p-type active region and the second conductive contacts connected to each n-type active region. 
     In one embodiment, the corrosion monitoring system includes a second metal region formed in a layer above the metal region and connected to the metal region by at least one conductive contact; wherein incident light on the p-n junction space charge region creates a current flow through the second metal region via a conductive path through the metal region, which drives chemical reactions that cause corrosion in the second metal region. 
     In one embodiment, the corrosion monitoring system includes (a) a first conductive probe region of the metal region or connected to the metal region at a first location, the first conductive probe region being configured for connection to a current source configured to supply a constant current through the metal region; and (b) a second conductive probe region of the metal region or connected to the metal region at a second location, the second conductive probe region being configured for connection to voltage measurement circuitry for measuring a voltage drop across the metal region. 
     In one embodiment, the first conductive probe region is connected to the metal region at the first location by a first vertically-extending contact or via, and the second conductive probe region is connected to the metal region at the second location by a second vertically-extending contact or via. 
     In one embodiment, the corrosion monitoring system includes a first conductive probe region connected to a first area of the metal region by a first vertically-extending contact or via; a second conductive probe region connected to a second area of the metal region by a second vertically-extending contact or via; a current source configured to supply a current from the first conductive probe region to the second conductive probe region via the first vertically-extending contact or via, the metal region, and the second vertically-extending contact or via; and voltage measurement circuitry configured to measure a voltage difference between the first conductive probe region and the second conductive probe region. 
     Another embodiment provides a system for monitoring corrosion in an integrated circuit device. The system may include a corrosion sensitive structure and a corrosion analysis system. The corrosion sensitive structure may include a p-type active region adjacent an n-type active region to define a p-n junction space charge region; a first conductive contact connected to the p-type active region, and a second conductive contact connected to the n-type active region; and a metal region connected to both the first conductive contact and the second conductive contact, to thereby define a short circuit. Incident light on the p-n junction space charge region creates a current flow through the metal region via the short circuit, which drives chemical reactions that cause corrosion in the metal region. The corrosion analysis system may be configured to analyze corrosion in the metal region of the corrosion sensitive structure. 
     In one embodiment, the corrosion analysis system includes a laser scattering based inspection system configured to analyze the metal region based on laser scattering. 
     In another embodiment, the corrosion analysis system includes an automated digital image comparison system configured to compare digital images of the metal region to the die on the left or/and the die on the right. 
     In another embodiment, the corrosion analysis system includes a current source, separate from the p-n junction space charge region, connected to the metal region and configured to supply a constant current across the metal region; voltage detection circuitry configured to measure a voltage drop across the metal region; and corrosion analysis circuitry configured to calculate a resistance or other measure of corrosion in the metal region based at least on the current supplied by the current source and the measured voltage drop across the metal region. 
     In one embodiment, the current source and voltage detection circuitry are connected directly to the metal region. 
     In another embodiment, the current source and voltage detection circuitry are connected to contact regions located in a different metal layer than the metal region and connected to the metal region by vertically-extending conductive contacts. 
     Another embodiment provides a method for monitoring corrosion in an integrated circuit device. The method includes providing a corrosion monitoring system as disclosed above, and analyzing corrosion in the metal region using an automated corrosion analysis system. 
     In one embodiment of the method, analyzing corrosion in the metal region includes performing a laser scattering based inspection of the metal region. 
     In another embodiment of the method, analyzing corrosion in the metal region includes performing an automated analysis of at least one digital image of the metal region. 
     In another embodiment of the method, analyzing corrosion in the metal region includes delivering a constant current across the metal region, measuring a voltage drop across the metal region, and calculating a measure of corrosion in the metal region based at least on the delivered constant current and the measured voltage drop across the metal region. 
     In one embodiment of the method, delivering a constant current across the metal region comprise supplying a constant current to a contact region located in a different metal layer than the metal region and connected to the metal region by at least one vertically-extending conductive contact. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Example aspects and embodiments of the present disclosure are described below in conjunction with the following appended drawings: 
         FIG.  1    is a cross-sectional side view of an example of a common copper structure in an integrated circuit device that is susceptible to corrosion; 
         FIGS.  2 A and  2 B  show a cross-sectional side view and a top view, respectively, of another common copper structure in an IC device that is susceptible to corrosion; 
         FIG.  3    is a cross-sectional side view of an example copper corrosion monitoring system for monitoring copper corrosion in an integrated circuit device, according to an example embodiment of the present invention; 
         FIG.  4 A  is an example top view image of an IC device including an array of IC structures including various copper components, and a single corrosion monitoring system in a corroded state, according to an example embodiment; and  FIG.  4 B  is an enlarged image of the corrosion monitoring system shown in  FIG.  4 A ; 
         FIG.  5    shows a top view of an example corrosion monitoring system, including a copper corrosion region extending over a single p-n junction space charge region, according to one example embodiment of the invention; 
         FIG.  6    shows a top view of another example corrosion monitoring system, including a copper corrosion region extending over multiple p-n junction space charge regions, according to one example embodiment of the invention; 
         FIG.  7    is a cross-sectional side view of an example multi-level corrosion monitoring system, according to one example embodiment of the invention; 
         FIG.  8    illustrates a top view of an example corrosion monitoring system including a corrosion-sensitive copper region and circuitry for performing electrical testing for detecting corrosion in the copper region, according to one example embodiment of the invention; and 
         FIGS.  9 A and  9 B  show a top view and a cross-sectional side view of an example corrosion monitoring system including a corrosion-sensitive copper region and circuitry for performing electrical testing for detecting corrosion in the copper region, wherein the testing circuitry is connected to probe regions located in a different metal layer than the corrosion-sensitive copper region, according to one example embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention provide systems and methods for monitoring copper corrosion in an integrated circuit (IC) device.  FIG.  3    is a cross-sectional side view of an example copper corrosion monitoring system  300  for monitoring copper corrosion in an integrated circuit device, according to an example embodiment of the present invention. Copper corrosion monitoring system  300  may include a continuous copper region  302  connected to both a p-doped silicon active region  304 A by a first conductive contact  306 A and an n-doped silicon active region  304 B (adjacent p-region  304 A to define a p-n junction “space charge region”  310 ) by a second conductive contact  306 B, to thereby define a conductive short circuit. Thus, corrosion monitoring systems according to embodiments of the present invention may be referred to as short-circuited corrosion monitoring systems. Copper region  302  may be formed over or within a barrier layer  314 , e.g., Ta or TaN barrier layer. Contacts  306 A and  306 B may be formed from any conductive material, e.g., tungsten, cobalt, copper, or aluminum. 
     Light incident on the space charge region  310  creates electron-hole pairs with electron drift to n-region  304 B and hole drift to p-region  304 A, which generates a current through the continuous copper region  302 . This current causes chemical reactions that result in corrosion of the copper  302 . In particular, at the copper surface in the area  302 A above the p-region contact  306 A, copper is oxidized according to the equation Cu→Cu 2+ +2e. At the same time, at the copper surface in the area  302 B above the n-region contact  306 B, Cu′ is reduced according to the equation Cu 2+ +2e→Cu. This current-based corrosion occurs when copper region  302  is subjected to a slurry or other solution (e.g., during a CMP process), when copper region  302  is subjected to water (e.g., during a CMP clean), and when copper region  302  is subjected to ambient moisture/humidity (e.g., immediately after a CMP process). 
     The corrosion that occurs in corrosion monitoring system  300  is significantly greater than the corrosion that occurs in other IC structures, such as structures  100  and  200  discussed above, as a result of higher current flow due to the short circuit configuration in corrosion monitoring system  300 . Thus, corrosion monitoring system  300  is significantly more susceptible or sensitive to corrosion than other copper-based structures in an IC device. 
     Based on this enhanced sensitivity to corrosion, corrosion monitoring system  300  may be used for monitoring copper corrosion in an IC device containing other, less corrosion-sensitive copper-based structures. For example, at least one corrosion monitoring system  300  may be formed in an IC device along with other copper-based, functional elements of the IC device (e.g., including structures such as structures  100  and  200 , for example). Copper region  302  may be monitored for corrosion, e.g., using known techniques such as laser scattering based inspection or pattern recognition by comparison of digitized images, for example. The enhanced corrosion sensitivity of copper region  302  may allow for more definitive, reliable, and consistent detection of copper corrosion in the IC device, and the copper-based, functional elements of the IC device, which are less corrosion-sensitive than copper region  302 , may be assumed to be less corroded than copper region  302 . Thus, the detected presence or extent of corrosion in copper region  302  (e.g., using laser scattering based inspection or pattern recognition) may be used as a conservative proxy for copper corrosion within the IC device. In some embodiments, the presence or extent of corrosion in copper region  302  may be compared against one or more defined threshold levels, to classify the IC device with respect to copper corrosion. 
       FIG.  4 A  is an example top image of an IC device  400  including an array of non-short circuited IC structures  402  including various copper components, and a single short-circuited corrosion monitoring system  300  in a corroded state, according to an example embodiment. In this image, lighter regions indicate exposed copper surfaces, while darker regions indicate silicon oxide surfaces. 
     Non-short circuited IC structures  402  may include, for example, structures including a p-type active region adjacent an n-type active region to define a p-n junction space charge region, a first conductive contact connected to the p-type active region, a second conductive contact connected to the n-type active region, and a first metal region coupled to the first conductive contact and a second metal region connected to the second conductive contact but physically discrete from the first metal region. For each non-short circuited IC structure  402 , incident light on the p-n junction space charge region may create a current flow through the first and second metal regions, which drives chemical reactions that cause corrosion at respective surfaces of the first and second metal regions, for example reactions occurring through a slurry, liquid, or ambient moisture to which the first and second metal regions are exposed. The corrosion exhibited at the surfaces of the first and second metal regions of the respective non-short circuited IC structure  402  is typically less severe than the corrosion in the metal (e.g., copper) region of the short-circuited corrosion monitoring system  302 . 
     In other embodiments, an IC device may include any number and combination of non-short circuited IC structures and short-circuited corrosion monitoring system(s), e.g., including one or more corrosion monitoring system  300 ,  500 ,  600 ,  700 ,  800 , and/or  900  as disclosed herein. 
     As shown, corrosion monitoring system  300  exhibits the only copper surface in the field of view where corrosion is observed due to its enhanced sensitivity to corrosion.  FIG.  4 B  is an enlarged image of region  410  shown in  FIG.  4 A , showing the corroded upper copper surface of corrosion monitoring system  300  (in the corroded state), surrounded by silicon oxide of IC device  400 . As shown, the corrosion monitoring system  300  in the corroded state is visibly distinguished from the surrounding (non-short circuited) structures, and can be distinctly identified by known detection techniques (e.g., laser scattering based inspection or digital image pattern recognition). 
     The corrosion sensitivity/susceptibility of a corrosion monitoring system according to the present invention may be depend in part on the ratio of the area of the p-n junction space charge region (from a top view) to the area of the continuous copper region that is susceptible to corrosion (again from a top view), which may be referred to an the “antenna ratio” of the corrosion monitoring system, where: 
     
       
         
           
             
               
                 
                   
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                     Ratio 
                   
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                         junction 
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                         space 
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                         charge 
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                         region 
                         ⁢ 
                             
                         area 
                         ⁢ 
                             
                         
                           ( 
                           cause 
                           ) 
                         
                       
                     
                     
                       copper 
                       ⁢ 
                           
                       corrosion 
                       ⁢ 
                           
                       area 
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     The corrosion current passing through the copper region (e.g., caused by light incident on the p-n junction), and thus the resulting corrosion in the copper region, is proportional to the antenna ratio. Thus, the corrosion sensitivity of each corrosion monitoring system according to the present invention may be selected, or “tuned,” by providing a desired antenna ratio. This concept is illustrated in  FIGS.  5  and  6   , for example. 
       FIG.  5    shows a top view of an example corrosion monitoring system  500 , generally similar in configuration to corrosion monitoring system  300  shown in  FIG.  3   , according to one example embodiment of the invention. Corrosion monitoring system  500  includes a continuous copper corrosion region  502  (e.g., metal layer  1 ) formed over a single p-n junction space charge region  510  defined between a single p-region  504 A and n-region  504 B, and connected to p-region  504 A and n-region  504 B by a number (any suitable number) of conductive contacts  506 A and  506 B (e.g., formed from tungsten or cobalt). According to Equation (1), the antenna ratio of example corrosion monitoring system  500  is equal to the top view area of p-n junction space charge region  510  divided by the top view area of copper corrosion region  502 . 
       FIG.  6    shows a top view of another example corrosion monitoring system  600 , according to another example embodiment of the invention. Unlike corrosion monitoring system  500 , corrosion monitoring system  600  includes a continuous copper corrosion region  602  (e.g., metal layer  1 ) extending over multiple p-n junction space charge regions  610  defined between adjacent pairs of p-regions and n-regions  604 . In this example, a first p-n junction space charge region  610 A is defined between p-region  604 A and n-region  604 B; a second p-n junction space charge region  610 B is defined between n-region  604 B and p-region  604 C; and a third p-n junction space charge region  610 C is defined between p-region  604 C and n-region  604 D. Copper corrosion region  602  may be connected to each p-region/n-region  604 A-D by any suitable number of conductive contacts  606 A,  606 B,  606 C and  606 D, respectively (e.g., formed from tungsten or cobalt). 
     According to Equation (1), the antenna ratio of example corrosion monitoring system  600  is equal to the total combined area of p-n junction space charge regions  610 A,  610 B, and  610 C divided by the top view area of copper corrosion region  602 , which provides a higher antenna ratio (all other things held equal) than the antenna ratio of corrosion monitoring system  500  having only a single p-n junction. Thus, one technique for tuning the antenna ratio of a corrosion monitoring system according to the present invention is to increase or decrease the number (and respective areas) of p-n junction space charge regions connected to the overlying copper corrosion region. In addition, a structure with great sensitivity to corrosion can be created within a limited space in the IC device, e.g., within the space of a scribe line for example. 
     In addition, in some embodiments of the invention, the corrosion monitoring system may extend across multiple metal layers in an IC device structure, e.g., to monitor for corrosion at each metal layer as the IC stack is built up, and/or to simultaneously monitor corrosion at multiple metal layers that have been formed. 
       FIG.  7    is a cross-sectional side view of an example multi-level corrosion monitoring system  700 , according to one example embodiment of the invention. In this example, multi-level corrosion monitoring system  700  includes a continuous metal layer  3  (M 3 ) corrosion structure  702 C used to detect corrosion at the M 3  level. Structure  702 C may be conductively connected, through metal layer  2  (M 2 ) and metal layer  1  (M 1 ), to an underlying silicon region including a p-type active region  704 A and n-type active region  704 B that define a p-n junction space charge region  710 , to thereby define a define a short circuit through M 3  level corrosion structure  702 C. 
     In the example shown in  FIG.  7   , corrosion monitoring system  700  includes a pair of M 1  copper regions  702 A, a pair of M 2  copper regions  702 B, and the M 3  copper corrosion region  702 C. Copper regions  702 A,  702 B, and  702 C may be conductively connected to each other, and to the underlying silicon ( 704 A,  704 B) by any suitable structures. In the illustrated example, M 1  copper regions  702 A may be connected to p-region  704 A and n-region  704 B by a number (any suitable number and type(s)) of conductive contacts  706 A and  706 B (e.g., formed from tungsten or cobalt), and copper regions  702 A,  702 B, and  702 C may be connected to each other by copper vias or contacts  712 , for example. In the illustrated embodiment, each copper region  702 A,  702 B, and  702 C has a corresponding surrounding barrier layer  714 , e.g., formed from Ta or TaN. 
     In the illustrated example, the M 3  corrosion region  702 C is (a) conductively connected at a first side or location to p-region  704 A through a respective M 2  copper region  702 B, a respective M 1  copper region  702 A, respective vias or contacts  712 , and a respective p-region contact  706 A, and (b) conductively connected at a second side or location to n-region  704 B through a respective M 2  copper region  702 B, a respective M 1  copper region  702 A, respective vias or contacts  712 , and a respective n-region contact  706 B. This configuration defines a short circuit extending through p-n junction space charge region  710  and though M 3  corrosion region  702 C, to thereby define a device for monitoring corrosion in the M 3  layer. 
     It should be understood that while example corrosion monitoring system  700  is configured for monitoring corrosion at the M 3  level (and thus extends through the M 2  and M 1  levels), multi-level corrosion monitoring systems may be constructed according to the present teachings for monitoring copper corrosion at any selected level in the IC stack (e.g., M 1 , M 2 , M 3 , M 4 , etc.). In addition, a multi-level corrosion structure may be connected to an array of multiple p-regions/n-regions that define any number of p-n junction space charge regions, e.g., according to the concepts shown in  FIG.  6    discussed above. 
     In addition, in some embodiments, the corrosion monitoring system may be configured for electric measurement of copper corrosion by using test instruments to apply a current through the corrosion-sensitive copper region and measure at least one electric property associated with the level of copper corrosion (e.g., voltage drop across the copper region, or resistance, without limitation), and using suitable corrosion analysis circuitry to calculate a measure of corrosion in the copper region based at least on the current supplied by the current source and the measured electric property.  FIGS.  8  and  9 A- 9 B  illustrate two example embodiments of such corrosion monitoring systems with the associated circuitry to form a corrosion monitoring system. 
       FIG.  8    illustrates a top view of an example corrosion monitoring system  800  including a corrosion-sensitive copper region  802  (e.g., M 1 ) extending over multiple p-n junction space charge regions  810  defined between adjacent pairs of p-regions and n-regions  804 , and connected to p-regions and n-regions  804  by conductive contacts  806 . In this example, a first p-n junction space charge region  810 A is defined between p-region  804 A and n-region  804 B; and a second p-n junction space charge region  810 B is defined between n-region  804 B and p-region  804 C. Copper corrosion region  802  may include, or be conductively coupled to, a pair of probe connection pads or regions  816 A and  816 B at opposing ends of copper corrosion region  802 . 
     Probe connection pads  816 A and  816 B may include or define probe connection sites for a four-point probe to test electromigration (corrosion) in copper corrosion region  802 , e.g., according to the van der Pauw method. 
     Thus, corrosion monitoring system  800  may include test instruments and evaluation circuitry for determining a measure of corrosion in the copper corrosion region  802 , e.g., a constant current source, a detector for detecting voltage drop, resistance, or other electrical property associated with the copper, and corrosion analysis circuitry  840  for calculating a measure of copper corrosion based at least on the detected electrical property. 
     In this example, probe connection pads  816 A and  816 B may include probe connection sites  820 A and  820 B (indicated at “1” and “2” in  FIG.  8   ) for connection to a current source  830  to pass a controllable current through copper corrosion region  802 . Probe connection regions  816 A and  816 B may also include probe connection sites  820 C and  820 D (indicated at “3” and “4” in  FIG.  8   ) for connection to a voltage detector/voltage detection circuitry  832 , to measure the voltage drop across copper corrosion region  802 . Suitable corrosion analysis circuitry  840  may then calculate a resistance of the copper corrosion region  802  based the current passed through copper corrosion region  802  and the measured voltage drop, which resistance may represent a level of electromigration/corrosion in the copper corrosion region  802 . In other embodiments, the corrosion analysis circuitry  840  may use the current through copper corrosion region  802  and the measured voltage drop to calculate any other electrical property that may represent an extent of corrosion in the copper corrosion region  802 . 
       FIGS.  9 A- 9 B  illustrates a top view ( FIG.  9 A ) and a cross-sectional side view ( FIG.  9 B ) of another example corrosion monitoring system  900  including a corrosion-sensitive copper region  902  (e.g., M 1 ) extending over p-n junction space charge regions  910 A and  910 B defined between adjacent pairs of p-regions and n-regions, and connected to the p-regions and n-regions by conductive contacts  906 , similar to the structure of corrosion monitoring system  800 . However, unlike corrosion monitoring system  800 , corrosion monitoring system  900  includes probe connection pads or regions  916 A and  916 B located in a different IC stack layer, e.g., a different metal layer, than the corrosion-sensitive copper region  902  (e.g., a higher or lower metal layer). Probe connection pads or regions  916 A and  916 B may be conductively coupled to copper region  902  by any suitable conductive contacts  922 A and  922 B, e.g., vias or interconnects. 
     Probe connection pads or regions  916 A and  916 B may include probe connection sites  920 A and  920 B (indicated at “1” and “2” in  FIG.  9   ) for connection to a current source  930 , to pass a controllable current through copper corrosion region  902  (through contacts  922 A,  922 B). Probe connection regions  916 A and  916 B may also include probe connection sites  920 C and  920 D (indicated at “3” and “4” in  FIG.  9   ) for connection to a voltage detector/voltage detection circuitry  932 , to measure the voltage drop across copper corrosion region  902 . Suitable corrosion analysis circuitry  940  may then calculate a resistance of the copper corrosion region  902  based the current passed through copper corrosion region  902  and the measured voltage drop, which resistance may represent a level of electromigration/corrosion in the copper corrosion region  902 . In other embodiments, the corrosion analysis circuitry  940  may use the current through copper corrosion region  902  and the measured voltage drop to calculate any other electrical property that may represent an extent of corrosion in the copper corrosion region  902 . 
     In a configuration such as shown in  FIGS.  9 A- 9 B  including multiple metal layers connected by via or other contacts, a common failure location is at the interface between the top surface of copper  902  and bottom surfaces of contacts  922 A,  922 B, indicated in  FIG.  9 B  at “F.” For example, in a structure including damascene copper interconnects, the via may be particularly susceptible to electromigration, especially when connected with a corroded metal surface underneath, e.g., at locations “F” shown in  FIG.  9 B . Thus, providing probe connection regions  916 A and  916 B connected to contacts  922 A and  922 B may provide an indication of overall corrosion of the respective device. 
     The present disclosure focuses on copper corrosion. However, it should be understood that the invention may be similarly utilized for monitoring corrosion of other suitable metals or materials, such as other metals that do not form an effective native oxide for preventing oxygen penetration, for example.