| CPC H01L 23/5223 (2013.01) [H01L 23/544 (2013.01); H01L 2223/54426 (2013.01)] | 7 Claims | 

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               1. A semiconductor device, comprising: 
              a first tier structure comprising a plurality of conductive features of the first tier structure positioned over a substrate, and a decoupling unit of the first tier structure positioned between the plurality of conductive features of the first tier structure; 
                a first set of solid alignment marks comprising a first-tier-alignment mark positioned on the decoupling unit of the first tier structure, and comprising a fluorescence material; 
                a second tier structure positioned on the first tier structure and comprising a plurality of conductive features of the second tier structure positioned over and deviated from the plurality of conductive features of the first tier structure, and a decoupling unit of the second tier structure positioned over the first tier structure, and positioned between the plurality of conductive features of the second tier structure; and 
                a first set of spaced alignment marks comprising a second-tier-alignment mark positioned on the decoupling unit of the second tier structure, and comprising a fluorescence material; 
                wherein the decoupling units of the first tier structure and the second tier structure comprise a low-k dielectric material and respectively comprise a bottle-shaped cross-sectional profile; 
                wherein the fluorescence material comprises azobenzene; 
                wherein the first tier structure comprises a first dielectric layer positioned on the substrate; 
              a second dielectric layer positioned on the first dielectric layer; a middle dielectric layer positioned on the second dielectric layer; a third dielectric layer positioned on the middle dielectric layer; and 
              a fourth dielectric layer positioned on the third dielectric layer; wherein the decoupling unit of the first tier structure is positioned in the middle dielectric layer and on the second dielectric layer; 
              wherein the first-tier-alignment mark of the first set of solid alignment marks is positioned along the fourth dielectric layer and the third dielectric layer, extending to the middle dielectric layer, and on the decoupling unit of the first tier structure; 
            wherein the first dielectric layer and the third dielectric layer comprise the same material; 
                wherein the second dielectric layer and the fourth dielectric layer comprise the same material; 
                wherein a sidewall of the first-tier-alignment mark of the first set of solid alignment marks is tapered; 
                wherein a width of a top surface of the first-tier-alignment mark of the first set of solid alignment marks is greater than a width of the first-tier-alignment mark of the first set of solid alignment marks at an interface between the middle dielectric layer and the third dielectric layer. 
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