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12:1 Aspect Ratio Mid-process TSV Integration and Functional Test Using Advanced Metallization Processes
Keywords: TSV Integration, Metallization, 3D Integration
TSV has become a key technology driver for 3D integration of heterogeneous devices. Among the different ways to create TSV, mid-process integration places the TSV realization between the front end and Back end of line. The aspect ratio of the TSV in these integrations are generally limited to 10 :1, with structures of 10x100 um for example. These limitations are mainly due to metallization limitations and specially the lack of step coverage of the standard barrier and seed layer deposition methods. However, interposers are becoming larger and, according to targeted applications like photonic, use specific materials such as thick SOI thus leading to severe deformation of the wafer during process and device during assembly. The generated bow can become a key limitation for 3D integration. Among the different methods to overcome this limitation, thicker silicon is considered as the most polyvalent one but appears as strongly challenging for conventional metallization. We have developed advanced barrier and seed deposition methods to reach >10:1 aspect ratio TSV with a sufficient maturity to be integrated in a conventional 3D integration process flow. Considering the barrier, MOCVD TiN gives excellent performances in terms of barrier efficiency and step coverage for aspect ratio up to 20:1. These results have already been reported [1]. Considering the seed layer, PVD seed layers are reaching their step coverage limits with <3% step coverage in 10:1 aspect ratios. Our development was focused on the eG3D(TM) process [2] which can be used as seed repair, repairing the PVD discontinuities to ensure void free filling or as Direct on Barrier deposition process, deposited in this case directly on barrier material. The paper will describe the development and performances of the eG3D(TM) process and its integrability in the standard process flow, including last chemistry generation copper filling (fig 1) and chemical reduction of copper overburden. Integrated extendibility of such a material has been proven for 12:1 aspect ratio for both approaches and will be discussed. Then electrical results from a 10x120 um lot including the TSV and both side interconnects will be presented giving very high yield and excellent resistance distribution for TSV daisy chains up to 754 TSVs (figure 2). The results will be compared to usual results obtained with conventional integration of 10x100um mid process TSV. The presented results demonstrate the ability to integrate advanced metallization processes in a conventional 3D mid-process TSV integration process flow to realize integration of 12:1 aspect ratio TSV with extendibility to deeper structures. The integrated materials (Titanium nitride for barrier and electrografted copper for seed layer) are fully compatible with existing annealing and CMP processes and are deposited in standard manufacturing worthy equipments thus allowing the proposed solution to fast transfer to industry.
Christophe Aumont,
Crolles , Cedex

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