Development of silicon and carbon foam low mass interposers

We propose fabrication methods and present prototyping results for a new wafer integration component called a low mass interposer (LMI). The LMI prototype is an assembly of silicon and carbon foam resulting in a composite 4 inch wafer of 4 mm thickness and average density 10% that of silicon. Rows of vertical copper contacts traverse the bulk on 4mm pitch. Each row can have a dense contact pitch, such that average contact densities can be or order order 25 mm−2. Actual pitch parameters can be varied by factors of 2 or more within the construction process proposed. The LMI could be used for copper-copper bonding to IC wafers in a 3D integration process. Present prototyping does not match any specific wafer design and was produced to develop a fabrication procedure and quantify the results. No 3D integration tests have been performed at this stage.