We have developed key technologies to form conductive interconnections through a thick silicon substrate, which are potentially applied for 3D device fabrication or packaging of optical MEMS devices. In this paper, we demonstrate to form metal filled Through-Holes (THs) in thick Silicon (Si) substrates (t=~500µm) mainly using Photo Assisted Electro-Chemical Etching (PAECE)[1][2] and Molten Metal Suctioned Method (MMSM) [3] . The THs that we experimentally made with these technologies had 15µm

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... the diameter and the aspect ratio of 35. And the maximum density was 500THs/cm 2 . The dielectric breakdown voltage of the THs was more than 500V. In the result of a radioisotope leak test using Kr-85, the leakage rate of THs between the front and the back of the substrate was lower than the detection limit (1 X 10 -15 Pa•m 3 /sec.). Figure 9 Photograph of cross section of through-holes by PAECE with the backside mask shade (left), the 'peripheral effect' in fully opened backside (right).