We have developed a high-density wiring interposer for 10 GHz 3D packaging using a photosensitive multiblock copolymerized polyimide. This new polyimide can realize micron-sized fine patterns without pattern shrinkage because of the nonrequirement of high-temperature thermal curing. The polyimide has good electric properties such as high breakdown voltage and low dielectric constant. Therefore, it is considered that by introducing this photosensitive polyimide as an insulator of the interposer, a high-performance interposer for LSI packaging can be realized. We confirmed experimentally that the high-density wiring interposer can be fabricated using the polyimide and gold. We optimized the basic properties of the photosensitive polyimide film for the fabrication of the interposer. Fine metal wirings were smoothly covered by the polyimide, as confirmed by scanning electron microscopy (SEM) of the cross section of the fabricated balance pair strip line structure. From the time domain reflectometry (TDR) measurement, it was determined that the characteristic impedance of the strip line is within 55.2 Ω ± 11.5% at the center of the interposer chip.

We have developed a high-density wiring interposer for 10-Gbps signal propagation using a photosensitive polyimide. We optimized the basic properties of the photosensitive polyimide film for the fabrication of the interposer. We experimentally confirmed that the high-density wiring interposer could be fabricated using the optimized polyimide and gold multilayered structure. Fine metal wirings were smoothly covered by the polyimide film, as confirmed by scanning electron microscopy (SEM) of the cross section of the fabricated balanced pair strip-line structure. From the high-resolution differential time domain reflectometry (TDR) measurement, the differential impedance Z diff of a 12.5-µm-wide 12.4-mm-long balanced-pair strip-line was evaluated to be within 100 Ω ± 14.6 %. From the high-resolution differential time domain transmission (TDT) measurement, an insertion loss (S-parameter: S dd21 ) of -2.96 dB at 10 GHz through the differential strip-line was evaluated. Finally, we confirmed eye diagram measurement at 10 Gbps through the differential strip-line on the fabricated interposer. The aperture size of the measured eye diagram at 10 Gbps was sufficient for ultrahigh-speed signal propagation. IntroductionWith the increase in the operational speed and integration density of LSI chips, high-performance digital electronic systems have been realized. The clock frequency of a CPU-LSI chip exceeds the GHz range. However, to realize a computing system with a higher performance, the high-speed signal propagation performance of not only the LSI chips of computing systems but also LSI packages and interconnects must be improved. To obtain high-speed signal transmission in LSI packages and interconnects, line impedances should be

Photosensitive polyimide is expected as a future interlayer dielectric material in LSI circuits. In this paper, we propose a new interlayer dielectric process using a positive photosensitive polyimide directly synthesized from aromatic dianhydride and aliphatic diamine by block-copolymerization. Photosensitive polyimide solution was prepared with N-methyl-2-pyrrolidone (NMP) solvent. A diazonaphthoquinone PC-5 was used as a photosensitizer. The thin film was spin-coated with changing polyimide concentration and rotation speed. The uniformity of the coated film was achieved less than ± 0.9 % on a 3-inch wafer of silicon. A 0.5 µm line and space pattern was obtained by i-line lithography. The γ value of the contrast was evaluated to 1.05. The dielectric constant of the base polyimide was measured for a thick film by the cavity perturbation method. The values from 2.4 to 3.0 were obtained within the frequency range from 1 GHz to 20 GHz. The break down voltage was measured to be 107 kV/mm without high-temperature heat treatment.

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