Au bump connection technology for 3D stacked sensors and detectors

3D- ICs are effective in reducing the manufacturing cost of advanced 2D LSIs while ensuring equivalent device performance and functionality. In pixel-type detectors, the detector and readout circuits are fabricated in separate chips and stacked in order to increase time-space resolution. In addition, sensor devices that stack compound semiconductor sensors with Si signal processing circuits may break due to the difference in thermal expansion coefficient when returned to room temperature if they are firmly connected at high temperatures for bonding. This is especially true when brittle CdTe is used, and conventionally soft materials such as indium bumps that can be bonded at low temperatures have been used. The author's group has been conducting research and development on gold-cylinder bumps as bumps that can be connected at fine pitch and can alleviate inter-chip shear stress caused by temperature changes. This paper reports on a unique bump connection using an ellipsoidal cylindrical gold bump. These bumps are formed on the upper chip and the lower chip and are connected in a crossed shape. This structure was considered in order to obtain electrical connection even if the position of the upper and lower chips is misaligned in the XY direction.Bumping Characteristic Evaluation Trial production of Daisy Chain TEG with UBM and Au bumps formed on the AL wiring was conducted to evaluate connectivity and yield. Bump pitches of 15 µm, 10 µm, and 6 µm were targeted, and three types of bump chains of 6 x 2 µm, 4 x 2 µm, and 3.5 x 2 µm were fabricated.