Micromachined stress-free TSV hole for AlGaN/GaN-on-Si (1 1 1) platform-based devices

Abstract

This paper presents a micromachined stress-free through silicon via (TSV) backend process for AlGaN/GaN-on-Si (1 1 1) platform-based devices, which was processed by assisted back grinding, chemical mechanical polishing, deep reactive ion etching (DRIE) and copper (Cu) electroplating for the TSV. The metal-filled TSV structure was formed to enhance thermal conduction from the frontend terminal to the backend terminal, especially the source region of the AlGaN/GaN-on-Si (1 1 1) platform-based RF power devices. At the end of a stress-free TSV dry etching process, we have changed RF power 600 W to 300 W to minimize thermal stress of the fabricated TSV electrode pad structure of the AlGaN/GaN-on-Si platform-based devices. Additionally, we have sputtered a multi-metal layer and electroplated Cu metal to interconnect a topside electrode to TSV. To protect the thinned TSV electrode pad structure from water pressure in a sawing process, we have covered photoresist (AZ4330RS) of 3.3 µm thickness on the top area of the structures. We confirmed that the proposed TSV formation method assisted by low-power operation DRIE and protection of the thinned TSV surface by using the thick photoresist is very effective to create minimally stressed TSV structures in AlGaN/GaN-on-Si platform-based devices. The improvement was proved by the yield of dice without bursting the pad structures on a 4 inch AlGaN/GaN-on-Si wafer.

An analytical model of thermal mechanical stress induced by through silicon via

“…8(a). (ii) Three TSVs are in a row, with the spacing between the two TSVs being 10 µm, [12] as shown in Fig. 8(b).…”

“…The CTE mismatch between copper and silicon causes inevitable stress on silicon and results in material failure. [10][11][12][13][14][15] It will also affect the performance of devices which are around the TSV and reduce the life of the electronic device. [16,17] Furthermore, the design parameters, such as the thickness and materials of Cu diffusion barrier and liner, have an impact on the mechanical reliability.…”