A COST-EFFECTIVE METHOD TO FABRICATE THROUGH-SILICON VIAS USING ANISOTROPIC WET ETCHING OF (100) SILICON WAFERS

摘要

Through-silicon via (TSV) technology is one of the critical and enabling technologies for three-dimensional (3D) integration of ICs. In this paper we present a cost-effective method for TSV fabrication using wet etching of silicon in tetramethylammonium hydroxide (TMAH) etch solution and a spin-applied photosensitive etch mask.Conventionally, silicon nitride applied using chemical vapor deposition (CVD) is used as an etch mask for wet silicon etching. The silicon nitride etch masks present several disadvantages including pinholes, stress cracks, and cost of ownership of process (due to the need to use a CVD tool and the number of processing steps).In this paper, we use a thick versiom of the spin-applied photosensitive etch mask that is also sensitive to i-line (365-nm) wavelengths and broadband light sources to cover topographies up to 5 μm. A comparison of undercut between silicon nitride protection and photosensitive etch mask protection is conducted to show that undercut for the polymeric mask is comparable that for the silicon nitride mask for stable etching conditions. Also, the effects of TMAH etch bath temperature and concentration on the undercut of etch mask and etch rate of silicon are also studied.We also present two generic methods for fabrication of TSVs using wet etching of silicon in TMAH solution using the photosensitive material as an etch mask. One of the methods also uses a temporary bonding material to bond the device wafer to a carrier wafer to facilitate thin wafer handling during TSV fabrication. These fabrication methods could be adopted for either via-first or via-last approaches.