Effect of Process Gases on Fabricating Tapered Through-Silicon vias by Continuous SF₆/O₂/Ar Plasma Etching

Abstract

We report on a continuous plasma etching process using SF 6 /O 2 /Ar gases for fabricating 100 μm deep tapered through-silicon vias (TSV). The mask diameters of the vias were 20, 30 and 50 μm. The flow rates of the process gases were changed to study their individual effect on the profile angle, via depth, sidewall roughness, and sideways undercut of the tapered vias. Tapered vias having profile angles varying from 70 • to 85 • and smooth sidewalls were etched by balancing the chemically-assisted isotropic etching of F * radicals, passivation film by O 2 , and ion-assisted passivation etching. Although, the profile angles of the etched vias were reduced by either increasing the SF 6 flow rate or by reducing the O 2 flow rate, the effect of SF 6 gas was found to be dominant. The flow rates of SF 6 and O 2 were found to be the important factors which determine the continuous tapering of the vias with smooth via sidewalls. Ar gas flow rate did not significantly affect the tapered silicon vias and the profile angle. After considering the individual effects of each gas, an optimized etching recipe was fixed, which was used to etch 100 μm deep vias having a profile angle of 83 • . Conformal layers of insulation and copper seed layers were deposited in the tapered vias. The tapered vias were partially filled by copper electrodeposition and redistribution lines were formed. The electrical resistance of tapered TSVs was measured to be between 3-8 m for the majority of the TSVs, making these TSVs suitable for various MEMS packaging applications.

High Speed Surface Illuminated Si Photodiode Using Microstructured Holes for Absorption Enhancements at 900–1000 nm Wavelength

“…The straight submicron holes, as shown in Figure S2, were created using deep reactive ion etch (DRIE), and the details are presented in Supporting Information S2. Isotropic dry etch (SF 6 -based DRIE etch) − as shown in Figure S3­(a) and silicon isotropic wet etch (HNO 3 /H 2 O/NH 4 F mixed solution) , as shown in Figure S3­(b) can create shallow tapered holes by enabling an undercut beneath the hardmask. The nature of the isotropic etch can easily cause the adjacent holes to interconnect with each other, especially in the holes with smaller periods.…”

Through-silicon via submount for the CuO/Cu2O nanostructured field emission display

“…Due to directed kinetic energy transfer by the ions, the bottom is by far more easily cracked than the sidewalls. Therefore, the DRIE etch reactions for the TSV structure are as shown in the following equations: 19 SF 6 + e − → S x F y + + S x F y ˙ + F˙ + 2e − O 2 + e − → O + + O˙ + 2e − …”

Fast ultra-deep silicon cavities: Toward isotropically etched spherical silicon molds using an ICP-DRIE

“…Moving on towards less vertical (anisotropic)etch processes, the continuous process using a SF 6 /O 2 plasma seems to be the best compromise between straigth sidewall and complete curvated shaped. Nevertheless, SF 6 /O 2 gas chemistry tends to generate bowing in silicon 38 . Although the fabrication of the tapered through silicon vias by SF 6 /O 2 and SF 6 /O 2 /Ar plasma has been reported 38,39 , the effect of SF 6 /O 2 /C 4 F 8 chemistry on both the slope angle and roughness has not been provided.…”

“…Nevertheless, SF 6 /O 2 gas chemistry tends to generate bowing in silicon 38 . Although the fabrication of the tapered through silicon vias by SF 6 /O 2 and SF 6 /O 2 /Ar plasma has been reported 38,39 , the effect of SF 6 /O 2 /C 4 F 8 chemistry on both the slope angle and roughness has not been provided. Recipe 2 resulted in an anistropy close to 0.7 @70 mTorr.…”