Example of Notching and Bowing Occuring in an Etched Sample

Example of Notching and Bowing Occuring in an Etched Sample

Material Name: Silicon
Record No.: 59
Primary Chemical Element in Material: Wafer
Sample Type: Wafer
Uses: Etching
Etchant Name: None
Etching Method: Dry etching
Etchant (Electrolyte) Composition: No data
Procedure (Condition): No data
Note: Notching/footing: Notching and footing occur at the bottom of the etched hole and the ions affect the oxide at the wafer back. The oxide is a nonconducting material that accumulates negative charges on its surface and leads to the deflection of the positive ions in the plasma. These deflected ions start etching into the Si walls at the bottom of the hole, as shown in Fig. 1. It may be possible to prevent notching by using a conducting material at the bottom of the wafer, so that the conducting material will not accumulate a charge and deflect the ions. To test this hypothesis, aluminum (Al) was deposited on the back side of a wafer as an etch stop, but the Al layer, being only 0.0005 mm thick, started breaking away faster than the oxide. Also, the thermal conduction was better on the Al etching surface than on the oxide, which changed the hole profile. The crystallographic effect appeared at the bottom of the holes. If the Al backing remained, the table temperature would need to be increased by at least 10 .C to stop the crystallographic angles (which are explained later in this section) forming at the hole bottom.
Reference: Ankita Verma, Joshah Jennings, Ryan D. Johnson, Marc H. Weber, and Kelvin G. Lynn, Fabrication of 3D charged particle trap using through-silicon vias etched by deep reactive ion etching, J. Vac. Sci. Technol. B 31, 032001 (2013); doi: 10.1116/1.4799662.

Figure 1: Example of notching and bowing occuring in an etched sample.