FexOy Particles

FexOy Particles

Material Name: Silicon
Record No.: 106
Primary Chemical Element in Material: Si
Sample Type: Wafer
Uses: Etching
Etchant Name: None
Etching Method: Wet etching
Etchant (Electrolyte) Composition: No data
Procedure (Condition): No data
Note: A particular phenomenon can be observed on these experimental wafers. After KOH etching, the etched surface was covered by particles. SEM EDS analysis shows that particles contain iron (Fe) and oxygen. When not removed, the particles cause shallow etch pits on the silicon surface in further KOH etching steps, as shown in Fig 1. It was also found that the particles can be removed by SC2 cleaning after the etching step. Bergenstof Nielsen et al. [Bergenstof Nielsen 2000] reported deposition of inorganic (FexOy) particles in connection with the KOH etching of silicon membranes. They reported that the source of the particles was the KOH pills used for making the etching bath.
Reference: Petteri Kilpinen, KOH anisotropic silicon etching for MEMS accelerometer fabrication, PhD Thesis, Aalto University, 2014, p. 109.

Figure 1: SEM picture of anisotropic KOH wet etched single crystalline silicon seismic mass and spring beam. In the spring beam, there is a shallow etch pit caused by (FexOy) particles.