Electrochemical etching of Si(001) in NH4F solutions: Initial stage and {111} microfacet formation

Abstract

In situ scanning tunneling microscopy (STM) has been used to examine the etching of an n-Si(001) electrode in 0.1 M NH4F. Cathodic polarization facilitated chemical etching of Si(001) to give {111} microfacets as a result of the tendency of Si to form a monohydride terminated surface. Time-dependent in situ STM atomic images were obtained to demonstrate the preferential etching at the kinks and steps. From the results of the time-dependent imaging, local etching rates were evaluated for the specific crystallographic directions. A Si(001):H-(1×1) square structure was also obtained, demonstrating the presence of dihydride configuration in the beginning of the etching.

Study of Ni Metallization in Macroporous Si Using Wet Chemistry for Radio Frequency Cross-Talk Isolation in Mixed Signal Integrated Circuits

“…Fluoride species which are strong oxidizing agents can further oxidize sub-oxide species for additional extraction of electrons to reduce Ni 2+ , and then cause dissolution of Si oxides, and eventually give rise to microporous Ni deposits on sidewalls. Some earlier detailed analysis of electrochemical kinetics and deposition chemistry in bath processes provides support to our findings [22]. Therefore transport of chemical species becomes possible through a microporous deposits layer to overreact with inner Si sidewall.…”

“…Firstly, Si underwent an anisotropic etching in <111> direction, which could be related to the existence of NH 4 F in the chemistry. NH 4 F is commonly used as part of buffered oxide etching (BOE) chemicals and study of its etching and oxidation processes on Si (100) affirms increasingly generated Si (111) micro facets soon after immersion [22]. The second is that Ni deposits are not in direct contact with Si but enclosed within a matrix of bright contrast located at the interfacial area in between Ni deposits and underneath Si (Figure 7b, TEM micrograph of higher mag).…”

Atomic structures of hydrogen-terminated Si(001) surfaces after wet cleaning by scanning tunneling microscopy

“…2 Several groups have observed atomic-scale structures by scanning tunneling microscopy ͑STM͒ with pH-modified buffered HF, 3,4 NH 4 F, 5 or the electrochemical method. 6 But their wet-chemical treatments are completely different from wet cleaning employed in the semiconductor industry. Only Nakagawa et al 7 succeeded in observing atomic-scale images by STM on a surface after dipping into 1% HF solution but the atomic arrangement is not clear.…”

Fabrication of SiGe quantum dots on a Si(100) surface

“…Note that, for simplification, we show straight ͑111͒ facets but they may have staircaselike morphology similar to those observed during electrochemical etching of the Si͑100͒ surface in NH 4 F solution. 27 Each facet might be composed of multiple ͑111͒ microfacets that are separated only by monolayer steps. This might explain why we could not clearly identify the facets before growth by ex situ AFM.…”