Etching Silicon with Aqueous Acidic Ozone Solutions: Reactivity Studies and Surface Investigations

Abstract

Aqueous acidic ozone (O 3 )-containing solutions are increasingly used for silicon treatment in photovoltaic and semiconductor industries. We studied the behavior of aqueous hydrofluoric acid (HF)-containing solutions (i.e., HF−O 3 , HF−H 2 SO 4 −O 3 , and HF−HCl−O 3 mixtures) toward boron-doped solar-grade (100) silicon wafers. The solubility of O 3 and etching rates at 20 °C were investigated. The mixtures were analyzed for the potential oxidizing species by UV−vis and Raman spectroscopy. Concentrations of O 3 (aq) , O 3 (g) , and Cl 2 (aq) were determined by titrimetric volumetric analysis. F − , Cl − , and SO 4 2− ion contents were determined by ion chromatography. Model experiments were performed to investigate the oxidation of Hterminated silicon surfaces by H 2 O−O 2 , H 2 O−O 3 , H 2 O−H 2 SO 4 −O 3 , and H 2 O−HCl−O 3 mixtures. The oxidation was monitored by diffuse reflection infrared Fourier transformation (DRIFT) spectroscopy. The resulting surfaces were examined by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). HF−H 2 O−O 3 mixtures show a polishing etching behavior, whereas HF−HCl−H 2 O−O 3 mixtures exhibit slight anisotropic etching. Formation of pyramidal-like morphologies on (100) silicon surfaces was observed. In all cases, cleaned and H-terminated silicon surfaces are obtained. The results were used to draw conclusions about the dissolution mechanism of silicon in the respective solutions. In HF−H 2 O−O 3 mixtures, silicon is dissolved by an O 3(aq) -diffusion-controlled tetravalent etching mechanism. Interestingly, in H 2 SO 4 -rich aqueous HF−H 2 SO 4 −O 3 solutions, only the native oxide is removed, whereas silicon is not attacked and dissolved. In HCl-containing solutions, Cl 2 or Cl 3− are responsible for silicon oxidation. HCl can be considered as a catalyst resulting in a divalent silicon dissolution mechanism similar to the etching in alkaline solutions.

Etching SiC‐slurry and diamond wire‐sawn silicon wafers with HF‐HCl‐Cl2 mixtures: Parameter influences on etch rates and surface structures

“…The solubility of gaseous chlorine is higher in higher concentrated hydrochloric acid due to the generation of Cl 3 − ‐anions (Eq. ) . Therefore, a higher etch rate would be expected because of the higher amount of the oxidizing agent.…”

“…We recently examined acidic mixtures based on hydrofluoric and hydrochloric acid with added oxidants for the generation of pyramidal structures on monocrystalline (100) wafers. The investigated oxidizing agents include ammonium persulfate ((NH 4 ) 2 S 2 O 8 ) , hydrogen peroxide (H 2 O 2 ) , and ozone (O 3 ) . In these mixtures, chlorine (Cl 2 ) and trichloride ions (Cl 3 − ) are formed by the oxidation of the chloride ions contained in the hydrochloric acid by the respective oxidizing agent (Eqs.…”

Selective Etching of Silicon from Ti3SiC2 (MAX) To Obtain 2D Titanium Carbide (MXene)

“…[13] It is well known that wet chemical etching of Si can be done in mixtures containing HF and an oxidant. [14] Many oxidants such as HNO 3 , [14b] H 2 O 2 , [15] O 3 , [16] persulfate [17] and permanganate salts [17b] have been shown to facilitate etching of Si by HF.T he etching mechanism of Si in HF/oxidant mixtures has been described as at wo-step process:1 )stepwise oxidation of Si by an oxidant and 2) dissolution of silicon oxides by HF. [14a, 15, 18] Moreover,w es howed that HNO 3 /HF mixtures can selectively etch polytypes of silicon carbide, producing nanometers-thin lamellas of SiC.…”

On The Mechanism of the Anisotropic Dissolution of Silicon in Chlorine Containing Hydrofluoric Acid Solutions

“…1,[14][15][16] In these solutions the reactivity is very low, for example in HF-O 3 -mixtures a dissolution rate of silicon of 0.6 nm s −1 is observed. 17 However, investigations on HF based solutions containing H 2 O 2 or O 3 with added hydrochloric acid or sulfuric acid to the etching mixtures showed an increase in the etching rates. 17 When adding an oxidant to a highly concentrated solution of hydrochloric acid, chlorine is formed (Equations 3, 4) which acts as a very good oxidant for the silicon surface.…”

“…17 However, investigations on HF based solutions containing H 2 O 2 or O 3 with added hydrochloric acid or sulfuric acid to the etching mixtures showed an increase in the etching rates. 17 When adding an oxidant to a highly concentrated solution of hydrochloric acid, chlorine is formed (Equations 3, 4) which acts as a very good oxidant for the silicon surface. 14,18,19 Also for bubbling gaseous chlorine into a solution containing hydrofluoric and hydrochloric acid a significant increase of the dissolution rate of silicon was reported.…”