Oxide etch rate

The etch rates were measured by a surface profiler and field emission scatming electron microscopy (FESEM), and the etch profile were observed by FESEM. In this study, a C /Ar gas chemistry was chosen to obtain high etch selectivity of Si film to niobium oxide mask since CI2 gas was known to be a good etch gas for Si films. The etch rate, etch selectivity and etch profile of niobium oxide nanopillars and Si films were explored by varying the CI2 concentration, coil RF power and dc bias voltage to substrate. 

The formation of Si nanodot arrays on a substrate was performed by ICPRIE of Si films using self-assembled niobium oxide pillars as an etching mask. The etch rates of niobium oxide pillars and Si films, and the etch selectivity of Si films to niobium oxide were investigated by varying etch parameters in a Ch/Ar gas. The main etch parameters used in this study were the concentration of CI2 gas, coil rf power, and dc-bias to substrate. 

Figure 1(a) shows the etch rates of niobium oxide pillar and Si film, and the etch selectivity of Si to niobium oxide as a function of CI2 concentration. The etch condition was fixed at coil rf power of 500 W, dc-bias to substrate to 300 V and gas pressure of 5 mTorr. As the CI2 concentration increased, the etch rate of niobium oxide pillar gradually decreased while Si etch rate increased. It indicates that the etch mechanism of niobium oxide in Cl2/Ar gas is mainly physical sputtering. As a result, the etch selectivity of Si film to niobium oxide monotonously increased. The effect of coil rf power on the etch rate and etch selectivity was examined as shown in Fig. 1(b). As the coil rf power increased, the etch rates of niobium oxide and Si increased but the etch rate of niobium oxide showed greater increase than that of Si. It is attributed to the increase of ion density with increasing coil rf power. Figure 1 (c)... 

Fig. 1. Etch rates of niobium oxide pillar and Si film, and etch selectivity of Si to niobium oxide piUar for the variation of (a) CI2 concentration, (b) coil rf power, and (c) dc-bias voltage to susceptor...

The 0 atom flow rate was measured by N02 titration as described elsewhere (21). At an 02 flow rate of 6.5 x 10-2 cm3 (STP)/s, reactor pressure of 73 Pa (0.55 torr) with the discharge off, and a power level of 15 W, the flow rate of 0 atoms was found to be 2.4 x 10-2 cm3 (STP)/s the latter figure represented an 18 conversion of 02 to 0 atoms. Assuming complete 0(3P)-induced oxidation of the polymer samples to C02 and H20, the flow rate of 0 atoms was at least eight times that required to maintain the highest etch rate observed (0.8 mg/cm2-h, in TB). 

Electrochemical etching is one way of controlling the etch rate and determine a clear etch stop layer when bulk micromachining Silicon. In this case, the wafer is used as anode in an HF-Electrolyte. Sufficiently high currents lead to oxidation of the silicon. The resulting oxide which is dissolved by the HF-solution. Since lowly doped silicon material is not exhibiting a notable etch rate, it can be used as an etch stop. 

Steady-State Oxide Thickness. The steady-state etching rate (R = S/M) does not contain any of the kinetic parameters thus it does not contain any information about the kinetics of the oxidation process. In contrast, the steady-state oxide thickness is determined by the kinetics of the transport and oxidation processes thus one can learn about these processes by studying the steady-state oxide thickness. The silicon material balance (Eq. 9)... 

Anodic oxide films formed under different kinetic conditions vary in structure, composition and property (e.g., etch rate) and they change with time during the anodization. 

Aqueous electrolytes of high pH etch silicon even at open circuit potential (OCP) conditions. The etch rate can be enhanced or decreased by application of anodic or cathodic potentials respectively, as discussed in Section 4.5. The use of electrolytes of high pH in electrochemical applications is limited and mainly in the field of etch-stop techniques. At low pH silicon is quite inert because under anodic potentials a thin passivating oxide film is formed. This oxide film can only be dissolved if HF is present. The dissolution rate of bulk Si in HF at OCP, however, is negligible and an anodic bias is required for dissolution. These special properties of HF account for its prominent position among all electrolytes for silicon. Because most of the electrochemistry reported in the following chapters refers to HF electrolytes, they will be discussed in detail. 

Alkaline etchants are anisotropic. The etch rate for the (111) crystal planes of the Si crystal is smaller by about two orders of magnitude than the etch rate of any other crystal plane. The etch rate ratio between other crystal planes like (100) and (110) depends on etchant concentration and temperature, but doesn t usually exceed a factor of two [Sa6]. Addition of oxidizing agents reduces the anisotropy. The etch rate of (100) Si and Si02 in KOH at different temperatures is shown in Fig. 2.2. 

Silicon is stable in acidic solutions that do not contain fluoride because the silicon surface is passivated by a native oxide. If only H F is present in an aqueous solution the etch rate remains low, showing values below 0.1 rim miri 1 on single crystalline silicon depending on the OFT concentration [Hu2]. This low etch rate... 

The OCP etch rate of p-type and highly doped n-type Si electrodes in HF-HNO3 mixtures increases by an order of magnitude under sufficiently anodic bias [Le20]. In the cathodic regime significant dark-currents are observed for p-type electrodes, as shown in Fig. 4.12. This is ascribed to hole injection from the electrolyte [Kol4]. Note that hole injection is not observed in aqueous HF free of oxidants. 

Etchants for defect and junction delineation are usually composed of HF and an oxidizing agent such as HN03 [Dal, Gr4, Ka4, Nel], K2Cr207 [Se5] or Cr03 [Sil, Jel, Sc7, Ya4, Me5]. Alkaline solutions are rarely used for defect delineation [Mal2], An etch pit will form on a silicon surface if the dissolution rate is enhanced locally. Enhancement of the etch rate may occur for various reasons ... 

Fig. 2.8 Etch rate of thermal oxide and CVD nitride (deposited at 850 °C) as a function of aqueous HF concentration at RT.

Etch rates in nm s I Thermal oxide CVD- nitride Undoped poly-Si Bulk Si (100) Aluminum... 

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