Measurement anisotropic etching

The simplest and perhaps the most useful measure of anisotropy is the ratio of lateral or horizontal undercut distance (dh) to the vertical etch distance (dy). This ratio is inversely related to the quality of replication. In anisotropic etching, djdv = 0, and exact dimensional transfer is achieved. A low-quality transfer is obtained with isotropic etching, in which djdv = 1. Anisotropic etching is imperative for high-density-device fabrication. 

A four-layer microchip has been constructed to generate total internal reflection (TIR) and an evanescent field (see Figure 7.8). Surface-adhered Nile red-labeled fluorescent microspheres (1 pm) are excited by the evanescent field for fluorescent measurement. An essential feature on the chip was the micromirror that was constructed by depositing Au/Cr on the slanted wall (54.7° due to anisotropic etch of Si). Operation near the critical angle 0C assures strong evanescent intensity [695]. 

The most characteristic feature of etching in KOH solution is its anisotropic nature, i.e., the etch rate varies with the crystal orientation of the silicon wafer. The etch rate for the major crystal planes follows 110 > 100 > 111. The exact difference between the etch rates of these planes depends on concentration, temperature, and measurement procedure. For example, in 20% KOH at 100 °C the etch rates for (110) (100) (111) are 930 560 19A/s corresponding to a ratio of 50 30 1. The difference between the etch rates of (110) and the (100) planes and that of the (111) plane is larger at room temperature, giving a ratio of 160 100 1 in 20% KOH. Addition of... 

The most characteristic feature of etching in KOH solution is its anisotropic nature, that is, etch rate varies with the crystal orientation of the silicon wafer. The etch rates for the major crystal planes are 110 > 100 > 111 [82], The exact difference between the etch rates of these planes depends on concentration, temperature, and measurement procedure. 

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