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Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim Part 6

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Tham khảo tài liệu 'microsensors, mems and smart devices - gardner varadhan and awadelkarim part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | ETCH-STOP TECHNIQUES 133 Worked Example E5.4 Fabrication of Cantilever Beams Objective The objective is to fabricate a cantilever beam that is a few microns thick on a 7-type silicon that supports wafers using electrochemical etching Linden et al. 1989 . Process Flow The starting silicon wafers used are again standard commercial 280 pm thick4 100 -oriented silicon wafers. The wafers are boron-doped with a resistivity of 7 to 10 ffcm which corresponds to a doping concentration approximately 1.50 X 1015 cm 3. Two different techniques can be used to define the beam. Technique A The diffused-pattern technique In the diffused-pattem technique an n-type a diffused -layer of n-doping concentration 10i7 cm-3 as described in Worked Example 5.3 pattern that describes the I beam is diffused into the wafer. The wafer is masked with SiO2 grown in wet o2 at 1000 C. Then by stripping the patterning oxide and by performing the electrochemical etch the beam will be totally defined by the diffusion process. The steps for the beam fabrication using this method are shown in Figure 5.15. The etching is performed in an apparatus similar to the one described in Worked Example 5.3 see Figure 5.14 b . In this technique the pattern is diffused thus resulting in an -type pattern defining the beam. Because of lateral diffusion during the drive-in this technique will result in beams with rounded corners Figure 5.15 c this means that we will not end up with the sharp comers that are usually associated with anisotropic etching. Technique B The etched-pattern technique I In the etched pattern technique an n-type layer dopant concentration 1017 cm 3 is diffused over the entire wafer. Oxidation is performed simultaneously with the drivein of the dopant. The oxide is patterned to cover the surfaces of the forming beam. The wafer is then immersed in the KOH etching solution as in Worked Example 5.3 Figure 5.14 b without any bias until the n-type layer is etched through and the p-type layer is .