MEMS LAB SESSION 2 Undercut Silicon Nitride using KOH Etching OVERVIEW OF LAB SESSION: This lab session utilizes potassium hydroxide(koh) wet etching to undercut and release the silicon nitride cantilevers and fixed-fixed beams. In Step 2. 1, KOH etching is used to anisotropically etch the silicon, and undercut the silicon nitride. The wafers undergo a series of solvent cleans and then are allowed to dry in the air in Step 2.2 LAB OBJECTIVES: This lab session has the following primary objectives Introduction to wet, anisotropic KOH etching Complete and release silicon nitride beams Complete electron-beam evaporation of chromium and gold Initial instruction on the following major pieces of lab equipment KOH Wet Station Acidhood 2 Wet station Electron-Beam Evaporative Deposition System Before the beginning of this lab, make sure to read the corresponding Standard-Operating Procedures(SOP)for these major pieces of equipment. The SOP for each of the equipments can be accessed at the following site http://www-mtl.mitedu/mtlhome/3mfab/sop.html LAB PROCEDURES MEMS Lab Session 2 has 2 major ster 2.1 RELEASE CANTILEVER 2.1.1 Tool: KOH Wet Station 2. 1.2 The silicon nitride beams are undercut using a solution of potassium hydroxide (KOH). This strong-base solution preferentially etches the <100> and <110> planes relative to the <111>, in single-crystal silicon, ther eby creating an an Pour 3 liters of DI water into the quartzware. Use the scale to measure out a sufficient amount of KoH pellets to create a 20% by weight solution Set the water bath temperature to 85C, which will give a KOH bath temperature of about 80C The etch rate is exponentially dependent on temperature, and therefore maintaining good temperature uniformity in the bath is important 2.2 EVAPORATED SOLVENT DRY 2.2.1 Tool: KOH Wet station 2.2.2 Due to the small scale of microfabricated devices surface forces become considerable compared to body forces. To try to avoid any stiction of the released Page 1 of 3MEMS LAB SESSION 2 Undercut Silicon Nitride using KOH Etching OVERVIEW OF LAB SESSION: This lab session utilizes potassium hydroxide (KOH) wet etching to undercut and release the silicon nitride cantilevers and fixed-fixed beams. In Step 2.1, KOH etching is used to anisotropically etch the silicon, and undercut the silicon nitride. The wafers undergo a series of solvent cleans and then are allowed to dry in the air in Step 2.2. LAB OBJECTIVES: This lab session has the following primary objectives: ¾ Introduction to wet, anisotropic KOH etching. ¾ Complete and release silicon nitride beams. ¾ Complete electron-beam evaporation of chromium and gold. ¾ Initial instruction on the following major pieces of lab equipment: KOH Wet Station Acidhood 2 Wet Station Electron-Beam Evaporative Deposition System Before the beginning of this lab, make sure to read the corresponding Standard-Operating￾Procedures (SOP) for these major pieces of equipment. The SOP for each of the equipments can be accessed at the following site: http://www-mtl.mit.edu/mtlhome/3Mfab/sop.html LAB PROCEDURES: MEMS Lab Session 2 has 2 major steps: 2.1 RELEASE CANTILEVER 2.1.1 Tool: KOH Wet Station 2.1.2 The silicon nitride beams are undercut using a solution of potassium hydroxide (KOH). This strong-base solution preferentially etches the <100> and <110> planes, relative to the <111>, in single-crystal silicon, thereby creating an anisotropic etch. Pour 3 liters of DI water into the quartzware. Use the scale to measure out a sufficient amount of KOH pellets to create a 20% by weight solution. Set the water bath temperature to 85o C, which will give a KOH bath temperature of about 80 o C. The etch rate is exponentially dependent on temperature, and therefore maintaining good temperature uniformity in the bath is important. 2.2 EVAPORATED SOLVENT DRY 2.2.1 Tool: KOH Wet Station 2.2.2 Due to the small scale of microfabricated devices, surface forces become considerable compared to body forces. To try to avoid any stiction of the released Page 1 of 3