OXIDATION || MODULE 4 || EC 465 || KTU MEMS || LECTURE 33

Hi all, today we are going to discuss about Oxidation In microelectronics, 4 types of thin films are used Let's see which are those 1. Thermal Oxidation for Electrical or Thermal Insulation Media 2. Dielectric Lays for Electrical Insulation 3. Polycrystalline Silicon for Local Electrical Conduction 4. Metals for Electrical Conduct and Junction There are 4 types of thin films that are frequently used in microelectronics 1. Thermal Oxidation for Electrical or Thermal Insulation Media 2. Dielectric Lays for Electrical Insulation 3. Polycrystalline Silicon for Local Electrical Conduction 4. Metals for Electrical or Thermal Conduct and Junction These are the 4 different types of thin films that are frequently used in microelectronics We are going to discuss about Silicon Dioxide Oxidation Process You might have studied about Oxidation process in VLS Oxidation is the process of adding an oxide layer on top of a silicon substrate Silicon Dioxide is used as an electrical insulator as well as for etching mask for silicon and sacrificial layers in surface micromachining Silicon Dioxide is used as an electrical insulator as well as for etching mask for silicon and sacrificial layers in surface micromachining There are several ways silicon dioxide can be produced on substrate surfaces The least expensive way to produce silicon dioxide film on silicon substrate is thermal oxidation There are several ways to produce silicon dioxide film on silicon substrate The least expensive way to produce silicon dioxide film on silicon substrate is thermal oxidation Chemical reactions used in this process as follows 1. Silicon plus Oxygen gas 2. Silicon dioxide 3. Steam passes through silicon dioxide Have you studied about Dry Oxidation and Wet Oxidation? Oxygen passes through Dry Oxidation and Steam passes through Wet Oxidation You can produce silicon dioxide in both of these ways Steam or Water is SI plus 2H2O gives SIO2 plus 2H2 gas 3. Resistance heating coil surrounded the tube to provide necessary high temperature in the tube This is how the oxidation process takes place Resistance heating coils are used to provide high temperature in the tube In this process, the wafers are placed in fused quartz cassettes that are pushed into the preheated furnace tube at a temperature in range of 900 to 1200 degrees Celsius The temperature range of the furnace tube is 900 to 1200 degrees Celsius Oxygen is blown into the tubular furnace for the oxidation of wafer surfaces Carrier gas passes through the furnace tube Oxidation process takes place Hydrogen gas goes out through the vent This is how the thermal oxidation process takes place Let's see about the thermal oxidation rate This figure shows the growth of the layer formation of silicon dioxide The silicon substrate is first exposed to the oxidizing species such as oxygen in dry air or wet steam in hot furnace This figure shows the growth of the layer formation of silicon dioxide The silicon substrate is first exposed to the oxidizing species such as oxygen in dry air or wet steam in hot furnace The oxygen molecules in the oxidizing species begin to diffuse into the surface of the fresh silicon wafer A silicon dioxide layer is formed with silicon dioxide molecules in solid circles While the drive from the oxidizing species continues, the silicon dioxide molecules that are already in the oxide layer diffuse and chemically react with the silicon molecules, crossing the layer boundary Thus, the process can be viewed as one that begins with the simple diffusion of the oxidizing species into the silicon substrate It is soon coupled with the diffusion of the same species into silicon dioxide The thickness of silicon dioxide can be controlled by the following equation x is equal to b divided by a into t plus tau x is equal to b square root of b into t plus tau a and b are constants The equation to obtain tau is given below d0 square plus 2d d0 divided by ks the whole into n1 whole divided by 2d n0 This is the equation for tau x is equal to b divided by a into t plus tau x is equal to b square root of b into t plus tau These are the different terms used to find the parameter tau Oxide thickness by color tan is equal to 0.050 0.075 is equal to brown 0.390 is equal to yellow 0.375 is equal to green to yellow These are the different colors used to find the oxide thickness This is all about oxidation There are two types of oxidation processes Dry oxidation and wet oxidation You have already studied this in your VLSI class See you in the next lecture