Doping

고려대학교 Center for MNB Sensor Technology 166

167 Korea University MNB Sensor Lab - To create a specific number and distribution of dopant atoms in the wafer surface. - To create a specific number and distribution of dopant atoms in a specific region below the wafer surface. - To create a p-n( or n-p) junction at a specific distance below the wafer surface. They are formed in the wafer by thermal diffusion or ion implantation techniques. Doping  Goals of Doping

168 Korea University MNB Sensor Lab Thermal Diffusion

169 Korea University MNB Sensor Lab  Diffusion Diffusion (or solid state diffusion) is the process whereby a solid will physically diffuse itself into another solid in close contact with it due to the random thermal movement of atoms. Two conditions for a diffusion : - Concentration gradient - Sufficient energy in the system  Thermal Diffusion Doping

170 Korea University MNB Sensor Lab  Models of Diffusion in Solids Substitutional or vacancy mechanism Interstitial mechanism Doping

171 Korea University MNB Sensor Lab  Dopant sources Doping

172 Korea University MNB Sensor Lab  Mathematical Model for Diffusion Constant-Source Diffusion Limited-Source Diffusion Compementary error function(erfc) Gaussian distribution Doping

173 Korea University MNB Sensor Lab  Two Step Diffusion - Predeposition - Drive-in (drive-in oxidation, reoxidation) Doping  Junction Formation Compementary error function Gaussian distribution

174 Korea University MNB Sensor Lab  Lateral Diffusion The impurities diffuse downward and sideways (laterally). In this case, we must consider a two- dimensional diffusion equation and use a numerical technique to obtain the diffusion profiles under different initial and boundary conditions. Doping

175 Korea University MNB Sensor Lab  Sheet Resistance Resistivity In diffused layers, resistivity is a strong function of depth. Sheet resistance eliminates the need to know the details of the diffused-layer profile. Sheet Resistivity - Average resistivity of the layer Doping

176 Korea University MNB Sensor Lab Ion Implantation

177 Korea University MNB Sensor Lab - A low-temperature technique for the introduction of impurities into semiconductors. -A very precise means to introduce a specific dose or number of dopant atoms into the silicon.  Ion Implantation Doping

178 Korea University MNB Sensor Lab  Ion Implantation Systems Main elements of Ion implanter - Ion source - Mass analyzer - High-voltage accelerator - Scanning system - Target chamber Doping

179 Korea University MNB Sensor Lab  Dopant Concentration Profile in Implanted Regions Ion range -Range R : The total distance an ion travels before it comes to rest. - R p : (mean) projected range Doping

180 Korea University MNB Sensor Lab Implantation profiles : Standard deviation or straggle : Lateral standard deviation or transverse straggle : Peak concentration Doping

181 Korea University MNB Sensor Lab Doping

182 Korea University MNB Sensor Lab  Junction Formation Doping

183 Korea University MNB Sensor Lab - Range distributions in single-crystal silicon targets differ from those in amorphous targets because of the possibility of implanted ions to find their way into open directions, or "channels" in the crystal and penetrate deeper than projected for amorphous targets.  Ion Channeling Doping

184 Korea University MNB Sensor Lab Dependence of channeling effect on dose for phosphorus implanted in Si. Doping

185 Korea University MNB Sensor Lab  Implantation Damage and Annealing Implantation disorder due to (a) light ions and (b) heavy ions. Damage(Disorder) production Doping

186 Korea University MNB Sensor Lab Annealing After implantation, we need an annealing step - to restore the silicon lattice to its perfect crystalline. - to put dopants into Si substitutional sites for electrical activation. Doping