Effect of two-step ion implantation and microwave annealing on dopants activation of high mobility SiGe material

Abstract

The strain engineering of the source/drain has been applied from the N45 till now When the size of transistor is reduced continuously it is necessary to increase the germanium concentration to add more stress but it reduce boron concentration with increasing the germanium The use of ion implantation compensates for the boron concentration well while caused some problems including ion implantation damage diffusion and activation of dopant ions Therefore improvement was based on the process flow to activate dopants by tuning different Ge content or pre- amorphized-implantation At the same time in order to cope with the low temperature process for Ge microwave annealing was added to compare with rapid thermal annealing There are three parts in this paper First part silicon germanium film covered with Si Ge and uncovered before ion implantation is investigated The sample covered with Ge undergoes surface loss after annealing making it behave close to the uncovered sample and the Si covering sample can effectively prevent the surface from roughness and further reduce the sheet resistance The other part of the samples is covered with SiO2 before annealing especially at a high temperature can be effectively prevent surface from oxidation thus to suppress surface loss The second part discusses the trend of the Boron activation in SiGe alloys with different Ge contents The boron activation level increases with the increase of Ge content When the content of Ge is higher the trend will gradually saturate and even segregate to cause the device degradation So there is a trade-off between different concentrations of SiGe and boron Experiments show that from 20% to 40% Ge with a dose of B (ISD 3 2x1020cm-2+I/I 3 x1015cm-2 and 2 x1015cm-2) Si0 65Ge0 35 is an optimum value For dopants activation in SiGe material thermal process is dominant but the influence of SiGe composition is gradually increasing The control of in-situ doping concentration has become an important issue Third part we focuse on the diffusion and electrical properties of various species pre-amorphized implantation repair implant damage by microwave annealing and rapid thermal annealing The sheet resistance Boron distribution and mobility of sample was investigated to infer the activation level and defect evolution The performance is the best with Ge PAI among the three samples and it can enhance the boron activation by microwave annealing to prevent the diffusion effectively

Date of Award	2020
Original language	English
Supervisor	Wen-Shi Lee (Supervisor)