Study Of Metal-Semiconductor Contacts For Group ? Ge And GeSn

In the past 50 years,the integrated circuit industry on the basis of Si CMOS devices obtained a rapid development by following the prediction of ‘Moore's law'.Through the scaling down of MOSFET devices(both in device size and work voltage),the performance of integrated circuit has been improved a lot in such aspects as switch speed,power consumption,integration,cost and so on.However,the short channel effects such as drain induced barrier lowering,punch-through effect and so on are becoming more and more serious.Recently,with the mass production of 10 nm COMS technology node,the traditional silicon integrated circuit devices are increasingly close to their physical limits.Improvement of device performance and integration simply by shortening the channel length is becoming more and more difficult.In order to further improve the device performance,Ge and Ge Sn have attracted extensive attentions of research institutions in semiconductor field due to their higher carrier mobility than Si,compatible process with Si CMOS and other advantages.Till now,surface passivation and strain engineering of Ge/Ge Sn PMOSFET have been thoroughly researched.And by these achievement,the performance of Ge/Ge Sn p MOSFETs has been improved greatly.However,there are still some problems required to be addressed in this field.Firstly,the growth of high quality Ge Sn is very difficult.Ge Sn material is grown mainly by MBE.However,MBE equipment is relatively expensive and other growth methods are not get well studied.In addition,because there is a low n type doping concentration and poor activated level in Ge/Ge Sn material,the contact between metal and n type Ge/Ge Sn is always schottky type and with poor quality,which grealty affects the performance of Ge and Ge Sn n MOS devices.For the two problems above,our study is carried out in two aspects respectively: material growth and metal-semiconductor contacts.In terms of material growth,sputtering method is used which has advantages of low cost and high efficiency comparing with the MBE growth method.So,in the first part of this paper,we epitaxially grew Ge Sn material on Ge substrates with sputtering method and studied the Ge Sn material quality.The Ge Sn epitaxial materials samples with different Sn components were obtained.In order to determine the sample quality and the material properties,the samples with different Sn components were studied by XRD,Raman,AFM and other methods.Besides,with the addition of Sn in the Ge Sn materials,the thermal stability will be decreased.Thus,the Ge Sn materials with different Sn components were annealed with different conditions and the influence of high temperature on Ge Sn was thoroughly investigated with XRD,Raman,AFM and etc.in this work.We found that Sn will be easily segregated from Ge Sn material at high temperature.For the same Sn component materials,the higher the annealing temperature the easier the segregation.And for the same temperature,the higher the Sn component the easier the segregation.Thus,we must adopt the suitable temperature condition,which gives a process window for the device fabrication.In terms of metal-semiconductor contacts,the contacts between metal and n/p type Ge/Ge Sn materials were studied with C-TLM method.After obtaining higher quality Ge Sn epitaxial materials with RF-Sputter method,Ge and Ge Sn samples was doped by ion implantation and then activated by rapid thermal processing(RTP).At last,we got different contact types of C-TLM samples with contact metal Ni.Firstly,thick Ni was used for contact meal.The n-type and p-type ohmic contacts between Ni and Ge/Ge Sn were acquired.The influence of annealing time and temperature on the quality of the contacts was studied.In order to further optimize the n type contact quality,thin metal Ni was used to contact with Ge/Ge Sn for the n type contact C-TLM sample fabrication.Finally,we achieved a better contac between Ni and n-type Ge.