Study on the failure temperature of Ti/Pt/Au and Pt5Si2-Ti/Pt/Au metallization systems

The Ti/Pt/Au metallization system has an advantage of resisting KOH or TMAH solution etching.To form a good ohmic contact,the Ti/Pt/Au metallization system must be alloyed at 400 ℃.However,the process temperatures of typical MEMS packaging technologies,such as anodic bonding,glass solder bonding and eutectic bonding,generally exceed 400 ℃.It is puzzling if the Ti/Pt/Au system is destroyed during the subsequent packaging process.In the present work,the resistance of doped polysilicon resistors contacted by the Ti/Pt/Au metallization system that have undergone different temperatures and time are measured.The experimental results show that the ohmic contacts will be destroyed if heated to 500 ℃.But if a 20 nm Pt film is sputtered on heavily doped polysilicon and alloyed at 700 ℃ before sputtering Ti/Pt/Au films,the Pt5Si2-Ti/Pt/Au metallization system has a higher service temperature of 500 ℃,which exceeds process temperatures of most typical MEMS packaging technologies.