Research And Development Of High Performance Piezoresistive Pressure Sensor Using SON Technology

Pressure sensor is the MEMS devices of first industrialization.In the past,pressure sensor was mainly used in the field of defence,industry,auto and so on.Recently,since the rising of intelligent electronics and Io T(Internet of Things),conventional technology,such as silicon wet etching and double side lithography,could not meet the demand of miniaturization,low cost and high performance.Robert Bosch and ST Microelectronics,the two International leading MEMS manufacturers,had developed the silicon diaphragm and cavity of pressure sensor using SON(Silicon-on-Nothing),which solved the problem of double side processing and scaled production.However,SON was formed by using the technology of APSM(Advanced Porous Silicon Membrane),a non CMOS-compatible process which demands dedicated equipment.Presently,only some foreign companies have mastered key technologies.At 2000,Toshiba Corporation have developed ESS(Empty-Space-Silicon),which was first applied on CMOS technology.Currently,it was paid attention to use such technology on pressure sensors manufacturing.However,No foreign companies reported producing pressure sensor with ESS,which involved some key technologies,such as an optimized matrix of trenches,trench etching,silicon migration at high temperature,etc.Moreover,these steps need to be integrated as a platform to meet the demand of production.This paper reported the process development and optimization of each single step of ESS technology based on the production line of CSMC Technology Co,Ltd.,and using the new technology to fulfill well-performed piezoresistive pressure sensors with ESS SON.The main research including:(1)The 1^stChapter introduced the development road of silicon pressure sensor.Three main process technology were discussed:backside silicon anisotropic etching by KOH,Cavity-SOI and SON.Then the capability of piezoresistive pressure sensors among several international companies were compared.(2)The 2^ndChapter described the development of SON and several technologies of realizing them:APSM,TUB(Thin Film Under Bulk)and ESS.ESS technology was discussed in details,including trench etching,which discussed BOSCH etching and Low Temperature Etching(SF₆/O₂),and high temperature processing,which discussed the principle of silicon migration and the dimensions of cavity before and after the temperature annealing.(3)The 3^rdChapter proposed a mask design of different structures of trenches to study the relationship between trenches sizes and the cavity in advance.The trenches etching were developed by Bosch etching and Low temperature etching respectively.Using high temperature annealing,the condition was also tuned to form the cavity as a whole.(4)The 4^thChapter first introduced the piezoresistive effect of mono-crystalline silicon,the piezoresistive coefficient with respect to different crystal orientation,doping,and temperature.According to the ESS SON technology,one kind of piezoresistive pressure sensor was designed and simulated.Then the pressure sensor was manufactured using the ESS technology developed in this work,and characterize the sensitivity,non-linearity,TCO(Temperature Coefficient of Offset),TCS(Temperature Coefficient of Span)and pressure hysteresis.Compared with the similar product in the world,the performance is excellent,for example,the pressure hysteresis reached as low as 0.009%FS.This dissertation studied the technology of ESS SON used for piezoresistive pressure sensor.Compared to APSM technology,ESS technology is easy to process,low in cost and good performance.It is ready for scaled production.