多晶硅纳米薄膜压力传感器工艺研究
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摘要
多晶硅纳米薄膜(PSNF)因其良好的压阻特性,有着广阔的应用前景,本文为PSNF在压阻式压力传感器上得到更好的应用,试制了PSNF压力传感芯片。研究的重点是PSNF压力传感芯片的工艺设计与仿真,并提取最佳工艺条件。
运用LPCVD技术生长出具有优越压阻特性的PSNF是制作PSNF压力传感芯片的核心技术。本文所提取的最佳工艺条件为:淀积温度620℃,薄膜厚度在80～100nm,掺杂浓度在3×10~(20)cm~(-3)左右。在这种工艺条件下得到的PSNF的应变系数可达到34,比普通的多晶硅薄膜高25%以上。在体加工中,通过对比分析几种各向异性腐蚀剂,最终选取KOH系统腐蚀硅杯。
为保护PSNF电阻免受污染和氧化,保证薄膜的优越压阻特性,起保护作用的绝缘层和钝化层的工艺设计显得尤为重要。然而,PSNF及其钝化层是在高温下通过化学气相淀积形成的,由于它们的热膨胀系数不同,温度恢复到室温后必然要形成残余应力。残余应力过大,不仅会破坏传感器的重复性和线性度,还会降低传感器的可靠性。为此,针对PSNF压力传感芯片的基本结构特点,分别以化学气相淀积SiO_2、Si_3N_4或两者的复合薄膜为钝化层,用有限元法分析了应力分布与钝化层结构之间关系。结果表明合理控制Si_3N_4-SiO_2-Si_3N_4复合钝化结构中各层的厚度,可有效降低材料热失配引起热应力。从而给出了压阻薄膜钝化层结构的设计方法。
本文按照优化的工艺条件制作芯片,所测传感器灵敏度为10mV/MPa.V,非线性误差为0.006%FS,迟滞误差为0.12%FS,重复性误差为0.07%FS,零位温度系数为0.062%FS/℃,灵敏度温度系数为-0.1%FS/℃,全精度可达到0.18%FS。可以看出由该工艺条件下制作出的PSNF压力传感器的优良性能,同时印证了本文所论述的工艺条件的可行性和优越性,验证了多晶硅隧道压阻理论。
There is a broad application prospects for Polysilicon nanofilm(PSNF) because of its favorable piezoresistive properties.PSNF pressure sensor chip is made in order to get better application of PSNF.Therefore,the main purpose of the paper is to do the researches in the process design simulation and optimization of pressure sensor chip based on PSNF, and find out the best process condition finally.
Low Pressure Chemical Vapor Deposition(LPCVD) method is the core technology which applied to form PSNF with superior piezoresistive properties.The best process condition is that the temperature of deposition is 620℃;the thickness of film is between 80nm and 100nm;simultaneity,the doping concentration is about 3×10~(20)cm~(-3).The strain coefficient of PNSF can reach 34 under the process condition above mentioned which is more than 25%higher than the normal polysilicon thin film.The optimal silicon cup corrosion of KOH system can be found out through the comparative analysis of a few corrosives which are anisotropic in the aspect of structure processing.
The process design of insulation layer and passivation layer is particularly important for protecting the resistance of PSNF from pollution and oxidation and ensuring favorable piezoresistive properties of the film.Repeatability and linearity can be influenced and the reliability of sensor can be reduced by the residual stress which is caused by back to the room temperature and the different coefficient of thermal expansion,because of the PSNF and passivation layer is made at high temperature.To this end,SiO2,Si_3N_4 or the composite films of the both are made in the passivation layer by chemical vapor deposition for the basic structural features of the PSNF pressure sensor chip.The relationship between stress distribution and structure of the passivation layer is simulated and analyzed by finite element analysis software.The results show that the thermal stress can be effectively reduced caused by the mismatch with reasonable control of the thickness of the Si_3N_4- SiO_2-Si_3N_4 composite passivation film.Thus the design method of passivation layer structure of piezoresistive thin film is given.
The chip is made according to the optimal technology condition in the paper.The test result shows that the sensitivity is 10mV/MPa.V;non-linear error is 0.006%FS; hysteresis error is 0.12%FS;repeatability error is 0.07%FS;zero temperature coefficient is 0.062%FS/℃;the sensitivity temperature coefficient is -0.1%FS/℃;the whole precision of the sensor is 0.18%FS.The performance of the PSNF pressure sensor which is made based on the optimal technology condition is so excellent.Meanwhile,the feasibility and the superiority of the technology condition discussed in the paper are conformed and the theory of polysilicon tunneling piezoresistive effect is validated.
运用LPCVD技术生长出具有优越压阻特性的PSNF是制作PSNF压力传感芯片的核心技术。本文所提取的最佳工艺条件为:淀积温度620℃,薄膜厚度在80～100nm,掺杂浓度在3×10~(20)cm~(-3)左右。在这种工艺条件下得到的PSNF的应变系数可达到34,比普通的多晶硅薄膜高25%以上。在体加工中,通过对比分析几种各向异性腐蚀剂,最终选取KOH系统腐蚀硅杯。
为保护PSNF电阻免受污染和氧化,保证薄膜的优越压阻特性,起保护作用的绝缘层和钝化层的工艺设计显得尤为重要。然而,PSNF及其钝化层是在高温下通过化学气相淀积形成的,由于它们的热膨胀系数不同,温度恢复到室温后必然要形成残余应力。残余应力过大,不仅会破坏传感器的重复性和线性度,还会降低传感器的可靠性。为此,针对PSNF压力传感芯片的基本结构特点,分别以化学气相淀积SiO_2、Si_3N_4或两者的复合薄膜为钝化层,用有限元法分析了应力分布与钝化层结构之间关系。结果表明合理控制Si_3N_4-SiO_2-Si_3N_4复合钝化结构中各层的厚度,可有效降低材料热失配引起热应力。从而给出了压阻薄膜钝化层结构的设计方法。
本文按照优化的工艺条件制作芯片,所测传感器灵敏度为10mV/MPa.V,非线性误差为0.006%FS,迟滞误差为0.12%FS,重复性误差为0.07%FS,零位温度系数为0.062%FS/℃,灵敏度温度系数为-0.1%FS/℃,全精度可达到0.18%FS。可以看出由该工艺条件下制作出的PSNF压力传感器的优良性能,同时印证了本文所论述的工艺条件的可行性和优越性,验证了多晶硅隧道压阻理论。
There is a broad application prospects for Polysilicon nanofilm(PSNF) because of its favorable piezoresistive properties.PSNF pressure sensor chip is made in order to get better application of PSNF.Therefore,the main purpose of the paper is to do the researches in the process design simulation and optimization of pressure sensor chip based on PSNF, and find out the best process condition finally.
Low Pressure Chemical Vapor Deposition(LPCVD) method is the core technology which applied to form PSNF with superior piezoresistive properties.The best process condition is that the temperature of deposition is 620℃;the thickness of film is between 80nm and 100nm;simultaneity,the doping concentration is about 3×10~(20)cm~(-3).The strain coefficient of PNSF can reach 34 under the process condition above mentioned which is more than 25%higher than the normal polysilicon thin film.The optimal silicon cup corrosion of KOH system can be found out through the comparative analysis of a few corrosives which are anisotropic in the aspect of structure processing.
The process design of insulation layer and passivation layer is particularly important for protecting the resistance of PSNF from pollution and oxidation and ensuring favorable piezoresistive properties of the film.Repeatability and linearity can be influenced and the reliability of sensor can be reduced by the residual stress which is caused by back to the room temperature and the different coefficient of thermal expansion,because of the PSNF and passivation layer is made at high temperature.To this end,SiO2,Si_3N_4 or the composite films of the both are made in the passivation layer by chemical vapor deposition for the basic structural features of the PSNF pressure sensor chip.The relationship between stress distribution and structure of the passivation layer is simulated and analyzed by finite element analysis software.The results show that the thermal stress can be effectively reduced caused by the mismatch with reasonable control of the thickness of the Si_3N_4- SiO_2-Si_3N_4 composite passivation film.Thus the design method of passivation layer structure of piezoresistive thin film is given.
The chip is made according to the optimal technology condition in the paper.The test result shows that the sensitivity is 10mV/MPa.V;non-linear error is 0.006%FS; hysteresis error is 0.12%FS;repeatability error is 0.07%FS;zero temperature coefficient is 0.062%FS/℃;the sensitivity temperature coefficient is -0.1%FS/℃;the whole precision of the sensor is 0.18%FS.The performance of the PSNF pressure sensor which is made based on the optimal technology condition is so excellent.Meanwhile,the feasibility and the superiority of the technology condition discussed in the paper are conformed and the theory of polysilicon tunneling piezoresistive effect is validated.
引文
[1]Erskine JC.olycrystalline Silicon-on-Metal Strain Gauge Transducers.IEEE Trans Electron Devices,1983,:6-801.
[2]Suki J,Mosser V,Goss J.Polusilicon SOI Pressure Sensor.Sensors and Acruarors,1989,17:521-527.
[3]Druzhinin A.,Lavitska E.,Maryamova I.Et al.Mechanical sensors based on laser-recrystallized SOI structures.Sensors and Actuators.1997,A61(1-3):400-404.
[4]V.Mosser,J.Suski,E.Obermeier.piezoresistive pressure sensors based on polycrystalline silicon.Sensors and Actuators.1991,A28:113-131.
[5]刘宝峰,李洪峰,金立国.半导体器件钝化层Si_3N_4 薄膜的制备及特性研究[J].哈尔滨理工大学学报,2003,8(6):1052108.
[6]CAN D W,YOON S,HOP S.Effects of passivation layer on stress relaxation in Cu line structures[C]// IEEE Interconnect Technology Conference.U S A:San Francisco,2003:1802182.
[7]D.J.Bell,T.J.Lu,N.A.Fleck,S.M.Spearing.MEMS actuators and sensors:Observations on their performance and selection for purpose.Journal of Micromechanics and Microengineering.2005,15(7):S153-S164.
[8]Li Xinxin,Zhar Yitshak,Wang Man.Fabrication and characterization of nickel-induced laterally crystallized polycrystalline silicon piezo-resistive sensors.Sensors and Actuators.2000,A82(1):281-285.
[9]Druzhinin A.,Lavitska E.,Maryamova I.et al.Mechanical sensors based on laser-recrystallized SOI structures.Sensors and Actuators.1997,A61(1-3):405-406.
[10]V.Mosser,J.Suski,E.Obermeier.piezoresistive pressure sensors based on polycrystailine silicon.Sensors and Actuators.1991,A28:113-131.
[11]C.Malhaire,D.Barbier.Design of a polysilicon-on-insulator pressure sensor with original polysilicon layout for harsh environment.Thin Solid Films.2003,427(1-2):362-366.
[12]G.Villanueva,J.Bausells,J.Montserrat,F.Perez-Murano.Polysilicon piezoresistive cantilevers for intermolecular force detection.Proceedings of 2005 Spanish Conference on Electron Devices.2005,495-498.
[13]J.Akhtar,B.B.Dixit,B.D.Pant,V.P.Deshwal.Polysilicon Piezoresistive Pressure Sensors Based on MEMS Technology.IETE Journal of Research.2003,49(6):365-377.
[14]Gustavo A.Roman,Jessica R.Bronson,Gloria J.Wiens,James F.Jones,James J.Allen.Design of a piezoresistive surface micromachined three-axis force transducer for microassembly.Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems(MEMS).2005,7:505-515.
[15]王善慈.多晶硅敏感技术.传感器技术.1994,(1):56-64.
[16]J.Suski,V.Mosser,J.Goss.Polysilicon SOI pressure sensor,Sensors and Actuators.1989,A17:405-414.
[17]Y.Onuma and K.Sekiya.Piezoresistive Properties of Polycrystalline Silicon Thin Film.Japanese Journal of Applied Physics.1972,11(5):20-23.
[18]J.M.Jaffe.Monolithic Polycrystalline-silicon Pressure Transducer.Electronics Letters.1974,10(20):420-421.
[19]J.Y.W.Seto.Piezoresistive properties of polycrystalline silicon.J.Appl.Phys.1976,47:4780-4783.
[20]E.Obermeier,P.Kopystynski.Polysilicon as a material for microsensor applications.Sensors and Actuators.1992,A30(1-2):149-155.
[21]T.I.Kamins.Hall mobility in chemically deposited polycrystalline silicon.Appl.Phys.1971,42:4357-4365.
[22]P.Rai-Choudhury,P.L.Hower.Growth and characterization of polycrystalline silicon.Electrochem.Soc.1973,120:1761-1766.
[23]J.Y.Seto.The electrical properties of polycrystalline silicon films.Appl.Phys.1975,46:5247-5254.
[24]G.Baccarani,B.Ricco,G.Spadini.Transport properties of polycrystalline silicon films.J.Appl.Phys..1978,49:5565-5570.
[25]N.C.C.Lu,L.Gerzberg,C.Y.Lu,J.D.Meindl.Modeling and Optimization of Monolithic Polycrystalline silicon resistors.IEEE Trans..1981,ED-28:818-830.
[26]N.C.C.Lu,L.Gerzberg,C.Y.Lu,J.D.Meindl.A new conduction model for polycrstalline silicon films.IEEE Electron.Dev.Lett..1981,EDL-2:95-98.
[27]刘晓为,霍明学,陈伟平等.多晶硅薄膜压阻系数的理论研究.半导体学报.2004,25(3):292-296.
[28]M.Wang,Z.Meng,and M.Wong,et al.Metal-lnduced Laterally Crystallized Polycrystalline Silicon for Integrated Sensor Applications.IEEE Transactions on Electron Devices.2001,48(4):794-800.
[29]霍明学,刘晓为,张丹等.多晶硅薄膜的高温压阻效应.半导体学报.2005,26(11):2115-2119.
[30]于晓梅,张大成,王丛舜等.U形阵列式微机械悬臂梁的研究.物理学报.2004,53(1):31-36.
[31]张威,王阳元.多晶硅集成高温压力传感器研究.电子学报.2003,31(11):1736-1738.
[32]姚素英,曲宏伟,张维新等.多晶硅双岛压力传感器应力分布的模拟计算.电子学报.1999,27(11):68-70.
[33]Bean,K.E.,Anisotropic Etching of Silicon.IEEE Transaction on Electron Devices,1987,ED 25:p.1185-1193.
[34]Smith,C.S.,Piezoresistance Effect in Germanium and Silicon.Physics Review,1954.94(1):p.42-49.
[35]French,P.J.,and A.G.R.Evans,Polycrystalline Silicon Strain Sensors.Sensors and Actuators A,1985.8:p.219-225.
[36]Geyling,F.T.,and J.J.Forst,Semiconductor Strain Transducers.The Bell System Technical Journal,1960.39:p.705-731.
[37]Petersen,K.E.,Silicon as a Mechanical Material.Proceedings of the IEEE,1982.70(5):p.420-457.
[38]Gabriewl,K.J.,Microelectromechanical Systems.Proceedings of the IEEE,1998.86(8):p.1534-1535.
[39]Angell,J.B.,S.C.Terry,and P.W.Barth,Silicon Micromechanical Devices.Scientific American Journal,1983.248:p.44-55.
[40]孙以材等.压力传感器的设计制造与应用[M].北京:冶金工业出版社,2000,04.
[41]黄庆安.硅微机械加工技术.北京:科学出版社,1995.12.
[42]M.M.Mandurah,K.C.Saraswat,C.R.Helms and T.I.Kamins.Dopant segregation in polycrystalline silicon.Appl.Phys.1980,51:5755-5763.
[43]王阳元,武国英,郝一龙等.硅基MEMS加工技术及其标准工艺研究[J].电子学报.2002,30,11:1577-1584.
[44]Ray Swati,Mukhopadhyay Sumita,S.C.Saha.Properties of polycrystailine silicon films prepared from fluorinated precursors.Thin Solid Films.1999,337(1-2):7-11.
[45]B.Lee,L.J.Quinn,P.T.Baine et al.Polycrystalline silicon film growth in a SiF4/SiH4/H2plasma.Thin Solid Films.1999,337(1-2):55-58.
[46]S.Moniruzzaman,T.Inokuma,Y.Kurata et ai.Structure of polycrystalline silicon films deposited at low temperature by plasma CVD on substrates exposed to different plasma.Thin Solid Films.1999,337(1-2):27-31.
[47]Q.Y.Tong,et al.,Void elimination by lateral gap diffusion in silicon direct bonding technology,Electron.Lett.,Vol.27,No.3,288(1991).
[2]Suki J,Mosser V,Goss J.Polusilicon SOI Pressure Sensor.Sensors and Acruarors,1989,17:521-527.
[3]Druzhinin A.,Lavitska E.,Maryamova I.Et al.Mechanical sensors based on laser-recrystallized SOI structures.Sensors and Actuators.1997,A61(1-3):400-404.
[4]V.Mosser,J.Suski,E.Obermeier.piezoresistive pressure sensors based on polycrystalline silicon.Sensors and Actuators.1991,A28:113-131.
[5]刘宝峰,李洪峰,金立国.半导体器件钝化层Si_3N_4 薄膜的制备及特性研究[J].哈尔滨理工大学学报,2003,8(6):1052108.
[6]CAN D W,YOON S,HOP S.Effects of passivation layer on stress relaxation in Cu line structures[C]// IEEE Interconnect Technology Conference.U S A:San Francisco,2003:1802182.
[7]D.J.Bell,T.J.Lu,N.A.Fleck,S.M.Spearing.MEMS actuators and sensors:Observations on their performance and selection for purpose.Journal of Micromechanics and Microengineering.2005,15(7):S153-S164.
[8]Li Xinxin,Zhar Yitshak,Wang Man.Fabrication and characterization of nickel-induced laterally crystallized polycrystalline silicon piezo-resistive sensors.Sensors and Actuators.2000,A82(1):281-285.
[9]Druzhinin A.,Lavitska E.,Maryamova I.et al.Mechanical sensors based on laser-recrystallized SOI structures.Sensors and Actuators.1997,A61(1-3):405-406.
[10]V.Mosser,J.Suski,E.Obermeier.piezoresistive pressure sensors based on polycrystailine silicon.Sensors and Actuators.1991,A28:113-131.
[11]C.Malhaire,D.Barbier.Design of a polysilicon-on-insulator pressure sensor with original polysilicon layout for harsh environment.Thin Solid Films.2003,427(1-2):362-366.
[12]G.Villanueva,J.Bausells,J.Montserrat,F.Perez-Murano.Polysilicon piezoresistive cantilevers for intermolecular force detection.Proceedings of 2005 Spanish Conference on Electron Devices.2005,495-498.
[13]J.Akhtar,B.B.Dixit,B.D.Pant,V.P.Deshwal.Polysilicon Piezoresistive Pressure Sensors Based on MEMS Technology.IETE Journal of Research.2003,49(6):365-377.
[14]Gustavo A.Roman,Jessica R.Bronson,Gloria J.Wiens,James F.Jones,James J.Allen.Design of a piezoresistive surface micromachined three-axis force transducer for microassembly.Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems(MEMS).2005,7:505-515.
[15]王善慈.多晶硅敏感技术.传感器技术.1994,(1):56-64.
[16]J.Suski,V.Mosser,J.Goss.Polysilicon SOI pressure sensor,Sensors and Actuators.1989,A17:405-414.
[17]Y.Onuma and K.Sekiya.Piezoresistive Properties of Polycrystalline Silicon Thin Film.Japanese Journal of Applied Physics.1972,11(5):20-23.
[18]J.M.Jaffe.Monolithic Polycrystalline-silicon Pressure Transducer.Electronics Letters.1974,10(20):420-421.
[19]J.Y.W.Seto.Piezoresistive properties of polycrystalline silicon.J.Appl.Phys.1976,47:4780-4783.
[20]E.Obermeier,P.Kopystynski.Polysilicon as a material for microsensor applications.Sensors and Actuators.1992,A30(1-2):149-155.
[21]T.I.Kamins.Hall mobility in chemically deposited polycrystalline silicon.Appl.Phys.1971,42:4357-4365.
[22]P.Rai-Choudhury,P.L.Hower.Growth and characterization of polycrystalline silicon.Electrochem.Soc.1973,120:1761-1766.
[23]J.Y.Seto.The electrical properties of polycrystalline silicon films.Appl.Phys.1975,46:5247-5254.
[24]G.Baccarani,B.Ricco,G.Spadini.Transport properties of polycrystalline silicon films.J.Appl.Phys..1978,49:5565-5570.
[25]N.C.C.Lu,L.Gerzberg,C.Y.Lu,J.D.Meindl.Modeling and Optimization of Monolithic Polycrystalline silicon resistors.IEEE Trans..1981,ED-28:818-830.
[26]N.C.C.Lu,L.Gerzberg,C.Y.Lu,J.D.Meindl.A new conduction model for polycrstalline silicon films.IEEE Electron.Dev.Lett..1981,EDL-2:95-98.
[27]刘晓为,霍明学,陈伟平等.多晶硅薄膜压阻系数的理论研究.半导体学报.2004,25(3):292-296.
[28]M.Wang,Z.Meng,and M.Wong,et al.Metal-lnduced Laterally Crystallized Polycrystalline Silicon for Integrated Sensor Applications.IEEE Transactions on Electron Devices.2001,48(4):794-800.
[29]霍明学,刘晓为,张丹等.多晶硅薄膜的高温压阻效应.半导体学报.2005,26(11):2115-2119.
[30]于晓梅,张大成,王丛舜等.U形阵列式微机械悬臂梁的研究.物理学报.2004,53(1):31-36.
[31]张威,王阳元.多晶硅集成高温压力传感器研究.电子学报.2003,31(11):1736-1738.
[32]姚素英,曲宏伟,张维新等.多晶硅双岛压力传感器应力分布的模拟计算.电子学报.1999,27(11):68-70.
[33]Bean,K.E.,Anisotropic Etching of Silicon.IEEE Transaction on Electron Devices,1987,ED 25:p.1185-1193.
[34]Smith,C.S.,Piezoresistance Effect in Germanium and Silicon.Physics Review,1954.94(1):p.42-49.
[35]French,P.J.,and A.G.R.Evans,Polycrystalline Silicon Strain Sensors.Sensors and Actuators A,1985.8:p.219-225.
[36]Geyling,F.T.,and J.J.Forst,Semiconductor Strain Transducers.The Bell System Technical Journal,1960.39:p.705-731.
[37]Petersen,K.E.,Silicon as a Mechanical Material.Proceedings of the IEEE,1982.70(5):p.420-457.
[38]Gabriewl,K.J.,Microelectromechanical Systems.Proceedings of the IEEE,1998.86(8):p.1534-1535.
[39]Angell,J.B.,S.C.Terry,and P.W.Barth,Silicon Micromechanical Devices.Scientific American Journal,1983.248:p.44-55.
[40]孙以材等.压力传感器的设计制造与应用[M].北京:冶金工业出版社,2000,04.
[41]黄庆安.硅微机械加工技术.北京:科学出版社,1995.12.
[42]M.M.Mandurah,K.C.Saraswat,C.R.Helms and T.I.Kamins.Dopant segregation in polycrystalline silicon.Appl.Phys.1980,51:5755-5763.
[43]王阳元,武国英,郝一龙等.硅基MEMS加工技术及其标准工艺研究[J].电子学报.2002,30,11:1577-1584.
[44]Ray Swati,Mukhopadhyay Sumita,S.C.Saha.Properties of polycrystailine silicon films prepared from fluorinated precursors.Thin Solid Films.1999,337(1-2):7-11.
[45]B.Lee,L.J.Quinn,P.T.Baine et al.Polycrystalline silicon film growth in a SiF4/SiH4/H2plasma.Thin Solid Films.1999,337(1-2):55-58.
[46]S.Moniruzzaman,T.Inokuma,Y.Kurata et ai.Structure of polycrystalline silicon films deposited at low temperature by plasma CVD on substrates exposed to different plasma.Thin Solid Films.1999,337(1-2):27-31.
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