【作者】 张凤田；

【导师】 唐祯安；

【作者基本信息】 大连理工大学 ， 微电子学与固体电子学， 2007， 博士

【摘要】 热传导真空传感器广泛用于各种真空设备中，采用微机械加工技术微型化后可用于微电子封装泄漏检测、集成真空计、便携式气压测试仪等领域，因此微型热传导真空传感器成为MEMS领域的重要研究方向。本文主要从设计理论、制造工艺、性能测试以及与电路单芯片集成等方面对基于微热板的热传导真空传感器进行了系统的研究。设计了两种加热电阻分别为多晶硅或铂金的微热板真空传感器，用经典传热理论与稀薄气体动力学，建立了微热板真空传感器的传热模型，利用该模型分析了微热板的传热特性以及微热板工作电流、工作温度、结构尺寸对传感器响应特性的影响，并用有限元法模拟了微热板的温度分布与热变形。结果表明，微热板支撑桥上的温度分布以及微热板中间区域通过支撑桥导热、气体导热散失的热量随气压变化而变化；设计的两种微热板真空传感器中间区域温度分布较均匀，热变形较小。对两种微热板真空传感器的表面微机械加工技术进行了研究。根据实际工艺条件制定了合理的工艺流程，讨论并解决了其中牺牲层腐蚀、腐蚀窗口刻蚀、牺牲层台阶平坦化、结构层介质薄膜残余应力控制等若干关键工艺。多晶硅或铂金加热电阻的微热板真空传感器分别采用0.5μm厚的多晶硅或铝作为牺牲层，牺牲层腐蚀分别采用不腐蚀Al压焊盘的TMAH腐蚀液或不腐蚀Pt/Ti的铝腐蚀液；退火温度、时间对微热板中的残余应力影响很大，两种传感器采用不同的退火工艺，较好的解决了微热板的残余变形问题，保证了较高的加工成品率。开展了微热板真空传感器测试技术的研究。建立了由真空系统、测试电路、计算机采集控制部分组成的传感器自动测试系统，测试了传感器在恒电流、恒电压、恒温三种工作模式下的响应特性。结果表明，恒电流与恒电压工作模式下，在1～5×10~4pa气压范围内传感器较灵敏，但气压更高时由于工作温度太低，传感器灵敏度很低，在1～10~5Pa气压范围内传感器输出电压摆幅仅为几百毫伏；恒温工作模式下传感器输出电压随气压增加而增加，输出摆幅达到几伏，在1～10~5Pa范围内都有较高灵敏度。进行了微热板真空传感器与电路单芯片集成技术的初步研究。制定了基于Post-IC的集成微热板真空传感器芯片的工艺流程。设计了工作在恒电压模式、集成有多晶硅加热电阻的微热板真空传感器、CMOS运算放大器的集成微传感器芯片，并以多晶圆代工的形式实现了该芯片的加工，芯片测试结果显示该芯片能够用于气压测量，为集成微热板真空传感器的深入研究奠定了基础。更多还原

【Abstract】 Thermal conductivity vacuum sensors which are widely used in various vacuumapparatuses, if miniaturized, can be extended into the fields of leak hunting of microelectronicpackage, integrated vacuum gauge, portable instruments for gas pressure measurement, etc.Therefore, thermal conductivity vacuum microsensors have become one of the most importantresearch directions in the MEMS fields. In this thesis, thermal conductivity vacuum sensorsbased on micro-hotplate (MHP)are systematically investigated, including design theory,fabricating processes, characteristics measurement and integration with circuit in a single chip,etc.Two types of MHP-based thermal conductivity vacuum sensors with polysilicon orplatinum heaters respectively are designed. According to typical heat transfer theory andrarefied gas dynamics, a heat transfer model for the MHP-based sensor is constructed toanalyze the MHP thermal characteristics, and effects of heating current and the MHP size onthe sensor response. Temperature distribution and thermal deformation of the MHP aresimulated with finite element method. The results show that temperature distribution alongthe MHP supporting beams, heat losses through supporting beams or through gas thermalconduction from the MHP central zone vary with gas pressure. For the two designed sensors,temperature distributions of the MHP central zone are uniform, and the thermal deformationis small.Surface micromachining technology for the two designed sensors is investigated. Theappropriate fabricating processes are designed according to the practical condition. Manypivotal technics including sacrificial layer etching, window etching, step smoothing, andresidual stress control of dielectric thin films, etc are discussed and solved. The MHP-basedthermal conductivity vacuum sensors with polysilicon or platinum heater respectively use0.5μm thick polysilicon film or 0.5μm aluminum thin film as sacrificial layer, which are wetetched with TMAH etchant which doesn’t etch exposed aluminum pads or aluminum etchantwhich doesn’t etch Pt/Ti layer. The annealing temperature and time have great influence onthe MHP residual stress, and two different annealing processes are applied for the two typesof sensor so that the MHP residual deformation is controlled successfully and output capacityis guaranteed. Measurement technology of the MHP-based thermal conductivity vacuum sensor isstudied. The automatic test system consisting of vacuum system, test circuit, computeradopting and controlling parts is constructed to measure the sensor response characteristics atconstant current, constant voltage, constant temperature respectively. The measurementresults show that for constant current and constant voltage operating mode, the sensor isapparently sensitive in the pressure range of 1～5×10~4pa, while the sensitivity falls down athigher gas pressure due to too low working temperature, and the output voltage amplitude isonly a few hundreds of millivolts from 1Pa to 10~5Pa. For constant temperature mode, thesensor output voltage increases if elevating gas pressure, and higher sensitivity appears in thepressure range of 1～10~5Pa so that the output voltage amplitude is about a few volts.Studies about integrating MHP-based thermal conductivity vacuum sensor withintegrated circuits are also implemented. The fabricating processes of monolithic MHP-basedthermal conductivity vacuum sensor chip are designed according to Post-IC technology. Thedesigned monolithic sensor chip integrates MHP-based thermal conductivity vacuum sensorwith polysilicon heater, CMOS operational amplifier and resistors to make the sensor operateat constant voltage mode. The monolithic sensor chip is fabricated through MPW approach.The test results show that the monolithic sensor chip can measure gas pressure. This researchprovides foundation for deeply studying integrated MHP-based thermal conductivity vacuumsensor.更多还原