MEMS 课件 litho&etching

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《MEMS加工工艺》PPT课件

《MEMS加工工艺》PPT课件
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MEMS加工工艺
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控制部分 电子学
机械 部分 传感 执行
微电子学 MEMS
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MEMS结构的特点
可动 三维 微尺度 形状复杂 材料的多样性
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MEMS加工工艺分类
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部件及子系统制造工艺
半导体工艺、集成光学工艺、厚薄膜工艺、微机械加 工工艺等
封装工艺
硅加工技术、激光加工技术、粘接、共熔接合、玻璃 封装、静电键合、压焊、倒装焊、带式自动焊、多芯 片组件工艺
这一反应为络合化反应
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HF的作用
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显然,HF的作用在于促进阳极反应,使 阳极反应产物SiO2溶解掉,不然,所生 成的SiO2就会阻碍硅与H2O的电极反应。
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H+离子 浓度的影响
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HF、HNO3可用H2O或CH3COOH稀释。在HNO3溶 液中HNO3几乎全部电离,因此H+浓度很高,而 CH3COOH是弱酸,电离度较小,HNO3+ CH3COOH的溶液中,H+与CH3COO-发生作用, 生成CH3COOH分子,而且CH3COOH的介电场数 (6.15)低于水的介电场数(81),因此在HNO3 +CH3COOH混合液中H+离子浓度低。
铸形成高深宽比微结构的方法。设备昂贵,需特制的X射线掩模 版,加工周期长,与集成电路兼容性差
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硅基微机械加工技术
体硅微机械加工技术
硅各向异性化学湿法腐蚀技术 熔接硅片技术 反应离子深刻蚀技术
表面微机械加工技术
利用集成电路的平面加工技术加工微机械装置 整个工艺都基于集成电路制造技术 与IC工艺完全兼容,制造的机械结构基本上都是二维的

微机电系统MEMS的学习 ppt课件

微机电系统MEMS的学习 ppt课件

先加工机械结构,再加工电路
几种重要的MEMS器件
微机电系统MEMS的学习
惯性MEMS器件
➢ 加速度计 ➢ 陀螺 ➢ 压力传感器
光学MEMS器件
➢ 微光开关 ➢ 微光学平台
微执行器
➢ 微喷 ➢ 微马达
生物MEMS器件 其它
微机电系统MEMS的学习
加速度计
➢压阻式加速度计 ➢电容式加速度计 ➢压电式加速度计
微机电系统MEMS的学习
美国喷气推进实验室(JPL)展示的采用MEMS技术的电阻电热 式微推进器样机(固体升华方式)。微推进器由推进剂出贮箱、 微阀、微过滤器、微型喷口等组成,微型喷口利用MEMS技术 中 的 体 硅 工 艺 制 作 。 其 性 能 目 标 为 : 比 冲 50 ~ 75s , 推 力 0.5mN,功率 <2W/mN,质量为几克,大小为1cm2。
微机电系统MEMS的学习
新概念的微型双组元火箭发动机结构图
组成: 由5到6片芯 片叠在一起,内有混合 燃烧室、喷口喷管、两 个泵和两个阀以及冷却 管道的多器件集成系统 。用液态氧和乙醇作燃 料
性能:能产生15N 的推力,推力重量比达 1500:1,是大火箭推进 器的10~100倍,反映了 微系统的潜力
微机电系统MEMS的学习 三种加速度计的特性比较
技术指标 阻抗
电负载影响 尺寸
电容式 高
非常大 大
压电式 高 大 小
压阻式 低 小
中等
温度范围 线形度误差
直流响应 交流响应 有无阻尼
灵敏度 冲击造成的零位漂移 旋转或无需校准功能
电路复杂程度 成本
交叉轴敏感度
非常宽

中等

中等

MEMS传感器及其应用 ppt课件

MEMS传感器及其应用  ppt课件


微机电系统(Microelectromechanical Systems,MEMS)是将微电子技术与机械 工程融合到一起的一种工业技术,它的操 作范围在微米范围内。比它更小的,在纳 米范围的类似的技术被称为纳机电系统。 MEMS(微机电系统)是指集微型传感器、 执行器以及信号处理和控制电路、接口电 路、通信和电源于一体的微型机电系统。
典型的MEMS压力传感器

典型的MEMS压力传感器管芯(die)结构和电原理如 图7所示,左是电原理图,即由电阻应变片组成的惠斯顿 电桥,右是管芯内部结构图。典型的MEMS压力传感器管 芯可以用来生产各种压力传感器产品,如图8所示。 MEMS压力传感器管芯可以与仪表放大器和ADC管芯封装 在一个封装内(MCM),使产品设计师很容易使用这个 高度集成的产品设计最终产品。
MEMS压力传感器

MEMS压力传感器广泛应用于汽车电子:如 TPMS(轮胎压力监测系统)、发动机机油压力传 感器、汽车刹车系统空气压力传感器、汽车发动 机进气歧管压力传感器(TMAP)、柴油机共轨 压力传感器;消费电子,如胎压计、血压计、橱用 秤、健康秤,洗衣机、洗碗机、电冰箱、微波炉、 烤箱、吸尘器用压力传感器、洗衣机、饮水机、 洗碗机、太阳能热水器用液位控制压力传感器;工 业电子,如数字压力表、数字流量表、工业配料 称重等。


1)影像传感器 简单说就是相机镜头,由于只牵涉到微光学与微电子,没有机械 成份在里头,即便加入马达、机械驱动的镜头,这类的机械零件 也过大,不到「微」的地步,所以此属于光电半导体,属于光 学、 光电传感器。 2)亮度传感器

外界并不清楚iPhone4用何种方式感应环境光亮度,而最简单的实现方式 是用一个光敏电阻,或者,iPhone4直接用影像传感器充当亮度侦测,也 是可行。无论如此,此亦不带机械成份,属于光电类传感器,甚至可能 不是微型的,只是一般光学、光电传感器。

MEMS简介3PPT课件

MEMS简介3PPT课件
全球微机电系统市场销售额分析:
✓在全球前30名MEMS公司的榜单中,很多公司受惠于智能手机市场的 蓬勃发展。例如瑞声科技(AAC)凭借MEMS麦克风的强劲增长(2012 年营收增长90%,达到6500万美元),首次挤进全球前30名。 ✓中国驻极体麦克风供应商购买英飞凌(Infineon)的MEMS裸片,然后 自己做封装、测试和销售,并成为苹果iPhone的第二货源。
• 意法半导体于2006 年成为全球首家以200 mm 晶圆生产MEMS 传感 器的厂商;
• IHS iSuppli 的统计数据显示:
a. 2012 年全球MEMS 芯片市场成长约5%,规模达到83 亿美元; b. 意法半导体与博世并列全球第一大MEMS 供应商,其中意法半导体营收年成长率23%
,博世年成长率为8%;
MEMS产业现状 及全球MEMS市场
(1)美国
MEMS的研究在60年代首先从斯坦福大学开始,逐步扩展到佐治亚理 工学院和加利福尼亚大学洛杉矶分校等大学,众多美国大学拥有了 100~150mm晶圆生产线。
(2)法国
法国有关MEMS的研发基地较为集中,主要由国立研究所法国LETI( Laboratoire dElectronique de Technologie de lInformation,电子和信息 技术实验室)承担。
➢ MEMS与CMOS制程技术的整合
➢ 3D 封装技术在异质整合特性下,可进一步整合模拟RF、数字Logic、 Memory、Sensor、混合讯号、MEMS 等各种组件
MEMS产业现状 及全球MEMS市场
MEMS产业现状 及全球MEMS市场
3.2.3 MEMS晶圆代工厂
• 近几年以来美国也有几家规模较小的晶圆代工厂,持续投入资源用 于MEMS晶圆代工;

MEMS英文课件4-MEMS

MEMS英文课件4-MEMS
Mask: A optically flat glass (transparent to near UV) or quartz plate (transparent to deep UV) with a metal (e.g. chromium layer) absorber pattern
Photo-lithography-4
MEMS Fabrication-In General
• Typical MEMS fabrication involves the following conventional microelectronic fabrication processes: – Cleaning Processes – Deposition Processes – Patterning Processes – Etching Processes
Outline
Overview pf microfabrication processes
Photolithography
Surface micromachining Bulk micromachining SOI & LIGA processes Wafer bonding Summary
MEMS Fabrication-In General
• Apply an acid-resistant coating (such as wax) • Scraped away the coating in the desired pattern • Etch with a weak acid (such as vinegar) • Accentuated by applying a colorant such as lamp-black to the cut-away portions

MEMS课件~

MEMS课件~

Inertia Sensor for Automobile “Air Bag”Micro inertia sensor (accelerometer) in place:Sensor-on-a-chip:(2 mm x 3 mm-smaller thanrice grain(Courtesy of Analog Devices, Inc)Rice grainsOver 100 micro-sensors and micro-actuators by MEMS technologyThe ENIAC Computer in 1946A “Palm-top”Computer in 2003This spectacular miniaturization took place in 50 years!!The ENIAC computerMobil phones 15 Years Ago:Current State-of-the Art:Transceive voice onlyTransceive voice+ others Palm-top Wireless PCThe only solution is to pack manyMicro pressure sensorsInertia Sensor for Automobile “Air Bag”Micro inertia sensor (accelerometer) in place:Sensor-on-a-chip:(the size of arice grain(Courtesy of Analog Devices, Inc) Unique Features of MEMS and Microsystems (1)-A great challenge to engineersComponents are in micrometers with complex geometryusing silicon, si-compounds and polymers:25 µmA microgear-train by(1)(10)(2)(3)(4)(5)(6)(8)(9)(2) Exhaust gas differential pressure sensor(1) Manifold or Temperature manifold absolute pressure sensor (3) Fuel rail pressure sensor(4) Barometric absolute pressure sensor (5) Combustion sensor(7) Fuel tank evaporative fuel pressure sensor (6) Gasoline direct injection pressure sensor (8) Engine oil sensor (9) Transmission sensor (10) Tire pressure sensorApplication of MEMS and MicrosystemsinAerospace IndustryCockpit instrumentation.Wind tunnel instrumentation MicrosattellitesCommand and control systems with MEMtronicsInertial guidance systems with microgyroscopes, accelerometers and fiber optic gyroscope.Attitude determination and control systems with micro sun and Earth sensors.Power systems with MEMtronic switches for active solar cell array reconfiguration, andMicro lenses:Micro switches: Micro Optical SwitchesMigratingElectrons The strains associated with the deformation of the diaphragm areplaced in “strategic locations”onThese tiny piezoresistors are madeThere is preset mismatch of pitches of the electrodes in the two sets.Stator RotorGear fortransmittingtorqueStationary electrodesMoving electrodeThe movement of the proof mass is carried out by measuring the change of capacitances between the pairs of electrodes.B e a m M ov e m e n tA c ce l e r a t i o nThe need for integrating microelectronics (ICs)and moving microstructures –A great challenge!A c c e l e r a t i o n3 mm2 mm。

MEMS加速度传感器PPT课件

MEMS加速度传感器PPT课件
G. rLoOuGpO3
压阻式加速度传感器
工艺流程
(d)在两面涂上光刻胶作为 湿法刻蚀的梁结构 (e)去除光刻胶以后两面重 新被氧化生成SiO2,随后再 EVG-100覆盖 (f)利用剩下的光刻胶进行刻 蚀然后移除光刻胶
G. rLoOuGpO3
压阻式加速度传感器
工艺流程
(g)等刻蚀完成,对 称梁结构形成
MLOEGMOS
传感器技术
加速度传感器
.
目录
1
简述加速度传感器
2
电阻式加速度传感器
3
电容式加速度传感器
4
其他类型加速度传感器
G. rLoOuGpO3
篇前语
❖ MEMS是什么?加速度传感器与MEMS什么关 系?
▪ 微机电系统(MEMS, Micro-ElectroMechanical System),也叫做微电子机械系统
目前广泛应用制备光学加速度计的
光波导式 迈克尔逊、马赫—曾德等干涉仪的
核心部件都包含3 dB耦合器。
微谐振式
谐振式加速度传感器是一种典型的 微机械惯性器件,基本工作原理是 利用振梁的力频特性,通过检测谐 振频率变化量获取输入的加速度。
热对流式
微型热对流加速度计是利用封闭空 气囊内的自由热对流对加速度敏感 性。两个温度传感器对称地在有气 体的腔体两侧,中间有一个热源。
•加速度传感器中的分类
加速度传感器的原理随其应用而不同,有压阻式,电容式,压 电式,谐振式、伺服式等。
G. rLoOuGpO3
压阻式加速度传感器
压阻式压阻式器件是最早微型化和商业化的一类加速度传感器。基于世界领先的 MEMS硅微加工技术,压阻式加速度传感器具有体积小、低功耗等特点,易于集 成在各种模拟和数字电路中,广泛应用于汽车碰撞实验、测试仪器、设备振动监 测等领域。

第十五章MEMS传感器讲述课件

第十五章MEMS传感器讲述课件

感谢您的观看
THANKS
应用范围
体微加工技术适用于制造 一些特殊类型的MEMS传 感器,如流体传感器、生 物传感器等。
键合与封装技术
定义
键合与封装技术是将MEMS传感 器与外部电路和保护壳体进行连
接和封装的过程。
工艺流程
键合与封装技术包括芯片粘接、引 线键合、密封填充等步骤,以确保 MEMS传感器能够在实际应用中稳 定工作。

集成化
MEMS传感器通常与其 他电子器件集成在一起 ,形成一个完整的系统

高精度
MEMS传感器的精度非 常高,能够实现高精度
的测量。
低功耗
MEMS传感器的功耗非 常低,能够延长设备的
续航时间。
材料选择
单晶硅
单晶硅是MEMS传感器的主要材料之一,具 有高强度、高刚度和良好的热稳定性。
多晶硅
多晶硅材料具有较好的塑性和韧性,适合用 于制造柔性MEMS传感器。
未来发展趋势
01
新材料应用
随着新材料的发展,MEMS传 感器的性能将得到进一步提升 。
02
智能化
未来MEMS传感器将更加智能 化,能够自适应调整参数以提 高性能。
03
网络化
随着物联网技术的发展, MEMS传感器将更加网络化, 实现远程监控和管理。
04
个性化与定制化
随着需求的多样化,MEMS传 感器的设计和应用将更加个性 化与定制化。
分辨率与精度
分辨率
分辨率是指传感器能够检测到的 最小输入信号变化量。分辨率越 高,传感器能够检测到的信号变 化越细微。
精度
精度是指传感器测量结果的准确 性。高精度的传感器能够提供更 接近真实值的测量结果。

微机电系统第二章MEMS设计基础PPT课件

微机电系统第二章MEMS设计基础PPT课件

式中的F0和 为常数
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固体在亚微米尺度内热流量的尺度规律
Q(l1)(l1)l2
表示尺寸减小10倍将导致热流量减小100倍。
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(2)对流中的尺度效应 对流时,固体与流体界面处出现边界层,由牛顿冷 却定律描述 式中Q为流体中两点间的热流总量,q 是相应的热通量,A是热流的横截面积,h为传热系 数,是两点之间的温差。
• 1962 年第一个硅微型压力传感器问世,现在国内外 出现了各种微型传感器,包括压力、加速度、气体、 湿度、生化传感器等。除了微型传感器,还出现了 微型执行器、微型机器人、微型动力系统。1988 年 美国加利福尼亚大学柏克利首次制作出转子直径为 60μm 的静电微电机,而我国清华大学92 年研制的 同步式静电微电机,在技术性能上已远远超过美国 第一台同类微电机的水平。
18

d10m
击穿电压随d的增加而增加,
V随尺度变化为 V l 3
平板电容中静电势能的尺
度为
Ul0l0l1l1(l1)2 l3 l
图2.27 Paschen效应
上 式 尺 度 说 明 如 果 W,L 和 d 同 时 减 小 10 倍 , 电 动 势 将 减 小 1000倍。下面是静电力的尺度规律;
35
4 硅化物材料
• 硅化物如TiSi2,CoSi2, PtSi等在VLSI 中作为接触 和互联材料有广泛的应用,它们的电阻率比多晶 硅更低,大大减少了期间的互联电阻和接触电阻, 显著改善了器件的导电特性。
• 硅化物的制备工艺与表面微机械制备技术兼容, 但是硅化物有较大的应力。至于如何减少硅化物 的应力还有待于进一步的研究、解决。
• 实际的机械性能取决于制成器件后硅的结晶取向、
几何尺寸、缺陷以及在生长、抛光、随后处理中

《MEMS微电感》课件

《MEMS微电感》课件

应用领域
01
通信领域
用于无线通信、卫星通信、雷达等高频信号处理系统。
02
能源领域
用于微型电源、储能系统等。
03
生物医学领域
用于生物传感器、医学诊断和治疗等。
02 MEMS微电感的设计与制造
设计流程
A
需求分析
明确MEMS微电感的应用场景和性能要求,如 工作频率、Q值、尺寸等。
原理图设计
根据需求,设计MEMS微电感的原理图, 包括结构、形状、尺寸等。
B
C
仿真优化
利用仿真软件对设计的MEMS微电感进行性 能分析和优化,提高性能参数。
版图绘制
将原理图转化为制版图,为后续制造提供依 据。
D
材料选择
01
02
03
材料类型
选择适合MEMS微电感制 造的材料,如单晶硅、多 晶硅、氮化硅等。
材料纯度
确保所选材料的纯度,以 满足MEMS微电感的性能 要求。
材料特性
《MEMS微电感》 PPT课件
目录
• MEMS微电感简介 • MEMS微电感的设计与制造 • MEMS微电感的性能测试与评估 • MEMS微电感的发展趋势与挑战 • MEMS微电感的应用案例
01 MEMS微电感简介
定义与特性
定义
MEMS微电感是指利用微电子机械系 统(MEMS)技术制作的微型电感器 。
案例二:MEMS传感器
总结词
MEMS传感器是利用微电感技术实现传感器功能的重要应用,具有高精度、高可靠性、低功耗等优点 。
详细描述
MEMS传感器利用微电感作为敏感元件,可以感知温度、压力、磁场、加速度等物理量,广泛应用于 汽车、医疗、航空航天等领域。MEMS传感器的精度和可靠性高,能够提供准确的测量数据,并且具 有低功耗的特点,能够延长设备的续航时间。

MEMS传感器技术 ppt课件

MEMS传感器技术  ppt课件

几种常见的MEMS传感器
微机械位移控制器
微机械位移控制器的主要应用是计算机 硬盘的磁头定位系统, 硬盘的磁道密度很 快将达到0. 25μm/ 道,此时对应的移动定 位精度是0. 025μm ,这时解决磁头移动控 制的办法是在现有位置控制系统上附加 一个微机械次级控制系统。
MEMS的基本介绍
MEMS(微机电系统),同时也是一门技术, 是在一个硅基板上,微米范围内集成了 微型传感器、执行器以及信号处理和控 制电路、接口电路、通信和电源于一体 的微型机电系统的高新技术。
MEMS的基本介绍
MEMS又是一种产业,采用ME空微电子器件、电 力电子器件等在航空、航天、汽车、农 业、生物医学、环境监控、军事以及几 乎人们所接触到的所有领域中都有着十 分广阔的应用前景。
MEMS的基本分类
MEMS一般可以以其核心元件分为两类: 传感型MEMS、致动型MEMS。
传感型MEMS
能量供给
输入信号
微传感元件
传输单元
输出信号
致动型MEMS
能量供给
输出动作
微致动元件
传输单元
几种常见的MEMS传感器
微压力传感器
微机械压力传感器是最早开始研制的微机械产 品,也是微机械技术中最成熟、最早开始产业化 的产品。从信号检测方式来看, 微压力传感器 可分为压阻式和电容式两类, 分别以体微机械 加工技术和牺牲层技术为主制造;从敏感膜结构 来看,微压力传感器可分为圆形、方形、矩形、 E 形等多种结构。
MEMS的加工方法
微机械加工方法LIGA 微机械加工方法LIGA以德国为代表,LIGA~IY法 是指采用同步x射线深层光刻、注塑复制和微 电铸制模等主要工艺步骤组成的一种综合性微 机械加工技术。LIGA技术首先采用同步X射线 光刻技术光刻出所要生产的图形,然后采用电 铸的方法加工出与光刻图形相反的金属模具撮 后采用微塑注来制备微机械结构。
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EE C245: Introduction to MEMS DesignLecM 4C. Nguyen8/20/091EE C245 –ME C218Introduction to MEMS DesignFall 2011Prof. Clark T.-C. NguyenDept. of Electrical Engineering & Computer SciencesUniversity of California at BerkeleyBerkeley, CA 94720Lecture Module 4: Lithography, Etching, & DopingLecture Outline•Reading: Senturia, Chpt. 3; Jaeger, Chpt. 2, 4, 5ªLithography ªEtching(Wet etching (Dry etchingªSemiconductor Doping (Ion implantation (DiffusionEE C245: Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 3LithographyLithographyLithographyªMethod for massive patterning of features on a wafer →pattern billions of devices in just a few steps I. Radiation SourceFour Main Components (that affect resolution)II. MaskIII. PhotoresistMask (glass/quartz)Photoresist (~1μm-thick)Film to be patterned (e.g., poly-Si)Designated pattern (clear or dark field)IV. Exposure System contact, step and repeatoptics this is where the real art is!emulsionchromeªGenerated from layoutEE C245: Introduction to MEMS DesignLecM 4C. Nguyen8/20/095Lithography (cont.)The basic Process –(Positive Resist Example)PRlight SiSiFilm Film SiFilmPRPR Remove PREtch PR protects film; open areas of film get etchedDip or spray wafer with developer if (+) resist, developer is often a base Exposed PR converts to another form afterreaction with light (e.g., (+)-resist:polymer organic acid)Lithography (cont.)With each masking step usually comes a film deposition, implantation and/or etch. Thus, the complexity of a process is often measured by # masks required.NMOS: 4-6 masks Bipolar: 8-15 masks BICMOS: ~20 masks CMOS: 8-28 masksComb-Drive Resonator: 3 masks GHz Disk: 4 masksNow, take a closer look at the 4 components:Multi-level metallizationEE C245: Introduction to MEMS DesignLecM 4C. Nguyen8/20/097I. Radiation SourceI.Radiation SourceªSeveral types: optical, (visible, UV, deep UV light), e-beam, X-ray, ion beamThe shorter the wavelength →Better the resolutionToday’s prime choice due to cost and throughput.Can expose billions of devices at once!Optical Sources:ªMercury arc lamp (mercury vapor discharge)200365405435546 nmªFor deep UV, need Excimer laser (very expensive)Glass opaque, so must use quartz mask and lensI-lineG-line (we have both in our μlab)we have all of these in our μlabII. MaskII. Mask →has become one of today’s biggest bottlenecks!Mask Material:ªFused silica (glass) inexpensive, but larger thermal expansion coeff.ªQuartz expensive, but smaller thermal expansion coeff.A single filecontains all layersElectronic computerrepresentation of layout (e.g., CIF, GDSII)Masks for each layertape mask generatorEE C245: Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 9SiSi PRPRdevelopSiSiPRPRdevelopExposed Area:Pictorial Description:remainsremovedIII. Photoresist (optical)Mechanism:NegativePositive photoactivation Polymerization (long, linked Carbonchains)Developer solventremoves unexposed PRphotoactivation Converts exposed PR to organic acid Alkaline developer (e.g.,kOH) removesacidEE C245: Introduction to MEMS Design LecM 4 C. Nguyen8/20/0911Issues:Polymerized PR swells in solvent →bridging problemExposed and polymerizedDoesn’t adhere well to SiO 2Need primer: HMDS(hexamethyl disilazane)PRSiO 2Poor adhesionPR SiO 2HMDS Good adhesion at both HMDS interfacesTypical Procedure for LithographyClean Wafer Dry Wafer Deposit HMDS Spin-on PR Soft Bake Very important step30 min. @ 120°C pre-bake(for oxide on wafer surface)30-60 sec @ 1000-5000 rpm2 min @ 90°CImprove adhesion and remove solvent from PR Topography very important:Thicker and unfocusedunderexpose overexposePRDescumAlign & Expose DevelopPost BakeOxygen plasma (low power ~ 50W)EE C245: Introduction to MEMS DesignLecM 4C. Nguyen8/20/0913IV. Exposure System/Optics•1X printing very useful for MEMS →can expose surfaceswith large topography (where reduction printers cannot)Contact PrintingProximity Printing•Mask in contact with wafer•Problem : mask pattern can become damaged with each exposure →must make a new mask after x number of exposures•Mask in very closeproximity but not touchingPhotoresistPhotoresistIV. Exposure System/Optics•Dominates in IC transistor fabrication •5X or 10X reduction typical•Mask minimum features can be largerthan the actual printed features by the focused reduction factor →less expensive mask costs•Less susceptible to thermal variation (in the mask) than 1X printing•Can use focusing tricks to improve yield:Projection PrintingStep & repeat PhotoresistDust particle willbe out of focus →better yield!wafermaskEE C245: Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 15EtchingEtching Basics•Removal of material over designated areas of the wafer •Two important metrics:1. Anisotropy 2. Selectivity1. Anisotropy –a) Isotopic Etching (most wet etches)If 100% isotropic: d f = d + 2h Define: B = d f –d If B = 2h ÖisotropicPRPRhd fdEE C245: Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 17b) Partially Isotropic: B < 2h(most dry etches, e.g., plasma etching)Degree of Anisotropy: (definition)PRPR021=−=hB A f if 100% isotropic 10≤<f A anisotropicEtching Basics (cont.)2. Selectivity -PR Poly-Si SiO 2SiPR Poly-Si SiO 2SiIdeal Etch Actual EtchOnly poly-Si etched (no etching of PR or SiO 2)Perfect selectivityPR Poly-Si SiO 2PR partially etchedSiO 2partially etched after some overetch of the polysiliconEE C245: Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 19μ1Why overetch ?mμ4.0PRdm =μ4.0Thicker spots due to topography!md d μ56.04.12==10nm Gate oxide45°Poly-Si →conformal if deposited by LPCVDThus, must overetch at least 40%:40% overetch →(0.4)(0.4) = 0.16 μm poly= ??? oxide Depends on the selectivity of poly-Si over the oxideEtching Basics (cont.)Define selectivity of A over B:∴Selectivity of A over Be.g., wet poly etch (HNO 3+ NH 4+ H 2O)=PR poly S Very high (but PR can still peel off aftersoaking for > 30 min., so beware)ba ab R E R E S ....=Etch rate of A Etch rate of B1152=SiO polyS (very good selectivity)e.g., polysilicon dry etch:1752−=SiO poly S 14=PR poly S (but depends on type of etcher)Regular RIEECR: 30:1Bosch:100:1 (or better)EE C245: Introduction to MEMS Design LecM 4C. Nguyen 8/20/09 21Etching Basics (cont.)oxide! of nm 20816.0=This will etch all poly over the thin oxide,etch thru the 10nm of oxide, then startetching into thesilicon substrate →needless to say, thisis bad!with better selectivity:e.g.,nm 3.53016.0=40% overetch removes(better )(Can attain with high density Cl plasma ECR etch!)If 40% overetch removes182=SiO poly S 1302=SiO poly S Wet EtchingEE C245: Introduction to MEMS DesignLecM 4C. Nguyen8/20/0923Wet Etching•Wet etching: dip wafer into liquidsolution to etch the desired film ªGenerally isotropic, thus, inadequate for defining features < 3μm-wide•General Mechanism - 1.Diffusion of thereactant to the film surface2.Reaction: adsorption,reaction, desorption 3.Diffusion of reactionproducts from the surfacewaferetchSolvent bathPRPRSiPRPRSio o Film to be etchedo ReactantReaction productsWet Etching (cont.)•There are many processes by which wet etching can occurªCould be as simple as dissolution of the film into the solvent solutionªUsually, it involves one or more chemical reactions (Oxidation-reduction (redox) is very common:(a)Form layer of oxide(b)Dissolve/react away the oxide•Advantages:1. High throughput process →can etch many wafers in a single bath2. Usually fast etch rates (compared to many dry etch processes)3. Usually excellent selectivity to the film of interestEE C245: Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 25Wet Etching Limitations1. IsotropicªLimited to <3μm featuresªBut this is also an advantage of wet etching, e.g., if used for undercutting for MEMS2. Higher cost of etchants & DI water compared w/ dry etch gas expenses (in general, but not true vs. deep etchers)3. SafetyªChemical handling is a hazard4. Exhaust fumes and potential for explosion ªNeed to perform wet etches under hood5. Resist adhesion problemsªNeed HMDS (but this isn’t so bad)Wet Etch Limitations (cont.)6. Incomplete wetting of the surface:ªFor some etches (e.g., oxide etch using HF), the solution is to dip in DI water first, then into HF solution →the DI water wets the surface betterwaferBut this will lead to nonuniform etching across the wafer.Pockets where wetting hasn’t occurred, yet(eventually, it will occur).Wetted surfaceSolvent bathEE C245: Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 27Wet Etch Limitations (cont.)7. Bubble formation (as a reaction by-product)ªIf bubbles cling to the surface →get nonuniform etchingNon-uniform etchingPRPRSi waferBubble (gaseous by-product)Film to be etchedSolution:Agitatewafers during reaction.Some Common Wet Etch ChemistriesWet Etching Silicon:Common: Si + HNO 3+ 6HF H 2SiF 6+ HNO 2+ H 2+ H 2O(isotropic)(nitric acid)(hydrofluoricacid)(1) forms a layerof SiO 2(2) etches awaythe SiO 2Different mixture combinations yield different etch rates.EE C245: Introduction to MEMS Design LecM 4C. Nguyen8/20/09 29Silicon Crystal Orientation•Silicon has the basic diamondstructureªTwo merged FCC cells offset by (a/4) in x, y, and z axes ªFrom right:# available bonds/cm 2<111># available bonds/cm 2<110># available bonds/cm 2<100>x y za[100](100) planeI n c r e a s i n g@ coordinate (1,0,0)<100> plane ⊥to this vectorx yza][110](110) planexyz a][111]e(111) plane coordinate(1,1,0) defines vector <110> plane ⊥to this vector@ coordinate (1,1,1), <111> plane ⊥to resulting vectorAnisotropic Wet EtchingAnisotropic etches also available for single crystal Si:ªOrientation-dependent etching: <111>-plane more densely packed than <100>-planeSlower E.R.Faster E.R.…in some solventsOne such solvent: KOH + isopropyl alcohol(e.g., 23.4 wt% KOH, 13.3 wt% isopropyl alcohol, 63 wt% H 2O)E.R.<100>= 100 x E.R.<111>EE C245: Introduction to MEMS DesignLecM 4C. Nguyen8/20/0931Anisotropic Wet Etching (cont.)Can get the following:(on a <100> -wafer)Si54.7°<111><100>SiO 2(on a <110> -wafer)Quite anisotropic!Si<110><111>SiO 2Wet Etching SiO 2SiO 2+ 6HF H 2+ SiF 6+ 2H 2OGenerally used to clear out residual oxides from contactsnative oxidecan get this just by exposing Si to air 1-2nm-thickProblem:Contact hole is so thin that surface tensions don’t allow the HF to get into the contactGenerally the case for VLSI circuits oxideHFbubblent300nmSolution:add a surfactant (e.g., Triton X) to the BHFbefore the contact clear etch1.Improves the ability of HF to wet the surface (hence, getinto the contact)2.Suppresses the formation of etch by-products, whichotherwise can block further reaction if by-products get caught in the contactEE C245: Introduction to MEMS DesignLecM 4C. Nguyen8/20/0933More Wet Etch Chemistries•Wet etching silicon nitrideªUse hot phosphoric acid: 85% phosphoric acid @ 180o C ªEtch rate ~ 10 nm/min (quite slow)ªProblem: PR lifted during such etchingªSolution: use SiO 2as an etch mask (E.R. ~2.5 nm/min)(A hassle →dry etch processes more common than wet •Wet etchining aluminumªTypical etch solution composition:ªProblem: H 2gas bubbles adhere firmlly to the surface →delay the etch →need a 10-50% overetch timeªSolution: mechanical agitation, periodic removal of wafers from etching solution80% phoshporic acid, 5% nitric acid, 5% acetic acid, 10% water(HNO 3)(CH 3COOH)(H 2O)(H 2PO 4)(1) Forms Al 2O 3(aluminum oxide)(2) Dissolves the Al 2O 3Wet Etch Rates (f/ K. Williams)Film Etch Chemistries•For some popular films:EE C245: Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 35Dry EtchingEE C245: Introduction to MEMS DesignLecM 4C. Nguyen8/20/0937Dry EtchingAll based upon plasma processes.~+++++++++waferE-fieldRF (also, could be μwave)Develop (-) bias)Plasma (partially ionized gas composed of ions, e -’s, and highly reactive neutral species)(+) ions generated by inelastic collisions with energetic e -1’sGet avalanche effect because more e -1’scome out as each ion is generated.Develops (+) charge to compensate for∴(+) ions will be accelerated to the wafer•Physical sputtering •Plasma etching•Reactive ion etchingPhysical Sputtering (Ion Milling)•Bombard substrate w/ energetic ions →etching via physicalmomentum transfer•Give ions energy and directionality using E-fields •Highly directional →very anisotropicPRPR film SiionsplasmaSteep vertical wallEE C245: Introduction to MEMS DesignLecM 4C. Nguyen8/20/0939Problems With Ion MillingPR etched down to here PRPR filmSi PR1.PR or other masking material etched at almostthe same rate as the film to be etched →very poor selectivity!2.Ejected species not inherently volatile →getredeposition →non-uniform etch →grass!•Because of these problems, ion milling is not used often(very rare)Once through the film, the etch will start barreling through the SiPlasma Etching•Plasma (gas glow discharge) creates reactive species thatchemically react w/ the film in question•Result: much better selectivity, but get an isotropic etchPlasma Etching Mechanism:1.Reactive species generated in a plasma.2.Reactive species diffuse to the surface of material to be etched.3.Species adsorbed on the surface.4.Chemical reaction.5.By-product desorbed from surface.6.Desorbed species diffuse into the bulk of the gasMOST IMPORTANT STEP! (determineswhether plasma etching PRPR Film to be etchedSi123456plasmaEE C245: Introduction to MEMS DesignLecM 4C. Nguyen8/20/0941Ex: Polysilicon Etching w/ CF 4and O 2•F°is the dominant reactant →but it can’t be given adirection →thus, get isotropic etch!CF 4CF 4++ CF 3++ CF 2++ CF ++ F ++ F 0+ CF 2++ …Neutral radical (highly reactive!)SiCF 6, SiF 4both volatile dry etching is possible.∴e -+ CF 4→CF 3+ F + e -SiplasmaPR polySiF 0F 0SiF 4isotropic componentEx: Polysilicon Etching w/ CF 4and O 2PR polySiF 0F 0SiF 4isotropic component•Problems:1.Isotropic etching2.Formation of polymer because of C in CF 4ªSolution: add O 2to remove the polymer (but notethat this reduces the selectivity, S poly/PR )•Solution:ªUse Reactive Ion Etching (RIE)EE C245: Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 43Reactive Ion Etching (RIE)•Use ion bombardment to aid and enhance reactive etching ina particular directionªResult: directional, anisotropic etching!•RIE is somewhat of a misnomerªIt’s not ions that react …rather, it’s still the neutral species that dominate reactionªIons just enhance reaction of these neutral radicals in a specific direction•Two principle postulated mechanisms behind RIE1. Surface damage mechanism2. Surface inhibitor mechanismRIE: Surface Damage Mechanism•Relatively high energyimpinging ions (>50 eV) produce lattice damage at surface•Reaction at these damaged sites isenhanced compared to reactions at undamaged areasfilmSiPRPR Enhanced reaction overplasma+++reactive radicalResult: E.R. at surface >> E.R. on sidewallsEE C245: Introduction to MEMS DesignLecM 4C. Nguyen8/20/0945RIE: Surface Inhibitor MechanismfilmSiPRPR plasma+++reactive radical(+) ions breakup the polymer layerno reaction•Non-volatile polymerlayers are a product of reaction•They are removed by high energy directional ions on the horizontal surface, but notremoved from sidewallsget reaction Result: E.R. @ surface >> E.R. on sidewallsDeep Reactive-Ion Etching (DRIE)The Bosch process:•Inductively-coupled plasma •Etch Rate: 1.5-4 μm/min •Two main cycles in the etch:ªEtch cycle (5-15 s): SF 6(SF x +) etches SiªDeposition cycle: (5-15 s): C 4F 8deposits fluorocarbon protective polymer (CF 2-)n•Etch mask selectivity:ªSiO 2~ 200:1ªPhotoresist ~ 100:1•Issue: finite sidewall roughness ªscalloping < 50 nm •Sidewall angle: 90o ±2oEE C245: Introduction to MEMS Design LecM 4C. Nguyen 8/20/09 47DRIE Issues: Etch Rate Variance•Etch rate is diffusion-limitedand drops for narrow trenchesªAdjust mask layout to eliminate large disparities ªAdjust process parameters (slow down the etch rate to that governed by the slowest feature)Etch rate decreases with trench widthEtch rate decreases with trench width Semiconductor DopingEE C245: Introduction to MEMS DesignLecM 4C. Nguyen8/20/0949•Semiconductors are not intrinsically conductive•To make them conductive, replace silicon atoms in the latticewith dopant atoms that have valence bands with fewer or more e -’s than the 4 of Si•If more e -’s, then the dopant is a donor: P, AsªThe extra e -is effectively released from the bonded atoms to join a cloud of free e -’s, free to move like e -’s in a metal ªThe larger the # of donor atoms, the larger the # of free e -’s →the higher the conductivityDoping of SemiconductorsSi ::Si :Si::Si ::P ::Si :Si:: Si ::: Si ::: Si :::: Si ::: Si :::. P ..:Dope.Extra free e -::::::::Doping of Semiconductors (cont.)•Conductivity Equation:•If fewer e -’s, then the dopant is an acceptor: BªLack of an e -= hole = h +ªWhen e -’s move into h +’s, the h +’s effectively move in the +pq n q p n μμσ+=conductivityelectron mobility hole mobilitycharge magnitudeon an electronelectron densityhole densitySi ::Si :Si::Si ::B :.Si:Si:: Si ::: Si ::: Si :::: Si ::: Si :::. B ..Dope.::::::::holeEE C245: Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 51Ion ImplantationIon Implantation•Method by which dopants can be introduced in silicon tomake the silicon conductive, and for transistor devices, to form, e.g., pn-junctions, source/drain junctions, …B+B+B+B+B+B-B-B-B-xSiThe basic process:Control current & time to control the dose.Charged dopant accelerated to high energy by an E-Field (e.g., 100 keV)Masking material(could be PR, could be oxide, etc.)Depth determined by energy & type of dopantResult of I/IEE C245: Introduction to MEMS DesignLecM 4C. Nguyen8/20/0953Ion Implantation (cont.)SiSiSiSiSiBSiIon collides with atoms and interacts with e -’s in the lattice all of which slow it down and eventually stop it.Damage Si layer attop becomes amorphous ª B not in the lattice, so it‘s not electrically active.SiSiSiSiSiBHigh Temperature Anneal (also, usually do a drive-in diffusion) (800-1200°C)ªNow B in the lattice & electrically active! (serves as dopant)This is a statistical process →implanted impurity profile can be approximated by a Gaussian distribution.Result of I/IStatistical Modeling of I/IImpurity concentration N(x)N pUnlucky ionsAvg. ions Lucky ionsΔR pΔR p ΔR p ΔR pR pDistance into Si material, xOne std. dev. away →0.61N p 2 std. dev. away →0,14N p 3 std. dev. away →0.11N pΔp R Projected range = avg. distance on ion trends before stoppingΔΔp R Straggle = std. deviation characterizing the spread of thedistribution.EE C245: Introduction to MEMS Design LecM 4C. Nguyen 8/20/09 55Analytical Modeling for I/I()()⎥⎥⎦⎤⎢⎢⎣⎡Δ−−=222exp )(ppp R R x N x N pp R N Q Δ=π2Mathematically:Implanted Dose =[]∫∞=02/ )(cm ions dx x N Q For an implant completely contained within the Si:Assuming the peak is in the silicon: (putting it in one-sided diffusion form)()()()⎥⎥⎦⎤⎢⎢⎣⎡Δ−−=222exp 2)(p p eff I R R x Dt D x N π()()22peffR Dt Δ=, where QD I =So we can track the dopant front during asubsequent diffusion step.Area under theimpurity distribution curveI/I Range GraphsFigure 6.1•Roughly proportional to ionenergy R p αion energy (some nonlinearties), R p•R p is a function of theenergy of the ion and atomic number of the ion and target material•Lindhand, Scharff and Schiott (LSS) Theory:•Assumes implantation into amorphous material, i.e,atoms of the target material are randomly positioned•Yields the curves of Fig. 6.1 and 6.2•For a given energy, lighter elements strike Si withhigher velocity and penetrate more deeplyEE C245: Introduction to MEMS DesignLecM 4C. Nguyen8/20/0957I/I Straggle GraphsFigure 6.2•Results for Si and SiO 2surfaces are virtuallyidentical →so we can use these curves for bothDiffusionEE C245: Introduction to MEMS DesignLecM 4C. Nguyen8/20/0959Diffusion in Silicon•Movement of dopants within thesilicon at high temperatures •Three mechanisms: (in Si)Substitutional Diffusion •Impurity moves along vacancies in the lattice •Substitutes for a Si-atom in the latticeInterstitialcy Diffusion •Impurity atom replaces a Si atom in the lattice •Si atom displaced to an interstitial site Interstitial Diffusion •Impurity atoms jump from one interstitial site to another•Get rapid diffusion ªHard to control ªImpurity not inlattice so not electrically activeDiffusion in Polysilicon•In polysilicon, still get diffusion into the crystals, but getmore and faster diffusion through grain boundaries•Result: overall faster diffusion than in silicon•In effect, larger surface area allows much faster volumetricdiffusionFast diffusion through grain boundariesRegular diffusion into crystalsEE C245: Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 61Basic Process for Selective Doping 1. Introduce dopants (introduce a fixed dose Q of dopants)(i) Ion implantation (ii) Predeposition2. Drive in dopants to the desired depthªHigh temperature > 900o C in N 2or N 2/O 2•Result:dopantsDrive-in Predeposition•Furnace-tube system using solid, liquid, or gaseous dopant sources •Used to introduced a controlled amount of dopants ªUnfortunately, not very well controlledªDose (Q) range: 1013–1016±20%ªFor ref: w/ ion implantation: 1011–1016±1% (larger range & more accurate)•Example: Boron predeposition O 2, B 2H 6Furnace tubewafer boat GasesO 2+ B 2H 6+ carrier gasdiborane (Inert gas: e.g., N 2or Ar)Predeposition Temp: 800-1100°CEE C245: Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 63Ex: Boron PredepositionSiO 2SiO 2SiB B B B B B 1. Deposit B 2O 3glass 2. B diffuses from B 2O 3→Si SiO 2diffusion barrier (masks out dopants)Furnace tube cross-section Less B concentration •Difficult to control dose Q, because it’s heavily dependent on partial pressure of B 2H 6gas flowªthis is difficult to control itselfªget only 10% uniformity•Basic Procedure:Ex: Boron Predeposition (cont.)For better uniformity, use solid source:Furnace tubewaferBoron/Nitride wafer →2% uniformitySi Si Si Si Si Si Reactions:B 2H 6+ 3O 2→3H 2O + B 2O 3Si + O 2 →SiO 2EE C245: Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 65General Comments on Predeposition •Higher doses only: Q = 1013–1016cm -2(I/I is 1011–1016)•Dose not well controlled: ±20% (I/I can get ±1%)•Uniformity is not good ª±10% w/ gas source ª±2%w/solid source •Max. conc. possible limited by solid solubility ªLimited to ~1020cm -3ªNo limit for I/I →you force it in here!•For these reasons, I/I is usually the preferred method for introduction of dopants in transistor devices •But I/I is not necessarily the best choice for MEMS ªI/I cannot dope the underside of a suspended beam ªI/I yields one-sided doping →introduces unbalanced stress →warping of structures ªI/I can do physical damage →problem if annealing is not permitted •Thus, predeposition is often preferred when doping MEMS Diffusion ModelingDiffusion Modeling (cont.)EE C245: Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 67 Diffusion Modeling (Predeposition)Diffusion Modeling (Limited Source)EE C245: Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 69 Diffusion Modeling (Limited Source)EE C245: Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 71Two-Step Diffusion •Two step diffusion procedure:ªStep 1: predeposition (i.e., constant source diffusion)ªStep 2: drive-in diffusion (i.e., limited source diffusion)•For processes where there is both a predeposition and a drive-in diffusion, the final profile type (i.e., complementary error function or Gaussian) is determined by which has the much greater Dt product:(Dt)predep »(Dt)drive-in Öimpurity profile is complementary error function(Dt)drive-in »(Dt)predep Öimpurity profile is Gaussian (which is usually the case)Successive Diffusions•For actual processes, the junction/diffusion formation is only one of many high temperature steps, each of which contributes to the final junction profile •Typical overall process:1. Selective doping(Implant →effective (Dt)1= (ΔR p )2/2 (Gaussian)(Drive-in/activation →D 2t 22. Other high temperature steps((eg., oxidation, reflow, deposition) →D 3t 3, D 4t 4, …(Each has their own Dt product 3. Then, to find the final profile, usein the Gaussian distribution expression.()iii tot t D Dt ∑=EE C245: Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 73The Diffusion Coefficient (as usual, an Arrhenius relationship)⎟⎠⎞⎜⎝⎛−=kT E D D A o exp Diffusion Coefficient GraphsSubstitutional & Interstitialcy DiffusersInterstitial Diffusers ªNote the much higher diffusion coeffs. than for substitutional。

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