第二章-1(光学光刻技术)

第二章第一节：光学光刻
Chapter II: Photo Lithography
主流的微电子制造过程中，光刻是最 复杂、昂贵和关键的工艺。大概占成 本的1/3以上。
Content
Resolution in Photolithography Exposure modes and their
advantages and disadvantages Photolithography resolution
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Alignment (套刻对准)
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对准标记
对准标记：置于掩模版和硅片上用来 确定它们的位置和方向的定位图形。
投影掩模版的对准标记(RA)在投影掩模版的左 右两侧。它将与安装在步进光刻机机身上的对 准标记对准。 整场对准标记(GA)在第一次曝光时被光刻在硅 片左右两边，它被用于每个硅片的粗对准。 精对准标记(FA)是在每个场曝光时被光刻，它 被用于每个硅片曝光场和投影掩模版的对准调 节。
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Exposure Modes (曝光模式)
1,Contact Mode
2, Proximity Mode
Simple equipment Direct contact, pollute, particle 2R2esolution: submicron
Complicate system No direct contact, long life Resolution: >3 mm
NA=nsinm
A way to extend 193nm DUV technique.
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Depth of Focus (焦深)
透镜焦点周围的一个范围，在这个范围内图像连续地保 持清晰，这个范围被称为焦深。
DOF
n NA2
=365nm NA=0.4 DOF =2.3mm
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Exercise 2,
4, Step & Repeat Alignment/Exposure
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26ቤተ መጻሕፍቲ ባይዱ
5，Projection Printer (步进+扫描投影曝光机)
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Theoretical resolution (曝光精度)
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Contact Printing (接触式曝光)
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Proximity Printing (接近式曝光)
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（3）Mask Aligner (光学光刻机)
Exposure system (maskaligner) consist of a light source, illumination optics, a mask, projection optics, an alignment system and a wafer stage.
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表面反射和驻波对曝光精度的影响
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造成侧壁粗糙
表面反射和驻波对曝光精度影响的消除
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Standing Wave Effect on Photoresist
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PEB Minimizes Standing Wave Effect
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Post Exposure Bake
Photoresist glass transition temperuature Tg Baking temperature higher than Tg Thermal movement of photoresist molecules Rearrangement of the overexposed and
DOF
n NA2
1.211 1.013 0.689 0.536
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光刻系统分辨率与焦深的关系
R
k NA
DOF
n NA2
What we need: Small R & Large DOF
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光刻系统分辨率与焦深的关系
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提高光学分辨率的其他手段
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Planarization (表面平整化)
Liquid films: Spin-on glass, resist Solid films: CVD deposition dioxide Chemical-mechanical polishing (CMP) [oxide, polysilicon, metal]
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光刻工艺的组成部分
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（1）光刻胶/光阻 (Photoresist)
光诱导化学反应
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光刻胶的涂覆
T= ( KC ) /W1/2
Where K=overall calibration C=polymer concentration in g/100mL solution =intrinsic viscosity W=rotations per minute (rpm)
underexposed PR molecules Average out standing wave effect Smooth PR sidewall and improve resolution
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Alignment (套刻对准)
套准精度：对准系统把版图套准到硅 片上图形的能力。
套准容差：要形成的图形层和前一层 图形的最大相对位移。一般而言，套 准容差为特征尺寸的1/3。
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Factor on the Exposure System Resolution
Resolution mainly limits by: Light source Optical system Mask Diffraction of light Photoresist sensitivity Alignment of mask to wafer Non-uniformities in wafer or mask flatness Debris between wafer and mask
of the lens system 33
Numerical Aperture (数值孔径)
透镜收集衍射光 的能力称为透镜 的数值孔径(NA)
NA=nsinm
（n媒介折射率 θ物镜接收角)
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通过增加透镜半径,达到增加NA的目的
k=0.75 NA=0.6 =365nm R=0.4mm 35
Exercise 1, K1=0.6
Resolution: 0.5~1 mm
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Historical note:lithography developing
130 years later, in 1961, photo-etching process been used to produce a large number of transistor on a thin slice of Si wafer.
(移相掩膜技术—以相消干涉原理为基础)
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Example：Phase Shift Mask Patterning
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Example：Phase Shift Mask Patterning
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Increase NA
Immersion Lithography 浸没式光刻
nair =1.0 nwater=1.4
Increase NA
Larger lens, could be too expensive and unpratical Reduce DOF and cause fabrication difficulties Immersion lithography 37
Reduce k1 Phase-shifting Masks
enhancement technology Planarization Alignment
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Historical note:lithography’s origins
Lithography [stone (lithos)+write (gráphein)]refer to a process invented in 1796 by Aloys Senefelder. He found that stone when properly inked and treated with chemicals, could transfer a carved image into paper.
Mask (掩模版) Photoresist (光刻胶) Spinning resist and soft baking (涂胶/前烘) Exposure and post-exposure treatment(曝光) Development (显影) De-scumming and post-baking（去胶） Inspections （检测）
Resolution: 5mm
Today, photolithography, X-ray lithography, chargeparticle lithography, all achieved submicro resolution.
Resolution: ~10-190nm
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Lithography Overview
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（3）Mask Aligners对准机/光刻机
主要性能标准： 1, 分辨率 2, 对准(套刻精度的度量) 3, 产量
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Resolution 分辨率
即是可以曝光出来的最小特征尺寸 通常表达为可分辨的且仍能保持一定 尺寸容差的最小特征尺寸。 典型值是取线宽分布六倍标准偏差值 （6s）不超过线宽的10％。
1822, France, Nicéphore Niépce, copy an etch print on oiled paper using bitumen mask---the advent of photography;
1827, France, Lemaître, using strong acid made an engraving of Cardinal d’Amboise (一位红衣 主教的雕像).