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).
33
The way to improve resolution
Increase NA
Larger lens, could be too expensive and unpratical Reduce DOF and cause fabrication difficulties
Reduce wavelength
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) 的数值孔径 NA=nsinθm θ
31
通过增加透镜半径,达到增加 的目的 通过增加透镜半径 达到增加NA的目的 达到增加
k=0.75 NA=0.6 λ=365nm R=0.4µm µ 32
Exercise 1,
21
Debris between wafer and mask
Expusure Light source
•Short wavelength •High intensity •Stable •High pressure mecury lamp •Excimer laser
22
Spectrum of the Mercury Lamp
Photoresist glass transition temperuature Tg Baking temperature higher than Tg Thermal movement of photoresist molecules Rearrangement of the overexposed and underexposed PR molecules Average out standing wave effect Smooth PR sidewall and improve resolution
DOF =
λ
2( NA)
2
λ =365nm NA=0.4 DOF =2.3µm 37
Exercise 2,
DOF =
λ
2( NA)
2
38
Planarization (表面平整化 表面平整化) 表面平整化
Liquid films: Spin-on glass, resist Solid films: CVD deposition dioxide Chemical-mechanical polishing (CMP) [oxide, polysilicon, metal]
Resolution: 5µm µ
Today, photolithography, X-ray lithography, chargeparticle lithography, all achieved submicro resolution.
Resolution: ~10-190nm
4
Lithography Overview
Mask Aligner (光学光刻机 光学光刻机) 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.
47
Alignment (套刻对准 套刻对准) 套刻对准
48
对准标记
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。 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 在投影掩模版的左 投影掩模版的对准标记 右两侧。 右两侧。它将与安装在步进光刻机机身上的对 准标记对准。 准标记对准。 整场对准标记(GA)在第一次曝光时被光刻在硅 整场对准标记 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。 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 是在每个场曝光时被光刻， 精对准标记 是在每个场曝光时被光刻 被用于每个硅片曝光场和投影掩模版的对准调 节。
8
9
Cr(铬) Glass(玻璃)
掩模版 (Mask)
ห้องสมุดไป่ตู้
dark field
light field 10
Negative and Positive Photoresist
11
Critical Dimension (特征尺寸 特征尺寸) 特征尺寸
The absolute size of minimum feature in an IC or a miniature device, whether it involves a line width, spacing, or contact dimension, is called the critical dimension.
Resolution: 0.5~1 mm
3
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.
6
光刻胶/光阻 光刻胶 光阻 (Photoresist)
光诱导化学反应
7
光刻胶的涂覆
T= ( KCβη γ ) /W1/2
Where K=overall calibration C=polymer concentration in g/100mL solution η=intrinsic viscosity W=rotations per minute (rpm)
Need develop light source, PR and equipment Limitation for reducing wavelength UV to DUV, to EUV, and to X-Ray
Reduce k1
Phase shift mask
34
Phase-shifting Masks
19
Projection Printer (步进式投影曝光机) 步进式投影曝光机 步进式投影
Step and repeat
20
Factor on the Exposure System Resolution
Resolution mainly limits by: Light source Optical system Mask Diffraction of light Resist sensitivity Alignment of mask to wafer Non-uniformities in wafer or mask flatness
第二章：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 enhancement technology Planarization Alignment
28
Light Diffraction With Lens
29
Projection Printing (投影式曝光)
k1: experimentally determined parameter λ: wavelength of the light NA: numerical aperture of the lens system 30
12
Mask Aligners对准机/光刻机
主要性能标准： 1, 分辨率(即可以曝光出来的最小特征尺寸) 2, 对准(套刻精度的度量) 3, 产量
13
Resolution 分辨率
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 取线宽分布三倍标准偏差值不超过线 宽的10％。
14
3, Projection Mode
17
Work like a projector over head Mask to wafer 1:1 Resolution: 1 µm
Scanning Projection System
18 Resolution: 0.25 µm
4, Step & Repeat Alignment/Exposure
39
光刻系统分辨率与焦深的关系
DOF =
λ
2( NA)
2
40
光刻系统分辨率与焦深的关系
41
表面反射和驻波对曝 表面反射和驻波对曝光精度的影响
42
造成侧壁粗糙
表面反射和驻波对曝 表面反射和驻波对曝光精度影响的消除
43
Standing Wave Effect on Photoresist
44
Post Exposure Bake
• • • • • • •
Mask (掩模版 掩模版) 掩模版 Photoresist (光刻胶 光刻胶) 光刻胶 Spinning resist and soft baking (涂胶 前烘 涂胶/前烘 涂胶 前烘) Exposure and post-exposure treatment(曝光 曝光) 曝光 Development (显影 显影) 显影 De-scumming and post-baking（去胶） （去胶） Inspections （检测） 检测）