Nano lithography etching technology

Nano Lithography and Etching Technologies Y.J. Chan, C.K. Lin, H.C. Chiu and S.C. Yang Department of Electrical Engineering National Central University

Solid State and Microwave Laboratory

The Semiconductor Device Revolution

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Moore’s Law

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Integrated Circuits (ICs) Scale of Integration In practice, many gates are manufactured on a single IC chip. Although there are no universally accepted definitions for level complexity, we define the level of complexity as follows

•

SSI (Small-Scale Integration)

1-10 gates on a chip

Simple gates, flip-flops, decoders, multiplexers, etc.

•

MSI (Medium-Scale Integration)

10-100 gates on a chip

Counters, shift-registers, 4-bit adders, etc.

•

LSI (Large-Scale Integration)

100-1000 gates on a chip

ALUs, simple microprocessors, higher-bit adders, etc.

•

VLSI (Very-Large-Scale Integration)

• •

ULSI (Ultra-Large Scale Integration) above 10000 gates on a chip WSI (Wafer-Scale Integration)

1000-10000 gates on a chip ALUs, 8-bit microprocessors, microcomputers, Digital signal processors, etc.

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Lemma of New Technology “ The principal applications of any sufficiently new and innovative technology always have been — and will continue to be — applications created by that technology ” — Herbert Kroemer

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Examples • The Transistor（1947） – was not just a replacement for vacuum tubes, it created the modern computer and the new industrial revolution.

• The Semiconductor Laser（1962） – has revolutionized the optoelectronics technology, it created optical fiber communication, CD, and DVD.

• The Nonvolatile Semiconductor Memory（1967） – has revolutionized the information storage technology, it created numerous portable electronic products. Solid State and Microwave Laboratory

From: S.M. Sze

Solid State and Microwave Laboratory

From: S.M. Sze

Computer Technology Development

Solid State and Microwave Laboratory

From: S.M. Sze

Progress in Microelectronics Year

1959

19701970

1999

Ratio

Design Rule (μm)

25

8

0.18

140↓

VDD (V)

5

5

1.5

3↓

Wafer diameter (mm)

5

30

300

60↑

Devices per chip

6

2 × 103

2 × 109

DRAM density (bit)

－

1k

1G

Nonvolatile memory density (bit)

－

2k

256 M

> 105 ↑

Microprocessor clock rate (Hz)

－

750 k

800 M

> 103 ↑

Transistor shipped / year

107

1010

1017

1010 ↑

Average transistor price ($)

10

0.3

10-6

10-7 ↓

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3 × 108 ↑ 106 ↑

From: S.M. Sze

Fundamental Challenge — Lithography • Wavelength limit of optical lithography – Can 193 nm ArF support 100 nm generation – λ ≈ minimum feature length

• Nonoptical lithography techniques – – – –

EPL EUV EBDW IPL

• Lithography-independent nanotechnology – Edge-defined MOSFET – Self-assemble – Self-organization Solid State and Microwave Laboratory

From: S.M. Sze

Economic Challenge

Solid State and Microwave Laboratory

From: S.M. Sze

Intellectual Power Rules the IT Society

Source of Power

Muscle Violence Money

2nd Wave Muscle

Money Wealth

IT Revolution

3rd Wave

The Rising Second Wave

Muscle

on i ut l vo Re al t gi Di ital

Money

Mind Mind

Mind

(Knowledge)

g Analo Wave

R 1980 2010

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ig D t s F ir C

c

1st Wave

Industrial Revolution

Se

Agricultural Revolution

1990

2000

The IT Revolution

Semiconductor Revolution

(Intelligence) ＝ (Size)×(Cost)×(Power)

IT Revolution

Figure of Merit

•1948: Invention of the Transistor •Digitization of Information •Moving from a Leading Industry to the Soil for all Industry

Internet Revolution •Self-developing Information System •An Ownerless Information System

Mobile Revolution •Ultimate Personalization of Information •Accelerates Human-oriented IT

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TOP 30 WORLD MARKETS IN YEAR 2020 Market

Sales ($Billions)

Market

Sales ($Billions)

★

Portable Data Communications

630.

Ultra-thin Monitor

170.

★

★

PC

470.

IC Card

165.

★

★

Mobile Phone Service

380.

Ground-Wave Broadcasting

160.

★

★

CPU

300.

DNA Agricultural Products

160.

★

Digital Contents Products

270.

Multi-Purpose Communication Equip.

155.

★

★

Magnetic Memory

250.

Semiconductor Equip.

150.

★

★

Electronic Commerce

250.

Electrical Vehicle

150.

★

Network Information Service

230.

Wall Ultra-thin TV

145.

★

★

High Density Mag. Memory Mat.

230.

Mobile TV

140.

★

★

Systems-On-Chip

210.

Direct inject. Vehicle

140.

★

Home Medical Equip.

210.

ITS Equipment

140.

★

Internet

200.

DNA Processed Food

135.

★

CATV

200.

LCD

120.

Intelligent Transportation Syst.

190.

Clone

115.

Agents Software

180.

Fuel-Cell Car

110.

★

★

Microelectronics related 22 Markets: $5 trillions.（Nikkei Business 1999）.

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The IC manufacturing

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Semiconductor Manufacturing Process

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Semiconductor Manufacturing Process

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Semiconductor Manufacturing Process

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Semiconductor Manufacturing Process

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IC Packages DIP

PGA

Dual Inline Package

SOJ

Pin Grid Array

PLCC

Small outline J-Leaded Package

Plastic Leadless Chip Carrier

SOIC

Small Outline IC

PQFP

Plastic Quad Flat Package

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TSOP

Thin Small outline Package

BGA

Ball Grid Array

高科技產業發展趨勢

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Functional device scales Nano-scale

Micro-scale

SETs GMR layers nanotubes

quantum dots in lasers

atoms

transistors

molecules

0.1

1.0

Field emitters

10

100

Nanometers Solid State and Microwave Laboratory

1000

10,000

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Atomic Image by Scanning Tunneling Microscopy

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Atomic Image by STM

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微影(lithography) 之定義 以光子束、電子束或離子束經由光罩(Mask) 或直接對晶圓上之光阻(resist)照射，使光阻產 生極性變化、主鏈斷鏈或主鏈交接等化學作 用，經顯影後將光罩或直寫之特定圓案轉移至 晶圓上。

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微米-微影技術(Micro-lithography)

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微影(lithography) 之定義 TSMC 0.15 CMOS Technology

一個製程所需要之微影次數或所需要光罩之 數量來代表其半導體加工製程的難易程度 Solid State and Microwave Laboratory

微米-微影技術(Micro-lithography)

Commercial Step and Scan Exposure System

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微米-微影技術(Micron-lithography)

低壓及高壓汞(Hg)或汞-氙(Hg-Xe)弧燈(ArcLamp)在近紫外光波長範圍(350~450nm)有2 條光強度甚強之發射光譜線

1. 436 nm ---- G line 2. 365 nm ---- I line 解析度 1~0.5 微米

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微米-微影技術(Micron-lithography)

波長248 nm氟化氪(KrF)準分子雷射，解析度在 0.25~0.18 um

波長193 nm氟化氬(ArF) 雷射，解析度在 0.18 ~0.15um

末代光學之波長157 nm氟 (F2) 雷射，解析度在 0.1 um

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光學微影系統的解析能力

Depth of Focus=λ /2(NA)2 其中， NA為光學微影系統之數值孔徑(numerical aperture)；k1為一數值，與設備系統、光阻製程、光罩類 型、特殊技術之運用等有關。由上式可知：波長愈短時則 解析度愈佳，而設備的成本與光源的波長成反比，因此若 想得到較小的圖案定義能力，勢必要投資更多的資本購置 波長更短的微影設備。當所採用的光源波長固定時，該設 備之解析能力有一定範圍

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科學發展月刊

Phase Shift Mask Using the phase interference to improve the diffraction and resolution

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科學發展月刊

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光子與光學儀裝工程師學會(The Society of Photooptical instrumentation Engineers, SPIE)出版之光學 工程報導指出:

半導商業化量產之微影解析度將停留在0.15~0.13 um 相當長之時間，因為線路更細線化、晶片更微小 化，相當不易，且不易降低量產成本

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Molecular Circuit Micro-machine

MEMS

IR Filter

static electricity motor

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Carbon Nanotube Field-effect Transistors

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奈米微影 (Nano-lithography Techniques)

To circumvent the limitation caused by the diffraction effects of visible light, the following are being developed • X-ray lithography • Electron Beam Lithography

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Trend in DRAM production

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X-ray lithography

Why is this radiation of interest in lithography? In short, because of its ability to define very high resolution images in thick materials. The resolution comes from the extremely short wavelength, of the order of 0.01-1.0 nm, and the high penetration ability.

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X-ray lithography

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X-ray lithography X-ray 之來源 1. 電子束撞擊金屬靶極 : 電子束撞擊金屬靶極X-光：傳統X-光 是在真空中以電子束撞擊金屬靶(Cu, Mo, A1等)而得。

2. 同步幅射X-光:電子或帶電粒子進行加速度或減速度運動時， 即產生輻射。電子繞圓周運動，方向改變，速度減慢，此時有負 加速運動，可產生輻射，釋出能量。但因受磁場作用力增速，可 維持速度不變。電子運動速度較低時，幾乎在任何方向皆產生輻 射。速度接近光速，即相對論速度時，在電子圓周運動平面沿其 切線方向，有輻射產生，發散度甚低，且限制在一小張角、錐體 形之範圍內。此輻射稱之同步輻射，波長涵蓋範圍甚廣，其中含 X-光

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X-ray 之來源 3. 雷射誘發脈衝電漿X-光 :釔鋁紅榴石(Nd:YAG, Neodymium: Yttrium Aluminum Garnet)雷射，因其脈衝能量、脈衝間隔、功 率等能符合誘發電漿之需要。其未處理波長為1064奈米，可利用 倍頻器使操作波段改變，如二倍頻則為532奈米，目前最高有5倍 頻212.8奈米。 常見誘發電漿原理是利用雷射聚焦於板狀靶材，雷 射提供能量，切除靶材表面的原子，並使原子離子化 (Ionization)，在靶材表面形成一電漿柱(Plume)。雷射不斷提供能 量，並與電漿柱耦合(Coupling)，使電漿柱升溫並擴大。在電漿柱 溫度夠高時，可激出原子K, L內層軌域之電子，當外層軌域之高 能電子填補此缺位時，釋出對應之能量，發出X-光

http://pilot.mse.nthu.edu.tw/micro/ Solid State and Microwave Laboratory

X-光微影半陰影效應

非同步輻射X-光，或稱點光源，因準直性 不佳，會在圖罩上圖案邊緣擴散(Diffusion)， 在阻劑表面產生模糊陰影。如晶圓因應力、 受熱等而變型，圖罩至阻劑表面之間隙(Gap) 較設計間隙為大，半陰影效應將更嚴重。半 陰影效應常以二參數表示。一為半陰影模糊 (Penumbral Blur) p，二為側向偏移(Lateral Shift, Run-Out) d。同步輻射X-光準直性良 好，在平坦晶圓上，幾無半陰影效應。但在 不平之變型晶圓上，仍有輕微半陰影效應。

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同步幅射X-光

A Picture of CNTech Beamlines Solid State and Microwave Laboratory

A Picture of CNTech Beamlines

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X-ray lithography 優點： 1. 波長短，解像度高，具有奈米製程能力。 2. 對0.10 ~ 0.05微米線幅而言，其繞射現象甚小，可以忽略。 3. 聚焦深度大，製程寬容度佳。 4. 穿透能力強，圖罩上的污染、微粒不會轉印在晶圓上。可用較厚 的阻劑，適用深寬比(Aspect Ratio)甚大之圖案。 5. 可大範圍的有效照射。 6. 晶圓在X-光波長之折射率趨近於1，近於空氣或真空，X-光可近 直線穿透晶圓，無駐波效應，故不需抗反射塗佈。 7. 小型同步輻射X-光功率高，光準直性甚佳，幾乎無半陰影效應， 且可開出多道光束線，成本降低，可與光學照射競爭。

Solid State and Microwave Laboratory

X-ray lithography

缺點： 1. 傳統金屬靶及雷射誘發X-光光源功率低，準直性差。 2. 傳統金屬靶及雷射誘發X-光有半陰影效應。 3. 縮小步進機製作不易。 4. 晶圓對準問題較不容易解決。 5. 圖罩製作不易。 6. X-光能量高，會加熱圖罩。

http://pilot.mse.nthu.edu.tw/micro/ Solid State and Microwave Laboratory

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E-beam lithography

電子束微影技術乃利用帶高 能量的電子群，經電磁裝置控制 方向後，照射於塗布感光性材料 (阻劑)的基板上，此時電子與阻 劑產生化學反應，在經過烘烤及 顯影步驟後，使阻劑內有／無電 子束反應的區域得以被區隔，阻 劑圖案因而顯現出來

Solid State and Microwave Laboratory

E-beam lithography

電子源 1. 熱游離發射(Thermionic Emission) 通常以鎢或六硼化鑭(LaB6)單晶體為電子源將該 材料置於陰極並且直接加熱，而所產生的電子束經 由電場加速後獲得能量。鎢電流亮度(A/cm2 sr)低， 真空度要求低(10-6 torr)，壽命短。六硼化鑭之電流 亮度較鎢高，真空度要求亦較高(10-8 torr)，壽命較 長，故目前廣為使用。

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E-beam lithography 電子源 2.場發射(Field Emission) 使用形狀尖銳的材料，並置於高電場環境下，所 以非常適合產生直徑極小的電子束，場發射以電場 吸出電子，較熱離子之電流亮度高，真空度要求亦 較高(10-9 ~ 10-10torr)，壽命亦長。較新的發展是使 用鋯/氧/鎢(Zr/O/W)合金以熱(Thermal)或冷(Cold) 場發射提供電子束，較LaB6之電流亮度可提高100 ~ 1000倍之多。 。

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E-beam lithography 電子散射效應

Solid State and Microwave Laboratory

Filament types

source type

brightness [A/cm²/sr] ~ 105

tungsten thermionic LaB6 thermionic ~ 106 thermal (Schottky) ~ 108 field emitter cold field emitter ~ 109

source energy spread Vacuum size [eV] [torr] 25µm 2-3 10-6 10µm 20nm

2-3 0.9

10-8 10-9

5nm

0.22

10-10

SPIE HANDBOOK OF MICROLITHOGRAPHY, MICROMACHINING AND MICROFABRICATION Volume 1: Microlithography, Chapter 2.2

Solid State and Microwave Laboratory

Beam Energy Influence 100 keV + Small scattering in resist + Small proximity effect

– High beam damage – Strong sample heating

20 keV + Small beam damage + Small sample heating

– Scattering in thick resist – Strong proximity effect

+ Best electron-optical performance 2 keV + No beam damage – High scattering in resist + No proximity effect – Needs very thin resists + High throughput (high resist sensitivity)

Solid State and Microwave Laboratory

Beam-blanking

Beam-blanker off

Beam-blanker on

Filament Anode +250V

Beam-blanker Aperture

Blank Frequency = 10MHz Solid State and Microwave Laboratory

GND

Beam deflection - electrostatic and magnetic Either magnetic or electrostatic fields can be used to focus electrons just as glass lenses are used to focus rays of light. Electro-magnetic

Electro-static

F = q · (E + v × B) (Mark A. McCord, Introduction to Electron-Beam Lithography, Short Course Notes Microlithograph 1999, SPIE's International Symposium on Microlithography 14-19 March, 1999; p. 22)

Solid State and Microwave Laboratory

EBL Writing Strategies Round (Gaussian) beam

Shaped beam

versus

Raster scan

Vector scan versus

(Mark A. McCord, Introduction to Electron-Beam Lithography, Short Course Notes Microlithogr 1999, SPIE's International Symposium on Microlithography 14-19 March, 1999; p.63)

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E-beam lithography 常用之光阻

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The Tri-layer PR System and The Dose Test

LO100nm

PMMA2% 1.0

Co-PMMA Normalized Development Depth(%)

HI500nm

LO180nm

PMMA5%

PMMA2 PMMA4 CoPMMA

0.8

0.6

0.4

0.2

0.0

0

50

100

150 2

Electron Dose(uC/cm )

Solid State and Microwave Laboratory

200

E-beam lithography 鄰近效應(proximity effect)

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E-beam lithography 鄰近效應(proximity effect) 修正方法

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Raith-150 e-beam Writer

Solid State and Microwave Laboratory

Raith-150 e-beam Writer - Beam resolution (30µm aperture) : 2nm @ 20 KeV - 150pA, 4nm @ 1 KeV - 70pA => > 3000 A/cm² beam current density - Energy range 200 eV - 30 KeV, continuous - Probe current 4 pA - 10 nA ( 6 x electromagnetic aperture selection ) probe current drift < 0.5 %/h - Electrostatic beam blanker >10 MHz switching time - Distortions K2SiO3 + 2H2

(100)

d (111) a

! Orientation selective etch of silicon occur in hydroxide solutions because of the close packing of some orientations relative to other orientations –Density of planes : > > –R(100)< R(110)< R(100) ! direction etches faster than direction –R(100)= 100 R(111) –It is reaction rate limited

2003 J.P. Krusius, D.G. Ast, Cornell Univesity

Solid State and Microwave Laboratory

Summary of Wet Etches

Wet etches are selective isotropic and fast –Usually reaction rate limited Advantages

Disadvantages

Simple & Fast

Undercutting

Selective

Strain at interface can enhance undercutting and lift-off film

Reproducible

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Why Dry Etching

Dimensional control in etching small geometries---necessary for advanced semiconductor devices and micromaching---is an important topic in micro-technology. To etch these structures, dry plasmaassisted etching increasingly used due to (1) the achievement of etch directionality without using the crystal orientation as in the case of wet etching of single crystal like silicon or GaAs (2) the ability to faithfully transfer lithographically defined photoresist patterns into underlying layers (3) high resolution and cleanliness.

Solid State and Microwave Laboratory

Dry Chemical Etching Mechanisms

Plasma flowing gas

1. Reactive species generation 1. Generation of etchant species

2. Diffuse to the solid 3. Adsorption at the surface 4. Reaction at the surface 5. Reactive cluster desorption

2. Diffusion to surface 3. Adsorption

6. Diffusion into bulk gas 5. Desorption

6. Diffusion away from the surface 4. Reaction

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Sample

Gas Phase (Dry) Etching Plasma etching has largely replaced wet etching in IC technology because of the directional etching possible with plasma etch systems ! Directional etching is due to presence of ionic species in the plasma and the electric field that direct them normal to the wafer ! Systems can be designed so that reactive chemical components or th ionic components dominate ! Inmost cases plasma systems use a combination of ionic and reactive chemical species acting in a synergistic manner leading to an etch rate that is much faster than the sum of individual etch rates when they are acting alone !Reactive chemical component of plasma etching often has high selectivity !Ionic component of plasma etching often has directionality !Utilizing both components, directionality could be achieved while maintaining an acceptable selectivity

Solid State and Microwave Laboratory

Dry Etching Types and Equipment Dry Etching Ion beam methods -Triode Set-ups

Glow discharge Methods -Diode Set-up

Physical etching Plasma etching Reactive gas plasma

Reactive ion etching sputtering Reactive gas plasma

Inert gas

Ion milling Inert gas ion

Ion beam assisted chem.etch Inert gas ion

Reactive ion beam etching Reactive gas ion beam

0.01-0.2 Torr

0.2 – 2 Torr Low energy bombard.

Sputter etching

High energy

No reactive neutrals

High energy

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Reactive neutrals

Some

-3 Torr 10-4-10 reactive

Review of RF Plasmas

!Application of electric field across two electrodes gas !Atoms/molecules are ionized, producing positive ions and free electrons, creating a plasma !Voltage bias develops between the plasma and electrodes because of the difference in mobilities (masses) of electrons and ions !Plasma is positively biased with respect to the electrodes Pressure:1 mTorr –1 Torr Energy:RF Source @ 13.56 MHz

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RF Plasma Potential Profile !Sheaths form next to electrodes and voltage drops occur at sheaths corresponding to dark region !Electrodes capacitively couple to plasma !Ions respond to the average sheath voltage while the electrons respond to instantaneous voltage !If electrodes have equal areas, the voltage drop at the sheaths are symmetrical !If the electrodes have un-equal areas, the voltage drop between the sheaths and the electrodes are asymmetrical with a much larger voltage drop occuring at the smaller electrode –Two capacitors in series

Solid State and Microwave Laboratory

Review of Plasma Processes

For a plasma with inlet flow of molecule AB, Plasma processes are

Dissociation

e* + AB →A + B + e

Atomic Ionization

e* + A → A++ e + e

Molecular Ionization e* + AB →AB++ e + e Atomic Excitation

e* + A → A* + e

Molecular Excitation e* + AB → AB* + e

Solid State and Microwave Laboratory

Plasma Etch Methods for Various Films

Compounds

! Most reactant gasses contain halogens – Cl, F, Br, or I ! Exact choice of reactant gasses to etch each specific film depends on – Ability to form volatile by-products – Etch selectivity to resist and underlying films – Anisotropicity ! Boiling points are good indicators of volatility of species –Lower boiling point, higher tendency to evaporate

Vapor Pressure (Torr)

AlF3

1 (1238 ℃)

InCl3

10-8 (100 ℃) 10-4 (180 ℃) 10-2 (250 ℃)

GaCl3

2 (50 ℃)

AsCl3

40 (25 ℃) 290 (100 ℃)

AlCl3

2 x 10-4 (25 ℃) 1 (100 ℃)

PCl3

400 (57 ℃)

AsF3

750 (56 ℃)

Solid State and Microwave Laboratory

Comparing Wet vs. Dry Etching (1)

Parameter

Dry Etching

Wet Etching

Directionality

Can be highly directional with most materials

Only directional with single crystal materials

Production-line automation

Good

Poor

Environmental impact

Low

High

Masking film adherence

Not as critical

Very critical

Cost chemicals

Low

High

Selectivity

Poor

Can be very good

Materials that can be etched

Only certain materials can be etched

All

Radiation damage

Can be severe

None

Solid State and Microwave Laboratory

Comparing Wet vs. Dry Etching (2) Parameter

Dry Etching

Wet Etching

Cleanliness

Good under the right operational conditions

Good to very good

CD control

Very good (< 0.1µm)

Poor

Equipment cost

Expensive

Inexpensive

Sub micron feature

Applicable

Not applicable

Typical etch rate

Slow (0.1 µm/min, isotropic )

Fast (1 µm/min, anisotropic)

Theory

Very complex, not well

Better understood

Operating Parameters

Many

Few

Control of etch

due to slow etching

Difficult

Solid State and Microwave Laboratory

Micrograph of Silicon Plates with a Gap of 2µm.

Solid State and Microwave Laboratory

Isotropic Etch of Silicon

Solid State and Microwave Laboratory

0.25-µm-diameter InP Dots

0.4-µm-wide InP Slabs

Solid State and Microwave Laboratory

Nano-structure Etching on 0.2-mm Photonic-crystal Pattern

Pattern: 0.2-µm holes Etched thickness: 5000 Å

Material: GaAs Mask: Si3N4 Etching Time: 150~200 Å/min Gas species: BCl3, CH4, Ar Working Pressure: 10 mTorr RF power: 50 Watts

Solid State and Microwave Laboratory

Deep Trench Etching on Si

Solid State and Microwave Laboratory