Surface Analysis by -AES -XPS -SIMS -XRD -SP1
대표적인분석방법 장비 입사광 측정신호 분석깊이 최소분석면적 원리 취득정보 XPS 특성 X-선 광전자 10~100A 100μm 광전자의측정으로에너지준위결정 화학결합상태, 원소분석 UPS 자외선 광전자 수십A 100μm 광전자의측정으로에너지준위결정 진동주파수, 화학결합상태 AES 전자 Auger전자 20~60A 20nm Auger 전자의측정에의한원소분석 표면원소분석 SIMS 이온 2차이온 50~300A 1μm 2차이온에의한질량분석 표면층의고감도원소분석 ISS 이온 산란이온 1nm 1mm 일정각도로산란된이온의측정 표면원소분석 SEM 전자 2차전자, X-선 100A 10A 가속전자에대한 2차전자나 X-선 표면의형상, 원소조성 TEM 전자 투과전자 50A 10A 투과전자의세기에따른명암영상 격자구조, 결함의관찰 STEM 전자 투과전자, X-선 10A 3A 투과전자의방출 X-선의영향 미소영역의화학조성 RBS He, H입자 산란이온 20~200A 1mm 후방산란된이온의세기측정 정성, 정량분석 LEED 전자 산란전자 수원자층 수백μm 표면 2차원격자에의한산란 표면구조, 흡착원자배열 EPMA 전자 X-선 1μm 1μm 특성 X-선에의한원소분포 원소정량 SAM 전자 Auger 전자 10~100A 0.1μm 방출된 Auger전자로영상구성 화학성분분포측정 AES : Auger electron Spectroscopy SAM : Scanning Auger Microscopy RBS : Rutherford Backscattering Spectroscopy XPS : X-ray Photoelectron Spectroscopy (ESCA) STEM : Scanning Transmission Electron Microscopy SEM : Scanning Electron Microscopy 표면분석금속 ( ~ 20A ), 유기물, 고분자물질 ( ~ 100A ) 의표면과계면의구성원소및화학적결합상태, 에너지준위등을알아내는기술
Auger Electron Spectroscopy (AES) AES (Auger Electron Spectroscopy) 수백 A 크기의 Electron beam을재료의표면에입사 방출되는 Auger electron의에너지를측정하여재료표면을구성하고있는원소의종류및양을분석해내는표면분석장비이다.
Surface Sensitivity 표면선택성 (Surface Sensitivity) 투과거리가긴 x-ray는표면이하깊은곳에서발생해도표면밖으로나올수있지만대부분의 Auger 전자는짧은투과거리때문에표면근처에서발생하는것만초기의에너지를보유한체밖으로나올수있다
Schematic diagram of AES Auger analysis Data acquisition 중샘플표면에불순물의흡착을방지하기위해 10-8 torr 이하의 UHV chamber 내에서이루어짐. Electron gun : Primary electron beam Electron energy analyzer and detector : measurement and collection of emitted electrons. Sample manipulator : to locate the area of interest at the analyzer focal point. Ion gun : cleaning of the sample and for depth profiling
Instrument Physical Electronics Model 25-130 CMA
Electron source & analyzer Electron sources (beam dia.) - Tungsten filament (3~5μm) - LaB 6 crystal (<20nm) - Field emission gun (<20nm) High resolution (min dia) - Beam voltage (higher) - Beam Current (lower) Auger electron scan -V -V Error (sample position) : roughness Cylindrical Mirror Analyzer(CMA) - Auger electron E A V - E/E mode N(E)*E spectrum
AES 분석 - 원소의정성및정량분석 (Auger peak) - 2차전자를이용한표면관찰 (SEM) - Depth profiling(ion beam) - line scan - Image mapping
Line scan & image mapping
원소의정성및정량분석 정성분석 I 정량분석 z = Ibσ(1 + rm ) γtd Ni ( z) exp( dz λm PA / S A X A = 100 i( P i / S i ) i ) X A : A 의 atomic%, P: Peck to peck, S:sensitivity factor
AES spectrum AES spectrum -Noise 혹은다른원소로부터의 peak중첩을고려해야함 -Spectrum 해석 (S/W) Depth profile data 획득 Chemical shifts in AES profiles -분석가능하지만일반적으로 ESCA사용 (Auger process중 3개의전자준위에의한간섭때문 )
Sputtering rate Sputtering rate -sputter angle, ion energy, ion species, sample composition, sample density -SiO 2 의 sputtering 속도와비례적인방법으로구함 v ( AlN) = v( SiO ) 2 S( AlN) S( SiO ) 2 / / N( AlN) N( SiO ) V : sputter 속도, S : sputter yield, N: atomic number density 2
Depth resolution -Unidirectional Sputtering 으로인한 Surface roughness 증가 ( depth Z)
AES_PHI660 system conventional SEM -Lanthanum hexaboride(lab6) cathode -Secondary electron detector -CMA(cylindrical mirror analyzer) Very small spot sizes (down 20 nm dia.) Sputtering (ino gun) - Remove surface contamination - Remove material for depth profiling Modes of operation -Survey - Line profile - Elemental mapping - Depth profile
Example1 SAM Image [air TiO 2 (24 nm) Ti (1 nm) Ag (17 nm) TiO 2 (24 nm) {TiO 2 (24 nm) Ti (1 nm) Ag (13 nm) TiO 2 (24 nm) } 2 glass] 100 80 2 kv Ar + (3.3 nm SiO 2 /min) Si Ag O O SEM Image Atomic % 60 40 Ti Ag Ti Ag 20 0 0 10 20 30 40 50 60 70 80 Sputter Time (min)
Summary 주요적용범위 표면 ( 수A ) 에대한조성분석 박막의깊이방향원소분석 (depth profiling) 미소부위조성분석 (point analysis) 이차원적인원소분포도측정 (image mapping) line scanning 장점및단점 표면선택성우수 (~25A ) 평면분해능이우수 ( 전자빔의집속 ~ 수백A ) 깊이에따른조성및결합상태분석 검출한계 (0.1at%) 이하농도분석이어려움 Bulk 절연체의분석이어려움 (Charging effect)
XPS
Overview X- 선광전자분광기는시료의표면으로부터 100A 의깊이에관한정보를얻을수있는표면민감성분석장비. 일정한에너지를가지는 X 선 ( 광자 ) 을시료에쬐면시료로부터광전자 (photoelectron) 들이방출되는데이광전자들의운동에너지를측정하면광전자를시료로부터방출하기위해필요한에너지인 binding energy 를알수있음. 광전자를방출하는원자의고유한성질인이 binding energy 의측정으로부터원소의정성및정량분석, 그리고화학결합상태등을분석하는기법. 사용예 : 반도체소재, 박막, 금속, 화합물, 유리, 촉매, 고분자및나노소재등의표면및계면특성분석
XPS(X-ray Photoelectron Spectroscopy) XPS 는이기술을개발한스웨덴 Uppsala 대학교의 Siegbahn 에의해붙여진 ESCA(Electron Spectroscopy for Chemical Analysis) 라는별명으로흔히알려져있으며그원리는다음과같다. ESCA 는전자를이용한표면분석방법으로표면의원소구성비 (elemental composition) 와각원소의화학결합상태 (chemical state) 까지알아낼수있다. 모든원소들의전자는 K 각, L 각등각 (Shell) 구조를이루고있으며, 그내각전자들은각기독특한에너지준위 (Binding Energy) 를가지고있다. EX) 산소의 1s 전자는결합에너지가 531eV 이고탄소의 1s 전자의결합에너지는 284eV, 실리콘원자의 2p 전자는 99eV 의결합에너지를가지고있다. 이와같이각원소마다내각전자들의결합에너지가다르기때문에, 내각전자들의결합에너지를측정하면어떤원소가있는지를유추할수있다. 이내각전자의결합에너지를측정하는방법은원소에 X-ray 를쏘여주어, 광전효과 (Photoelectric effect) 에의하여튀어나오는내각전자의운동에너지를측정함으로써알아낸다. 이렇게측정된전자의결합에너지와알려진원소들의내각전자결합에너지를비교함으로써그전자가어느원소의어떤내각으로부터나왔는지알아낼수있고, 따라서시료내에존재하는원소성분을알수있는것이다. 같은원소라도화학결합상태가다르면내각전자의결합에너지도조금씩변화하는데이것을 Chemical shift 라한다. 이현상은화학결합에의해최외각전자의분포가바뀌므로이에따른정전기적상호작용에너지때문이라고풀이된다. 이 Chemical shift 현상을이용하면전자의결합에너지를정확히측정함으로써원소의성분만이아니라그원소의화학결합상태까지알아낼수있다.
Photoelectric effect Ek = hv -EB -W0 Ek : Kinetic energy of photoelectron hv : Photon energy EB : Binding energy of the electron W0 : Work function of the material X-ray: Mg과 Al의 Kα선텅스텐필라멘트로부터방출되는열전자가속되어 target물질에충돌 target물질의특성 X선발생 Mg의 Kα선은 1253.6eV, Al은 1486.6eV
Kinetic energy F= qe =m(v²/r) F : Force V : Speed R : trajectory radius E : electrical fields established by U potential m : electron mass q : electron charge
Energy level diagram Principle of ESCA
X-Ray Photoelectron Spectrometer Samples are irradiated with monochromatic X-rays which cause the ejection of photoelectrons from the surface. The electron binding energies, as measured by a high resolution electron spectrometer, are used to identify the elements present and, in many cases, provide information about the valence state(s) or chemical bonding environment(s) of the elements thus detected. The depth of the analysis, typically the outer 3 nm of the sample, is determined by the escape depth of the photoelectrons and the angle of the sample plane relative to the spectrometer. Busan Branch
Surface sensitiveness X-ray Beam Electrons are extracted only from a narrow solid angle. X-ray penetration depth ~1mm. m. Electrons can be excited in this entire volume. 1 mm 2 10 nm X-ray excitation area ~1x1 cm 2. Electrons are emitted from this entire area not attenuated attenuated by exp[-d/λ(e, matrix)cosθ] top layer d Bulk layer Busan Branch
Surface sensitiveness The dependence of electron mean free path on electron energy
Auger peak shifts The photoelectron kinetic energy is depending on the source nature. The Auger electron kinetic energy is independent of the source nature. Changing the source will easily distinguish between photoelectrons and Auger el
Auger transition
Ghost peak hν photons from the X-ray source are produced by electron bombardment on an anticathode. If anticathode is slightly oxidised, oxygen atom will be excited. The specimen is then excited by two sets of photons and it will in response generate two superimposed spectra. Contamination Mg Al O Cu Al +233 -- +961.7 +556.9 Mg -- -233 +728.7 +323.9
Practical approach Binding energy 전자의계수율 [counting rate, cps(counts per second)] Survey spectrum High resolution spectrum Fermi energy
Example of result on SiO2 film Survey O1s Intensity(count) 14000 7000 0 Intensity(counts) (slurry) Intensity(counts) (DI) Intensity(counts) (ph2) Intensity(counts) (ph11) Intensity(count) 25000 20000 15000 10000 5000 0 0 200 400 600 800 1000 1200 Binding Energy [ev] 528 530 532 534 536 538 540 Binding Energy [ev]
SIMS
What is SIMS (Secondary ion mass spectroscopy)? 수 kev ~ 10keV 로가속된이온빔을재료의표면에입사시켜방출되는 2 차이온들의질량을측정하여재료표면을구성하고있는원자및분자의종류및양을분석하는표면분석장비이다. 이온원으로는 Ar +, Ne +, He +, O -, N - 2 등이사용된다. Primary Ion Beam To mass spectrometer Beam of Secondary Ions to be Analyzed Extraction Lens Secondary Ions Samples
Composition 1. Cesium ion source 2. Duoplasmatron 3. Electrostatic lens 4. Sample 5. Electrostatic sector ion energy analyzer 6. Electromagnet mass analyzer 7. Electron multiplier / Faraday cup 8. Ion image detector SIMS 는일차이온을생성시키는일차이온발생장치 (primary ion source), 생성된일차이온을시료까지운반하는일차칼럼 (primary column), 시료로부터이차이온이생성되고, 가속되는시료장착부 (sample chamber), 생성된이차이온을에너지차와질량차등에의해걸러내고검출기 (detector) 까지운반하는이차칼럼 (secondary column), 그리고선별된이차이온의양을측정하는검출부로구분된다.
Primary ion source Primary column Duoplasmatron은주로산소이온을, 표면이온화일차이온발생장치는주로세슘 (cesium) 이온을발생시키기위해사용된다원소마다일차이온의종류에따라생성되는이차이온의양에커다란차이가있다. 대부분의 SIMS는두종류의일차이온발생장치를모두갖추고분석에적합한일차이온을선택할수있도록하고있다. 일반적으로음이온의형태로분석하고자할때는 133 Cs + 를, 양이온의형태로분석하고자할때는 16 O - 를일차이온으로사용하게된다. 생성된일차이온은가속전압에의해일차칼럼을통과하여시료로운반된다.
Ion beam sputtering sputtering 일차이온은약 350km/s의고속으로시료표면에충돌한다. 고속의일차이온이고체시료표면에충돌하게되면충돌에너지가시료표층부의입자들에전파되게되고일부입자들은 bonding 을끊고시료에서방출되게된다. ( 중성의원자, 분자이온의형태 ) 충돌에너지가전파되는깊이 : 10nm 입자가방출되는깊이 : 약 1nm 시료표면에적절한전압 (4.5~10kV) 을걸어주면방출된이차이온들은질량분석장치를향해가속된다. Ionization efficiency ( 이온화효율 ): sputtering에의해특정원소가이온화되는정도 Sputtering을이용하므로, 액체나기체시료는 SIMS로분석할수없으며, 고체시료의경우에도 He, Ne, Ar등불활성기체는 sputtering에의해이온화되지않기때문에분석할수없다.
Ion energy analyzer, mass analyzer SIMS는일반적으로고체시료를화학적처리과정없이바로분석한다. 따라서, 표면에서생성되는이차이온의종류는매우다양하며, 이때문에 SIMS의검출기에도달하는신호 ( 질량스펙트럼 ) 는매우복잡하여분석을어렵게만든다. 이를극복하기위해일반적인질량분석기에비해분해능이좋은대형편자장장치 (magnetic sector) 를장착한다. 또한분자이온의간섭을최소화하기위해질량과에너지에의해이중으로이차이온을걸러내는이중초점방식 (double focusing method) 을채택한다.
Secondary ion detector SIMS는 Faraday cup과전자증폭기 (Electron multiplier), 두종류의검출기를장착하고있어이차이온의강도에따라검출기의종류를선택할수있다. 주성분원소로부터적게는 ppm(100만분의 1) 또는 ppb(10 억분의 1) 이하의미량원소까지분석할수있다.
SIMS는 1ng 이하의시료로도분석이가능해일반적으로수 mg이상의시료가필요한다른질량분석기에비해극소량의시료로도분석이가능하다. Sputtering에의해이차이온을발생시키는분석기술은시료표면에도달하는일차이온의크기를매우작게조절하여마이크론단위의좁은영역에대한미세분석을가능하게한다. 분석하고자하는원소에대한화학적전처리과정이필요없이연마편이나연마박편상의광물을직접분석 (in-situ analysis) 할수있다. 따라서광학현미경에서얻어지는암석학적정보, 전자현미분석기등다른표면분석기기에서얻어지는광물화학적정보와 SIMS 에서얻어지는동위원소정보를 1:1로비교할수있다. 정량화의어려움, 복잡한질량스펙트럼에따른질량간섭등이있다. 정량화의어려움은가능한한분석하고자하는시료와동일한조성과구조를갖는표준시료를사용하여, 질량간섭문제는높은질량분해능을사용하거나이중초점방식을이용하여부분적으로해결가능하다. 질량분해능을크게하면서도운반효율을높게유지하기위해서는기기를대형화시켜야한다.
Mass spectra 시료표면분석 깊이방향분석 동위원소분석 질량분석 표면분석 (Static SiMS) : 넓은물질의 10~20 으로부터얻어지는양이온, 음이온질량스펙트럼으로부터표면분자의성분을분석하는방법
Static SIMS (surface analysis)
Depth profiling Trace metal contamination in SiO2 수직분표분석 (Dynamic Sims) : 이온빔을이용하여표면을깎아내려가는동안깊이방향으로원소의분포도를측정하는분석방법.
Dynamic SIMS (depth analysis)
Ion imaging Image dimensions : from 100um to less than 10um 이미지분석 (Imaging Sims) : 표면분석중에발생되는이차이온을이미지모드로바꾸어특정영역에서의조성및균일도를분석하는방법불균일촉매, 전자, 재료, 반도체, 전극, 금속, 재료, 고분자등의표면조성, 산화상태등을분석하는데쓰인다. 불균일촉매, 전자, 재료, 반도체, 전극, 금속, 재료, 고분자등의표면조성, 산화상태등을분석
Imaging SIMS (spatial analysis)
SIMS VS XPS + higher sensitivity + More direct identification of organics + faster imaging & depth information + differentiation of isotopes - More complex elemental quantification Application Surface coatings Surface treatments Electronic components Semiconductors (GaAs, Si) Electrodes & sensors Catalysts Adhesives Lubricants Packing materials Corrosion studies Polymer, Ceramic, Lubricants, Biological Catalysts, Semiconductor, Thin Film, Corrosion Studies, Molecular information, Organic, Inorganic
X-Ray Diffraction (XRD)
회절 (Diffraction) 입자의진행경로에틈이있는장애물이있으면입자는그틈을지나직선으로진행한다. 이와달 리파동의경우, 틈을지나는직선경로뿐아니라그주변의일정범위까지돌아들어간다. 이처럼 파동이입자로서는도저히갈수없는영역에휘어져도달하는현상이회절이다.
Bragg s Law n l = 2 d Sin q
Basic Features of Typical XRD Experiment
Application of XRD Nondestructive technique Measure thickness of thin films and multi-layers Determine the orientation of a single crystal or grain Find the crystal structure of an unknown material Measure the size, shape and internal stress of small crystalline regions Detection limits: ~3% in a two phase mixture; can be ~0.1% with synchrotron radiation
Several atomic planes and their d-spacings in a simple cubic
XRD pattern of NaCl powder
Phase Identification
Phase analysis 같은물질이라도상이다르면물리적, 화학적성질이다름. Ex) α-sio2, β-sio2, α-al2o3, γ-al2o3, δ-al2o3, rutile(tio2), anatase(tio2), brookite(tio2), Austenite, ferrite 등
Residual stress in thin film M C E
Residual stress in thin film do (hkl) planes dhkl σ σ Unstressed crystal z Crystal subjected to biaxial stress y εzz = 탄성변형시, 면간거리 (dhkl) 의변화 면간거리측정을통한변형률계산 Hooke s law를이용한응력계산
Merits of using X-Ray Diffraction for residual stress Non-destructive Specific phase Desired crystallographic and/or sample orientations Penetration depth (~10μm) surface Small area (~100µm)
Surfscan SP1 TBI Operations and Overview Course KLA-Tencor 660 Alder Drive Milpitas, CA 95035
How does the Surfscan work? Illuminates wafer with scanning laser Uses normal incidence for 62X0 (SP1) Grazing-angle incidence for 64X0 (SP1 TBI ) Collects scattered light from particles Sizes and counts particles Accepts or rejects and then sorts wafers Displays information and writes information to file
Dark field and bright field basic definitions Dark field detection: refers to the collection and registration of scattered radiation. Bright field detection: refers to operations performed on the reflected light.
LPDs & Haze Particles are High Amplitude & High Frequency Haze is Low Amplitude & Low Frequency Particles PMT Output Signal Haze Time/Position
Fundamentals of Light Scattering Light from laser illuminates particles on wafer and surrounding surface Particles and surface scatter light simultaneously Maximize detection of particle scatter and minimize detection of surface scatter
SP1 TBI Optics & measurement principle Detector Laser Static Optics Wafer Translation Rotation Moving Sample
Detector B Dark Field vs. Bright Field (Scattered Light vs. Reflected Light) Scattered Light (Dark Field) Detector A (Dark Field) Reflected Light (Bright Field) Scattered Light (Dark Field) Incident Light Defect
Two Dark Field detection channels increase sensitivity and dynamic range
Surface scattering (haze) limits ability to detect particles on unpatterned wafers. Photoelectrons from PMT photocathode 200 150 100 Particle signal Threshold level Noise 50 Background (100 photoelectrons) 0 0 2000 4000 6000 8000 10000 12000 14000 Position in μm
Light Scattering Inspection Process Collector Dark Field / Bright Field Detector Scan Point Defect Surface Information Surface Data Display Defect Display
LPDs & Areas scatter light into different polar angles narrow collector wide collector Scattering Intensity large PSL sphere small PSL sphere Si Surface 0 20 40 60 80 Scattering Polar Angle [degree]
Different defect types scatter light into different polar angles... allowing distinction of defect types (particle) (crystal defect)
Distinction of Defects with multiple DF-Collectors DFW vs DFN Size 3000 2500 2000 DFN Size 1500 1000 500 0 0 200 400 600 800 1000 1200 1400 1600 DFW Size DFN/DFW Defect Distribution 20 18 16 14 Frequency [#] 12 10 8 6 4 2 0 0.0 0.4 0.7 1.1 1.4 1.8 2.2 2.5 2.9 3.2 3.6 4.0 DFN/DFW ratio [] 4.3 4.7 5.0 5.4 5.8 No Particles