X-ray diffraction techniques for thin films Rigaku Corporation Application Laboratory Takayuki Konya 1 Today s contents (PM) Introduction X-ray diffraction method Out-of-Plane In-Plane Pole figure Reciprocal space mapping High resolution rocking curve X-ray reflectivity 2 1
Advantage of X-ray diffraction (XRD) method Probed depth control by incidence angle Nondestructive Measurement under atmosphere pressure 3 What can we see? a,b,c Thickness, Density, Roughness Phase Identification Interface, transition layer, etc Crystal structure Crystal quality, lattice parameter, etc Crystal orientation Single: orientation relation of substrate & film Poly: preferred orientation? (hkl) ρ, σ d 4 2
What XRD reveals Position and coordinate of reciprocal lattice points lattice constant crystal orientation lattice distortion K spread of reciprocal lattice points degree of preferred orientation Shape of a reciprocal lattice distribution crystal perfection defects mosaicity 5 Structure parameters Structure Parameter Order Analysis Method Thickness 1~10 3 nm Precision :~several % Xray Reflectivity Density H 2 O~Heavy Metals Xray Reflectivity Roughness 0.2~several nm Xray Reflectivity Phase ID - In-Plane XRD Out-of-Plane XRD etc Crystal System - In-Plane XRD Out-of-Plane XRD etc Lattice Constant ~several nm Precision : 0.05~0.00005nm In-Plane XRD Out-of-Plane XRD etc Crystal quality Poly~Single, Perfect In-Plane XRD Crystals Out-of-Plane XRD etc Preferred Random~Preferred Orientation Orientation ~Single Crystal Pole Figure ect Orientation Relation Relation between Film & Substrate Rocking Curve Reciprocal Space Map etc Layer Structure Crystal Structure 6 3
Today s contents (PM) Introduction X-ray diffraction method Out-of-Plane In-Plane Pole figure Reciprocal space mapping High resolution rocking curve X-ray reflectivity 7 Today s contents (PM) Introduction X-ray diffraction method Out-of-Plane In-Plane Pole figure Reciprocal space mapping High resolution rocking curve X-ray reflectivity 8 4
Difference between Scan Modes The orientation of observed crystal plane depends on scanning mode. Out-of-Plane scan Film scan In-Plane scan Observed plane is.. Observed plane is.. parallel to the surface tilting (changing during a scan) perpendicular to the surface 9 What is In-Plane XRD? The detector moves parallel to the surface. Incident x-ray Diffracted x-ray α Diffraction angle 2θ B Reflected x-ray Grazing incidence (fixed angle) Observing planes are perpendicular to the surface. 10 5
Outward of In-Plane Attachment Scanning motion is completely perpendicular to θ/2θ scan. θ/2θ scan In-Plane measurement (2θχ/φ scan) 11 In-plane effect Intensity (cps) 100 80 60 40 20 0 20 022 In Plane 111 30 40 50 311 400133 422 60 2θχ/φ (degree) 70 80 90 In-Plane 220 Intensity (cps) 111 1400 1200 1000 800 600 400 200 0 20 111 30 40 Out of Plane 220 113 004 331 224 50 60 2θ/ω (degree) 70 80 90 Out-of-plane poly-si Glass 12 6
Probed depth control? 1 extinction distance (nm) 1000 100 10 0.1 0.01 0.001 0.0 0.2 0.4 0.6 0.8 1.0 0.0001 incident angle (degree) Sample:Al Wavelength:1.54056Å(CuKα1) 13 Surface & Interface Structure 250 In-Plane XRD Intensity (cps) 200 150 100 50 0 30 Al(111) 40 Al+Cu Al+Cu Cu(111) Cu(200) 50 60 2θχ/φ(degree) Incident angle 0.2 deg. 0.5 deg. Al(220) Al(311) Cu(220) Al(222) 70 80 ~300nm Transition layer Al Al+Cu SiO 2 Si (substrate) Cu Ta 14 7
Today s contents (PM) Introduction Advantage of reciprocal lattice vector X-ray diffraction method Out-of-Plane In-Plane Pole figure Reciprocal space mapping High resolution rocking curve X-ray reflectivity 15 Single crystal and random orientation Single crystal Fiber orientation Random orientation 16 8
Orientation conditions and pole figure (111) pole figure (220) pole figure α=90 β=0 α=90 β=0 Random orientation β=90 β=270 β=90 β=270 β=180 β=180 {111} fiber orientation α=90 β=0 β=90 β=270 β=180 α=90 β=0 α=70.5 α=90 β=0 β=90 β=270 β=180 α=90 β=0 α=35.3 (111) single crystal β=90 β=270 β=90 β=270 β=180 β=180 17 Today s contents (PM) Introduction Advantage of reciprocal lattice vector X-ray diffraction method Out-of-Plane In-Plane Pole figure Reciprocal space mapping High resolution rocking curve X-ray reflectivity 18 9
Reciprocal space mapping Diffraction intensity distribution is plotted on reciprocal space. 2θ/ω g hkl Δω k g 2θ/ω k o ω 19 Epitaxial layer structures Relaxation Strain Misorientation 00l cubic[112] 00l substrate[001] cubic[112] 00l film[001] tetragonal[112] hh0 hh0 hh0 20 10
Reciprocal space mapping Mosaic spread GaAs115 q y / -1 AlGaAs115 Broadening in direction of sample rotation Mismatch (strained) q x / -1 Broadening in direction of radial scan 21 Today s contents (PM) Introduction Advantage of reciprocal lattice vector X-ray diffraction method Out-of-Plane In-Plane Pole figure Reciprocal space mapping High resolution rocking curve X-ray reflectivity 22 11
High- resolution rocking curve The differences of lattice spacing between the substrate and epitaxial films are observed. Thickness and composition ratio of epitaxial films (when the degree of relaxation is known. ) 2θ/ω K ghkl k g log(i ) k o Δ2θ/ω 23 When the sample has multilayer structure Complicated oscillation composed of oscillation from each layer is observed. Reflectivity 10-1 10-2 10-3 10-4 10-5 10-6 GeSi GeSi Si (004) Ge x Si (1-x) 50nm Ge x Si (1-x) 300nm x=0.015 Si substrate 10-7 -2000-1000 0 1000 Deviation Angle (arcseconds) x=0.050 x=0.015 24 12
When the sample has superlattice structure Satellite peaks are observed. 10-1 10-2 0 GaAs (004) Reflectivity 10-3 10-4 10-5 10-6 10-7 10-8 -3-2 -1 1 2 3 4 GaAs 5nm In x Ga (1-x) As 5nm GaAs substrate 10L -8000-4000 0 4000 8000 Deviation Angle (arcseconds) x=0.200 25 How to interpret the profile Si substrate (004) 10-1 2SiGe mismatch Reflectivity Intensity 10-2 1SiGe mismatch 10-3 Oscillation period 10-4 1SiGe thickness 10-5 Ge x Si (1-x) 50nm x=0.050 Ge x Si (1-x) 300nm x=0.015 Si substrate 10-6 10-7 Oscillation period 2SiGe thickness -2000-1000 0 1000 diffraction Deviation Angle angle (arcseconds) (Δarcsec.) 26 13
Today s contents (PM) Introduction X-ray diffraction method Out-of-Plane In-Plane Pole figure Reciprocal space mapping High resolution rocking curve X-ray reflectivity 27 What reflectivity reveals X-ray reflectivity nondestructively reveals - layer structure of multi layers - thickness (1 to 1000nm) - density as an absolute value - surface and interface roughness Interface roughness thickness layer 1 thickness layer 2 density substrate 28 14
How to interpret the profile Critical angle c Density Reflectivity 10 0 10-1 10-2 10-3 Amplitude of 10-4 oscillation Contrast 10-5 of density 0 2 Period of oscillation Thickness 4 2θ/θ (degree) roughness 1 roughness 2 roughness 3 Decay of amplitude Interface roughness 6 8 density 1 density 2 density 3 layer 1 layer 2 substrate Decay of reflectivity Surface roughness thickness 1 thickness 2 29 X-ray reflectivity measurement of TiN film 10 0 TiN SiO 2 Si Reflectivity 10-1 10-2 10-3 10-4 10-5 10-6 10-7 Simulation Experimental Layer density (g/cm 3 ) Thickness (nm) Roughness (nm) TiN 3.680 1.230 1.420 TiN 2.900 8.400 1.000 SiO 2 2.260 127.700 0.220 Si substrate 0.0 0.5 1.0 Grancing angle α (degree) 1.5 Coating layer 2.0 30 15