FREQUENCY CHARACTERISTICS: A SOURCE OF INFORMATION IN PHOTOACOUSTICS Mirosław Maliński Department of Electronics and Computer Studies Technical Univeristy of Koszalin, Poland

Contents Introduction Multilayer optically opaque systems Optically semitransparent systems Determination of thermal parameters Determination of recombination parameters Air-tightness measurements of packagings

Introduction Photoacoustics uses frequency amplitude and phase characteristics of the FA signal for determination of several parameters of samples such as: thermal diffusivity and effusivity of the material, thickness of thin films, detection of delaminations or voids in layer systems, determination of recombination parameters of carriers, air-tightness of packagings and others. This presentation is limited to the analysis of frequency domain FA characteristics measured with a microphone or piezoelectric methods

Temperature spatial distribution

Photoacoustic signals Microphone detection Piezoelectric detection

Experimental set-up

Multilayer optically opaque systems

Theoretical frequency domain dependencies of a phase of a photoacoustic signal for a transistor structure of a thickness l 1 =230  m, a lead frame of the thickness l 3 =350  m for different values of air delaminations: 1–  m, 2 – 0.05  m, 3–  m, 4– 0.1  m, 5– 0.15  m, 6– 0.2  m.

Multilayer optically opaque systems Correlation of the phase of the PA signal and the force of detachment of the transistor structure from a lead frame. Solid line is a theoretical curve, circles are experimental points, BC 237 transistor structures Phase(S) = (180/  )arg (S 1 ( d 2 = 0  m)p + S 2 (d 2 = 0.1  m)(1-p) ) Force necessary for detachment is proportional to the parameter p

Multilayer optically opaque systems Frequency characteristics of water on an aluminum plate of the thickness 40  m. Description: line 1 – R = 1(air), line 2 – R = (water), line 3 – R = 0.75, circles and boxes are experimental results. Frequency characteristics of ethanol on an aluminum plate of the thickness 40  m. Description: line 1 – R = 1 (air), line 2 – R = 0.95 (ethanol), line 3 – R = 0.75, circles and boxes are experimental results.

Optically semitransparent systems Schematic diagram of a thin semitransparent layer on the semitransparent backing Application – characterization of thin semiconductor films on semiconductor thick substrates

Optically semitransparent systems

Amplitude and phase photoacoustic frequency characteristics of a l 1 = 10  m thick layer on the thick substrate. Parameters taken for computations:  1 =0 cm -1,  2 =10000 cm -1 (solid line),  1 =10 4 cm -1,  2 =10 3 cm -1 ( dash line),  1 =0.3 cm 2 /s,  2 =0.9 cm 2 /s, GaAs/Si FREQUENCY [Hz] AMPLITUDE [a.u] FREQUENCY [Hz} PHASE [degs]

Optically semitransparent systems Application of the frequency characteristics for detection of the thickness SCL in semiconductors Comparison of the amplitude spectra and frequency characteristics SCL- is the subsurface layer of the semiconductor where light is absorbed but does not give the contribution to the FA signal

Optically semitransparent systems Theoretical characteristics presenting the predicted influence of a SCL on the photoacoustic amplitude and phase characteristics in the front configuration. Parameters:  =0.01 cm 2 /s, thickness of the layer l 1 =5  m – dash line, l 1 =10  m – dotted line, l 1 =15  m – solid line,  1 =0 cm - 1,  2 =1000 cm -1, R 12 =0.

Optically semitransparent systems The phase frequency characteristics of the PS/Si structure in the reflection configuration. Diamonds and circles are for exc =514 nm and exc =670 nm. Parameters of PS layer  =0.016cm 2 /s, k c = cal(cmKs) -1,  1 (514nm)=1900 cm -1,  1 (670nm)=903 cm -1. M.Maliński, L.Bychto, A.Patryn, J.Gibkes, B.K.Bein, J.Pelzl ‘Investigations of the optical and thermal parameters of porous silicon layers with the two wavelength photoacoustic method’ J.de Physique IV France (2005) accepted.

Determination of thermal parameters

ZnSe crystal l = cm  =0.01 cm 2 /s ( solid line),  = 0.05 cm 2 /s, 0.1 cm 2 /s, 0.2 cm 2 /s. Zn 0.83 Be 0.17 Se l= cm  =0.05 cm 2 /s,  =0.01 cm 2 /s,  =0.1 cm 2 /s and  = 0.2 cm 2 /s M.Maliński, J.Zakrzewski ‘Advances in photoacoustics and photothermal spectroscopy of semiconductors’ OSA’ 04 Conference Sobieszewo Poland

Determination of thermal parameters Si sample l=240  m and  =0.6 cm 2 /s. Description of lines: line 1 – R = 1, line 2 – R = 0.9, line 3 – R = 0.76, line 4 – R = 0.5. Circles and diamonds are experimental lines, lines are theoretical curves.

Determination of thermal parameters Dependance of the thermal conductivity of SiGe on the composition CONCENTRATION of Si in SiGe THERMAL CONDUCTIVITY [W/mK]

Determination of recombination parameters in TWI-PW model

Determination of recombination parameters Computations of Ge samples:  = 0.4 cm 2 /s, l = 0.1 cm,  = 20  s, D = 44 cm 2 /s, V = 500 cm/s a)  = 0.1  s and D = 22 cm 2 /s b).

Determination of recombination parameters Si:  =0.37 cm 2 /s, L=0.1 cm, E 1 =2.0 eV, E 2 =1.4 eV, E g =1.1 eV, D=44 cm 2 /s, V=800 cm/s,  = 100  s  FREQUENCY [Hz] AMPLITUDE RATIO [a.u.]  FREQUENCY [Hz] PHASE SHIFT [degs]

Air-tightness measurements

Parameters taken for computation:  = 17  10-6 [Ns/m2], L = 6-4 [m], M = 28  10-3 [kg/mole], V 2 = 2.16  10-6 [m3], V 2 /V 1 = 3.19, r = 20  m...60  m,  = 1.3 [kg/m3], N a = 6  [mole-1], T = 300 K, k = 1.38  [J/K].

Air-tightness measurements 1) r = 108  m;2) r = 91  m;3) r = 78  m; 4) r = 69  m;5) r = 42  m; 6) r =24  m; 1) r = 115  m;2) r = 86  m; 3) r = 83  m; 4) r = 71  m; 5) r = 50  m; 6) r = 24  m; L.Majchrzak, M.Maliński ‘Analysis of a Thermoacoustic Approach for the Evaluation of Hermeticity of Packaging of Electronic Devices’ XXIV IMAPS Poland Conf 2005

Air-tightness measurements - theory L.Bychto, M.Maliński ‘Determination of air-tightness of the packagings’ submited to AAuA 2005

Air-tightness measurements Silicon layer: d 1 =0.08[cm],  1 =1.2[W/cmK],  =0.6[cm 2 /s] Substrate (copper): d 2 =0.2[cm],  2 =3.9[W/cmK],  =1.1[cm 2 /s] Radius of holes:  m,  m,  m, 4- 5  m, 5- 1  m

Conclusions Frequency FA characteristics are a useful tool bringing information about: Multilayer optically opaque systems Optically semitransparent systems Thermal parameters Recombination parameters of carriers Air-tightness of packagings

Thank You for Your attention