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Submitted on 1 Jan 1989
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LIGHT BEAM INDUCED CURRENT IMAGING OF THE ELECTRICAL ACTIVITY OF STACKING
FAULTS IN CZ SILICON
A. Castaldini, A. Cavallini, A. Poggi, E. Susi
To cite this version:
A. Castaldini, A. Cavallini, A. Poggi, E. Susi. LIGHT BEAM INDUCED CURRENT IMAGING OF
THE ELECTRICAL ACTIVITY OF STACKING FAULTS IN CZ SILICON. Journal de Physique
Colloques, 1989, 50 (C6), pp.C6-169-C6-169. �10.1051/jphyscol:1989626�. �jpa-00229657�
REWE DE PHYSIQUE APPLIQUEE
C o l l o q u e C6, S u p p l b m e n t a u n 0 6 , Tome 24, J u i n 1989
LIGHT BEAM INDUCED CURRENT IMAGING OF THE ELECTRICAL ACTIVITY OF STACKING FAULTS IN CZ SILICON
A. CASTALDINI, A. CAVALLINI, A. POGGI* a n d E. SUSI'
Department o f P h y s i c s , U n i v e r s i t y o f Bologna, V i a I r n e r i o
4 6 ,Bologna, I t a l y
'CNR-LAMEL
I n s t i t u t e , V i a C a s t a g n o l i
1 ,Bologna, I t a l y
ABSTRACTMicroscopic inhomogeneities i n t h e electrical properties of semiconductors a r e of great importance to device performances, particularly i n advanced device technology. Then i n t h e l a s t few y e a r s great a t t e n t i o n was paid t o t h e processes which can change t h e material microstructure, and, above all, t o t h e gettering techniques, on account of t h e i r wide impact on t h e overall yield of electronic tailored materials. With t h i s aim, therefore, extended investigations were carried out, mainly by electron and optical beam testing. In t h i s respect, we report here some results of a spectroscopic analysis performed on Si intrinsically gettered samples by a scanning photocurrent microscopy technique[lj similar, i n principle, t o t h e light beam induced current (LBIC) method. However, some differences i n t h e experimental set-up h a v e turned out to be fundamental from t h e point of view of t h e instrument-sample interaction and, then, of t h e information obtainable by t h e induced photocurrent signals. To probe t h e material, a n above-band-gap energy light from a n halogen lamp i s focused onto t h e sample, where a Schottky barrier was provided. The light p a t h is intercepted by interferential filters i n t h e visible-infrared range, so a s t o select t h e beam wavelength. To probe point-by-point t h e object, t h e sample i s moved i n a r a s t e r fashion across a s t a t i o n a r y spot. As i n EBIC and LBIC methods, t h e electron-hole pairs generated by t h e beam give rise t o a n induced current I(x,y). This current is measured a s analog signal corresponding t o t h e irradiated point, amplified by t h e lock-in technique, converted from analog-to-digital form and, lastly, noise-cleaned by filtering algorithms. This procedure makes i t possible t o detect current changes a s low a s 10-14-10-i5A.
Since a defect causes a local variation i n t h e photoinduced carrier concentration, it is detected by t h e induced current changes. It should be pointed out t h a t t h e investigation method described above and from now on called IRBIC (Infra-Red Beam Induced Current) method, even if very similar t o t h e LBIC one, differs from it for a n essential element: t h e extremely low injection level. The use of a n halogen lamp a s light source, instead of t h e laser employed i n t h e LBIC method, gives very low values of irradiance. This gives rise t o problems i n t h e signal processing, but, on t h e other side, generates a very low bulk current level ( a s low a s 10-13A).
allowing t h e detection of current changes equal t o some p a r t s per c e n t of t h i s value. In LBIC mode [21 t h e r a t e of above-band-gap photon emission from a I-mW He-Ne (63288) l a s e r produces 3.2*1015photons*sec-1. Usually it is supposed t h a t t h e beam i s a t t e n u a t e d by a n amount a=0.01, so t h a t , on impinging t h e semiconductor surface, 3.2*1013 electron-hole pairs a r e generated per second. In our investigation we examined t h e samples with a beam power equal t o 3.6*10-BmW. The electron-hole pair generation r a t e G was calculated by t h e expression [3]:
G = PbQ(1-t)/(qEd where P b is t h e beam power, Q t h e quantum efficiency, r t h e back- scattering coefficient, q t h e electronic charge and Eg t h e band gap. In our experimental conditions G is 1.2'108sec-1. The i n t e n s i t y of t h e light impinging on t h e sample resulted a decisive factor i n t h e imaging t h e electrical activity of t h e stacking faults. Moreover, due t o t h e ease of changing t h e wavelength of t h e light beam probing t h e sample, depth profiling of t h e stacking f a u l t electrical a c t i v i t y was obtained. By t h i s way we detected t h e occurrence of minority carrier recombination and generation processes a t some stacking faults, corresponding, respectively, t o dark and bright levels i n a grey-shade imaging. A possible explanation based on t h e presence of fixed charges 141 a t t h e defect-silicon matrix interface is proposed.
REFERENCES
1. A.Castaldini and A.Cavallini: Proc. SPIE 0-E LASE '88, Conference on "Scanning Microscopy Technologies and Applications", Jan.1988, Los Angeles, CA (in press)
2. T.Wilson and C.Sheppard, Scanning Optical Microscopy, Sector 9.2, p.179-181 (Academic Press, London, 1984).
3. S.M.Davidson and C.A.Dimitriadis: J.Microscopy, 118 (3) p.275-290 (1980).
4.A.Henry, J.L.Pautrat and K.Saminadayar, J.Appl.Phys. 60 (9). p.3192-3195 (1986) Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1989626
