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Submitted on 1 Jan 1980
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LASER IMPLANTATION OF Fe IN SILICON
Yu. Petrikin, S. Damgaard, M. Oron, J. Petersen, G. Weyer
To cite this version:
Yu. Petrikin, S. Damgaard, M. Oron, J. Petersen, G. Weyer. LASER IMPLANTATION OF Fe IN SIL- ICON. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-423-C1-424. �10.1051/jphyscol:19801164�.
JOURNAL Dl3 PHYSIQUE Colloque C1, supplkment au n o 1,
Tome41, janvier 1980, page C1-423
LASER IMPLANTATION OFFe
Yu, V. petrikin*, S. Damgaard, M. oron*
*,J.W. Petersen and G. Weyer I n s t i t u t e of Physics, University o f A&s DK 8000 Aarhus C, Denmark
1. Introduction 3. Experimental results and discussion
As an alternative to diffusion and ion implanh ation techniques, laser irradiation has been ap- plied to incorporate dopants from a deposited layer on the surface into the bulk of silicon [I]. The limit of solid solubility may be exceeded by this method. In contrast to ion implantation, where this
can also be achieved, problems from radiation dam- age are less severe. Here we report on the implant- ation of iron in silicon by laser irradiation. The location of iron in the silicon lattice is investig ated by conversion electron Mdssbauer spectroscopy.
2. Experimental procedure
Layers of metallic iron (3
-30 ug/cm2 en- riched in s Fe) were deposited on the <Ill> surface of silicon single crystals (Fz,n-type,5Qcm) by an electron gun evaporation technique. The iron layers were irradiated with (3
-4 slightly overlasping) light pulses which covered about 1 cm2 ( ~ 1 0 0 ns dur- ation time) from a Nd glass laser (A= 1.06um )
ter the laser irradiation the surface was cleaned from residual iron with HC1.
Conversion electron M6ssbauer spectra were measured in a backscattering geometry with a paral-
lel-plate avalanche counter 121 where the samples were used as cathodes. A 10 mCi 57Co(Rh) source was moved on a conventional constant acceleration drive system.
To investigate the depth distribution of the implanted iron, surface layers of 100
-1000 fi were stripped off by an anodic oxidation technique.
fpermanent addres~ : Moscow Physical-Engineering Institute, Moscow, 115 409 USSR.
A spectrum of an iron layer (30 ug/cn12) irrad- iated with a power density of 2.6 J/cm2 is shown in
VELOCITY Cmmlsec I
Figure 1 : Mossbauer spectrum measured at room tem- perature of a sample (30 g/cm2 Fe) irradiated with 2.6 J/cm2. A surface layer of%100 fi has been stripped off.
figure 1. Similar spectra were obtained for layer thicknesses of 3 to 30 uq/cm2 irradiated with power densities of 2.1 to 3.5 J/cm2. Except for a de- crease in intensity, the spectra did not change upon a stripping of up to 3500 fi from the surface of the samples. The spectra are similar to those found for ion implanted samples of 5 7 ~ e in Si that have been annealed at high temperatures [ 3 ] . The lines are interpreted as a quadrupole split doublet
-0.2 mm/sec rel.to 01-Fe, AE = 0.4 mm/sec, Q
r= 0.4 mm/sec) due to FeSi2
The observation of large amounts of iron deep inside the silicon can hardly be accounted for by a diffusion of iron into solid silicon. A diffusion constant of D
210-'cm2/sec I41 limits the diffu- sion length to %I00 A if the diffusion time is not considerably longer than,the duration of the laser
*%emanent address: Soreq research center,Yavne,Israel.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19801164
C 1-424 JOURNAL DE PHYSIQUE
pulse. It seems more reasonable to assume that a silicon surface layer of several thousand dnqstroms thickness has been molten as an effect of the laser irradiation. These assumptions seem to be justified by recent experiments 
.Thus iron atoms are in- corporated as a result of laser induced diffusion in the liquid phase. About 1% 02 the deposited iron layer is implanted yielding an iron concentration several orders of magnitude above the maximum solid solubility.
For an irradiation with a power density of 1.6 J/cm of an iron layer of 30 bg/cm2, a spectrum as displayed in figure 2 is found. An analysis with
I I I I I
VELOCITY [mm lsecl
Figure 2 : Idbssbauer spectrum measured at room temperature Of a sample ( 3 0 ~-lg/cm*- " ~ e ) irradiat- ed with 1.6 ~/cm'.
three independent lines as indicated in the figure suggests that the spectrum consists of a doublet
( 6 -0.3 mm/sec, A E 0.7 mm/sec,
rz 0.5 mm/sec) I!
and an additional single line ( 6 ~ 0 . 2 mm/sec,
0.3 mm/sec). No measurable fraction of iron had pen- etrated a surface layer %I00 A. Thus contrary to the higher power density laser irradiations, in this case a fraction of the iron atoms may have dif- Fused into the silicon in the solid state. This spr- cies should then occupy well defined positions in the silicon lattice. These expectations are in agreement with the occurrence of the narrow line at 6 = 0.2 mm/sec in the spectrum. It should be
noted that the concentration of this species ex- ceeds the maximum solid solubility of iron by sever- al orders of magnitude. The parameters of the doub- let which are inbetween those found for annealed and non-annealed ion implanted samples [ 3 ] may sup- port the assumption that the temperature of the sample has been lower for this low power density ir- radiation.
The irradiation of thin evaporated layers of iron on silicon with short laser pulses has been de- monstrated to result in an implantation of a substan- tial fraction of the iron atoms into the silicon cry- stal. For high laser power densities, a silicon sur- face layer is molten; the iron is incorporated in the liquid phase and is found in precipitates after the resolidification. For low laser power densities,iron atoms are implanted in a shallow surface layer. It is proposed that an appreciable amount of the iron at- oms diffuse into the silicon in the solid phase. This fraction is related to a single line in the spectra which is attributed to iron in well defined lattice positions.
This work has been supported by the Danish Nat- ural Science Research Council.
1 See, e.q., Narayan, J., Young, R.T., Wood, R.F., and Christie, W.H.,Appl.Phys.Lett.z (1978) 3 3 8 2 Weyer, G., Mossb.Eff.Method.(eds,Gruvermann,
I.J. an6 Seidel, C.W.)
3 Damgaard, S., Petersen, J . W . , and Weyer, G., this conference
4 Struthers, J.D., Appl.Phys.3 (1956) 1560 5 Auston,D.H., Surko, C.M., V~nkateson, T.N.C.,
Slushev, R.E., and Golovchenko, J.A., Appl.
Phys.Lett.2 11978) 437