SPECTROSCOPIC ELLIPSOMETRY AND RAMAN SCATTERING ANALYSIS OF Be SHALLOW IMPLANTATION IN GaAs

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SPECTROSCOPIC ELLIPSOMETRY AND RAMAN SCATTERING ANALYSIS OF Be SHALLOW

IMPLANTATION IN GaAs

M. Erman, P. Chambon, B. Prévot, C. Schwab

To cite this version:

M. Erman, P. Chambon, B. Prévot, C. Schwab. SPECTROSCOPIC ELLIPSOMETRY AND RAMAN

SCATTERING ANALYSIS OF Be SHALLOW IMPLANTATION IN GaAs. Journal de Physique

Colloques, 1983, 44 (C10), pp.C10-261-C10-265. �10.1051/jphyscol:19831055�. �jpa-00223512�

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JOURNAL DE PHYSIQUE

Colloque CIO, supplément au n°12, Tome M, décembre 1983 page C10-261

SPECTROSCOPIC ELLIPSOMETRY AND RAMAN SCATTERING ANALYSIS OF Be SHALLOW IMPLANTATION IN GaAs

M. Erman, P . Chambon, B. P r e v o t * and C. Schwab*

Laboratoires d'Electronique et de Physique Appliquée, 3, Avenue Descartes, 94450 Limeil Brévannes, France

* Université Louis Pasteur, Laboratoire de Spectrosoopie et d'Optique du Corps Solide, L.A. CNRS 232, b, rue de l'Université, 67084 Strasbourg, France

Résumé - Des échantillons de GaAs semi-isolant implantés Be sont analysés en utilisant 1'ellipsométrie spectroscopique (SE) et la diffusion Raman (RS).

L'étude par SE de la double structure E, , E. + A de la partie imaginaire de la fonction diélectrique permet d'accéder a la perfection cristalline et a l'activation électrique. Les spectres RS du 1er ordre donnent des informations quali- tatives alors qu'une analyse plus fine de la largeur des raies TO et 1.0 permet de caractériser la qualité cristalline. Les modes couplés plasmon-LO (L~ et L ) permettent d'observer 1'activation 'électrique.

Abstract - Spectroscopic ellipsometry (SE) and Raman scattering (RS) analysis of Be shallow implantation in semi-insulating GaAs are reported. Crystalline quality and informations about electrical activation are obtained from the SE analysis of the E. , E, + ^ , structure in the imaginary part of the dielectric function . Qualitative informations are obtained from the 1st order RS spectra. Energy position and line width of TO and L0 modes give a lattice potential perfection scale. Electrical activation can be observed via coupled plasmen L0 modes .

Introduction - Ion implantation of Be acceptors into GaAs coupled with annealing at moderate temperatures can provide device-quality p-type layers. It has been established that high electrical activation (^80 - 100 %) can be achieved for fluences less than 1.10 ions.cm 2, whereas for higher doses the electrical activation rate decreases (1). We have studied Be shallow ion implantation - 70 keV - (Rp - 0.15/1 )with doses 10 and 10 ions.cm 2 into semi-insulating GaAs at room temperature. Crystalline quality and information about electrical activation are obtained using Raman scattering (R S ) and Spectroscopic

Ellipsometry (S E ) on encapsulated (-vlOOO A Si,N. )GaAs. The two optical methods lead to the same conclusions : the lattice perfection recovery occurs after a 450 °C annealing, while the electrical activation reaches a maximum in carrier concentration at 700 °C.

Experimental

The R.S. yields informations about the vibrational properties of the crystal through the coupling of its phonons with the incoming photons. The Raman spectra have been obtained using the Brewster angle configuration with the standard 488 nm of an Ar ion laser. The 1st order R S of the crystal depends strongly on the geometrical arrangement ; we used a scattering surface 6° away from a (001) plane. The analysis of the intensities of the LO and TO Raman lines (2) shows that either the (001) pure type selection rules are obeyed (LO only allowed) or a

mixed situation (TO and L0 allowed) (Fig. 1-a) can be observed. In fact, Fig. 1-b shows that many different L0 and TO intensities are observable by varying the angle a. Previous experiments done on either capped or uncapped samples demonstra- te that RS measurements are not affected by the Si,N. overlayer. The scattered

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19831055

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C 10-262 J O U R N A L DE PHYSIQUE

l i g h t i s a n a l y z e d t h r o u q h a 3 a r r c l - A s h d o u b l e filonochror,iator e q u i p p e d w i t h a c o o l e d RCA O u a n t a c o n PM and p h o t o n c o u n t i n g e l e c t r o n i c s . The monochromator band nitith h a s b e e n set a t 1 . 6 c m - l .

F i g . 1 - a

a ( d e g r e e s )

F i g . 1 - b

F i g . 1

-

Geometrical s c a t t e r i n g c o n f i g u r a t i o n s f o r t h e R S a n a l y s i s ( a ) . The v a r i a - t i o n o f t h e G o r G g e o m e t r i c a l f a c t o r s as a f u n c t i o n o f t h e a n g l e a

.

( b ) f o r two p o l a r i z a t f s n conA?tions (HH) and (HV) : ( t i : h o r i z o n , V : v e r t i c a l ) .

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The experimental set up of the spectroscopic ellipsometer is of the rotating polarizer type ; the detailled description as well as the data processing can be found elsewhere (3). The equipment is fully computer controlled and Covers a spectral range extending from 1.6 to 5.4 eV.

Typical SE measurements of as-implanted GaAs and annealed at 500 "C are shown in Fig. 2. The peaks in tan Y curves are due to interferences in the Si3NL layer.

-nan annealed

2 3 4 5 e v

For properly chosen thickness of this overlayer (*1000 A), one can still observe the double structure El, El

+ A l

which is characteristic of GaAs. So the crystalline quality as well as the electrical activation can be checked without removing Si3N4.

The thermal treatments have been performed in the cumulative mode with 12 min. time periods in an atmosoheric H- furnace bv steos of 50 OC uo to

Results and discussion

As already reported (3,4) both techniques lead to informations about the ion implantation induced disorder : in the case of RS, the pedk position of the LO mode and its line width are %ell suitable.

In fact, the impinging ions reduce &he crystallo- graphic periodicity, therefore the k conservation rule is severely relaxed, allowing the 1st order density of states (DOS) to appear. Furthermore, the long range order Jc~leaSeS giving rise to a softe- ning of the phonon energy ELo. The life-time of the Fig. 2 - Typical SE vibratiorcALO is also affected through decay IIIeas~t-ements on encapsulated processes on the defects.

~ e + implanted samples.

Concerning the S E spectrum, the E l , E, +

A1

double structure appears to be the

- -

most sensitive feature. A quantitative evaluation of this double struct.ure is given by the following integral quantity :

which is unsensitive to pinor surface roughness, and to native oxide overlayer.

Our results prove that a nearly crystalline perfection is recovered for annealing steps over 450 "C.

The electrical activation is observed as a perturbation appearing on the evolution of our parameters. For instance in the S E measurements, the "contrast" of the double structure decreases (i.e. S increases) when the doping level increases This is due to the lattice perturbation caused by the incorporation of implanted species in substitutional lattice sites. This situation is also seen by R S : the coupling of the plasma waves with the LO mode through their effective elec- tric fields, giving rise to coupled plasmon LO modes L and L+ (6).

At this point, one has also to take into account the presence of a fully depleted space charge layer at the surface. At 488 nm the penetration+depth of the light is large enough to observe RS from both the bulk material (L and L- modes) and from the depleted layer (unscreened LO mode). This situation is

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ClO-264 JOURNAL DE PHYSIQUE

LO : 292.2 cm-'

+ ^zone

n W

250 300 350 250 300 350

STOKES RAMAN SHIFT (cm-I)

-

depicted in Fig. 3. From the very narrow TO line width, we conclude that the lattice perfection is

bution with a carrier concentration of the order of 2.10~' i ~ n s . c m - ~ (6).

Fig. 4 shows the variation good ; however the width of LO suggests that the unscreened LO peak is broadened by a L+ contri- -.

1 -

of with the LO

annealing temperature steps. Three regimes are clearly seen : up to 450°C the crystalline perfection is first recovered,

SI,N~/GOAS ~ d70 -kev-lot4 a o n s . ~ r n - ~ annealed 700'~

k

²⁶⁸⁴^.^.^-^I

(H-)a-180" (H-)~=O"

then electrical activa- Fig. 3

-

Raman spectra obtained for two scattering

tion takes place with a configurations after 700 OC annealing

step.Insets refer to the amount of mode maximum efficiency at

-

'E participation ( G ' s ) for each configura- 700 OC.

Y tion.

Fig. 4 - Evolution of the experimental LO-line width vs the temperature steps of annealing for an encapsulated sample implanted with 1015 ions-cm-'.

-- -

For higher temperature,

A

^LOdecreases rapidly without the appearence of a separated L+ in the RS spectrum. The same three stages in thermal treatment of Be implanted GaAs are found using SE (Fig. 5). The decrease of the S parameter 0 5 00 1000'~ and

A

LO after 700 OC indicates a decreasing of the carrier concentration in the implanted layer. We believe this to be due to outdiffusion of Be atoms (7).

Fig. 5

-

Evolution of the S parameter vs temperature of annealing.

S

-0.1 -

-0.2- O.O-\-\

fl

\

e\ectricai

\ I

activation

$ I

crystaiIisation:

y),

t:

-

70keV. 10"ias c;'

p,:

.... 7OkcV. f0"'a. ' =;

outdiffusion?

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References

1

-

NOJIMA S., KAWASAKI Y., Sapan. 3. o f A p p l i e d Physics,

17,

n o 10 (1978) 1845.

2

-

BIELLMANN 3., PREVOT B., SCHWA6 C., 3. Phys. C. S o l i d S t a t e Phys., 1 6 (1983) 1135-1142.

-

3

-

ERMAN M., THEETEN 3.B., Surface and I n t e r f a c e A n a l y s i s ,

4

(1983) 98-108.

4

-

BLELLMANN 3., PREVOT B., SCHWA0 C., THEETEN 3.B., ERMAN M.,to appear i n t h e Proceeding o f M a t e r i a l Research Society, Boston (1982).

5

-

ERMAN M., THEETEN 3.B., VOD3DANI N., DEMAY Y., Proceeding o f t h e 1ntern.Conf.

on Metastable and modulated Semiconductor S t r u c t u r e s , Pasadena, C a l i f o r n i a (Dec. 1982).

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G.B. WRIGHT E d i t . ( S p r i n g e r V e r l a g New-York), (1968) 291.

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2

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