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INTERFACE STATES PARAMETERS DEDUCED FROM DLTS, ICTS AND CONDUCTANCE
METHODS ON TiAu/Si3N4/GaInAs MIS STRUCTURES
J. Barrier, M. Renaud, P. Boher, Jodi Schneider
To cite this version:
J. Barrier, M. Renaud, P. Boher, Jodi Schneider. INTERFACE STATES PARAMETERS DEDUCED FROM DLTS, ICTS AND CONDUCTANCE METHODS ON TiAu/Si3N4/GaInAs MIS STRUCTURES. Journal de Physique Colloques, 1988, 49 (C4), pp.C4-227-C4-230.
�10.1051/jphyscol:1988447�. �jpa-00227945�
JOURNAL DE PHYSIQUE
Colloque C4, supplement au n09, Tome 49, septembre 1988
INTERFACE STATES PARAMETERS DEDUCED FROM DLTS, ICTS AND CONDUCTANCE METHODS ON TiAu/Si,N,/GaInAs MIS STRUCTURES
J. BARRIER, M. RENAUD, P. BOHER and J. SCHNEIDER
Laboratoires dlElectronique et de Physique Appliquee (LEP)"), 3, Av. Descartes, F-94451 L i m e i l - B r e v a ~ e s Cedex, France
RESUME: Plusieurs mCthodes de caractCrisation Clectrique utilisant les tcchniques de DLTS, dfICTS, et de conductance ont BtC mises au point et associies. En prenant en compte les cor- rections dues B la variation de la section efficace de capture en fonction de YCnergie, ces mCthodes permettent une dktermination cohCrente des caractCristiques des Ctats d'interface et ont CtC utilisCes sur des structures MIS ( T ~ A u / S ~ ~ N , / G ~ , , , I ~ , , ~ ~ A S ). L'application
A
I'optimisation d'un procCdC de passivation efficace de l'interface Si3N4/GalnAs utilisant un retrait de l'oxyde natif de la surface de GaInAs suivi d'un dCp6t de Si,N4 par plasma multipolaire en ambiance ultra vide a permis la rCalisation de transistors MISFET sur GalnAs posskdant de bonnes performances.ABSTRACT: A set of electrical characterization methods has been developed using DLTS, ICTS and Conductance techniques. Taking into account corrections due to the variation of cap- ture cross section versus energy , this method allows for a coherent determination of interface states parameters and has been used on TiAu/Si3N,/Gcg,71n,,53As MIS structures. It has been applied to perform an efficient passivation process of the Si3N4/GaInAs interface consisting in an in situ native oxide removal and Si,N4 deposition by multipolar plasmas in a ultra high vacuum system. GaInAs MISFETs with good performances could be achieved using such an optimized process.
I. INTRODUCTION
G%,,In,,,,As is a very attractivc material for the fabrication of high speed electronic compo- nents due to its excellent electronic properties. Several gate configurations of field effect transistors (JFET, HFET, MODFET ) have been investigated with good results.
For insulated gate field effect transistola (MISFETs) technology, large interface states densi- ties and drain current drift can appear with thc insulator deposition, especially on 111-V compounds MISFETS. Theses difficulties hampcrcd the development of this technology but, recently, few works have demonstrated possibility to overcome them /1,2/. Such application requires an efficient passivation process to reduce the density of interfacc states while kceping a high stability with time. Many passivation methods have been applied with various results but main conditions are a low temperature process and a low energetic insulator deposition due to the 111-V compounds surface instability.
Here, we have used a ultra high vacuum system and multipolar plasma treatments. Because
"native oxide" seems to be responsible of the drain current drift /3/, we have chosen to remove it in a multipolar plasma treatment.
In order to improve this passivation process, we needed to develop a set of sensitive charac- terization methods. DLTS, ICTS, Conductance and Capacitance measurements have been performed on TiAu/Si31V4/GaInAs MIS structures. Then, two kinds of treatments and there effects on the deduced interface state density were studied.
II. SAMPLE PREPARATION
Electrical measurements have been made on GalnAs layers lattice matched to n+InP substrate grown by vapor phase epitaxy using the chloride method. The samples are chemically deoxidized in di-
("LEP : a Member of the International Philips Research Organization
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1988447
C4-228 JOURNAL DE PHYSIQUE
luted HF before introduction into the U H V system. Then, the native oxide is completely removed in a H, multipolar plasma with a given hydrogen ion density that we have varied during this study. Finally, a Si,N, film is deposited using a multipolar plasma of SiH, and N2 a t room temperature. Both steps can be monitored by in situ kinetic and spectroscopic ellipsometry /4/. After passivation, one hour annealing at 400°C is performed and TiAu dots are evaporated followed by a 15mn anneal at 400°C.
III. CHARACTERIZAI TION TECHNIQUES 1II.A. DL TS-ICTS
We have recently presented a general method to extract the density distribution N,,(E) and the capture cross section cr,(E) from DLTS and ICTS measurements (J.M. Lopez Villegas, P. Boher, M.
Renaud submitted to 4. Appl. Phys. 1987). The coherence between the two spectroscopies is assumed only taking into account the variation of a, versus energy. This method is the most sensitive one but it assumes that the capture cross section is constant versus temperature.
III. B. CONDUCTANCE
Conductance method has also been applied on the same samples. Using a HP4192A impedance analyzer, Capacitance and Conductance can be measured from 500Hz to lOMHz a t a con- stant bias on the metal gate of the sample which can be heated from room temperature to 110°C. The analytical expression of interface states admittance (Y,) has been calculated by Deuling /5/ only in two cases:
i) When the capture cross section and the density of states d o not change with energy over a few KT:
elv, In(1
+
0 2 2 3Yt. = 7
1 --
2+
j tan- '((1)~)1
where z is the interface time constant classically related to the capture cross section.
ii) For a variation of a, versus energy dcfined by y = (KT/e) x (d In(a,)/dJt) = 0.5
,
where the effect of the variation of a, is maximum. (The first casc corresponds to y =O):eNss 1 / A -?- or12
Y , = 7 { I I I ~ - A ] + j A I n
I 1)
where A = (1+
w2r2/4)-112 1 / A-
( A ) T / ~Interface states parameters are obtained by fitting the experimental curves with both models.
N,,
,
o, ( variance of surface potential fluctuation ) and time constant are deduced from Gp/w(F) curve and $,( surface potential) from Cp(F) curve. a, is calculated fro 7 and $,.
This method needs the precise knowledge of the impurity concentration. Measurements at various temperatures allows for the deter- mination of any thermal activation of capture cross section.IV. INTERFACE CHARACTERIZATIONS
Figure I reports the fit of Gp/(o(F) and Cp(F) curves with the two hypothesis ( y = O and y=0.5 ) for conductance measurements made at room temperature on one sample (gate bias: -1.4 V)
.
Figure 1: Experimental and theoretical parallel capacitance Cp and conductance divided by the angular frequency G p l o versus frequency for the sample treated with the lowest hydrogen ion density ( sample I).
y = 0 : N,, = 3.4 x 1012cm-2eV-1
,
a,= 0.03, a, = 5.6 x 10-15cm2 ,JI,
= 0.388 eV y =0.5: N m = 3 . 3 x 1012cm-2eV-1,
a,=0.67, a,= 1.03 x 10-14cm2 , $,=0.351 eVThe Gp/o(F) curve cannot be well fitted by the constant cross section model even with no charge fluctuation ( a, = 0.03 ). On the contrary, the variable cross section model improves both fits of Gp/w(F) and Cp(F) curves and confirms DLTS and ICTS measurements which show a strong variation of a, (fig. 3a)
Effects of different hydrogen ionic densities during the UHV treatment on the interface states characteristics are shown on figure 2 for the density of states and on figure 3a and 3b for the capture cross section
.
It clearly appears that higher hydrogen ion dcnsity which is the more energetic one (sample 2) provide larger interface states density and also larger capture cross section and so faster interface states.ENERGETIC POSITION E c - E ( e V ) 3
7 6 5 4 3 2
2 0
Figure 2: Interface states densities versus energy on GaInAs M I S structures fabricated either with a low ( sample I) or high ( sample 2 ) hydrogen ion densities during the oxide removal treatment. The values extracted from conductance have been obtained using a variation of the capture cross section in the fits.
The density of states measured on the same samples by DLTS and ICTS methods are also reported.
-
0 CONDUCTANCE ( T = 3 0 O o K )# / -
-- -
ICTS -DLTS 0 0-
-
- -
/ /-
- - - _ e - _ _ _ _ _ _ - ) @'
(c-
-
<G2</+
-
-
- 4
- 4
S a m p l e 1
+
-
I I I Io I n 2 0 5 0 4 0
JOURNAL DE PHYSIQUE
h l E . 1 2 N
I E - 1 . 3 -
-
ICTS-DLTS- . .
rn Conductance y = . 5 Z I € - , . -
2
I f - I S - W
,
! E - 1 8 - v, 0 I E - 1 7SAMPLE 2
2 I P - 1 9 - R
S I E - 1 0 ' I I I I I I I
0 1 0 2 0.3 0.4
,lT-lZ
N Conductance y=.5
5
I c Ronm temp-
ENERGETIC POSITION Ec-E (eV) ENERGETIC POSITION Ec-E (eV)
F i g
J u
F i g 3 bZ t r - l r -
0 I- v I € 1 5 - W vl
,
I E > s -vl I E - ! 7 - 0 W I E - I l l -
I> E
& 1 E - 1 9 -
a <
O I E ? O
Figure 3a & 3b: Capture cross sections versus energy on GaInAs MIS structures fabricated either with a low ( sample I ) or high ( sample 2 ) hydrogen ion densities during the oxide removal treatment. The values extracted from conductance have been obtained using a variation of the capture cross section in the fits.
The capture cross sections measured on the same samples by DLTS and ICTS methods are also reported
.
5 0 ' ~0 R O ~ C 0 110%
-
ICTS-DLTSSAMPLE 1
' ' ' '
This result confirms that the whole process must be the less energetic as possible , especially for the oxide removal and for the Si,N, first layers deposition. The excellent agreement between conductance method
,
DLTS and ICTS measurements can only be obtained taking into account the variation of on versus energy. Conductance measurements have been made from room temperature to 110°C on the sample processed with the lowest hydrogen ion density.
Capture cross sections calculated from the variable cross section model fit are reported on figure 3b and no thermal activation could be observed.0. i 0.2 0.3 0.4
V. CONCLUSION
This work shows the necessity to take into account the capture cross section variation versus energy to correctly extract interface states parameters from conductance measurements on MIS struc- tures. With these conditions, this method allows for the determination of a constant capture cross section versus temperature. Applied to the characterization of different multipolar plasmas treatments, this method shows the great damages produced by energetic ions in the plasma on the electrical properties of the interface. The optimized passivation process has permitted to the fabricate GaInAs MISFETS with good performances (140 mS/mm and no drain current drift, see other paper in the proceedings).
ACKNOWLEDGEMENTS
The authors would like to thanks J.P. CHANE for the growth of GaInAs samples. Thanks are also due to Y. HILY and E. BOUCHEREZ for the fabrication of MIS structures.
This work has been partly supported by the European Community within ESPRIT project 927.
REFERENCES:
I. P.D. GARDNER, S . G . LIU, S . Y . NARAYAN, S . D . COLVIN, .I.P. P A C Z K O W S K I and D.R. CAPEWELL IEEE Electron Device Lett., Vol. EDL-7, no 6, p. 363, 1986
2. Y. TAKAHASIfl, T . TAKAIIASlfI, T . SNITARA, Y . ]WAS& Y-11. JEONG, S. TKAGI, F. ARAl and T. SUGANO 14rh Int Conf on GaAs and Rel. Compounds, Heraklion (Crete) 1987, Int. Phys. Qonf. Ser. No 91, pp 731-716
3. M . ERMAN, M . RENAUD and S. GOURRlER Japenese Journal of Appl. Phys., Vol. 26, no 11, pp.
1891-1897, 1987
4. P. BOIfER, M . RENAUD, J.M. LOPEZ-VII,I,EGAS, J . SCIfNE1DI:'R and J.P. C l f A N E Appl. Surf. Science 30, pp.
100-107, (1987)
5. H . DEULING, E. KY.A(ISMANN and A. GOETZBERR(;ER Solid State Elec. no 15, p. 5-59, (1972)
