EFFECT OF DEPOSITION TEMPERATURE ON PLASMA GROWN ALUMINUM OXIDE FILMS

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1 EFFECT OF DEPOSITION TEMPERATURE ON PLASMA GROWN ALUMINUM OXIDE FILMS C. Bourreau, Y. Catherine To cite this version: C. Bourreau, Y. Catherine. EFFECT OF DEPOSITION TEMPERATURE ON PLASMA GROWN ALUMINUM OXIDE FILMS. Journal de Physique Colloques, 1988, 49 (C4), pp.c4-409-c < /jphyscol: >. <jpa > HAL Id: jpa Submitted on 1 Jan 1988 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2 JOURNAL DE PHYSIQUE Colloque C4, suppl6ment au n09, Tome 49, septembre 1988 EFFECT OF DEPOSITION TEMPERATURE ON PLASMA GROWN ALUMINUM OXIDE FILMS C. BOURREAU and Y. CATHERINE Laboratoire des Plasmas et des Couches Minces. CNRS-UA 838, Institut de Physique et Chimie des Materiaux de Nantes, 2, rue de la Houssini&re, F Nantes Cedex 03, France R6surn6.- Les proprietbs physiques et Blectriques de couches minces d'oxyde d'aluminium depos6es par plasma (13,56 MHz) B partir de trim6thylaluminium sur du silicium sont fortement dependantes de la temperature B laquelle est effectuee cette croissance. On montre que les couches se densifient lorsque la temperature de d6p6t passe de I'ambiante B 300 C. La caracterisation par la m6thode C(V) des structures MOS fait apparaftre une dispersion des r6sultats. Toutefois, un recuit dans Ar + O2 B 350 C et pendant une heure apporte une amelioration sensible des caract6ristiques de ces films (diminution de la tension de bande plate et de 11hyst6r6sis). Abstract.- The physical and electrical properties of aluminum oxide films deposited from aluminumtrimethyl under plasma conditions have been studied as a function of the silicon substrate temperature. It is shown that an increase of the temperature enhances the oxidation reaction and gives dense films. The C(V) characterization of MOS structures shows a large scattering in the results. However higher temperature (up to 300 C) gives lower flat band voltage, lower hysteresis which indicates a lowering of the free charges in the oxide. 1 - INTRODUCTION During the past years there has been a great interest in low temperature techniques for the deposition of insulator films for the purpose of insulation, charge storage, diffusion inhibition and processing of optoelectronic devices/?/. Silicon oxide is now frequently used in electronic devices but silicon nitride and aluminum oxide present several advantages compared with silicon oxide : a hfgher dielectric constant, a good radiation resistivity and are good barrier against the diffusion of impurities. These dielectric characteristics are necessary if one wants to obtain electronic components with stable and reproducible behaviour. The plasma method in other respects permits the deposition of dielectric films at low temperature (< 400 C) and enables the use of temperature sensitive substrate as 111- V compounds. The present work deals with the influence of the deposition temperature on plasma deposited aluminum oxide films using aluminumtrimethyl as aluminum carrier gas. 2 - EXPERIMENTAL METHODS The figure 1 is a schematic diagram of the glow discharge apparatus used in this study. Aluminum oxide films have been deposited by decomposition of aluminum trimethyl diluted in helium (- 1 % MA) in a radiofrequency discharge (13.56 MHz) with carbon dioxide (COr) or nitrous oxide (N20) as oxidizing agent. The influence of several parameters such as RF power, pressure, has already been studied/z/. Typical deposition pressures of 13.3 Pa (0.1 torr) are used and deposition powers are in the range W. The deposition temperature can be choosen between room temperature and 450 C. More experimental details can be found in reference 2. Article published online by EDP Sciences and available at

3 JOURNAL DE PHYSIQUE R.F. Fig. 1 - Schematic diagram of the glow discharge set up for AIOx film deposition. 3 - INFLUENCE OF THlE DEPOSITION TEMPERATURE UPON GROWTH KINETICS As shown in figure 2 an Arrhenius plot of the deposition rate as a function of the temperature results in a decrease of the growth rate with the temperature rise. This plot also gives a low negative apparent activation energy of kcal/mole( ev). Such a low apparent activation energy is representative of a deposition rate controlled by radical flux 131. J /mn Oc I I I Fig. 2 - Arrhenius plot of the dependence of the growth rate on the substrate temperature : Pressure 13.3 Pa, flow rate : 25 sccm 60% CO, 50 % C02. The negative temperature coefficient can be interpreted by the competition of two processes: aluminum incorporation via adsorption of aluminum trimethyl radicals and the oxidation of aluminum which inhibits deposition sites. Thus the increase of the oxidation reaction rate with the temperature involves the decrease of the film growth rate by aluminum incorporation. Similar results have been observed with N EVOLUTION OF PHYSICAL PROPERTIES AS FONCTION OF THE DEPOSITION TEMPERATURE The evolution of the refractive index and etch rate (room temperature, 1% HF) are reported in fig. 3. nmts Fig. 3 - Etch rate 25 sccm, and refractive 60% CO,. index versus deposition temperature : Pressure 13.3 Pa, flow rate :

4 It clearly shows the densification of the films with the higher deposition temperature. This densification is characterized by the increase of the refractive index n from 1.55 up to This variation of n corresponds to an increase of the film density from 1.8 up to 3.2 g/cm3. These density values are always lower than sapphire density values : from 3.4 up to 3.7 g/cm3. ESCA analysis confirms this enhancement of the oxidation of Aluminum with the deposition temperature (Table 1). Table 1 - Atom deposition of AIOx layers measured by -ESCA. DEPOSITION TEMPERATURE T C ATOM X WITHOUT CLEANING [Ol [All [C] ATOM X AFTER At ION CLEANING [01 [All LC] room (50 1 CO~) 47,4 27,6 25 3OO0C (5OXCO2) 53, ,l 3OO0C (60 X C02) 44,5 32,7 22,9 60,6 30 9,4 56,3 38,7 5 55,3 44,7 - Most of the carbon of the high temperature films is due to pollution of the la ers during storage while low temperature films exhibit A1 - C bonds as was shown by IR spectroscopy ELECTRICAL PROPERTIES 5.1. As deposited films C(V) curves of film deposited on n type silicon have been obtained by using a mercury probe in order to constitute a MOS structure. The results present a large dispersion and no significant evolution of the flat band voltage can be observed with the deposition temperature variation. A typical C(V) curve for as grown films is given in fig. 4 a and is dominated by a large hysteresis, that is the C(V) curve is dominated by large flat band voltage'shifts as for sputerred A1203 films 141 or CVD films from AI(CH3), 5 Typical values for effective charge levels QTare given in Table 2 and compared with the results of other authors. Fig. 4 - C(V) curves of A1203 MOS structure. a : as deposited film, b: after one hour 350 C annealing in Arlo, (l/l), 3500C annealing in Ar/O,(l/l), d: theoretical curve. c: after two hours Table 2 - Effective charge level for as grown A1203 films deposited by various methods. Deposited Method C V 0 AI(CH3 I3 C V D AICI3 Plasma oxidation This work Charge density QT ( C ~ - ~ E -1.5, (COz ) 810 l1 410~~,210~~ N ,6 lo1' Reference 5 6 7

5 C4-412 JOURNAL DE PHYSIQUE 5.2. Effects of annealing processes We have studied the effect of a one hour annealing (ArloP (1/1) 350 C) on the electrical and physical characteristics of these layers. After one hour annealing a noticeable densification occurs : thickness varies from 2034 a down to while refractive index grows from 1.55 up to The evolution of the C(V)'curve shown in figure (4 b) gives a decrease of the hysteresis and of the flat band voltage which are characteristics of a lowering of the effective and free charge levels. After a second annealing of one hour (At = 2 h) there is a slight variation of thickness 1410 a down to 1380 a but a deterioration of the film structure substantiated by the lowering of the refractive index from 1.59 down to 1.49 and of the oxide capacitance from 277 pf down to 162 pf. This effect was also observed in oxide films obtained by plasma oxidation CONCLUSION Aluminum oxide layers obtained using plasma deposition from A1 (CH3), at temperature of 300 and more present good physical and structural properties, however the electrical characterization shows the importance of the insulator, semiconductor interface and the need of a better control of trapped and free charges. This will be the goal of our future work. REFERENCES /I/ K.P. PANDE, V.K.R. NAIR and D. GUTIERREZ, J. Appl. Phys., 54 (19831, /2/ Y. CATHERINE and A. TALEBIAN, J. of Electron. Mat., 17 (1988), 127. /3/ D.J. ERLICH and R.M. OSGOOD, Chern. Phys. Lett. 79 (1981), R.S. NOWICKI, J. Vac. Sci. Technol., 14 (1977), 127. /5/ M.T. DUFFY, A.G. REVESZ, J. Electrochem. Soc. 117 (1970) /6/ K.M. SCHLESIER, J.M. SHAW and C.W. BENYON, R.C.A.Rev. 37 (1976), 360. /7/ I4.J. BURLOW, W. ECCLESTON and S. TAYLOR, Appl. Surf. Sci. 30 (1987). 47.