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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-C4-412.
�10.1051/jphyscol:1988486�. �jpa-00227984�
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
8 3 8 ,Institut de Physique et Chimie des Materiaux de Nantes,
2,rue de la
Houssini&re,
F-44072Nantes Cedex
0 3 ,France
R6surn6.-
Les proprietBs physiques e t Blectriques de couches minces d'oxyde d'aluminium depos6es par plasma(13,56
MHz)B
p a r t i r de trim6thylaluminium sur du silicium sont fortement dependantes de l a temperatureB
laquelle est effectuee c e t t e croissance. On montre que les couches se densifient lorsque l a temperature de d6p6t passe de I'ambianteB
300°C.L a caracterisation par l a m6thode C(V) des structures M O S f a i t apparaftre une dispersion des r6sultats. Toutefois, un r e c u i t dans Ar
+
O2B
350°C e t pendant une heure apporte une amelioration sensible des caract6ristiques de ces f i l m s (diminution de l a tension de bande plate e t de 11hyst6r6sis).Abstract.- The physical and e l e c t r i c a l properties o f aluminum oxide f i l m s deposited f r o m aluminumtrimethyl under plasma conditions have been studied as a function o f the silicon substrate temperature. It is shown t h a t an increase o f the temperature enhances the oxidation reaction and gives dense films.
The C(V) characterization o f M O S structures shows a large scattering i n the results. However higher temperature (up t o 300°C) gives lower f l a t band voltage, lower hysteresis which indi- cates a lowering o f the free charges i n the oxide.
1
- INTRODUCTION
During the past years there has been a great interest i n l o w temperature techniques f o r the deposition o f insulator f i l m s f o r the purpose o f insulation, charge storage, diffusion inhibition and processing o f optoelectronic devices/?/. Silicon oxide i s now frequently used i n electronic devices b u t silicon n i t r i d e and aluminum oxide present several advantages compared w i t h silicon oxide : a hfgher dielectric constant, a good radiation resistivity and are good barrier against the diffusion o f impurities. These dielectric characteristics are necessary i f one wants t o obtain electronic components w i t h stable and reproducible behaviour. The plasma method i n other respects permits the deposition o f dielectric f i l m s a t low temperature ( < 400°C) and enables the use o f temperature sensitive substrate as 111- V compounds.
The present work deals w i t h the influence of the deposition temperature on plasma deposited aluminum oxide f i l m s using aluminumtrimethyl as aluminum carrier gas.
2 - EXPERIMENTAL METHODS
The figure 1 i s a schematic diagram o f the glow discharge apparatus used i n this study.
Aluminum oxide f i l m s have been deposited by decomposition o f aluminum t r i m e t h y l diluted i n helium (- 1 % M A ) i n a radiofrequency discharge (13.56 MHz) w i t h carbon dioxide (COr) or nitrous oxide (N20) as oxidizing agent. The influence of several parameters such as R F power, pressure, has already been studied/Z/. Typical deposition pressures of 13.3 Pa (0.1 t o r r ) are used and deposition powers are i n the range 1 0 - 30 W. The deposition temperature can be choosen between room temperature and
450°C. More experimental details can be found i n reference 2.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1988486
JOURNAL DE PHYSIQUE
R.F.
Fig. 1 - Schematic diagram o f the glow discharge set up f o r A I O x f i l m deposition.
3 - INFLUENCE OF THlE DEPOSITION TEMPERATURE UPON GROWTH KINETICS
As shown i n figure 2 an Arrhenius plot of the deposition r a t e as a function o f the temperature results in a decrease o f the growth r a t e w i t h the temperature rise. This plot also gives a l o w negative apparent activation energy o f - 0.4 kcal/mole(-0.017 eV). Such a l o w apparent activation energy is representative o f a deposition r a t e controlled by radical flux 131.
30 50 100 200 300 400 O c
I I I
J
/mnFig. 2
-
Arrhenius p l o t o f the dependence o f the growth r a t e on the substrate temperature : Pressure 13.3 Pa, f l o w r a t e : 25 sccm 60% CO, 50 % C 0 2 .The negative temperature coefficient can be interpreted by the competition o f t w o processes: aluminum incorporation via adsorption o f aluminum t r i m e t h y l radicals and the oxidation o f aluminum which inhi- bits deposition sites. Thus the increase o f the oxidation reaction r a t e w i t h the temperature involves the de- crease o f the f i l m growth r a t e by aluminum incorporation. Similar results have been observed w i t h
N20.
4 - EVOLUTION OF PHYSICAL PROPERTIES AS FONCTION OF THE DEPOSITION TEMPERATURE
The evolution o f the r e f r a c t i v e index and etch r a t e (room temperature, 1 % HF) are reported i nfig. 3.
nmts
Fig. 3
-
E t c h r a t e 25 sccm,and r e f r a c t i v e 60% CO,.
index versus deposition temperature : Pressure 13.3 Pa, flow rate :
It clearly shows the densification o f the f i l m s w i t h the higher deposition temperature. This densification i s characterized by the increase o f the r e f r a c t i v e index n f r o m 1.55 up t o 1.65. This variation o f n corresponds t o an increase o f the f i l m density f r o m 1.8 up t o 3.2 g/cm3. These density values are always lower than sapphire density values : f r o m 3.4 up t o 3.7 g/cm3. E S C A analysis c o n f i r m s this enhancement o f the oxidation o f Aluminum w i t h the deposition temperature (Table 1).
Table 1
-
A t o m deposition o f AIOx layers measured by -ESCA.Most o f the carbon o f the high temperature f i l m s is due t o pollution o f the l a ers during storage while l o w temperature f i l m s exhibit A1 - C bonds as was shown by I R spectroscopy 721.
DEPOSITION TEMPERATURE
T ° C
room (50 1 C O ~ ) 3OO0C (5OXCO2) 3OO0C (60 X C 0 2 )
5 - ELECTRICAL PROPERTIES
5.1. Asdeposited films
ATOM X WITHOUT CLEANING
[ O l [ A l l [ C ] 47,4 27,6 25 53,9 33 13,l 44,5 32,7 22,9
C(V) curves o f f i l m deposited on n type silicon have been obtained by using a mercury probe i n order t o constitute a M O S structure. The results present a large dispersion and no significant evolution o f the f l a t band voltage can be observed w i t h the deposition temperature variation. A typical C(V) curve for as grown films is given i n fig. 4 a and is dominated by a large hysteresis, t h a t is the C(V) curve is dominated by large f l a t band voltage'shifts as f o r sputerred A 1 2 0 3 f i l m s
141
o r C V D f i l m s f r o m AI(CH3), 5 Typical values f o r e f f e c t i v e charge levels Q T a r e given i n Table 2 and compared w i t h the results o f other authors.ATOM X AFTER At ION
CLEANING [ 0 1 [ A l l LC]
60,6 30 9,4 56,3 38,7 5 55,3 44,7
-
Fig. 4
-
C(V) curves o f A1203 M O S structure.a : as deposited film, b: a f t e r one hour 350°C annealing i n Arlo, ( l / l ) , c : a f t e r t w o hours 3500C annealing i n Ar/O,(l/l), d: theoretical curve.
Table 2 - E f f e c t i v e charge level f o r as grown A1203 f i l m s deposited b y various methods.
Deposited Method
Charge density QT ( C ~ - ~ E
Reference C V 0 AI(CH3 I3
-1.5,-51012
5
C V D AICI3
- 31011
6
Plasma oxidation
8 1 0 l1
7
This work (COz )
4 1 0 ~ ~ , 2 1 0 ~ ~ N2 0
-41011,6 lo1'
C4-412 JOURNAL DE PHYSIQUE
5.2.
Effects of annealing processes
We have studied the e f f e c t o f a one hour annealing ( A r l o P (1/1) 350°C) on the e l e c t r i c a l and physical characteristics o f these layers. A f t e r one hour annealing a noticeable densification occurs : thickness varies f r o m 2034
a
down t o 14104
while r e f r a c t i v e index grows f r o m 1.55 up t o 1.59.The evolution of the C ( V ) ' c u r v e shown i n figure ( 4 b) gives a decrease o f the hysteresis and o f the f l a t band voltage which are characteristics o f a lowering o f the e f f e c t i v e and free charge levels.
A f t e r a second annealing o f one hour ( A t = 2 h) there is a slight variation o f thickness 1410
a
downt o 1380
a
b u t a deterioration o f the f i l m structure substantiated by the lowering o f the r e f r a c t i v e index f r o m 1.59 down t o 1.49 and o f the oxide capacitance f r o m 277 pF down t o 162 pF. This e f f e c t was also observed i n oxide f i l m s obtained by plasma oxidation 171.6 - CONCLUSION
Aluminum oxide layers obtained using plasma deposition f r o m A1 (CH3), a t temperature o f 300° and more present good physical and structural properties, however the electrical characterization shows the importance o f the insulator, semiconductor interface and the need o f a b e t t e r control o f trapped and free charges. This w i l l be the goal o f our future work.
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R.S. N O W I C K I ,J. Vac. Sci. Technol., 14
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