- Email: [email protected]
Residual stress in silicon films deposited by LPCVD from disilane
thin
o
jums ELSEVIER
Thin Solid Films 310 (1997) 234-237
Residual stress in silicon films deposited by LPCVD from disilane P. Temple-Boyer *, E. Scheid, G. Faugere, B. Rousset LAAS-CNRS, 7 Avenue du ColonelRoche, Toulouse Cddex 3107Z France
Received l0 April 1997; accepted 25 June i997
Abstract
Measurements of the thermomechanical stress in amorphous silicon films deposited by low pressure chemical vapour deposition (LPCVD) from disilane SiaH 6 are reported as a function of the deposition parameters (temperature, gas pressure and wafer spacing). Major influences of the deposition temperature and the deposition rate are put into evidence and related to the films ordering and hydrogenation. The effects of a 600°C anneal are also investigated and a transition from highly compressive to highly tensile stress is characterised whatever the deposition. Such behaviour has been explained thanks to hydrogen atoms out-diffusion and crystallisation effects. © 1997 Elsevier Science S.A. Ke>~vords: Crystallization; Silicon; Stress
1. I n t r o d u c t i o n With the development of microtechnologies and the realisation of complex micromechanicat elements, it has become necessary to investigate the mechanical properties of silicon-based materials. Polysilicon films have been no exception to the rule and the influences of deposition parameters and crystallisation anneal on their intrinsic stress have been reported in the literature [1-4]. However, with the use of silane Sill 4 as gaseous source, silicon crystallisation occurs during film deposition and it has been almost impossible to separate the influences of the two phenomena. Since deposition temperatures from disilane Si2H 6 (450-480°C) are lower than the silicon crystallisation temperature ( = 600°C), this gaseous source has been used to obtain amorphous silicon films and should allow to tackle this problem. The aim of this work is to present the intrinsic stress results of amorphous silicon films deposited by low pressure chemical vapour deposition (LPCVD) from disilane and to characterise the influences of a crystallisation postanneal at 600°C.
* Corresponding author. 0040-6090/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved. PII S 0040-6090(97)00387-8
2. Experiments Thin amorphous silicon films were deposited by low pressure chemical vapour deposition (LPCVD) from disilane Si2H 6 on 10 cm, (111), oxidised (about 120 nm of oxide) silicon wafers. The deposition temperature T ranged from 450 to 480°C and the total pressure P from 13.5 to 54 Pa. In our horizontal furnace, the distance 8 between two consecutive wafers was set at 10 or 20 mm in order to obtain different deposition rates for the same temperature and pressure of deposition. After removal of the back side silicon deposition by chemical etching ( H N O 3 : 5 0 cm 3CH3COOH: 20 cm3-HF: 2 cm3), the curvature R of the wafer was determined by profilometry and the average stress cr of the deposited film was calculated thanks to the formula of Stoney [5]: 1
o-=
E
6R 1 - v
D2 d '
(1)
where d is the film thickness (assessed by ellipsometry at a 830 nm wavelength), E, v and D are the Young Modulus, the Poisson ratio and the thickness of the substrate, respectively, (for silicon (111), E / ( 1 - v ) equals 2.3 × 1011 Pa). The accuracy of the technique was not worse than 10%. Crystallisation anneals were finally performed at 600°C into a conventional thermal furnace under neutral ambient and the crystallisation level was analysed by scanning
P. Temple-Boyer et al. / Thin Solid Films 310 (1997) 2 3 4 - 2 3 7
235
100
electron microscopy (SEM) observations after etching the samples into a SECCO etch in order to make the polysilicon grains more distinct.
,, • =
50"
~,
450oc 465oc 480oc
-50"
3. Results and discussion -IO0"
3.1. Influences of the deposition parameters
-150 "
Let us discuss about the mechanisms of stress generation. In the general case, the thermomechanical stress is the sum of the thermal stress crth and the intrinsic stress cri. The thermal stress is caused by a difference in the thermal expansion coefficients of the monocrystalline silicon substrate (ce .s,) and the deposited film (C~s~) and by a difference between the deposition temperature T and the ambient temperature during stress measurement. In our case, since thermal expansion coefficient is a macroscopic parameter, it should not depend on silicon microstructure and we will assume that C~s~= Ces~ whatever the crystallisation level, i.e., that crth is negligible compared to the intrinsic stress o-~: O" =
%
(2)
-1- dr i = O"i .
The experimental results obtained for the different amorphous silicon films show that. for given temperature T and total pressure P, the stress value still depends on the wafer spacing & In order to have a good understanding of stress phenomena, we have therefore supposed that the total pressure and the wafer spacing have no direct impact except for the variations of the deposition rate Vd and we finally only considered the influences of the deposition temperature and the deposition rate of the films in order to have a full analysis of the stress variations. Stresses in as-grown amorphous silicon films are compressive irrespective of the deposition parameters and linear relations with the deposition rate are evidenced whatever the deposition temperature (Fig. 1). The use of disilane Si2H(, is responsible for high
-200 " 0
00
-250 " -3o0 0
lo
20
30 40 50 deposition rate (,3drnin)
60
70
Fig. 2. A v e r a g e s t r e s s e s o f the f i l m s a n n e a l e d 15 m i n at 600°C.
deposition rate due to the very reactive radical Sill 2 contribution and to hydrogenation phenomena, leading to the obtaining of amorphous Si(H) films [6-8]. In addition to the hydrogenation effects, Nakazawa [7] aIso explained the crystallisation behaviour of amorphous silicon deposited from disilane thanks to differences of the films structural disorder despite their amorphous structure. This phenomenology has been kept and the influence of the silicon microstructure will be taken into account by introducing the film ordering 0: the lowest 0 value, the lowest ordering and the highest structural disorder. Finally, we will assume that the intrinsic stress o-~ only results from the influences of the film ordering 0 and the hydrogen content [H]: cr = cri = or0 + O'H.
(3)
In order to put in clear evidence the influence of hydrogenation, the average stress cra of the different amorphous silicon films annealed 15 min at 600°C has been evaluated (Fig. 2). During such an annealing, silicon structure remains amorphous, hydrogen atoms out-diffuse from the film as verified by SIMS experiments (CAMECA IMS 4f equipment, primary ion: Cs +, energy: 10 keV) and
-IO0
•
["
600
465°(2
-150
4so c
" • u
400
-2OO
a-Si/Si(11 I) a-Si/SiO2 a-Si/Si3N4
"o o
~" 200
o
8
g
-250 ©
o
t=
tensile stress
•
o
-300 O o
0
ta
0 compressive stress
m
-200
-350 O •
-400
400
zo
20
30 40 50 deposition rate U~,Jmin)
6o
vo
F i g . 1. A v e r a g e s t r e s s e s o f the a s - d e p o s i t e d a m o r p h o u s silicon films.
s0
So
i
O
2
4
6 8 l0 annealing duration (h)
12
F i g . 3. Stress v a r i a t i o n s d u r i n g a 6 0 0 ° C anneal.
I4
236
P. Temple-Boyer et al. / Thin Solid Films 310 (t997) 234-237
Fig. 4. (a-d) Scanning electron micrograph~. (a) After a 5 h anneal at 600°C. (b) After a 7 h anneal at 600°C. (c) After a 8 h 30 min anneal at 600°C. d) After a 12 h anneal at 600°C.
stress increases greatly, i.e., is less compressive, whatever the deposition parameters. After annealing, the influence of hydrogenation should be negligible (o-,H ~ 0) and experimentaI results evidence linear relation between o-~ and Va whatever the temperature (Fig. 2): o-~ = o',u + o-a. = Crao= o-~o(T ) + a , ( T ) V d .
(4)
By assuming that Eq. (4) can be generalised to % , the dependence of the stress with the film ordering can be expressed by: o-o = O-oo(T ) + a o ( T ) V d with a o > 0.
(5)
Since it has been demonstrated that the hydrogen content of amorphous silicon films obtained from disilane increases with deposition rate ~,~ [7,8] and if we assume a linear behaviour by analogy with the experimental results, the dependence of the stress with the hydrogen content can be expressed as follows: o'tt = O'Ho(T) -- a H ( T ) V d with ctH > 0.
(6)
From Eqs. (3), (5) and (6) and in agreement with the experimental results (Fig. 1), we finally obtain: or= O-o(T ) + a ( r ) v ~ ,
(7)
with: o-0(T) = %0(r) + o-H0(T) and a(T) = a o ( T ) - a H ( r ) , Thanks to Eq. (7) and according to literature [7,8], the influences of the deposition rate Vd and the deposition temperature T can be summarised as follows: Vd increases **
T increases ~
0decreasesando- increases ) [H] increases and crH decreases ' 0 increases and % decreases [H] decreases and crn increases
Therefore, the intrinsic stress of amorphous silicon films is the cumulated result of the influence of its microstructure ordering and its hydrogen content, both responsible for compressive (negative) stress. No stress (o-= 0) will be obtained in case of no hydrogenation ([HI = 0) and perfect
P. Temple-Boyer et al. / Thfil Solid Films 310 (1997) 2 3 4 - 2 3 7
disorder (0 = 0). This result prevents from realising no stress amorphous silicon films since it has been shown that the lowest orderings are obtained for the highest hydrogen contents and vice versa [7,8]. To go further, the variations of a o and a H should be studied. Since the highest orderings are obtained for the highest temperatures, and by considering saturation effects, the lowest influences of the deposition rate on stress should be obtained at high temperature, showing that ao(T) decreases when temperature increases as can be seen on Fig. 2. The same assumptions could be done for the hydrogen content, demonstrating that an(T) increases with temperature. Finally, as can be seen on Fig. I, a(T)= ao(T)-aH(T) should decrease when temperature increases.
237
always been contained in the range 400 + 25 MPa, whatever the deposition parameters. Finally, the crystallisation influences on the residual stress of semicrystalline silicon films can be described as follows: o- ( x ) = O"min -]- ¥( O'max -- O-min).
(8)
where x represents the polycrystalline phase percent and crmin is the silicon films stress at the germination phase end, roughly equal to cr~e (Fig. 3). These results demonstrate that the average stress of semicrystalline silicon films should be studied by considering two separate influences related to deposition and crystallisation: Cr =
O'deposition
"4- O'crystallisation ,
(9)
3.2. hlfluences of the co'stallisatiotl amzeaI
4. Conclusion
The residual stress variations during a 600°C anneal have been studied on amorphous silicon films de~oosited (T = 465°C, P = 200 mTorr, a = 20 ram, Vd = 34 A / r a i n ) on bare, oxidised (about 120 nm of oxide) or nitrided (about 80 nm of silicon nitride) silicon wafers (Fig. 3). The curves obtained are identical whatever the substrate type and put into evidence a transition from highly compressive to highly tensile stress. Such transition has already been evidenced in the literature for silicon deposition from silane [ I - 4 ] . In our case, four different steps can be distinguished: an initial rapid increase, a period of latency, a quasi-linear increase and a final level. If the initial rapid increase has already been explained thanks to dehydrogenation effects at the anneal beginning (see below), the following two steps are directly related to crystallisation phenomena: the period of latency and the linear increase corresponds to germination and crystallisation phases, respectively. Fig. 4 a - d represents the different amorphous/polycrystalline structures (revealed in SECCO etch) obtained for different annealing duration. The results demonstrate that the stress positive (tensile) shift is due to the amorphous/polycrystaIline conversion and confirm that crystallisation is associated with a volume contraction producing a tensile field [3]. Finally, when the silicon film is completely crystallised, the average stress stays constant, roughly equal to 400 MPa. It should be mentioned that the influence of the 600°C anneal has been studied on several samples and, even if the crystallisation phenomena did not occur for the same annealing duration, the final maximal stress O-max of the polycrystalline silicon has
By studying the average stress siIicon films obtained from disilane Si2H 6, the influences of the deposition parameters and the crystallisation phenomena have been separated for stress determination. The initial compressive stress has been related to the deposition temperature and the deposition rate through the cumulate effects of the films ordering and hydrogenation and it has been shown that crystallisation was responsible for a transition from compressive to tensile stress values. Thus, the residual stress of semicrystalline silicon films has been studied as the sum of a deposition stress and a crystallisation stress related to the deposition parameters and the polycrystalline phase percent, respectively. Such results should allow to better understand the stress origin into silicon films deposited from silane Sill 4.
References [1] V.M. Koleshko, V.F. Belitsky, I.V. Kiryushin, Thin Solid Films 162 (1988) 181. [2] D.G. OeL S.L. Mc Carthy, Mater. Res. Symp. Proc. 276 (1992) 85. [3] A. Benitez, J. Bausells, E. Cabruja, J. Esteve, J. Samitier, Sensors and Actuators 37-38 (1993) 723. [4] D. NIaier-Schneider, J. Maibach, E. Obermeier, D. Scneider, J. Micromech. Microeng. 5 (1995) 121. [5] G.G. Stoney. Proc. R. Soc. London 9 (1909) 172. [6] E. Scheid. B. de Mauduit, P. Taurines, D. Bielle Daspet, Jpn. J. Appl. Phys. 27 (2) (i990) 2105. [7] N. Nakazawa, J. AppI. Phys. 69 (3) (1991) 1703. [8] E. Scheid, J.J. Pedroviejo, P. Duverneuil, M. Gueye, J. Samitier, A. E1 Hassani, D. Biel[e Daspet, Mater. Sci. Eng. B17 (I993) 72.
o
jums ELSEVIER
Thin Solid Films 310 (1997) 234-237
Residual stress in silicon films deposited by LPCVD from disilane P. Temple-Boyer *, E. Scheid, G. Faugere, B. Rousset LAAS-CNRS, 7 Avenue du ColonelRoche, Toulouse Cddex 3107Z France
Received l0 April 1997; accepted 25 June i997
Abstract
Measurements of the thermomechanical stress in amorphous silicon films deposited by low pressure chemical vapour deposition (LPCVD) from disilane SiaH 6 are reported as a function of the deposition parameters (temperature, gas pressure and wafer spacing). Major influences of the deposition temperature and the deposition rate are put into evidence and related to the films ordering and hydrogenation. The effects of a 600°C anneal are also investigated and a transition from highly compressive to highly tensile stress is characterised whatever the deposition. Such behaviour has been explained thanks to hydrogen atoms out-diffusion and crystallisation effects. © 1997 Elsevier Science S.A. Ke>~vords: Crystallization; Silicon; Stress
1. I n t r o d u c t i o n With the development of microtechnologies and the realisation of complex micromechanicat elements, it has become necessary to investigate the mechanical properties of silicon-based materials. Polysilicon films have been no exception to the rule and the influences of deposition parameters and crystallisation anneal on their intrinsic stress have been reported in the literature [1-4]. However, with the use of silane Sill 4 as gaseous source, silicon crystallisation occurs during film deposition and it has been almost impossible to separate the influences of the two phenomena. Since deposition temperatures from disilane Si2H 6 (450-480°C) are lower than the silicon crystallisation temperature ( = 600°C), this gaseous source has been used to obtain amorphous silicon films and should allow to tackle this problem. The aim of this work is to present the intrinsic stress results of amorphous silicon films deposited by low pressure chemical vapour deposition (LPCVD) from disilane and to characterise the influences of a crystallisation postanneal at 600°C.
* Corresponding author. 0040-6090/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved. PII S 0040-6090(97)00387-8
2. Experiments Thin amorphous silicon films were deposited by low pressure chemical vapour deposition (LPCVD) from disilane Si2H 6 on 10 cm, (111), oxidised (about 120 nm of oxide) silicon wafers. The deposition temperature T ranged from 450 to 480°C and the total pressure P from 13.5 to 54 Pa. In our horizontal furnace, the distance 8 between two consecutive wafers was set at 10 or 20 mm in order to obtain different deposition rates for the same temperature and pressure of deposition. After removal of the back side silicon deposition by chemical etching ( H N O 3 : 5 0 cm 3CH3COOH: 20 cm3-HF: 2 cm3), the curvature R of the wafer was determined by profilometry and the average stress cr of the deposited film was calculated thanks to the formula of Stoney [5]: 1
o-=
E
6R 1 - v
D2 d '
(1)
where d is the film thickness (assessed by ellipsometry at a 830 nm wavelength), E, v and D are the Young Modulus, the Poisson ratio and the thickness of the substrate, respectively, (for silicon (111), E / ( 1 - v ) equals 2.3 × 1011 Pa). The accuracy of the technique was not worse than 10%. Crystallisation anneals were finally performed at 600°C into a conventional thermal furnace under neutral ambient and the crystallisation level was analysed by scanning
P. Temple-Boyer et al. / Thin Solid Films 310 (1997) 2 3 4 - 2 3 7
235
100
electron microscopy (SEM) observations after etching the samples into a SECCO etch in order to make the polysilicon grains more distinct.
,, • =
50"
~,
450oc 465oc 480oc
-50"
3. Results and discussion -IO0"
3.1. Influences of the deposition parameters
-150 "
Let us discuss about the mechanisms of stress generation. In the general case, the thermomechanical stress is the sum of the thermal stress crth and the intrinsic stress cri. The thermal stress is caused by a difference in the thermal expansion coefficients of the monocrystalline silicon substrate (ce .s,) and the deposited film (C~s~) and by a difference between the deposition temperature T and the ambient temperature during stress measurement. In our case, since thermal expansion coefficient is a macroscopic parameter, it should not depend on silicon microstructure and we will assume that C~s~= Ces~ whatever the crystallisation level, i.e., that crth is negligible compared to the intrinsic stress o-~: O" =
%
(2)
-1- dr i = O"i .
The experimental results obtained for the different amorphous silicon films show that. for given temperature T and total pressure P, the stress value still depends on the wafer spacing & In order to have a good understanding of stress phenomena, we have therefore supposed that the total pressure and the wafer spacing have no direct impact except for the variations of the deposition rate Vd and we finally only considered the influences of the deposition temperature and the deposition rate of the films in order to have a full analysis of the stress variations. Stresses in as-grown amorphous silicon films are compressive irrespective of the deposition parameters and linear relations with the deposition rate are evidenced whatever the deposition temperature (Fig. 1). The use of disilane Si2H(, is responsible for high
-200 " 0
00
-250 " -3o0 0
lo
20
30 40 50 deposition rate (,3drnin)
60
70
Fig. 2. A v e r a g e s t r e s s e s o f the f i l m s a n n e a l e d 15 m i n at 600°C.
deposition rate due to the very reactive radical Sill 2 contribution and to hydrogenation phenomena, leading to the obtaining of amorphous Si(H) films [6-8]. In addition to the hydrogenation effects, Nakazawa [7] aIso explained the crystallisation behaviour of amorphous silicon deposited from disilane thanks to differences of the films structural disorder despite their amorphous structure. This phenomenology has been kept and the influence of the silicon microstructure will be taken into account by introducing the film ordering 0: the lowest 0 value, the lowest ordering and the highest structural disorder. Finally, we will assume that the intrinsic stress o-~ only results from the influences of the film ordering 0 and the hydrogen content [H]: cr = cri = or0 + O'H.
(3)
In order to put in clear evidence the influence of hydrogenation, the average stress cra of the different amorphous silicon films annealed 15 min at 600°C has been evaluated (Fig. 2). During such an annealing, silicon structure remains amorphous, hydrogen atoms out-diffuse from the film as verified by SIMS experiments (CAMECA IMS 4f equipment, primary ion: Cs +, energy: 10 keV) and
-IO0
•
["
600
465°(2
-150
4so c
" • u
400
-2OO
a-Si/Si(11 I) a-Si/SiO2 a-Si/Si3N4
"o o
~" 200
o
8
g
-250 ©
o
t=
tensile stress
•
o
-300 O o
0
ta
0 compressive stress
m
-200
-350 O •
-400
400
zo
20
30 40 50 deposition rate U~,Jmin)
6o
vo
F i g . 1. A v e r a g e s t r e s s e s o f the a s - d e p o s i t e d a m o r p h o u s silicon films.
s0
So
i
O
2
4
6 8 l0 annealing duration (h)
12
F i g . 3. Stress v a r i a t i o n s d u r i n g a 6 0 0 ° C anneal.
I4
236
P. Temple-Boyer et al. / Thin Solid Films 310 (t997) 234-237
Fig. 4. (a-d) Scanning electron micrograph~. (a) After a 5 h anneal at 600°C. (b) After a 7 h anneal at 600°C. (c) After a 8 h 30 min anneal at 600°C. d) After a 12 h anneal at 600°C.
stress increases greatly, i.e., is less compressive, whatever the deposition parameters. After annealing, the influence of hydrogenation should be negligible (o-,H ~ 0) and experimentaI results evidence linear relation between o-~ and Va whatever the temperature (Fig. 2): o-~ = o',u + o-a. = Crao= o-~o(T ) + a , ( T ) V d .
(4)
By assuming that Eq. (4) can be generalised to % , the dependence of the stress with the film ordering can be expressed by: o-o = O-oo(T ) + a o ( T ) V d with a o > 0.
(5)
Since it has been demonstrated that the hydrogen content of amorphous silicon films obtained from disilane increases with deposition rate ~,~ [7,8] and if we assume a linear behaviour by analogy with the experimental results, the dependence of the stress with the hydrogen content can be expressed as follows: o'tt = O'Ho(T) -- a H ( T ) V d with ctH > 0.
(6)
From Eqs. (3), (5) and (6) and in agreement with the experimental results (Fig. 1), we finally obtain: or= O-o(T ) + a ( r ) v ~ ,
(7)
with: o-0(T) = %0(r) + o-H0(T) and a(T) = a o ( T ) - a H ( r ) , Thanks to Eq. (7) and according to literature [7,8], the influences of the deposition rate Vd and the deposition temperature T can be summarised as follows: Vd increases **
T increases ~
0decreasesando- increases ) [H] increases and crH decreases ' 0 increases and % decreases [H] decreases and crn increases
Therefore, the intrinsic stress of amorphous silicon films is the cumulated result of the influence of its microstructure ordering and its hydrogen content, both responsible for compressive (negative) stress. No stress (o-= 0) will be obtained in case of no hydrogenation ([HI = 0) and perfect
P. Temple-Boyer et al. / Thfil Solid Films 310 (1997) 2 3 4 - 2 3 7
disorder (0 = 0). This result prevents from realising no stress amorphous silicon films since it has been shown that the lowest orderings are obtained for the highest hydrogen contents and vice versa [7,8]. To go further, the variations of a o and a H should be studied. Since the highest orderings are obtained for the highest temperatures, and by considering saturation effects, the lowest influences of the deposition rate on stress should be obtained at high temperature, showing that ao(T) decreases when temperature increases as can be seen on Fig. 2. The same assumptions could be done for the hydrogen content, demonstrating that an(T) increases with temperature. Finally, as can be seen on Fig. I, a(T)= ao(T)-aH(T) should decrease when temperature increases.
237
always been contained in the range 400 + 25 MPa, whatever the deposition parameters. Finally, the crystallisation influences on the residual stress of semicrystalline silicon films can be described as follows: o- ( x ) = O"min -]- ¥( O'max -- O-min).
(8)
where x represents the polycrystalline phase percent and crmin is the silicon films stress at the germination phase end, roughly equal to cr~e (Fig. 3). These results demonstrate that the average stress of semicrystalline silicon films should be studied by considering two separate influences related to deposition and crystallisation: Cr =
O'deposition
"4- O'crystallisation ,
(9)
3.2. hlfluences of the co'stallisatiotl amzeaI
4. Conclusion
The residual stress variations during a 600°C anneal have been studied on amorphous silicon films de~oosited (T = 465°C, P = 200 mTorr, a = 20 ram, Vd = 34 A / r a i n ) on bare, oxidised (about 120 nm of oxide) or nitrided (about 80 nm of silicon nitride) silicon wafers (Fig. 3). The curves obtained are identical whatever the substrate type and put into evidence a transition from highly compressive to highly tensile stress. Such transition has already been evidenced in the literature for silicon deposition from silane [ I - 4 ] . In our case, four different steps can be distinguished: an initial rapid increase, a period of latency, a quasi-linear increase and a final level. If the initial rapid increase has already been explained thanks to dehydrogenation effects at the anneal beginning (see below), the following two steps are directly related to crystallisation phenomena: the period of latency and the linear increase corresponds to germination and crystallisation phases, respectively. Fig. 4 a - d represents the different amorphous/polycrystalline structures (revealed in SECCO etch) obtained for different annealing duration. The results demonstrate that the stress positive (tensile) shift is due to the amorphous/polycrystaIline conversion and confirm that crystallisation is associated with a volume contraction producing a tensile field [3]. Finally, when the silicon film is completely crystallised, the average stress stays constant, roughly equal to 400 MPa. It should be mentioned that the influence of the 600°C anneal has been studied on several samples and, even if the crystallisation phenomena did not occur for the same annealing duration, the final maximal stress O-max of the polycrystalline silicon has
By studying the average stress siIicon films obtained from disilane Si2H 6, the influences of the deposition parameters and the crystallisation phenomena have been separated for stress determination. The initial compressive stress has been related to the deposition temperature and the deposition rate through the cumulate effects of the films ordering and hydrogenation and it has been shown that crystallisation was responsible for a transition from compressive to tensile stress values. Thus, the residual stress of semicrystalline silicon films has been studied as the sum of a deposition stress and a crystallisation stress related to the deposition parameters and the polycrystalline phase percent, respectively. Such results should allow to better understand the stress origin into silicon films deposited from silane Sill 4.
References [1] V.M. Koleshko, V.F. Belitsky, I.V. Kiryushin, Thin Solid Films 162 (1988) 181. [2] D.G. OeL S.L. Mc Carthy, Mater. Res. Symp. Proc. 276 (1992) 85. [3] A. Benitez, J. Bausells, E. Cabruja, J. Esteve, J. Samitier, Sensors and Actuators 37-38 (1993) 723. [4] D. NIaier-Schneider, J. Maibach, E. Obermeier, D. Scneider, J. Micromech. Microeng. 5 (1995) 121. [5] G.G. Stoney. Proc. R. Soc. London 9 (1909) 172. [6] E. Scheid. B. de Mauduit, P. Taurines, D. Bielle Daspet, Jpn. J. Appl. Phys. 27 (2) (i990) 2105. [7] N. Nakazawa, J. AppI. Phys. 69 (3) (1991) 1703. [8] E. Scheid, J.J. Pedroviejo, P. Duverneuil, M. Gueye, J. Samitier, A. E1 Hassani, D. Biel[e Daspet, Mater. Sci. Eng. B17 (I993) 72.