- Email: [email protected]
Growth rate and deposition process of silicon carbide film by low-pressure chemical vapor deposition
,outN.tor CRVSTAL OROWTH
ELSEVIER
Journal of Crystal Growth 169 (1996) 485-490
Growth rate and deposition process of silicon carbide film by low-pressure chemical vapor deposition Ken-ichi Murooka
*, Iwao
Higashikawa,
Yoshio Gomei
Research and Decelopment Center, Toshiba Corporation, I Komukai Toshiba-cho, Saiwai-ku, Kawasaki 210, Japan Received
I November 1995; accepted 16 April 1996
Abstract The growth rate and deposition process of polycrystalline silicon carbide by low-pressure chemical vapor deposition with the introduction of hydrogen chloride gas were investigated. Analogous to the case of silicon, the growth rate was well described by a model that included nucleation of particles in the gas phase, a change of the reaction species from hydrides to chlorides, and etching or inhibition of growth by hydrogen chloride. The film stress was considerably influenced by the introduction of hydrogen chloride, which is thought to change the reaction path.
1. Introduction Stability to high temperature and chemicals makes silicon carbide (Sic) a promising material for a variety of applications [ 1,2]. Its high electric breakdown field, saturation drift velocity, and thermal conductivity are expected to be useful in high-power or high-temperature environment electric devices [36]. A theoretical study on the deposition process of Sic was carried out by Allendorf and Kee [7], and Fuentes studied the deposition process of polycrystalline Sic as an X-ray mask membrane 181. In our previous report [9], adding HCl to the chemical vapor deposition source gases influenced the characteristics of the deposited film such as stress, optical transparency, and surface roughness. The growth rate with HCl, which is a basic parameter in chemical
* Corresponding
author.
0022-0248/96/$15.00 Copyright PII SOO22-0248(96)00415-O
vapor deposition (CVD), however, has not been thoroughly investigated, and details of the reactions with HCl have not yet been clarified. This paper reports studies on the growth rate and deposition process of polycrystalline Sic film by low-pressure chemical vapor deposition (LPCVD) with the introduction of HCl, analogous to the case of silicon [lo].
2. Experimental
procedure
Three-inch-diameter Si(100) wafers were used as substrates. Sic was deposited in an inductive heating barrel-type LPCVD apparatus. SiH, and C, H, were used as the source gases for Si and C, respectively, and H, as the carrier gas. The substrate temperature was measured by a thermocouple inside the susceptor calibrated using an infrared-radiation thermometer. Emissivity correction of the thermometer was previously determined by using a wafer in which
0 1996 Elsevier Science B.V. All rights reserved
thermocouples were embedded. The total gas pressure was maintained at 0.33 kPa, and the ratio of C to Si in the source gas was maintained at 0.93. The H, flow was 10 SLM, and the quantity of HCI was O-250 seem. The film thickness was measured using a Nanospec, and the film stress was calculated by comparing the flatness of the wafer before and after deposition.
3. Results and discussion Fig. 1 shows the growth rate versus HCl flow rate, which was proportional to the HCl concentration, at various substrate temperatures. The growth rate dependence was simple at low temperature, but complicated at high temperature. At high temperature, the growth rate first decreased with increasing HCl flow rate, but increased above 7.5 seem, decreasing again above 150 seem. At low temperature, the growth rate decreased monotonically with increasing HCl flow rate. The curves in Fig. 1 were fitted to the following model, which is analogous to the one employed for Si by Bloem and Claassen [ 101. The main roles of HCI in this model are the suppression of gas phase nucleation, the change of the reactant species from hydrides to chlorides, and the etching 60 I. 1040°c . 99OT I ‘. 940°c,
50
1
\
‘\ \\
R d? =
(4 - uG‘w1 /&[HCllZ + k,
-\
‘.-.
k2k,[H,][HC1]
. ‘,. .-. _. --. .. .- .-. ._. _., _ .
0 100
200
300
[HCI] (seem)
Fig. I, Growth rate vs. HCI flow rate, which was proportional the HCI concentration, at various hbntrate temperatures.
’
(2)
dX +
1 + ex
-,fx?.
(3)
In the case of no HCl (x = O), the growth rate is given by (u - c), which was measured previously and used in the curve fitting. The curve fitting in Fig. 1 was carried out by assuming that b, d, e, and ,f have an Arrhenius equation form (= A exp(-E,/RT)). The result of the fitting was evaluated by using the reliability factor (R factor), which is often used in diffraction analysis,
------_____
.-.-.-- .-.. -. _*__~. .__
+ k,k,
R,, is the rate of deposition for the reaction path that is direct from A*, and Rd2 is the rate of deposition for the reaction path by way of ACI;. The total growth rate is determined by adding R,, and R,, and deducing the rate of etching by reaction with HCl CR,), which is proportional to the square of the HCl concentration [lo]. In this study, HZ and AH, concentrations were kept constant, therefore, the growth rate R is given by the following equation with normalizing each term and denoting the HCl flow rate by X, since the HCI concentration is proportional to the HCI flow rate. 1 +bx’
. ---------____________
(‘1
’
k,h]kzk,[W][HCl]
u--L L.
0
Rd,=
R=-
‘\
10
of Sic. Reactant species were assumed to be represented by one component A, although SIC is a two-component material. The initial gas species AH, becomes the active species A*. A* is divided into two paths, one diffusing onto the substrate and contributing to growth (while a portion nucleates and becomes particles without contributing to growth) and the other converting AClG by reacting with HCl. AC]; rarely nucleates in the gas phase, and is again divided into two paths, one diffusing onto the substrate and contributing to growth and the other converted to high-class chlorides reacting with HCI without contributing to growth. Then, the following equations are obtained by considering the equilibrium conditions of the concentration of each species (see Appendix), as the reverse reaction rates are thought to be negligibly small.
to
R=
Cl oh\
-
=oh\
I,,,1 ’
K.-i. Murooka
rt cd./ Journal
of CIytal
60
-10
-20
-30 0
100
200
300
[HCI] (seem)
Fig. 2. Dependence of each term of the growth rate model on the HCI flow rate at 1040°C.
where Ioh\ are the observed values and Ical are the calculated values. At first. the parameter space region, which gives an R factor of less than lo%, was selected from all parameter space by using random functions. The selected region seemed to be simply connected. Next, the optimization of the parameters was carried out from more than fifty starting points in the selected region, so as to minimize the R factor. Though a few of them were trapped in the local minimum, most of them converged almost to the same point and the minimized value of the R factor was 3.5%. Some modified equations from Eq. (3) were also applied for fitting as a test; however, the minimized R factors in such cases were more than that obtained in the case of Eq. (3). For example, taking the case that the last term of Eq. (3) was given by -fx, which corresponded to the case where the etching occurs with the monochloride species, the minimized R factor was 9%, which means less agreement with the experiment. Although Eq. (3) was derived by rough approximations, the fitted curves in Fig. 1 coincide with the experimental results. Taking the case at 1040°C as an example, the total growth rate R and each term R,, , R,,, R, are plotted in Fig. 2. Fig. 2 describes the reason for the
Growth
487
169 (19961485-490
growth rate dependence on the HCl flow rate shown in Fig. 1, that is, the rate of A” direct reaction R,, initially falls with the addition of HCl, the rate of reaction through ACI; Rd2 then increases, and the growth rate finally falls again due to the increase of etching R, as shown in Fig. 2. The durability of bulk SIC to HCl is, however, known quite well, and the etching rate is thought to be small compared to the value in Fig. 2. Therefore, inhibition of the growth process rather than etching was assumed to occur due to the adsorption of Cl atoms. Fig. 3 shows the dependence of the growth rate on substrate temperature (Arrhenius plot) for an HCl flow rate of 1.50 seem. The curve fitting in Fig. 3 was carried out as follows: At first, the values u - c were calculated by using the plotted data in Fig. 3 and Eq. (3) with the fitted results of h. d, e, and .f; which were used in Fig. 1. Next, assuming that particle nucleating reaction c is negligibly small in the low-temperature region and a is dominant in the low-temperature region, the parameters of a were determined from the region 1/T > 7.8 X lo-’ of the Arrhenius plot of u - c by applying the Arrhenius equation form. Finally, the values c were calculated by using the above results, and the parameters of c was also determined by applying the Ahrrenius equation form. The slope of the curve in Fig. 3 varies from the low-temperature to the high-temperature
loo I
7.4
7.6
7.6
6
a.2
6.4
l/T (lO-?K) Fig. 3. Dependence of growth rate on substrate (Arrhenius plot) for an HCl flow rate of 150 seem.
temperature
488
K.-i. Murooka et al./Joumal
of Crystal
Growth 169 (19%) 485-490
Table 1 Fitted results of the parameters
1600
A 0 h (’
ti P
.t
2.0x 3.6~ 1.8X 5.7 x 7.7x 1.3x
EA (kcal/mol) lo’? 10’ lo?’ 10’ IO_‘4 10”’
61 33 111 5.8 -66 75
3
3 f g
7.8
8
. without
800
1.
A I-ICI0 seem ~. HCI 75 seem i e HCI 250 SCCIJI_;
7.6
.
1200
% 1000
region; however, it is not as flat as expected in a typical diffusion-limited region, even in the hightemperature region. Therefore, the diffusion-limited region did not seem to appear in this case, and Eq. (3) is valid at high temperature, although the model used in this study does not contain the diffusion process explicitly. Table 1 shows the values of each parameter as a result of fitting. The value of the activation energy EA in parameter a, which gives the slope of the Arrhenius plot in the low-temperature region without HCl, is nearly equal to that of the hydrogen desorption reaction from Si and C adopted by Allendorf and Kee [7]. Fig. 4 shows other examples of the Ahrrenius plot. The plotted data are the experimental values, and the curves are the calculated ones obtained from Eq. (3) with the same parameters. The case without HCl indicates some
7.4
.
a.2
a.4
l/T (iO-?K) Fig. 4. Dependence of growth rate on substrate temperature (Arrhenius plot) for an HCl flow rate of 0, 75, and 250 seem.
A
0
600
; v,
400
0
HCI
with HCI 150 seem 1
1
900
950
1000
1050
1100
1150
T (“Cl Fig. 5. Dependence of SIC film stress on substrate with and without HCl.
temperature
discrepancy between the experimental and the calculated results in the high deposition rate region. This is supposed to be the effect of the diffusion process, which affects mainly the high deposition rate condition, and is neglected in the model. The dependence of Sic film stress on substrate temperature with and without HCl is shown in Fig. 5. The dependence is completely different for the two cases. The film stress is considerably high and decreases fast with increasing the substrate temperature in the case without HCl, while the film stress is relatively low and increases slowly with increasing the substrate temperature about more than 1000°C in the case with HCl 150 seem. This result indicates that HCl influences on the film stress, as reported previously [9]. In Ref. [9], the change of the stress is considered to be due to the change of the effective source gas C/Si ratio caused by the indirect effect of a different etching rate to the C and Si species. If this mechanism only affects the film stress, the difference between with and without HCl seems to become large with increasing substrate temperature because the higher the temperature, the more the reaction rate increases and the effect of the different etching rate to the C and Si species is thought to become large. Thus, there should be other mechanisms to change the film stress. Since the change in R,, and R,, between the HCl flow rates of 0 and 150 seem is
K.-i. Murookrr rt ul. / Journal of Crytul
much larger than that in R,, as shown in Fig. 2. the change of the reaction species from A’ to ACl; is thought to be another reason for the change in the stress, rather than the effect of etching or inhibition of growth. The determination of species AH2 is difficult in the present situation. For example, Allendorf and Kee showed that the carbon species determine the deposition rate and reactions involving species with silicon-carbon bonds did not have an influence on the mechanism [7]. These results indicate AH, may be the carbon species like CH, and there are no silicon-carbon bonds in the gas phase. Nagasawa and Yamaguchi studied the effect of the surface reaction of silicon species and carbon species on the growth mechanism, and showed that the film became epitaxial by suppressing the gas phase reaction between silicon species and carbon species while the film was polycrystalline in the case that silicon species and carbon species reacted freely [I 11. They also showed the growth rate was only affected by the Cz H, flow rate, which again suggests only the carbon species determine the deposition rate. On the other hand, Fuentes reported that the dependence of the deposition rate on the source gas ratio Si/(Si + C) had a maxima around Si/(Si + C> = 0.55 in the case of polycrystalline growth 181. This result suggests not only the carbon species determine the deposition rate. Moreover. Powell et al., and Karmann et al., showed that the deposition rate was determined mainly by the silicon species, and slightly affected by the carbon species [ 12,131. These results indicate that AH, may be the silicon species like SiH,. It is difficult to explain all the results without a contradiction. The determination of species AH, is a subject to be studied in the future.
4. Summary The growth rate and deposition process of Sic with the introduction of HCl were investigated. The growth rate was well described by a model, which included nucleation of particles in the gas phase, a change of the reaction species from hydrides to chlorides, and etching or inhibition of growth by HCl. The film stress was considerably influenced by HCl, which is thought to change the effective source gas ratio and the reaction path.
Growth 16Y (lYY61 485-4Y0
Acknowledgements The authors would like to thank Dr. T. Takigawa for his encouragement.
Appendix
A
The following model:
reactions
were considered
AH, + A* + H,,
in the
(4)
A” + 2HCl -+ ACl;
+ H,.
(5)
A’ 2 A( particle),
(6)
A” 2 A(growth).
(7)
AC15 + HCl 2 AHCl,,
(8)
ACl;
+ Hz 2 A(growth)
+ 2HCl.
(9)
Then the following equations are given by the equilibrium conditions of the concentration A* and AC1 $ :
k,bw
[A* ] =
k,[HCl]’
+ k, + k, ’
(10)
k,[A* ][HCl]’ [ACl;]
= ks[HCl] + kh[Hz]
(11)
Since k, is considered to be subtracted by the particle nucleation process k, from its original reaction rate k,, k, is replaced by k, - k,. Then, Eqs. (I) and (2) are obtained from Eqs. (71, (9), (10). (11) by leaving the main two terms of the power series in [HCl] to simplify the results.
References [I] K. Minato and K. Fukuda, J. Nucl. Mater. 60 (1987) 233. [21 J. Federer, Thin Solid Films 40 (1977) 89. [3] H. Daimon, M. Yamanaka, M. Shinohara, E. Sakuma, S. Misawa, K. Endo and S. Yoshida. Appl. Phys. Lett. 51 (1987) 1106.
490
K.-i. Murooka et al. /Journal
of Crytul
[4] J.W. Palmour, H.S. Kong and R.F. Davis, J. Appl. Phys. 64 (19881 2168. [5] W. von Muench and P. Hoeck, Solid-State Electron. 21 (19781479. [6] Y.C. Wang, R.F. Davis and J.A. Edmond, J. Electron. Mater. 20 (19911 289. [7] M.D. Allendorf and R.J. Kee, J. Electrochem. Sot. 138 (19911 841. [8] R.I. Fuentes, J. Vat. Sci. Technol. B 10 (1992) 3159. [9] K. Murooka, M. Itoh. H. Komano and Y. Gomei, Jpn. J. Appt. Phys. 30 (19911 3074.
Growth 169 (19961 485-490
[lo] J. Bloem and W.A.P. Claassen, J. Crystal Growth 49 (19801 435. [I I] H. Nagasawa and Y. Yamaguchi, Appl. Surf. Sci. 82/83 (I 9941 405. [I21 J.A. Powell, L.C. Matus and M.A. Kuczmarski, J. Electrochem. Sot. 134 (1987) 1558. [ 131 S. Karmann, C. Haberstroh, F. Engelbrecht, W. Suttrop, A. Schoner, M. Schadt, R. Helbig, G. Pensl, R.A. Stein and S. Leibenzeder, Physica B 185 (19931 75.
ELSEVIER
Journal of Crystal Growth 169 (1996) 485-490
Growth rate and deposition process of silicon carbide film by low-pressure chemical vapor deposition Ken-ichi Murooka
*, Iwao
Higashikawa,
Yoshio Gomei
Research and Decelopment Center, Toshiba Corporation, I Komukai Toshiba-cho, Saiwai-ku, Kawasaki 210, Japan Received
I November 1995; accepted 16 April 1996
Abstract The growth rate and deposition process of polycrystalline silicon carbide by low-pressure chemical vapor deposition with the introduction of hydrogen chloride gas were investigated. Analogous to the case of silicon, the growth rate was well described by a model that included nucleation of particles in the gas phase, a change of the reaction species from hydrides to chlorides, and etching or inhibition of growth by hydrogen chloride. The film stress was considerably influenced by the introduction of hydrogen chloride, which is thought to change the reaction path.
1. Introduction Stability to high temperature and chemicals makes silicon carbide (Sic) a promising material for a variety of applications [ 1,2]. Its high electric breakdown field, saturation drift velocity, and thermal conductivity are expected to be useful in high-power or high-temperature environment electric devices [36]. A theoretical study on the deposition process of Sic was carried out by Allendorf and Kee [7], and Fuentes studied the deposition process of polycrystalline Sic as an X-ray mask membrane 181. In our previous report [9], adding HCl to the chemical vapor deposition source gases influenced the characteristics of the deposited film such as stress, optical transparency, and surface roughness. The growth rate with HCl, which is a basic parameter in chemical
* Corresponding
author.
0022-0248/96/$15.00 Copyright PII SOO22-0248(96)00415-O
vapor deposition (CVD), however, has not been thoroughly investigated, and details of the reactions with HCl have not yet been clarified. This paper reports studies on the growth rate and deposition process of polycrystalline Sic film by low-pressure chemical vapor deposition (LPCVD) with the introduction of HCl, analogous to the case of silicon [lo].
2. Experimental
procedure
Three-inch-diameter Si(100) wafers were used as substrates. Sic was deposited in an inductive heating barrel-type LPCVD apparatus. SiH, and C, H, were used as the source gases for Si and C, respectively, and H, as the carrier gas. The substrate temperature was measured by a thermocouple inside the susceptor calibrated using an infrared-radiation thermometer. Emissivity correction of the thermometer was previously determined by using a wafer in which
0 1996 Elsevier Science B.V. All rights reserved
thermocouples were embedded. The total gas pressure was maintained at 0.33 kPa, and the ratio of C to Si in the source gas was maintained at 0.93. The H, flow was 10 SLM, and the quantity of HCI was O-250 seem. The film thickness was measured using a Nanospec, and the film stress was calculated by comparing the flatness of the wafer before and after deposition.
3. Results and discussion Fig. 1 shows the growth rate versus HCl flow rate, which was proportional to the HCl concentration, at various substrate temperatures. The growth rate dependence was simple at low temperature, but complicated at high temperature. At high temperature, the growth rate first decreased with increasing HCl flow rate, but increased above 7.5 seem, decreasing again above 150 seem. At low temperature, the growth rate decreased monotonically with increasing HCl flow rate. The curves in Fig. 1 were fitted to the following model, which is analogous to the one employed for Si by Bloem and Claassen [ 101. The main roles of HCI in this model are the suppression of gas phase nucleation, the change of the reactant species from hydrides to chlorides, and the etching 60 I. 1040°c . 99OT I ‘. 940°c,
50
1
\
‘\ \\
R d? =
(4 - uG‘w1 /&[HCllZ + k,
-\
‘.-.
k2k,[H,][HC1]
. ‘,. .-. _. --. .. .- .-. ._. _., _ .
0 100
200
300
[HCI] (seem)
Fig. I, Growth rate vs. HCI flow rate, which was proportional the HCI concentration, at various hbntrate temperatures.
’
(2)
dX +
1 + ex
-,fx?.
(3)
In the case of no HCl (x = O), the growth rate is given by (u - c), which was measured previously and used in the curve fitting. The curve fitting in Fig. 1 was carried out by assuming that b, d, e, and ,f have an Arrhenius equation form (= A exp(-E,/RT)). The result of the fitting was evaluated by using the reliability factor (R factor), which is often used in diffraction analysis,
------_____
.-.-.-- .-.. -. _*__~. .__
+ k,k,
R,, is the rate of deposition for the reaction path that is direct from A*, and Rd2 is the rate of deposition for the reaction path by way of ACI;. The total growth rate is determined by adding R,, and R,, and deducing the rate of etching by reaction with HCl CR,), which is proportional to the square of the HCl concentration [lo]. In this study, HZ and AH, concentrations were kept constant, therefore, the growth rate R is given by the following equation with normalizing each term and denoting the HCl flow rate by X, since the HCI concentration is proportional to the HCI flow rate. 1 +bx’
. ---------____________
(‘1
’
k,h]kzk,[W][HCl]
u--L L.
0
Rd,=
R=-
‘\
10
of Sic. Reactant species were assumed to be represented by one component A, although SIC is a two-component material. The initial gas species AH, becomes the active species A*. A* is divided into two paths, one diffusing onto the substrate and contributing to growth (while a portion nucleates and becomes particles without contributing to growth) and the other converting AClG by reacting with HCl. AC]; rarely nucleates in the gas phase, and is again divided into two paths, one diffusing onto the substrate and contributing to growth and the other converted to high-class chlorides reacting with HCI without contributing to growth. Then, the following equations are obtained by considering the equilibrium conditions of the concentration of each species (see Appendix), as the reverse reaction rates are thought to be negligibly small.
to
R=
Cl oh\
-
=oh\
I,,,1 ’
K.-i. Murooka
rt cd./ Journal
of CIytal
60
-10
-20
-30 0
100
200
300
[HCI] (seem)
Fig. 2. Dependence of each term of the growth rate model on the HCI flow rate at 1040°C.
where Ioh\ are the observed values and Ical are the calculated values. At first. the parameter space region, which gives an R factor of less than lo%, was selected from all parameter space by using random functions. The selected region seemed to be simply connected. Next, the optimization of the parameters was carried out from more than fifty starting points in the selected region, so as to minimize the R factor. Though a few of them were trapped in the local minimum, most of them converged almost to the same point and the minimized value of the R factor was 3.5%. Some modified equations from Eq. (3) were also applied for fitting as a test; however, the minimized R factors in such cases were more than that obtained in the case of Eq. (3). For example, taking the case that the last term of Eq. (3) was given by -fx, which corresponded to the case where the etching occurs with the monochloride species, the minimized R factor was 9%, which means less agreement with the experiment. Although Eq. (3) was derived by rough approximations, the fitted curves in Fig. 1 coincide with the experimental results. Taking the case at 1040°C as an example, the total growth rate R and each term R,, , R,,, R, are plotted in Fig. 2. Fig. 2 describes the reason for the
Growth
487
169 (19961485-490
growth rate dependence on the HCl flow rate shown in Fig. 1, that is, the rate of A” direct reaction R,, initially falls with the addition of HCl, the rate of reaction through ACI; Rd2 then increases, and the growth rate finally falls again due to the increase of etching R, as shown in Fig. 2. The durability of bulk SIC to HCl is, however, known quite well, and the etching rate is thought to be small compared to the value in Fig. 2. Therefore, inhibition of the growth process rather than etching was assumed to occur due to the adsorption of Cl atoms. Fig. 3 shows the dependence of the growth rate on substrate temperature (Arrhenius plot) for an HCl flow rate of 1.50 seem. The curve fitting in Fig. 3 was carried out as follows: At first, the values u - c were calculated by using the plotted data in Fig. 3 and Eq. (3) with the fitted results of h. d, e, and .f; which were used in Fig. 1. Next, assuming that particle nucleating reaction c is negligibly small in the low-temperature region and a is dominant in the low-temperature region, the parameters of a were determined from the region 1/T > 7.8 X lo-’ of the Arrhenius plot of u - c by applying the Arrhenius equation form. Finally, the values c were calculated by using the above results, and the parameters of c was also determined by applying the Ahrrenius equation form. The slope of the curve in Fig. 3 varies from the low-temperature to the high-temperature
loo I
7.4
7.6
7.6
6
a.2
6.4
l/T (lO-?K) Fig. 3. Dependence of growth rate on substrate (Arrhenius plot) for an HCl flow rate of 150 seem.
temperature
488
K.-i. Murooka et al./Joumal
of Crystal
Growth 169 (19%) 485-490
Table 1 Fitted results of the parameters
1600
A 0 h (’
ti P
.t
2.0x 3.6~ 1.8X 5.7 x 7.7x 1.3x
EA (kcal/mol) lo’? 10’ lo?’ 10’ IO_‘4 10”’
61 33 111 5.8 -66 75
3
3 f g
7.8
8
. without
800
1.
A I-ICI0 seem ~. HCI 75 seem i e HCI 250 SCCIJI_;
7.6
.
1200
% 1000
region; however, it is not as flat as expected in a typical diffusion-limited region, even in the hightemperature region. Therefore, the diffusion-limited region did not seem to appear in this case, and Eq. (3) is valid at high temperature, although the model used in this study does not contain the diffusion process explicitly. Table 1 shows the values of each parameter as a result of fitting. The value of the activation energy EA in parameter a, which gives the slope of the Arrhenius plot in the low-temperature region without HCl, is nearly equal to that of the hydrogen desorption reaction from Si and C adopted by Allendorf and Kee [7]. Fig. 4 shows other examples of the Ahrrenius plot. The plotted data are the experimental values, and the curves are the calculated ones obtained from Eq. (3) with the same parameters. The case without HCl indicates some
7.4
.
a.2
a.4
l/T (iO-?K) Fig. 4. Dependence of growth rate on substrate temperature (Arrhenius plot) for an HCl flow rate of 0, 75, and 250 seem.
A
0
600
; v,
400
0
HCI
with HCI 150 seem 1
1
900
950
1000
1050
1100
1150
T (“Cl Fig. 5. Dependence of SIC film stress on substrate with and without HCl.
temperature
discrepancy between the experimental and the calculated results in the high deposition rate region. This is supposed to be the effect of the diffusion process, which affects mainly the high deposition rate condition, and is neglected in the model. The dependence of Sic film stress on substrate temperature with and without HCl is shown in Fig. 5. The dependence is completely different for the two cases. The film stress is considerably high and decreases fast with increasing the substrate temperature in the case without HCl, while the film stress is relatively low and increases slowly with increasing the substrate temperature about more than 1000°C in the case with HCl 150 seem. This result indicates that HCl influences on the film stress, as reported previously [9]. In Ref. [9], the change of the stress is considered to be due to the change of the effective source gas C/Si ratio caused by the indirect effect of a different etching rate to the C and Si species. If this mechanism only affects the film stress, the difference between with and without HCl seems to become large with increasing substrate temperature because the higher the temperature, the more the reaction rate increases and the effect of the different etching rate to the C and Si species is thought to become large. Thus, there should be other mechanisms to change the film stress. Since the change in R,, and R,, between the HCl flow rates of 0 and 150 seem is
K.-i. Murookrr rt ul. / Journal of Crytul
much larger than that in R,, as shown in Fig. 2. the change of the reaction species from A’ to ACl; is thought to be another reason for the change in the stress, rather than the effect of etching or inhibition of growth. The determination of species AH2 is difficult in the present situation. For example, Allendorf and Kee showed that the carbon species determine the deposition rate and reactions involving species with silicon-carbon bonds did not have an influence on the mechanism [7]. These results indicate AH, may be the carbon species like CH, and there are no silicon-carbon bonds in the gas phase. Nagasawa and Yamaguchi studied the effect of the surface reaction of silicon species and carbon species on the growth mechanism, and showed that the film became epitaxial by suppressing the gas phase reaction between silicon species and carbon species while the film was polycrystalline in the case that silicon species and carbon species reacted freely [I 11. They also showed the growth rate was only affected by the Cz H, flow rate, which again suggests only the carbon species determine the deposition rate. On the other hand, Fuentes reported that the dependence of the deposition rate on the source gas ratio Si/(Si + C) had a maxima around Si/(Si + C> = 0.55 in the case of polycrystalline growth 181. This result suggests not only the carbon species determine the deposition rate. Moreover. Powell et al., and Karmann et al., showed that the deposition rate was determined mainly by the silicon species, and slightly affected by the carbon species [ 12,131. These results indicate that AH, may be the silicon species like SiH,. It is difficult to explain all the results without a contradiction. The determination of species AH, is a subject to be studied in the future.
4. Summary The growth rate and deposition process of Sic with the introduction of HCl were investigated. The growth rate was well described by a model, which included nucleation of particles in the gas phase, a change of the reaction species from hydrides to chlorides, and etching or inhibition of growth by HCl. The film stress was considerably influenced by HCl, which is thought to change the effective source gas ratio and the reaction path.
Growth 16Y (lYY61 485-4Y0
Acknowledgements The authors would like to thank Dr. T. Takigawa for his encouragement.
Appendix
A
The following model:
reactions
were considered
AH, + A* + H,,
in the
(4)
A” + 2HCl -+ ACl;
+ H,.
(5)
A’ 2 A( particle),
(6)
A” 2 A(growth).
(7)
AC15 + HCl 2 AHCl,,
(8)
ACl;
+ Hz 2 A(growth)
+ 2HCl.
(9)
Then the following equations are given by the equilibrium conditions of the concentration A* and AC1 $ :
k,bw
[A* ] =
k,[HCl]’
+ k, + k, ’
(10)
k,[A* ][HCl]’ [ACl;]
= ks[HCl] + kh[Hz]
(11)
Since k, is considered to be subtracted by the particle nucleation process k, from its original reaction rate k,, k, is replaced by k, - k,. Then, Eqs. (I) and (2) are obtained from Eqs. (71, (9), (10). (11) by leaving the main two terms of the power series in [HCl] to simplify the results.
References [I] K. Minato and K. Fukuda, J. Nucl. Mater. 60 (1987) 233. [21 J. Federer, Thin Solid Films 40 (1977) 89. [3] H. Daimon, M. Yamanaka, M. Shinohara, E. Sakuma, S. Misawa, K. Endo and S. Yoshida. Appl. Phys. Lett. 51 (1987) 1106.
490
K.-i. Murooka et al. /Journal
of Crytul
[4] J.W. Palmour, H.S. Kong and R.F. Davis, J. Appl. Phys. 64 (19881 2168. [5] W. von Muench and P. Hoeck, Solid-State Electron. 21 (19781479. [6] Y.C. Wang, R.F. Davis and J.A. Edmond, J. Electron. Mater. 20 (19911 289. [7] M.D. Allendorf and R.J. Kee, J. Electrochem. Sot. 138 (19911 841. [8] R.I. Fuentes, J. Vat. Sci. Technol. B 10 (1992) 3159. [9] K. Murooka, M. Itoh. H. Komano and Y. Gomei, Jpn. J. Appt. Phys. 30 (19911 3074.
Growth 169 (19961 485-490
[lo] J. Bloem and W.A.P. Claassen, J. Crystal Growth 49 (19801 435. [I I] H. Nagasawa and Y. Yamaguchi, Appl. Surf. Sci. 82/83 (I 9941 405. [I21 J.A. Powell, L.C. Matus and M.A. Kuczmarski, J. Electrochem. Sot. 134 (1987) 1558. [ 131 S. Karmann, C. Haberstroh, F. Engelbrecht, W. Suttrop, A. Schoner, M. Schadt, R. Helbig, G. Pensl, R.A. Stein and S. Leibenzeder, Physica B 185 (19931 75.