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Study on the growth of CVD diamond thin films by in situ reflectivity measurement
Diamond and Related Materials 11 (2002) 1871–1875
Study on the growth of CVD diamond thin films by in situ reflectivity measurement Jinlong Luo, Xuantong Ying*, Peinan Wang, Liangyao Chen State Key Lab for Advanced Photonic Materials and Devices, Fudan University, Department of Optical Science and Engineering, Shanghai 200433, PR China Received 5 February 2002; received in revised form 25 June 2002; accepted 1 July 2002
Abstract Study on the growth of CVD diamond thin films by in situ reflectivity measurement was reported. SEM pictures show that the time dependent reflectivity is related to the evolution of the surface morphology. According to the principle of multiple beam interference, we present in this work a mathematical model to interpret laser reflectance interference on the surface of the growing diamond films. Using this model, a reflectivity curve was fitted. The optical refractive index, the surface roughness and the growth rate of the polycrystalline diamond thin films were determined from the fitted results in real time. Therefore, this is a useful method to study the growth of CVD diamond thin films. 䊚 2002 Elsevier Science B.V. All rights reserved. Keywords: CVD; Diamond films; Growth; In situ
1. Introduction The excellent properties of diamond such as its high hardness, chemical inertness and wide range optical transparency have led to considerable researches in the field of chemical vapor deposition (CVD) diamond thin films w1–3x. Diamond films have been ex situ characterized by a number of powerful diagnostic techniques including Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). In order to obtain the growth information of diamond films in real time, some laser reflectance interference (LRI) methods w4–8x have been developed. Compared with the ex situ measurement techniques, these indestructive LRI methods present growth information in real time, and the experimental system is compact, economical and relatively easier to set up. In this paper we reported the study on the growth of CVD diamond thin films by in situ reflectivity measure*Corresponding author: Tel.: q86-216-564-5938; fax: q86-216579-2662. E-mail address: [email protected] (X. Ying).
ment. Oscillations and attenuation of the reflectivity were observed as the film grew. SEM pictures of the diamond thin films, deposited under the same growth condition but in different growth stages, were compared with each other. The results show that the attenuation of the reflectivity was related to the evolution of the surface morphology. According to the principle of multiple beam interference w9x, a mathematical model was presented. Using this model, we fitted the surface reflectivity data of the growing diamond continuous thin film at different growth times. The optical refractive index, the average surface roughness and the growth rate of the diamond thin films were determined from the fitted results in real time. To verify the fitted data, the average surface roughness was also ex situ measured. The results show that the fitted data are in good agreement with those ex situ measured data. These results are helpful to the deposition of diamond thin films for optical applications. For the optical applications of diamond thin films, the refractive index n1, the surface roughness s and the thickness d are very important parameters to be determined. Since these parameters depend on the growth
0925-9635/02/$ - see front matter 䊚 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 9 6 3 5 Ž 0 2 . 0 0 1 8 3 - 8
1872
J. Luo et al. / Diamond and Related Materials 11 (2002) 1871–1875
n˜ sn1qik
(1)
as4pkyl
(2)
Considering the increasing thickness d and the surface roughness s of the diamond film with the growing time, we assume that the time dependent thickness d and roughness s are represented by dsd0qvd t
(3)
sss0qvs t
(4)
where, t is the growth time, d0 and s0 are two parameters to be fitted, vd and vs are the growth rate of the thickness and surface roughness, respectively. When the light beam goes a round trip through the diamond film, the phase shift f is Fig. 1. Schematic diagram of the experimental system for diamond thin film syntheses and in situ reflectivity measurement.
process, this in situ LRI measurement is a useful method to fabricate optical diamond thin films. 2. Experiment The experimental apparatus was shown in Fig. 1. Diamond syntheses were undertaken using a hot filament chemical vapor deposition (HFCVD) reactor. Diamond films were deposited on (100) silicon substrates that had been scratched with diamond powders and then rinsed. The deposition parameters were kept unchanged for all the diamond films synthesized in this paper as shown in Table 1. In order to reduce the effect of the variation in the power of the laser beam on our measurement, a He–Ne laser beam at wavelength ls632.8 nm was divided into two equal intensity beams by a beam splitter. The light intensity It of one beam was directly detected by a photocell with a He–Ne laser line filter. Another beam fell on the substrate through a reactor window approximately at normal incidence. The reflected light intensity Ir from the surface of the growing diamond thin film was detected by another detector. Meanwhile, the light emitted from the hot filament was filtrated by the He– Ne laser filters. After subtracting the reflection effect from the both sides of the reactor window, the ratio Ir y It was considered as the measured reflectivity R of the growing diamond surface.
Compared with the rough surface of growing diamond films, the diamond–silicon interface is regarded as smooth enough. According to the principle of multiple beam interference, therefore, the amplitude reflection coefficient of laser beam from the surface of the growing diamond films could be represented by the following equation rsr901qt901 t910 eyad eif r12 (1qr12 r910 eyad eif q(r12 r910 eyad eif)2q««) sr901qt901 t910 eyad eif r12 y(1yr12 r910 eyad eif) (6) where, r9ij and t9ij are the Fresnel amplitude reflection and transmission coefficient at a rough interface from medium i to medium j, while rij and tij are those at a smooth interface. For i and j, 0, 1, 2 means gas, diamond film and silicon, respectively. Considering the normal incidence of the laser beam, rij and tij are deduced as rijs(niynj)y(niqnj)
(7)
tijs2ni y(niqnj)
(8)
where, n0s1.00 and n2s3.88 are the refractive indices for gas and silicon at wavelength ls632.8 nm, respectively. Table 1 Typical deposition parameters for a HFCVD system Gas mixture
3. Mathematical model Assume that n1 is the refractive index and k is the extinction coefficient of the diamond thin film, respectively, then the complex optical refractive index n˜ and the absorption coefficient a are represented by
(5)
fs4pn1dyl
Methane Remain
Gas flow Deposition pressure Filament temperature Substrate temperature Grow rate
Nucleation period 2–5% Grow period 0.5–2% Hydrogen 50–200 sccm 20–40 torr 1900–2200 8C 650–900 8C 0.1–1 mmyh
J. Luo et al. / Diamond and Related Materials 11 (2002) 1871–1875
1873
A.J. Gatasman et al. w10x presented the following equations for light at wavelength l scattered from a rough surface when the surface roughness s
(9)
r910sr10 expwy2 (2psyl)2 n12x 2
(10) 2
t901st01 expwy (2psyl) (n1yn0) y2x
(11)
t910st10 expwy (2psyl)2 (n0yn1)2 y2x
(12)
In conclusion, the surface reflectivity R to be fitted can be derived from the Eqs. (6)–(12) Rsrr*
Fig. 2. In situ reflectivity of diamond thin film 259噛. The first minimum, the first maximum and the second maximum of the reflectivity are denoted as points A, B and C, respectively.
(13)
where, r * is the complex conjugate of r. The absorption coefficient of natural bulk diamond is below 0.1 cmy1 in the normal absorption range. For the high quality CVD diamond thin films deposited at the condition in our laboratory, their average roughness is more than 7 nm. Compared with the scattering, the absorption can be negligible. Namely, assuming ks0 is reasonable for the reflectivity data fitting. According to
Fig. 3. SEM pictures of diamond thin film 3321噛 (left), 3322噛 (middle) and 3324噛 (right). These diamond thin films were deposited under the same growth condition but in different growth stages A, B and C, respectively, as shown in Fig. 2.
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J. Luo et al. / Diamond and Related Materials 11 (2002) 1871–1875
Fig. 4. Multi-parameter non-linear fitting of the time dependent surface reflectivity of diamond thin film 259噛.
the reflectivity R shown as Eq. (13), therefore, the parameters n1, d0, vd, s0 and vs are the five parameters to be fitted. 4. In situ reflectivity fitting and discussions The results of in situ reflectivity measurement of diamond thin film 259噛 were shown in Fig. 2. Oscillations and attenuation of the reflectivity were observed as the film grew. Oscillation period is approximately 18 min. According to the above mathematical model, each oscillation indicates an increase in film thickness Dds ly2n1. In case the refractive index n1 is 2.41 (the refractive index of natural bulk diamond), the growth rate estimated by LRI is approximately 0.43 mmyh.
Fig. 2 also shows that the first peak B of the reflectivity curve is much lower than the second peak C. The reason may be that a lot of small polycrystalline grain islands were formed on the scratched silicon substrate for the peak B and the thickness of these diamond islands reached ly2n1. Therefore, there is an enhanced light reflection due to the multiple beam interference occurred in these islands, but part of the reflected light was scattered from the rough surface since these islands did not fully coalesced. However, for peak C, the polycrystalline grain islands coalesced into rather smooth surface and the thickness of the film reached lyn1, so that the enhanced interference took place in most of the measured area. Hence, the enhanced interference at peak C is stronger than that at peak B. The attenuation of the reflectivity is attributed to the increasing surface roughness that led to the stronger light scattering. SEM pictures shown in Fig. 3 were ex situ taken with a Philips XL30FEG SEM. These pictures confirmed the above analyses. The left picture (DM3321) of Fig. 3 shows that a lot of small islands were formed in the early stage when the reflectivity reached the first minimum (point A in Fig. 2), and the nucleation density was estimated as high as 109 –1010 cmy2. As the reflectivity reached the first maximum (point B in Fig. 2), the diamond film still did not coalesced as shown in the middle picture (DM3322) of Fig. 3. When the second maximum (point C in Fig. 2) happened, the rather smooth continuous film was formed as shown in the right picture (DM3324) of Fig. 3. Therefore, the reflectivity was clearly related to the evolution of surface morphology of the diamond thin films. Since the above mathematical model is only suitable for the continuous smooth films (s
Fig. 5. Calculated average surface roughness of diamond film 259噛 from the fitted parameters s0 and vs. The point 1, point 2 and point 3 are the ex situ measured roughness of diamond film 3324, 3325 and 292噛, which were synthesized under the same growth condition for 53.5, 63.0 and 81.0 min, respectively.
The refractive index n1 agrees well with that for natural diamond. According to the Eq. (3), the thickness of diamond films could be determined. The time dependent average roughness s can be calculated from the fitted parameters s0 and vs as the line shown in Fig. 5. For a verification, the roughness of diamond thin film 3324噛, 3325噛 and 292噛 were ex situ measured with an Alpha-Step 200 instrument. These diamond films were synthesized for 53.5, 63 and 81 min, respectively. The measured roughness is 8.0 nm (point 1 in Fig. 5), 12.0 nm (point 2 in Fig. 5) and 21.5 nm (point 3 in Fig. 5), respectively, which are in good agreement with the
J. Luo et al. / Diamond and Related Materials 11 (2002) 1871–1875
calculated result 7.6 nm, 12.9 and 22.8 nm. This fact confirms that the above assumption s
1875
Acknowledgments We wish to acknowledge the financial support from the National Natural Science Foundation of China (60178031 and 10075012), the Science and Technology Foundation of Shanghai City (99JC14038), Beijing Synchrotron Radiation Facility (99024) and Synchrotron Radiation Center of Fudan University. References
5. Conclusions Study on the growth of CVD diamond thin films by in situ reflectivity measurement was reported. SEM pictures show that the reflectivity is related to the evolution of the surface morphology. According to the principle of multiple beam interference, a mathematical model is presented to interpret laser reflectance interference on the surface of the growing diamond films. Using this model, the optical refractive index, the surface roughness and the growth rate of the polycrystalline diamond thin films were determined in real time by reflectivity curve fitting. Since the system used in this experiment is compact, economical and relatively easier to set up, this indestructive measurement method is considered to be a useful and convenient technique for the in situ growth study on CVD diamond thin films. This method has been successfully used to fabricate diamond filter windows for industrial applications.
w1x W.A. Yarbrough, N.D. Rosen, L.J. Pilione, W.R. Drawl, in: Proc. Diamond Optics II, 1989, SPIE Vol. 1146, San Diego, California, 1989, p. 2. w2x M. Seal, in: Proc. Third International Conference on Application of diamond films and related materials, 1995, NIST SP 885, Gaithersburg, MD, 1995, p. 3. w3x X. Ying, X. Xu, Thin Solid Films 368 (2000) 297. w4x A.M. Bonnot, R. Schauer, B. Weidner, Diamond Relat. Mater. 7 (1998) 205. w5x C.D. Zuiker, D.M. Gruen, A.R. Krauss, J. Appl. Phys. 79 (7) (1996) 3541. w6x A.M. Bonnot, B.S. Mathis, S. Moulin, Appl. Phys. Lett. 63 (13) (1993) 1754. w7x Wu. Ching-Hsong, W.H. Weber, T.J. Potter, M.A. Tamor, J. Appl. Phys. 73 (6) (1993) 2977. w8x B.R. Stoner, B.E. Williams, S.D. Wolter, K. Nishimura, J.T. Glass, J. Mater. Res. 7 (2) (1992) 257. w9x M. Born, E. Wolf, Principles of Optics, 6th. Ed, Pergamon Press, Oxford, 1980, p. 323. w10x A.J. Gatasman, R.H. Giles, J. Waldman, in: Proc. Diamond Optics III, 1990, SPIE Vol.1325, San Diego, California, 1990, P.170. w11x X. Ying, X. Xu, J. Luo, H. Cui, X. Wang, Y. Xu, Diamond Relat. Mater. 9 (2000) 1730.
Study on the growth of CVD diamond thin films by in situ reflectivity measurement Jinlong Luo, Xuantong Ying*, Peinan Wang, Liangyao Chen State Key Lab for Advanced Photonic Materials and Devices, Fudan University, Department of Optical Science and Engineering, Shanghai 200433, PR China Received 5 February 2002; received in revised form 25 June 2002; accepted 1 July 2002
Abstract Study on the growth of CVD diamond thin films by in situ reflectivity measurement was reported. SEM pictures show that the time dependent reflectivity is related to the evolution of the surface morphology. According to the principle of multiple beam interference, we present in this work a mathematical model to interpret laser reflectance interference on the surface of the growing diamond films. Using this model, a reflectivity curve was fitted. The optical refractive index, the surface roughness and the growth rate of the polycrystalline diamond thin films were determined from the fitted results in real time. Therefore, this is a useful method to study the growth of CVD diamond thin films. 䊚 2002 Elsevier Science B.V. All rights reserved. Keywords: CVD; Diamond films; Growth; In situ
1. Introduction The excellent properties of diamond such as its high hardness, chemical inertness and wide range optical transparency have led to considerable researches in the field of chemical vapor deposition (CVD) diamond thin films w1–3x. Diamond films have been ex situ characterized by a number of powerful diagnostic techniques including Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). In order to obtain the growth information of diamond films in real time, some laser reflectance interference (LRI) methods w4–8x have been developed. Compared with the ex situ measurement techniques, these indestructive LRI methods present growth information in real time, and the experimental system is compact, economical and relatively easier to set up. In this paper we reported the study on the growth of CVD diamond thin films by in situ reflectivity measure*Corresponding author: Tel.: q86-216-564-5938; fax: q86-216579-2662. E-mail address: [email protected] (X. Ying).
ment. Oscillations and attenuation of the reflectivity were observed as the film grew. SEM pictures of the diamond thin films, deposited under the same growth condition but in different growth stages, were compared with each other. The results show that the attenuation of the reflectivity was related to the evolution of the surface morphology. According to the principle of multiple beam interference w9x, a mathematical model was presented. Using this model, we fitted the surface reflectivity data of the growing diamond continuous thin film at different growth times. The optical refractive index, the average surface roughness and the growth rate of the diamond thin films were determined from the fitted results in real time. To verify the fitted data, the average surface roughness was also ex situ measured. The results show that the fitted data are in good agreement with those ex situ measured data. These results are helpful to the deposition of diamond thin films for optical applications. For the optical applications of diamond thin films, the refractive index n1, the surface roughness s and the thickness d are very important parameters to be determined. Since these parameters depend on the growth
0925-9635/02/$ - see front matter 䊚 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 9 6 3 5 Ž 0 2 . 0 0 1 8 3 - 8
1872
J. Luo et al. / Diamond and Related Materials 11 (2002) 1871–1875
n˜ sn1qik
(1)
as4pkyl
(2)
Considering the increasing thickness d and the surface roughness s of the diamond film with the growing time, we assume that the time dependent thickness d and roughness s are represented by dsd0qvd t
(3)
sss0qvs t
(4)
where, t is the growth time, d0 and s0 are two parameters to be fitted, vd and vs are the growth rate of the thickness and surface roughness, respectively. When the light beam goes a round trip through the diamond film, the phase shift f is Fig. 1. Schematic diagram of the experimental system for diamond thin film syntheses and in situ reflectivity measurement.
process, this in situ LRI measurement is a useful method to fabricate optical diamond thin films. 2. Experiment The experimental apparatus was shown in Fig. 1. Diamond syntheses were undertaken using a hot filament chemical vapor deposition (HFCVD) reactor. Diamond films were deposited on (100) silicon substrates that had been scratched with diamond powders and then rinsed. The deposition parameters were kept unchanged for all the diamond films synthesized in this paper as shown in Table 1. In order to reduce the effect of the variation in the power of the laser beam on our measurement, a He–Ne laser beam at wavelength ls632.8 nm was divided into two equal intensity beams by a beam splitter. The light intensity It of one beam was directly detected by a photocell with a He–Ne laser line filter. Another beam fell on the substrate through a reactor window approximately at normal incidence. The reflected light intensity Ir from the surface of the growing diamond thin film was detected by another detector. Meanwhile, the light emitted from the hot filament was filtrated by the He– Ne laser filters. After subtracting the reflection effect from the both sides of the reactor window, the ratio Ir y It was considered as the measured reflectivity R of the growing diamond surface.
Compared with the rough surface of growing diamond films, the diamond–silicon interface is regarded as smooth enough. According to the principle of multiple beam interference, therefore, the amplitude reflection coefficient of laser beam from the surface of the growing diamond films could be represented by the following equation rsr901qt901 t910 eyad eif r12 (1qr12 r910 eyad eif q(r12 r910 eyad eif)2q««) sr901qt901 t910 eyad eif r12 y(1yr12 r910 eyad eif) (6) where, r9ij and t9ij are the Fresnel amplitude reflection and transmission coefficient at a rough interface from medium i to medium j, while rij and tij are those at a smooth interface. For i and j, 0, 1, 2 means gas, diamond film and silicon, respectively. Considering the normal incidence of the laser beam, rij and tij are deduced as rijs(niynj)y(niqnj)
(7)
tijs2ni y(niqnj)
(8)
where, n0s1.00 and n2s3.88 are the refractive indices for gas and silicon at wavelength ls632.8 nm, respectively. Table 1 Typical deposition parameters for a HFCVD system Gas mixture
3. Mathematical model Assume that n1 is the refractive index and k is the extinction coefficient of the diamond thin film, respectively, then the complex optical refractive index n˜ and the absorption coefficient a are represented by
(5)
fs4pn1dyl
Methane Remain
Gas flow Deposition pressure Filament temperature Substrate temperature Grow rate
Nucleation period 2–5% Grow period 0.5–2% Hydrogen 50–200 sccm 20–40 torr 1900–2200 8C 650–900 8C 0.1–1 mmyh
J. Luo et al. / Diamond and Related Materials 11 (2002) 1871–1875
1873
A.J. Gatasman et al. w10x presented the following equations for light at wavelength l scattered from a rough surface when the surface roughness s
(9)
r910sr10 expwy2 (2psyl)2 n12x 2
(10) 2
t901st01 expwy (2psyl) (n1yn0) y2x
(11)
t910st10 expwy (2psyl)2 (n0yn1)2 y2x
(12)
In conclusion, the surface reflectivity R to be fitted can be derived from the Eqs. (6)–(12) Rsrr*
Fig. 2. In situ reflectivity of diamond thin film 259噛. The first minimum, the first maximum and the second maximum of the reflectivity are denoted as points A, B and C, respectively.
(13)
where, r * is the complex conjugate of r. The absorption coefficient of natural bulk diamond is below 0.1 cmy1 in the normal absorption range. For the high quality CVD diamond thin films deposited at the condition in our laboratory, their average roughness is more than 7 nm. Compared with the scattering, the absorption can be negligible. Namely, assuming ks0 is reasonable for the reflectivity data fitting. According to
Fig. 3. SEM pictures of diamond thin film 3321噛 (left), 3322噛 (middle) and 3324噛 (right). These diamond thin films were deposited under the same growth condition but in different growth stages A, B and C, respectively, as shown in Fig. 2.
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J. Luo et al. / Diamond and Related Materials 11 (2002) 1871–1875
Fig. 4. Multi-parameter non-linear fitting of the time dependent surface reflectivity of diamond thin film 259噛.
the reflectivity R shown as Eq. (13), therefore, the parameters n1, d0, vd, s0 and vs are the five parameters to be fitted. 4. In situ reflectivity fitting and discussions The results of in situ reflectivity measurement of diamond thin film 259噛 were shown in Fig. 2. Oscillations and attenuation of the reflectivity were observed as the film grew. Oscillation period is approximately 18 min. According to the above mathematical model, each oscillation indicates an increase in film thickness Dds ly2n1. In case the refractive index n1 is 2.41 (the refractive index of natural bulk diamond), the growth rate estimated by LRI is approximately 0.43 mmyh.
Fig. 2 also shows that the first peak B of the reflectivity curve is much lower than the second peak C. The reason may be that a lot of small polycrystalline grain islands were formed on the scratched silicon substrate for the peak B and the thickness of these diamond islands reached ly2n1. Therefore, there is an enhanced light reflection due to the multiple beam interference occurred in these islands, but part of the reflected light was scattered from the rough surface since these islands did not fully coalesced. However, for peak C, the polycrystalline grain islands coalesced into rather smooth surface and the thickness of the film reached lyn1, so that the enhanced interference took place in most of the measured area. Hence, the enhanced interference at peak C is stronger than that at peak B. The attenuation of the reflectivity is attributed to the increasing surface roughness that led to the stronger light scattering. SEM pictures shown in Fig. 3 were ex situ taken with a Philips XL30FEG SEM. These pictures confirmed the above analyses. The left picture (DM3321) of Fig. 3 shows that a lot of small islands were formed in the early stage when the reflectivity reached the first minimum (point A in Fig. 2), and the nucleation density was estimated as high as 109 –1010 cmy2. As the reflectivity reached the first maximum (point B in Fig. 2), the diamond film still did not coalesced as shown in the middle picture (DM3322) of Fig. 3. When the second maximum (point C in Fig. 2) happened, the rather smooth continuous film was formed as shown in the right picture (DM3324) of Fig. 3. Therefore, the reflectivity was clearly related to the evolution of surface morphology of the diamond thin films. Since the above mathematical model is only suitable for the continuous smooth films (s
Fig. 5. Calculated average surface roughness of diamond film 259噛 from the fitted parameters s0 and vs. The point 1, point 2 and point 3 are the ex situ measured roughness of diamond film 3324, 3325 and 292噛, which were synthesized under the same growth condition for 53.5, 63.0 and 81.0 min, respectively.
The refractive index n1 agrees well with that for natural diamond. According to the Eq. (3), the thickness of diamond films could be determined. The time dependent average roughness s can be calculated from the fitted parameters s0 and vs as the line shown in Fig. 5. For a verification, the roughness of diamond thin film 3324噛, 3325噛 and 292噛 were ex situ measured with an Alpha-Step 200 instrument. These diamond films were synthesized for 53.5, 63 and 81 min, respectively. The measured roughness is 8.0 nm (point 1 in Fig. 5), 12.0 nm (point 2 in Fig. 5) and 21.5 nm (point 3 in Fig. 5), respectively, which are in good agreement with the
J. Luo et al. / Diamond and Related Materials 11 (2002) 1871–1875
calculated result 7.6 nm, 12.9 and 22.8 nm. This fact confirms that the above assumption s
1875
Acknowledgments We wish to acknowledge the financial support from the National Natural Science Foundation of China (60178031 and 10075012), the Science and Technology Foundation of Shanghai City (99JC14038), Beijing Synchrotron Radiation Facility (99024) and Synchrotron Radiation Center of Fudan University. References
5. Conclusions Study on the growth of CVD diamond thin films by in situ reflectivity measurement was reported. SEM pictures show that the reflectivity is related to the evolution of the surface morphology. According to the principle of multiple beam interference, a mathematical model is presented to interpret laser reflectance interference on the surface of the growing diamond films. Using this model, the optical refractive index, the surface roughness and the growth rate of the polycrystalline diamond thin films were determined in real time by reflectivity curve fitting. Since the system used in this experiment is compact, economical and relatively easier to set up, this indestructive measurement method is considered to be a useful and convenient technique for the in situ growth study on CVD diamond thin films. This method has been successfully used to fabricate diamond filter windows for industrial applications.
w1x W.A. Yarbrough, N.D. Rosen, L.J. Pilione, W.R. Drawl, in: Proc. Diamond Optics II, 1989, SPIE Vol. 1146, San Diego, California, 1989, p. 2. w2x M. Seal, in: Proc. Third International Conference on Application of diamond films and related materials, 1995, NIST SP 885, Gaithersburg, MD, 1995, p. 3. w3x X. Ying, X. Xu, Thin Solid Films 368 (2000) 297. w4x A.M. Bonnot, R. Schauer, B. Weidner, Diamond Relat. Mater. 7 (1998) 205. w5x C.D. Zuiker, D.M. Gruen, A.R. Krauss, J. Appl. Phys. 79 (7) (1996) 3541. w6x A.M. Bonnot, B.S. Mathis, S. Moulin, Appl. Phys. Lett. 63 (13) (1993) 1754. w7x Wu. Ching-Hsong, W.H. Weber, T.J. Potter, M.A. Tamor, J. Appl. Phys. 73 (6) (1993) 2977. w8x B.R. Stoner, B.E. Williams, S.D. Wolter, K. Nishimura, J.T. Glass, J. Mater. Res. 7 (2) (1992) 257. w9x M. Born, E. Wolf, Principles of Optics, 6th. Ed, Pergamon Press, Oxford, 1980, p. 323. w10x A.J. Gatasman, R.H. Giles, J. Waldman, in: Proc. Diamond Optics III, 1990, SPIE Vol.1325, San Diego, California, 1990, P.170. w11x X. Ying, X. Xu, J. Luo, H. Cui, X. Wang, Y. Xu, Diamond Relat. Mater. 9 (2000) 1730.