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CVD diamond thin film for IR optics and X-ray optics
Thin Solid Films 368 (2000) 297±299
www.elsevier.com/locate/tsf
CVD diamond thin ®lm for IR optics and X-ray optics Xuantong Ying*, Xinmin Xu State Key Laboratory for Material Modi®cation by Laser, Ion and Electron Beams, Fudan University, Department of Physics, Shanghai 200433, China
Abstract Optical quality diamond thin ®lms have been deposited using a hot ®lament chemical vapor deposition (HFCVD) system. The diamond ®lms were characterized by Raman shift spectra, X-ray diffraction spectra, scanning electron microscopy. Diamond near infrared antire¯ective ®lter window and diamond X-ray window have been fabricated using above technology. The diamond near infrared antire¯ective ®lter windows have been successfully used in on-line monitoring at Shanghai Baosteel Works. It has produced annual bene®t as much as 2.4 million RMB Yuan. q 2000 Elsevier Science S.A. All rights reserved. Keywords: Antire¯ective; Chemical vapor deposition; Diamond; Film; IR optics; Near-infrared; Window; X-ray diffraction
1. Introduction Diamond has been considered as an ideal material for wide range of electromagnetic wave spectrum because of its excellent physical and chemical properties. However, cost and size of natural diamond limited its practical applications. The recent developments in the ®eld of low pressure vapor deposition technique for diamond ®lms have made it as a practical useful materials with reasonable cost in various applications. One of the most interesting uses is in the ®eld of infrared optics. Diamond thin ®lm is transparent from ultraviolet through visible to far-infrared wavelength because of its wide band width 5.4 eV. It possesses the greatest hardness and very good chemical stability, therefore it is an ideal material for infrared antire¯ective and protective ®lm [1±2]. The other application of diamond ®lm is used as ultra thin X-ray window. The traditional X-ray window is a thin (8±12 m) beryllium window. However, the necessary thickness to assure a vacuum-tight seal reduces the transmission of soft X-ray from light elements, such as boron, carbon, nitrogen, oxygen and ¯uorine. Ultra-thin freestanding diamond ®lm is the best candidate for beryllium window as a very strong, corrosion resistant and safety window for energy dispersive X-ray ¯uorescence (EDXRF) detectors for elemental analysis and as an energy ®lter of soft X-ray in synchrotron radiation light source. Using hot ®lament chemical vapor deposition (HFCVD) method, the optical quality diamond ®lms were deposited on * Corresponding author. Tel.: 186-21-65645938; 65104949. E-mail address: [email protected] (X. Ying).
fax:
186-21-
silicon substrates at Fudan University. The diamond ®lms were characterized by Raman shift spectra, X-ray diffraction (XRD), scanning electron microscopy (SEM), and other techniques. A diamond near-infrared antire¯ective protective ®lter window and an ultra-thin diamond X-ray window were designed and fabricated. Their applications in IR optics and X-ray optics were reported in this paper. 2. Experiment A hot ®lament chemical vapor deposition system was used to deposit optical quality diamond thin ®lm [3]. The schematic diagram of the HFCVD system is shown in Fig. 1. During the deposition period we adopted two steps (nucleation period and growth period) to keep high density (10 9±10/ cm 2) of diamond nucleation and mufti-beam interference technology to monitor and accurately control the thickness of diamond thin ®lm. The typical deposition parameters are shown in Table 1. The deposition parameters such as pressure, ®lament temperature, particularly the substrate temperature were carefully controlled to keep k100l crystallographic faces dominant on the surface of diamond ®lms therefore the surface roughness of the diamond ®lms could be signi®cantly reduced. 3. Characterization The Raman shift spectrum, X-ray diffraction spectrum, SEM picture and surface pro®le measurement show the specimens deposited in our laboratory are high optical qual-
0040-6090/00/$ - see front matter q 2000 Elsevier Science S.A. All rights reserved. PII: S 0040-609 0(00)00786-0
298
X. Ying, X. Xu / Thin Solid Films 368 (2000) 297±299
Fig. 2. The Raman shift spectrum of diamond ®lm R0302. Fig. 1. Schematic diagram of hot ®lament chemical vapor deposition system.
4. Scanning electron microscopy
ity polycrystalline diamond thin ®lms. The surface roughness of the sample is less than 10 nm. Its absorption and scattering is quite weak in near-infrared range.
Fig. 3 shows the SEM picture of the specimen D-1 that was taken on HITACHIS-20. It is observed that the specimen is polycrystalline diamond thin ®lm and k100l crystallographic faces dominant. The sizes of the crystallites are around 5 m.
3.1. Raman shift spectrum
5. Diamond near-infrared antire¯ective ®lter window
A Raman shift spectrum, measured on JOBIN-YZON U1000, from one of the ®lms deposited in our laboratory is shown in Fig. 2. A sharp peak is observed at 1332 cm 21, which is the position of Raman peak of nature diamond. Near 1500 cm 21, another much weak and broad Raman peak is attributed to a little amount of graphite and amorphous carbon deposited on the substrate with diamond. Since the sensitivity of Raman shift spectrum for diamond is much higher compared with that for graphite and amorphous carbon, the diamond purity is very high.
5.1. The main speci®cation of the diamond near-infrared window (model DIFW-1)
3.2. X-ray diffraction spectrum X-ray diffraction measurement was made on a D/max-B X-ray diffractometer. Table 2 compares the lattice spacings of a diamond ®lm specimen D-2 with the lattice spacings of nature diamond. They are quite similar to each other. Table 1 Deposition conditions for diamond thin ®lm at Fudan University a Gas ¯ow (sccm) Deposition pressure (kPa) Filament temperature (8C) Substrate temperature (8C) Grow rate (m/h)
50±200 1±10 1900±2200 750±900 0.1±1
a Gas mixture: Methane, Nucleation period 2±5%, growth period 0.5± 1.5%. remainder: hydrogen.
Transparent range (m) Detective range (m)
.1.1 1.3±1.8
Environment test Temperature test (8C) 350 (atmosphere) Corrosive test HNO3/HF (1:3, room temperature) Anti water test Pressure (MPa) Temperature (8C) Humidity (%)
Transparence .65% Test time (h) Test time (h)
15 15
0.18 125 100 Test time (h)
15
5.2. Application in IR optics and industry The diamond near-infrared window DIFW-1 has been successfully designed, and fabricated as an IR antire¯ective protective ®lter window [4±5]. The detectors with the diamond window DIFW-1 have been successfully used in on-line monitoring at Shanghai Baosteel Works. It is sensitive and reliable, working very well in the high temperature, and corrosive environment. The signal/noise ratio was increased at least two times. It could decrease the rolling time from 9.5 to 6.5 s for each seamless pipe at pipe opening procedure. It also decreases the error operations of the rolling machine, therefore decreases the reject
X. Ying, X. Xu / Thin Solid Films 368 (2000) 297±299
299
Table 2 Ê , Angstroms) Diamond lattice spacings (A hkl
Natural diamond
Fudan University diamond ®lm
111 220 311
2.060 1.261 1.075
2.058 1.259 1.076
rate of waste pipe. In addition, it yields the life of the IR detector because it protects the detector from acid, dust, steam and high temperature on the production line. It has produced annual bene®t as much as 2.4 million RMB Yuan for Shanghai Baosteel Works. Fig. 3. SEM picture of diamond thin ®lm D-1.
6. Ultra-thin diamond X-ray window Ultra-thin (0.5±1.0 m) diamond ®lm was deposited on silicon substrate. The substrate was partly etched by HF acid to form a 6 mm diameter ultra-thin freestanding diamond window (model FUX-1). The transmission of the window for Oxygen K-a X-ray ¯uorescence is compared with other ultra-thin diamond windows and beryllium window as the following
Thickness (mm) Transmission (%)
FUX-1
Crystallume NIST window [6] window [7]
0.5±1 21
0.4 22.5
0.3 27
Be window
0.5 8 10 Opaque
This kind of ultra-thin diamond X-ray window was designed and fabricated as an energy ®lter of soft X-ray at Shanghai New Synchrotron Radiation Light Source, which will be established in the beginning of next century. 7. Summary The optical quality diamond thin ®lm was deposited on silicon substrate at Fudan University using HFCVD method. The diamond ®lm was characterized by Raman shift spectroscopy, X-ray diffraction, SEM and other techniques. The diamond near-infrared window DIFW-1 has been designed, fabricated as an IR antire¯ective ®lter window.
The window DIFW-1 has been successfully used in on-line monitoring at Shanghai Baosteel Works. It has produced annual bene®t as much as 2.4 million RMB Yuan for Shanghai Baosteel Works. An ultra-thin freestanding diamond window (model FUX-1) for EDXRF detector and Shanghai New Synchrotron Radiation Light Source in the soft X-ray range was designed and fabricated. It is a strong, corrosion resistant and safety window with excellent transmission in soft X-ray range.
References [1] W.A. Yarbrough, N.D. Rosen, L.J. Pilione, W.R. Drawl, Proc. SPIE 1146 (1989) 2. [2] M. Seal, The current status of CVD diamond applications and prospects for the future, Applications of diamond ®lms and relative materials: Third International Conference, NIST SP 885 (1995) 3± 10. [3] X. Ying, Y. Shen, H. Xue, L. Jianhai, Z. Xing, Proc. SPIE 1759 (1992) 218. [4] Xuantong Ying, Albert Feldman, E.N. Farabaugh, J. Appl. Phys. 67 (4) (1990) 2056. [5] Y. Xuantong, S. Jiang, S. Yuanhua, Fabrication of CVD diamond thin ®lms and its application in IR Optics, Proceedings of '95 Beijing International Conference for Surface Science and Engineering, Beijing, China, May 15±19, 1995, p. 148. [6] M.G. Peters, J.L. Knowles, M. Breen, J. McCarthy, Proc. SPIE 1146 (1989) 217. [7] D.A. Fischer, W. Phillips, J. Vac. Sci. Technol. A 10 (4) (1992) 2119.
www.elsevier.com/locate/tsf
CVD diamond thin ®lm for IR optics and X-ray optics Xuantong Ying*, Xinmin Xu State Key Laboratory for Material Modi®cation by Laser, Ion and Electron Beams, Fudan University, Department of Physics, Shanghai 200433, China
Abstract Optical quality diamond thin ®lms have been deposited using a hot ®lament chemical vapor deposition (HFCVD) system. The diamond ®lms were characterized by Raman shift spectra, X-ray diffraction spectra, scanning electron microscopy. Diamond near infrared antire¯ective ®lter window and diamond X-ray window have been fabricated using above technology. The diamond near infrared antire¯ective ®lter windows have been successfully used in on-line monitoring at Shanghai Baosteel Works. It has produced annual bene®t as much as 2.4 million RMB Yuan. q 2000 Elsevier Science S.A. All rights reserved. Keywords: Antire¯ective; Chemical vapor deposition; Diamond; Film; IR optics; Near-infrared; Window; X-ray diffraction
1. Introduction Diamond has been considered as an ideal material for wide range of electromagnetic wave spectrum because of its excellent physical and chemical properties. However, cost and size of natural diamond limited its practical applications. The recent developments in the ®eld of low pressure vapor deposition technique for diamond ®lms have made it as a practical useful materials with reasonable cost in various applications. One of the most interesting uses is in the ®eld of infrared optics. Diamond thin ®lm is transparent from ultraviolet through visible to far-infrared wavelength because of its wide band width 5.4 eV. It possesses the greatest hardness and very good chemical stability, therefore it is an ideal material for infrared antire¯ective and protective ®lm [1±2]. The other application of diamond ®lm is used as ultra thin X-ray window. The traditional X-ray window is a thin (8±12 m) beryllium window. However, the necessary thickness to assure a vacuum-tight seal reduces the transmission of soft X-ray from light elements, such as boron, carbon, nitrogen, oxygen and ¯uorine. Ultra-thin freestanding diamond ®lm is the best candidate for beryllium window as a very strong, corrosion resistant and safety window for energy dispersive X-ray ¯uorescence (EDXRF) detectors for elemental analysis and as an energy ®lter of soft X-ray in synchrotron radiation light source. Using hot ®lament chemical vapor deposition (HFCVD) method, the optical quality diamond ®lms were deposited on * Corresponding author. Tel.: 186-21-65645938; 65104949. E-mail address: [email protected] (X. Ying).
fax:
186-21-
silicon substrates at Fudan University. The diamond ®lms were characterized by Raman shift spectra, X-ray diffraction (XRD), scanning electron microscopy (SEM), and other techniques. A diamond near-infrared antire¯ective protective ®lter window and an ultra-thin diamond X-ray window were designed and fabricated. Their applications in IR optics and X-ray optics were reported in this paper. 2. Experiment A hot ®lament chemical vapor deposition system was used to deposit optical quality diamond thin ®lm [3]. The schematic diagram of the HFCVD system is shown in Fig. 1. During the deposition period we adopted two steps (nucleation period and growth period) to keep high density (10 9±10/ cm 2) of diamond nucleation and mufti-beam interference technology to monitor and accurately control the thickness of diamond thin ®lm. The typical deposition parameters are shown in Table 1. The deposition parameters such as pressure, ®lament temperature, particularly the substrate temperature were carefully controlled to keep k100l crystallographic faces dominant on the surface of diamond ®lms therefore the surface roughness of the diamond ®lms could be signi®cantly reduced. 3. Characterization The Raman shift spectrum, X-ray diffraction spectrum, SEM picture and surface pro®le measurement show the specimens deposited in our laboratory are high optical qual-
0040-6090/00/$ - see front matter q 2000 Elsevier Science S.A. All rights reserved. PII: S 0040-609 0(00)00786-0
298
X. Ying, X. Xu / Thin Solid Films 368 (2000) 297±299
Fig. 2. The Raman shift spectrum of diamond ®lm R0302. Fig. 1. Schematic diagram of hot ®lament chemical vapor deposition system.
4. Scanning electron microscopy
ity polycrystalline diamond thin ®lms. The surface roughness of the sample is less than 10 nm. Its absorption and scattering is quite weak in near-infrared range.
Fig. 3 shows the SEM picture of the specimen D-1 that was taken on HITACHIS-20. It is observed that the specimen is polycrystalline diamond thin ®lm and k100l crystallographic faces dominant. The sizes of the crystallites are around 5 m.
3.1. Raman shift spectrum
5. Diamond near-infrared antire¯ective ®lter window
A Raman shift spectrum, measured on JOBIN-YZON U1000, from one of the ®lms deposited in our laboratory is shown in Fig. 2. A sharp peak is observed at 1332 cm 21, which is the position of Raman peak of nature diamond. Near 1500 cm 21, another much weak and broad Raman peak is attributed to a little amount of graphite and amorphous carbon deposited on the substrate with diamond. Since the sensitivity of Raman shift spectrum for diamond is much higher compared with that for graphite and amorphous carbon, the diamond purity is very high.
5.1. The main speci®cation of the diamond near-infrared window (model DIFW-1)
3.2. X-ray diffraction spectrum X-ray diffraction measurement was made on a D/max-B X-ray diffractometer. Table 2 compares the lattice spacings of a diamond ®lm specimen D-2 with the lattice spacings of nature diamond. They are quite similar to each other. Table 1 Deposition conditions for diamond thin ®lm at Fudan University a Gas ¯ow (sccm) Deposition pressure (kPa) Filament temperature (8C) Substrate temperature (8C) Grow rate (m/h)
50±200 1±10 1900±2200 750±900 0.1±1
a Gas mixture: Methane, Nucleation period 2±5%, growth period 0.5± 1.5%. remainder: hydrogen.
Transparent range (m) Detective range (m)
.1.1 1.3±1.8
Environment test Temperature test (8C) 350 (atmosphere) Corrosive test HNO3/HF (1:3, room temperature) Anti water test Pressure (MPa) Temperature (8C) Humidity (%)
Transparence .65% Test time (h) Test time (h)
15 15
0.18 125 100 Test time (h)
15
5.2. Application in IR optics and industry The diamond near-infrared window DIFW-1 has been successfully designed, and fabricated as an IR antire¯ective protective ®lter window [4±5]. The detectors with the diamond window DIFW-1 have been successfully used in on-line monitoring at Shanghai Baosteel Works. It is sensitive and reliable, working very well in the high temperature, and corrosive environment. The signal/noise ratio was increased at least two times. It could decrease the rolling time from 9.5 to 6.5 s for each seamless pipe at pipe opening procedure. It also decreases the error operations of the rolling machine, therefore decreases the reject
X. Ying, X. Xu / Thin Solid Films 368 (2000) 297±299
299
Table 2 Ê , Angstroms) Diamond lattice spacings (A hkl
Natural diamond
Fudan University diamond ®lm
111 220 311
2.060 1.261 1.075
2.058 1.259 1.076
rate of waste pipe. In addition, it yields the life of the IR detector because it protects the detector from acid, dust, steam and high temperature on the production line. It has produced annual bene®t as much as 2.4 million RMB Yuan for Shanghai Baosteel Works. Fig. 3. SEM picture of diamond thin ®lm D-1.
6. Ultra-thin diamond X-ray window Ultra-thin (0.5±1.0 m) diamond ®lm was deposited on silicon substrate. The substrate was partly etched by HF acid to form a 6 mm diameter ultra-thin freestanding diamond window (model FUX-1). The transmission of the window for Oxygen K-a X-ray ¯uorescence is compared with other ultra-thin diamond windows and beryllium window as the following
Thickness (mm) Transmission (%)
FUX-1
Crystallume NIST window [6] window [7]
0.5±1 21
0.4 22.5
0.3 27
Be window
0.5 8 10 Opaque
This kind of ultra-thin diamond X-ray window was designed and fabricated as an energy ®lter of soft X-ray at Shanghai New Synchrotron Radiation Light Source, which will be established in the beginning of next century. 7. Summary The optical quality diamond thin ®lm was deposited on silicon substrate at Fudan University using HFCVD method. The diamond ®lm was characterized by Raman shift spectroscopy, X-ray diffraction, SEM and other techniques. The diamond near-infrared window DIFW-1 has been designed, fabricated as an IR antire¯ective ®lter window.
The window DIFW-1 has been successfully used in on-line monitoring at Shanghai Baosteel Works. It has produced annual bene®t as much as 2.4 million RMB Yuan for Shanghai Baosteel Works. An ultra-thin freestanding diamond window (model FUX-1) for EDXRF detector and Shanghai New Synchrotron Radiation Light Source in the soft X-ray range was designed and fabricated. It is a strong, corrosion resistant and safety window with excellent transmission in soft X-ray range.
References [1] W.A. Yarbrough, N.D. Rosen, L.J. Pilione, W.R. Drawl, Proc. SPIE 1146 (1989) 2. [2] M. Seal, The current status of CVD diamond applications and prospects for the future, Applications of diamond ®lms and relative materials: Third International Conference, NIST SP 885 (1995) 3± 10. [3] X. Ying, Y. Shen, H. Xue, L. Jianhai, Z. Xing, Proc. SPIE 1759 (1992) 218. [4] Xuantong Ying, Albert Feldman, E.N. Farabaugh, J. Appl. Phys. 67 (4) (1990) 2056. [5] Y. Xuantong, S. Jiang, S. Yuanhua, Fabrication of CVD diamond thin ®lms and its application in IR Optics, Proceedings of '95 Beijing International Conference for Surface Science and Engineering, Beijing, China, May 15±19, 1995, p. 148. [6] M.G. Peters, J.L. Knowles, M. Breen, J. McCarthy, Proc. SPIE 1146 (1989) 217. [7] D.A. Fischer, W. Phillips, J. Vac. Sci. Technol. A 10 (4) (1992) 2119.