- Email: [email protected]
TiN thin films by X-ray and synchrotron radiation due to heat treatment
ARTICLE IN PRESS
Vacuum 80 (2006) 836–839 www.elsevier.com/locate/vacuum
Alteration of internal stresses in SiO2/Cu/TiN thin films by X-ray and synchrotron radiation due to heat treatment Tatsuya Matsuea,, Takao Hanabusab, Yasukazu Ikeuchia, Kazuya Kusakab, Osami Sakatac a
Niihama National College of Technology, 7-1 Yagumo-cho, Niihama 792-8580, Japan Faculty of Engineering, Tokushima University, 2-1 Minamijyosanjima-cho, Tokushima 770-8506, Japan c Japan Synchrotron Radiation Research Institute/SPring-8, Kouto 1-1-1 Mikazuki Sayo, Hyogo 679-5198, Japan b
Abstract A break of wiring by stress-migration becomes a problem with an integrated circuit such as LSI. The present study investigates residual stress in SiO2/Cu/TiN film deposited on glass substrates. A TiN layer, as an undercoat, was first deposited on the substrate by arc ion plating and then Cu and SiO2 layers were deposited by plasma coating. The crystal structure and the residual stress in the deposited multi-layer film were investigated using in-lab. X-ray equipment and a synchrotron radiation device that emits ultra-high-intensity Xrays. It was found that the SiO2 film was amorphous and both the Cu and TiN films had a strong {1 1 1} orientation. The Cu and TiN layers in the multi thick (Cu and TiN:1.0 mm)-layer film and multi thin (0.1 mm)-layer film exhibited tensile residual stresses. Both tensile residual stresses in the multi thin-layer film are larger than the multi thick-layer film. After annealing at 400 1C, these tensile residual stresses in both the films increased with increasing the annealing temperature. Surface swelling formations, such as bubbles were observed in the multi thick-layer film. However, in the case of the multi thin-layer films, there was no change in the surface morphology following heat-treatment. r 2005 Elsevier Ltd. All rights reserved. Keywords: Multi layers film; Residual stress; Crystal structure; Surface morphology; X-ray diffraction; Synchrotron radiation
1. Introduction In recent years, the technology for manufacturing highly integrated circuits has improved remarkably. With improvements, wiring materials have changed from aluminum to copper, which is characterized by low electrical resistance and high resistance to metal migration. However, copper diffuses through the silicon wafer substrate, so therefore a layer of TiN or TaN is generally deposited between the copper and silicon wafer to act as a diffusion barrier. During thin-film growth, residual stresses arise from the deposition process in thin-film coatings, and Corresponding author. Tel.: +81 897 37 7800; fax: +81 897 37 7842.
E-mail addresses: [email protected] (T. Matsue), [email protected] (T. Hanabusa), [email protected] (Y. Ikeuchi), [email protected] (K. Kusaka), [email protected] (O. Sakata). 0042-207X/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2005.11.033
these residual stresses depend on the mechanical properties of the materials involved. In addition, with an integrated circuit, thermal stress occurs by heating of a circuit at the time of use, and it becomes a problem that a break of wiring occurs for stress-migration caused by thermal stress [1–4]. The present study investigates the residual stress and crystallographic structure of SiO2/Cu/TiN multi-layer films, which imitated an integrated circuit, deposited on glass substrates. A TiN film is first deposited onto the substrate, as an undercoat layer, using arc ion plating (AIP), followed by a Cu film deposited by plasma coating (PC), and finally a SiO2 film for prevention of oxidation is deposited by PC. The crystallographic structure and residual stress of the deposited multi-layer film were investigated using X-ray diffraction and synchrotron radiation, as a function of the thickness of the Cu and TiN layers and the annealed treatments.
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Cu 1.0 mm/TiN 1.0 mm) and a multi thin-layer film (SiO2 0.1 mm/Cu 0.1 mm/TiN 0.1 mm).
2. Experimental details 2.1. Specimens Glass plates were used as substrates (Borosilicate glass: Corning 7059, 50 50 1 mm). An AIP system (Kobe Steel Co.) was used to prepare the TiN films on these substrates [5]. After degassing, nitrogen gas was injected into the chamber at a pressure of 1.0 Pa. An arc current of 60 A, and a bias voltage of 0 V were used. Films were grown to a thickness of approximately 1.0 and 0.1 mm. The substrate surface was positioned perpendicular to the Ti target during deposition. Prior to deposition, the substrate surfaces were treated by ion cleaning (using Ti) to remove impurities. Ion cleaning was performed twice for 2 min, each at an arc current of 60 A, and a bias voltage of 600 V. Specimens reached a temperature of approximately 200 1C during the cleaning process. After TiN Film deposition, Cu or SiO2 films were then deposited by PC. Fig. 1 shows a schematic of the PC system. The Cu or SiO2 targets are evaporated in the presence of an Ar plasma produced by a plasma gun. The evaporated target metal ionizes in the Ar plasma and is attracted by the bias voltage to the substrate surface, where it is deposited to form a Cu and a SiO2 film. During the deposition of Cu films, an arc current of 100 A and a bias voltage of 44 V were applied to the plasma, and the pressure in the chamber was 6.3 102 Pa, with resultant film thicknesses of approximately 1.0 and 0.1 mm. For the SiO2 film, an arc current of 150 A, and a bias voltage of 0 V were applied to the plasma, with a deposition chamber pressure of 6.3 102 Pa, and the film thickness was approximately 0.1 mm. In this study, two types of specimens were examined: a multi thick-layer film (SiO2 0.1 mm/
Substrate glass
Plasma gun
2.2. Annealed treatment As for the copper, the physics fixed number, such as the elasticity fixed number, changes in heat environment of 400 1C from 200 1C. In order to investigate how the structure and the residual stress in the film are changed by heating–cooling cycles, the specimens were heated in a vacuum furnace at temperatures of 100, 200, 300 and 400 1C. The duration of each temperature treatment was 60 min, after which, the specimens were cooled down to room temperature. 2.3. Measurement of residual stress in the multi-layer films using X-ray radiation and ultra-high-intensity synchrotron radiation The texture and the residual stresses in the multi thicklayer films were measured with a laboratory X-ray diffraction system (lab. X-ray), using CuKa radiation (wavelength 0.15 nm) under the following conditions: tube voltage 40 kV, tube current 20 mA, irradiated area 2 6 mm. The residual stress in the multi thick-layer film was evaluated using diffraction measurements of Cu 222 and TiN422. However, in the case of the multi thin-layer films, residual stress evaluation was difficult because X-ray strength from diffraction plane was very weak. The residual stress in the multi thin-layer films was measured using synchrotron radiation (SR) from the BL13XU beam line, at the SPring-8 facility, with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) located in the Harima district, Japan. The energy of the SR was 12.4 keV, which corresponds to an X-ray wavelength of 0.10 nm. This was confirmed by the (2 1 1) diffraction peak value of a standard iron powder. The size of the incident SR beam was 1.0 1.0 mm. Residual stress in the multi thin-layer films was evaluated using diffraction measurements of Cu111 and TiN111 [6].
Evaporative metal (Cu)
2.4. Stress measuring method
Plasma (Ar+)
Plasma beam control unit Target (Cu or SiO2)
Fig. 1. Schematic illustration of the apparatus used for plasma coating.
The two–tilt method [7] was used to measure stresses in the {1 1 1}-oriented films, because sufficient diffraction intensity could only be obtained at two c angles. TiN111, Cu111 and 222 diffraction peaks were found at c ¼ 01 and 70.51, and TiN422 diffraction peaks were found at c ¼ 19:51 and 61.91 [8]. Stresses in the Cu and TiN films were determined using the following equation: s ¼ 1=ðS44 =2Þðec1 ec2 Þ=ðsin2 c1 sin2 c2 Þ,
(1)
where S44 is the elastic compliance of Cu and TiN single crystals, and the values are 13.26 103/ GPa [9] and 5.95 103/ GPa [10], ec1 and ec2 are lattice strains at angles c1 and c2, respectively. In addition, measured value
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of residual stress becomes the mean value of an X-ray domain to go through.
5
annealing temperature 400 °C 300°C 200°C 100 °C
30
70
Cu222
Cu200
0
Tin222
As-deposited TiN111 Cu111
Intensity,×103 arbitrarily unit
SiO2/ Cu / TiN glass substrate
110 2 ,deg
150
Fig. 2. Change in the X-ray diffraction patterns of SiO2/Cu/TiN films with annealing temperature.
Residual stress, MPa
Fig. 2 shows the lab. X-ray diffraction pattern provided from the multi thick-layer films that were heat treated. Because of the highly oriented {1 1 1} structure of the Cu layer and the TiN layer, only two very large intensity peaks of 111 and 222 diffractions were detected by y–2y scanning for both the as-deposited and the heat treated multi thicklayer films. The results revealed that the peak intensity of the 111 and 222 diffractions did not change by heat treatment below 400 1C. In addition, a similar result was provided in the multi thin-layer films. By the way, hello diffraction pattern of X-ray in the glass substrate was observed from Fig. 2. Therefore, it is thought that X-ray beam goes through the multi thick-layer film. Fig. 3 shows the residual stresses measured in the multi thick-layer films evaluated using lab. X-rays. Residual stress of the Cu and TiN layers were measured five times. The as-deposited Cu and TiN layers in the multi thicklayers films have tensile residual stresses of approximately 220 and 250 MPa, respectively. Residual stresses in the Cu layers increased to 350 MPa with increasing heat treatment temperatures up to 300 1C. However, these values decreased at 400 1C. On the other hand, residual stresses in the TiN layers increased to 600 MPa with increased heating temperatures up to 400 1C. Fig. 4 shows the residual stresses measured in the multi thin-layer films using synchrotron radiation. Residual stress of the Cu and TiN layers was measured three times. The as-deposited Cu and TiN layers in the multi thin-layers films have tensile residual stresses of approximately 400 and 570 MPa, respectively. Residual stresses of the Cu layers increased to 570 MPa for heat treatment tempera-
600
Residual stress Cu layer (1.0µm) TiN layer (1.0µm)
400
200
0 0
100
200 300 Annealed temperature,°C
400
Fig. 3. Relationship between the residual stresses of the Cu (1.0 mm) and TiN (1.0 mm) layers and the annealing temperature of SiO2/Cu/TiN films on glass substrate, laboratory X-ray.
1200
Residual stress, MPa
3. Results and discussion
800
900
600
Residual stress Cu layer (0.1µm) TiN layer (0.1µm)
300
0 0
100
200 300 Annealed temperature, °C
400
Fig. 4. Relationship between the residual stresses of the Cu (0.1 mm) and TiN (0.1 mm) layers and the annealing temperature of SiO2/Cu/TiN films on glass substrates, synchrotron radiation.
tures of 200 1C. In the case of heat treatment over 200 1C, the stress value of the Cu layer was almost constant. On the other hand, residual stresses in the TiN layers increased to 930 MPa for heating temperatures up to 200 1C. For heat treatments over 200 1C, the stress of the TiN layers had the same tendency as that observed for the Cu layers. The surface condition of the annealed multi-layer films was examined using Field Emission Scanning Electron Microscope (FESEM). Fig. 5 shows that the heat treatment has an influence on the surface of the SiO2/Cu/TiN films. Fig. 5(a) shows a FESEM image of the surface of an asdeposited multi thick-layer film. In case of the TiN film deposited by AIP, many craters were formed by the surface [11]. It seems that the number of craters in the surface of the multi thick-layer films was formed by the influence of the lower TiN layer. After heat treatment at 400 1C, surface swelling deformations, such as bubbles were observed in the multi thick-layer film (Fig. 5(b)). In the case of the multi thin-layer film, there was no change in the surface morphology after heat treatment (Fig. 5(c)). It is thought
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the deposition temperature and room temperature, and afilm and asubs: are the thermal expansion coefficients of the film and the substrate, respectively. The values for acu , aTiN and aglass are 16.8 106, 9.35 106 and 4.6 106 K1 [12], respectively. The thermal stresses given by Eq. (2) are tensile for both the Cu layer deposited on TiN and for the TiN layer deposited on glass. However, the measured value was smaller than the value calculated using Eq. (2). Therefore, it is thought that the tensile residual stress in the Cu and TiN layers is formed by the thermal stress and the intrinsic stress caused by ion bombardment. However, in this study, the details remain unclear, and further research is necessary. 4. Conclusion
Fig. 5. Morphological change (a) of SiO2/Cu (1.0 mm)/TiN (1.0 mm) film surfaces, and (b) of Cu (1.0 mm) and TiN (1.0 mm), and (c) of Cu (0.1 mm) and TiN (0.1 mm): (a) as-deposited; (b) annealed at 400 1C; (c) annealed at 400 1C.
The crystalline structure and residual stresses of SiO2/ Cu/TiN films deposited using AIP and PC were investigated. TiN layers deposited using AIP on the glass substrates were found to exhibit strong {1 1 1} orientation, as did the Cu layers deposited the TiN layer using PC. The crystalline structure of the Cu and TiN layers did not change with heating below 400 1C. In the case of multi thick-layer film of SiO2 (0.1 mm)/Cu (1.0 mm)/TiN (1.0 mm), after heating at 400 1C, the Cu and TiN layers exhibited tensile residual stresses of 220–350 and 250–600 MPa, respectively. Whereas in the multi thin-layer film of SiO2 (0.1 mm)/Cu (0.1 mm)/TiN (0.1 mm), the Cu and TiN layers exhibited tensile residual stresses of 400–570 and 570–930 MPa, respectively. Therefore, tensile residual stresses has a larger one of the multi thin-layer film than the multi thick-layer film. In addition, after heating at 400 1C, surface swelling formations, such as bubbles were observed in the multi thick-layer film. However, in the case of the multi thin-layer films, there was no change in the surface morphology following heat treatment. References
that relaxation of the tensile residual stress in the Cu layer of the multi thick-layer film was due to a change of the surface morphology. However, a detailed cause of relaxation is unclear, and further research is necessary. The magnitude of the residual stress in films depends on the deposition conditions, such as ion bombardment (in the PC and AIP method), temperature and environment. Mismatched thermal contraction coefficient between the film and the substrate generates thermal residual stress after cooling from the deposition temperature to room temperature. Assuming that there is no stress at the deposition temperature, the thermal residual stress (sth ) is given by sth ¼ ðE film =ð1 nfilm ÞÞðafilm asubs: Þ DT,
(2)
where Efilm and nfilm are Young’s modulus and Poisson’s ratio for the film. DT is the temperature difference between
[1] Pintschovius L, Ka¨mpfe A, Eigenmann B, Lo¨he D. Z Metallkd 2001;92:275. [2] Ho¨hl F, Stock H-R, Mayr P. Surf Coat Technol 1992;54/55:160. [3] Bull SJ, Jones AM, McCabe AR. Surf Coat Technol 1992;54/55:173. [4] Chang TP, Graham ME, Sproul WD, Cheng HS. Surf Coat Technol 1992;54/55:490. [5] Matsue T, Hanabusa T, Ikeuchi Y. Vacuum 2002;66:435. [6] Hanabusa T, Kusaka K, Matsue T, Nishida M, Sakata O, Sato T. Vacuum 2004;74:571. [7] Matsue T, Hanabusa T, Ikeuchi Y. Thin solid films 1996; 281–282:344. [8] Cullity BD. Elements of X-ray diffraction. Massachusetts: AddisonWesley Co Inc; 1978. p. 75. [9] Simmons G, Wang H. Single crystal elastic constants and calculated aggregate properties: a Handbook. 2nd ed. Cambridge, MA: The MIT Press; 1971. p. 24. [10] Perry AJ. Thin Solid Films 1989;170:63. [11] Matsue T, Hanabusa T, Ikeuchi Y. Vacuum 2004;74:647. [12] Hanabusa T, Nishida M. Mater Sci Res Int 2001;7:54.
Vacuum 80 (2006) 836–839 www.elsevier.com/locate/vacuum
Alteration of internal stresses in SiO2/Cu/TiN thin films by X-ray and synchrotron radiation due to heat treatment Tatsuya Matsuea,, Takao Hanabusab, Yasukazu Ikeuchia, Kazuya Kusakab, Osami Sakatac a
Niihama National College of Technology, 7-1 Yagumo-cho, Niihama 792-8580, Japan Faculty of Engineering, Tokushima University, 2-1 Minamijyosanjima-cho, Tokushima 770-8506, Japan c Japan Synchrotron Radiation Research Institute/SPring-8, Kouto 1-1-1 Mikazuki Sayo, Hyogo 679-5198, Japan b
Abstract A break of wiring by stress-migration becomes a problem with an integrated circuit such as LSI. The present study investigates residual stress in SiO2/Cu/TiN film deposited on glass substrates. A TiN layer, as an undercoat, was first deposited on the substrate by arc ion plating and then Cu and SiO2 layers were deposited by plasma coating. The crystal structure and the residual stress in the deposited multi-layer film were investigated using in-lab. X-ray equipment and a synchrotron radiation device that emits ultra-high-intensity Xrays. It was found that the SiO2 film was amorphous and both the Cu and TiN films had a strong {1 1 1} orientation. The Cu and TiN layers in the multi thick (Cu and TiN:1.0 mm)-layer film and multi thin (0.1 mm)-layer film exhibited tensile residual stresses. Both tensile residual stresses in the multi thin-layer film are larger than the multi thick-layer film. After annealing at 400 1C, these tensile residual stresses in both the films increased with increasing the annealing temperature. Surface swelling formations, such as bubbles were observed in the multi thick-layer film. However, in the case of the multi thin-layer films, there was no change in the surface morphology following heat-treatment. r 2005 Elsevier Ltd. All rights reserved. Keywords: Multi layers film; Residual stress; Crystal structure; Surface morphology; X-ray diffraction; Synchrotron radiation
1. Introduction In recent years, the technology for manufacturing highly integrated circuits has improved remarkably. With improvements, wiring materials have changed from aluminum to copper, which is characterized by low electrical resistance and high resistance to metal migration. However, copper diffuses through the silicon wafer substrate, so therefore a layer of TiN or TaN is generally deposited between the copper and silicon wafer to act as a diffusion barrier. During thin-film growth, residual stresses arise from the deposition process in thin-film coatings, and Corresponding author. Tel.: +81 897 37 7800; fax: +81 897 37 7842.
E-mail addresses: [email protected] (T. Matsue), [email protected] (T. Hanabusa), [email protected] (Y. Ikeuchi), [email protected] (K. Kusaka), [email protected] (O. Sakata). 0042-207X/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2005.11.033
these residual stresses depend on the mechanical properties of the materials involved. In addition, with an integrated circuit, thermal stress occurs by heating of a circuit at the time of use, and it becomes a problem that a break of wiring occurs for stress-migration caused by thermal stress [1–4]. The present study investigates the residual stress and crystallographic structure of SiO2/Cu/TiN multi-layer films, which imitated an integrated circuit, deposited on glass substrates. A TiN film is first deposited onto the substrate, as an undercoat layer, using arc ion plating (AIP), followed by a Cu film deposited by plasma coating (PC), and finally a SiO2 film for prevention of oxidation is deposited by PC. The crystallographic structure and residual stress of the deposited multi-layer film were investigated using X-ray diffraction and synchrotron radiation, as a function of the thickness of the Cu and TiN layers and the annealed treatments.
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Cu 1.0 mm/TiN 1.0 mm) and a multi thin-layer film (SiO2 0.1 mm/Cu 0.1 mm/TiN 0.1 mm).
2. Experimental details 2.1. Specimens Glass plates were used as substrates (Borosilicate glass: Corning 7059, 50 50 1 mm). An AIP system (Kobe Steel Co.) was used to prepare the TiN films on these substrates [5]. After degassing, nitrogen gas was injected into the chamber at a pressure of 1.0 Pa. An arc current of 60 A, and a bias voltage of 0 V were used. Films were grown to a thickness of approximately 1.0 and 0.1 mm. The substrate surface was positioned perpendicular to the Ti target during deposition. Prior to deposition, the substrate surfaces were treated by ion cleaning (using Ti) to remove impurities. Ion cleaning was performed twice for 2 min, each at an arc current of 60 A, and a bias voltage of 600 V. Specimens reached a temperature of approximately 200 1C during the cleaning process. After TiN Film deposition, Cu or SiO2 films were then deposited by PC. Fig. 1 shows a schematic of the PC system. The Cu or SiO2 targets are evaporated in the presence of an Ar plasma produced by a plasma gun. The evaporated target metal ionizes in the Ar plasma and is attracted by the bias voltage to the substrate surface, where it is deposited to form a Cu and a SiO2 film. During the deposition of Cu films, an arc current of 100 A and a bias voltage of 44 V were applied to the plasma, and the pressure in the chamber was 6.3 102 Pa, with resultant film thicknesses of approximately 1.0 and 0.1 mm. For the SiO2 film, an arc current of 150 A, and a bias voltage of 0 V were applied to the plasma, with a deposition chamber pressure of 6.3 102 Pa, and the film thickness was approximately 0.1 mm. In this study, two types of specimens were examined: a multi thick-layer film (SiO2 0.1 mm/
Substrate glass
Plasma gun
2.2. Annealed treatment As for the copper, the physics fixed number, such as the elasticity fixed number, changes in heat environment of 400 1C from 200 1C. In order to investigate how the structure and the residual stress in the film are changed by heating–cooling cycles, the specimens were heated in a vacuum furnace at temperatures of 100, 200, 300 and 400 1C. The duration of each temperature treatment was 60 min, after which, the specimens were cooled down to room temperature. 2.3. Measurement of residual stress in the multi-layer films using X-ray radiation and ultra-high-intensity synchrotron radiation The texture and the residual stresses in the multi thicklayer films were measured with a laboratory X-ray diffraction system (lab. X-ray), using CuKa radiation (wavelength 0.15 nm) under the following conditions: tube voltage 40 kV, tube current 20 mA, irradiated area 2 6 mm. The residual stress in the multi thick-layer film was evaluated using diffraction measurements of Cu 222 and TiN422. However, in the case of the multi thin-layer films, residual stress evaluation was difficult because X-ray strength from diffraction plane was very weak. The residual stress in the multi thin-layer films was measured using synchrotron radiation (SR) from the BL13XU beam line, at the SPring-8 facility, with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) located in the Harima district, Japan. The energy of the SR was 12.4 keV, which corresponds to an X-ray wavelength of 0.10 nm. This was confirmed by the (2 1 1) diffraction peak value of a standard iron powder. The size of the incident SR beam was 1.0 1.0 mm. Residual stress in the multi thin-layer films was evaluated using diffraction measurements of Cu111 and TiN111 [6].
Evaporative metal (Cu)
2.4. Stress measuring method
Plasma (Ar+)
Plasma beam control unit Target (Cu or SiO2)
Fig. 1. Schematic illustration of the apparatus used for plasma coating.
The two–tilt method [7] was used to measure stresses in the {1 1 1}-oriented films, because sufficient diffraction intensity could only be obtained at two c angles. TiN111, Cu111 and 222 diffraction peaks were found at c ¼ 01 and 70.51, and TiN422 diffraction peaks were found at c ¼ 19:51 and 61.91 [8]. Stresses in the Cu and TiN films were determined using the following equation: s ¼ 1=ðS44 =2Þðec1 ec2 Þ=ðsin2 c1 sin2 c2 Þ,
(1)
where S44 is the elastic compliance of Cu and TiN single crystals, and the values are 13.26 103/ GPa [9] and 5.95 103/ GPa [10], ec1 and ec2 are lattice strains at angles c1 and c2, respectively. In addition, measured value
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of residual stress becomes the mean value of an X-ray domain to go through.
5
annealing temperature 400 °C 300°C 200°C 100 °C
30
70
Cu222
Cu200
0
Tin222
As-deposited TiN111 Cu111
Intensity,×103 arbitrarily unit
SiO2/ Cu / TiN glass substrate
110 2 ,deg
150
Fig. 2. Change in the X-ray diffraction patterns of SiO2/Cu/TiN films with annealing temperature.
Residual stress, MPa
Fig. 2 shows the lab. X-ray diffraction pattern provided from the multi thick-layer films that were heat treated. Because of the highly oriented {1 1 1} structure of the Cu layer and the TiN layer, only two very large intensity peaks of 111 and 222 diffractions were detected by y–2y scanning for both the as-deposited and the heat treated multi thicklayer films. The results revealed that the peak intensity of the 111 and 222 diffractions did not change by heat treatment below 400 1C. In addition, a similar result was provided in the multi thin-layer films. By the way, hello diffraction pattern of X-ray in the glass substrate was observed from Fig. 2. Therefore, it is thought that X-ray beam goes through the multi thick-layer film. Fig. 3 shows the residual stresses measured in the multi thick-layer films evaluated using lab. X-rays. Residual stress of the Cu and TiN layers were measured five times. The as-deposited Cu and TiN layers in the multi thicklayers films have tensile residual stresses of approximately 220 and 250 MPa, respectively. Residual stresses in the Cu layers increased to 350 MPa with increasing heat treatment temperatures up to 300 1C. However, these values decreased at 400 1C. On the other hand, residual stresses in the TiN layers increased to 600 MPa with increased heating temperatures up to 400 1C. Fig. 4 shows the residual stresses measured in the multi thin-layer films using synchrotron radiation. Residual stress of the Cu and TiN layers was measured three times. The as-deposited Cu and TiN layers in the multi thin-layers films have tensile residual stresses of approximately 400 and 570 MPa, respectively. Residual stresses of the Cu layers increased to 570 MPa for heat treatment tempera-
600
Residual stress Cu layer (1.0µm) TiN layer (1.0µm)
400
200
0 0
100
200 300 Annealed temperature,°C
400
Fig. 3. Relationship between the residual stresses of the Cu (1.0 mm) and TiN (1.0 mm) layers and the annealing temperature of SiO2/Cu/TiN films on glass substrate, laboratory X-ray.
1200
Residual stress, MPa
3. Results and discussion
800
900
600
Residual stress Cu layer (0.1µm) TiN layer (0.1µm)
300
0 0
100
200 300 Annealed temperature, °C
400
Fig. 4. Relationship between the residual stresses of the Cu (0.1 mm) and TiN (0.1 mm) layers and the annealing temperature of SiO2/Cu/TiN films on glass substrates, synchrotron radiation.
tures of 200 1C. In the case of heat treatment over 200 1C, the stress value of the Cu layer was almost constant. On the other hand, residual stresses in the TiN layers increased to 930 MPa for heating temperatures up to 200 1C. For heat treatments over 200 1C, the stress of the TiN layers had the same tendency as that observed for the Cu layers. The surface condition of the annealed multi-layer films was examined using Field Emission Scanning Electron Microscope (FESEM). Fig. 5 shows that the heat treatment has an influence on the surface of the SiO2/Cu/TiN films. Fig. 5(a) shows a FESEM image of the surface of an asdeposited multi thick-layer film. In case of the TiN film deposited by AIP, many craters were formed by the surface [11]. It seems that the number of craters in the surface of the multi thick-layer films was formed by the influence of the lower TiN layer. After heat treatment at 400 1C, surface swelling deformations, such as bubbles were observed in the multi thick-layer film (Fig. 5(b)). In the case of the multi thin-layer film, there was no change in the surface morphology after heat treatment (Fig. 5(c)). It is thought
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the deposition temperature and room temperature, and afilm and asubs: are the thermal expansion coefficients of the film and the substrate, respectively. The values for acu , aTiN and aglass are 16.8 106, 9.35 106 and 4.6 106 K1 [12], respectively. The thermal stresses given by Eq. (2) are tensile for both the Cu layer deposited on TiN and for the TiN layer deposited on glass. However, the measured value was smaller than the value calculated using Eq. (2). Therefore, it is thought that the tensile residual stress in the Cu and TiN layers is formed by the thermal stress and the intrinsic stress caused by ion bombardment. However, in this study, the details remain unclear, and further research is necessary. 4. Conclusion
Fig. 5. Morphological change (a) of SiO2/Cu (1.0 mm)/TiN (1.0 mm) film surfaces, and (b) of Cu (1.0 mm) and TiN (1.0 mm), and (c) of Cu (0.1 mm) and TiN (0.1 mm): (a) as-deposited; (b) annealed at 400 1C; (c) annealed at 400 1C.
The crystalline structure and residual stresses of SiO2/ Cu/TiN films deposited using AIP and PC were investigated. TiN layers deposited using AIP on the glass substrates were found to exhibit strong {1 1 1} orientation, as did the Cu layers deposited the TiN layer using PC. The crystalline structure of the Cu and TiN layers did not change with heating below 400 1C. In the case of multi thick-layer film of SiO2 (0.1 mm)/Cu (1.0 mm)/TiN (1.0 mm), after heating at 400 1C, the Cu and TiN layers exhibited tensile residual stresses of 220–350 and 250–600 MPa, respectively. Whereas in the multi thin-layer film of SiO2 (0.1 mm)/Cu (0.1 mm)/TiN (0.1 mm), the Cu and TiN layers exhibited tensile residual stresses of 400–570 and 570–930 MPa, respectively. Therefore, tensile residual stresses has a larger one of the multi thin-layer film than the multi thick-layer film. In addition, after heating at 400 1C, surface swelling formations, such as bubbles were observed in the multi thick-layer film. However, in the case of the multi thin-layer films, there was no change in the surface morphology following heat treatment. References
that relaxation of the tensile residual stress in the Cu layer of the multi thick-layer film was due to a change of the surface morphology. However, a detailed cause of relaxation is unclear, and further research is necessary. The magnitude of the residual stress in films depends on the deposition conditions, such as ion bombardment (in the PC and AIP method), temperature and environment. Mismatched thermal contraction coefficient between the film and the substrate generates thermal residual stress after cooling from the deposition temperature to room temperature. Assuming that there is no stress at the deposition temperature, the thermal residual stress (sth ) is given by sth ¼ ðE film =ð1 nfilm ÞÞðafilm asubs: Þ DT,
(2)
where Efilm and nfilm are Young’s modulus and Poisson’s ratio for the film. DT is the temperature difference between
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