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Microelectronic Engineering 63 (2002) 353–361 www.elsevier.com / locate / mee
Inductively coupled plasma etching of a Pb(Zr x Ti 12x )O 3 thin film in a HBr /Ar plasma Chee Won Chung*, Yo Han Byun, Hye In Kim School of Chemical Engineering, Inha University, 253 Yonghyun-Dong, Nam-Ku, Incheon 402 -751, South Korea Received 19 November 2001; accepted 13 December 2001
Abstract The etching of Pb(Zr x Ti 12x )O 3 (PZT) thin films was performed using HBr /Ar gas in an inductively coupled plasma. The etch rate and etch profile of the PZT films were investigated as a function of the gas concentration of the HBr /Ar mixture. In addition, the etch parameters, including coil power, dc bias and gas pressure, were examined to characterize the etching process of the PZT films. An enhancement of the etch rate with increasing gas concentration was found, which indicates that PZT etching by HBr /Ar follows the reactive ion etching mechanism. It was found that the maximum etch rate and selectivity for Pt films was around 40% HBr under the etch conditions used in this study. From X-ray photoelectron spectroscopy (XPS) analysis, it was observed that the Pb component in PZT solid solution showed a faster etching than the Zr and Ti components. The etch rate and the degree of anisotropy of the PZT films were enhanced by increasing the coil power and dc-bias voltage, ˚ / min and a steep etch profile of . 708 could be and by lowering the gas pressure. An etch rate of 900 A achieved with HBr /Ar chemistry. 2002 Elsevier Science B.V. All rights reserved. Keywords: Inductively coupled plasma; High-density etching; Pb(Zrx Ti 12x )O 3 thin film; HBr /Ar gas
1. Introduction PZT films have been studied for many applications such as ferroelectric random access memory (FeRAM), microelectromechanical systems (MEMS), and pyroelectric detectors. The fabrication of these devices requires the development of etching processes for PZT films as well as deposition processes. Many studies have been reported on the etching of PZT films using reactive ion etching
* Corresponding author. E-mail address: [email protected] (C.W. Chung). 0167-9317 / 02 / $ – see front matter PII: S0167-9317( 02 )00550-6
2002 Elsevier Science B.V. All rights reserved.
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C.W. Chung et al. / Microelectronic Engineering 63 (2002) 353 – 361
(RIE) [1–3], magnetically enhanced reactive ion etching (MERIE) [4], and high-density plasma etching, such as electron cyclotron resonance (ECR) [5,6] and inductively coupled plasma (ICP) [7–9]. Most of the previous works on the etching of PZT films were performed with chlorine-based [5,6,8] or fluorine-based gases [3,5,8,9]. In general, chlorine chemistries showed faster etching than fluorine chemistries, while the etch profiles could be varied depending on the etch conditions, including the etch gases. A high selectivity of PZT films for photoresist masks can be obtained in fluorine-based gases, but etch residues like polymers are readily formed. On the other hand, it is known that chlorine chemistries generally exhibit clean etch profiles, but the selectivity is poor compared with fluorine chemistries. Therefore, in order to take advantage of chlorine and fluorine chemistries, a mixture of chlorine and fluorine gases has been proposed for a clean etch profile of PZT films with a fast etch rate [7–9]. In this work, the etching of PZT films was carried out using HBr /Ar chemistry as an alternative to a mixture of chlorine and fluorine gases. The etch rate and etch profile were investigated using various gas concentrations and the etch parameters, including coil power, bias voltage and gas pressure, were also explored. XPS analysis of the etched surface was performed to determine the surface states of each element of the PZT film during etching in a HBr /Ar plasma.
2. Experimental ˚ thickness were deposited on Pt-coated Ti / SiO 2 / Si substrates Pb(Zr x Ti 12x )O 3 thin films of 2000 A ˚ as an electrode, were deposited using by a chemical solution deposition method. Pt films (1500 A), ˚ was used as an adhesion layer between the Pt and DC magnetron sputtering and a Ti layer of 150 A SiO 2 films. The precursor solution for the PZT films was prepared using the precursors lead acetate trihydrate, zirconium n-propoxide, and titanium isopropoxide. Acetic acid and n-propanol were used as solvents. The solution was spun on the substrates at 2500 rpm for 35 s. The coated PZT films were annealed at 650 8C for 30 min to form the PZT perovskite phase. The deposited PZT films were examined by X-ray diffraction (XRD) for analysis of the crystal structure. The etching samples were patterned using a conventional photoresist with a thickness of 1.2 mm. A high-density inductively coupled plasma reactive ion etch system (ICPRIE), which has a loadlock chamber and a cooling system to wafer platen by a helium gas [6], was used. The coil, which was connected to a 13.56 MHz rf power supply, was wound around the ceramic chamber to generate a high-density plasma. An rf bias voltage induced by rf power at 13.56 MHz was capacitively coupled to the substrate susceptor in order to control the ion energy. The coil rf power can be varied up to 1200 W and the rf power to the substrate was 600 W. The etch rates were measured by a surface profiler and the etch profiles were observed by field emission scanning electron microscopy (FESEM). The dry etching of the PZT films was studied using HBr /Ar gas chemistry by varying the concentration of the etch gases. Systematic studies were carried out as a function of the etching parameters, including the coil RF power (400–800 W), the dc bias voltage to the substrate (200–400 V), and the gas pressure (2–10 mTorr). The surface states of each element in PZT solid solution were examined by XPS analysis before and after etching of the PZT films.
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Fig. 1. Effect of gas concentration on the etch rates of PZT and Pt films.
3. Results and discussion Changes in the etch rates of the PZT and Pt films are shown in Fig. 1 as a function of gas concentration. The etch conditions used were a coil rf power of 600 W, a gas pressure of 5 mTorr, and 300 V dc bias to the wafer susceptor. The etch selectivity of the PZT film to the Pt film was also determined. As the gas concentration increased, the etch rate of the PZT film increased to reach a maximum and began to decline on further increasing the concentration. This indicates that the etching of PZT films with HBr /Ar gas exhibits the characteristics of a reactive ion etching mechanism. The reason for the decrease in etching rate at a gas concentration of . 40% HBr can be explained by the fact that excess etch gas inhibits the sputtering of ions to the film surface by forming a thin passivation layer and / or that the sputtering to the films by ions becomes less effective than for Ar ion, resulting in a slow etch rate. The etch rate of Pt films decreased monotonously with increasing gas concentration. The selectivity of the PZT to the Pt film showed a maximum at a gas concentration of 40% HBr. The etch profiles of HBr /Ar gas are shown in Fig. 2. From Fig. 2a, the low gas concentration of 10% HBr /Ar gave rise to a severely eroded etch profile. This indicates the corrosive nature of Br gas. As the proportion of HBr in the gas mixture increases to 40%, the slope of the etched sidewall becomes steep with the help of a passivation layer of hydrogen atoms from HBr gas, as shown in Fig. 2b. With a further increase of HBr gas to over 60%, the sidewall slopes of the patterns become shallow. In addition, redeposition along the sidewall of the patterns was observed (Fig. 2c and d). A clean and steep etch profile was achieved with the etch conditions giving the highest etch rate in Fig. 1. Fig. 3 show the etch rates of PZT films as a function of etch parameters such as coil RF power, dc bias voltage and gas pressure. As the coil RF power increases, the etch rates of PZT and Pt films increase. It is believed that the plasma density increases at higher coil power, resulting in a higher etch rate due to increased ions and radicals (Fig. 3a). With increasing dc bias voltage, the etch rates of PZT and Pt films increase linearly, as shown in Fig. 3b. As the dc bias voltage increases, more ions are drawn onto the film surface, which leads to an increase in the etch rate. When the gas pressure
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Fig. 2. SEM micrographs of PZT films etched in (a) 10% HBr /Ar, (b) 40% HBr /Ar, (c) 60% HBr /Ar, and (d) 80% HBr /Ar.
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Fig. 3. Etch rates of PZT and Pt films as a function of (a) coil rf power, (b) dc bias voltage, and (c) gas pressure with 40% HBr / 60% Ar.
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increases, the etch rates of PZT and Pt films decrease. The etch rate of the Pt film decreases more rapidly than that of the PZT film. This is believed to be caused by the distinct etch mechanisms of the PZT and Pt films. As the gas pressure increases, ion sputtering to the film surface becomes less effective, which leads to slow etching. This affects the etching of Pt films more than that of PZT films because the etch mechanism of Pt films is known to be chemically assisted sputtering etching [10], while PZT etching shows a reactive ion etching mechanism [8]. The etch profiles of PZT films etched under various etch conditions were observed systematically to investigate the effect of etch conditions on the etch profiles (Fig. 4). The etch conditions correspond to those given in Fig. 3. The specimens for the etch profiles of Fig. 4 were real capacitors corresponding to 4M FeRAMs, which consisted of a PZT film as ferroelectric, and iridium and platinum films as upper and lower electrodes, respectively. The specimens were etched onto the upper electrode of iridium films and patterned by photolithography with a photoresist mask for the etching of PZT films. The PZT films were then etched under specified etch conditions with known etch rates. The etch residues on the upper electrode were thought to come from incomplete photoresist stripping. As can be seen from Fig. 4a1–a3, the etch profiles become cleaner and steeper with increasing coil power. As the bias voltage decreases, which corresponds to slow etching, a thick redeposition occurs along the etched pattern (Fig. 4b1). However, at higher bias voltages, a steep etch profile without redeposition was obtained (Fig. 4b3). As the gas pressure increases, a heavy redeposition was formed around the edge of the etched films (Fig. 4c3). A steep and clean etch profile was achieved at lower gas pressure, as shown in Fig. 4c1. As a result, good etch profiles were obtained at high coil power, high bias voltage and low gas pressure, which correspond to etch conditions where the etch rates of the PZT films were fast. This implies that the sputtering of ions to the films plays a critical role in obtaining a good etch profile. To determine the surface states of the PZT films during the etching process, the etched samples were analyzed by XPS. All samples were scanned after 1 min sputtering in order to remove contamination effects from the film surface. XPS data before and after etching were compared for three peaks, Pb 4f, Zr 3d and Ti 2p (Fig. 5). The Pb 4f peak before etching showed the presence of PbO, since the PZT film was a solid solution composed of three components (PbO, ZrO 2 and TiO 2 ) of the PZT solid solution (Fig. 5a). PbO after etching was divided into two peaks, which indicated PbBrx and Pb. It is evident that PbBr x was formed by the reaction of Pb with Br. However, the binding energies of PbO and PbBr x are very similar and the PbO peak may overlap the PbBr x peak. In contrast to the Pb 4f peak, little change in the Zr 3d and Ti 2p peaks was found, as shown in Fig. 5b and c. This indicates that the ZrO 2 and TiO 2 components of PZT films are not readily decomposed to metallic Zr and Ti after reaction with Br. Therefore, it can be concluded that the etch rate of the PbO component of PZT films is fastest. The etching of the ZrO 2 and TiO 2 components is the rate-limiting step in PZT etching. These results are in agreement with previous results observed for Cl 2 / C 2 F 6 /Ar gas chemistry.
4. Conclusion Reactive ion etching of PZT thin films masked with a photoresist was performed using a high-density inductively coupled plasma. HBr /Ar gas was examined in terms of etch rate, etch selectivity and etch profile. As the HBr concentration increased, the etch rate of PZT films increased,
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Fig. 4. SEM micrographs of etched PZT films as a function of (a) coil rf power, (b) dc bias voltage, and (c) gas pressure at 40% HBr / 60% Ar. Coil rf power: (a1) 400 W, (a2) 600 W, (a3) 800 W, dc-bias voltage: (b1) 200 V, (b2) 300 V, (b3) 400 V, Gas pressure: (c1) 1 mTorr, (c2) 5 mTorr, (c3) 10 mTorr.
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Fig. 5. XPS spectra of PZT films before and after etching: (a) Pb 4f, (b) Zr 3d and Ti 2p. Etch gas, 40% HBr / 60% Ar; coil rf power, 600 W; dc bias voltage, 300 V; gas pressure, 5 mTorr.
giving a maximum at 40% HBr /Ar. The etch profile was also best at 40% HBr concentration. At higher concentrations of . 60% HBr, the sidewall slope of the etched films became shallower and redeposition took place around the edge of the patterns. By increasing the coil power and bias voltage and by reducing the gas pressure, the etch rates increased and the etch profiles improved. XPS analysis revealed that etching of the Pb component of PZT films was fastest and the etching of the Zr ˚ / min and Ti components can be the rate-limiting step due to the slow etch rates. An etch rate of 900 A and a high degree of anisotropy of 708 could be achieved with HBr /Ar chemistry.
Acknowledgements This research was funded by the Center for Ultra-microchemical Process Systems sponsored by KOSEF.
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References [1] J.J. van Glabbeek, G.A.C.M. Spierings, M.J.E. Ulenaers, G.J.M. Dormans, P.K. Larson, Mater. Res. Soc. Symp. Proc. 310 (1993) 127. [2] D.P. Vijay, S.B. Desu, W. Pan, J. Electrochem. Soc. 140 (1993) 2635. [3] M. Bale, R.E. Palmer, J. Vac. Sci. Technol. A 17 (1999) 2467. [4] Y.Y. Lin, Q. Liu, T.A. Tang, X. Yao, W.N. Huang, Jpn. J. Appl. Phys. 39 (2000) 320. [5] B. Charlet, K.E. Davies, Mater. Res. Soc. Symp. Proc. 310 (1993) 363. [6] H. Mace, H. Achard, L. Pcccoud, Microelectron. Eng. 29 (1995) 45. [7] C.W. Chung, W.I. Lee, J.K. Lee, Integr. Ferroelectr. 11 (1995) 259. [8] C.W. Chung, J. Vac. Sci. Technol. B 16 (1998) 1894. [9] J.K. Jung, W.J. Lee, Jpn. J. Appl. Phys. 40 (2001) 1408. [10] C.W. Chung, H.G. Song, J. Electrochem. Soc. 144 (1997) L294.
Inductively coupled plasma etching of a Pb(Zr x Ti 12x )O 3 thin film in a HBr /Ar plasma Chee Won Chung*, Yo Han Byun, Hye In Kim School of Chemical Engineering, Inha University, 253 Yonghyun-Dong, Nam-Ku, Incheon 402 -751, South Korea Received 19 November 2001; accepted 13 December 2001
Abstract The etching of Pb(Zr x Ti 12x )O 3 (PZT) thin films was performed using HBr /Ar gas in an inductively coupled plasma. The etch rate and etch profile of the PZT films were investigated as a function of the gas concentration of the HBr /Ar mixture. In addition, the etch parameters, including coil power, dc bias and gas pressure, were examined to characterize the etching process of the PZT films. An enhancement of the etch rate with increasing gas concentration was found, which indicates that PZT etching by HBr /Ar follows the reactive ion etching mechanism. It was found that the maximum etch rate and selectivity for Pt films was around 40% HBr under the etch conditions used in this study. From X-ray photoelectron spectroscopy (XPS) analysis, it was observed that the Pb component in PZT solid solution showed a faster etching than the Zr and Ti components. The etch rate and the degree of anisotropy of the PZT films were enhanced by increasing the coil power and dc-bias voltage, ˚ / min and a steep etch profile of . 708 could be and by lowering the gas pressure. An etch rate of 900 A achieved with HBr /Ar chemistry. 2002 Elsevier Science B.V. All rights reserved. Keywords: Inductively coupled plasma; High-density etching; Pb(Zrx Ti 12x )O 3 thin film; HBr /Ar gas
1. Introduction PZT films have been studied for many applications such as ferroelectric random access memory (FeRAM), microelectromechanical systems (MEMS), and pyroelectric detectors. The fabrication of these devices requires the development of etching processes for PZT films as well as deposition processes. Many studies have been reported on the etching of PZT films using reactive ion etching
* Corresponding author. E-mail address: [email protected] (C.W. Chung). 0167-9317 / 02 / $ – see front matter PII: S0167-9317( 02 )00550-6
2002 Elsevier Science B.V. All rights reserved.
354
C.W. Chung et al. / Microelectronic Engineering 63 (2002) 353 – 361
(RIE) [1–3], magnetically enhanced reactive ion etching (MERIE) [4], and high-density plasma etching, such as electron cyclotron resonance (ECR) [5,6] and inductively coupled plasma (ICP) [7–9]. Most of the previous works on the etching of PZT films were performed with chlorine-based [5,6,8] or fluorine-based gases [3,5,8,9]. In general, chlorine chemistries showed faster etching than fluorine chemistries, while the etch profiles could be varied depending on the etch conditions, including the etch gases. A high selectivity of PZT films for photoresist masks can be obtained in fluorine-based gases, but etch residues like polymers are readily formed. On the other hand, it is known that chlorine chemistries generally exhibit clean etch profiles, but the selectivity is poor compared with fluorine chemistries. Therefore, in order to take advantage of chlorine and fluorine chemistries, a mixture of chlorine and fluorine gases has been proposed for a clean etch profile of PZT films with a fast etch rate [7–9]. In this work, the etching of PZT films was carried out using HBr /Ar chemistry as an alternative to a mixture of chlorine and fluorine gases. The etch rate and etch profile were investigated using various gas concentrations and the etch parameters, including coil power, bias voltage and gas pressure, were also explored. XPS analysis of the etched surface was performed to determine the surface states of each element of the PZT film during etching in a HBr /Ar plasma.
2. Experimental ˚ thickness were deposited on Pt-coated Ti / SiO 2 / Si substrates Pb(Zr x Ti 12x )O 3 thin films of 2000 A ˚ as an electrode, were deposited using by a chemical solution deposition method. Pt films (1500 A), ˚ was used as an adhesion layer between the Pt and DC magnetron sputtering and a Ti layer of 150 A SiO 2 films. The precursor solution for the PZT films was prepared using the precursors lead acetate trihydrate, zirconium n-propoxide, and titanium isopropoxide. Acetic acid and n-propanol were used as solvents. The solution was spun on the substrates at 2500 rpm for 35 s. The coated PZT films were annealed at 650 8C for 30 min to form the PZT perovskite phase. The deposited PZT films were examined by X-ray diffraction (XRD) for analysis of the crystal structure. The etching samples were patterned using a conventional photoresist with a thickness of 1.2 mm. A high-density inductively coupled plasma reactive ion etch system (ICPRIE), which has a loadlock chamber and a cooling system to wafer platen by a helium gas [6], was used. The coil, which was connected to a 13.56 MHz rf power supply, was wound around the ceramic chamber to generate a high-density plasma. An rf bias voltage induced by rf power at 13.56 MHz was capacitively coupled to the substrate susceptor in order to control the ion energy. The coil rf power can be varied up to 1200 W and the rf power to the substrate was 600 W. The etch rates were measured by a surface profiler and the etch profiles were observed by field emission scanning electron microscopy (FESEM). The dry etching of the PZT films was studied using HBr /Ar gas chemistry by varying the concentration of the etch gases. Systematic studies were carried out as a function of the etching parameters, including the coil RF power (400–800 W), the dc bias voltage to the substrate (200–400 V), and the gas pressure (2–10 mTorr). The surface states of each element in PZT solid solution were examined by XPS analysis before and after etching of the PZT films.
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Fig. 1. Effect of gas concentration on the etch rates of PZT and Pt films.
3. Results and discussion Changes in the etch rates of the PZT and Pt films are shown in Fig. 1 as a function of gas concentration. The etch conditions used were a coil rf power of 600 W, a gas pressure of 5 mTorr, and 300 V dc bias to the wafer susceptor. The etch selectivity of the PZT film to the Pt film was also determined. As the gas concentration increased, the etch rate of the PZT film increased to reach a maximum and began to decline on further increasing the concentration. This indicates that the etching of PZT films with HBr /Ar gas exhibits the characteristics of a reactive ion etching mechanism. The reason for the decrease in etching rate at a gas concentration of . 40% HBr can be explained by the fact that excess etch gas inhibits the sputtering of ions to the film surface by forming a thin passivation layer and / or that the sputtering to the films by ions becomes less effective than for Ar ion, resulting in a slow etch rate. The etch rate of Pt films decreased monotonously with increasing gas concentration. The selectivity of the PZT to the Pt film showed a maximum at a gas concentration of 40% HBr. The etch profiles of HBr /Ar gas are shown in Fig. 2. From Fig. 2a, the low gas concentration of 10% HBr /Ar gave rise to a severely eroded etch profile. This indicates the corrosive nature of Br gas. As the proportion of HBr in the gas mixture increases to 40%, the slope of the etched sidewall becomes steep with the help of a passivation layer of hydrogen atoms from HBr gas, as shown in Fig. 2b. With a further increase of HBr gas to over 60%, the sidewall slopes of the patterns become shallow. In addition, redeposition along the sidewall of the patterns was observed (Fig. 2c and d). A clean and steep etch profile was achieved with the etch conditions giving the highest etch rate in Fig. 1. Fig. 3 show the etch rates of PZT films as a function of etch parameters such as coil RF power, dc bias voltage and gas pressure. As the coil RF power increases, the etch rates of PZT and Pt films increase. It is believed that the plasma density increases at higher coil power, resulting in a higher etch rate due to increased ions and radicals (Fig. 3a). With increasing dc bias voltage, the etch rates of PZT and Pt films increase linearly, as shown in Fig. 3b. As the dc bias voltage increases, more ions are drawn onto the film surface, which leads to an increase in the etch rate. When the gas pressure
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Fig. 2. SEM micrographs of PZT films etched in (a) 10% HBr /Ar, (b) 40% HBr /Ar, (c) 60% HBr /Ar, and (d) 80% HBr /Ar.
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Fig. 3. Etch rates of PZT and Pt films as a function of (a) coil rf power, (b) dc bias voltage, and (c) gas pressure with 40% HBr / 60% Ar.
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increases, the etch rates of PZT and Pt films decrease. The etch rate of the Pt film decreases more rapidly than that of the PZT film. This is believed to be caused by the distinct etch mechanisms of the PZT and Pt films. As the gas pressure increases, ion sputtering to the film surface becomes less effective, which leads to slow etching. This affects the etching of Pt films more than that of PZT films because the etch mechanism of Pt films is known to be chemically assisted sputtering etching [10], while PZT etching shows a reactive ion etching mechanism [8]. The etch profiles of PZT films etched under various etch conditions were observed systematically to investigate the effect of etch conditions on the etch profiles (Fig. 4). The etch conditions correspond to those given in Fig. 3. The specimens for the etch profiles of Fig. 4 were real capacitors corresponding to 4M FeRAMs, which consisted of a PZT film as ferroelectric, and iridium and platinum films as upper and lower electrodes, respectively. The specimens were etched onto the upper electrode of iridium films and patterned by photolithography with a photoresist mask for the etching of PZT films. The PZT films were then etched under specified etch conditions with known etch rates. The etch residues on the upper electrode were thought to come from incomplete photoresist stripping. As can be seen from Fig. 4a1–a3, the etch profiles become cleaner and steeper with increasing coil power. As the bias voltage decreases, which corresponds to slow etching, a thick redeposition occurs along the etched pattern (Fig. 4b1). However, at higher bias voltages, a steep etch profile without redeposition was obtained (Fig. 4b3). As the gas pressure increases, a heavy redeposition was formed around the edge of the etched films (Fig. 4c3). A steep and clean etch profile was achieved at lower gas pressure, as shown in Fig. 4c1. As a result, good etch profiles were obtained at high coil power, high bias voltage and low gas pressure, which correspond to etch conditions where the etch rates of the PZT films were fast. This implies that the sputtering of ions to the films plays a critical role in obtaining a good etch profile. To determine the surface states of the PZT films during the etching process, the etched samples were analyzed by XPS. All samples were scanned after 1 min sputtering in order to remove contamination effects from the film surface. XPS data before and after etching were compared for three peaks, Pb 4f, Zr 3d and Ti 2p (Fig. 5). The Pb 4f peak before etching showed the presence of PbO, since the PZT film was a solid solution composed of three components (PbO, ZrO 2 and TiO 2 ) of the PZT solid solution (Fig. 5a). PbO after etching was divided into two peaks, which indicated PbBrx and Pb. It is evident that PbBr x was formed by the reaction of Pb with Br. However, the binding energies of PbO and PbBr x are very similar and the PbO peak may overlap the PbBr x peak. In contrast to the Pb 4f peak, little change in the Zr 3d and Ti 2p peaks was found, as shown in Fig. 5b and c. This indicates that the ZrO 2 and TiO 2 components of PZT films are not readily decomposed to metallic Zr and Ti after reaction with Br. Therefore, it can be concluded that the etch rate of the PbO component of PZT films is fastest. The etching of the ZrO 2 and TiO 2 components is the rate-limiting step in PZT etching. These results are in agreement with previous results observed for Cl 2 / C 2 F 6 /Ar gas chemistry.
4. Conclusion Reactive ion etching of PZT thin films masked with a photoresist was performed using a high-density inductively coupled plasma. HBr /Ar gas was examined in terms of etch rate, etch selectivity and etch profile. As the HBr concentration increased, the etch rate of PZT films increased,
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Fig. 4. SEM micrographs of etched PZT films as a function of (a) coil rf power, (b) dc bias voltage, and (c) gas pressure at 40% HBr / 60% Ar. Coil rf power: (a1) 400 W, (a2) 600 W, (a3) 800 W, dc-bias voltage: (b1) 200 V, (b2) 300 V, (b3) 400 V, Gas pressure: (c1) 1 mTorr, (c2) 5 mTorr, (c3) 10 mTorr.
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Fig. 5. XPS spectra of PZT films before and after etching: (a) Pb 4f, (b) Zr 3d and Ti 2p. Etch gas, 40% HBr / 60% Ar; coil rf power, 600 W; dc bias voltage, 300 V; gas pressure, 5 mTorr.
giving a maximum at 40% HBr /Ar. The etch profile was also best at 40% HBr concentration. At higher concentrations of . 60% HBr, the sidewall slope of the etched films became shallower and redeposition took place around the edge of the patterns. By increasing the coil power and bias voltage and by reducing the gas pressure, the etch rates increased and the etch profiles improved. XPS analysis revealed that etching of the Pb component of PZT films was fastest and the etching of the Zr ˚ / min and Ti components can be the rate-limiting step due to the slow etch rates. An etch rate of 900 A and a high degree of anisotropy of 708 could be achieved with HBr /Ar chemistry.
Acknowledgements This research was funded by the Center for Ultra-microchemical Process Systems sponsored by KOSEF.
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361
References [1] J.J. van Glabbeek, G.A.C.M. Spierings, M.J.E. Ulenaers, G.J.M. Dormans, P.K. Larson, Mater. Res. Soc. Symp. Proc. 310 (1993) 127. [2] D.P. Vijay, S.B. Desu, W. Pan, J. Electrochem. Soc. 140 (1993) 2635. [3] M. Bale, R.E. Palmer, J. Vac. Sci. Technol. A 17 (1999) 2467. [4] Y.Y. Lin, Q. Liu, T.A. Tang, X. Yao, W.N. Huang, Jpn. J. Appl. Phys. 39 (2000) 320. [5] B. Charlet, K.E. Davies, Mater. Res. Soc. Symp. Proc. 310 (1993) 363. [6] H. Mace, H. Achard, L. Pcccoud, Microelectron. Eng. 29 (1995) 45. [7] C.W. Chung, W.I. Lee, J.K. Lee, Integr. Ferroelectr. 11 (1995) 259. [8] C.W. Chung, J. Vac. Sci. Technol. B 16 (1998) 1894. [9] J.K. Jung, W.J. Lee, Jpn. J. Appl. Phys. 40 (2001) 1408. [10] C.W. Chung, H.G. Song, J. Electrochem. Soc. 144 (1997) L294.