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A comparative study on a high aspect ratio contact hole etching in UFC- and PFC-containing plasmas
ARTICLE IN PRESS
Microelectronics Journal 38 (2007) 125–129 www.elsevier.com/locate/mejo
A comparative study on a high aspect ratio contact hole etching in UFC- and PFC-containing plasmas Hyun-Kyu Ryua,1, Yil-Wook Kimb,2, Kangtaek Leec, CheeBurm Shind, Chang-Koo Kimd, a
LG Chemical, Limited, Daejeon 305-380, Republic of Korea Hynix Semiconductor Inc., Ichon 467-701, Republic of Korea c Department of Chemical Engineering, Yonsei University, Seoul 120-749, Republic of Korea d Department of Chemical Engineering, Ajou University, Suwon 442-749, Republic of Korea b
Received 3 July 2006; accepted 23 September 2006 Available online 20 November 2006
Abstract An etching of a SiO2 contact hole with a diameter of 0.19 mm and an aspect ratio of 13, using C4F6/Ar/O2/CH2F2 and c-C4F8/ Ar/O2/CH2F2 plasmas, was performed for a feasibility test of the use of unsaturated fluorocarbons (UFCs) as an alternative to perfluorocarbon (PFC) gases for a high aspect ratio contact hole etching. The etch profile of the contact hole obtained in the C4F6/Ar/O2/CH2F2 plasma was shown to have 23% lower degree of bowing than that in the c-C4F8/Ar/O2/CH2F2 plasma. The Kelvin and chain contact resistances of the contact holes etched in the C4F6/Ar/O2/CH2F2 plasma were 10–12% higher than those in the c-C4F8/ Ar/O2/CH2F2 plasma, but they were within the device spec. The integration of device with 0.1 mm design rule using C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/CH2F2 plasmas during the contact hole etching was also conducted, and it was found that etch profiles, metal coverage, and bottom critical dimensions of the contact in the C4F6/Ar/O2/CH2F2 plasma were nearly identical to those in the c-C4F8/ Ar/O2/CH2F2 plasma, suggesting that the use of C4F6 gas as an etchant gas for a high aspect ratio contact hole etching can be a good alternative to PFC gases. r 2006 Elsevier Ltd. All rights reserved. Keywords: Contact hole etching; Unsaturated fluorocarbons; Perfluorocarbons; Bowing; Contact resistance
1. Introduction Plasma etching is widely used for patterning of a high aspect ratio contact hole (e.g., SiO2), which is a crucial process in developing the next generation ultra-large-scale integrated (ULSI) devices because of the rapid shrinkage of the design rule to the nanometer level. Perfluorocarbon (PFC) gases such as CF4, C2F6, and c-C4F8 are currently used as etchant gases for the contact hole etching [1,2]. These PFCs, however, are considered to be problematic from an environmental point of view because of their long atmospheric lifetimes and high global warming potentials [3–5]. Several classes of environmentally benign chemistries Corresponding author. Tel.: +82 31 219 2389; fax: +82 31 219 1612.
E-mail address: [email protected] (C.-K. Kim). Current address: DuPont Korea Inc., Seoul 135-719, Korea. 2 Current address: FOI Korea Corporation, Seongnam 463-828, Korea. 1
0026-2692/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.mejo.2006.09.002
have been examined as alternatives including unsaturated fluorocarbons (UFCs) such as hexafluoropropene (C3F6, CF2QCF–CF3), hexafluoro-1, 3-butadiene (C4F6, CF2Q CF–CFQCF2), octafluorocyclopentene (c-C5F8), etc., and their etch characteristics have been studied [6,7]. However, there are few reports on etch profiles and electrical measurements of high aspect ratio contact holes etched in UFC-containing plasmas. In this work, we report on an etching of a SiO2 contact hole with a diameter of 0.19 mm and an aspect ratio of 13 using a C4F6/Ar/O2/CH2F2 plasma (UFC-containing plasma) and a c-C4F6/Ar/O2/CH2F2 plasma (PFC-containing plasma). This study is to find feasibility for the use of UFCs as an alternative to PFC gases for a high aspect ratio contact hole etching A comparison of etch characteristics between UFC- and PFC-containing plasmas was made by measuring etch profiles and contact resistances of the high aspect ratio contact holes etched in both plasmas.
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Fig. 1. SEM micrographs of the 0.19 mm diameter contact holes etched in (a) C4F6/Ar/O2/CH2F2 and (b) c-C4F8/Ar/O2/CH2F2 plasmas. The dotted lines represent the position of the maximum bowing occurred during etching.
2. Experimental A 2.5-mm-thick SiO2 film was grown on a p-type Si wafer by plasma-enhanced chemical vapor deposition (PECVD) with tetraethoxysilane (TEOS). Prior to SiO2 growth, Ti (100 A˚)/TiN (400 A˚)/W (1000 A˚) films were deposited and patterned on the Si wafer to form a bottom metal layer. A KrF photoresist (PR) was deposited and a hole pattern of 0.19 mm diameter was delineated. A 600 A˚ antireflective coating (ARC) layer was coated on the TEOS oxide film before spinning on the PR. A high aspect ratio contact hole etching was conducted in a magnetically enhanced reactive ion etching (MERIE) system (UNITY 85, Tokyo Electron Ltd.). To compare the etch performance between UFC- and PFC-containing plasmas, two gas mixtures were used to generate plasmas by applying a 13.56 MHz radio-frequency (RF) power: C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/CH2F2. Throughout this study, the power was fixed at 1700 W, the pressure 40 mTorr, the Ar flow at 400 sccm, O2 flow at 20 sccm, and
the CH2F2 flow at 20 sccm. The C4F6 and c-C4F8 flows were also maintained at 15 and 10 sccm, respectively. The etching of the oxide films was followed by PR stripping and cleaning. To conduct electrical tests, the contact hole was filled with W by CVD. Ti (100 A˚)/TiN (300 A˚) films were deposited as barrier metals prior to filling the W film. Then, a top metal layer of Ti (100 A˚)/Al (4500 A˚)/Ti (100 A˚)/TiN (250 A˚) was deposited and patterned. Cross-sectional profiles of etched samples and integrated structures were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. Chain resistance and Kelvin resistance were measured to investigate the electrical characteristics of the contact hole. 3. Results and discussion In our previous study, it was shown that the addition of CH2F2 gas to a C4F6/Ar/O2 plasma allowed one to
ARTICLE IN PRESS H.-K. Ryu et al. / Microelectronics Journal 38 (2007) 125–129
maintain the critical dimension (CD) of the contact hole during a high aspect ratio contact hole etching [8]. When CH2F2 gas was not added to the C4F6/Ar/O2 plasma, erosion of PR layer occurred around the contact hole. This finally led to deform the CD of the deep contact hole. On the contrary, relatively thick fluorocarbon films are deposited on the PR layer and around the contact hole for addition of 20 sccm of CH2F2 gas to a C4F6/Ar/O2 plasma. This resulted in maintaining the CD after ashing the PR layer and cleaning the fluorocarbon films. Therefore, CH2F2 gas was added to C4F6/Ar/O2 and c-C4F8/Ar/ O2 plasmas as well during etching of the SiO2 contact holes in this study. Fig. 1 shows the SEM micrographs of the deep contact holes, with a diameter of 0.19 mm and an aspect ratio of 13, etched in C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/CH2F2 plasmas, respectively. Development inspection critical dimensions (DICDs) of the contact holes were 0.19 mm, but final inspection critical dimensions (FICDs) were increased by ca 0.02 mm in both C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/CH2F2 plasmas. It is seen that contact hole profile angles are also similar in both plasmas: 89.01 for the C4F6-containing plasma and 89.11 for the c-C4F8-containing plasma. However, it is apparently seen that bowing at the side walls of the hole etched in the c-C4F8/Ar/O2/ CH2F2 plasma is more severe compared to that etched in the C4F6/Ar/O2/CH2F2 plasma. To reduce bowing of deep contact holes, it is believed that a protective film should be formed on the sidewall during etching [9]. Li et al. [10] have conducted a gas phase and surface chemistry study on C4F6/Ar and c-C4F8/Ar plasmas. In their study, the fluorocarbon deposition rate was higher for the C4F6/Ar plasma than that for the cC4F8/Ar plasma while the fluorocarbon etch rate was lower for the C4F6/Ar plasma than that for the c-C4F8/Ar plasma. In addition, the steady-state fluorocarbon film thickness formed during Si and SiO2 etching was greater for the C4F6/Ar plasma than that for the c-C4F8/Ar plasma. This thicker fluorocarbon film formed using the C4F6-containing plasma can protect the sidewall more effectively, resulting in the reduction of bowing during contact hole etching in the C4F8/Ar/O2/CH2F2 plasma. For a better comparison, the degree of bowing (defined as the ratio of the width at the maximum bowing position to the diameter of the contact hole) was calculated and it was obtained that the degree of bowing were 1.05 and 1.29 for C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/CH2F2 plasmas, respectively. Therefore, it can be said that the etch profile of the contact hole obtained in the C4F6-containing plasma is more improved than that in the c-C4F8-containing plasma. Fig. 2 shows the resistance distributions of the contact holes etched in C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/ CH2F2 plasmas, respectively. Both Kelvin and chain contact resistances are shown to have about 10–12% higher values for the C4F6/Ar/O2/CH2F2 plasma compared to those for the c-C4F8/Ar/O2/CH2F2 plasma. This results
127
Fig. 2. Resistance distributions of the contact holes etched in C4F6/Ar/O2/ CH2F2 and c-C4F8/Ar/O2/CH2F2 plasmas: (a) Kelvin and (b) chain resistances.
from lower bottom CD of the contact hole etched in the C4F6/Ar/O2/CH2F2 plasma (see Fig. 1(a)). Although the absolute values of the contact resistance are higher for the C4F6/Ar/O2/CH2F2 plasma, they are still within the device spec. Furthermore, the use of the C4F6-containing plasma in a high aspect ratio contact hole etching reduced the top CD loss (also see Fig. 1(a)) so that it can offer wider process windows to succeeding operations (e.g., wider alignment margin in the metallization). So far, it has been shown that the use of the C4F6containing plasma in a high aspect ratio contact hole etching presented etch profiles and electrical characteristics equivalent to or better than those obtained in the c-C4F8containing plasma. Therefore, we conducted the integration of the device with 0.1 mm design rule using C4F6- and c-C4F8-containing plasmas for the contact hole etching.
ARTICLE IN PRESS H.-K. Ryu et al. / Microelectronics Journal 38 (2007) 125–129
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Fig. 3. TEM micrographs of the deep contacts using (a) C4F6/Ar/O2 and (b) C4F6/Ar/O2/CH2F2 plasmas during the contact hole etching.
Fig. 3 shows the TEM micrographs of high aspect ratio deep contacts processed through a 0.1 mm device process flow. It is seen that the contact holes have profile angles of about 891 in both C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/ CH2F2 plasmas. It is also seen that W metals as well as barrier metals fill the contact hole with good coverage. Since the bottom CDs obtained in both C4F6- and c-C4F8containing plasmas show similar values, it is expected that the electrical characteristics would have the same behaviors in both cases. Therefore, it can be said that the use of C4F6 gas instead of c-C4F8 gas for a high aspect ratio contact hole etching finds no problems in device integration as well as unit process. 4. Conclusions A comparative study on an etching of a high aspect ratio contact hole (diameter ¼ 0.19 mm, aspect ratio ¼ 13) was made using C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/CH2F2 plasmas. The shape of etched profiles showed that the contact profile angles were nearly constant (891) in both C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/CH2F2 plasmas. The degree of bowing, however, was greatly reduced (23%) in the C4F6/Ar/O2/CH2F2 plasma, implying that the etch profile of the contact hole etched in the C4F6containing plasma was improved. The resistance distributions of the contact holes etched in the C4F6/Ar/O2/CH2F2 plasma had Kelvin and chain contact resistances 10–12% higher, but they were within the device specifications. TEM analyses of high aspect ratio deep contacts processed through a 0.1 mm device process flow showed that etch profiles, metal coverage, and bottom CDs of the contact in the C4F6/Ar/O2/CH2F2 plasma were nearly
identical to those in the c-C4F8/Ar/O2/CH2F2 plasma. Correspondingly, the use of C4F6 gas as an etchant gas for a high aspect ratio contact hole etching can be a good alternative to PFC gases. Acknowledgments This work was supported by the Basic Research Program of the Korea Science and Engineering Foundation (Grant nos. R01-2003-000-10103-0 and R01-2006-000-11264-0) and FOI Corporation. References [1] O. Joubert, P. Czuprynski, Characterization of dielectric etching processes by X-ray photoelectron spectroscopy analyses in high aspect ratio contact holes, Jpn. J. Appl. Phys. 38 (1999) 6154. [2] N. Ikegami, A. Yabata, G.L. Liu, H. Uchida, N. Hirashita, J. Kanamori, Vertical profile control in ultrahigh-aspect ratio contact hole etching with 0.05 mm diameter range, Jpn. J. Appl. Phys. 37 (1998) 2337. [3] L. Pruette, S. Karecki, R. Reif, L. Tousignant, W. Reagan, S. Kesari, L. Zazzera, Evaluation of C4F8O as an alternative plasma-enhanced chemical vapor deposition chamber clean chemistry, J. Electrochem. Soc. 147 (2000) 1149. [4] S. Karecki, R. Chatterjee, L. Pruette, R. Reif, T. Sparks, L. Beu, V. Vartanian, K. Novoselov, Evaluation of oxalyl fluoride for a dielectric etch application in an inductively coupled plasma etch tool, J. Electrochem. Soc. 148 (2001) G141. [5] R. Chatterjee, S. Karecki, R. Reif, V. Vartanian, T. Sparks, The use of unsaturated fluorocarbons for dielectric etch applications, J. Electrochem. Soc. 149 (2002) G276. [6] S. Samukawa, T. Mukai, New radical control method for highperformance dielectric etching with nonperfluorocompound gas chemistries in ultrahigh-frequency plasma, J. Vac. Sci. Technol. A 17 (1999) 2551.
ARTICLE IN PRESS H.-K. Ryu et al. / Microelectronics Journal 38 (2007) 125–129 [7] S. Samukawa, T. Mukai, Difference in radical generation due to chemical bonding of gas molecules in a high-density fluorocarbon plasma: effects of the C ¼ C bond in fluorocarbon gases, J. Vac. Sci. Technol. A 17 (1999) 2463. [8] H.-K. Ryu, B.-S. Lee, S.-K. Park, I.-W. Kim, C.-K. Kim, Effects of CH2F2 addition on a high aspect ratio contact hole etching in a C4F6/O2/Ar plasma, Electrochem. Sold-State Lett. 6 (2003) C126.
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[9] N. Ikegami, A. Yabata, T. Matsui, J. Kanamori, Y. Horiike, Characteristics of very high-aspect-ratio contact hole etching, Jpn. J. Appl. Phys. 36 (1997) 2470. [10] X. Li, X. Hua, L. Ling, G.S. Oehrlein, M. Barela, H.M. Anderson, Fluorocarbon-based plasma etching of SiO2: comparison of C4F6/ Ar and c-C4F8/Ar discharges, J. Vac. Sci. Technol. A 20 (2002) 2052.
Microelectronics Journal 38 (2007) 125–129 www.elsevier.com/locate/mejo
A comparative study on a high aspect ratio contact hole etching in UFC- and PFC-containing plasmas Hyun-Kyu Ryua,1, Yil-Wook Kimb,2, Kangtaek Leec, CheeBurm Shind, Chang-Koo Kimd, a
LG Chemical, Limited, Daejeon 305-380, Republic of Korea Hynix Semiconductor Inc., Ichon 467-701, Republic of Korea c Department of Chemical Engineering, Yonsei University, Seoul 120-749, Republic of Korea d Department of Chemical Engineering, Ajou University, Suwon 442-749, Republic of Korea b
Received 3 July 2006; accepted 23 September 2006 Available online 20 November 2006
Abstract An etching of a SiO2 contact hole with a diameter of 0.19 mm and an aspect ratio of 13, using C4F6/Ar/O2/CH2F2 and c-C4F8/ Ar/O2/CH2F2 plasmas, was performed for a feasibility test of the use of unsaturated fluorocarbons (UFCs) as an alternative to perfluorocarbon (PFC) gases for a high aspect ratio contact hole etching. The etch profile of the contact hole obtained in the C4F6/Ar/O2/CH2F2 plasma was shown to have 23% lower degree of bowing than that in the c-C4F8/Ar/O2/CH2F2 plasma. The Kelvin and chain contact resistances of the contact holes etched in the C4F6/Ar/O2/CH2F2 plasma were 10–12% higher than those in the c-C4F8/ Ar/O2/CH2F2 plasma, but they were within the device spec. The integration of device with 0.1 mm design rule using C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/CH2F2 plasmas during the contact hole etching was also conducted, and it was found that etch profiles, metal coverage, and bottom critical dimensions of the contact in the C4F6/Ar/O2/CH2F2 plasma were nearly identical to those in the c-C4F8/ Ar/O2/CH2F2 plasma, suggesting that the use of C4F6 gas as an etchant gas for a high aspect ratio contact hole etching can be a good alternative to PFC gases. r 2006 Elsevier Ltd. All rights reserved. Keywords: Contact hole etching; Unsaturated fluorocarbons; Perfluorocarbons; Bowing; Contact resistance
1. Introduction Plasma etching is widely used for patterning of a high aspect ratio contact hole (e.g., SiO2), which is a crucial process in developing the next generation ultra-large-scale integrated (ULSI) devices because of the rapid shrinkage of the design rule to the nanometer level. Perfluorocarbon (PFC) gases such as CF4, C2F6, and c-C4F8 are currently used as etchant gases for the contact hole etching [1,2]. These PFCs, however, are considered to be problematic from an environmental point of view because of their long atmospheric lifetimes and high global warming potentials [3–5]. Several classes of environmentally benign chemistries Corresponding author. Tel.: +82 31 219 2389; fax: +82 31 219 1612.
E-mail address: [email protected] (C.-K. Kim). Current address: DuPont Korea Inc., Seoul 135-719, Korea. 2 Current address: FOI Korea Corporation, Seongnam 463-828, Korea. 1
0026-2692/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.mejo.2006.09.002
have been examined as alternatives including unsaturated fluorocarbons (UFCs) such as hexafluoropropene (C3F6, CF2QCF–CF3), hexafluoro-1, 3-butadiene (C4F6, CF2Q CF–CFQCF2), octafluorocyclopentene (c-C5F8), etc., and their etch characteristics have been studied [6,7]. However, there are few reports on etch profiles and electrical measurements of high aspect ratio contact holes etched in UFC-containing plasmas. In this work, we report on an etching of a SiO2 contact hole with a diameter of 0.19 mm and an aspect ratio of 13 using a C4F6/Ar/O2/CH2F2 plasma (UFC-containing plasma) and a c-C4F6/Ar/O2/CH2F2 plasma (PFC-containing plasma). This study is to find feasibility for the use of UFCs as an alternative to PFC gases for a high aspect ratio contact hole etching A comparison of etch characteristics between UFC- and PFC-containing plasmas was made by measuring etch profiles and contact resistances of the high aspect ratio contact holes etched in both plasmas.
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Fig. 1. SEM micrographs of the 0.19 mm diameter contact holes etched in (a) C4F6/Ar/O2/CH2F2 and (b) c-C4F8/Ar/O2/CH2F2 plasmas. The dotted lines represent the position of the maximum bowing occurred during etching.
2. Experimental A 2.5-mm-thick SiO2 film was grown on a p-type Si wafer by plasma-enhanced chemical vapor deposition (PECVD) with tetraethoxysilane (TEOS). Prior to SiO2 growth, Ti (100 A˚)/TiN (400 A˚)/W (1000 A˚) films were deposited and patterned on the Si wafer to form a bottom metal layer. A KrF photoresist (PR) was deposited and a hole pattern of 0.19 mm diameter was delineated. A 600 A˚ antireflective coating (ARC) layer was coated on the TEOS oxide film before spinning on the PR. A high aspect ratio contact hole etching was conducted in a magnetically enhanced reactive ion etching (MERIE) system (UNITY 85, Tokyo Electron Ltd.). To compare the etch performance between UFC- and PFC-containing plasmas, two gas mixtures were used to generate plasmas by applying a 13.56 MHz radio-frequency (RF) power: C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/CH2F2. Throughout this study, the power was fixed at 1700 W, the pressure 40 mTorr, the Ar flow at 400 sccm, O2 flow at 20 sccm, and
the CH2F2 flow at 20 sccm. The C4F6 and c-C4F8 flows were also maintained at 15 and 10 sccm, respectively. The etching of the oxide films was followed by PR stripping and cleaning. To conduct electrical tests, the contact hole was filled with W by CVD. Ti (100 A˚)/TiN (300 A˚) films were deposited as barrier metals prior to filling the W film. Then, a top metal layer of Ti (100 A˚)/Al (4500 A˚)/Ti (100 A˚)/TiN (250 A˚) was deposited and patterned. Cross-sectional profiles of etched samples and integrated structures were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. Chain resistance and Kelvin resistance were measured to investigate the electrical characteristics of the contact hole. 3. Results and discussion In our previous study, it was shown that the addition of CH2F2 gas to a C4F6/Ar/O2 plasma allowed one to
ARTICLE IN PRESS H.-K. Ryu et al. / Microelectronics Journal 38 (2007) 125–129
maintain the critical dimension (CD) of the contact hole during a high aspect ratio contact hole etching [8]. When CH2F2 gas was not added to the C4F6/Ar/O2 plasma, erosion of PR layer occurred around the contact hole. This finally led to deform the CD of the deep contact hole. On the contrary, relatively thick fluorocarbon films are deposited on the PR layer and around the contact hole for addition of 20 sccm of CH2F2 gas to a C4F6/Ar/O2 plasma. This resulted in maintaining the CD after ashing the PR layer and cleaning the fluorocarbon films. Therefore, CH2F2 gas was added to C4F6/Ar/O2 and c-C4F8/Ar/ O2 plasmas as well during etching of the SiO2 contact holes in this study. Fig. 1 shows the SEM micrographs of the deep contact holes, with a diameter of 0.19 mm and an aspect ratio of 13, etched in C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/CH2F2 plasmas, respectively. Development inspection critical dimensions (DICDs) of the contact holes were 0.19 mm, but final inspection critical dimensions (FICDs) were increased by ca 0.02 mm in both C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/CH2F2 plasmas. It is seen that contact hole profile angles are also similar in both plasmas: 89.01 for the C4F6-containing plasma and 89.11 for the c-C4F8-containing plasma. However, it is apparently seen that bowing at the side walls of the hole etched in the c-C4F8/Ar/O2/ CH2F2 plasma is more severe compared to that etched in the C4F6/Ar/O2/CH2F2 plasma. To reduce bowing of deep contact holes, it is believed that a protective film should be formed on the sidewall during etching [9]. Li et al. [10] have conducted a gas phase and surface chemistry study on C4F6/Ar and c-C4F8/Ar plasmas. In their study, the fluorocarbon deposition rate was higher for the C4F6/Ar plasma than that for the cC4F8/Ar plasma while the fluorocarbon etch rate was lower for the C4F6/Ar plasma than that for the c-C4F8/Ar plasma. In addition, the steady-state fluorocarbon film thickness formed during Si and SiO2 etching was greater for the C4F6/Ar plasma than that for the c-C4F8/Ar plasma. This thicker fluorocarbon film formed using the C4F6-containing plasma can protect the sidewall more effectively, resulting in the reduction of bowing during contact hole etching in the C4F8/Ar/O2/CH2F2 plasma. For a better comparison, the degree of bowing (defined as the ratio of the width at the maximum bowing position to the diameter of the contact hole) was calculated and it was obtained that the degree of bowing were 1.05 and 1.29 for C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/CH2F2 plasmas, respectively. Therefore, it can be said that the etch profile of the contact hole obtained in the C4F6-containing plasma is more improved than that in the c-C4F8-containing plasma. Fig. 2 shows the resistance distributions of the contact holes etched in C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/ CH2F2 plasmas, respectively. Both Kelvin and chain contact resistances are shown to have about 10–12% higher values for the C4F6/Ar/O2/CH2F2 plasma compared to those for the c-C4F8/Ar/O2/CH2F2 plasma. This results
127
Fig. 2. Resistance distributions of the contact holes etched in C4F6/Ar/O2/ CH2F2 and c-C4F8/Ar/O2/CH2F2 plasmas: (a) Kelvin and (b) chain resistances.
from lower bottom CD of the contact hole etched in the C4F6/Ar/O2/CH2F2 plasma (see Fig. 1(a)). Although the absolute values of the contact resistance are higher for the C4F6/Ar/O2/CH2F2 plasma, they are still within the device spec. Furthermore, the use of the C4F6-containing plasma in a high aspect ratio contact hole etching reduced the top CD loss (also see Fig. 1(a)) so that it can offer wider process windows to succeeding operations (e.g., wider alignment margin in the metallization). So far, it has been shown that the use of the C4F6containing plasma in a high aspect ratio contact hole etching presented etch profiles and electrical characteristics equivalent to or better than those obtained in the c-C4F8containing plasma. Therefore, we conducted the integration of the device with 0.1 mm design rule using C4F6- and c-C4F8-containing plasmas for the contact hole etching.
ARTICLE IN PRESS H.-K. Ryu et al. / Microelectronics Journal 38 (2007) 125–129
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Fig. 3. TEM micrographs of the deep contacts using (a) C4F6/Ar/O2 and (b) C4F6/Ar/O2/CH2F2 plasmas during the contact hole etching.
Fig. 3 shows the TEM micrographs of high aspect ratio deep contacts processed through a 0.1 mm device process flow. It is seen that the contact holes have profile angles of about 891 in both C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/ CH2F2 plasmas. It is also seen that W metals as well as barrier metals fill the contact hole with good coverage. Since the bottom CDs obtained in both C4F6- and c-C4F8containing plasmas show similar values, it is expected that the electrical characteristics would have the same behaviors in both cases. Therefore, it can be said that the use of C4F6 gas instead of c-C4F8 gas for a high aspect ratio contact hole etching finds no problems in device integration as well as unit process. 4. Conclusions A comparative study on an etching of a high aspect ratio contact hole (diameter ¼ 0.19 mm, aspect ratio ¼ 13) was made using C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/CH2F2 plasmas. The shape of etched profiles showed that the contact profile angles were nearly constant (891) in both C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/CH2F2 plasmas. The degree of bowing, however, was greatly reduced (23%) in the C4F6/Ar/O2/CH2F2 plasma, implying that the etch profile of the contact hole etched in the C4F6containing plasma was improved. The resistance distributions of the contact holes etched in the C4F6/Ar/O2/CH2F2 plasma had Kelvin and chain contact resistances 10–12% higher, but they were within the device specifications. TEM analyses of high aspect ratio deep contacts processed through a 0.1 mm device process flow showed that etch profiles, metal coverage, and bottom CDs of the contact in the C4F6/Ar/O2/CH2F2 plasma were nearly
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