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Advanced sputtering techniques for high rate-, plasma free- deposition and excellent target utility with uniform erosion
Pergamon PII: S0042-207X(98)00274-7
Vacuum/volume 51/number 4/pages 683 to 686/1998 ã 1998 Published by Elsevier Science Ltd All rights reserved. Printed in Great Britain 0042-207X/98 Sl - see front matter
Advanced sputtering techniques for high rate-, plasma free- deposition and excellent target utility with uniform erosion S Kadokuraa* and M Naoeb, aFTS Corp., 940-165 Utsukimachi, Hachioji-shi, Tokyo 192, Japan, and bDep. of Physical Electronics, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152, Japan
This paper focuses mainly on the techniques of facing target sputtering (FTS) for improving the deposited film quality as well as high productivity in comparison with conventional sputtering method. The plasma confinement technique of a newly developed FTS (NFTS) may realize that almost all the g-electrons can be densely confined in the space between facing target planes under the magnetron mode near the outside surface and the facing target mode of Lorentz force in the plasma space. This new technique of the NFTS may easily satisfy almost all the key factors for forming the advanced thin film qualities as well as the highest productivity in the sputtering method. ã 1998 Published by Elsevier Science Ltd. All rights reserved
Introduction Morphology of thin ®lms formed by the conventional sputtering is characterized by the Thornton model1 which shows a lot of thin ®lm growth patterns depending on the substrate temperature and sputtering gas pressure, and implies the generation of defects such as open grain boundaries in thin ®lms. Facing target sputtering FTS technologies have been developed for high deposition rate of ferromagnetic materials and low substrate temperature deposition due to dense plasma con®nement in the space between facing targets and plasma free on the deposition plane.2, 3 We have proposed that the voidless morphology of thin ®lms formed by the FTS technologies is dierent from those of the Thornton model.4 A newly developed facing target sputtering (NFTS) apparatus is characterized by the layout of permanent magnets and the position of facing target planes generating magnetic ®elds and electric ®elds for con®ning plasma in the space between facing targets by the magnetron mode in addition to the facing target mode of Lorentz force. This paper discusses why the sputtering plasma con®nement technique of this NFTS apparatus have advanced characteristics on deposition rate, target erosion pattern and plasma free on deposition plane. Plasma con®nement technique of NFTS apparatus The plasma con®nement principle of the NFTS modeled by a pair of magnets arranged outside of the target holders is *Corresponding author
shown in Figure 1. A pair of symmetrically arranged target planes may form a con®ned plasma space between the target planes by the aid of the magnetic ®elds generated from the magnet assemblies in Figure 1. The magnet layout and the con®guration of a pair of target planes in Figure 1 generate closed magnetic ¯uxes from the N-pole to the S-pole of the same magnets around the outside regions of both facing target planes, and also generates the closed vertical magnetic ¯ux from the N-pole to the S-pole of the facing magnets around outside space of both target plane edges. The almost symmetrical distributions of in-plane magnetic ¯ux (Fi) around the outside surface of the rectangular target planes (T1, T2) may be formed from the layout of the magnet assemblies (M1, M2) and the protruded position (P1, P2) of the yoke plates in Figure 1. The unsymmetrical vertical magnetic ¯ux distributions (Fv) around the outside space between the facing rectangular target planes may be almost same under the dierent thickness of the targets and the target materials due to the geometrical arrangement of the magnet arrays and the facing target edges. This means that the NFTS plasma con®nement technique is characterized by the magnetron mode of the outside surface regions of both target planes and the facing target sputtering mode of Lorentz force between the facing target planes. As a result, the magnetron mode will mainly govern the outside regions of rectangular target erosion, and also will in¯uence the contours of electron-beam drift with Lorentz force in the space between the facing target planes. The strength and the distribution of magnetic ¯uxes of the conventional FTS techniques, on the other hand, change 683
S Kadokura and M Naoe: Advanced sputtering techniques
Figure 1. The distribution of in-plane (Fi) and vertical (Fv) magnetic fluxes with NFTS due to the layout of the facing magnets (M1, M2) and the facing targets (T1, T2).
according to the distance between target planes D, the target size and the magnetic properties of target materials. In the case of unsymmetrical con®guration of the facing targets such as rectangular target planes, Lorentz force in the plasma space distributes unsymmetrically from the magnet arrangement. Unsymmetrical distribution of the Lorentz force in the plasma space between a facing rectangular target planes may result in the distorted erosion patterns of the rectangular target planes.
Experimental test results and discussion on the NFTS apparatus Table 1 shows main parameters of the NFTS apparatus test conditions. Rectangular targets of 575 mm width, 125 mm length and 20 mm thick were tested on the application for CoCr perpendicular magnetic tapes in the case of Co-20 at%Cr, MoFeNi (permalloy) and pure Fe materials. The characteristics of the Co-Cr thin ®lm media including tapes and ¯exible disks under the sputtering conditions in Table 1 were reported in detail elsewhere.3±5 Figure 2 shows a typical con®guration of the NFTS target holders. Two sets of magnet holders are arranged in the outside space of the target holders. The target parts (E1, E2) of the holders (H1, H2) recoil g-electrons. The shield plates (Sh1, Sh2) of the apparatus are placed in the outer space from the magnet holders. The NFTS target holders have a superior cooling eect on sputtered targets, because the cooling liquid such as water can ¯ow rapidly and make turbulence eects on the adjacent surface of the target plates due to the separation layout between the target holders and magnet ones.
Figure 2. Layout model of the NFTS configuration.
Plasma characteristics and distance between facing targets Figure 3 shows Ar gas pressure dependence of the sputter voltage Va at the sputter current Id of 10 ampere at the distance between facing target planes of 130 mm, 160 mm and 200 mm in the case of the MoFeNi target. Figure 3 reveals that almost the same sputtering characteristics were achieved under the changeable distance from 130 mm to 200 mm between facing target planes in the NFTS technique. This test result suggests that the combination of the in-plane and the vertical magnetic ¯ux distributions may compensate the plasmas con®nement conditions and realize the almost same plasma con®nement characteristics in the space between the facing target planes when the distance between the facing targets D changes from 130 mm to 200 mm. The improved plasma con®nement technique due to the NFTS apparatus is characterized by the con®gurations of the magnet layouts and the repulsion plates which generate ecient magnetic ®eld distributions for con®ning plasmas in combination with the aid of repulsion plates for recoiling g-electrons outside of the target plates.
Target erosion of MoFeNi material An example of the MoFeNi target erosion characteristics after a long period of operation is shown in Figure 4. The hatched portion of the residual target in Figure 4 shows the excellent target utility above 60%. A slightly distorted erosion pattern was observed as the marks of Y and Y' in this test. When the in-plane magnetic ¯uxes in Figure 1 were not added by the position change of magnet layout (the modi®ed NFTS) apparatus, more largely distorted patterns of the target erosions
Table 1. Experimental conditions of the NFTS apparatus Target Size (mm) Target materials Distance between facing target planes D(mm) Distance of target to substrate plane L(mm) Sputtering gas pressure PAr (Pa) Input power Pi (watts/cm2)
684
575 width 125 length 20 thickness 125 width 125 length 20 thickness Co-20 at%Cr, Mo-permalloy, Fe 80±200 30 0.1±2 max. 70
S Kadokura and M Naoe: Advanced sputtering techniques
Figure 3. Sputtering voltage Va characteristics depending on argon gas pressure PAr (target size of 125 mm 125 mm 20 mm, sputtering current of 10 ampere).
than those of the conventional FTS test result6 were obtained. These test results concluded that the magnetron mode plasma con®nement in addition to the facing target mode by Lorentz force surely improve the erosion pattern of the rectangular target to be symmetrically eroded, and also increase the target utility ratio due to the improved erosion near the outside region of the facing target surfaces in addition to the center of the target planes.
Input power characteristics Figure 5 shows the dependence of the deposition rate Rd on the in-put power Pi in the case of Fe targets and the target size of 125 mm width, 125 mm length and 20 mm thick. Arcing was not observed under Pi of 70 watt/cm2. In the case of the target size of 575 mm width, 125 mm length and 20 mm thick, Rd at the same Pi increased more
Figure 4. Target erosion pattern of Mo-permalloy material after a long period of sputtering operation.
685
S Kadokura and M Naoe: Advanced sputtering techniques utility and plasma-free condition as well as superior kinetic energy with adatoms on the deposition plane. The following remarks are summarized from experimental results and techniques of the NFTS con®guration.
Figure 5. Deposition rate Rd characteristics depending on input Pi in the case of 125 mm 125 mm 20 mm targets of Fe.
than 50% in comparison with the case in Figure 5 due to the eect of the target size and the target holder con®guration. The geometrical separation of the target holder and the magnet arrays are easily designed from the con®guration of the NFTS which means a superior cooling construction of the targets and the magnet assemblies in comparison with a planer magnetron sputter (PMR) as well as the conventional FTS. The upper limit of Pi is only dependent on the target cooling technique in the case of the NFTS apparatus. Concluding remarks This paper discusses why the newly developed FTS (NFTS) apparatus has advanced characteristics for thin ®lm formation on ®lm quality, deposition rate, target erosion pattern, target
686
1. The newly developed NFTS method is characterized by a unique sputtering plasma con®nement due to the combination of the magnetron mode and the facing target mode in the space between facing targets. 2. The combination technique of the NFTS apparatus realized almost the same characteristics of the sputtering plasma voltage, when the distance between the facing target planes D changes in the range of 130 mm to 200 mm. 3. More than 60% eective usage of ferromagnetic materials such as permalloy targets and Co-Cr ones were con®rmed after a long period of sputtering operation in the NFTS apparatus. 4. Deposition rate of more than 3 mm/min. may be realized in the NFTS apparatus when an ecient cooling mechanism of the target holder is designed.
References 1. Thornton, J. A., J. Vac. Sci. Technol., 1986, A4(6), 3059±3065. 2. Hoshi, Y., Naoe, M. and Yamanaka, S., Jpn. J. Appl. Phys., 1977, 16, 1715. 3. Kadokura, S. and Naoe, M., IEEE Trans. on Mag., 1982, MAG18, 1113. 4. Kadokura, S. and Naoe, M., Mat. Res. Soc. Symp. Proc., 1992, 239, 653. 5. Kadokura, S. and Naoe, M., IEEE Trans. on Mag., 1996, MAG32, 3816. 6. Kadokura, S. and Honjyo, K., Trans. Mat. Res. Soc. Jpn., 1993, 15B, 737.
Vacuum/volume 51/number 4/pages 683 to 686/1998 ã 1998 Published by Elsevier Science Ltd All rights reserved. Printed in Great Britain 0042-207X/98 Sl - see front matter
Advanced sputtering techniques for high rate-, plasma free- deposition and excellent target utility with uniform erosion S Kadokuraa* and M Naoeb, aFTS Corp., 940-165 Utsukimachi, Hachioji-shi, Tokyo 192, Japan, and bDep. of Physical Electronics, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152, Japan
This paper focuses mainly on the techniques of facing target sputtering (FTS) for improving the deposited film quality as well as high productivity in comparison with conventional sputtering method. The plasma confinement technique of a newly developed FTS (NFTS) may realize that almost all the g-electrons can be densely confined in the space between facing target planes under the magnetron mode near the outside surface and the facing target mode of Lorentz force in the plasma space. This new technique of the NFTS may easily satisfy almost all the key factors for forming the advanced thin film qualities as well as the highest productivity in the sputtering method. ã 1998 Published by Elsevier Science Ltd. All rights reserved
Introduction Morphology of thin ®lms formed by the conventional sputtering is characterized by the Thornton model1 which shows a lot of thin ®lm growth patterns depending on the substrate temperature and sputtering gas pressure, and implies the generation of defects such as open grain boundaries in thin ®lms. Facing target sputtering FTS technologies have been developed for high deposition rate of ferromagnetic materials and low substrate temperature deposition due to dense plasma con®nement in the space between facing targets and plasma free on the deposition plane.2, 3 We have proposed that the voidless morphology of thin ®lms formed by the FTS technologies is dierent from those of the Thornton model.4 A newly developed facing target sputtering (NFTS) apparatus is characterized by the layout of permanent magnets and the position of facing target planes generating magnetic ®elds and electric ®elds for con®ning plasma in the space between facing targets by the magnetron mode in addition to the facing target mode of Lorentz force. This paper discusses why the sputtering plasma con®nement technique of this NFTS apparatus have advanced characteristics on deposition rate, target erosion pattern and plasma free on deposition plane. Plasma con®nement technique of NFTS apparatus The plasma con®nement principle of the NFTS modeled by a pair of magnets arranged outside of the target holders is *Corresponding author
shown in Figure 1. A pair of symmetrically arranged target planes may form a con®ned plasma space between the target planes by the aid of the magnetic ®elds generated from the magnet assemblies in Figure 1. The magnet layout and the con®guration of a pair of target planes in Figure 1 generate closed magnetic ¯uxes from the N-pole to the S-pole of the same magnets around the outside regions of both facing target planes, and also generates the closed vertical magnetic ¯ux from the N-pole to the S-pole of the facing magnets around outside space of both target plane edges. The almost symmetrical distributions of in-plane magnetic ¯ux (Fi) around the outside surface of the rectangular target planes (T1, T2) may be formed from the layout of the magnet assemblies (M1, M2) and the protruded position (P1, P2) of the yoke plates in Figure 1. The unsymmetrical vertical magnetic ¯ux distributions (Fv) around the outside space between the facing rectangular target planes may be almost same under the dierent thickness of the targets and the target materials due to the geometrical arrangement of the magnet arrays and the facing target edges. This means that the NFTS plasma con®nement technique is characterized by the magnetron mode of the outside surface regions of both target planes and the facing target sputtering mode of Lorentz force between the facing target planes. As a result, the magnetron mode will mainly govern the outside regions of rectangular target erosion, and also will in¯uence the contours of electron-beam drift with Lorentz force in the space between the facing target planes. The strength and the distribution of magnetic ¯uxes of the conventional FTS techniques, on the other hand, change 683
S Kadokura and M Naoe: Advanced sputtering techniques
Figure 1. The distribution of in-plane (Fi) and vertical (Fv) magnetic fluxes with NFTS due to the layout of the facing magnets (M1, M2) and the facing targets (T1, T2).
according to the distance between target planes D, the target size and the magnetic properties of target materials. In the case of unsymmetrical con®guration of the facing targets such as rectangular target planes, Lorentz force in the plasma space distributes unsymmetrically from the magnet arrangement. Unsymmetrical distribution of the Lorentz force in the plasma space between a facing rectangular target planes may result in the distorted erosion patterns of the rectangular target planes.
Experimental test results and discussion on the NFTS apparatus Table 1 shows main parameters of the NFTS apparatus test conditions. Rectangular targets of 575 mm width, 125 mm length and 20 mm thick were tested on the application for CoCr perpendicular magnetic tapes in the case of Co-20 at%Cr, MoFeNi (permalloy) and pure Fe materials. The characteristics of the Co-Cr thin ®lm media including tapes and ¯exible disks under the sputtering conditions in Table 1 were reported in detail elsewhere.3±5 Figure 2 shows a typical con®guration of the NFTS target holders. Two sets of magnet holders are arranged in the outside space of the target holders. The target parts (E1, E2) of the holders (H1, H2) recoil g-electrons. The shield plates (Sh1, Sh2) of the apparatus are placed in the outer space from the magnet holders. The NFTS target holders have a superior cooling eect on sputtered targets, because the cooling liquid such as water can ¯ow rapidly and make turbulence eects on the adjacent surface of the target plates due to the separation layout between the target holders and magnet ones.
Figure 2. Layout model of the NFTS configuration.
Plasma characteristics and distance between facing targets Figure 3 shows Ar gas pressure dependence of the sputter voltage Va at the sputter current Id of 10 ampere at the distance between facing target planes of 130 mm, 160 mm and 200 mm in the case of the MoFeNi target. Figure 3 reveals that almost the same sputtering characteristics were achieved under the changeable distance from 130 mm to 200 mm between facing target planes in the NFTS technique. This test result suggests that the combination of the in-plane and the vertical magnetic ¯ux distributions may compensate the plasmas con®nement conditions and realize the almost same plasma con®nement characteristics in the space between the facing target planes when the distance between the facing targets D changes from 130 mm to 200 mm. The improved plasma con®nement technique due to the NFTS apparatus is characterized by the con®gurations of the magnet layouts and the repulsion plates which generate ecient magnetic ®eld distributions for con®ning plasmas in combination with the aid of repulsion plates for recoiling g-electrons outside of the target plates.
Target erosion of MoFeNi material An example of the MoFeNi target erosion characteristics after a long period of operation is shown in Figure 4. The hatched portion of the residual target in Figure 4 shows the excellent target utility above 60%. A slightly distorted erosion pattern was observed as the marks of Y and Y' in this test. When the in-plane magnetic ¯uxes in Figure 1 were not added by the position change of magnet layout (the modi®ed NFTS) apparatus, more largely distorted patterns of the target erosions
Table 1. Experimental conditions of the NFTS apparatus Target Size (mm) Target materials Distance between facing target planes D(mm) Distance of target to substrate plane L(mm) Sputtering gas pressure PAr (Pa) Input power Pi (watts/cm2)
684
575 width 125 length 20 thickness 125 width 125 length 20 thickness Co-20 at%Cr, Mo-permalloy, Fe 80±200 30 0.1±2 max. 70
S Kadokura and M Naoe: Advanced sputtering techniques
Figure 3. Sputtering voltage Va characteristics depending on argon gas pressure PAr (target size of 125 mm 125 mm 20 mm, sputtering current of 10 ampere).
than those of the conventional FTS test result6 were obtained. These test results concluded that the magnetron mode plasma con®nement in addition to the facing target mode by Lorentz force surely improve the erosion pattern of the rectangular target to be symmetrically eroded, and also increase the target utility ratio due to the improved erosion near the outside region of the facing target surfaces in addition to the center of the target planes.
Input power characteristics Figure 5 shows the dependence of the deposition rate Rd on the in-put power Pi in the case of Fe targets and the target size of 125 mm width, 125 mm length and 20 mm thick. Arcing was not observed under Pi of 70 watt/cm2. In the case of the target size of 575 mm width, 125 mm length and 20 mm thick, Rd at the same Pi increased more
Figure 4. Target erosion pattern of Mo-permalloy material after a long period of sputtering operation.
685
S Kadokura and M Naoe: Advanced sputtering techniques utility and plasma-free condition as well as superior kinetic energy with adatoms on the deposition plane. The following remarks are summarized from experimental results and techniques of the NFTS con®guration.
Figure 5. Deposition rate Rd characteristics depending on input Pi in the case of 125 mm 125 mm 20 mm targets of Fe.
than 50% in comparison with the case in Figure 5 due to the eect of the target size and the target holder con®guration. The geometrical separation of the target holder and the magnet arrays are easily designed from the con®guration of the NFTS which means a superior cooling construction of the targets and the magnet assemblies in comparison with a planer magnetron sputter (PMR) as well as the conventional FTS. The upper limit of Pi is only dependent on the target cooling technique in the case of the NFTS apparatus. Concluding remarks This paper discusses why the newly developed FTS (NFTS) apparatus has advanced characteristics for thin ®lm formation on ®lm quality, deposition rate, target erosion pattern, target
686
1. The newly developed NFTS method is characterized by a unique sputtering plasma con®nement due to the combination of the magnetron mode and the facing target mode in the space between facing targets. 2. The combination technique of the NFTS apparatus realized almost the same characteristics of the sputtering plasma voltage, when the distance between the facing target planes D changes in the range of 130 mm to 200 mm. 3. More than 60% eective usage of ferromagnetic materials such as permalloy targets and Co-Cr ones were con®rmed after a long period of sputtering operation in the NFTS apparatus. 4. Deposition rate of more than 3 mm/min. may be realized in the NFTS apparatus when an ecient cooling mechanism of the target holder is designed.
References 1. Thornton, J. A., J. Vac. Sci. Technol., 1986, A4(6), 3059±3065. 2. Hoshi, Y., Naoe, M. and Yamanaka, S., Jpn. J. Appl. Phys., 1977, 16, 1715. 3. Kadokura, S. and Naoe, M., IEEE Trans. on Mag., 1982, MAG18, 1113. 4. Kadokura, S. and Naoe, M., Mat. Res. Soc. Symp. Proc., 1992, 239, 653. 5. Kadokura, S. and Naoe, M., IEEE Trans. on Mag., 1996, MAG32, 3816. 6. Kadokura, S. and Honjyo, K., Trans. Mat. Res. Soc. Jpn., 1993, 15B, 737.