Fabrication and magnetic characterization of embedded permalloy structures T.Tezuka, T.Yamamoto, K. Machida, T. Ishibashi, Y. Morishita, A. Koukitu and K.Sato Faculty of Technology, Tokyo University of Agriculture and Technology, Koganei, Tokyo Abstract Regularly aligned magnetic patterns of square (1  m  1  m), rectangular (300 nm  100 nm) and circular (100 nm in diameter) dots with thickness of 150 nm and pattern-separation of 300 nm embedded in silicon wafers have been successfully fabricated by the damascene technique using an electron beam (EB) lithography and chemical mechanical polishing (CMP): Mask patterns were exposed using an EB pattern generator on the resist films spin-coated on Si(100) wafer. Using the mask pattern the Si wafer was dry-etched using CF 4 gas. Permalloy films were deposited using an electron beam evaporator on to the pit arrays and the magnetic materials outside the pit was polished out by CMP. The magnetic structures of these nano dot arrays were observed using a magnetic force microscope (MFM:SPA-300/SPI3800N with high moment-tip coated CoPtCr:500A (SII)). Details have been published elsewhere. In the present study, we investigated cross-shaped array structures of permalloy (Ni 80 Fe 20 ), in order to elucidate spin structures of magnetic dots with more complicated shape. Fabrication of the cross-shaped patterns was performed using the same damascene technique as mentioned above. Two kinds of structures named CROSS1 [200 nm in width, 3  m in length with separation of 3  m] and CROSS2 [100 nm in width, 1.5  m in length with separation of 1.5  m] were fabricated. All the MFM images (with high-moment tips) of these cross-shaped patterns show magnetic poles at the end of the cross bars. The left edge of horizontal wing (tip scan direction) is always bright regardless of magnetization direction of the sample, suggesting that the MFM image is subjected to the influence of the stray field from the tip. Therefore, we tried to use low-moment probe tips (MFM:SPI-4000/SPA300HV with low-moment probe tip coated CoPtCr:240A(SII)). A preliminary theoretical work on the spin structure of the pattern using LLG equation does not show the presence of magnetic poles at the end of the cross-bar, suggesting that the importance of the static magnetic interaction between patterns in the array structure. Fabrication by Damascean technique Spin coating of resist EB exposureEtchingResist removalflatting Si substrate Chemical mechanical polishing Electron beam deposition Development EB-patterning process Embedding of permalloy Dry etching process 〔 1 〕 Etching gas: CF 4 〔 2 〕 Vacuum: 3.0×10 -3 Pa 〔 3 〕 Gas pressure 9.2Pa 〔 4 〕 RF power: 400W 〔 5 〕 Etching rate: 1.6nm/sec 〔 6 〕 Etching time: 90sec 〔 1 〕 material ： permalloy （ Ni 80 Fe 20 ） 〔 2 〕 Vacuum ： 3.0×10 -6 Torr 〔 3 〕 Accelerating voltage ： 4kV 〔 4 〕 Deposition rate ： 0.4 ～ 0.8 Å /sec 〔 1 〕 Slurry: Al 2 O 3 /Grain-size: 20nm 〔 2 〕 Polishing chemicals: Si wafer GLANZOX SP-15 ( FUJIMI ) pH:11 〔 3 〕 Weight: 320g 〔 4 〕 Rotation: 150rpm 〔 1 〕 EB-resist （ ZEP-520 ） thickness ： 300 nm 〔 2 〕 Rotation : 1000rpm/5sec→5000 rpm/90sec 〔 3 〕 Baking : 160 ℃ /20min （ after development 120 ℃ /20min ） 〔 4 〕 Accelerating voltage ： 50kV 〔 5 〕 Beam current ： 20pA 〔 6 〕 Patterned area ： 3mm×3mm 1500nm CROSS2 (small) CROSS1 (large) 3000nm 200nm 1400nm 3000nm 700nm 100nm 1500nm 2 models of cross-patterned dot array Silicon wafer Buried Permalloy Comparison between AFM image and MFM images AFM imageMFM image 100nm ×300nm rectangular dots ( 300nm space ) AFM imageMFM image 1  m ×1  m square dots ( 300nm space ) Past Data AFM image MFM image 200nm ×3000nm cross dots ( 3000nm space ) AFM imageMFM image Zoom up at center of a cross dot MFM observation with a high - moment probe tip Magnetization Sample Probe tip Pattern variations with different magnetization direction of the sample CROSS1 CROSS2 Comparison between high-moment-tip and low-moment-tip observations [ Ⅰ ] High-moment tip (CoPtCr/500 Å in Air) Square dots Rectangular dots Low-moment tip (CoPtCr/240 Å in HV) Comparison between high-moment-tip and low-moment-tip observations [ Ⅱ ] CROSS1 High-moment tip (CoPtCr/500 Å in Air) Low-moment tip (CoPtCr/240 Å in HV) Comparison between high-moment-tip and low-moment-tip observations [ Ⅲ ] High-moment tip (CoPtCr/500 Å in Air) Low-moment tip (CoPtCr/240 Å in HV) CROSS2 Comparison of MFM observations for different directions of a tip-magnetization Magnetization Sample Probe tip Magnetization direction of the tip was changed Demagnetized sample VSM measurements of CROSS1 To parallelTo perpendicular VSM measurements of CROSS2 To parallelTo perpendicular Theoretical cross-dot spin structure calculated using LLG equation L W H z = 20 kOe → 0 Oe x z y (E.A.) divM divM z Saturation magnetization (Ms)800 emu/cm 3 Exchange field (A)1×10 -6 erg/cm 3 Anisotropic constant (Ku)1000 erg/cm 3 Gyro magnetic constant （ γ)-1.76×10 7 rad/(s ・ Oe) Damping constant （ α ） 0.2 Easy axisZ direction Cross-pattern size500 (L) nm×100 (w) nm ×50 (T)nm Number of cross-pattern1 Mesh size10 nm×10 nm×10 nm Acknowledgements We are very grateful to Dr. Yamaoka of Seiko Insturuments Inc. for his help in MFM measurements with a low-moment probe tip. This work has been carried out under the 21 st -century COE program of TUAT on “Future Nano Materials.” Summary Regularly aligned permalloy dots with sub-micron cross-shaped pattern have been successfully fabricated using Damascene technique on the silicon substrates. All the MFM images clearly show magnetic poles at the end of the cross bars and complicated structures at the crossing region. The upper edge of the vertical wing shows bright or dark spots depending on the magnetization direction of the sample. All the MFM patterns of the cross-array structure are aligned in the same direction, even though it is demagnetized. Since the such phenomenon occurred with a demagnetized tip, the magnetic alignment cannot be attributed to the stray field from the probe tip. A vortex-like image is observed at the crossing region using a high-moment probe tip, while asymmetrical domain-like pattern is observed with a low- moment tip. An LLG analysis on a single cross-shaped pattern does not show poles at the end of the cross bar. Non negligible effect of magneto-static interaction between patterns is suggested. Further theoretical studies are underway including magneto-static interactions. MFM observation with demagnetized tip