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1 Wet etching of magnetic thin films ( )

2 Wet etching of magnetic thin films

3 20032

4 Wet etching of magnetic thin films by

5 Submitted to the faculty of in partial fulfillment of the requirements for the degree of Department of Chemical Engineering February 2003

6 NiFe, CoFe, IrMn HNO 3, HCl, H 2 SO 4, H 3 PO 4, HF profile.. NiFe HNO 3, profilehcl H 2 SO 4. NiFe HCl, field emission auger electron spectroscopy(feaes) x-ray photoelectron spectroscopy(xps) ClNiFe. CoFe NiFe HNO 3, HCl. CoFe profilehno 3 HNO 3. HCl. FEAES XPS ClCoFe. IrMn HNO 3, HCl, HF

7 . HNO 3 HCl, HF. : Magnetic material, Wet etching, Etchant, Magnetoresistive random access memory(mram), Tunneling magnetoresistance (TMR)

8 The wet etching characteristics of magnetic materials such as NiFe, CoFe, and IrMn were investigated in terms of etch rate and etch profile by using various etching solutions (etchants). Among the various etching solutions, HNO 3, HCl, H 2 SO 4, H 3 PO 4, and HF were selected for the etching of magnetic materials and the etch results were interesting and showed different characteristics. In the case of NiFe films, faster etch rate were obtained with HNO 3 solution and the HCl and H 2 SO 4 solutions gave rise to better etch profile than HNO 3 solution. When NiFe films were etched with HCl solution, white etch residues were found on the surface of etched films. From field emission auger electron spectroscopy(feaes) analysis and x-ray photoelectron spectroscopy(xps) analysis of these etch residues, they were confirmed to be the by-products from the reaction of NiFe with Cl. The variation of etch rate of CoFe thin films showed the similar trend to the that case of NiFe films. They were etched fast in HNO 3 solution while they showed slow etching in HCl solution. The etch profiles of CoFe films were smooth in dilute HNO 3 solution but revealed the partial etching around the patterns in HNO 3 solution of relatively high concentration. It was observed that the etched surface etched with HCl solution was clean and smooth while white etch residues were also

9 remained on the etched films. From FEAES and XPS analyses of these etch residue, they were proved to be by-product from the reaction of CoFe with Cl. IrMn thin films were etched fast for HNO 3, HCl and HF solutions. However the film surfaces etched with HNO 3, and HCl solutions were craked and in case of HF solution, the etched surface was smooth. Keywords: Magnetic material, Wet etching, Etchant, Magnetoresistive random access memory (MRAM), Tunneling magnetoresistance (TMR)

10 Table of Contents......i Abstract...iii List of figures...vi List of table...ix 1. Introduction Theoretical Background...8 (1)...8 (2) Experimental Results and Discussion...13 (1) NiFe...15 (2) CoFe...26 (3) IrMn...35 (4) TMR stackwet cleaning Conclusions References Acknowledgements...45

11 List of Figures Fig.1.MTJ. 2 Fig.2.MRAM. 4 Fig.3.FESEMmicrographsoftypicalwetetching. 10 Fig.4.Flowchartofexperimental. 12 Fig. 5. Etch depth of NiFe as a function of etch time in HNO 3 solutions at 25 o C. 16 Fig. 6. Etch depth of NiFe as a function of etch time in HCl solutions at 25 o C. 16 Fig. 7. Etch depth of NiFe as a function of etch time in H 2 SO 4 solutions at 25 o C. 17 Fig. 8. Etch depth of NiFe as a function of etch time in H 3 PO 4 solutions at 25 o C. 17 Fig. 9. FESEM micrographs of NiFe films etched by using HNO 3 :H 2 O=1:8 solutionsat25 o C. (a) Etch time : 1 min 30 sec (b) Etch time : 2 min 30 sec (c) Etch time : 3 min 19

12 Fig. 10. FESEM micrographs of NiFe films etched by using pure HCl solutions at25 o C. (a) Etch time : 2 min (b) Etch time : 3 min 20 Fig. 11. FEAES analysis of NiFe films etched bypurehcl. 2 Fig. 12. XPS ful spectra of NiFe films etched bypurehcl. 23 Fig. 13. XPS narrow scanofnifefilmsetchedbypurehcl. 24 Fig. 14. FESEM micrographs of NiFe films etched by using H 2 SO 4 :H 2 O=1:5 solutionsat25 o C.(Etchtime:9min) 25 Fig. 15. Etch depth of CoFe as a function of etch time in HNO 3 solutions at 25 o C. 27 Fig. 16. Etch depth of CoFe as a function of etch time in HCl solutions at 25 o C. 27 Fig. 17. Etch depth of CoFe as a function of etch time in H2SO 4 solutions at 25 o C. 28 Fig. 18. Etch depth of CoFe as a function of etch time in H3PO 4 solutions at 25 o C. 28 Fig. 19. FESEM micrographs of CoFe films etched by using etch solutions at25 o C 31. (a) HNO 3 :H 2 O=1:700, Etch time : 50 sec (b) HCl:H 2 O=1:1, Etch time : 5 min

13 Fig. 20. FEAES analysis of CoFe films etched by HCl solutions. 32 Fig. 21. XPS ful spectra of CoFe films etched by HCl solutions. 33 Fig. 22. XPS narrow scan of CoFe films etched by HCl solutions. 34 Fig. 23. Etch depth of IrMn as a function of etch time in HNO 3 solutions at 25 o C. 36 Fig. 24. Etch depth of IrMn as a function of etch time in HCl solutions at 25 o C. 36 Fig. 25. Etch depth of IrMn as a function of etch time in HF solutions at 25 o C. 37 Fig. 26. FESEM micrographs of IrMn films etched by using etch solutions at25 o C. 38 (a) HNO 3 :H 2 O=1:700, Etch time : 1 min (b) HCl:H 2 O=1:700, Etch time : 1 min (c) HF:H 2 O=1:1000, Etch time : 1 min Fig. 27. FESEM micrographs of TMR stack etched by using etch solutions at25 o C. 40 Fig. 28. FESEM micrographs of TMR stack etched by using etch solutions at25 o C. 40

14 List of Tables Table 1. melting point boilingpoint. 14

15 1. Introduction 21.,,, /, Ubiquitous,, Video-phone/Video-conference, 3-D. non-volatile memory. DRAMscaling down dopant level, interconnect RC delay, gate GDRAM. Flash memoryspeed ferroelectric random access memory(feram).

16 spin magnetoresistive random access memory (MRAM). MRAM tunnel (magnetic tunnel junction; MTJ). MTJ2 nm Al 2 O 3. tunnel conductance spin spin tunnel (tunneling magnetoresistance; TMR). Tunnel 1 spin Antiferromagnet Ferromagnet Insulator Ferromagnet Fig. 1. MTJ.

17 spin switch spin valve [1]. MRAM 2(a) matrix bit (BL)word(WL) memory cell. cell spin. 1, 0 TMR. cell switch 2(b)bit1MTJ 1 MOS transistor. DRAMcapacitorMTJ. MTJspin ns SRAM DRAM memory [2]. IBM 1 k-16 klow density MRAM [2]. MRAM non-volatile DRAM read/write. MRAM MTJ, power, architecture, LSIprocess. LSI TMR ion milling

18 Word line Current TMR cell Bit line (a) Insulating layer M2 M1 Bit line M3 M4 TMR cell Word line M1 p n + Gate n + MOSFET (b) Fig. 2. MRAM.

19 (reactive ion etching; RIE) [3]. spintronics anisotropic magnetoresistance(amr), gaint magnetoresistance(gmr), tunneling magnetoresistance(tmr), cell,,. TMR cell ion milling m MR % micron. GMR TMR cellmram TMR stack AT&T Bell lab chemically assisted ion beam etching(caibe) NiFe (NRIM) NiFeMo (reactive ion etching; RIE) Honeywell, IBM, NiFe, NiFeCo, FeMn, NiMnSb

20 2000 MotorolaGMR. HoneywellIBM1999 ion beam etching(ion milling) GMR TMR cell. 1 m ion beam etching GMR TMR cell. Ion beam etching. (a) (etch residue) (b) (radiation damage) (c) (d) (redeposition) 4 inch6 inch wafer ion milling GMR TMR integration uniformity (etch damage) yield. TMR cell MRAM

21 integration. MRAM NiFe, CoFe, IrMn, (etchant) HNO 3, HCl, H 2 SO 4, H 3 PO 4, HF, [4-6]. profile. field emission auger electron spectroscopy (FEAES)xray photoelectron spectroscopy (XPS)., MRAMTMR stack, TMR stack (etch residue) cleaning.

22 2. Theoretical Background 2.1 Microelectronic. 2.2 (a) Wet etching (b) Dry etching Non-reactive plasma : Reactive plasma : High density plasma : Sputtering Ion beam etching (Ion milling) Plasma etching Reactive ion etching Reactive ion beam etching Chemically assisted ion beam etching Magnetron RIE Electron cyclotron resonance(ecr) RIE Inductively coupled plasma(icp) RIE Transformerly coupled plasma(tcp) RIE..

23 ,...,, hard mask SiO 2. (isotropic). 3 FESEM [7].

24 Fig. 3. FESEM micrographs of typical wet etching. 3. Experimental

25 SiO 2 Si NiFe, CoFe, IrMn dc magnetron sputtering (photoresist) 1.2 lithography. gradehno 3, HCl, H 2 SO 4, H 2 SO 4, HF deionized(di) water [8-9]., dektak surface profilometer(dektak 3), profilefield emission scanning electron microscopy(fesem ; Hitachi S-4500). field emission auger electron spectroscopy(feaes ; VG 350)x-ray photoelectron spectroscopy(xps ; PHI Quantum 2000, µ-xps).

26 Fig. 4. Flow chart of experimental. 4. Results and Discussion

27 (photoresist) NiFe, CoFe, IrMn.. FEAES.,. 1 [10]., NO 3, F IrF 6..,, NO 3 HNO 3, IrMn F HF.

28 Table 1. melting point boiling point. 4.1 NiFe

29 HNO 3.., HNO 3 :H 2 O 2:1 550 /min, 1:2 900 /min, 1:81: /min. 6, 7 8 HCl, H 2 SO 4, H 3 PO 4. 50~100 /min HNO 3. HF HF:H 2 O 1:10, 1:5, 1:1, 1:0 NiFe HF.

30 2500 Etch depth () HNO 3 :H 2 O 2:1 1:2 1:8 1: Etch time (sec) Fig. 5. Etch depth of NiFe as a function of etch time in HNO 3 solutions at 25 o C HCl:H 2 O 1:10 1:0 Etch depth () Etch time (min) Fig. 6. Etch depth of NiFe as a function of etch time in HCl solutions at 25 o C.

31 H 2 SO 4 :H 2 O 2:1 1:5 Etch depth () Etch time (min) Fig. 7. Etch depth of NiFe as a function of etch time in H 2 SO 4 solutions at 25 o C H 3 PO 4 :H 2 O 1:1 1:5 Etch depth () Etch time (min) Fig. 8. Etch depth of NiFe as a function of etch time in H 3 PO 4 solutions at 25 o C.

32 NiFe profile 9. 9(a), 9(b) 9(c)HNO 3 :H 2 O 1:8 NiFe FESEM. NiFe HNO 3,.,. 10(a) 10(b) HCl NiFe profilefesem. 10(a) 10(b) HCl HNO 3.. NiFe HCl, FEAESXPS. 11NiFe HCl FEAES. 11 NiFe Cl., HCl ClNiFe. FESEM. mask

33 Fig. 9. FESEM micrographs of NiFe films etched by using HNO 3 :H 2 O=1:8 solutions at 25 o C. (a) Etch time : 1 min 30 sec (b) Etch time : 2 min 30 sec (c) Etch time : 3 min

34 Fig. 10. FESEM micrographs of NiFe films etched by using pure HCl solutions at 25 o C. (a) Etch time : 2 min (b) Etch time : 3 min

35 CO. 12NiFe HCl, sputter XPS full spectra. full spectra Clpeak. COpeak. Nipeak Fe peak. sputter XPS full spectrasputter full spectra Clpeak. C Opeak, NiFepeak. 12 sputter Clsputter,, NiFe HCl Cl. 13NiFe pure HCl NiFe Ni 2p3sputter sputter XPS narrow scan. Sputter narrow scanni 2p3 peak binding energy856.6 ev. Sputter Ni 2p3 peakbinding energy ev NiFe

36 . Reference Nihalides Ni 2p3 peakbinding energy855~867.5 ev. XPS narrow scannihalides., NiCl, NiCl 2. NiFe films kcounts/ev Fe Fe Fe Ni/Fe Ni C O Cl Ni Kinetic Energy(eV) Fig. 11. FEAES analysis of NiFe films etched by pure HCl.

37 after sputtering before sputtering Fe Fe2p3 Fe2p1 Fe Ni Fe Ni Ni Ni2p1 Intensity (arb. units) Ni2s C Ni2p1 Ni2p3 O Fe O1s Ni Ni C1s Cl2s C1s Cl2p Cl2p Ni2p3 Ni3s Fe3s Fe3p Ni3p Ni3s O2s Ni3p Binding Energy (ev) Fig. 12. XPS full spectra of NiFe films etched by pure HCl.

38 Ni2p Ni2p3 Intensity (arb. units) after sputtering before sputtering Binding Energy (ev) Fig. 13. XPS narrow scan of NiFe films etched by pure HCl.

39 14H 2 SO 4 :H 2 O 1:5H 2 SO 4 NiFe FESEM. HCl, HCl. Fig. 14. FESEM micrographs of NiFe films etched by using H 2 SO 4 :H 2 O=1:5 solutions at 25 o C ; Etch time: 9 min.

40 4.2 CoFe 15 18HNO 3, HCl, H 2 SO 4, H 3 PO 4 CoFe. 15 CoFe HNO 3. HNO 3 :H 2 O 1:500, HNO 3 :H 2 O 1: HNO 3 :H 2 O 1: /min. 16NiFe, CoFe HCl. 50 /min H 2 SO 4 H 3 PO 4. H 2 SO 4 H 3 PO 4 100~200 /min. HF HF:H 2 O 1:10, 1:5, 1:1 1:0 CoFe 10.

41 2500 Etch depth () HNO 3 :H 2 O 1:100 1:700 1: Etch time (sec) Fig. 15. Etch depth of CoFe as a function of etch time in HNO 3 solutions at 25 o C. Etch depth () HCl:H 2 O 1:0 1:1 1: Etch time (min) Fig. 16. Etch depth of CoFe as a function of etch time in HCl solutions at 25 o C.

42 H 2 SO 4 1:1 1:5 Etch depth () Etch time (min) Fig. 17. Etch depth of CoFe as a function of etch time in H 2 SO 4 solutions at 25 o C H 3 PO 4 1:1 1: Etch depth () Etch time (min) Fig. 18. Etch depth of CoFe as a function of etch time in H 3 PO 4 solutions at 25 o C.

43 19CoFe HNO 3 HCl FESEM. 19(a)HNO 3 :H 2 O 1:700 CoFe profile. NiFe HNO 3. 19(b)HCl:H 2 O 1:1 profile. NiFe HCl,., FEAESXPS. 20CoFe HCl FEAES. 20 NiFe Cl., HCl CoFe. FESEM. mask CO. 21 CoFe XPS full spectra. Cl., COpeak, NiFe

44 . Copeak Fepeak. sputterfull spectra Clpeak. Cpeaksputter O peak., CoFepeak. 21 sputter sputter XPS full spectracofe HCl Cl. Cl Co Co 2p3. 22 CoFe Co 2p3 peakxps narrow scan CoFe sputter Co 2p3 peakxps narrow scan. Sputter Co2p3 peakbinding energy778.5 evcoreference data., sputtercofe Co Co., sputter Co 2p3 peakbinding energy782 ev. Cohalides. CoFe HCl FESEM CoCl, CoCl 2.

45 Fig. 19. FESEM micrographs of CoFe films etched by using etch solutions at 25 o C. (a) HNO 3 :H 2 O=1:700, Etch time : 50 sec (b) HCl:H 2 O=1:1, Etch time : 5 min

46 CoFe films kcounts/ev Fe Fe Cl O Co/Fe Co/Fe C Co Kinetic Energy (ev) Fig. 20. FEAES analysis of CoFe films etched by HCl solutions.

47 after sputtering C Co2p before sputtering Fe2p3 Fe2p1 O Co Co Co O1s Co C1s Co2p1 Co2p3 Intensity (arb. units) Co2s Cl2s C1s Cl2p Co3p Co3s Co3s Co3p O2s Binding Energy (ev) Fig. 21. XPS full spectra of CoFe films etched by HCl solutions.

48 Co2p Co2p3 Intensity (arb. units) after sputtering before sputtering Binding Energy (ev) Fig. 22. XPS narrow scan of CoFe films etched by HCl solutions.

49 4.3 IrMn 23 25HNO 3, HCl HF IrMn IrMn HNO 3 HCl. 400~500 /min. HNO 3 :H 2 O, HCl:H 2 O 1: HF HF:H 2 O 1:2000. H 2 SO 4 H 3 PO 4 H 2 O1:1000 IrMn. 26(a) 26(b)IrMn HNO 3 HCl FESEM. 26(a) 26(b). 25(c)HF FESEM..

50 HNO 3 :H 2 O 1:700 1:1000 Etch depth () Etch time (sec) Fig. 23. Etch depth of IrMn as a function of etch time in HNO 3 solutions at 25 o C HCl:H 2 O 1:700 1:1000 Etch depth () Etch time (sec) Fig. 24. Etch depth of IrMn as a function of etch time in HCl solutions at 25 o C.

51 HF:H 2 O 1:1000 1:2000 Etch depth () Etch time (sec) Fig. 25. Etch depth of IrMn as a function of etch time in HF solutions at 25 o C.

52 Fig. 26. FESEM micrographs of IrMn films etched by using etch solutions at 25 o C. (a) HNO 3 :H 2 O=1:700, Etch time : 1 min (b) HCl:H 2 O=1:700, Etch time : 1 min (c) HF:H 2 O=1:1000, Etch time : 1 min

53 4. 4 TMR stackwet cleaning ion milling. ion milling... HNO 3, HCl profile cleaning. 27HNO 3 :H 2 O 1:50 TMR stackwet cleaningfesem. Wet cleaning. 28 FESEM. HNO 3 :HCl:H 2 O=1:1:50.

54 . (a) before cleaning (b) after cleaning Fig. 27. FESEM micrographs of TMR stack etched by using etch solutions at 25 o C. (a) before cleaning (b) after cleaning Fig. 28. FESEM micrographs of TMR stack etched by using etch solutions at 25 o C.

55 5. Conclusions MRAM NiFe, CoFe, IrMn HNO 3, HCl, H 2 SO 4, H 3 PO 4 HF.,. HNO 3, HCl, H 2 SO 4, H 3 PO 4, HF NiFe, CoFe, IrMn profile. NiFeHNO 3,. HCl. HCl, FEAESXPS HCl ClNiFe. H 2 SO 4 HCl profile, HCl. H 3 PO 4

56 , HF. CoFe, HNO 3. HCl. FEAESXPS ClCoFe. H 2 SO 4 H 3 PO 4 HCl. HF. IrMn HNO 3 HCl, H 2 SO 4 H 3 PO 4 IrMn. HF HF:H 2 O 1:2000. TMR stackion milling cleaning. FESEM cleaning.

57 , cleaning.

58 6. References [1] S. Tehrani, J. M. Slaughter, E. Chen, M. Durlam, IEEE ransactions on Magnetics, 35(5) (1999). [2] S. S. P. Parkin, K. P. Roche, M. G. Samant, P. M. Rice, R. B. eyers, R. E. Scheuerlein, et al., J. Appl. Phys., 85(8), 5828 (1999). [3] Nikkei Electronics, p.65 ( ). [4] X. A. CAO, J. A. Caballero, K. B. Jung, J. W. Lee, S. Onishi, J. A. Childress and S. J. Pearton, Solid-State Electronics. 42(9), 1705 (1998). [5] A. O. Adeyeye, J. A. C. Bland, C. Daboo, D. G. Hasko and H. Ahmed, J. Appl. Phys. 82(1), 469 (1997). [6] Y. H. Byun, H. I. Kim and C. W. Chung, Proceedings of 2001 KIChE, Fall Meeting, 7(2), 5159 (2001). [7] C. Y. Chang and S. M. Sze, ULSI Technology, The McGRAW-HILL, 329 (1996). [8] Y. H. Byun,, C. W. Chung,, 15(2), 105 (2002). [9] Y. H. Byun, H. I. Kim, Y. S. Song, J. K. Yoon and C. W. Chung, J. Ind. Eng. Chem., 8(3), 257 (2002). [10] David R. Lide, CRC Handbook of Chemistry and Physics 81 st Edition, CRC Press, (2000).

59 7. Acknowledgements

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41(6)-09(김창일).fm 269 Ar v Na 0.5 K 0.5 NbO 3 t ½ t,, ½ w,, ½ w»œw Surface Reaction of Na 0.5 K 0.5 NbO 3 Thin Films in Inductively Coupled Ar Plasma w t œwz J. Kor. Inst. Surf. Eng. Vol. 41, No. 6, 2008. < > Dong-Pyo Kim,

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