23P006-O

Etching reactions of magnetic thin films by ion irradiation
in methanolplasma etching processes
メタノールプラズマエッチングプロセス中のイオン照射による磁気材料エッチング反応
Tomoko Ito,Kazuhiro Karahashi, and Satoshi Hamaguchi
伊藤智子，唐橋一浩，浜口智志
DCenter for Atomic and Molecular Technologies, Graduate School of Engineering,OsakaUniversity,
2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
大阪大学大学院工学研究科原子分子イオン制御理工学センター，〒565-0871 大阪府吹田市山田丘2-1
Dry etching processes based on CH3OH is a candidate for selective etching of magnetic thin films. In thisstudy, we have examined etching processes of Co and Ta thin films by energetic CO+, O+ ,C+ or OH+ions, which are considered to be major etchants of CH3OH plasmas. We have determined the etchingyields and analyzed surface reactions, using a mass-selected ion beam system. The etching yields of Co by
CO+ ions are higher than that by O+ ions but lower than the yields of possible physical sputtering, which
are estimated from interpolation of sputtering yield data of inert atom ions. From XPS analysis for O+
irradiated Co surfaces, oxidation is found to occur under O+ irradiation, which suggests that the oxide layer
hinders sputtering by ion bombardment. It is found that little oxidation occurs on Co surfaces under CO+ion irradiation and etching by CO+ ion bombardments proceeds. On a Ta surface, on the other hand, in theboth cases of O+ and CO+ irradiations, oxidation occurs and its etching yield is far smaller than the yieldof its possible physical sputtering. Etching characteristics by OH+ irradiation were also studied in a similarmanner.

1. Introduction
Dry etching of magnetic thin films is a
crucial step in micro fabrication of magnetic
random access memories (MARMs) andread/write heads for magnetic data storages.
Argon (Ar) ion milling seems to be almost theonly etching technique available in the current
manufacturing processes. However Ar ion
milling is incapable of achieving anisotropic
and selective etching of magnetic films (Ni, Coetc.) over hardmasks (Ta, Ti etc.) and therefore
highly selective reactive ion etching (RIE) ofmagnetic thin films is a highly sought-aftertechnology. RIE processes based on CH3OH is acandidate for selective etching of magnetic thinfilms[1]. In this study, we have examinedetching processes of Ni, Co and Ta thin films byenergetic CO+, O+, C+ or OH+ ions, which areconsidered to be major etchants of CH3OH
plasmas.
2. Experimental
The ion beam system can irradiate a sample (e.g.,Co, or Ta) film surface with mono-energetic
single-species ions (e.g., CO+, or Ar+ ions) in ultra-highvacuum conditions [2]. The reaction chamber, where asample is placed, is equipped with a quadrupole mass
spectrometer (QMS), and an X-ray photoelectron
spectroscopy (XPS) (Fig.1). The XPS is used for in-situ
chemical analyses of irradiated sample surfaces. The
kinetic energies of O+, CO+ , O+, C+ and OH+ion beams
used in this study were in the range of 300-1000eV. The
etching yields were determined from depth profiles ofirradiated surfaces measured by stylus profilometry. The
200nm thick sample films were deposited on Si
substrates by sputtering deposition prior to the beam
experiments.

3. Results
The etching yields are determined frommeasured depth profiles of irradiated surfaces
and ion fluxes. The etching yields of Co by CO+ions are higher than that by O+ ions but lower
than the yields of possible physical sputtering,which are estimated from interpolation ofsputtering yield data of inert atom ions (He+,Ne+, Ar+, Kr+ etc.)(Fig.2). XPS analysis for O+

irradiated Co surfaces, oxidation is found tooccur under O+ irradiation(Fig.3), whichsuggests that the oxide layer hinders
sputtering by ion bombardment. It is foundthat little oxidation occurs on Co surfaces
under CO+ ion irradiation and etching by CO+
ion bombardments proceeds.

Fig. 3XPS spectra Co2p

Fig.1 schematic view of scattering chamber.
Fig.4.Etching yield of Ta
On a Ta surface, on the other hand, in the bothcases of O+ and CO+ irradiations, oxidation
occurs and its etching yield is far smaller than
the yield of its possible physical sputtering(Fig4, Fig.5). Therefore we have found thathigh selectivity of Ni and Co etching against
hard masks (Ta, TaN) arises from theprevention of sputtering by mask oxidation.
Etching characteristics by OH+ irradiation
were also studied in a similar manner.
Thiswork
wassupportedby
theSemiconductor Technology Academic ResearchCenter (STARC).

Fig. t XPS spectra Ta4f
References[1] K. Kinoshitaet al., Jpn. J. Appl. Phys. 49(2010)
208JB02.
[2]K. Karahashiet al.: J. Vac. Sci. Technol. A
22(2004) 1166.

Fig.2.Etching yield of Co