S10-5
Gas cluster ion beam etching for etch-resistant materials
難エッチング材料加工のためのガスクラスターイオンビームエッチング技術
Noriaki Toyoda and Isao Yamada
豊田紀章, 山田公Graduate School of Engineering, University of Hyogo
2167 Shosha, Himeji, Hyogo, 671-2280, Japan
兵庫県立大学大学院工学研究科 〒671-2280 兵庫県姫路市書写2167
Etching of etch-resistant materials using gas cluster ion beam (GCIB) with acetic acid circumstance wasstudied for future nonvolatile memory process. With acetic acid vapor supply during O 2-GCIB irradiation,
etching depth of various etch-resistant materials (Pt, Ru, Ta, CoFe) showed 1.8 – 10.7 times higher values
than those without acetic acid. High-pressure and high-temperature effects of GCIB enhance chemical
reactions between reactive gas and substrate surface at room temperature. Thus, halogen free and room
temp. etching of etch-resistant materials was achieved.

1. Introduction
Various next-generation nonvolatile memories
have been developed in recent years. In thesedevices, exotic materials such as Pt, Ru, Ta, andCoFe are used. In general, there are manydifficulties with current etching process for thesematerials. It is also desirable that etching process
is performed at low-temperature, with lowdamage, without halogen.
Gas cluster ion beam (GCIB) has beendeveloped in the past two decades. It can be usedfor various applications such as surface
smoothing, low-damage etching, high-rate
sputtering, thin film formations, surface analysis
and so on [1-4]. As thousands of atoms or
molecules bombard on areas of a few nm at thesame time, the bombarded areas experience both
high pressure and temperature. As a result,enhancement of chemical reactions among
reactive gas, adsorbed molecules and substratesurface occurs. In addition, desorption of etchingproducts will occur.
We have reported Cu etching with O 2-GCIB
irradiation under acetic acid vapor at room
temperature without halogen gas [5]. In this study,
we examined etching effects of Pt, Ru, Ta, CoFe,
Si3N4, SiO2 by Ar-GCIB or O2-GCIB irradiation
under acetic acid vapor. In addition, surface
morphology, and surface composition analysis
were carried out for Pt after O 2-GCIB irradiation
with or without acetic acid in order to understandthe etching process.
2. ExperimentFig. 1 shows a schematic diagram of GCIB
system with acetic acid vapor supply. Neutral Ar or
O2 cluster beams were formed by supersonic
expansion of gas through a nozzle. Subsequently

they were ionized by electron bombardments. Gas
cluster ions were accelerated up to 20 kV. In thisstudy, partial pressure of acetic acid gas was fixedat 10-5 Torr. Pt, Ru, Ta, CoFe, Si3N4, SiO2 films
were partially covered with stainless-mask, andetching depths were measured with a contact
surface profiler. Surface morphologies after GCIBetching were observed with an atomic force
microscope. In addition, Pt surface after Ar-GCIBor O2-GCIB irradiation with or without acetic acidvapor were characterized with XPS. The
acceleration voltage and ion dose were 10 kV and 1
× 1016 ions/cm2, respectively.

Fig. 1. GCIB system with acetic acid supply

3. Results and Discussions
Fig. 2 shows the etching depths of Pt, Ru, Ta,CoFe, Si3N4, and SiO2 with or without acetic acidvapor during Ar or O2-GCIB irradiations. The
acceleration voltages of O2-GCIB were 10kV, 20kV,and 20keV for Ar-GCIB. The ion dose was 2 × 1016
ions/cm2. Etching depth of Pt irradiated by 20kV
O2-GCIB without acetic acid was 18.4 times higher
than that irradiated by Ar-GCIB. Also, etching
depth of Ru by O2-GCIB was 5.5 times higher thanthat irradiated by Ar-GCIB, because of volatile
RuO4 (M.P. 25.4oC) formation.

Ar-GCIB
Va:20kV

Pt Ru Ta CoFe

Pt Ru Ta CoFe SiN SiO2

PtEtching depth [nm]2001000Ru Ta CoFe SiN SiO2Fig. 2. Etching depth of Pt, Ru, Ta, CoFe, Si3N4, SiO2
irradiated by Ar or O2-GCIB with or without acetic acidWith acetic acid vapor supply during 20kV
O2-GCIB irradiation, etching depths of variousmetals (Pt, Ru, Ta, CoFe) increased by 1.8 – 10.7
times than those without acetic acid. Etching depthof Ru, Ta, CoFe by Ar-GCIB with acetic acidshowed 2.2 – 16.1 times higher than those without
acetic acid. These results indicate that O2 or
Ar-GCIB bombardments enhance chemical
reactions between acetic acid and target metals.
On the other hand, the etching depths of SiO2 andSi3N4 by O2-GCIB didn’t change either with orwithout acetic acid, which means that there is no
chemical reaction enhancement. Therefore, thesecan be used as mask materials.
Surface morphology of Pt irradiated by O2-GCIB
with or without acetic acid was examined. Fig.3(a)shows the AFM image of the virgin Pt surface. The
average roughness (Ra) and root mean squareroughness (Rq) were 1.85 nm and 2.39 nm,respectively. Fig.3(b) shows AFM of Pt after
O2-GCIB irradiation without acetic acid. Fig.3(c)shows that with acetic acid. Acceleration voltage
and ion dose of O2-GCIB were 20 kV and 5 × 1015
ions/cm2, respectively. Ra of Pt after O2-GCIB
irradiation without or with acetic acid were 1.00 nm,and 0.96nm, respectively. Although the etching
depth was 1.8 times deeper than that without acetic
acid, there was no surface roughening by O2-GCIB
etching with acetic acid.
initial(a)Ra=1.85nm
1µm

O2-GCIB without acetic acidVa=20kV, 5×1015 ions/cm2(b)O2-GCIB with acetic acidVa=20kV, 5×1015 ions/cm2(c)Ra=1.00nm

Ra=0.96nm

1µm1µmFig. 3. AFM images of virgin Pt (a), O2-GCIB withoutacetic acid (b), O2-GCIB with acetic acid (c).

Next, Pt surface after irradiation of Ar-GCIB andO2-GCIB with or without acetic acid werecharacterized with XPS. Fig.4 (a)-(d) show the XPSof Pt 4f7/2 before irradiation (initial) (a), afterirradiation by Ar-GCIB without acetic acid (b),O2-GCIB without acetic acid (c) and O2-GCIB withacetic acid (d). Acceleration voltage and ion dosewere 10 kV and 1 × 1016 ions/cm2, respectively.
After irradiation of Ar-GCIB without acetic acid(Fig.4(b)), spectrum was identical to the initial one(Fig.4(a)). After irradiation of O2-GCIB withoutacetic acid (Fig.4(c)), Pt, PtO and PtO2 peaks
appeared. In contrast, after O2-GCIB irradiation
with acetic acid (Fig.4(d)), PtOx peaks were very
weak, and the spectrum was almost the same as theinitial one. PtOx layer was formed by O2-GCIB
irradiation. However, PtOx reacted with acetic acidat the same time. Consequently, etchingenhancement by removal of PtOx layer wasobserved. Therefore, oxidation of Pt by O2-GCIB isnecessary in order to etch Pt.
4000

4000

(a) initial(b) Ar-GCIB without AcOH

Pt 4f7/2
3000

Intensity [arb. unit]

O2-GCIB
Va:20kV

2000

1000

3000

2000

1000

08078767472

70

080

68787674
72
Binding energy [eV]

Binding energy [eV]7068(c) O2-GCIB without AcOH 5000 (d) O -GCIB with AcOH
21500

PtO

1000

PtO2

Pt

500

Intensity [arb. unit]

O2-GCIB
Va:10kV

Intensity [arb. unit]

2

Intensity [arb. unit]

16

without acetic acidwith acetic acid

Dose:2x10 ions/cm
300

4000
3000
2000
1000

08078767472
Binding energy [eV]706808078767472
Binding energy [eV]7068Fig. 4. Pt 4f7/2 XPS on initial Pt (a), Ar-GCIB withoutacetic acid (b), O2-GCIB without acetic acid (c),O2-GCIB with acetic acid (d)Acknowledgments
We would like to acknowledge K. Hara at Tokyo
electron Ltd. for fruitful discussions.
References[1] I. Yamada, J. Matsuo, Z. Insepov, D. Takeuchi, M.
Akizuki, and N. Toyoda: J. Vac. Sci. Technol. A 14(1996) 781.
[2] W. K. Chu, Y. P. Li, J. R. Liu, J.Z. Wu, S. C. Tidrow,
N. Toyoda, J. Matsuo, and I. Yamada: Appl. Phys.
Lett. 72 (1998) 246.
[3] M. Nagano, S. Yamada, S. Akita, S. Houzumi, N.
Toyoda, and I. Yamada: Jpn. J. Appl. Phys. 44 (2005)
L164.
[4] N. Toyoda, H. Kitani, J. Matsuo, and I. Yamada:
Nucl. Instrum. Methods Phys. Res., Sect. B 121(1997) 484.
[5] T. Suda, N. Toyoda, K. Hara, and I. Yamada: Jpn. J.
Appl. Phys. 51 (2012) 08HA02.