Download New applications for SEM specimen preparation by an ion

New applications for SEM specimen preparation by an ion
beam etching/milling/coating
system
R. Alanil, R.J. Mitral, K. Ogura2 and H. Zhang 3
1 Gatan R&D, 5933 Coronado Lane, Pleasanton, CA 94588, USA.
2 JEOL Ltd. l-2 Musasino 3- Chome Akishima, Tokyo 196, Japan
3 Applied Materials, 4250 Burton Drive, Santa Clara, CA 95054, USA.
The effectiveness of a broad ion-beam based etching and coating system for SEM specimen
preparation of IC cross-sections (tungsten plugs) as well as metallographic specimens (stainless steel and
aluminum bronze) has already been described [l]. As an update to that work, we report new application
examples for the preparation of SEM specimens of ceramics and advanced materials/structures used in
semiconductor industries. Furthermore, we report a new approach for preparing precision SEM crosssections from microcleaved semiconductor structures.
Evaluating the system’s ability in handling ceramics, a mechanically polished yttria (Y203)
specimen was etched at 10 KeV, coated with 208+ chromium and examined in a SEM. Fig.la,b show the
yttria specimen before and after etching for 2 minutes. Note, the surface pores (see arrows), grain
boundaries and the grain size variation (gradient), which increases from left to right in Fig lb.
SEM cross-sections of semiconductors are routinely prepared for new process developments
and fabrication problem solving. In this connection, we applied the combined etching/coating technique
to study several advanced structures and materials. Fig.2 shows a typical cross-sectional SEM view of a
tungsten layer grown on high aspect ratio “contacts” after etching at 6KeV and applying a 2OA tungsten
coating. The uniform nucleation of tungsten layer can be seen. Fig. 3 is an SEM cross-section of new
technology copper metallization layer/“contacts”, used in next generation IC devices, after etching (at.
4KeV) and coating ( 2OA tungsten). Well etched Cu grains and the Ta barrier layer are clearly observed.
In this system, a major advancement for the preparation of precision SEM cross-sections is
reported, which is based on perpendicular broad ion-beam milling technique. The controlled milling
feature exposes any desired cross-section through a given feature of the specimen. As a typical example,
Figs. 4a-b show SEM cross-sectional images of a Si based wafer before and after milling. Fig.4a is the
as-cleaved wafer containing six tungsten “contacts” (labeled). Fig.4b shows all “contacts” are thinned
after 15 minutes milling at lOKeV, e.g. “contacts” #4 and #5 are milled beyond their centerline, while
“contacts” #2, #3 and #6 are cross-sectioned through the middle, exposing the tungsten grains and
barrier layers. “Contact” #l is only partially niilled. This result provided an estimation on the milling
rate of the tungsten layer ( = 3pm/hr, at 1OKeV and 300pA beam current).
In conclusion, the integrated etching/milling/coating system used in this work, is capable of
providing alternative/complementary techniques to traditional methods of SEM specimen preparation for
a variety of applications. For example, it can provide an alternative approach to: i) “thermal etching” of
ceramics, ii) “wet chemical” etching for new materials and structures in advanced semiconductors, e.g.
copper metallization layers/contacts and iii) precision mechanical polishing, followed by “wet chemical”
etching for IC cross-sections. In this regard, it can also provide a more economical substitute for FIB
systems for the preparation of precision SEM cross sections.
Reference
1) Alani, R, et al. Proc. 55th. Annual. Meeting of MSA, p 363, (1997)
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19 la,b
xx
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show an yttria
arrows)
..:
w,
specimen
before
and the grain
size change
Figs. 4a.b are SEM images showng
I
and after Ar ion-beam
across
a cross-seci~onal
etching
Note the surface
pores
the specimen
view of a cleaved SI based wafer before and after milling (see text).