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Method of preparing TEM plan view sections on semiconductor devices

IP.com Disclosure Number: IPCOM000013586D
Original Publication Date: 2000-Sep-01
Included in the Prior Art Database: 2003-Jun-18
Document File: 5 page(s) / 275K

Publishing Venue

IBM

Abstract

Disclosed is a method of preparing plane view sections of semiconductor devices for transmission electron microscopy (TEM), by which a plane view section of a specific layer in a specific area can be prepared with spatial resolution of·less than one micron. This method uses tripod polishing for thinning the specified area, and chemical etching for extracting a specific layer. Figure 1a shows a cross-section of a silicon semiconductor device. Self-aligned (Salicide) titanium silicide is used in diffusion areas (TiSi2), which are isolated by buried trenches (SiO2-3). The gates are two layers of polycrystalline silicon (p-Si) and tungsten silicide (WSi). The shaded portion is a titnium silicide, which is a few ten nanometer in typical CMOS devices. Conventional sample preparation methods such as Forcosed Ion Beam (FIB) etching [1] or mechanical polishing [2] do not have selectivity of one layer over the others. So it is difficult to prepare a plane view sections of a thin layer as the silicide layer, especially when a specified area is of interest. By using the method described below, a plane view section of the silicide layer of a specified area can be prepared for TEM observation. First, the sample is cut down to a 10 mm by 10 mm piece with the area of interest at the center. Then the intervening layers above TiSi2 are removed; the insulating silicon dioxide layer (SiO2-1) is dry-etched and metal layer (Al) is removed by chemical etching. Then the silicon dioxide layer (SiO2-3) above the silicon nitride layer SiNx) is grind down by chemical mechanical polishing using colloidal silica. Polishing is stopped when the surface is less than five hundred nanometers from the silicide layer as illustrated in Figure 1b. It is when the SiNx is removed and WSi can be observed from the top in an optical micrograph. The first side should be finished as flat as possible, in order to avoid any contamination to stick to edges during

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Method of preparing TEM plan view sections on semiconductor devices

Disclosed is a method of preparing plane view sections of
semiconductor devices for transmission electron microscopy (TEM), by
which a plane view section of a specific layer in a specific area can
be prepared with spatial resolution of·less than one micron. This
method uses tripod polishing for thinning the specified area, and
chemical etching for extracting a specific layer.

Figure 1a shows a cross-section of a silicon semiconductor device.
Self-aligned (Salicide) titanium silicide is used in diffusion areas
(TiSi2), which are isolated by buried trenches (SiO2-3). The gates are
two layers of polycrystalline silicon (p-Si) and tungsten silicide
(WSi). The shaded portion is a titnium silicide, which is a few ten
nanometer in typical CMOS devices. Conventional sample preparation
methods such as Forcosed Ion Beam (FIB) etching [1] or mechanical
polishing [2] do not have selectivity of one layer over the others. So
it is difficult to prepare a plane view sections of a thin layer as
the silicide layer, especially when a specified area is of interest.

By using the method described below, a plane view section of the
silicide layer of a specified area can be prepared for TEM
observation.

First, the sample is cut down to a 10 mm by 10 mm piece with the area
of interest at the center. Then the intervening layers above TiSi2 are
removed; the insulating silicon dioxide layer (SiO2-1) is dry-etched
and metal layer (Al) is removed by chemical etching. Then the silicon
dioxide layer (SiO2-3) above the silicon nitride layer ( SiNx) is
grind down by chemical mechanical polishing using colloidal silica.
Polishing is stopped when the surface is less than five hundred
nanometers from the silicide layer as illustrated in Figure 1b. It is
when the SiNx is removed and WSi can be observed from the top in an
optical micrograph. The first side should be finished as flat as
possible, in order to avoid any contamination to stick to edges during

1

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the following process.

Then, the sample is further cut down to fit in a TEM holder, and
attached to a Pyrex insert by a high strength wax. The tripod should
be made coplanar with the Pyrex insert beforehand, then both the rear
micrometers are advanced in order to make the sample wedge-shaped [3,
4]. The wedge angle is less than a few degrees. The long side of the
silicide pattern is placed along the edge of the wedge as illustrated
in Fig. 2b.

The silicon on the bottom side is polished as illustrated in Fig. 1c,
first on diamond lapping films and then on cloth with colloidal
silica. The sample is polished while frequently observed in
transmitted light until it looks light orange or yellow near the
region of interest. The silicon on the bottom side should be about 1
um thick. Then the sample is glued to a tungsten TEM aperture grid
with epoxy resin, in order to reinforces the sample and eases the
handling in the following chemical etching.

As the mechanical polish does not ha...