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Method of preparing TEM plan view sections on semiconductor devices Disclosure Number: IPCOM000013586D
Original Publication Date: 2000-Sep-01
Included in the Prior Art Database: 2003-Jun-18

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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