Convergent beam electron diffraction investigation of strain induced by Ti self-aligned silicides in shallow trench Si isolation structures

Abstract

The deformation induced onto silicon by the formation of Ti self-aligned silicides (salicides) in shallow trench isolation structures has been investigated by the convergent beam electron diffraction technique (CBED) in the transmission electron microscope (TEM). The splitting of the high order Laue zone (HOLZ) lines in the CBED patterns taken in TEM cross sections close to the salicide/silicon interface has been explained assuming that the salicide grains induce a local bending of the lattice planes of the underlying matrix. This bending, which affects in opposite sense the silicon areas below adjacent grains, decreases with the distance from the interface, eventually vanishing at a depth of 300–400nm. The proposed strain field has been implemented into a fully dynamical simulation of the CBED patterns and has proved to be able to reproduce both the asymmetry of the HOLZ line splitting and the associated subsidiary fringes. This model is confirmed by the shift of a Bragg contour observed in large angle CBED patterns, taken in a cross section cut along a perpendicular direction. The whole experimental results cannot be explained by just a strain relaxation of the TEM cross section, induced by the salicide film onto the underlying silicon.

Method for determination of the displacement field in patterned nanostructures by TEM/CBED analysis of split high‐order Laue zone line profiles

“…This typically occurs when a stressor source or a thin layer with different elastic properties are deposited on a substrate. The diffraction patterns recorded very close to the interface shows the strongest deviation with respect to the patterns recorded on undeformed silicon, with a higher HOLZ line separation and a larger number of inner fringes (Clément et al ., 2004; Armigliato et al , 2006). Thus some aspects of the displacement field become more evident, as an asymmetrical distribution of the gradient in the various directions, and these effects could make the reconstruction of the field from experimental patterns quite difficult.…”

“…As an experimental application we selected some patterns taken in silicon at different distances from the polycrystalline TiSi 2 /Si interface of a shallow trench isolation (STI) structure. The main motivation for this choice is related to the complexity of the observed effects (Armigliato et al , 2006) that allowed us to relate in an accurate way how different features of the displacement field modify the HOLZ line intensity profiles.…”

Shallow trench isolation liners and their role in reducing lattice strains

“…This is in comparison to the smallest recorded STI structures measured by CBED to date that have an active area and trench of approximately 130 and 250 nm, respectively. 7 All three samples are a series of STI structures that have ϳ60 nm active areas separated by ϳ80 nm wide trenches, as shown in Fig. 1, with the x, y, and z axes labeled along the ͓110͔, ͓−110͔, and ͓001͔ crystallographic directions, respectively.…”

“…6 Micro-Raman spectroscopy ͑-RS͒ and convergent beam electron diffraction ͑CBED͒ are the dominant techniques in measuring and quantifying strain, but with devices reaching submicron sizes, the spatial resolution of -RS is insufficient, presently leaving CBED as the most suitable tool. [7][8][9][10] In this paper, different STI trench fill methods are examined to help determine a formula that can offset the strain. CBED is employed to measure and compare the strains produced by the nominal 80 nm wide trenches on nominal 60 nm wide active areas.…”

“…All samples received the same 1000°C thermal oxidation as a final STI-related operation and were prepared identically for transmission electron microscopy ͑TEM͒ using the "H-bar" technique, which retains the sample's strain better than the "lift-out" method. 7 The CBED patterns were obtained with a JEOL 2100F TEM along the ͓340͔ and ͓230͔ crystallographic zone axes. These axes are found to contain high order Laue zone lines free from dynamical interactions, thus allowing the Java version of electron microscopy software ͑JEMS͒ to use kinematical simulations to match the experimental CBED patterns quickly.…”