Backscattering substrate effect

Although the single-layer negative resists commonly utilized are simple, they typically do not resolve narrow (0.5 ftm) gaps between wide lines or pads due to proximity effects from backscatter from the substrate during electron beam (E-beam) exposure. Further, there are variations in linewidth which occur when images are written in a single-layer resist which overlies steps in the substrate. 

Figure 10. Contrast versus linewidth for 25 kV and 50 kV electrons exposing a 1 / thick resist layer on a silicon substrate. Improved immunity to proximity effect has been reported by Neill and Bull (64). Backscattering for 50 kV electrons was obtained by extrapolation from data given in references...

The bottom thick layer has the ability of planarizing the topographic surface of the substrate and reducing the backscattering effect from the substrate in electron beam lithography. 

The two processes that contribute to the photoemission current are the direct emission from the adsorbate orbital into a plane wave final state /) and the indirect emission from the adatom orbital via backscattering from the substrate lattice. Formally both effects are taken into account by replacing the matrix element of Eq. (14) by... 

In a typical direct write e-beam lithographic system, the resolution of a dense line-space array is often limited by the effect of electrons backscattered from the substrate. In these arrays, the backscattered electrons from one exposed line increase the net exposure density in an adjacent line. While this problem of non-uniform exposure can be corrected by varying the exposure dose within the pattern, this form of proximity correction requires sophisticated algorithms and extensive computer facilities. 

The resuts described in the following correspond to Pd evaporated at a rate of about 2.10 at.cm. min on a sample maintained at room temperature. Whatever the system, the monolayer will be defined with respect to the number of metal atoms in the outer plane of the metallic substrate. The calibration of the evaporation rate of the source and/or the quantification of adlayers following metal on metal deposition is not straightforward. A good way to do it is to combine quantification results from in-situ techniques such as AES or XPS and a further absolute quantification by Rutherford Backscattering Spectroscopy (RBS). For absolute quantification, it is better to use polycrystalline samples in order to avoid any channeling effects during RBS measurements. 

Experimental profiles in the case of Te implanted Si samples irradiated at different substrate temperatures with 1.5 J/cm -30 nm ruby laser pulses are shown in Fig.9. The concentrations as measured by channeling effect technique in combination with MeV He Rutherford backscattering, indicate that the higher surface accumulation is obtained at 600K substrate temperature. 

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