Dopant profiles, boron

Figure 4.15 Experimental and simulated boron dopant profiles, for two batch operating recipes [165].

Although the surface Si seems to be melted during FLA, crystallization after complete melting of the whole Si is unlikely in this case. This is because the dopant profiles for boron (B) and phosphorus (P) show no significant... 

SRP. Spreading resistance profiling measures the response of the dopant atoms that reside at electrically active sites in the lattice. Combining NDP and SRP allows one to distinguish dopants, such as boron, that ire activated into electrically active sites from those located in nonactivated sites, such as in precipitates or interstitials. Therefore, the techniques can be used to select treatment methods that best activate the boron dopant and to provide information on the regions where non-electrically active dopant resides. 

Another application of the combined techniques is in the study of overlapping dopants. When one element of a dopant pair is profilable by NDP, SRP would measure the combined response of both dopants, whereas NDP would map only the boron distribution. Subtracting the distribution, each dopant profile could be determined Independent of the other. 

Fig. 15.7. Dependence of as-implanted dopant profiles for 0.5 keV boron decel implants on the source extraction energy...

In the semiconductor industry, SIMS has been particularly useful for the depth profiling of dopants that are present in silicon in very low concentrations. As an example, a SIMS depth profile for boron implanted into silicon is shown in Figure 27. One of the significant features is that we can detect about 101S boron atoms/cm3 in a silicon matrix of 5 x 1022 atoms/cm3. This illustrates an ability to detect 20 ppb. Also, the method spans 5 orders of magnitude in boron concentration. No other technique can span such a large range accurately. 

The development of the neutron depth profiling technique has been motivated by the importance of boron in both optical and microelectronic materials. Boron is widely used as a p-type dopant in semiconductor device fabrication and in the insulating oxide barriers applied as an organometallic or in vapor phase deposition glasses. 

SIMS is used for quantitative depth profile determinations of trace elements in solids. These traces can be impurities or deliberately added elements, such as dopants in semiconductors. Accurate depth prohles require uniform bombardment of the analyzed area and the sputter rate in the material must be determined. The sputter rate is usually determined by physical measurement of the crater depth for multilayered materials, each layer may have a unique sputter rate that must be determined. Depth prohle standards are required. Government standards agencies like NIST have such standard reference materials available for a limited number of applications. For example, SRM depth profile standards of phosphorus in silicon, boron in silicon, and arsenic in silicon are available from NIST for calibration of SIMS instmments. P, As, and B are common dopants in the semiconductor industry and their accurate determination is critical to semiconductor manufacture and quality control. 

Diffusion profiles of acceptor dopants have a standard form and can be described by one diffusion coefficient when boron surface concentrations are low ((Vbs < 3 X 10 cm ). Diffusion profiles became more complicated with increasing boron concentration. A steep region... 

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