Implantation distributions, boron

One of the key issues in a MD simulation is extracting relevant information from the large amount of data obtained, since the outcome of these simulations is the space trajectory of all the particles considered. Therefore, we must develop methodologies to identify, in this particular case, those defects produced by the implantation of boron. We have to determine which atoms remain in perfect lattice sites and those that are displaced from ideal locations. Figure 2 shows the distribution of atoms as a function of the distance to a perfect lattice site after irradiation. Three regions may be distinguished in this case. Atoms closer than 0.7 A to a perfect lattice site are considered occupying that site consequently none of them are defects. For such distances, the lattice points are considered to be occupied by either the atom that initially was at such... 

Implantation. Ziegler and co-workers (1,14,24,25) introduced NDP by determining the range and shape of boron implantation distributions in intrinsic and doped silicon wafers. With the resultant profiles, they were able to calculate diffusion coefficients for boron in crystalline, amorphous, and arsenic-doped silicon. Since little experimental data existed for the case of boron to judge the validity of the current range theories, the shape of the boron profiles from NDP were of great interest. NDP and other techniques have since been able to show that a Pearson IV model rather than a gaussian profile is required to describe accurately the Implant distribution (21,26-28). 

In related experiments by Johnson (1985), atomic deuterium was used instead of Hx to neutralize boron in Si. Similar results on spreading resistance were obtained. Furthermore, the distribution profile of D was measured by secondary-ion mass spectrometry (SIMS), as shown in Fig. 4. The distribution profile of D reveals 1) that the penetration depth of D is in good agreement with the resistivity profile and 2) that the D concentration matches the B concentration over most of the compensated region. In another sample, the B was implanted at 200 keV with a dose of 1 x 1014 cm-2, the damage was removed by rapid thermal anneal at 1100°C for 10 sec., and then D was introduced at 150°C for 30 min. As shown in Fig. 5, it is remarkable that the D profile conforms to the B profile. 

For implanted acceptor activation there have been several reviews during the last few years since Troffer et al. s often-cited paper on boron and aluminum from 1997 [88]. Aluminum is now the most-favored choice of acceptor ion despite the larger mass, which results in substantially more damage compared with implanted boron. Mainly it is the high ionization energy for boron that results in this choice, as well as its low solubility. In addition, boron has other drawbacks, such as an ability to form deep centers like the D-center [117] rather than shallow acceptor states and, as shown in Section 4.3.2, boron ions also diffuse easily at the annealing temperatures needed for activation. The diffusion properties may be used in a beneficial way, although it is normally more convenient if the implanted ion distribution is determined by the implant conditions alone. 

Interfacial Profiling. Neutron depth profiling is well suited for measurements across interfacial boundaries. Kvitek et al. ( ) and others (16,17,21,30) have studied profiles of boron implanted and diffused across the interfacial region of Si/Si02. Other NDP experiments (33,34) have been described for interfaces of silicon, silicon dioxide or metal on metal, where diffusion distributions and segregation coefficients were studied. 

An example of the measurement of a disorder distribution is shown in Fig. 8.10 for a silicon implant at a substrate temperature of -150°C, with 5 x 1014 boron ions cuf2 at an energy of 200 keV, analyzed at room temperature with 1.8-MeV ions. The open circles in the upper part of the curve are the aligned yield. The dashed curve is the dechanneled fraction determined by use of the iterative procedure using multiple scattering theory to obtain the dechanneling factor at,. In this procedure, for example, the number of displaced atoms represented by the... 

An example of the measurement of a disorder distribution is shown in Fig. 8.10 for a silicon implant at a substrate temperature of -150°C, with 5 x 10 boron ions cm at an energy of 200 keV, analyzed at room temperature with... 

The lattice diffusion of B implanted into cobalt disilicide was studied. The bulk substrate, prepared by solidification from a melt, had grain sizes in the mm range. The B was introduced by ion implantation. After heat treatment at 450 to 700C, the boron distribution was monitored using secondary ion mass spectrometry. The lattice diffusion was described by ... 

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