Implantation depth

The bombardment of a sample with a dose of high energetic primary ions (1 to 20 keV) results in the destruction of the initial surface and near-surface regions (Sect. 3.1.1). If the primary ion dose is higher than 10 ions mm the assumption of an initial, intact surface is no longer true. A sputter equilibrium is reached at a depth greater than the implantation depth of the primary ions. The permanent bombardment of the sample with primary ions leads to several sputter effects more or less present on any sputtered surface, irrespective of the instrumental method (AES, SIMS, GDOES. ..). 

Implantation of Primary Ions. The primary ions are implanted in the sample and thereby influence the chemical constitution. For energies in the 20 keV range the implantation depth is approximately 30 nm. The sputter yield, i. e. the ratio of secondary to primary particles (not only ions), is energy-dependent and has a maximum in the 10 keV range. 

Boron implant with laser anneal. Boron atoms are accelerated into the backside of the CCD, replacing about 1 of 10,000 silicon atoms with a boron atom. The boron atoms create a net negative charge that push photoelectrons to the front surface. However, the boron implant creates defects in the lattice structure, so a laser is used to melt a thin layer (100 nm) of the silicon. As the silicon resolidihes, the crystal structure returns with some boron atoms in place of silicon atoms. This works well, except for blue/UV photons whose penetration depth is shorter than the depth of the boron implant. Variations in implant depth cause spatial QE variations, which can be seen in narrow bandpass, blue/UV, flat fields. This process is used by E2V, MIT/LL and Samoff. 

In this chapter, we review the current status of doping of SiC by ion implantation. Section 4.2 examines as-implanted depth profiles with respect to the influence of channeling, ion mass, ion energy, implantation temperature, fluence, flux, and SiC-polytype. Experiments and simulations are compared and the validity of different simulation codes is discussed. Section 4.3 deals with postimplant annealing and reviews different annealing concepts. The influence of diffusion (equilibrium and nonequilibrium) on dopant profiles is discussed, as well as a comprehensive review of defect evolution and electrical activation. Section 4.4 offers conclusions and discusses technology barriers and suggestions for future work. 

Figure 4.17 Ion implantation depth profile as calculated by SRIM. Al was implanted at 700°C. Multiple implants starting at 1 75 keV were used to achieve the box profile. (From [87], 2000 Trans Tech Publications Inc. Reprinted with permission.)...

The diffusional displacement of B is a function of implant dose and energy. The energy dependence is illustrated in Figure 24, which shows the diffusion of B at a concentration of 1 X 1017/cm3 versus Rp, the projected range of B implantation. The implants were 1 X 1014-2 X 1014 B atoms per cm2 annealed at 800-850 °C for approximately 0.5 h. The displacement increases with implant depth and then reaches saturation. The calculated curve in Figure 24 is based on the concentration of excess self-interstitials in the tail of the implant that increases directly with range, up to a maximum value. 

Figure 10.11 Figure of merit calculated for candidate fluorophores as a function of implantation depth, (a) Showing FOM on a linear y-scale. (b) Showing the same data on a log scale. 

Figure 7.4 Simulation of 3-to-2 photon ratio for increasing diffusion lengths in the sample as a function of mean implantation depth into the sample (density p = 1 g/cm3).

The energetic positron slows down on its track to it s implantation depth, it ionizes the sample and leaves a spur of free electrons behind [27, 28]. The number of electrons at the terminal of the spur and their mobility determine the formation likelihood for positronium. The cross section for positronium formation becomes constant independent of incident energy. The second path to positronium formation is the 0re process [29]. When the potential energy needed to ionize an electron from a molecule is less than the binding... 

Figure 7.6 3-to-2 photon ratio versus mean implantation depth for samples with porogen load from 0 to 90%. Samples with isolated and closed pores are shown with lines and symbols (0 to 23%) partially open porosity sample data are shown as lines (26 to 60%) totally open porosity sample data are shown with open symbols (70 to 90%). 

Figure 7.10 Two cases of the 3-to-2 photon ratio versus mean implantation depth (p 1 g/cm3). Open symbol data show a thin skin layer, which seals the surface and prevents positronium escape. In the layer no positronium can exist The closed symbols represent a sample with a 200 nm thick capping layer deposited on top of the film. It, too, does not allow the existence of...

Figure 7.17 Mean lifetime versus porogen load. Up triangles the aperture is inserted down triangles the aperture is removed. The mean 2771 implantation depth chosen for 2.55 j a given porogen load is shown 2.351 on the top axis. The pore diameters (right axis) are meant as guides and should be used only for the data with the aperture and up to a 50% load. A typical error (including an estimate of systematic errors) is shown for 40% porogen load.

For now, the bimodal distribution may be an artifact. The two lifetimes can be considered as lower and upper bounds of the pore size distribution. This technique is the only one available that can provide non-destructive depth profiles without sample preparations other than mounting them in the vacuum system. Depth profiled lifetime data are currently being collected. This is practical due to the high data acquisition rate of 3TO3 to 104 lifetime events per second, depending on the implantation depth. 

Positronium formation is also sensitive to ion-implanted amorphous Si02. Figure 9.7 shows the intensity of the long-lived component, IL, as a function of the positron incident energy for Xe ion-implanted amorphous Si02 ([22]). The sample was obtained by a vapor-phase axial deposition (VAD) method. Xe ions of 400 keV were implanted into the sample to doses of 1 x 1014 and 5 x 1015 ions/cm2 at room temperature. While there is a small difference between IL of 1 x 1014 and II of 1 x 1015, both have a minimum at around 4-5 keV, corresponding to the mean positron implantation depth of -200 nm at which the ions are implanted. 

Figure 11.13 —AS vs positron implantation depth for commercial coatings after 2688 h of natural weathering. Lines in the Figure are fitted with eq. 11.

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