Implanted layers depth profiling

Figure 7 SIMS depth profile of Si implanted into a 1- im layer of Al on a silicon substrate for 6-keV O2 bombardment The substrate is B doped.

Equation (10.1) can be used to determine the doping density of a silicon substrate and its depth profile, even if the flat band potential is not known accurately. Diffusion doping, ion implantation or the growth of an epitaxial layer are common methods of producing doped regions in semiconductor substrates. The dopant concentration close to the surface can be measured by SRP or capacitance-... 

Figure 19. Depth profiles of oxygen incorporated into the surface layer of PE implanted with 150 keV Sb ions to the following fluences 2xl0 ( ).

The hardening and embrittlement of polyimides by ion implantation has been also studied (Pivin, 1994). Nanoindentation tests performed using a sharp diamond pyramid of apical angle 35° provided very quantitative depth profiles of microhardness in polyimides implanted with C, N, O, Ne or Si ions. In all cases the microhardness increased steeply when the amount of deposited energy reached the order of 20 eV atom". For energies of 200 eV atom" the polymer is transformed into an amorphous hydrocarbon and the microhardening factor saturates at a value of 13-20. However, the carbonized layer is poorly adherent, as is evidenced by reproducible discontinuities in the depth vs load curves, when the indenter tip reached the interface. 

This is an alternative ion for forming an nMayer by implantation. This ion is, however, heavier than N hence, the diffusion coefficient is extremely small. Suzuki et al [6] reported that no change in the depth profile occurred after annealing, but the activation is much lower than that of N (approximately half that of N). Davis [1,18] reported the critical dose of 1015 cm 2 at which the implanted layer could be recrystallized. 

As in the presence of Ge in Ge ,SWSi-layered alloys [338] and impurity copper depth profiles in As-implanted Si [339]. 

It should be noted that during the implantation of low-energy ions (e.g., 100-keV B ) in polyethylene, polyamide, and some other polymers, the carbon enrichment turns out to be maximal at some depth below the surface of the irradiated target, which is evidenced by the depth profile of carbon excess in the implanted layer reconstructed from RBS spectra. In this case the oxygen depth profile is, generally, saddle shaped, because the additional maximum of oxygen concentration... 

It should be noted that even at a low energy of implanted species (100 keV) the size of nanopores that are formed in the implanted layer turns out to be enough to make the insertion of large molecules possible (for instance, the dicarbollyl complex of cobalt readily diffuses into polyethylene implanted with 150-keV ions [75]). In the case of energetic ions (with energies of several hundreds of MeV), the pore size increases and the implanted polymer can be doped with fullerenes [61]. Thus, the concentration of C o molecules that difhise into polyimide implanted with 500-MeV ions from toluene solution amounts to as much as 1.8 x 10 fullerene molecules per track (the fullerene concentration was evaluated by a neutron depth profiling technique using Li ions, known to form the insoluble adduct with Cfio as the tracer [61]). 

The crater depth value is included with Relation 5.5 as aerial dose values are used, i.e. this allows for the conversion of atoms/cm to atoms/cm. Of note is the fact that a constant sputtering rate is assumed during the course of the depth profile. As any variation in the sputter rate will result in the introduction of errors, implants should remain within a particular film, i.e. should not cross any interface and should not exist within the surface transient region (discussed within Section 3.3.2.2). If a multilayered substrate is to be examined, matrix-matched reference samples for each layer must be examined, with the associated RSF derived. In highly simplified... 

The implanted layer is thin, typically between 0.1 and 1 pm in depth. Impurities such as C and H often follow the implantation profile. 

An example of the distribution of implanted atoms is given in Fig. 17 for the profile of CO implantation, as measured by HEBS. The maxima of implanted C (29 at.%) and O (23 at.%) are reached at a depth of ca. 170 nm with a FWHM of the layer of ca. 200 nm. Due to the large cross sections the yields of C and O are strongly enhanced with respect to that of the substrate. The formation of an oxide layer in air after implantation leads to an O concentration at the surface higher than in the implanted layer. It can also be seen that the implantation profiles are nonzero at the surface, implying that there are implanted atoms in the outer surface layers, an observation that turns out to be important for the wear process. 

Figure 20 shows an AES depth profile taken from the N-implanted conventional Cr layer showing film composition as a function of depth, The predominant constituents of the film are O, Cr and N. The outermost layers of the film consist of oxides. The implantation has produced a broad N profile down to 250 nm with a maximum concentration of 33 at. % at a depth of 70 nm. If a higher ion dose were to be implanted, it would result not in a higher concentration but in a broader profile, The composition of the implanted layer does not quite reach the stoichiometry of CrN, which would correspond to 50 at.% N if all Cr were converted into CrN. It seems that in this region a significant amount of Cr is bound to O. 

---