Spreading resistance profiling

Fig. 2. Spreading resistance profiles from (a) Au-diffused n-type Si, (b) same sample after hydrogen plasma-exposure for lh at 200°C and (c) another position of the sample in (b). The bar represents the range of initial resistance values of the Si prior to Au diffusion (Mogro-Campero et al., 1985). 

A comparison of the deuterium profile measured by SIMS and the spreading resistance profile obtained on deuterated samples is shown in Fig. 6. The region over which there is a reduction in thermal donor concentration matches well with the depth of deuterium incorporation. There is an excess of deuterium over the amount needed to passivate all the oxygen-donor centers. This is frequently observed in hydrogenation experiments and indicates there is hydrogen present in several states. 

Fig. 2. Spreading resistance profile of four B-doped samples of (100) Si hydrogenated at 122°C. The three higher resistivity samples were hydrogenated for one hour the lowest resistivity sample was treated for four hours. The resistivities were obtained from a calibration curve. Note the greater penetration depth of atomic hydrogen as the boron concentration decreases.

Fig. 3. Spreading resistance profiles for 10-0 cm, B-doped (100) Si hydrogenated as shown.

Fig. 10. Spreading resistance profiles for silicon doped with indium, gallium, and aluminum.

Fig. 17. Advance of a passivated region into silicon uniformly doped with 5 x 1018 boron atoms per cm3, after exposure for 30 min. at about 150°C to atomic deuterium from a plasma source (Johnson, 1985a). (a) Spreading resistance profile, (b) Depth distribution of total deuterium and of boron from SIMS.

An example of such a plot is shown in Figure 3, where the increment between experimental data points is 35A, making this an extremely high resolution instrument. It is preferable to a conventional C-V profiler because it has no depth limitation and uses wafers without the need to fabricate devices. It is destructive, however, by leaving an approximately 1 mm diameter hole in the wafer. Spreading Resistance Profiling... 

Figure 1 Illustrates the experimental procedure used In making spreading resistance measurements. Two probes are carefully aligned and then stepped across the bevelled surface of a semiconductor sample at each point, the probes are lowered onto the sample surface and the resistance between the two probes Is measured and plotted. The technique Is referred to as the spreading resistance technique because the dominant resistance of a point contact diode occurs In a very small volume beneath the probe, where the current rapidly spreads out Into the sample. Spreading resistance profiles are usually computer-processed to yield resistivity or dopant concentration profiles.

The Improvement in spreading resistance profiles obtained through controlling probe penetration is Illustrated In Figure 5. 

Figure 5. Spreading resistance profiles of an NPHIT transistor structure, as measured with penetrating probes and with controlled low penetration probes. Reproduced with permission from Ref. 5. Copyright 1984 American Society for Testing and Materials.

Figure 6. Spreading-resistance profiles of a narrow base NPN transistor.

Figure 7 Is an example of a spreading resistance profile corrected with a multilayer procedure. It shows a shallow boron Ion Implant Into a P-type substrate, along with the carrier...

Figure 8 Is a more recent spreading resistance and carrier concentration profile of a low dose boron lon-lmplant Into an N-type substrate. The peak In the spreading resistance profile at about 9 X 10 ohms Indicates the position of the PN junction. The...

We expect to get a better Idea of spreading resistance profile accuracy from a "round robin" test now In progress In the ASTM F-1 committee. This test Is being done In various laboratories throughout the world and will result In an experimental... 

Second, there Is a hump In the boron concentration at about 0.2 Urn in both the SIMS and NDP profiles which Is not seen In the spreading resistance profile because It Is due to undissolved boron which Is also not electrically active. 

Spreading resistance profiles are generated quickly, so the technique Is useful when speed Is essential. Most silicon structures can be bevelled and measured and the raw data then processed and plotted as a resistivity or carrier concentration profile In less than thirty minutes. 

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. 

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