Spreading resistance technique

MAZUR Dopant Profiles by the Spreading Resistance Technique... 

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 spreading resistance technique Is characterized by four major features ... 

Figure 1. A schematic Illustration of dopant profiling with the spreading resistance technique. Reproduced with permission from Ref. Copyright 1984 American Society for Testing and Materials.

Calibration. The third key feature of the spreading resistance technique Is Its use of calibration curves. Because measurements are made on real silicon surfaces, the relationship expected on the basis of simple theory doesn t hold (Figure 1, equation 1). 

Therefore, we make resistivity measurements by first generating calibration curves on known-reslstlvlty samples of the same type, orientation, and surface finish as the test specimens to be profiled. Calibration curves are generated for a particular pair of probes at a particular time, using known-reslstlvlty samples of the highest quality available. This calibration procedure Is a particularly noteworthy characteristic of the spreading resistance technique. It means that spreading resistance Is a comparison method, and that Its ultimate accuracy Is therefore limited only by the calibration material available. Fortunately, It s now possible to obtain complete sets of calibration samples from the National Bureau of Standards. 

These profiles show three major differences between the two physical profiling methods and the spreading resistance technique. 

The spreading resistance technique does take a bit of learning, practice, and patience. However, when it s done right, there is really no match to the sensitivity and detail in the resultant profiles. That s why the spreading resistance technique has made and will continue to make a significant contribution to the activity that we re all concerned with—the never-ending task of characterizing semiconductor materials. 

Figure 5. Carrier concentration profile of same Si n-p-n structure as shown in Figure 4. The profile was measured by two different labs using the spreading resistance technique. (Adapted from Ref. 1.)...

An investigation was made of diffusion into (lll)-type samples by using the spreading resistance technique to determine impurity concentration profiles. It was... 

By using the spreading resistance technique, a study was made of diffusion into (111) samples from doped epitaxial source layers. It was found that, at 1167 to 1394C, the data could be described by ... 

The diffusion of Au in disiocation-free or piasticaiiy deformed Si (10 I to 10 3disiocations/m2) was measured using the spreading-resistance technique. The Au profiies produced in disiocation-free Si slices by indiffusion from both surfaces had non-erfc-type U-shapes. The kick-out model was used to calculate the contribution of self-interstitials to the (uncorrelated) Si self-diffusion coefficient,... 

The diffusion was studied by using the spreading resistance technique under intrinsic conditions, where the dopant concentrations were not allowed to exceed the intrinsic carrier concentration in Si at any diffusion temperature. The experiments were conducted in H2 or Ar atmospheres, and the matrix used was float-zone, epitaxial and... 

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