1. Junction depth:

To determine the junction depth, a small chip of diffused slice is lapped on an angle so as to expose the actual junction.

This angle is of order of $0.5^0$ to $1^0$ so that the junction region is visually magnified.

The junction is then delineated by means of selected etch.

In operation, acid serves to dissolve surface oxide; the $CuSO_4$ selectively plates the region with copper so as to delineate the junction.

Additionally the sample is strongly illuminated in order to cause the junction to be forward biased.

2. Sheet resistance:

Consider a rectangular layer of diffused material of length l, width w and thickness t. if the resistance is measured across the faces of width w and thickness t, then

$R=\frac{ρ(t)}{t} \frac{l}{w}$

Where ρ(t) is specific resistivity of material (in Ω-cm) and it varies with depth. This equation can be rewritten as

$R=R_s \frac{l}{w}$

Where $R_s$ is defined as sheet resistance of layer (in Ω)

Sheet resistance of diffused layer can be directly measured if it is made in patterned shape as show in figure below. Here for a p channel MOS transistor, p-type source/ drain diffusion is made into an n-type substrate.

Contact current is applied across the points AB and the voltage developed across points CD is measured using high impedance voltmeter.

$R_S=\frac{V}{I} \frac{w}{l}$

Since w⁄l is known as specific pattern, sheet resistance can be directly calculated.

3. Surface concentration:

The surface concentration can be determined from the sheet resistance and the junction depth.