Semiconductor >Applications >Diffusion Length

Diffusion Length

Diffusion length is a property of a bulk semiconductor material, telling how long an excess carrier travels, on average, before recombining to achieve equilibrium carrier concentration.  The diffusion length of a semiconductor with a perfect crystal lattice and no comtamination will be long, and any imperfections in the semiconductor material or contamination will reduce the diffusion length.  Thus, monitoring diffusion length is an excellent method to detect contamination.

The most common way of measuring diffusion length is via SPV, a technique that uses the SPV response of multiple wavelengths to calculate diffusion length.  This measurement technique works well in semiconductor grade silicon where the wafer thickness is greater than 3 times the diffusion length.

Technical Note #201 explains the theory of SPV measurement of diffusion length.

The WT-2000 offers maps of diffsion length measurements for semiconductor wafers, via a benchtop system.  The WT-3000 offers similar capability via a dual FOUP system for 300mm wafers.