Differential Hall Effect Metrology (DHEM) measures critical electrical properties at depths upto a few nanometers in semiconductor samples. Successive layers of the sample are exposed by etching or oxidation and sheet resistance and mobility measurements performed using Hall effect and Van der Pauw techniques. Infinita Lab, USA, offers this test to clients in the USA and across the world, through its laboratory network.
Differential Hall Effect Metrology (DHEM)
Differential Hall Effect Metrology (DHEM) is an electrical characterization technique for surface layers of semiconductors. DHEM enables critical electrical properties to be measured at depths upto a few nanometres in semiconductor samples. It uses the principle of Differential Hall effect (DHE) and the Van der Pauw technique, to measure mobility and sheet resistance on successive layers of the semiconductor. To reach into inner layers, the technique employs successive processing steps, typically involving chemical or electrochemical etching or oxidation.
The DHEM procedure involves creating an electrically isolated test area on the test sample, by forming a mesa pattern there, with four electrical contacts at the corners (termed Van der Pauw cross). The size of the test region can typically be adjusted from 0.5 mm × 0.5 mm to 2 mm × 2 mm so that the data collected is representative of that area. The Mesa pattern electrically isolates the test area from the surrounding bulk of the sample. There should also be an insulating barrier at the bottom of the test portion. This could be an oxide layer, a semi-insulating substrate or a p-n junction. A nozzle from a small process chamber, delivering chemical solutions, DI water or nitrogen gas, is sealed into the test region in the middle of the mesa test-pattern, to perform successive etching or oxidation of each layer. Starting from the surface layer of the mesa pattern, measurements of sheet resistance and mobility are done on each successive layer that is exposed by etching or oxidation. Data collected can then be analysed to obtain depth profiles of mobility, resistivity and carrier concentration. For example, Si and Ge or SiGe samples are profiled for these properties, up to 100 nm depth.
The electrochemical etching/oxidation process in DHEM needs to be precise and controllable. Different chemical recipes and process selection (etching or oxidation) are applicable for various materials.
DHEM is useful in applications that need knowledge of the electrical properties at semiconductor surface layers or at thin film interfaces. Through recipe development, it may be possible to carry out DHEM measurements not only through semiconductor films but also through metal/semiconductor or insulator/semiconductor to elucidate electrical properties of the specific layers and interfaces. DHEM is a valuable tool for fab manufacturers, process control engineers and developers,
Common Uses of Differential Hall Effect Metrology
- Optimizing dopant activation
- Ultra-shallow junction measurements
- epi-layer optimization
- Studying composition/defectivity/stress/mobility relationships in layers such as n-well, p-well regions
Advantages of Differential Hall Effect Metrology
- The DHEM technique is automated with high depth resolution (≤1nm)
- The technology is affordable for widespread use.
Limitations of Differential Hall Effect Metrology
- Depth resolution of the data obtained from DHEM depends on precision and controllability of the layer removal.
- It is a destructive testing method
- Recipe needs to be developed for etching/oxidation development for each class of material to be characterized.
Industrial Applications of Differential Hall Effect Metrology
- Semiconductor development and manufacture