A blanket layer of silicon can be added to a silicon substrate by a CVD process to achieve changes in the properties, like resistivity, type and defect density. This CVD process is called epi (or epitaxial) deposition. The thickness monitoring of the epi layer is part of the production process of making the epi wafers. This monitoring is executed on a sample basis, or only to confirm that the epi reactor is set up properly.
Semilab can offer non-contact optical solution for Epi thickness monitoring, depending on infrared reflection techniques.
Figure 1. Resistivity measurement flow
Spreading Resistance Profiling (SRP) gives the user the ability to see the entire carrier density, depth and resistivity profile in a silicon device. SRP has no practical limits on carrier density range, conductivity type, orientation or profile depth. With help of SRP Designers can easily check how closely their models represent actual fabricated devices and Yield Enhancement Engineers can “fingerprint” a fabrication process for easy failure analysis. Additionally Process Engineers can troubleshoot all silicon doping operations, including: epi, ion implantation, and diffusion.
1. Probe conditioning and qualification - The contact resistance measuring method requires an ideal contact of the probe and the sample surface. In order to obtain the correct measurement outcome the surface of the probe has to be covered with microcontacts, this is the reason why the probe is conditioned with help of Gorey-Schneider Grinder.
Different probe surfaces
2. Calibration (if needed) - during the measurement is obtained the Resistance value and based on the calibration curve is possible to read the corresponding Resistivity.
3. Sample preparation - because the resistance measurement happens on the cleaved edge of the sample, the sample has to be polished. For polishing is suggested to use a J90 polishing machine. The BSM angle depends on the inspected structure and layer thickness and the desired spatial resolution.
Bevelled and mounted specimens
Sample with cleaved edge
4. Measurement - resistance measurement is realized alongside the bevelled edge. The built-in microscope (various magnifications available depending on tool type and configuration) gives a good opportunity to operator to easily designate the measurement path and the operator can easily avoid scratches, dirt, end of sample.
Mesaurement path(s) in the microscope
5. Analysis - The measured values can be quickly and easily analyzed with the software and is possible to realize the following:
If the item of the interest is the doping level, depth of the layers, this value can be calculated from the Bevel Angle Measurement (BAM). BAM sensor senses the probe displacement on original surface compared to beveled surface. Further calculations are realized by the software.
The SRP product line can be used in the following applications:
Explore the structure determination and profile monitoring of compound semiconductors and measurement of resistivity and carrier density profiles in all silicon semiconductor structures of device processing with this automated system. Measurement range covers state-of-the art application needs.
Explore the entire carrier density and resistivity profile in all silicon semiconductor structures of device processing with this automated system. Measurement range covers state-of-the art application needs.
The SRP-170 system is a cost effective, commercially available spreading resistance profiling metrology system for resistivity and carrier density profiling in all silicon semiconductor structures of device processing.