Spreading resistance analysis is done by stretching the desired depth into a distance across the surface. We take the longest dimension and find the shallowest angle that will reach
the desired depth within that distance. Then, by varying the x-step increment, various depth resolutions can be selected. These calculators provide the highest and lowest resolutions for
- Enter numeric values (in microns) for pattern width, length and desired depth. For non-patterned samples over several mm square, enter "tw" (for test wafer) for width or length.
- The longest dimension will be used for resolution calculation.
- Normal bevel lengths are between 500um - 1000um. Longer bevels are possible but have a much higher level of scratches due to debris getting on the bevel when it hydroplanes. Too
many scratches will ruin the sample.
- On patterned samples, the probes need to start and finish at least 10um (1/2 the probe spacing) away from the beginning or end of the pattern. Getting too close to the end of a pattern
causes current crowding conditions which artificially alter the resistances measured in those locations.
- Patterns need at least 20um width in order to accommodate both probes being placed in the structure without shorting against each other.
- Patterns need at least 100um length in order to provide meaningful data for a simple structure using our smallest x-stepping increment. More length will be required for multiple layers.
- Our smallest x-step increment is 2um. We carefully shape each probe so that the contact area is only a few microns tall by almost 2um wide. Each time we make a measurement a
damaged area (footprint) is created which we have to avoid when our next measurement is taken.
- Depths too great for our steepest angle (5:1) may be done perpendicularly. The highest resolution would then be 1 point every 2 microns.
- Angles shallower than 400:1 require special ultra-shallow techniques which have a surcharge.
- The current limit is 240 points per profile. However, having that many points in a profile may create more noise than meaningful characterization. We will provide profiles with the best
ratio whenever possible. Sometimes this will mean running both fine and course resolutions to detail certain parts of the structures.
- Use the "predetermined angle" rows to find potential resolutions for a second scan on an existing bevel. Example: a 20um depth of interest on a 50x500um pattern would require a 20:1 angle. The initial profile may be run with a 5um step which would provide 0.4um depth resolution. If a second scan were run to look at just 2um, using a 2um step would provide 20 points with a 0.1um resolution - 2.5 times the resolution on that 20:1 bevel. Additional scans can be run from the surface down or start somewhere below the surface and expand the detail of an area the original full scan went through quickly.
- These calculators assume perfect bevel angles. In reality, there is enough uncertainty in the mounting and beveling process that we have to measure the actual bevel angles after they are
created. Therefore we cannot guarantee achieving these precise resolutions. We can say that the angles will be accurate to within +/-3%!
- That last number in the resolution response is the x-step increment. It's a hold-over from alpha which the beta testers said they liked.