SSRM：Scanning Spreading Resistance Microscopy
Features
SSRM is a method of visualizing the spatial distribution of electrical resistance spreading directly under the probe by scanning the surface of the sample. The conductive probe is biased with a voltage and the measurement yields the two-dimensional resistance spreading distribution. The minimum carrier density is 1016cm3for silicon but it depends on the desired spatial resolution. Features include:
- Local resistance can be measured at nanometre lateral resolution.
- Semiconductor dopant concentration distribution is measured but type of carrier cannot be determined Absolute resistivity cannot be measured.
Application Examples
- Diffusion layer shape of both silicon and compound semiconductor devices such as LEDs, LASERs, and power MOSFETs, e.g., GaN, SiC.
- Resistance distribution of compound semiconductor solar cells and lithium-ion batteries.
- • Insulation film conductivity leak spots.
Principle of operation
A bias voltage is applied to the sample and carriers located directly under the probe thereby flow into the probe. The resulting current is amplified by a logarithmic amplifier and the resistance is calculated. Due to the current flow, there is a large local voltage drop just below the probe so only carriers that are in the vicinity of the probe contribute to the current, and hence it is the local resistance that is measured. This is called spreading resistance.
The SSRM probe often consists of diamond-coated silicon, the tip of which is sharpened to a radius of 10-20 nm (see Figure 2). Since SSRM only detects carriers directly below the probe, high spatial resolution is possible.
Data examples
SSRM像
The SSRM image visualizes the spatial distribution of spreading resistance calculated from the SSRM raw signal and the bias voltage. The resistance values can be indicated by different colour scales depending on the application.
By mechanically polishing the sample, the desired lateral cross sections of the sample can be exposed. Since the polishing rate depends on the material, polishing will create a topological variation that can be measured by AFM.
Data format of deliverables
Specifications
Items for enquiries
- Purpose and scope of the analysis
- Sample information:
● Number of samples, availability of preliminary samples.
● Measurement location (CAD drawing or optical micrograph) , cross-sectional shape, diffusion layer shape, type of material, doping polarity, estimated carrier concentration, desired field of view for measurement, etc.
● Handling instructions.
- Details on delivery
● Preferred due date for preliminary analysis report.
● Due date for delivery of final report.
- Additional relevant information
Caution
- Samples will not be returned.
- Conversion to absolute value of carrier concentration is not possible.
［SSRM］走査型広がり抵抗顕微鏡法の分析事例はこちらからご覧ください。