scanning spreading resistance microscopy
**SSRM** (Scanning Spreading Resistance Microscopy) is a **contact-mode AFM technique that measures local spreading resistance by pressing a hard conductive diamond tip into the sample** — providing two-dimensional dopant profiles with sub-nanometer spatial resolution and six decades of dynamic range.
**How Does SSRM Work?**
- **Tip**: Hard, conductive doped diamond tip pressed into the sample with ~μN force.
- **Measurement**: Apply DC bias and measure the current -> spreading resistance $R =
ho / (4a)$ where $a$ is the contact radius.
- **Cross-Section**: Map 2D cross-sections of devices by scanning across polished/cleaved surfaces.
- **Calibration**: Convert resistance to carrier concentration using staircase calibration samples.
**Why It Matters**
- **Best Resolution**: Sub-nanometer resolution for 2D dopant profiling — the highest-resolution electrical technique.
- **Dynamic Range**: 6+ decades (from $10^{14}$ to $10^{20}$ cm$^{-3}$) in a single measurement.
- **FinFET Characterization**: Essential for 3D dopant profiling of FinFETs, GAA-FETs, and nanoscale devices.
**SSRM** is **the sharpest electrical probe** — pushing a diamond nanotip into the sample to map dopant concentrations with unmatched resolution.