Dynamic SIMS is the high-flux primary ion beam mode of Secondary Ion Mass Spectrometry used for depth profiling, where a continuous, high-current primary ion beam (O2^+ or Cs^+) aggressively erodes the sample surface at rates of 0.5-10 nm/s while continuously monitoring secondary ion signals as a function of depth — enabling measurement of dopant profiles from the near-surface region to depths of several micrometers with high sensitivity (10^14 to 10^17 cm^-3) and depth resolution of 1-10 nm depending on beam energy.
What Is Dynamic SIMS?
- Continuous Erosion: Unlike Static SIMS (which uses extremely low primary ion doses to avoid surface damage), Dynamic SIMS continuously bombards the surface with a high-flux primary beam (current density 1-100 µA/cm^2), eroding through the sample at a controlled, steady rate. The term "dynamic" refers to this ongoing surface destruction that is fundamental to the depth profiling process.
- Depth Calibration: The erosion rate (nm/s) is determined by measuring crater depth with a profilometer (stylus or optical) after the analysis and dividing by total sputtering time. This post-measurement depth calibration converts the time axis of the SIMS signal to a depth axis. Crater depth measurement accuracy limits depth calibration uncertainty to approximately 1-3%.
- Primary Beam Options:
- O2^+ (Oxygen): Oxidizes the crater floor, dramatically enhancing positive secondary ion yields. Used for profiling electropositive elements: boron (B), aluminum (Al), indium (In), sodium (Na). O2^+ is the standard beam for boron profiling in silicon — the single most common SIMS analysis in semiconductor manufacturing.
- Cs^+ (Cesium): Cesates the crater floor, dramatically enhancing negative secondary ion yields. Used for electronegative elements: phosphorus (P), arsenic (As), antimony (Sb), oxygen (O), carbon (C), fluorine (F), chlorine (Cl). Cs^+ is essential for phosphorus and arsenic profiling in CMOS source/drain engineering.
- Raster Pattern: The primary beam is rastered over a square or circular area (100-500 µm per side) to produce a flat-bottomed crater. Only secondary ions from the central flat region are detected (gated electronics exclude the crater walls) to avoid crater-edge artifacts that contaminate the signal.
Why Dynamic SIMS Matters
- Deep Profile Capability: Dynamic SIMS profiles dopants to depths of 1-10 µm, covering the full range from ultra-shallow source/drain extensions (5-20 nm) through deep well implants (0.5-2 µm) and retrograde well profiles (1-3 µm). A single analysis can span the entire device vertical architecture from gate to substrate.
- High Sensitivity for Trace Impurities: With O2^+ primary beam and detection of positive secondary ions, boron sensitivity reaches 10^14 atoms/cm^3 (detection limit ~10^15 cm^-3 in practice), sufficient to quantify boron channel profiles at threshold concentrations and detect boron background in n-type regions.
- Carbon and Oxygen Profiling: Cs^+ + negative ion detection profiles carbon and oxygen — critical for characterizing epitaxial layer purity, carbon-doped SiGe layers (for HBT base regions), oxygen concentration in CZ silicon, and oxynitride gate dielectric composition.
- SiGe Composition Profiling: SIMS simultaneously profiles silicon and germanium in strained SiGe layers (using Si^- and Ge^- or SiGe^+ signals), providing layer-by-layer composition with 1 nm depth resolution — essential for HBT and FinFET strained-channel process development.
- CMOS Process Control: Dynamic SIMS is the primary analysis tool for qualifying new implant/anneal processes, investigating yield failures with unusual junction behavior, and measuring diffusion coefficients for new dopant/material combinations. It is considered the definitive result when electrical measurements (SRP, ECV) and TCAD disagree about a junction profile.
Dynamic SIMS Operating Modes
Depth Profile Mode (Standard):
- Continuous raster erosion with real-time signal monitoring.
- Typical analysis: 30 minutes - 2 hours for 1 µm depth at standard sensitivity.
- Produces concentration vs. depth profile for 1-5 elements simultaneously.
High-Depth-Resolution Mode (Low Energy):
- Primary beam energy reduced to 0.5-1 keV (versus standard 3-10 keV) to minimize ion mixing depth.
- Erosion rate decreases to 0.05-0.2 nm/s, increasing measurement time to 4-8 hours for 30 nm depth.
- Required for ultra-shallow junction profiles (5-15 nm) at advanced nodes.
Magnetic Sector vs. Quadrupole:
- Magnetic Sector SIMS (CAMECA IMS series): High mass resolution (separates ^31P from ^30SiH), high sensitivity, high mass range. Gold standard for dopant profiling. Cost: $2-5M.
- Quadrupole SIMS (ATOMIKA, HIDEN): Lower mass resolution, faster mass switching, lower cost. Suitable for routine profiling without isobaric interferences.
Dynamic SIMS is layer-by-layer atomic excavation — aggressively removing silicon atom by atom while simultaneously mass-analyzing the debris to reconstruct the vertical distribution of every dopant and impurity, providing the definitive depth profile that calibrates all other characterization methods and guides every advanced node process development decision.