Meaning
Analytical mass spectrometry techniques used to measure the concentration and depth distribution of chemical elements in solid materials provide critical data for semiconductor manufacturing and material science. In the analysis of thin films and doped semiconductor layers, dynamic sims profiling uses a continuous ion beam to sputter the sample surface while measuring the emitted secondary ions. The term refers to the dynamic mode of secondary ion mass spectrometry where the high sputtering rate allows the system to drill through the material and create a continuous depth profile.
This method is highly sensitive, with the ability to detect trace elements at concentrations as low as parts per billion. The application of this profiling is limited by the destructive nature of the sputtering process and the need for a high vacuum environment to prevent contamination and scattering of the ions.
Sputtering Dynamics
High energy primary ion beams directed at the sample surface drive the continuous removal of material and the generation of secondary ions for analysis. During the execution of dynamic sims profiling, primary ions such as oxygen or cesium are accelerated and focused onto a small spot on the specimen. This bombardment creates a crater on the surface, with the sputter rate determined by the primary beam energy, the ion species and the sample material.
As the beam drills into the sample, the sputtered secondary ions are collected by an electrostatic lens and directed into a mass spectrometer. The mass spectrometer separates the ions based on their mass-to-charge ratio, allowing the system to monitor the changes in chemical composition as a function of depth.
Depth Resolution
Parameter optimization of the primary ion beam and the analysis crater is necessary to achieve high depth resolution and avoid distortion of the concentration profiles. To maintain a flat crater bottom during dynamic sims profiling, the primary ion beam is rastered over a square area, and only the secondary ions from the center of the crater are collected. This gating technique prevents ions from the crater walls, which represent shallower depths, from interfering with the measurements from the bottom of the crater.
The choice of primary ion energy is also critical, as lower energy beams reduce the mixing of atoms across different layers, which improves the sharpness of the measured interfaces. These adjustments allow the system to resolve thin layers and sharp doping profiles with nanometer-scale precision.
Quantification Standards
Calibration procedures using reference samples with known implant doses are required to convert the measured ion intensities and sputtering times into concentration and depth profiles. To calculate the absolute concentration of an element from dynamic sims profiling data, the relative sensitivity factors for the specific material matrix must be determined. These factors are obtained by measuring calibration standards that have been prepared under identical conditions and have a known concentration of the target element.
The conversion of sputtering time to depth is achieved by measuring the final depth of the sputtered crater using a stylus profilometer or an optical interferometer. These calibration steps ensure that the analytical results are highly accurate and can be used to optimize the semiconductor manufacturing processes.
