Quality control is quintessential in all manufacturing industries as it allows pinpointing problematic areas before entering a production-ready environment.
In industrial environments, such as semiconductor manufacturing, the stakes are even higher as a single wafer plate can contain up to three million components. Not being able to identify even the slightest trap that might restrict the flow and movement of electrons could cause a significant amount of unusable end products. Traps can occur due to residue contamination or imperfections in the crystals’ structure.
The key to sustainable manufacturing is to find imperfections in semiconductors as early as possible. The Deep Level Transient Spectroscopy (DLTS) technique is a highly sensitive, rapid, and easily operated analysis technique for university research labs’ and manufacturers’ daily use. It is a powerful method enabling the detection and identification of electrically active defects (traps) in semiconductors, distinguishing the majority- and minority-carrier traps. It shows you the concentrations, energy, and capture rates in wafers – known as a highly pure, nearly defect-free single crystalline material, with a purity of 99.9999999% (9N) or higher.
DLTS is an extremely versatile method for defining all parameters associated with deep-level traps, including:
How sensitive is DLTS?
It can find one outsider atom among 1 000 000 000 000 atoms. Semilab DLTS solutions allow the identification of impurities below 2×108 atoms/cm3.
How does DLTS work?
DLTS is a capacitance transient thermal scanning technique, operating in the high frequency (Megahertz) range. It is a destructive technique, as it requires forming either a Schottky-diode or a p-n junction with a small sample, usually cut from a complete wafer - two methods to let electrons pass through the sample. The process is destructive because faulty components may not withstand the level of energy and will be rendered completely useless in the process.
*Schottky barrier diode or hot-carrier diode: forms a junction with both a semiconductor and a piece of metal. It has a low forward voltage drop and a very fast switching action. When sufficient forward voltage is applied (approximately: 150–450 mV), a current flows in the forward direction indicating whether the semiconductor is capable of forwarding electrons through itself (in other words: does it work as intended or does it not).
The *p-n junction is a boundary or interface between two types of semiconductor materials, a positive type and a negative type, inside a single crystal of semiconductor. It allows the electrical current to pass through the junction in only one direction. Yet again, the purpose here is to indicate whether the electrons can pass through the semiconductor.
The majority of traps are observed by a reverse bias pulse, while the minority can be monitored by a forward bias pulse. The technique works by following the capacitance transient, also known as current changes, as electrons deplete from one side and accumulate on the other, and the time this process takes.
As the process is very fast, the sample will likely be overheated. In order to have better measurement and quality evaluation, an additional system, cryostat, can be used to prevent overheating by cooling the sample.
Semilab provides DLTS solutions with over 30 years of global experience
The very first Semilab DLTS system was introduced in 1989. Since then, we have helped research labs and semiconductor manufacturers - with our DLS systems and other semiconductor metrology solutions – all around the world.
DLS is available as an out-of-the-box technology in the Semilab solution portfolio called DLS-83D and DLS-1000. The complete range of the functionality includes temperature scanning, frequency scanning, depth profiling, C-V characterization, capture cross-section measurement, optical injection, and conductance transient measurement. All our DLS systems are specifically designed to ensure that wafer trap containment is identified in time and a high level of quality control is maintained across the entire production line.
Cryostats also play an important role in improving measurement results by preventing samples from overheating. Semilab offers several Cryostats for DLS with wide temperature ranges (min. 30K, max. 800K), depending on the application requirements.
Learn more about how DLTS technology works in practice!
Discover Semilab DLTS solutions here.
Have you been using DLTS for a while and are interested in advanced-level literature?
Read our publications here.