THz-SEMICON: Precise Semiconductor Testing With Terahertz Technology

Semiconductors are at the heart of modern technologies – whether in smartphones, electric cars, solar systems or high-performance computers. In the »THz-SEMICON« project (terahertzsemiconductor inspection), we are working with our partners to develop an innovative, non-destructive testing system for the semiconductor industry. Using terahertz time-domain spectroscopy (THz-TDS), we measure thin layers of semiconductor materials such as silicon carbide (SiC) or gallium nitride (GaN) with high precision and as quickly as possible. In the future, this will support companies in quality control and process monitoring in microelectronics, especially for layer systems in the micrometer range.

Increasingly complex layer structures and material systems are being used in the modern semiconductor industry. The resistance, the charge carrier density and the thickness of the layers are decisive parameters for the respective microelectronics. The fast, non-destructive and non-contact measurement of these values is particularly important for material development, quality control, cost management and process monitoring. In addition to classic semiconductors such as silicon, semiconductor materials with a large band cap such as gallium nitride (GaN) and silicon carbide (SiC) are increasingly in demand – particularly in the development of high-performance electronics for mobile telephony and satellite communication. Established methods such as the four-tip measurement or the Mercury probe method must be brought into direct contact with the sample for measurement, which entails considerable disadvantages.

Efficient Test Systems With Terahertz Technology

Non-contact methods based on microwaves or radio waves are established in materials research, but they reach their limits with layer systems in the micrometer range. Our terahertz time-domain spectroscopy offers a promising alternative. Thanks to its high frequency, it enables precise and fast testing of semiconductor materials that are difficult to measure with previous methods or can only be measured on a contact basis. We are using our expertise to bring this technology to market maturity.

In addition to the technical feasibility, the integration of the terahertz system into a complete testing system is particularly interesting for companies. Non-contact measurement not only offers the advantage of avoiding the risk of damaging or contaminating the wafer being inspected. The measurement speed can also be significantly faster than if the sample has to be contacted for each measurement point. 

Our Expertise: Data Analysis and Modeling at the Fraunhofer Itwm

In addition to its expertise in the industrial design of testing devices, our team at the Fraunhofer ITWM also contributes its strengths in modeling and the development of precise and fast evaluation algorithms. With our algorithms, we analyze reflection and transmission data in order to reliably determine important material parameters such as resistance, charge carrier density and layer thickness.

The project focuses on semiconductor epitaxial layers with coating thicknesses of 10 μm and thinner – close to the resolution limit of current terahertz spectrometers – as well as thicker wafers. At the same time, a high measurement speed of over 1,000 terahertz pulses per second is to be achieved. These requirements place high demands on the signal quality and the performance of the analysis algorithms.