Identification and localisation of contamination in a microelectronic component

Semiconductors are at the heart of the electronics industry. They are used in all electrical and electronic devices. These crystalline materials have electrical properties intermediate between those of conductors and insulators. Under certain conditions, they let current through, while under others they block it, making them a good way of controlling the direction and intensity of electric current in electronic components. This hybrid property is the foundation of all modern computing and enables connected objects to function.

Semiconductors are the basis of modern computing and the foundation of Industry 4.0. They are used in the vast majority of electronic devices, from computers and medical equipment to cell phones and car dashboards. Semiconductors are everywhere in our daily lives.

These components, whose dimensions today are less than 5 namometers for the most advanced, are the fruit of a complex manufacturing process involving numerous complex processes (photolithography, etching, ion implantation, epitaxy, passivation, thermal oxidation). and chemical processes. The production stages require "clean rooms" where temperature, humidity and relative pressure are maintained at precise levels to eliminate any risk of contamination. Despite these precautions, contamination of various origins can occur during the process. In such cases, ToF-SIMS is an invaluable tool for chemical characterization and localization.

Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is a highly sensitive method for elemental and molecular analysis at the extreme surface (< 1 nm). It is also possible to obtain depth distribution profiles down to 20 µm by alternating analysis and abrasion cycles with an Argon cluster (GCIB) for organic materials, or a Cesium (Cs⁺) or Oxygen (O₂⁺) gun for inorganic materials.

ToF-SIMS can detect trace elements down to ppb at the extreme surface (< 1 nm) and up to 20 µm in profile mode on vacuum-compatible samples of all types.

By alternating acquisition and abrasion sequences, a composition profile can be traced with nanometric depth resolution. The primary ion beam, reduced to a small diameter spot, scans the surface to be imaged. The secondary optics for extraction and mass analysis are fixed. The image is reconstructed by synchronizing the secondary signal with the primary beam scan. Lateral image resolution depends on the size of the micro-beam (from 100 nm to 3 µm in diameter, depending on analysis conditions).

TESCAN ANALYTICS has over 20 years' expertise in the use of ToF-SIMS on all types of materials, whether insulating or conducting... With state-of-the-art instruments, our team of experts works with all industrial sectors.

 

Figure 1: 3D ToF-SIMS reconstruction for the ions: Si⁺, Ga⁺, Al⁺, In⁺.


Figure 2: 3D ToF-SIMS reconstruction for ions: K⁺, Na⁺.

ToF-SIMS analysis in high-resolution imaging mode is carried out in 300 x 300 µm² in the defect zone. Analysis/abrasion cycles with O₂⁺ ions are performed over a 500 x 500 µm² area, to avoid edge effects. The profile is acquired to a depth of 300 nm, with one image every 10 abrasion scans. A 3-D reconstruction is then obtained from the 2D images recorded along the profile.

Figure 1 shows reconstructions of the different parts of the component for the Silicon, Gallium, Aluminium and Indium ions. Its basic structure consists mainly of Silicon in the upper part and Gallium in the lower part. Internal structures are observed with different compositions, such as Aluminum or Indium. With this reconstruction, the various elements of the component can be isolated according to their chemical composition.

In Figure 2, Na⁺ and K⁺ contamination is visible on the upper outer part of the component. This contamination is not only localized on the surface, but also appears to have diffused into the volume of the semiconductor. This type of reconstruction makes it possible to identify and locate contamination in the various layers of the component.
 

With element detection down to ppb and abrasion depths down to 20 µm, ToF-SIMS gives access to depth distribution profiles enabling highly informative 3D reconstructions for process control and failure analysis in the semiconductor industry. In this example, the nature of the contamination has been identified and localized.

ToF-SIMS is a valuable tool for the chemical characterization and localization of submicron contamination.

In other work, ToF-SIMS has been used to map 2D contaminants on the surface of technical parts or biological materials.

For more semiconductor analysis applications with ToF-SIMS or our other techniques, visit our topics page.

Other complementary techniques can be used to characterize semiconductors, such as TEM or SEM.