Deposition of atomic layers for applications in semiconductor- and nano-technology
The continuous miniaturization of integrated circuits has led in recent years to the displacement of traditional deposition methods in favor of Atomic Layer Deposition (ALD). ALD layers are deposited in cycles by the controlled reaction of gaseous starting molecules (precursors). In this way homogeneous (= hole-free and uniform thickness) layers are created, that are used in microelectronics and nanotechnology. Variables in the development of ALD processes include temperature, pressure, chemistry of the precursor, and cycle times. Due to its extreme surface specificity, Low Energy Ion Scattering (LEIS) is the established technique to determine layer closure and to study the nucleation behavior.
ALD - for thin, yet closed layers
Analytical support in process development
The requirements of ALD layers with respect to layer closure and homogeneity are strict when they are used in the field of microelectronics as diffusion barriers or dielectric layers. Low Energy Ion Scattering (LEIS) has established itself as an analytical tool for controlling the quality of ALD films from established deposition processes as well as in the development of new ALD processes.
Figure 1 (left) shows LEIS spectra of WNxCy layers investigated as part of a project with ASM. The aim of the work at that time was the deposition of very thin, pinhole-free WNxCy diffusion barriers by means of an optimized ALD process. The LEIS investigations served to quantify the elemental composition of the uppermost atomic layer and to determine the mean layer thickness of the ALD films. The evaluation of the data yields the representation shown in Figure 2 (right). It shows that a closed WNxCy layer is reached after 50 ALD cycles. In addition, the data allow conclusions to be drawn about the growth process of the ALD layers.