e-CVD of Ge using Ge(II)-triazenide

Sammanfattning

To sustain Moore’s Law and enable continued transistor scaling, new area-selective bottom-up methods need to be developed to replace the photolithography steps in microchip fabrication, which today have reached their resolution limits. By selectively depositing germanium (Ge), a semiconductor with significantly higher electron and hole mobilities than silicon (Si), on electrically conductive features, transistors can be further miniaturized without compromising their quality. The aim of this thesis is to investigate the deposition of Ge thin films on conductive substrates using electron-chemical vapor deposition (e-CVD) with the novel precursor bis(1,3-di-tert-butyltriazenide)germanium(II) (Ge-triazenide). This method attracts electrons from a plasma to electrically conductive materials by applying a positive substrate bias, enabling area-selective deposition (ASD). The goal is to understand the e-CVD process when using the Ge-triazenide and evaluate how parameters such as plasma power, plasma exposure time, substrate temperature, and deposition mode affect film growth and composition. QCM was used to analyze film growth in situ, revealing that lower substrate temperatures caused precursor condensation and multilayer formation, while higher temperatures promoted more controlled adsorption. Additionally, higher plasma power and longer exposure times increased mass loss during the electron-atomic layer deposition (e-ALD) mode. XPS analysis showed that pulsed e-CVD films contained approximately 45 at.% Ge with less than 5 at.% carbon (C) and no detectable nitrogen (N), whereas continuous mode films had around 25 at.% Ge with over 25 at.% C. XPS analysis also revealed that the film is oxidized, possibly due to air exposure after deposition or from the oxygen (O) content present in the chamber during deposition. Optical emission spectroscopy (OES) detected Ar, Ar+, N2, O, H, and Ge+ in the plasma, indicating precursor fragmentation and partial reduction of Ge2+. Changes in plasma power, substrate bias, and argon flow affect the ratio of detected emissions lines, meaning that that plasma parameters influence the dynamics of the plasma. Quadrupole mass spectrometry (QMS) was used to study plasma species and gas-phase precursor decomposition, supporting the understanding of the e-CVD process. This study provides a valuable grounding for understanding the e-CVD method using the Ge-triazenide precursor, marking an important step toward optimizing ASD of Ge film. By clarifying the effects of plasma dynamics and process parameters, these findings open new pathways for developing the e-CVD process, with the potential to overcome current lithography limits and support continued transistor scaling in future microchips.