Browsing by Author "Tuoriniemi, Iiris"

Atomic layer deposition (ALD) is a promising processing method for the next generation semiconductor devices. Major advantages of ALD include conformality, uniformity over large areas, precise thickness control, repeatability and high quality of films produced. ALD thin film deposition is done inside an ALD reactor. Typical construction materials of ALD reactors include metal alloys such as stainless steel, aluminum and titanium. These materials contain multiple metallic elements that can be detrimental to the performance, reliability and yield of semiconductor devices. In order to process semiconductor devices with ALD, metal impurity levels originating from the ALD reactor must be controlled. Allowed levels of metal impurities in semiconductor processing are stringent and showing a tightening trend. This has led into the development of new methods for contamination control together with the adoption of more sensitive and robust detection methods for metallic impurities, such as inductively coupled plasma mass spectrometry (ICP-MS). This master thesis focuses on the metallic impurities originating from an ALD reactor and their prevention with ALD coatings. Three typical construction materials, aluminum, titanium and stainless steel were examined. The studied coatings were ALD deposited aluminum oxide (Al2O3), hafnium oxide (HfO2) and their nanolaminate (Al2O3/HfO2). The ability of the coatings to prevent metal impurity transfer from the metals to silicon substrates through the gas phase was studied by exposing the coated metals to two ALD precursors, trimethyl aluminum (TMA) and tris(dimethylamino) cyclopentadienyl hafnium (CpHf(NMe2)3). Metal impurity concentrations on silicon were measured with ICP-MS. Since academic literature concerning control of metal contamination from ALD reactors does not directly exist, the literature part of this thesis was based on relevant related topics. The selected topics included the development of semiconductor industry, role of ALD in this development and new ALD materials and chemistries required. Additionally, protective ALD films and the effects of metal impurities in semiconductor products were reviewed. The overall conclusion of this study was that the ALD coatings provide a worthy solution for metal contamination control. Some differences between the passivation efficiencies of different metal – coating systems were found.