Effectiveness of self-carbon and titanium capping layers in NiSi formation with Ni film deposited by atomic layer deposition

We firstly deposit a Ni film, directly after removing the native oxide, by atomic layer deposition (ALD) using a N²hydroxyhexafluoroisopropyl- N¹ (Bis-Ni) precursor, H₂ as the reactant gas and Ar purging gas at 220 °C at a deposition rate of 1.25 Å/cycle. The as-deposited Ni and Ni₃C films exhibited sheet resistances of 5 Ω/□ (sample B) and 18 Ω/□ (sample A), respectively. The formation of a Ni₃C phase was easily controlled by varying the flow rate of the H₂ reactant as above gas. A rapid thermal process (RTP) was then performed in a nitrogen ambient to form NiSi at different temperatures from 400 to 900 °C. We estimated the process window temperature for the formation of low-resistance NiSi to be between 600 and 800 °C for self-carbon and Ti capping layers, as below while in the case of only Ni deposition the process window temperature changes to 700 to 800 °C. The respective sheet resistances of the films were changed to 3Ω/□ (sample B) and 4Ω/□ (sample A) after silicidation. The reaction between Ni and Si could be increased by the self-carbon and Ti capping layers due to a decrease in the oxidation contamination and impurity incorporation in the Ni film during the silicidation process. This self-carbon capping layer is formed by the carbon-containing Ni₃C phase, which segregates to the surface during the annealing process and forms a relatively thick surface layer. Additionally, this layer also protects the surface from oxygen contamination. The deposition of Ni by ALD and the improved formation of the low-resistance NiSi with increased temperature stability will be useful in the fabrication of advanced devices, such as nano meter-scale complementary metaloxide semiconductor (CMOS) or three-dimensional (3-D) devices.