Synthesis And Characterization Of HfS₂ And MoS₂ Thin Films By Remote Plasma Atomic Layer Deposition

Two-dimensional transition metal dichalcogenides(2D TMDs),which has excellent electronic,optical and mechanical properties,is considered as the most promising candidate materials for optoelectronic devices.As members of the TMDs family,hafnium disulfide(HfS2)and molybdenum disulfide(MoS2)have shown excellent performance in a wide range of studies.However,there are still many problems in material preparation at present.One of the big challenges in the preparation of two-dimensional material photoelectric devices is how to obtain large-area,high-quality HfS2 and MoS2 films.Atomic layer deposition(ALD)with low growth temperature below 500℃,is compatible well with CMOS process.As a result,ALD is an essential method to combine two-dimensional materials with traditional semiconductors.Targeting this issue,this thesis carried out a study on the synthesis and characterization of HfS2 and MoS2 films by remote plasma-assisted atomic layer deposition(RPALD)technology.The main work contents and innovations are as follows:1.A novel synthetic method of HfS2 nanocrystalline thin films by RPALD at low temperatures was proposed with TEMAH((Hf(C2H5)(CH3)N)4)as the metal source and H2S as the sulfur source.In the temperature range of 150～350 ℃,the growth rate was about 0.11 nm/cycle,and the self-limiting growth behavior was observed.The surface of the deposited HfS2 thin films was smooth and the nanocrystalline grains were uniform.The size of nanocrystalline grains depends on growth temperature,substrate,and HfS2 film thickness.It was found that HfS2 films were mixed with HfO2,and HfS2 was easily oxidized under the atmospheric environment.Pulsed laser annealing and tube furnace annealing experiments were conducted on the deposited HfS2 thin films.The crystallinity of HfS2 will not be changed after annealing,while the surface morphology of HfS2 film may be changed by changing the annealing conditions.In addition,the annealing process will accelerate the oxidation of HfS2.2.A method of synthesizing MoOx films by RPALD at low temperature was proposed with Mo(CO)6 as the metal source and O2 as the oxygen source.It is found that the growth temperature window of MoOx film was 145～175 ℃,and the growth rate was about 0.05 nm/cycle.When the optimized Mo(CO)6 pulse time of 2 s and O2 plasma pulse time of 20 s were applied,uniform and smooth MoOx films with large size were obtained in the temperature window.It was characterized by XPS that the surface component of MoOx film is MoO3,while the internal component is MoO2.3.The postsulfidation was performed with in situ hydrogen sulfide plasma and saturated sulfur vapor in order to convert MoOx to crystalline MoS2 films.After the three-step sulfurization process under saturated sulfur vapor,the crystal MoS2 oriented(002)was obtained from MoOx films with varous thicknesses.Higher crystal intensity of MoS2 crystallization peak was obtained with larger thickness of MoOx.The crystallinity of MoS2 films increases with the annealing temperature rising from 700℃ to 900℃.