Study On ALD Preparation And Accurate Thickness Measurement Methods Of HfO₂ Nanoscale Films

HfO₂ nanoscale film is considered to be one of the most possible high-k materials to replace SiO₂ nanoscale film as the gate dielectrics layer,and it has a wide range of applications.The thickness of HfO₂ nanoscale films significantly affects their performance,so it's necessary to control and measure the thickness accurately.As a preparation method of nanoscale films,atomic layer deposition(ALD)has the unique advantage to control the thickness accurately and simply.In this thesis,the ALD techniques and accurate thickness measurement methods of HfO₂ nanoscale films were studied.(1)The ALD thermal oxidation preparation process of HfO₂ nanoscale films was optimized systematically.Tetrakis[ethylmethylamino]hafnium(TEMAH)and H2O were separately selected as the hafnium source and oxygen source to deposit HfO₂ nanoscale films on the Si(100)substrate.The effects of process parameters such as reaction temperature and typical times on the growth rate(GPC)were investigated.The optimum process parameters were as follows:the reaction temperature of 260?,the hafnium source temperature of 75?,the hafnium source pulse time of 0.2 s,the hafnium source purge time of 6 s,the oxygen source pulse time of 0.3 s,and the oxygen source purge time of 6 s.HfO₂ nanoscale films with nominal thickness of 1-7 nm were prepared on 6-inch Si substrate,the thickness measurement results showed that standard deviation(SD)was between 0.01 nm and 0.04 nm,the relative standard deviation(RSD)was between 0.56%and 1.29%,indicating the thickness uniformity was good.The film thickness had a good linear relationship with the number of ALD cycles,and the GPC is about 0.07 nm/cycle.Through process optimization,the preparation of HfO₂ nanoscale films on 6-inch Si substrate with high-uniformity is successfully achieved,and the uniformity is better than 1.29%in the thickness range of 1-7 nm.(2)Single wavelength ellipsometry(SWE),grazing incidence X-ray reflection(GIXRR),X-ray photoelectron spectroscopy(XPS),and transmission electron microscopy(TEM)were used to measure the thickness of HfO₂ nanoscale film samples with a nominal thickness of 1-7 nm prepared by ALD.The accurate thickness measurement by SWE method was achieved by establishing the SWE optical model as HfO₂/SiO₂/Si;the GIXRR data fitting model was optimized,and the fitted curve coincided well with the measurement points with the thin film structural model as surface contamination layer/HfO₂/SiO₂&Si;based on the XPS method and the basic formula (?),the thickness of HfO₂/SiO₂ was accurately measured;the TEM cross-section samples of HfO₂ nanoscale films were successfully prepared,and the accurate TEM measurement of the HfO₂ nanoscale films thickness was achieved.Compare the thickness measurement values of the four methods,the results show that the SD of thickness measurements of the four methods are between 0.10 nm and 0.23 nm,the thickness measurement values of the four methods have good consistency and a good linear correlation with the average value.