Hf-silicate gate dielectrics were formed by atomic layer deposition ͑ALD͒ technology using the liquid Hf͓N͑CH 3 ͒͑C 2 H 5 ͔͒ 4 and SiH͓N͑CH 3 ͒ 2 ͔ 3 precursors. The advantages of these precursors as good materials is because their melting points and vapor pressures are in a comfortable working range. In SiO 2 ALD film formation, the growth rate per cycle was dependent on reactor pressures between 0.5 and 5.0 Torr chamber pressure. In order to obtain a good uniformity of less than 5%, the pressures of the reactor chamber were kept at 0.5 and 5.0 Torr for ALD of HfO 2 and ALD of SiO 2 films, respectively. The SiH͓N͑CH 3 ͒ 2 ͔ 3 precursor made it possible to deposit the SiO 2 layers not only on SiO 2 films but also on HfO 2 films. Hf-silicate films were deposited at 275°C using alternating HfO 2 and SiO 2 ALD cycles. The thickness and the Hf/͑Hf + Si͒ compositions of Hf-silicate films could be easily controlled by the number of the deposition cycles.Conventional thermal silicon dioxide ͑SiO 2 ͒ films have been used as a gate dielectric for standard complementary metal oxide semiconductor ͑CMOS͒ devices because of their superior properties such as large energy bandgap ͑8.9 eV͒, low leakage current, low interface state density, and low impurities in the SiO 2 films. For the gate oxide thickness of less than 3.5 nm, direct tunneling current increases 100 times for every 0.4-0.5 nm decrease of thickness. 1,2 This high gate leakage current would increase standby power consumption. In order to reduce the leakage current by direct tunneling, the high dielectric constant ͑high-k͒ materials allow for an increase in the physical thickness to maintain a low equivalent oxide thickness. Among many high-k materials, Hf-based and its nitride films are good for low leakage current and high carrier mobility. Therefore, sputter and or metal organic chemical vapor deposition ͑MOCVD͒ methods are currently used for the high-k film formation. [3][4][5][6][7][8][9][10][11] Atomic layer deposition ͑ALD͒ technology is desirable for precise control of composition, film thickness, conformality, and uniformity among many high-k film deposition techniques. [12][13][14][15][16][17][18][19] Hafnium-tetrachloride ͑HfCl 4 ͒ and water ͑H 2 O͒ were widely used for ALD HfO 2 film formations. [12][13][14][15] Recently, there were reports using Hf amide-type precursors such as Hf͓N͑CH 3 ͒͑C 2 H 5 ͔͒ 4 for ALD of HfO 2 or Hf-aluminate films to solve the problem of particle formation or residual chlorine with HfCl 4 precursors. 15,16,19 Furthermore, ALD HfO 2 films were deposited at low temperature ͑around 300°C͒ using Hf͓N͑CH 3 ͒͑C 2 H 5 ͔͒ 4 precursor and O 3 as the oxidant during ALD instead of H 2 O, those films contained a much smaller amount of residual impurities such as carbon or nitrogen from previous precursors. 16 However, there are few papers about Hf-silicate gate dielectric fabrication by the ALD method because of the lack of the applicable Si precursor. 19 We described a newly developed ALD Hf-silicate film formation that could fabricate t...
Ultrathin HfO2 gate dielectric was fabricated by atomic layer deposition (ALD) technology using tetrakis(ethylmethylamino)hafnium {Hf[N(CH3)(C2H5)]4}, with O3 as an oxidant for use in replacement metal gate transistors. From secondary ion mass spectrometry analyses, the ALD process temperature was very important for the fabrication of high-quality HfO2 films. The dielectric constant with 275 °C deposition was higher than that at 200–250 °C. Furthermore, the VFB with 200 °C deposition was about 0.1–0.15 V lower than that at 275 °C, due to formation of high residual impurity concentrations, such as carbon, in the HfO2 films. The leakage current densities in the 275 °C case were reduced by about five orders with respect to reference SiO2 films. From these results, it was judged that the ALD process temperature of 275 °C was suitable for the fabrication of ultrathin HfO2 gate dielectrics necessary to improve the leakage current characteristics.
The electrical properties have been studied for hafnium (Hf)-based gate stack structures, fabricated using atomic layer deposition (ALD) technology. The very thin ALD Hf-silicate layers on the top of HfO2 gate structures were very important in obtaining good electrical properties, because these surface films prevented a reaction between the polysilicon electrodes and HfO2 films during high temperature activation annealing. From subthreshold characteristic measurements, Ioff values were less than about 10pA∕μm and Ion values at ∣Vg∣=1.1V were greater than 350 and 120μA∕μm for n- and p- metal oxide semiconductor field effect transistors, respectively. The effective mobility curves for the Hf-based gate stack structures were at the same level as those of 1.6 nm SiON reference films at 0.8MV∕cm. Furthermore, the interfacial trap densities were less than 5*1010cm−2 for the Hf-based gate stack structures, achieving the same level as in the 1.6 nm SiON reference films.
Thin hafnium ͑Hf͒ silicate films were deposited by alternating HfO 2 and SiO 2 layers with atomic layer deposition ͑ALD͒ technique. Hf͑N͑CH 3 ͒͑C 2 H 5 ͒͒ 4 was used for HfO 2 layer, and bis͑dimethylamino͒silane ͓BDMAS: SiH 2 ͑N͑CH 3 ͒ 2 ͒ 2 ͔ or tris͑dim-ethylamino͒silane ͓TDMAS: SiH͑N͑CH 3 ͒ 2 ͒ 3 ͔ precursors were used for SiO 2 layers, respectively. O 3 was used as an oxidant. The thickness of SiO 2 deposited using ALD process is controlled by the number of growth cycles and the growth rate per cycle was different for each precursor, that for BDMAS being 1.5 times that for TDMAS at the same reactor pressure. Furthermore, the thickness and the Hf/͑Hf + Si͒ compositions of ALD Hf-silicate films deposited using BDMAS and TDMAS precursors can be easily controlled by the number of growth cycles. The carbon impurity in the Hf-silicate film deposited using BDMAS was about an order of magnitude less than that using for TDMAS.Conventional thermal silicon dioxide ͑SiO 2 ͒ films has been used as the gate dielectric in standard complementary metal oxide semiconductor ͑CMOS͒ devices because of its excellent properties, such as the large energy bandgap ͑8.9 eV͒, low leakage current, low interface state density, and low impurity levels in the film. For gate oxide thicknesses of less than 3.5 nm, the direct tunneling current increases by a factor of 100 times for each 0.4-0.5 nm decrease in thickness. 1,2 This high gate leakage current increases the standby power consumption. 2 To reduce the leakage current due to direct tunneling, high dielectric constant ͑high-k͒ materials allow for an increase in the physical thickness while maintaining a low equivalent oxide thickness. 3-10 Among the many high-k materials available, those based on Hf and its nitride exhibit low leakage currents and high carrier mobility. [7][8][9] Sputtering or metallorganic chemical vapor deposition ͑MOCVD͒ are two methods for the high-k film formation. 3-11 Of other deposition techniques, atomic layer deposition ͑ALD͒ technology is desirable for precise control of the composition, film thickness, conformality, and uniformity. 12-20 Hafnium tetrachloride ͑HfCl 4 ͒ and water ͑H 2 O͒ have been widely used for depositing HfO 2 using ALD. [12][13][14][15] Recently, there have been reports of using Hf amide type precursors such as Hf͑N͑CH 3 ͒͑C 2 H 5 ͒͒ 4 for HfO 2 or Hf-aluminate to overcome problems such as the excessive particles or residual chlorine obtained when using HfCl 4 precursors. 15,16,19 ALD HfO 2 films have been deposited using a Hf͑N͑CH 3 ͒ 2 ͒ 4 precursor and O 3 instead of H 2 O as the oxidant, that these films using O 3 have contained much lower amounts of residual impurities such as carbon and nitrogen compared to those films using H 2 O. 16 However, there have been few papers on the deposition of Hf-silicate gate dielectrics using the ALD method because of the lack of a suitable Si precursor. 19,20 We investigated Hf-silicate films using bis͑dimethylamino͒silane ͓BDMAS: SiH 2 ͑N͑CH 3 ͒ 2 ͒ 2 ͔ and tris͑dimethylamino͒silane ͓TD-MAS: SiH͑N͑...
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