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Electrical properties of (Ba, Sr)TiO3[BST] films have been investigated on RuO2/Ru and Ru electrodes instead of Pt, because they are easy to be etched. BST films were deposited at a substrate temperature of Ts=420° C and a reactor pressure of P=1.5 Torr by employing a two-step liquid source chemical vapor deposition (CVD) process. BST films on RuO2/Ru were electrically shorted, which was considered to be caused by surface roughening during BST film deposition and/or post-annealing. In the case of Ru electrodes, an equivalent SiO2thickness of teq=0.50 nm (a dielectric constant of ?r=190), a leakage current of JL=4.6×10-8A/cm2at +1.1 V, and a dielectric loss of tan ?=0.018 were achieved at a total film thickness of 250 Å, by restricting Ru surface oxidation and its surface roughening. Moreover, BST film deposition on Ru storage nodes, 0.24 µ m wide, 0.6 µ m deep, 0.15 µ m high, and each spaced by 0.3-0.14 µ m, verified that the storage capacitance can be successfully increased by using sidewalls of the storage node, without a significant increase in the leakage current.

Thin films of (Ba, Sr)TiO3with high dielectric constant were prepared on Pt/SiO2/Si substrates of 6-inch-diameter by chemical vapor deposition using liquid sources. Ba(DPM)2and Sr(DPM)2dissolved into tetrahydrofuran were vaporized in a vaporizer at 523 K, and Ti(O-i-C3H7)4was bubbled at 313 K. The mixture of the source vapors with O2and N2O was supplied to the reactor (10 Torr) at uniform velocities through a shower-type nozzle, which realized uniform profiles in the deposited film thickness and composition. The electrical properties are significantly influenced by the film composition, and the typical properties obtained for a 800-Å-thick film prepared at the substrate temperature of 823 K are an equivalent SiO2thickness teqof 5.2 Å, a leakage current JLof 2.4× 10-6A/cm2(at 1.65 V), and a dielectric loss tan ? of 0.07.

Thin films of (Ba, Sr)TiO3(BST) with high dielectric constant were prepared on Pt/ SiO2/Si substrates of 6-inch-diameter by liquid source chemical vapor deposition using Ba(DPM)2, Sr(DPM)2and TiO(DPM)2(DPM=dipivaloylmethanato; C11H19O2) dissolved in tetrahydrofuran (THF). The reproducibility of ±3 % for the film composition was achieved by optimizing the deposition procedures. It was found that the coverage of 72%, obtained at the substrate temperature Ts=753 K, was better than those obtained using other Ti sources such as Ti(O-i-Pr)4(TTIP) and Ti(O-i-Pr)2(DPM)2. The electrical properties of the 480-Å-thick BST film, deposited at Ts=753 K using TiO(DPM)2, were as follows: dielectric constant ?=230, equivalent SiO2thickness teq=7.8 Å, leakage current density JL=6.7×10-6A/cm2at 1.65 V and dielectric loss tan ?=0.013.

The reaction mechanism in liquid source chemical vapor deposition (CVD) of (Ba,Sr)TiO3[BST] films has been studied using dipivaloylmethanato (DPM) source materials. Effects of substrate temperature and deposition atmosphere on film characteristics were investigated, such as deposition rate of each source material, step coverage, and electrical properties of the film deposited. The decomposition of DPM source materials for BST film deposition was found to be enhanced in O2atmosphere, as compared with that in N2atmosphere. Furthermore, the source materials were easier to decompose at higher substrate temperatures. The BST film step coverage became less conformal at higher temperatures and in O2atmosphere, implying that more precursors with large sticking probabilities were produced therein. Although O2gas was not necessary to form the BST crystalline structure and to improve the step coverage, the addition of O2during deposition was found to be necessary to improve the crystallinity and electrical properties of CVD-BST films.

Protrusions of (Ba, Sr)TiO3(BST) crystallites were found to appear on BST film surfaces prepared by liquid source chemical vapor deposition (CVD) at a substrate temperature Ts=420° C and a reactor pressure P=1.5 Torr. Such protrusions were successfully suppressed by two-step deposition, where BST films consisted of a buffer layer and a main layer; the buffer layer was a CVD-BST film about 60 Å thick annealed in N2ambient. By this two-step deposition on Pt electrodes, the BST film properties of equivalent SiO2thickness teq=0.56 nm, leakage current JL=1.2×10-8A/cm2at +1.1 V and dielectric loss tan ?=0.011 were achieved at a total film thickness of 230 Å, along with a coverage of 80% at a trench of aspect ratio 0.65 and sufficiently low absorption current.

The surface reaction probabilities of CFxradicals are determined with a trench deposition method for C:H:F films deposited by the discharge in a CF4/H2mixture. It is found that the overall sticking probability of CFxis ?=0.1-0.2 and 0.2 for substrates placed on the reactor wall and on the earth electrode, respectively. The respective roles of the sticky and less-sticky radicals (probably CF and CF2, respectively) are derived by making use of the film profiles, and their sticking probabilities are found to be about 1.0 and 0.05, respectively. Moreover, it is shown that the method is applicable to estimate the contribution of the ion-enhanced deposition, e.g., 50-60% of the film thickness for the present condition of the gas flow ratio of CF4/H2=19/16 at the rf discharge pressure of 0.4 Torr.

Thermal desorption characteristics of (Ba, Sr)TiO3[BST] thin films prepared by metalorganic chemical vapor deposition (CVD) using liguid sources have been studied, together with their crystallinity and electrical properties. Thermal desorption was observed for CO2at 400° C and 900° C, and CO at 600° C. The intensities of the CO2peaks at 400° C and 900° C increased with the increasing atomic composition ratio of (Ba+Sr)/Ti, in relation to the excess Ba and Sr in the BST films; in particular, the CO2peak at 900° C may originate from BaCO3and/or SrCO3lumps formed in the films, and the CO2peak at 400° C may be attributed to gases adsorbed on the sites of contaminants such as BaOxand/or SrOxin films, due to excess Ba and Sr coming from the atmosphere after deposition. On the other hand, the CO peak at 600° C occurred most strongly from BST films with high dielectric constants at (Ba+Sr)/Ti?1, or perovskite crystalline structures having large grains. Moreover, the desorption of CO at 600° C was also observed from films kept in the atmosphere after annealed above 600° C in vacuum. These results imply that the BST crystalline perovskite grains may have adsorption sites for CO from the atmosphere.

Silicon dioxide thin films have been deposited from silane and oxygen at 540 K and 3.5 Torr in a cold-wall reactor. The trench deposition method is applied to clarify the behavior of film precursors for the SiO2deposition. It has been found that surface reactions scarcely contribute to the deposition in the present conditions, and that the overall sticking probability of the film precursor changes significantly with the substrate temperature. This phenomenon is shown to be satisfactorily explained by the model that the precursors formed by gaseous reactions consist of several kind of radicals with different sticking probabilities. It is also shown that the decrease in the deposition rate for O2-excess region corresponds to the radical concentration in the gasphase.