Dynamic random access memory (DRAM) is used as the main memory of every modern computer, due to its high density, high speed and efficient memory function. Each DRAM cell consists of one transistor, which functions as a switch for the stored charge, and one capacitor where the positive or negative electric charges corresponding to the digital 1 or 0 data are stored (see Fig. 1a). For successful operation of DRAM, a large cell capacitance ($25 fF) and low leakage current at the operation voltage (10 À7 A cm À2 or 1 fA/ cell) are required because of the following reasons; during the reading operation, stored charge is shared between the cell capacitor and bit line, which is connected to the sense amplifier. In modern DRAMs, hundreds of capacitors are connected to one bit-line so that the bit-line capacitance is usually a few ten times larger than that of the capacitor. Therefore, for a bit-line voltage variation of $100 mV through the charge sharing, which is the sensing margin of the circuit, at least $25 fF of cell capacitance is necessary. [1][2][3] The low leakage current is also essential to ensure a sufficient refresh time.In a traditional Si-based capacitor, the target cell capacitance has been achieved by increasing the surface area of the capacitor (semiconductor-insulator-semiconductor, SIS, in Fig. 1b) while the dielectric thickness is scaled down according to the design rules.[4] More recently, innovations have been made in the component materials. A metal electrode, TiN or Ru, and a dielectric material with a higher-k value (k is the relative dielectric constant) than that of the SiO 2 /Si 3 N 4 layer (k $ 6-7), such as HfO 2 (k $ 25), [5,6] ZrO 2 (k $ 40) [7] and Ta 2 O 5 (k $ 25-60) [8,9] are being explored in giga-bit scale DRAMs (metal-insulator-semiconductor, MIS, and metalinsulator-metal, MIM, in Fig. 1b). The ability of a dielectric film to store charge is conveniently represented by the equivalent oxide thickness (t ox , ¼ t phy  3.9/k, where t phy is the physical thickness of the film). The minimum achievable t ox is $0.7 nm for HfO 2 , ZrO 2 and Ta 2 O 5 which are currently being used in the DRAM industry. However, the technology road map for memory devices states that t ox less than 0.5 nm is necessary for the DRAMs with a design rule of <40 nm.[10] It is also noted that there are no known material solutions to serve this purpose. Reducing the thickness of the dielectric films with k values $20-30 to achieve the required t ox results in unacceptably high leakage currents. Therefore, a dielectric material with a higher k value is in demand. Perovskite-based dielectric films such as SrTiO 3 [11,12] and (Ba,Sr)TiO 3 [13] were reported to exhibit k values of several hundreds and therefore t ox of $0.24 nm is feasible with these materials. [14] However, growth of these films is extremely difficult with the atomiclayer-deposition (ALD) which is a method of choice for the growth of the dielectric films in microelectronic devices. A low thermal budget of 500-600 8C during the deposition and post-de...

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The effect of the O3 feeding time on the physical and electrical properties of TiO2 thin films on Ru electrodes was investigated. The density, composition, chemical state, and crystalline structure of the TiO2 films were almost identical, irrespective of the O3 feeding time, even when the TiO2 films were grown under subsaturated conditions with respect to the O3 feeding. However, increasing the O3 feeding time to more than 3s brought about surface roughening and severe local protrusion of the films, which significantly increased their leakage current density. The conduction band offset of the film surface was generally small and was not increased by increasing the O3 feeding time nor was the leakage current improved. Consequently, a minimum tox of 0.8nm with a leakage current density &lt;∼1×10−7A∕cm2 at an applied voltage of 0.8V was achieved at an O3 feeding time of 2–3s.

This study examined the effect of a Ru buffer layer growth on a TiN electrode on the structural and electrical properties of a TiO 2 dielectric film grown by atomic layer deposition. The growth of a TiO 2 film directly on TiN resulted in the formation of a mixture of anatase and rutile TiO 2 with a dielectric constant of only 42. However, interposing a thin Ru layer altered the crystal structure of TiO 2 from a mixed phase to almost pure rutile, which was accompanied by an abrupt increase in the dielectric constant to ϳ130. This is a much better result compared with the TiO 2 film deposited on a bulk Ru film, which showed a dielectric constant of ϳ80. This improvement was attributed to a change in the preferred growth direction of a TiO 2 film on the Ru/TiN layer compared with that on a thicker Ru film.Among the various simple binary oxides, TiO 2 and Al-doped TiO 2 dielectric films have attracted considerable attention as high dielectric constant ͑k͒ materials for the capacitors in dynamic random access memory ͑DRAM͒ with sub-40 nm design rules because of their high k value. 1,2 TiO 2 exists in three main phases, rutile, anatase, and brookite. The k values of rutile along the a and c axes ͑90 and 170, respectively͒ are much larger than those of anatase ͑30-40͒ 3 and other comparable binary oxides such as ZrO 2 and HfO 2 . Al doping shifts the Fermi level of the metal to the midpoint of the bandgap of TiO 2 , resulting in a significant decrease in leakage current density. 2 It was recently reported that rutile ͑k value of ϳ80͒ and Al-doped TiO 2 thin films could be grown on a Ru electrode by atomic layer deposition ͑ALD͒ at temperatures as low as 250°C using O 3 as the oxidant, 1,2 even though they are the stable polymorphs at temperatures Ͼ ϳ 700°C. 4 This has been attributed to the local epitaxial relationship between the in situ formed RuO 2 on the Ru electrode and rutile TiO 2 . Rutile-structured RuO 2 induces the local epitaxial growth of TiO 2 with a lattice mismatch along the a and c axes of only 2.09 and 4.76%, respectively. 1,2 TiO 2 films showed a conformal growth behavior over the severe threedimensional capacitor hole structure due to the self-regulating nature of ALD. 5 The higher oxidation potential of O 3 than H 2 O is essential for achieving rutile TiO 2 because the in situ formation of RuO 2 on the Ru electrode during the ALD of TiO 2 is the prerequisite. 6,7 Although the growth of rutile and Al-doped TiO 2 films with a high k value and sufficiently low leakage current is quite promising, the use of Ru electrodes imposes a serious impediment to scaling up to a mass-production compatible process for DRAM fabrication due to the extremely high cost of Ru and metallorganic Ru precursors for ALD. 8 TiN is currently the most common electrode used in the fabrication of metal-insulator-metal ͑MIM͒ capacitors in DRAM. TiN electrodes are usually deposited by either chemical vapor deposition ͑CVD͒ or ALD using TiCl 4 and NH 3 as the Ti precursor and reactant, respectively. 9,10 The cost of TiCl 4 is almos...

CVD Co film was investigated as an alternative barrier layer to the conventional PVD TaN\Ta in V1\M2 structure for 32nm node. We improved via filling performance and upstream (V1→M2) electromigration (EM) lifetime by more than three times. Excellent step coverage of CVD barrier makes it possible to reduce the thickness of the barrier metal by 30% and to increase the volume of Cu in metal lines. RC delay also reduced with decrease in resistance. Since adhesion at the interface between the barrier-Co and Cu also is strong, migration of Cu atoms is dramatically slowed down. EM in the via is finally deterred due to absence of pre-existing voids, consequently lifetime increases. This CVD Co process is expected to be beneficial for the next technology generation beyond 20nm node.

Rutile-structured TiO2 and Al-doped TiO2 dielectric thin films were grown on a sputtered Ru electrode by atomic layer deposition (ALD) using normalO2 - or normalN2O -plasma oxidants. The normalO2 -plasma-based ALD process produced films with a similar growth rate and electrical performance to those deposited using the normalO3 -oxidant-based ALD process, which has been reported previously [ S. K. Kim et al. , Appl. Phys. Lett. , 85 , 4112 (2004) ; S. K. Kim et al. , Chem. Mater. , 20 , 3723 (2008) ]. In contrast, the normalN2O -plasma-based ALD process resulted in a 1.8 times higher growth rate than that of the normalO3 -oxidant-based ALD process with identical electrical performance. Denser and uniform oxidation of Ru is essential for achieving pure rutile TiO2 films with a higher dielectric constant (up to 100) on Ru electrodes.

, with errors in the first ͑line 11͒ and second ͑line 7͒ full paragraphs of column 2 on page G13. ECS apologizes for these errors.