Noh-Jung Kwak

Highly Scalable Saddle-Fin (S-Fin) Transistor for Sub-50nm DRAM Technology

Highly scalable saddle-fin cell transistor(S-Fin) has been successfully developed by combining FinFET with recess channel array transistor(RCAT). The S-Fin is simply integrated by dry-etching techniques and the desirable threshold voltage is easily obtained. The S-Fin exhibits feasible transistor characteristics such as excellent short channel effect, driving current, and refresh characteristics as compared with both RCAT and damascene-FinFET. We suggest the S-Fin is a very promising transistor structure for the sub-50nm DRAM technology

Modified atomic layer deposition of RuO2 thin films for capacitor electrodes

The authors investigated the modified atomic layer deposition (ALD) of RuO2 films using bis(ethylcyclopentadienyl)ruthenium [Ru(EtCp)2] at a deposition temperature of 265°C. Oxygen gas diluted with argon was supplied throughout all of the ALD steps. The growth rate of the modified ALD RuO2 was about 1.4A∕cycle, which is higher than that of conventional Ru ALD due to the increase in the amount of Ru(EtCp)2 adsorption per cycle, as well as the difference in the unit cell volumes of Ru and RuO2. The film thickness increased linearly with the number of cycles, and the incubation cycle in the initial stage was negligible.

A Comparative Study of the Atomic-Layer-Deposited Tungsten Thin Films as Nucleation Layers for W-Plug Deposition

The properties of three different kinds of atomic-layer-deposited (ALD) W thin films were comparatively characterized and investigated as nucleation layers for the W-plug process of 70 nm design-rule dynamic random access memory. ALD-W (A) film was deposited using alternating exposures of WF 6 and SiH 4 and ALD-W (B) film was treated with B 2 H 6 for 5 s prior to W ALD using WF 5 and SiH 4 . Finally, ALD-W (C) film was deposited using alternating exposures of WF 6 and B 2 H 6 . All the ALD-W films showed excellent step coverage at the contact with an aspect ratio of ∼ 14, but their resistivities were as high as 125-145 μΩ cm at the thickness of 20 nm. High resistivities of ALD-W films are discussed on the basis of impurities cooperation such as Si and B, phase (body-centered-cubic α-W or primitive cubic β-W), crystallinity (crystalline or amorphous), and grain size. It was found that ALD-W (C) film formed an amorphous phase, which was stable until 900°C annealing. This is clearly different from ALD-W (A) and ALD-W (B) with polycrystalline grains of α-W and β-W, and β-W was transformed to α-W after 800°C annealing. The formation of amorphous W resulted in the formation of large-size grains of chemical-vapor-deposited W film deposited on ALD-W (C) and the reduction in the resistivity of W-plug stack. The integration results showed that the reduced resistivity of W-plug stack with ALD-W (C) provided a significantly lower resistance at the W bit line contact. Another advantage of the integration scheme with ALD-W (C) was its stable contact resistance at the ultrahigh aspect ratio (UHAR) contact even though the step coverage of the underlayer, TiN, was poor. It was also found that the B 2 H 6 pretreatment was effective for obtaining the low and stable contact resistance at UHAR contact.

Development of New TiN/ZrO2/Al2O3/ZrO2/TiN Capacitors Extendable to 45nm Generation DRAMs Replacing HfO2 Based Dielectrics

New ZrO₂/Al₂O₃/ZrO₂ (ZAZ) dielectric film was theoretically designed and successfully demonstrated to be applicable to 45nm DRAM devices. ZAZ dielectric film is a combined structure from tetragonal ZrO₂ and amorphous Al ₂O₃. Thus prepared ZAZ TFT capacitors showed very small Tox.eq value of 6.3Aring and low leakage current less than 1fA/cell. It was also confirmed that ZAZ TFT capacitor was thermally robust during backend full thermal process by applying it to the final DRAM product in mass production

Characteristics of ALD Tungsten Nitride Using B2H6, WF6, and NH3 and Application to Contact Barrier Layer for DRAM

Tungsten nitride (WN x ) thin films were grown by atomic layer deposition (ALD) within the temperature range of 200-350°C from diborane (B 2 H 6 ), tungsten hexafluoride (WF 6 ), and ammonia (NH 3 ) for application to a contact barrier layer in dynamic random access memory (DRAM). Herein, B 2 H 6 was used as an additional reducing agent to produce a low-resistivity ALD-WN x film, and its resistivity was in the range of 300-410 μΩ cm, depending on the deposition conditions for the ∼ 10 nm thick film. An increase in the growth rate was observed with increasing deposition temperature, but an almost constant growth rate of ∼0.28 nm/cycle was obtained in the temperature range from 275 to 300°C. The properties of the as-deposited film, including the resistivity, W/N ratio, density, B and F impurity content, and phase, were affected by the deposition temperature and B 2 H 6 flow rate during the process. As the deposition temperature and B 2 H 6 flow rate increased, the W/N ratio and film density increased and the impurity content decreased, leading to a reduction in the resistivity of the film. An increased W/N ratio was found to be favorable to the formation of a face-centered-cubic β-W 2 N phase. Excellent step coverage was obtained even on a 0.14 μm diameter contact hole with an aspect ratio of 16:1. The ALD-WN x film in this study was thermally stable to annealing at 800°C for 30 min, but after annealing at 900°C, it converted to body-centered-cubic α-W with the accompanying release of N. The ALD-WN x film was evaluated as a barrier layer for W-plug deposition for 70 nm design-rule DRAM. The results showed that the integration scheme with ALD-WN x showed lower contact resistance than metallorganic chemical vapor deposition TiN or TiCl 4 -based chemical vapor deposited TiN.

Atomic layer deposition of low-resistivity and high-density tungsten nitride thin films using B2H6, WF6, and NH3

Tungsten nitride thin films were grown by atomic layer deposition using alternating exposures of B 2 H 6 , WF 6 , and NH 3 at 300°C. The film thickness linearly increased with the number of the reaction cycles and the determined growth rate was ∼0.28 nm/cycle with B 2 H 6 , WF 6 , and NH 3 at pulsing times of 5, 0.25, and 2 s, respectively. The film had a resisitivity of ∼350 μΩ cm with a metallic W-N bond and density of ∼15 g/cm 3 at the thickness of 10 nm. X-ray diffractometry analysis showed that the film had nanocrystalline grains with β-W 2 N and δ-WN phase. Step coverage was approximately 100% even on the 0.14 μm diameter contact hole with a 16:1 aspect ratio.

Characteristics of Cobalt Films Deposited by Metal Organic Chemical Vapor Deposition Method Using Dicobalt Hexacarbonyl tert-Butylacetylene

Cobalt films were deposited by metal organic chemical vapor deposition (MOCVD) using C12H10O6(Co)2 (dicobalt hexacarbonyl tert-butylacetylene, CCTBA) as the Co precursor and H2 reactant gas. The impurity content of the Co films was monitored as a function of the partial pressure of H2 reactant gas. The carbon and oxygen content of as-deposited Co films greatly decrease with the increase of H2 partial pressure, and at H2 partial pressure of 10 Torr and a substrate temperature of 150 °C were 2.8 at. % and less than 1 at. %, respectively. As the H2 partial pressure increased, carbon and oxygen content decreased markedly. Excellent conformality of Co film over 80% was achieved on a patterned wafer with aspect ratio of 15:1, 0.12 µm wide and 1.8 µm deep. The phase transition was analyzed with X-ray diffraction (XRD) depending on RTA temperature. CoSi was observed at 500 °C annealing, and was transformed to CoSi2 at 600 °C annealing. In addition, Auger electron spectroscopy (AES) data showed a 1:2 atomic ratio of Co:Si in the CoSi2 layer.

Highly Reliable and Scalable Tungsten Polymetal Gate Process for Memory Devices Using Low-Temperature Plasma Selective Gate Reoxidation

We applied a very low-temperature plasma-type selective gate reoxidation process to W/poly-Si gate for suppression of abnormal oxidation of a low contact resistive WSix/WN diffusion barrier. The device with the plasma selective gate reoxidation showed superior gate oxide reliability and improved stress immunity of transistor compared to the thermally selective gate reoxidized devices

Phase and Microstructure of ALD-W Films Deposited Using B2H6 and WF6 and Their Effects on CVD-W Growth

We report on the deposition properties of W nucleation layers prepared using a sequential supply of B 2 H 6 and WF 6 and their effects on the growth of the subsequent chemical vapor deposited (CVD)-W. The structural properties of the W nucleation layers such as their phase, crystallinity, and grain size depended on the deposition temperature, B 2 H 6 flow rate, and B 2 H 6 pulsing time. The formation of an amorphous and two forms of crystalline W film [primitive cubic p-phase and body-centered-cubic (bcc) α-one] was observed, depending on the deposition temperature. X-ray diffractometry and transmission electron microscopy diffraction analysis showed that the amorphous W was dominantly deposited at temperatures of up to 350°C and that when the deposition temperature was increased to 395°C, the film formed the p-phase. At a deposition temperature of 425°C, the phase of the film started to be transformed into α-phase and was completely transformed to single phase α-W with a very large grain size of approximately 120-180 nm at 450°C. We were also able to deposit the α-phase W film at 395°C with a lower B 2 H 6 flow rate, but its grain size was only approximately 20-30 nm. The W nucleation layers had a significant effect on the final grain size and resistivity of the CVD-W films deposited on them. The minimum resistivity of the 50 nm thick CVD-W film with the optimized B 2 H 6 -based nucleation layer was ∼ 10 μΩ cm, while the conventional CVD-W film with a SiH 4 -based nucleation layer showed a resistivity of 25 μΩ cm at the same thickness.

Effects of phase of underlying W film on chemical vapor deposited-W film growth and applications to contact-plug and bit line processes for memory devices

This article presents the effects of phases of underlying nucleation layers prepared using two different reaction schemes, one is with B2H6 and WF6 and the other with SiH4 and WF6, on the properties of chemical vapor deposited (CVD)-tungsten (W) thin film. From the x-ray diffractometry and transmission electron microscopy analysis, the B2H6-based nucleation layer was found to form as a poorly crystallized metastable β-phase W while SiH4-based one as a well-crystallized equilibrium α phase. The subsequently grown CVD-W film, as deposited with α phase, has significantly larger grains and, consequently, mitigated the increase of CVD-W resistivity due to size effect as well as lower resistivity on the B2H6-based nucleation layer than on SiH4-based one. CVD-W film on the B2H6-based nucleation layer integrated on memory devices disclosed the improved electrical properties of interconnection such as lowered contact resistance at the metal line to bit line contact, lowered bit line resistance, and reduced parasit...