Resistance of siloxane-based, low-dielectric-constant ͑low-k͒ dielectrics against heat and moisture stress is clarified. The organosilica-glass ͑OSG͒ and the silicon-oxycarbide are shown to be the most reliable: the k-values are stable even after a heating test at 650°C and a pressure cooker treatment for 100 h. This stability is high enough to ensure the low-k property throughout fabricating multilevel interconnects and long-term reliability after the fabrication. This is shown to be due to the stability of Si-CH 3 bonds and Si-CH n -Si bonds incorporated in the OSG and the silicon-oxycarbide. The stability of the OSG in real low-k interlevel dielectric structure was also demonstrated using four-level interconnect test devices. The low-k property still remains even after the reliability tests, showing that the low-k interlayer dielectric structure is sufficiently resistant to heat and moisture stresses.Low-parasitic-capacitance multilevel interconnects using lowdielectric-constant ͑low-k͒ interlevel dielectrics ͑ILDs͒ are essential for high speed ultralarge-scale integrated circuits ͑ULSIs͒. Siloxanebased low-k materials, as well as carbon-based aromatic polymers, are promising as low-k ILDs with k of about 3. The siloxane-based materials are classified into the following: fluorinated-silica-glass ͑FSG, k ϭ 3.5-3.8͒, hydrogen-silsesquioxane ͑HSQ, k ϭ 2.7-3.3͒, organo-silica-glass ͑OSG, k ϭ 2.7-3.3͒. 1-6 Their typical chemical bonding structure is shown in Fig. 1a. The structure consists of siloxane networks ͑-Si-O-Si-͒ terminated by R. The R stands for F, H, and CH 3 in FSG, HSQ, and OSG, respectively. This R makes the film have low density and low moisture content, so the film has low-k properties. On the other hand, the R degrades the mechanical strength of the film because of network termination. Recently, we have proposed a new low-k material, silicon-oxycarbide, with high mechanical strength. 7,8 The structure of this material is shown in Fig. 1b. This material contains much less terminating CH 3 ͑R͒. Instead, it contains CH n ͑RЈ, n ϭ 0-2͒ bridging the siloxane networks.To assure the performance of the high-speed ULSIs, the electrical properties ͑k and breakdown voltage͒ of the low-k ILDs are needed to be resistant against heat and moisture stresses. The heat resistance is necessary to prevent degradation during the interconnect fabrication process. The ILDs are submitted to heating at over 400°C during fabrication of upper-level interconnects. The length of the heating is dependent on the process. If a conventional batch-type furnace is used for curing the low-k materials, the heating per layer is estimated to be 0.5-1 h. As a result, the lower level ILDs are subjected to many hours of heating. In addition, the moisture resistance is necessary for the long-term reliability after packaging. This is because, in real operating conditions, the ILDs are subjected to moisture penetrating from the outside the package. In the package reliability area, the effect of this moisture penetration was evaluated by accel...

We have developed a new Cu-barrier dielectric film suitable for Cdlow-k integration. The film has an SiOl composition and is deposited using trimethoxysilane and N20 chemistry. The Cu barrier properties of the film are as good as those of the conventional barrier material (P-SiN). The dielectric constant (k) of the film is 3.9, which is about half the dielectric constant of P-SiN filmThe new film has been successfully integrated into damascene Cu interconnections as a Cu cap-layer material. The Cu interconnections had remarkably low line-to-line leakage current ( 4 0 pA/cm2) and sufficient dielectric breakdown lifetime under normal operating conditions.

Oxygen plasma resistance of low-k organosilica glasses ͑OSGs͒ is shown to be strongly dependent on the material structure: a silicon oxycarbide has a higher oxygen plasma resistance compared to a conventional OSG. The silicon oxycarbide is stable at pressures up to 300 mTorr, which is 10 times higher than those of the conventional OSG. Even at higher pressures, the degradation is much lower. Structural analysis using wet etching demonstrated that the stability at low pressures is due to a thin protecting layer: dense oxide formed by impingement of directional oxygen ions. The inside layer is shown to have the same k-value as the original film. The superior oxygen plasma resistance of the silicon oxycarbide is probably due to lower methyl group content, which provides greater volume reduction toward achieving a dense siloxane networks that protects the inside.

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A new low-k material (silicon-oxycarbide, k=3.3) is developed to improve the mechanical strength of Cdlow-k interconnects. The film is shown to be over three-times stronger than conventional ones. The film qualities are high enough: the heat resistance is good up to 65OoC, and the breakdown voltage is 5.5 MV/cm.The film is applied to interconnection test devices without using an oxide-cap. The k remains as low as 3.3, showing that an equivalent capacitance reduction with conventional materials (k=2.5-2.9) can be achieved using a simpler and more reliable structure. IntroductionReduction in wiring capacitance is essential to improving the operational speed of ULSI. To reduce the capacitance, low-permittivity (low-k) inter-level dielectrics (ILDs) have been extensively investigated. Organo-silicates and aromatiopolymers have been proposed as ILDs with k about 3 .O (Table 1 ) [ 1,23.In practical applications, they need an oxide-cap to prevent overlying metal from delaminating during CMP. In the case of the organo-silicates, this delamination is due to the methyl-groups (-CH3) which terminate the Si-0-Si networks and cause the films to fragile. In the case of the polymers, the oxide-cap is also used as a hard-mask for patteming as well as an adhesion layer with the metal.