Heat and Moisture Resistance of Siloxane-Based Low-Dielectric-Constant Materials

Abstract

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...

Effects of Deposition Pressure on Properties of Carbon-Doped Silicon Oxide Low Dielectric Constant Films

“…It has been reported that lowering the discharge power density decreases the dielectric constant of SiO͑C,H͒ films. 13,14 An increase in the process pressure produces the same effect as seen from our results. This similarity is understandable, as lower discharge power density or higher pressure ͑leading to reduced mean free path of the species͒ both lower the degree of dissociation of the radicals 15,16 and result in an increased incorporation of Si-͑CH 3 ͒ m group in the films.…”

Enhancement of moisture resistance of spin-on low-k HSQ films by hot wire generated atomic hydrogen treatment

“…For the moisture reliability test, the as cured as well as the HWGAH treated HSQ films were immersed in water at 80 -C for 3 h in a closed beaker (container). These conditions were chosen for accelerated testing and are similar to the pressure cooker test (PCT) in an earlier study [6]. The chemical structure of the cured HSQ films before and after the hot wire and water treatment was investigated by Fourier transform infrared (FTIR) spectroscopy.…”

Modifications of dielectric films induced by plasma ashing processes: Hybrid versus porous SiOCH materials

“…These results demonstrate that ͑1͒ oxidizing chemistries and reducing chemistries with nitrogen transform the porous SiOCH film in an hydrophilic film, while ͑2͒ nitrogen-free reducing chemistries maintain the hydrophobic properties of the porous SiOCH material. Previous studies [22][23][24][25][26] have shown that in oxidizing plasmas oxygen reactive species can deeply diffuse into the film through the pores and react with methyl groups producing Si-OH bonds leading to moisture uptake. In the case of reducing plasmas with nitrogen, 24-26 hydrogen reactive species ͑NH x ,H͒ can react with Si-O-Si and Si-CH 3 to form Si-NH 2 and Si-OH terminating bonds which can also lead to moisture uptake.…”