Effect of Silylation Hardening on the Electrical Characteristics of Mesoporous Pure Silica Zeolite Film

Abstract

A pure silica zeolite film was formed by use of hydrothermally crystallized zeolite nanoparticles in a porous silica precursor. The effects of silylation hardening by tetramethylcyclotetrasiloxane ͑TMCTS͒ vapor treatment on the electrical characteristics of pure silica zeolite films were investigated. The results from Fourier-transform-IR spectroscopy indicated that the O-H bond decreased by zeolite formation, resulting in the decrease of the leakage current by 1/10. Silylation hardening by TMCTS vapor treatment could reduce the leakage current by 4 orders of magnitude due to the reduction of Si-OH and O-H bonds. The elastic modulus of 5.18 GPa and the dielectric constant of 1.96 were achieved simultaneously by silylation hardening. Consequently, the electrical and mechanical characteristics of the pure silica zeolite film as well as the time dependent dielectric breakdown lifetime were improved.With the shrinking of interconnect feature sizes of silicon ultralarge-scale integrated circuits, 1 the signal delay time increases due to the increase of interconnect resistance and parasitic capacitance. To overcome this problem, low-dielectric-constant interlayer dielectric films are needed. Mesoporous silica with pore sizes ranging from 2 to 50 nm have been studied as a potential candidate for ultralow-k materials. 2 However, the mechanical strength of the low-k film is degraded when mesopores are introduced into the skeletal materials to reduce the film density. Chemical mechanical polishing may cause damage to the porous low-k material. Moreover, it is known that the low-k film to which mechanical strength is weak receives damage in the packaging, so both low-k and high mechanical strength are required. Pure silica zeolite is a promising candidate as an advanced low-k material. 3,4 The Young's modulus of the zeolite is 110 GPa, 3 which is larger than that of SiO 2 ͑73 GPa͒. This is because the silica network in the zeolite has a three-dimensional crystal structure. The zeolite also has low-k because the film density is lower than that of quartz due to the micropores in the crystalline silica. It has a higher elastic modulus, thermal conductivity, and hydrophobicity than SiO 2 . 4-10 The mobile 11 ͑MEL͒-type zeolite was adopted in this work. 11,12 The zeolite was made by a hydrothermal crystallization method. MEL-type zeolite has a 10-membered ring with pore diameters of 0.53 and 0.54 nm as shown in Fig. 1. In this paper, the effects of silylation on the film properties of pure silica zeolite dielectric films are investigated. ExperimentalThe formation process of MEL-type zeolite is shown in Fig. 2. A few nanometers thick native oxide was formed on the surface of Si wafer. First, the precursor solution of tetrabutyl ammonium hydroxide ͑TBAOH͒, tetraethyl orthosilicate ͑TEOS͒, and ethyl alcohol ͑EtOH͒ were mixed and stirred for 24 h at room temperature. Hydrolysis of TEOS was caused by EtOH. TBAOH was purified by filtering with the ion exchange resin. Both TEOS and EtOH were of semiconductor grade. The hydrothermal cr...

Sealed ultra low-k organosilica films with improved electrical, mechanical and chemical properties

“…4,6 Further, the pores are interconnected and relatively large in size (3 nm or more). 7 This means that gaseous metal ions, which are released during integration processes, can easily diffuse into the pores leading to higher leakage current densities, lower breakdown voltage or even complete failure of the dielectric low-k lm. 8 The latter can be avoided by sealing the pores.…”

Pore Narrowing of Mesoporous Silica Materials

“…Dealing with very small (<1 nm) or not interconnected pores, the previous described issues are negligible. However, as the dielectric constant approaches values below 2.2, pore sizes tend to increase and the pores are highly interconnected [ 5 ]. Therefore, a pore narrowing step or pore sealing step is necessary.…”

A new procedure to seal the pores of mesoporous low-k films with precondensed organosilica oligomers

“…Such ultra low-k materials (ULK) generally have a porosity exceeding 50% and a pore size of 3 nm or more. 6 Here, all existing sealing technologies are no longer efficient. Plasma sealing e.g.…”