Influence of CMP Chemicals on the Properties of Porous Silica Low-k Films

Abstract

This paper describes the influence of the chemical mechanical polishing ͑CMP͒ process on the degradation in the leakage currents and dielectric constants of porous silica low-k films. It is found that the leakage current and dielectric constant increased by post-CMP cleaning solution due to the increase of CH x and OH bonds according to Fourier transform infrared ͑FTIR͒ absorption. This is because the surfactant in the post-CMP cleaning solution permeated into the porous silica. The permeated surfactant in the porous silica can be removed by rinsing with 2-propanol or ethanol after the CMP process. Degradations of the leakage current density and dielectric constant can be recovered by ethanol rinse and subsequent 1,3,5,7-tetramethyl-cyclo-tetrasiloxane vapor treatment, which makes the pore wall surfaces hydrophobic.The chemical mechanical polishing ͑CMP͒ process is necessary to form copper damascene interconnects in ultralarge-scale integrated circuits ͑ULSI͒. Recently, low-dielectric-constant ͑low-k͒ materials have been used for interlayer dielectrics to meet the demands for high-speed operation and low-power consumption in ULSI. For the 65 nm half-pitch technology node, low-k materials whose dielectric constants are 2.4 or less are required. 1 It was reported that degradation in low-k materials was caused during the Cu/low-k damascene process. Yoon et al. 2 and Kodera et al. 3 reported that the film peeling and the crack occurred during the CMP process because the adhesion between the low-k material and other films was weak. Baklanov et al. 4 reported that the low-k material with porous structure was degraded by etching gas and wet chemicals. In order to solve the problems, the low-pressure CMP process was developed to suppress the film peeling and the crack in the CMP process. In addition, the cap film was layered in damascene structure to protect the low-k film from the CMP chemicals ͑CMP slurries and post-CMP cleaning solutions͒.It is necessary to lower the effective dielectric constant ͑k eff ͒ to achieve higher-speed operation and lower power consumption. Figure 1 shows a typical structure of Cu/low-k damascene for 32 nm half-pitch technology node. Table I shows properties of cap layer and stopper layer for two cases considered in the present work: A and B. Figure 2 shows the calculated effective dielectric constant as a function of thickness of cap layers for the two cases. As seen, it is necessary to lower the dielectric constant and the thickness of the cap layer. As an extreme case, the damascene structure without the cap layer is worth considering. To achieve this cap-layer-less structure, it is necessary to clarify the degradation of low-k materials due to the CMP chemicals to establish the recovery process of degradation and the CMP chemicals free from degradation. Kondo et al. 5 investigated the deterioration of low-k material due to the post-CMP cleaning solution and reported on a post-CMP cleaning solution by which the deterioration of dielectric constant was not caused. However, neither the c...

Experimental Investigation of Material Removal Characteristics in Silicon Chemical Mechanical Polishing

“…1) The CMP process is a more well-known planarization method for fabricating patterned wafers used in integrated circuit (IC) devices [2][3][4][5] than the silicon CMP process. Also, only a few studies on the use of the CMP process for IC fabrication have presented results on silicon CMP.…”

Dependency of the Underlying Surface Condition on Dielectric Film Removal at Wafer Edge

“…Since the low-k film is porous and includes more moisture (H 2 O) in general, 26 we estimated that the degasification of moisture is accelerated as the slope of the area not covered by the cap layer increases. In other words, the relative amount of degasification also becomes evident as the slope distance changes.…”

Post‐CMP Cleaning

“…In addition to organic acids or bases, a post-CMP cleaning solution may also contain surfactants [44] that can profoundly influence the zeta potentials of the surfaces and alter their mode of interaction. For example, as shown in Fig.…”