Methyl Silsesquioxane Research Articles

Chemical Mechanical Polishing of Low‐Dielectric‐Constant Polymers: Hydrogen Silsesquioxane and Methyl Silsesquioxane

In the study, the film properties and chemical mechanical polishing (CMP) characteristics of the low‐dielectric‐constant materials hydrogen silsesquioxane (HSQ) and methyl silsesquioxane (MSQ) were presented. The Fourier transform infrared spectra, refractive index, dielectric constant, and atomic force microscopy results showed the successful preparation of the HSQ and MSQ films. The CMP characteristics of both materials were studied by two different slurries, A‐1 and B‐1. Our results showed that the CMP removal rate and nonuniformity increased with increasing the slurry solid content. The removal rate of the polished HSQ film was much larger than that of the polished MSQ film due to the hydrophobic surface of the MSQ film. The removal rate using the A‐1 slurry was larger than the B‐1 slurry for polishing both films. This result can be explained from the consideration of the isoelectric point and the electrostatic force between the abrasive surface and the film surface. The downforce pressure of the CMP process also showed a significant effect on the removal rate and the nonuniformity of the polished HSQ film. © 1999 The Electrochemical Society. All rights reserved.

Enhancing the Oxygen Plasma Resistance of Low-k Methylsilsesquioxane by H2 Plasma Treatment

The organic silsesquioxane, methylsilsesquioxane (MSQ), has a low dielectric constant because of its low film density compared to thermal oxide. However, the quality of the MSQ film is degraded by the damage caused by oxygen plasma and hygroscopic behavior during photoresist stripping. In this work, we have studied the ability of H2 plasma treatment to improve the quality of MSQ. The leakage current of MSQ decreases as the H2 plasma treatment time is increased. The dielectric constant of treated samples remains constant (∼2.7). In addition, the thermal stability of MSQ film is significantly promoted. The H2 plasma treatment can provide additional hydrogen to passivate the inner structure of porous MSQ film, and reduce the probability of moisture uptake. Therefore, H2 plasma treatment can improve the quality of low-k MSQ film and reduce the issue of photoresist stripping in the integrated process.

Patterning of fluorine-, hydrogen-, and carbon-containing SiO2-like low dielectric constant materials in high-density fluorocarbon plasmas: Comparison with SiO2

Successful pattern transfer of 0.36–0.62 μm features into fluorinated silicon dioxide, hydrogen silsesquioxane (HSQ), and methyl silsesquioxane (MSQ) has been demonstrated in a transformer coupled plasma (TCP) source using fluorocarbon feedgas chemistries. These films have a lower dielectric constant than conventional SiO2. It is this property that makes them attractive for implementation in future integrated circuit technology. The etching of these novel dielectrics was compared to conventional SiO2. We have observed that the different chemical makeup of these SiO2-like dielectrics does not affect the etching when weakly polymerizing gases are used, such as CF4. In this case, the etch rate is primarily dependent on the ion energy. For more polymerizing chemistries, like CHF3 or C3F6/H2 gas mixtures, x-ray photoelectron spectroscopy analysis showed that an increasing steady state fluorocarbon film thickness limits the ion and neutral flux at the interface of the various dielectrics. It is suggested that, as the fluorocarbon film thickness increases, the etching becomes more dependent on neutral species from the gas phase. In this case, hydrogen and carbon impurities in HSQ and MSQ, respectively, limit the etch rate. On the other hand, fluorine in the fluorinated SiO2 film enhances the etch rate as compared with the etch rate of conventional SiO2. In line with these observations, we conclude that fluorine from the gas phase is most likely the controlling etchant as the fluorocarbon film increases beyond the ion penetration depth.

Density functional theory applied to the calculation of dielectric constant of low-k materials

Abstract The interest of low-k dielectric materials to reduce capacitance in multilevel metal interconnects of integrated circuits is well known in the semiconductor industry. The use of these materials (especially hydrogen silsesquioxane (HSQ) and methyl silsesquioxane (MSQ): intermetal dielectric applications in the back end of line fabrication) leads to a reduction of the dielectric constant from k≅4 in a traditional intermetal dielectric material of silicon dioxide to a value of ≅2.5–3. The physical difference between HSQ or MSQ and a-SiO2 is the presence of Si–H bonds (for HSQ) or Si–CH3 bonds (for MSQ) and the density of the material. A theoretical calculation of bond polarizability (Si–H or Si–CH3) associated to experimental values of electric dipole densities can lead, using the Clausius-Mossotti relationship, to the calculation of the dielectric constant. After validation of the calculation methods both on simulation and experimental values, it is shown that for a constant density, the difference between the materials could be due to the bond polarizability and furthermore that this difference accounts, in part, for the value of dielectric constant. Consequently, even if densification remains the main parameter explaining low-k values, the polarizability of building units of these materials is not negligible.

Low k, Porous Methyl Silsesquioxane and Spin-On-Glass

Low dielectric constant, porous silica was made from commercially available methyl silsesquioxane (MSQ) by the addition of a sacrificial polymer, substituted norbornene polymer containing triethoxysilyl groups (NB), to the MSQ. The silsesquioxane-NB polymer film mixture was thermally cured followed by decomposition of the NB at temperatures above 400°C. The dielectric constant of the MSQ was lowered from 2.7 to 2.3 by creating 70 nm pores in the MSQ. The voids created in the MSQ exhibited a closed-pore structure. The concentration of NB in the MSQ affected the number of pores but not their size. Porous films were also created in a methyl siloxane spin-on-glass and its dielectric constant was lowered from 3.1 to 2.7. Infrared spectroscopy was used to follow the curing of the MSQ and decomposition of the NB. © 1999 The Electrochemical Society. S1099-0062(98)09-026-9. All rights reserved.

Low-K Porous Spin-On-Glass

AbstractPreviously, the fabrication of air-gap structures for electrical interconnections was demonstrated using a sacrificial polymer encapsulated in conventional dielectric materials. The air-gaps were formed by thermally decomposing the sacrificial polymer and allowing the by-products to diffuse through the encapsulating dielectric. The diffusivity of the polymer decomposition products is adequate at elevated temperatures to allow the formation of air-gaps. This process was extended to form low dielectric constant, porous silica from commercially available methylsilsesquioxane (MSQ) by the addition of the sacrificial polymer to the MSQ. The porous MSQ film was thermally cured followed by decomposition of the NB at temperatures above 400°C. The dielectric constant of the MSQ was lowered from 2.7 to 2.3 by creating 70 nm pores in the MSQ. The voids created in the MSQ appeared to exhibit a closed-pore structure.

Mechanical Properties and Toughening of a Polymethylsilsesquioxane Network

AbstractPolysilsesquioxanes are finding wider uses in microelectronics. However these materials are brittle and their mechanical behaviors need to be better understood. In this paper the mechanical properties of a cured methyl silsesquioxane network are studied and they are found to vary strongly with curing conditions. In the investigated curing temperature range there seems to be a correlation between the fracture toughness (KIc) and the viscoelastic transitions, which are affected by the network crosslink density. A higher crosslink density suppresses the cc and β transitions and reduces the KIc. A toughening approach is designed and its applicability is demonstrated by the increased fracture toughness.

Characterization of Thin Dielectric Films as Copper Diffusion Barriers Using Triangular Voltage Sweep

AbstractAs technology progresses, the need for thinner Cu diffusion barrier caps is becoming more important, and it is advantageous if these barriers have low dielectric constants (κ). Towards this end, we characterized Cu penetration in several thin (35 nm to 70 nm) dielectrics, including silicon nitrides, silicon oxynitrides, an amorphous hydrogenated carbon film, and a methyl silsesquioxane layer. Metal Insulator Silicon (MIS) structures were used as the test vehicle. The barrier dielectrics were deposited on 100 nm thermal oxide which was grown on 2 Ω-cm, n-type Si wafers. After the deposition of 50 nm TEOS capping layers, both Al and Cu dots were evaporated on each wafer through a mask. Both Al and Cu dot samples were stressed at +2.7 MV/cm at 300°C for 10 minutes. For Cu dots, the applied stress pushed Cu ions into the dielectric stack. Stressing Al dots characterized the effects of the stress on the dielectric stacks and the quantity of Na ions in the films. Since C-V shifts are subject to stress-related instabilities in the interfaces as well as within the dielectrics themselves, triangular voltage sweep (TVS) was used after the applied stress to measure the concentration of Cu which reached the underlying thermal oxide film. The sensitivity of the TVS test with the structures used is about 5×109/cm2. Secondary ion mass spectroscopy (SIMS) analyses were performed on some of these samples to verify the electrical results.

Characterization of Thin Dielectric Films as Copper Diffusion Barriers using Triangular Voltage Sweep

AbstractAs technology progresses, the need for thinner Cu diffusion barrier caps is becoming more important, and it is advantageous if these barriers have low dielectric constants (κ). Towards this end, we characterized Cu penetration in several thin (35 nm to 70 nm) dielectrics, including silicon nitrides, silicon oxynitrides, an amorphous hydrogenated carbon film, and a methyl silsesquioxane layer. Metal Insulator Silicon (MIS) structures were used as the test vehicle. The barrier dielectrics were deposited on 100 nm thermal oxide which was grown on 2 Ω-cm, n-type Si wafers. After the deposition of 50 nm TEOS capping layers, both Al and Cu dots were evaporated on each wafer through a mask. Both Al and Cu dot samples were stressed at +2.7 MV/cm at 300°C for 10 minutes. For Cu dots, the applied stress pushed Cu ions into the dielectric stack. Stressing Al dots characterized the effects of the stress on the dielectric stacks and the quantity of Na ions in the films. Since C-V shifts are subject to stress-related instabilities in the interfaces as well as within the dielectrics themselves, triangular voltage sweep (TVS) was used after the applied stress to measure the concentration of Cu which reached the underlying thermal oxide film. The sensitivity of the TVS test with the structures used is about 5×109/cm2. Secondary ion mass spectroscopy (SIMS) analyses were performed on some of these samples to verify the electrical results.

High-Density Plasma Etching of Low Dielectric Constant Materials

ABSTRACTThe patterning of several novel low dielectric constant (K) materials has been studied in a high-density plasma (HDP) tool. Recent results obtained on oxide-like materials, such as fluorinated oxide, hydrogen silsesquioxane (HSQ), and methyl silsesquioxane (MSQ), are reviewed. These materials can be successfully patterned using a fluorocarbon etching chemistry. The etching is in this case controlled by a thin fluorocarbon film at the surface. The patterning of polymer dielectrics can be performed in an oxygen etching chemistry. As an example, the patterning of Parylene-N in an oxygen chemistry is discussed. In this case, the ion and the oxygen radical flux need to be properly controlled to obtain a directional etching process. After the dielectric etch, either in a fluorocarbon or oxygen based chemistry, fluorocarbons and oxygen contamination remain at the exposed metal surfaces. We recently demonstrated how a plasma treatment following the dielectric etch reduces these contaminants. The results of this treatment on copper surfaces and the resulting modification to the dielectric are reviewed.

A novel silicon containing chemical amplification resist for electron beam lithography

A new negative working electron beam resist which is applicable to a bi-layer resist system has been developed. This resist consists of an onium salt cationic initiator and poly(methyl silsesquioxane). The resist can be developed in aqueous base solutions and shows very high sensitivity of 0.2 μC/cm2 on an electron beam exposure and high resistance to etching in an oxygen plasma.

Polydimethylsiloxanes with methyl and vinyl silsesquioxane units in the chains

It has been found that oligomeric dimethylsiloxanes with methyl and vinyl silsesquioxane units in the chain prepared with use of organoacetoxysilanes condense at a lower temperature than oligomers based on organochlorosilanes. As the amount of silsesquioxane fragments in the chain increases, the rate at which the specific viscosity of the polymers rises is reduced. It has been found for polymers obtained using organochlorosilanes that the degree of branching occurring in the thermal polycondensation reaction increases as the amount of silsesquioxane fragments in the chain rises. There is a linear relationship between the degree of branching and the specific viscosity of the polymers obtained.