Takashi Yoda

Properties of high-performance porous SiOC low-k film fabricated using electron-beam curing

In this paper, we describe the effect of electron-beam (EB) curing on ultra-low-k dielectric porous SiOC material (k=2.2) and the application of this technology to the 90-nm-node Cu/low-k multilevel damascene process. A significant improvement of dielectric porous SiOC films with EB curing has been demonstrated. The mechanical and adhesion strength of these films were increased by a factor of 1.5–1.6 without degrading the films k. This result can be explained by the reconstruction of a Si–O random network structure from cage Si–O bonds and Si–CH3 bonds through EB curing. Additionally, the EB curing of spin-on dielectric (SOD) porous low-k films contributes to a decrease in their curing temperature and a decrease in their curing time. Under optimum EB curing conditions, no degradation of transistor performance was revealed. The excellent adhesion strength obtained by EB curing, has contributed to the success of multilevel damascene integration. On the basis of our findings, this EB curing technology can be applied in devices of 65-nm-node and higher.

Structural Studies of High-Performance Low-k Dielectric Materials Improved by Electron-Beam Curing

With the use of a newly developed electron beam (EB) curing process, an advanced methylsilsesquioxane (MSQ) low-k dielectric (LKD) film of k=2.9 was developed. It is noteworthy that the EB curing process can drastically improve the mechanical strength of LKD film and reduces the thermal budget without increasing the k value. The X-ray absorption fine structure (XAFS) study on the LKD was conducted to clarify the structural change upon EB curing. The structure of the film was compared with those of two different types of other MSQ films, the ladder-network structure and the random-network structure, and a chemical vapor deposition (CVD) film. The Si–O–Si bond angle and Si–O (Si–C) bond length were determined by fitting the Fourier transformed extended X-ray absorption fine structure (EXAFS) spectra. Si–O–Si bond angle of LKD film was found to be between those of the ladder and the random structure, which are 135° and 147°, respectively. The X-ray absorption near-edge structure (XANES) spectra of LKD film revealed two broad features corresponding to a mixture of the two structures. In contrast, Si–O–Si angles of the EB-cured LKD film and the CVD film were similar, and the XANES features of both films were almost identical with those of the random structure. The electronic structure as determined from XANES spectra was also discussed by comparing three-dimensional-linkage models obtained by ab initio calculations. We confirmed that the EB curing process of LKD film causes a drastic structural change. The change from the mixture of ladder and random structures to the completely random structure was caused by C–H bond breaking followed by the formation of new polymer-like clusters with C–C bonds.

The application of simultaneous ebeam cure methods for 65 nm node Cu/low-k technology with hybrid (PAE/MSX) structure

High performance low-k hybrid-DD structure (poly-arylene-ether (PAE)/ poly-methylsiloxane (MSX)) is realized by simultaneous electron beam (ebeam) curing technique, and applied to a 65 nm node Cu/low-k multilevel damascene process. By eBeam curing for MSX, while maintaining a k value, both mechanical strength and adhesion strength of the bottom interface have been improved. In addition, since the introduction of the ebeam cure technique reduces cure temperature and time of spin on dielectric formation, the thermal budget is dramatically reduced. The simultaneous ebeam curing of PAE/MSX hybrid structure realizes low-cost and high reliability Cu/low-k interconnects. It is also considered that this ebeam cure technology will be very effective in 65 nm node devices and beyond.

High-Performance SiOF Film Fabricated Using a Dual-Frequency-Plasma Chemical Vapor Deposition system

With the use of a newly developed dual-frequency-plasma chemical vapor deposition (DFP-CVD) system, an advanced SiOF film of k = 3.4, which exhibits excellent resistance for moisture absorption, was developed. The physical and chemical properties of the SiOF film were compared to those of typical SiOF films deposited by both conventional high-density-plasma CVD (HDP-CVD) and plasma-enhanced CVD (PE-CVD) systems, with the same k value. The DFP-CVD SiOF film appears to be significantly superior to the HDP-CVD SiOF film, as revealed by the following results. The moisture absorption rate measured by thermal desorption spectroscopy (TDS) (after 4 days of air exposure) is about 5 times lower, the hardness was 1.8 times higher, and the hygroscopicity (after 1 hour of boiling) was 2.6 times lower. These results confirm that the DFP-CVD SiOF film is applicable to Al and Cu interconnect structures for devices of the 130 nm scale and beyond.

Stranski-Krastanov growth of tungsten during chemical vapor deposition revealed by micro-auger electron spectroscopy

Chemical vapor deposition (CVD) of tungsten is an important process to make interconnections in advanced integrated-circuit devices. As device dimensions continue to decrease, incomplete nucleation inside the trenches and via holes is becoming a crucial issue. In this work, micro-Auger electron spectroscopy with in-plane spatial resolution was applied for the first time to study the nucleation and growth process of W islands. Results showed that W grew slowly and uniformly on TiN surfaces up to about one-monolayer coverage, and then W islands nucleated and started to grow rapidly. This transition from layer to island shows that W grew by Stranski–Krastanov mode during CVD on TiN from WF6 and SiH4. Drastic difference might exist in chemical reactivity between the initial W layer on TiN surfaces and the W islands, causing the change in W growth rate.

Investigation of Cu ion drift through CVD TiSiN into SiO2 under bias temperature stress conditions

Cu gate metal oxide semiconductor (MOS) capacitors with and without thin chemical vapor deposition (CVD) TiSiN diffusion barrier were subjected to bias temperature stress (BTS) conditions. Cu drift flux for the MOS capacitor with CVD TiSiN diffusion barrier was about one order of magnitude smaller than that without the diffusion barrier. The activation energy of the drift flux was larger by a factor of 1.5 than that without the diffusion barrier. Cu thermal diffusion in the CVD TiSiN is dominant for Cu ion drift into the plasma enhanced (PE)-CVD SiO2. The Cu concentration depth profile in SiO2 showed that the Cu dose in PECVD SiO2 under thermal stress is significantly smaller than that under BTS conditions.

Electrochemical Study of Model Additives on Aluminum Single-Crystal Surfaces

An electrochemical study of additives such as phosphoric acid and oxalic acid on Al chemical-mechanical polishing (Al-CMP) is presented. To design a robust Al-CMP slurry, which shows no dependency upon the Al texture, finding suitable additives for the slurry is crucial. Phosphoric acid forms a passivated film on an Al (111) surface, while oxalic acid exhibits a high removal rate on an Al (111) surface. A mixture of these additives can satisfy the requirements for developing a robust Al-CMP process.

X-ray absorption studies of high performance Low-k dielectric materials

The XAFS measurement of the MSQ type low-k dielectrics (LKD™) was conducted to clarify the structure change with and without the EB cure. Furthermore, three different types of other MSQ films, the ladder structure, the random structure and the CVD film, have been investigated as references. We have determined Si-O-Si bond angle and Si-O(Si-C) bond length by fitting the Fourier transformed EXAFS spectra. The ladder structure and the random structure have Si-O-Si bond angle of 133 and 146, respectively. Si-O-Si bond angle of LKD™ film is among that of the ladder and the random structure, and the XANES spectrum of LKD™ film displays two broad features, corresponding to the mixture of both structures. In contrast, Si-O-Si angles of the EB cured LKD™ film and the CVD film resemble each other, and the XANES features of both films are almost identical with that of the random structure. We have confirmed that the EB cure process for LKD™ film makes drastic structure change from the mixture of ladder and random structure to the random network structure.