This article presents the oxidation kinetics of Cu thin films in dry and wet oxygen at temperatures from 100 to 600 °C. Spectroscopic ellipsometry and reflectometry, which yield refractive index and thickness of the Cu oxide, were used in kinetic study of Cu film oxidation. Cabrera–Mott (C–M) theory was used for the calculation of oxidation activation energies, yielding 0.68 eV for dry oxidation and 0.43 eV for wet oxidation. The scanning electron microscopy (SEM) and Rutherford backscattering spectrometry were used to investigate the cross-sectional profile, grain size, and chemical composition of the Cu oxides. A formula for Cu oxide thickness calculation was derived from the C–M theory and experimental data. Good agreement has been observed in thickness values from formula calculation, spectroscopic reflectance and SEM has been confirmed. A study of the effect of trace O2 on Cu film anneal is also presented.
Copper is widely accepted as a next-generation metallization material for ultralarge-scale integration ͑ULSI͒ because of its low resistivity and high electromigration resistance. It is well known that Cu oxidizes easily at low temperatures. This characteristic has impeded the application of Cu in integrated circuits. However, the high oxidation rate of Cu and high reduction rate of its oxides at low temperature can be exploited for some potential applications. This paper presents the kinetic studies of Cu film oxidation and in situ reduction of its oxide films. The Cu oxidation experiments were performed in dry and wet oxygen at temperatures from 100 to 600°C for oxidation times from 10 to 718 s. Scanning electron microscopy, Rutherford backscattering spectrometry, spectroscopic ellipsometry and reflectometry, and X-ray photoelectron spectroscopy were used for analyzing the chemical composition of the processed material and determining the oxidation/reduction kinetics of the films. The results showed that the oxide phase is CuO at higher temperature and Cu 2 O at lower temperature ͑Ͻ400°C͒. In situ reduction of copper oxide was studied using secondary ion mass spectroscopy, indicating that the reduction of Cu oxides proceeds from the interface to the surface with a high reduction rate. The infrared reflectivity of Cu surface is over 99%. This is a problem when the Cu process is performed in a rapid thermal processing ͑RTP͒ system, since most of the radiation from the lamps is consequently reflected by the Cu surface. An improved process, called shield-enhanced RTP, results in higher lamp power efficiency and better within wafer temperature uniformity.
Multiple-input multiple-output (MIMO) wireless system is a hot research topic in 5th generation mobile communication technology (5G), which can increase the channel capacity of the antenna system to meet new communication demands without changing the bandwidth and transmission power. However, adding the number of antenna elements in a limited space size can lead to mutual coupling effects and impair the communication quality. Therefore, it is significant to design a compact MIMO wireless system using decoupling techniques. Several studies on the reduction of mutual coupling effects have been proposed. However, a concrete overview of the features and resemblances of these decoupling techniques is lacking. In this review, we provide a brief description of the research background on the mutual coupling effect of MIMO. Then, various decoupling techniques worthy of reference are classified and outlined. We further summarize the additional impacts due to the existence of different decoupling structures, and the possible usability and defects of these techniques are revealed clearly in this paper. Finally, a future outlook on the development direction of decoupling techniques for MIMO wireless systems is also concluded and discussed.
The required temperature in semiconductor process technology is going into two extreme directions. Either very high temperatures up to 1300 • C with very short durations in the order of a millisecond or even shorter for highest dopant activation is required, or extremely low temperatures near room temperature or slightly above are needed for forming high-quality dielectrics with minimum dopant deactivation and redistribution. This letter describes a new microwave plasma oxidation apparatus with unique features addressing the aforementioned low-temperature process. With this new technique the oxide growth rate was studied as a function of time, gaseous ambient, pressure, applied microwave power and silicon substrate parameters to determine crystallographic oxidation rate anisotropy and dopant concentration-dependent oxidation at temperatures much below 400 • C. Some tests have also been performed on doped and undoped SiGe material and on patterned structures. The plasma oxides grown on silicon have been electrically characterized regarding fixed charges, interface state densities and breakdown strength. In addition the selective oxidation regimes in the presence of various metals such as W, TiN and TaN were evaluated and determined.
The residual impurity gases in the atmospheric rapid thermal processing (RTP) equipment are becoming an important factor in sub-micron ULSI industry. For example, 1% nitrogen in oxygen decreases the RT oxide thickness, and a small amount of moisture or oxygen in nitrogen may strongly affect the RT titanium silicidation. The effective method to reduce the residual gases is to use process gas to purge the chamber. In the present paper the gas purging mechanisms were in-situ investigated in the flow rate range of 10 to 60 slpm using a Quadrapole Residual Gas Analyser (RGA) and gas sensors. The gases for purging studies are N2, O2, He and Ar. It has been found that there are two regimes in the dependence of the residual gas concentration on purging time. Based on the results of systematic experiments, a purging equation, called Pseudo-PST (“perfectly stirred tank) model, has been developed and was used to give the interpretation of the purging process in the atmospheric RTP system. The limitation of the RGA and the oxygen analyzer used to atmospheric RTP system was also discussed.
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