Mechanical and tribological properties of various doped and undoped oxide low-k materials like undoped (SiO 2 ), carbon-doped ͑SiOC͒, and fluorine-doped ͑SiOF͒ oxides are investigated by studying the removal rates at different pressure and velocity conditions. In addition to verifying the Preston equation, a comprehensive physics and statistics based model called the abrasion model is modified and validated based on experimental data. The model is derived on the basis that the material removal rate ͑MRR͒ is equal to the material removed by a single abrasive and the number of active abrasives involved in material removal. Apart from the primary factors like pressure and velocity, details like pad hardness, pad roughness, abrasive size, and abrasive size distributions are also included in the model. It is found that with the increase in pressure, MRR increases due to increase in the number of active abrasives. The model is validated by comparing the results with experimental results. The planarization of the research specimens has been carried out on a prototype of an actual CMP machine called the Universal Bench Top CMP tester.
Understanding the tribological, mechanical, and structural properties of an inorganic and organic dielectric layer in the chemical mechanical planarization (CMP) process is crucial for successful evaluation and implementation of these materials with copper metallization. Polishing behaviors of different carbon- and fluorine-doped silicon dioxide (SiO2) low dielectric constant materials in CMP process are discussed in this paper. Films were deposited using both chemical vapor deposition and spin-on method. Carbon and fluorine incorporation in the Si–O network weaken the mechanical integrity of the structure and behave differently in slurry selective to SiO2 films. Mechanical properties of the films were measured using depth-sensing nanoindentation technique, and it was found that undoped SiO2 film has the highest and spin-on carbon-doped oxide films have the lowest hardness and modulus values. Wear behavior of the doped SiO2 is studied in a typical SiO2 CMP environment, and results are analyzed and compared with those of the undoped SiO2 films. Coefficient of friction and acoustic emission signals have significant effect on the polishing behavior. Surface of the films are investigated before and after polishing using atomic force microscopy. Roughness and section analysis of the films after polishing show the variation in wear mechanism. Validation of Preston’s equation is discussed in this study. Additionally, different wear mechanisms are presented, and a two body abrasion model is proposed for the softer films.
Chemical mechanical planarization (CMP) occurs at an atomic level at the slurry/wafer interface and hence slurries and the interaction of the films and polishing pads play a critical role in the successful implementation of this process. Understanding the tribological properties of a dielectric layer in the CMP process is critical for successful evaluation and implementation of the materials. In this paper, we present the effect of tribological properties of undoped and florine doped silicon dioxide films on their CMP process. A micro-CMP tester was used to study the fundamental aspects of CMP process. We have studied the CMP process of oxides on polyurethane pads (IC1000-B4/SubaIV) with colloidal silica slurry at different conditions. The coefficient of friction (COF) and acoustic emission signal was monitored during process. The COF was measured during the process and was found to varies differently for different samples and with down force and platen roatation. The effects of machine's parameters on the polishing performance and correlation of physical phenomena with the process has been discussed.
Lower mechanical strength, reduced cohesive strength and lack of compatibility with other interconnect materials, are the major challenges involved in chemical mechanical polishing (CMP) of Cu metallization with ultra low-k materials as interlayer dielectrics. In this study we have investigated the polishing behavior of patterned Cu samples with underneath different low-k materials using two different slurries and a wide range of machine parameters. CMP micro tribometer was used to polish the samples with different rotations of platen (50 to 250 RPM) and down forces (1-6 PSI). Friction co-efficient and wear behavior were also investigated at different conditions. Optical and scanning electron microscopy was used to investigate the polished surface. It was observed that the two different Cu slurries used for polishing have marked effects on the polishing of Cu-low-k stack with respect to wear and delamination.
Ultra low-k materials used in Cu damascene process are inherently soft and weak in nature; hence the evaluation of tribological properties of these materials is an issue of paramount importance in the field of semiconductor fabrication. Chemical Mechanical Polishing (CMP) of these films is a major challenge due to their reduced modulus and cohesive strength. The objective of this research is to develop a strong understanding of the tribological properties of Cu ultra low-k dielectric materials for successful implementation in the semiconductor devices. The Cu ultra low-k systems are polished at different conditions of load and platen rotation and their polishing behavior is compared with the standard Cu-SiO2 system. The polishing behavior of Cu and the barrier Ta material is studied in order to effectively detect the end point of the Cu CMP process. Delamination studies, post process surface characterization using scanning electron microscopy and the reliability issues of these materials also come within the scope of this study.
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