| Summary: | 博士 === 國立交通大學 === 材料科學與工程系所 === 97 === Fluorine-doped silicon oxide film (SiOF) has been found to be very effective in the reduction of dielectric constant and has been widely used in the manufacturing of deep-submicron integrated circuits (IC). However, the film stability of low-k fluorinated silicon oxides (SiOF) is an important issue. The instability of the films may be due to metal corrosion, dielectric etching and the reaction product formation, caused by moisture attack and fluorine degassing during operation. The process includes SiOF film deposition by plasma enhanced chemical vapor deposition (PECVD) under 2 Torr pressure with SiH4, SiF4 and N2O as reactant gases. The purposes of this work are to modify the conventional processes and to examine its structure evolution and the corresponding stability problems, and followed by examining effect of post N2O plasma treatment. The structure evolutions of the films and their stabilities in each process step were characterized by air exposure testing under various humidities and then IC compatibility testing. The optical, mechanical and electrical properties of the films were also evaluated. From the experimental results, the following conclusions can be drawn:
For the as-deposited SiOF films, the results of air exposure testing indicate that the film is unstable in air atmosphere and a serious F degassing near the film surface by exposing to air with higher humidities. Furthermore, the surface F degassing combining with higher humidities in air shows a great tendency to form the reaction products and HF acid to seriously etch the film. In other words, the greater F% in the as-deposited film can result in more the reaction products formation and acid attack, as indicated by SIMS, XPS, FTIR and Raman bonding analyses. In consequence, the bonding configuration reconstruction due to F degassing may lead to more porous microstructure, so a slightly degraded mechanical strength, higher HF acid etching rate, higher leakage current and lower breakdown voltage will result, although a slight increase in k value will occur due to presence of moisture and loss of F%.
For the post plasma treated SiOF films, the results show that the the reaction products are not detectable by 14 hours air exposure under 80% relative humidity. From surface analyses of XPS, the plasma-treated SiOF films appeal to be an oxidized surface with depletion in F and rich in O. These oxidized films with greater atomic density may form an effective case or surface barriers to prevent moisture penetration and F from degassing. In other words, except the surface, there are no significant structure changes and so properties changes within the films under various air exposure testing conditions. Therefore, it is noted that the refractive index, dielectric constant and bonding FTIR spectra indicate no significant variations for the post N2O plasma-treated SiOF films. In summary, the post N2O plasma treatment is an effective IC compatible process which can maintain various excellent properties of the low-k SiOF films and minimize the reaction product formation, and so enhance the stability of the devices to prolong their life.
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