The Flatness Technology Of Semiconductor Surface And Study Of Advanced Bran-New Wet Cleaning Methods

In accordance with Moore's law, the integration of ULSI circuit has been advanced, and Metal Oxide Silicon Field-Effect-Transistor (MOSFET) has been miniaturized. As the miniaturization, new problems have been appeared, one of which is the interface micro roughness between gate insulator and Si surface that causes large flicker noise (1/f noise) and degradation of circuit drivability in MOSFET. Therefore, we should develop new technologies to solve these problems.According to research, MOSFET owning the atomically flat gate insulator and atomically flat silicon surface is able to exhibit much better performance than manufactured on the traditional wafer, especially the higher mobility of carrier and much lower noise. Moreover, due to the much higher mobility of hole at the surface (110) and (551), MOSFET manufactured at these special crystal wafers have admirably application foreground. Then, it is also need to find the flat methods for these unordinary wafers. In the thesis, according to looking for the best methods which are separately applicable to flatten Si(100), Si(110) and Si(551), the flatness mechanisms of different flat methods are investigated, including the traditional wet oxidation, chemical flatness and bran-new radical oxidation.On the other hand, annealed in argon ambient at 1200℃, the surface of silicon wafer crystal orientation of which is 100 becomes atomically flat. In order to keep the atomic flatness during process, it is necessary to find the optimized cleaning method which is not apt to deteriorate the surface roughness before gate insulator manufactured. With the flat wafers including Si(100), Si (110), Si(551) and the atomic flat wafer, after cleaned by the representative solutions separately in the traditional RCA cleaning and the new cleaning method called 5-step room temperature cleaning which has been brought out by Prof. T. Ohmi of Tohoku University in Japan, the surface roughness is measured by Atomic Force Microscopy (AFM) to find the best cleaning methods and the mechanisms. Moreover, the same experiments are also carried out separately in air ambient and nitrogen ambient without any light irradiation, in which oxygen concentration is below 20ppb. According to experiments, it is found that the cleaning conditions have effects on surface roughness. After comparing the changes of roughness, the best cleaning condition is found. Furthermore, according to the experiments, light has effects on the roughness during cleaning. In order to study the origins, the effects of different wavelengths and light densities on the roughness are also investigated. During experiments, the blue light of short wavelength and red light whose wavelength is much longer with different light densities respectively are separately used to find the changes of the roughness. Finally, the relationship between light and surface roughness during cleaning is found.According to experiments above, a new mode cleaning method which is able to maintain the surface flatness of atomically flat wafers and unordinary wafers is found, and themechanisms are also discussed.