| Summary: | 碩士 === 中興大學 === 材料工程學系所 === 94 === This research mainly employs electrochemical methods under alkaline, acid, and neutral electrolytes to strip the chromium nitride thin films that were deposited by cathodic arc plasma technique on Si wafer (CrN/Si). Moreover, the CrN coated on 304 stainless steel substrate (CrN/SUS304) also strpped on same conditions for comparison. The galvanostatic method is applied to observe the shortest completely stripping time and investigate the influences of stripping rate and stripping results in different concentration of KOH, H2SO4, and Na2SO4 solutions. In addition, a mathematical expression is also utilized to analyze the relationship between film thickness, electrolyte concentration, and stripping time. The results indicate that CrN films can be completely stripped in KOH, H2SO4, and Na2SO4 solutions. It has never used neutral solution to strip the coated films in correlated reports. It is not only satisfied the protection of environment but also the operation safety, hence, should possess good industrial potential.
The shortest completely stripping time (tc) could be obtained from the relation of responded potential and stripping time. Because of the resistivity of Si is much higher then CrN. It makes the potential to change obviously during stripping CrN/Si process. We can easily control the stripping completely without attacking Si wafer by stop the power source when the potential start rising. The thickness of CrN films decreases as stripping time increases in all stripping process. The relation between these two factors could be described as L/L0 = 1-(t/tc)n and L-L0=-kt. The n and k value can be regarded as stripping mechanism and the stripping rate, respectively. It obtained n value approximate 0.6~1.3 that may indicate the CrN films has a similar stripping mechanism in deferent solutions. Moreover, the smallest k value that represents the stripping rate of CrN films is the slowest is observed in strong alkaline solution (1M KOH). On the other hand, during stripping the CrN/SUS304, it also obtained the shortest completely stripping time from the change of potential. Because of SUS304 and CrN are both conductors with similar resistivity. It makes that the potential changes obviously just in some solution. After the stripping process done, it still has a little residue stick on the surface of SUS304 substrate. It may need longer time to strip completely. And the surface of SUS304 has different extent of corrosion. It may be the SUS304 is a metal with Cr (18%) that is easily attack. Of the total, it has little corrosion in 1M KOH solution, it may be because that produces a passive film on surface. Additionally, this method can also completely strip the CrN thin films that were deposited by unbalance magnetron sputtering on Si wafer.
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