| Summary: | 碩士 === 國立勤益科技大學 === 化工與材料工程系 === 106 === The high-power and high-frequency electronic devices made with silicon carbide is better than Si based devices, because silicon carbide wafer possess reduced switch losses, higher charge carrier mobility, higher power density, better heat dissipation and increased band width capability, therefore silicon carbide wafer(SiC) is the best choice to apply in electric car、renewable energy、high frequency communication, and etc.
But Silicon carbide wafer always can be found defect. Because, crystal growth process will happen temperature gradient and corrosion in the silicon carbide wafer, that lead to the silicon carbide crystal defect. So we try to form a graphite film via heat Polyimide film to 2200 ℃ on back surface of the SiC wafer, the purpose is to decrease defect when growth process.
In this study, I have five step: (1) Polyimide characterization and Modification ; (2) Characterization of silane coupling agent/polyimide coating on sic wafer ; (3) Characterization of silane coupling agent/polyimide coating on sic wafer after carbonization ; (4) Characterization of silane coupling agent/polyimide coating on sic wafer after graphitization ; (5) Characterization of graphitization degree.
Part I: Polyimide characterization and Modification
Silane coupling agent was used to modify polyimide, so silane coupling agent/polyimide film could be evaluated by FTIR, furthermore TGA was used to evaluate the residue rates of curves. In our study, the residual rate of the four polyimides was found to be over than 50%. The thermal expansion coefficient of BPDA-PDA was 3 (ppm/°C) and PMDA-ODA was 33 (ppm/°C) by TMA.
PartⅡ: Characterization of silane/polyimide coating on sic wafer
The second part is the silane coupling agent/polyimide coating on the sic wafer and then, the white light interferometer could use to observe the surface, the results showed that the polyimide cover the whole wafer’s surface and polyimide’s surface is very smooth. In the adhesion test, silane coupling agent/polyimide have good adhesion on the sic wafer, polyimide without silane coupling agent will not.
PartⅢ: Characterization of silane coupling agent/polyimide coating on sic wafer after carbonization
The third part is carbonization test of silane coupling agent/polyimide coating on sic wafer, the results showed the polyimide with NO.1 agent (3-Aminopropyl)trimethoxysilane (APrTMOS) is best in the storage test. So I choose APrTMOS to finish experiment. However, PMDA-ODA-1 is rougher than BPDA-PDA-1, moreover, cross section of PMDA-ODA-1 is a loose layer structure, as observed by white light interferometer and SEM.
PartⅣ: Characterization of silane coupling agent/polyimide coating on sic wafer after graphitization
The fourth part is graphitization test of silane coupling agent /polyimide coating on sic wafer, after rearrangement the surface like balloon leak out the gas, we can observe same phenomenon between the white light interferometer and SEM. The cross-section SEM image of PMDA-ODA-1 showed the Interlamellar spacing is smaller than carbonization after graphitization. On the other hand, the BPDA-PDA-1 after graphitization the surface damage seriously, such as wave.
PartⅤ: Characterization of graphitization degree
The fifth part was used X-ray photoelectron spectroscopy (XPS)、four-point probe、 X-ray diffraction (XRD)、Raman spectroscopy (Raman) to evaluate the graphitization of PMDA-ODA-1 and BPDA-PDA-1, the result of XPS showed the 94.32% of Carbon、1.97% of silicon、3.71% of oxygen in the graphitization of PMDA-ODA-1 film.
The result of four-point probe showed the PMDA-ODA-1 and BPDA-PDA-1’s sheet resistance dropped dramatically to 0.2029 and 0.7715(Ω/□) after graphitization. Finally, used XRD and Raman to calculate the graphitization degree of PMDA-ODA-1 and BPDA-PDA-1, the result showed the BPDA-PDA-1 only have 30.23%, however, the graphitization degree of PMDA-ODA-1 was up to 100 %. On the other hand, we almost could find the D-band that was mean PMDA-ODA-1 have very high graphitization degree. Therefore, I choose PMDA-ODA-1 to be the Precursor in our study.
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