Prepareation And Characterization Of Zr-Based Getter Film

With the technology trend of increased miniaturization and integration of MEMS devices, maintaining the needed vacuum level in such packages for the entire MEMS device life becomes a real technical challenge due to the very high surface to volume ratio. The most common and technically accepted way to maintain a controlled ambient environment in a hermetically sealed MEMS device is to use a non-evaporable getter(NEG) capable of chemically absorbing active gasses. However, conventional getters used in vacuum devices, could not be used in these minimizing MEMS devices due to the restricted space and high activation temperature. It is urgently required to develop the highly porous thin-film-type getters with several μm thickness for the applications of MEMS vacuum devices. Researches abroad on miniaturizing the vacuum packaging of MEMS devices based on NEG film for vacuum maintenance have been carried out for a long time, and great progress has been achieved both in the academic research and engineering applications. Domestic researches on NEG film have only been carried out recently and rarely reported. There will be important academic and engineering significance to strengthen our country independent innovation in the field of NEG film.In this paper, a ZrCoCe alloy is selected as getter material. Magnetron sputtering method is employed to deposite the ZrCoCe film. The film structure characteristics and sorption properties depending on various deposition parameters are investigated. The effective way to optimize the sorption properties of the film is explored. The activation mechanism for this film is studied. The practical performance of the film is evaluated. The specific research work and the main conclusions are as follows.(1) Highly porous ZrCoCe films are deposited on silicon substrates by magnetron sputtering. Film morphology and performance dependence on power supply, deposition pressure, substrate temperature, glancing angle and working gas flow are investigated. DC magnetron sputtering has been proved a more ef?cient way to produce ZrCoCe film with isolated columnar-like structure as compared to ordinary RF magnetron sputtering. It has been found that the film structure and morphology of ZrCoCe getter films are significantly influenced by the pressure of the Ar sputtering gas and substrate temperature. Relatively high sputtering pressure and substrate temperature is more advantageous to obtain porous membrane of columnar structure. The specific surface area and proisty of the films increases with the increase of glancing angle, as well as the effect of self-shadowing by the initial nuclei on the substrate surface and the number of columnar structure. The deposition rates and roughness of the films increase with the increase of Ar gas flow, resulting in larger specific surface area and better sorption performance than that of others. The relatively ideal sorption performance are obtained with production parameters of 150 ℃, 3 Pa, 70 ° and 45 sccm, shows a high initial sorption speed of 238 cm3·s-1·cm-2 after activated at 300 ℃ for 30 min.(2) The effect of substrate outgassing on sorption properties of the film is investigated. It reveals that the residual active substrate adsorption gases is one of the important reasons leading to the poison of the film during activation process. In order to study the relationship between the film structure and sorption performance, a multi-layed ZrCoCe film consisted of barrier layer and protection layer respectively, are designed and prepared. It shows that proisty and sorption properties of the films can be clearly improved by depositing a compact barrier layer of ZrCoCe. The same effect can also be obtained by depositing a layer of a substantially nonreactive material of Ni, which plays an important role as a protection layer against oxidation.(3) Influence of activation temperature and repeated activation on structure and sorption properties, as well as the capability withstanding wafer cleaning processes and air-exposure of ZrCoCe films, are studied based on the research of MEMS vacuum packaging. It shows that the porous ZrCoCe film can be activated at 300~400 ℃ for 30 min and demonstrates excellent stable hydrogen sorption properties. Low activation temperature mainly leads to the reduction of surface passivation, while crystalline structure has no obvious change and sorption performance is relatively low. High activation temperature can not only change the surface chemical activity, but also affect the microcrystalline structure, and leads to further improvement of the film sorption performance. The initial sorption speed of the ZrCoCe film increases by about 23% and 57% after treated with isopropanol and argon ion sputtering, indicating its good capability of cleaning resistance. Sorption properties significantly decreased with the extension of air-exposure time and the initial sorption speed decreases to 30.6% of the initial one after 50 days air-exposure.(4) During the activation process of ZrCoCe film, the variation for its surface chemical composition, valence and residual gases in the vacuum chamber was first studied by X-ray photoelectron spectroscopy(XPS) and Quadrupole Mass Spectroscopy(QMS), respectively. It reveals that the surface layer of the air-exposed ZrCoCe film was covered with H2 O, CO2 and hydrocarbons, both Zr and Ce exist in the oxidized state, and zirconium oxide starts to reduce at 250 ℃. The activation also results in a sizable Co segregation on the film surface and the formation of zirconium carbide in the subsurface region of the film. H2 O, CO2 and hydrocarbons sequentially desorb from the film surface with the increase of activation temperature. H2 is the main gas which desorbs above 200 ℃ and O2 is not found in the activation process. ZO2 is reduced to near-metallic or metallic state because O in ZO2 leaves the film surface through diffusing into film bulk.