Post-annealing process

The properties of PPS are strongly influenced by the degree of crystallinity, which is optimized by hot processing and post-annealing. 

In contrast to the dry methods, there are other conventional methods related to post heat treatment from precipitates from the aqueous solutions. The ambient aqueous routes and the hydrothermal methods at elevated temperature usually lead to rare earth precipitates like hydroxides, carbonates, instead of oxides. In fact, the hydrothermal treatment of rare earth oxide powders results in a hydration process to form hydroxides. Subsequently, the precursor could be used to produce rare earth oxide nanocrystals with post annealing at varied temperatures and in appropriate atmosphere. 

When solid state (Ba,Sr)C03 and TiO are formed, the formation of (Ba, Sr)Ti03 from these two phases by solid state reaction usually requires a temperature higher than 1100°C, which is unacceptable in the DRAM capacitor process. One factor to consider is that the actual chemical bond status of the carbon in the films may not be that of stable (Ba, Sr)C03 but can be more unstable which renders the elimination of the carbon or related impurities more feasible by a proper post-annealing than thermodynamics predicts. One must consider the atmosphere and surface status of the films during the aimealing... 

MOCVD process as well as the oxidation problem of the diffusion barrier, the low temperature MOCVD process is required which usually results in amorphous or weekly crystallized as-deposited thin films. Therefore, high temperature post-annealing is an absolute necessity. The upper limit temperature of the post-annealing is about 800°C considering the interdiffusion between the BST and electrodes at higher temperature and process integration issues such as degradation of the metal contact resistance. 

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