| Summary: | 碩士 === 國立交通大學 === 材料科學與工程系 === 88 === In order to overcome sever limitation of DOP (deep of focus) in deep sub-micro lithography would be necessary to eliminate surface topography a globe planarization technology only by CMP. And based on the problem of RC delay, Cu process must be the major tendency for deep-submicro semiconductor manufacturing; and Cu-CMP takes an important role.
Material polished by Cu CMP contains upper copper film and diffusion barrier layer. Because of differences of material properties, it's difficult to use a single slurry to remove copper barrier layer and stop on the underlying dielectric. In the past, it does not work well especially in the removal selectivity of copper to barrier layer. Thus, it is an avenue for Cu-CMP research.
In our study, we major focus on the polishing behavior and mechanism of various additives to our abrasive and wafers, which contain copper, oxide, and tantalum films.
A different abrasive "colloidal silica " is adopted here. It has four advantages, high activity, well dispersion, smaller particle size, and cheaper as abrasives of CMP.
In this search, the polishing behavior of CMP is deeply involved by slurry pH and the surface-charge-related interactions between the slurry and polishing surface. The slurry pH of slurries is an important factor of removal rate. Because in different pH value, the films of metal or silica will has different phases and lead different removal behaviors. Besides, the solubility of metal, metal oxide and silica depended on pH value.
The surface-charge-related interactions between the slurry and polishing surface is related to the pH. Besides, the collision frequency of abrasive and the surface of wafer affects by the attraction and expulsive Force. It will depend on adsorption of cations and ion strength of slurry.
So, in KOH added slurry has the smaller size of cations and complete dissolution constant than TMAH, NH4OH to reduce the width of diffusion layer; increase collision frequency and then get higher removal rate.
Carboxylic acids form complexeing of copper in acid solution, and lead to the increase of copper film removal rate. But it is not the same in slurries taking HNO3 as oxidizer. With increasing the citric acid concentration in slurry, the removal rate of copper is decreasing. Based on citric acid inhibits the removal rate of copper by forming a passivation layer of CuO, Cu2O, Cu(OH)2.
Combined all result, we can use this colloidal based slurries to achieve high or low any selectivity during all polishing step in Cu CMP just adding proper different alkaline and organic solution.
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