The Effect of Amino Acids on Step Height Reduction in STI CMP

Shallow trench isolation (STI) process has been a crucial technology to isolate the transistors in ultra large scale integration (ULSI) device [1]. In STI process, step height of dielectric material is inevitably formed after gap-filling process due to the different pattern density. Chemical mechanical planarization (CMP) process has been employed to remove the step height. Remaining step height would cause defects such as dishing and erosion, therefore the reduction of step height can be considered as one of the critical issues in STI-CMP process.

Several groups have studied about the step height reduction using ceria due to its high removal rate of SiO₂ [2]. Lim et al. reported that the effect of particle size on step height reduction. They showed that the large particle size could improve the step height reduction by its high removal rate. Recently, the needs of small particle have been increased because the defect control has been more important as the design rule is getting narrow. Therefore,  it is inevitable to develop new methodology to enhance the step height reduction. Here, we used different amino acid to modify the surface of ceria and enhance the interaction between the ceria slurry and SiO₂.

We investigated the effect of ceria slurries prepared with L-serine, proline, glutamine and amino butyric on step height reduction. We calculated the interaction forces between ceria with different amino acids and SiO₂ film by Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The result shows that ceria slurry with L-serine or proline has higher attractive interaction forces with SiO2 than the slurry with glutamine or amino butyric acid (Fig. 1).

The results of SiO₂ pattern as different pattern density and line width show that the ceria slurry with L-serine or proline produces higher step height reduction than the slurry with glutamine or amino butyric (Fig. 2). As a result, we found that the high interaction forces between ceria slurry and SiO₂ contribute to high step height reduction and it is stronger in case of the slurry with L-serine or proline than the slurry with glutamine and amino butyric acid.