Y. Nagendra Prasad

Role of Amino-Acid Adsorption on Silica and Silicon Nitride Surfaces during STI CMP

Selectivity (oxide/nitride polish rate) is a critical factor during chemical mechanical polishing (CMP) of shallow trench isolation (STI) structure, and it can be modified by adding amino acids to the slurry. The role of adsorption of the amino acids L-proline and L-arginine, on silicon dioxide and silicon nitride surfaces was characterized as a function of pH and concentration using thermogravimetric analysis. The results suggest that the adsorption behavior does not correlate with the polishing behavior of STI CMP and hence it may not play a key role in changing the selectivity.

Analysis of Scratches Formed on Oxide Surface during Chemical Mechanical Planarization

Scratch formation on patterned oxide wafers during the chemical mechanical planarization process was investigated. Silica andceria slurries were used for polishing the experiments to observe the effect of abrasives on the scratch formation. Interleveldielectric patterned wafers were used to study the scratch dimensions, and shallow trench isolation patterned wafers were used tostudy the effect of polishing parameters, such as pressure and rotational speed head/platen . Similar shapes of scratches chattertype were observed with both types of slurries. The length of the scratch formed might be related to the period of contact betweenthe wafer and the pad. Large particles would play a significant role in increasing the number of scratches. The probability ofscratch generation is more at higher pressures due to higher friction force and removal rate. The optimization of the head to platenvelocity could decrease the number of scratches.© 2009 The Electrochemical Society. DOI: 10.1149/1.3265474 All rights reserved.Manuscript submitted August 10, 2009; revised manuscript received October 26, 2009. Published December 15, 2009.

Synthesis of Fe metal precipitated colloidal silica and its application to W chemical mechanical polishing (CMP) slurry.

The objective of this paper is to develop a new method of Fe (metal) precipitation on colloidal silica to overcome the stability problem, which would be responsible in producing defects, with commercially available fumed silica slurry containing Fe ions. The slurry was developed by using sodium silicate (Na(2)SiO(3)) as a raw material and the concentration of precipitation of metal was controlled by addition of Fe salt (Fe(NO(3))(3)). To compare the concentration of precipitated Fe with directly added Fe ions in slurry solutions, static electrochemical and peroxide decomposition experiments were performed. Although the performance of the Fe precipitation appeared to be lower than Fe ion addition during these experiments, nearly equal removal rate was observed due to the dynamic condition during polishing. The Fe precipitated colloidal silica particles at the concentration of 52ppm showed the similar W removal rate and selectivity of W to TEOS (tetraethylorthosilicate) to commercially available fumed silica slurry containing externally added Fe ions. The introduction of Fe particle precipitation on colloidal silica particles would result in a longer shelf life time and hence lower defect level in W CMP.

The Synergetic Role of Pores and Grooves of the Pad on the Scratch Formation during STI CMP

The polishing pad plays a vital role in achieving the desired removal rates and level of surface planarity during the chemical mechanical planarization (CMP) process. Generally the pad containing both pores and grooves is used for the shallow trench isolation (STI) CMP process. After polishing the wafer, many scratches would be produced on the surface, especially chatter mark scratches on the oxide surface. In this work, the role of pores and grooves of the pad on scratch formation was studied with STI-patterned wafers with three types of pads: pad with only pores, pad with only grooves, and pad with both grooves and pores. The pad with only grooves produced more irregular-shaped scratches when compared to the pad with only pores, but the length of the scratch was smaller. A regular chatter mark type scratch would be formed only when the pad contained both pores and grooves. The most likely occurring phenomenon might be the stick-slip motion during the process. The removal rates with three different pads were compared and they were inversely correlated to each other. The presence of pores would be essential to decrease the scratch number. However the scratch number could be greatly reduced with the combination of both pores and grooves. Overall, the number of scratches would be greater with the absence of pores, and the scratch number and intensity substantially reduced with the combination of both pores and grooves.

Effect of Polysilicon Wettability on Polishing and Organic Defects during CMP

This study investigated the wettability effect of polysilicon on the polishing performance and organic defect contamination during polysilicon chemical mechanical polishing (CMP). Contact angle measurement was utilized to understand the nature of polysilicon surfaces. An oxidizer, H 2 O 2 , was added to the silica slurry to modify a hydrophobic polysilicon surface to a hydrophilic surface during polishing. The adhesion force was measured between a polymeric pad particle and a poly-Si wafer surface in KOH solution (pH 11) as a function of H 2 O 2 concentration. The adhesion force of the polymeric pad particle on the polysilicon decreased from 14 to 8 nN as the peroxide concentration increased to 10 vol %, at which the surface became hydrophilic. The hydrophilization of the polysilicon surface during polishing drastically reduced the organic contamination on the polysilicon wafers after polishing. The removal rate, frictional force, and pad temperature during CMP, with and without oxidizing the surface, were measured. They all decreased with the increasing concentrations of the oxidizer. The decrease was attributed to the formation of the lubrication layer of the oxide surface due to the oxidation of polysilicon.

Effect of Alkaline pH on Polishing and Etching of Single and Polycrystalline Silicon

In this paper, the polishing and etching behavior of single and polycrystalline silicon were studied. Prior to chemical mechanical polishing (CMP) process, the surfaces were treated with dilute hydrofluoric acid (DHF) to remove native oxides. The surface analysis shows that the poly contains trace amount of oxygen even after DHF treatment. The static and dynamic etch rates, and removal rates were measured as a function of slurry pH. The single silicon showed a higher static etch rate than the poly. After static etch rate measurements, poly showed higher surface roughness and more hydrophilic which indicates that the surface of poly is different from single crystal silicon. The friction force between pad and substrate and pad temperature was also measured as a function of pH during polishing in order to get more understanding of polishing process. At all the pH values being investigated, poly showed lower dynamic and removal rates, higher friction force and higher temperature. This indicates that the removal of poly in CMP is predominantly by mechanical actions. Also, these results, suggest a mechanism in which the oxygen present in the poly grain boundaries strongly influences the etching and removal mechanism.