Sang-Yeob Han

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 Poly Silicon Wettability on Polymeric Residue Contamination

The planarization has been implemented on the IC manufacturing such as a DRAM process including the shallow trench isolation (STI) and the self aligned memory cell contact pad (SAC) process. Poly silicon CMP has also been implemented to reduce the step height of gate poly Si in the construction of RCAT (recess channel array transistor) and FinFET three dimension structures. Poly silicon CMP uses either the same or similar pads or slurries as those for oxide CMP. Poly Si CMP is consecutively used in order to form self aligned memory cell contact pad [1]. The adhesion and removal rate of the polymeric residues was investigated as a function of wettability of the poly silicon surface during poly silicon CMP process. An oxidizer makes more hydrophilic poly silicon wafer surface and acts as a function of oxidant on the poly silicon surface in the DI water. Adhesion force between pad particle and poly silicon wafer decreased and saturated as a function of concentration of solution A, as an oxidizer. Figure 1 shows the contact angle of poly surface in the DI (Deionized) water as a function of concentration of solution A as an oxidizer. Contact angles of poly Si surface decreased from 69° to 23° as the concentration of solution A increases to 10 vol% and then reaches a constant value. A high contact angle indicates poor surface wetting while a low angle shows good wetting. The solution A acts as a surface oxidant on the poly Si surface and makes more hydrophilic surface in the DI water. The adhesion force of pad particle on the poly Si wafer surfaces was measured in the KOH solution (pH 11) as a function of solution A concentration. KOH was used for alkaline based slurry of poly silicon polishing and solution A was added in the KOH based solution in order to control the wettability of the poly silicon surface. Adhesion force decreased and saturated as a function of concentration of Solution A. When solution A was added to slurry, the poly silicon surface became hydrophilic due to oxidation reaction of silicon by Solution A. The change of surface wettability affects the order of contamination level on wafer because the interactions between particles and substrates are dependent on the wettability of the surface [2]. Figure 2 shows the changes of the contact angle of poly silicon in the alkaline silica based slurry solution as a function of solution A concentration. Complete wetting behavior was observed below 10° in the mixture solutions of the commercial alkaline based fumed oxide slurry and solution A. However, the only KOH based solution was not sufficient to make complete wetting on the hydrophobic poly silicon surface as shown in Fig 2. The polymeric particle contamination on poly silicon surface wafer in the KOH solution as a function of solution A concentration as show in Fig. 3. In case of KOH solution, polymeric particle was contaminated on poly silicon surface. However, if added the solution A in KOH based solution that not generated the contaminated on poly silicon wafer surface. So, the control of poly silicon wettability during polishing could reduce the attraction force of organic particles thus leads to a lower organic defects after CMP. Much more pad particles with water marks were observed at hydrophobic poly silicon surface than hydrophilic. The mechanism of wettability and high adhesion force of hydrophobic surfaces indicates that the controlling of the wettability of wafer surface played an important role in the adhesion and remove force organic residues on the poly silicon surface. The control of poly silicon wettability during polishing could reduce the attraction force of organic particles thus leads to a lower organic defects after CMP.

Effect of Wettability of Poly Silicon on CMP Behavior

The hydrophobicity of poly Si is reported to introduce different polishing behavior with careful control of post CMP cleaning process. The purpose of this study was to investigate the effect of poly Si wettability on its CMP behavior. The adhesion force of polymeric particle on the poly Si wafer surfaces was measured in the KOH solution (pH 11) as a function of solution A concentration. Adhesion force decreased and saturated as a function of concentration of solution A. The change of surface wettability affects not only the polishing rates but also the level of contamination on wafer because the interactions between particles and substrates are dependent on the wettability of the surface. Also, hydrophobic poly Si surfaces attracted much more pad particles with water marks than hydrophilic