Young-Jae Kang

Effect of Sodium Periodate in Alumina-Based Slurry on Ru CMP for Metal–Insulator–Metal Capacitor

In this study, a ruthenium (Ru) chemical mechanical planarization (CMP) slurry was developed and characterized to fabricate Ru bottom electrodes in capacitor structures. Sodium periodate (NaIO 4 ) was chosen as both the oxidant and etchant due to its strong oxidizing power. The effect of NaIO 4 on Ru etching and polishing behaviors was investigated as a function of its concentration and polishing condition. The largest removal rate of 70 nm/min was obtained in a slurry of 0.1 M NaIO 4 and 2 wt % alumina particles at pH 9 and a polishing pressure of 4 psi. Planarization and isolation of each capacitor was successfully performed with the developed Ru slurry.

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.

Laser Shock Removal of Nanoparticles from Si Capping Layer of Extreme Ultraviolet Lithography Masks

A new dry laser shock wave generated by a Nd:YAG laser was applied to remove nanosized polystyrene latex (PSL) particles on the silicon capping layer of an extreme ultraviolet lithography (EUVL) mask. UV laser was irradiated on the surface before irradiation with laser shock waves to increase the removal efficiency of the organic PSL particles. Owing to the expected damage to the surfaces, the energy of the UV laser was reduced to 8 mJ and the gap distance between the laser shock wave and the surface was increased to 10.5 mm. UV irradiation alone resulted in the removal of 50% of the particles. Exposure to the UV laser three times increased the removal efficiency to 70%. Over 95% particle removal efficiency was found when a laser shock wave was combined with the UV laser. However, the removal efficiency of the particles was below 25% by laser shock wave cleaning alone. Enhanced removal efficiency by UV laser irradiation may be attributed to the photothermal and chemical effects of UV light on the organic PSL particles.

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 Corrosion Inhibitor, Benzotriazole, in Cu Slurry on Cu Polishing

In this study, the effect of benzotriazole (BTA) in Cu slurry on Cu polishing behavior was investigated as functions of H2O2 and slurry pH. The addition of BTA to slurry effectively prevented Cu from being etched by forming a passivation layer of Cu–BTA regardless of pH and H2O2 concentration in the slurry. The passivation layer on the Cu wafer exhibited a contact angle of 50° in solution with BTA and H2O2. The dynamic etching rate, i.e., the Cu polishing rate using abrasive-free slurry, also decreased when BTA was added to the slurry at pH 2, 4, and 6. The removal rate of Cu in slurry without BTA was strongly dependent on H2O2 concentration and pH. In slurry with BTA, Cu–BTA on the Cu surface prevented the etching of Cu. At pH 2 and 4, the removal rates were lower in slurry with BTA than in slurry without BTA. However, slurries of pH 6 or higher with BTA showed higher removal rates at higher concentrations of H2O2 than 10%, which was explained by the thick passivating oxide layer formed at higher pH and H2O2 concentrations.

Effect of Polish By-Products on Copper Chemical Mechanical Polishing Behavior

The stains on the pad caused by polishing by-products can be observed in a copper chemical and mechanical polishing (CMP) process. In this study, the effects of stains on CMP performance such as erosion, dishing, and nonuniformity were evaluated as a function of the degree of stains accumulated on the pad. The stains on the pad deteriorate the nonuniformity of removal rate and result in the increase in erosion and dishing. CMP by-products adhere on both pores and grooves of the pad and block the flow of slurry through the grooves, resulting in the deterioration of nonuniformity. The selectivity (ratio of removal rate, Cu to TaN or dielectric film) is important in order to minimize erosion. When wafers were polished on a stained pad, the removal rate of Cu decreased ∼ 30% due to the poor slurry distribution and the selectivity decreased more than 40% because the mechanical abrasion was enhanced by the presence of by-products on pad surfaces. The lower the selectivity, the higher the level of erosion on the polished patterned wafers. The higher frictional force on a stained pad results in higher temperature and etch rate of Cu which might be the reason for recess and dishing of Cu lines.

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.

The Effect of Hydrogen Peroxide on Frictional and Thermal Behaviors in a Citric Acid-Based Copper Chemical Mechanical Planarization Slurry

The effect of H2O2 on the frictional and thermal behaviors of a citric acid-based slurry was characterized during Cu polishing. As the H2O2 concentration increased, the static and dynamic etching rates gradually decreased. The removal rate of Cu initially increased and reached the maximum value at a slurry concentration of 5 vol % H2O2 after which the removal rate gradually decreased with further increases in H2O2 due to the formation of a thick Cu oxide layer. The frictional force gradually decreased with increased H2O2 concentration. The friction force was high in spite of the low removal rate in the 1 vol % H2O2 slurry. The pad temperature changed as a function of H2O2 concentration in a manner similar to at that of the friction force. The higher pad temperature resulted in higher static etching and corrosion rates of Cu during polishing.

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