Acidic Slurry Research Articles

Effects of N-Face Finishing on Geometry of Double-Side Polished GaN Substrate

Difficulties involved in producing Double-Side Polished (DSP) GaN substrate are extracted and approaches to overcoming them are reported in this paper. Mechanical polishing with a neutral diamond slurry of pH 7.0 for the N-face and CMP for the Ga-face are widely applied to obtain DSP GaN substrates. Accordingly, the substrate exhibits transparency. However, this is accompanied by approximately 100 µm of bowing due to the Twyman effect. In this paper, the reduction of the substrate bowing to 10 µm is successfully achieved through the use of an acidic diamond slurry with a pH of 1.8 instead of a neutral slurry. Cathode luminescence reveals that an acidic diamond slurry also induces less subsurface damage in the N-face than does the neutral one. We conclude that the stress on the N-face induced by the subsurface damage in the case of polishing with an acidic diamond slurry comes closer to that of the Gaface finished via CMP.

Chemical roles on Cu-slurry interface during copper chemical mechanical planarization

In order to optimize the existing slurry for low down-pressure chemical mechanical polishing/planarization (CMP), copper CMP was conducted in H2O2 based slurries with benzotriazole (BTA) and glycine at different pH values. The film composition was investigated by the Nano Hardness Tester and XPS tests. Furthermore, the film structure forming on the copper surface at different pH values was investigated by adopting electrochemical impedance spectroscopy (EIS) technology. In the acidic slurry, discontinuous and porous BTA film covering the Cu/Cu2O surface enhanced the mechanical effect during Cu CMP process, resulted in highest CMP removal rate. In neutral slurry, the lowest CMP removal rate and static corrosion rate were resulted from compacted passivation film on the copper surface. In the alkaline slurry, the mechanical effect was limited by the rapid chemical dissolution. The results will benefit optimization of the slurry and operate conditions during low down-pressure CMP process.

Effect of the Hydrogen Peroxide on the Ti0.4Sb2Te3 Chemical Mechanical Polishing in Acidic Slurry

In this work, chemical mechanical polishing (CMP) of Ti0.4Sb2Te3 (TST) was investigated in the presense of hydrogen peroxide (H2O2) as an oxidizer. The polishing rate of TST reached a maximum at 0.5 wt% H2O2 concentration and then decreased with a further increase in H2O2 concentration. The eletrochemical techniques were applied to investigate the passivation behabivor of the TST under static conditons at pH 2.3 with varying H2O2 concentrations. The TST static etched surface morphology indicated that there were strong chemical reactions taking place between TST surface and H2O2 at 0.5 wt% H2O2 concentration. With the H2O2 concentration further increasing, the chemical reactions were inhibited by the passivation behavior, which was obtained using eletrochemical techniques. In addition, the surface compounds of the TST in the presence of H2O2 were analyzed by the X-ray photoelectron spectroscope (XPS). Finally, Atomic Force Microscope (AFM) was used to characterize the surface quality after CMP. By combining the experimental results, we proposed a possible mechanism of TST in the presence of H2O2.

Multi-variable Control for HPAL Using Nonlinear Multivariable Decoupling PID Control based on Predictive Model

High pressure acid leaching process is the use of strong acid slurry in the high temperature & pressure conditions, and acid leaching to useful metal ions process. It is a typical multiple-input multiple-output system. The efficiency of acid leaching is sensitively influenced by temperature, pressure and level of the autoclave, and in general the single loop PI method is always adopted for designing each loop controller. But due to the coupling effects among those variables, the method cannot control the temperature, pressure and level stable, which result in the decrease of efficiency of acid leaching. By analyzing high pressure acid leaching characteristics a nonlinear decoupling predictive control approach is employed based on mechanistic models established. The method has been successful applied to a real large-scale abroad nickel hydroxide cobalt smelt plant. The results demonstrate that the method can effectively and steadily control the temperature, pressure and level of the autoclave at their targets nearby, and improve the efficiency of acid leaching.

A multifunctional device to simulate oral ageing: the “Rub&Roll”

This article describes an in vitro fatigue and/or wear simulator enabling controlled application of force, speed, type of liquids and duration, to mimic challenges representative for the human oral environment.The device consists of a container in which a cylinder with specimen holder is placed which drives another cylinder (rod). The rod rotates in an opposite direction to the rotation of the stirring motor, rolling over the specimens mounted in the cylinder. When the rod contacts the specimen a force is applied to mimic processes in the oral environment. The design, working and construction principles of a new device, the Rub&Roll, and some of the possible applications are described Four different application examples are presented: occlusal wear in an low acidic abrasive slurry; combined erosive and abrasive wear of enamel exposed to apple juice or apple pulp; the wear of sealant material in natural teeth in an abrasive slurry; and the influence of mechanical loading cycles on micro tensile bond strength of an adhesive system to dentin Application of the “Rub & Roll” device showed results which are clinically relevant, reproducible and in accordance with existing literature. ConclusionsThe Rub&Roll enables controlled application of chemical and mechanical loading, allowing variation of force, sliding distance, velocity, number of cycles, and frequency, and a combination with erosive and abrasive challenges representative of those in the oral environment.

Planarization mechanism of alkaline copper CMP slurry based on chemical mechanical kinetics

The planarization mechanism of alkaline copper slurry is studied in the chemical mechanical polishing (CMP) process from the perspective of chemical mechanical kinetics. Different from the international dominant acidic copper slurry, the copper slurry used in this research adopted the way of alkaline technology based on complexation. According to the passivation property of copper in alkaline conditions, the protection of copper film at the concave position on a copper pattern wafer surface can be achieved without the corrosion inhibitors such as benzotriazole (BTA), by which the problems caused by BTA can be avoided. Through the experiments and theories research, the chemical mechanical kinetics theory of copper removal in alkaline CMP conditions was proposed. Based on the chemical mechanical kinetics theory, the planarization mechanism of alkaline copper slurry was established. In alkaline CMP conditions, the complexation reaction between chelating agent and copper ions needs to break through the reaction barrier. The kinetic energy at the concave position should be lower than the complexation reaction barrier, which is the key to achieve planarization.

Effect of pH on Hard Disk Substrate Polishing in Glycine-Hydrogen Peroxide System Abrasive-Free Slurry

The effect of pH on the material removal rate (MRR) and surface roughness (Ra) of hard disk substrate in glycine–hydrogen peroxide system abrasive-free slurry was investigated. The results show that, the MRR of hard disk substrate increases when both glycine and H2O2 are used in acidic slurries (pH=3.0) and decreases drastically in alkaline slurries (pH=10.0). The Ra of hard disk substrates is small in acidic slurries and increases drastically in alkaline slurries. Further, the effects of glycine, H2O2, and solution pH on hard disk removal were investigated by auger electron spectroscopy (AES), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. We also develop a reaction scheme describing the surface chemistry of the hard disk in this system.

Chemical mechanical planarization of amorphous Ge2Sb2Te5 with a soft pad

Chemical mechanical planarization (CMP) of amorphous Ge2Sb2Te5 (a-GST) is investigated using two typical soft pads (politex REG and AT) in acidic slurry. After CMP, it is found that the removal rate (RR) of a-GST increases with an increase of runs number for both pads. However, it achieves the higher RR and better surface quality of a-GST for an AT pad. The in-situ sheet resistance (Rs) measure shows the higher Rs of a-GST polishing can be gained after CMP using both pads and the high Rs is beneficial to lower the reset current for the PCM cells. In order to find the root cause of the different RR of a-GST polishing with different pads, the surface morphology and characteristics of both new and used pads are analyzed, it shows that the AT pad has smaller porosity size and more pore counts than that of the REG pad, and thus the AT pad can transport more fresh slurry to the reaction interface between the pad and a-GST, which results in the high RR of a-GST due to enhanced chemical reaction.

Effect of iron(III) nitrate concentration on tungsten chemical-mechanical-planarization performance

Investigating the catalytic effect of Fe(NO3)3 on the performance of tungsten (W) chemical mechanical planarization in H2O2-based acidic slurries, we found that the trend of the polishing rate with increasing Fe(NO3)3 concentration was divided into two regions. The polishing rate in region I (<0.10wt%) increased rapidly because of the increase of the WO3 layer formed by the reaction of Fe(NO3)3 and H2O2. The polishing rate in region II (>0.10wt%), on the other hand, increased only slightly with increasing Fe(NO3)3 concentration. We suggest the excess ferric ions in the slurry were rapidly supplied to the W surface. Consequently, the addition of Fe(NO3)3 resulted in the rapid formation of the WO3 layer because of the decomposition of H2O2 into O2 by Fe3+ ion, and polishing rate increased with the Fe(NO3)3 concentration. This polishing trend was explained through the opposite trend of static etch rate, the confirmation of the surface morphology, the trend of the WO3 content on the W surface, and the trend of the corrosion potential and the corrosion current density.

Corrosion behaviour of 316L stainless steel in PTA slurry

The corrosion behaviour of 316L stainless steel (SS) in acetic–10% formic acid mixture containing Br− and in simulated purified terephthalic acid (PTA) slurry was investigated to understand the corrosion mechanism of 316L SS in the drying process of PTA slurry. The results show that in acetic–10% formic acid mixture containing Br−, the corrosion rate of 316L SS increases with the increase in Br− concentration and temperature. In the PTA slurry, the corrosion rate of 316L SS changes in a parabolic form with an increase in the solid/liquid ratio of the slurry. The slurry has the strongest corrosivity when the solid/liquid ratio of the slurry reaches ̃6·25. In a half dry–half wet PTA slurry, when the 316L steel surface remained at a suitable temperature to avoid continuous liquid film on the surface, the corrosion rate of the steel will be greatly reduced.

In Situ Characterization of Triboelectrochemical Effects on Topography of Patterned Copper Surfaces

The topographic response of patterned copper surfaces to chemical–mechanical polishing (CMP) was investigated using a triboelectrochemical approach. Experimental methods include using a combined system containing a tribometer and a potentiostat. Results showed that more step height reduction and lower average surface roughness were obtained via CMP in acidic than in alkaline slurry. The increased contact area between wafer, pad, and abrasives was associated with the increase in friction. It was found that pH-dependent oxide formation and removal dominate the step height reduction for both acidic and alkaline slurries. The in situ approach pinpointed interactions between mechanical stimulation, chemical reaction, and electrochemical passivation. This research is beneficial to understanding triboelectrochemistry in Cu chemical–mechanical polishing of patterned wafers, an important application in semiconductor manufacturing.

(Invited) Poly-Silicon Opening Polishing Slurry Development for Advanced HKMG Process

Tunable silicon nitride to silicon oxide selectivity plays the key role to meet the stringent requirement of poly silicon opening polishing in the advanced HKMG applications. Independent silicon oxide removal rates tuning by surface modified colloidal silica abrasives, specific additives and abrasive loading has been demonstrated, accompanied with high silicon nitride removal rates in acidic slurry pH and unique additive, large selectivity window can be obtained.

Mechanism of amorphous Ge2Sb2Te5 removal during chemical mechanical planarization in acidic H2O2 slurry

In this paper, chemical mechanical planarization (CMP) of amorphous Ge2Sb2Te5 (a-GST) in acidic H2O2 slurry is investigated. It was found that the removal rate of a-GST is strongly dependent on H2O2 concentration and gradually increases with the increase in H2O2 concentration, but the static etch rate first increases and then slowly decreases with the increase in H2O2 concentration. To understand the chemical reaction behavior of H2O2 on the a-GST surface, the potentiodynamic polarization curve, surface morphology and cross-section of a-GST immersed in acidic slurry are measured and the results reveal that a-GST exhibits a from active to passive behavior for from low to high concentration of H2O2. Finally, a possible removal mechanism of a-GST in different concentrations of H2O2 in the acidic slurry is described.

Study of Chelating Agents in Silicon Wafer Polishing Slurry

Several chelating agents in silicon polishing slurries were studied about their effects on copper adhesion to the surface of silicon wafer. The copper contamination level on the Si wafer surface was measured with GFAAS. The results indicate that PAA and HEDP for acid slurries can reduce 80% copper contamination with respect to the situation of without chelating agent. EDTA, the most common chelating agent for alkaline slurries, has no predominant compared with FA/O and AEEA. The copper contamination on Si wafer surface can reduce nearly 50% by adding EDTA while the addition of FA/O or AEEA in the same concentration for alkaline slurries can reach more than 70% reduction of copper contamination level.

Material Removal Mechanism of Copper CMP from a Chemical–Mechanical Synergy Perspective

The material removal in chemical–mechanical planarization/polishing (CMP) of copper involves both chemical and mechanical effects. The roles of chemical corrosion, abrasive wear, and their synergistic effects on the material removal mechanism were studied by electrochemical analysis and nano-scratching method using atom force microscopy, respectively. Combining with the results of CMP experiments, dominant factors (chemistry and mechanics) in slurries within the range of pH 3.0–10.0 were assessed. Consequently, a removal mechanism map of copper CMP depending on pH values was constructed. In the alkaline slurry, the wear–corrosion effect predominated in the material removal at pH 8.0 and 9.0; while the copper removal mechanism changed to corrosion–wear action in the acidic slurry from pH 4.0 to 6.0, and good surface quality was also obtained. The results and the strategies provide thorough understanding of the material removal mechanism and further optimization of the CMP process.

Minimizing the effects of galvanic corrosion during chemical mechanical planarization of aluminum in moderately acidic slurry solutions

In the fabrication of integrated circuits, certain steps of materials processing involve chemical mechanical planarization (CMP) of Al deposited on thin layers of diffusion barrier materials like Ta/TaN, Co, or Ti/TiN. A specific example of this situation is found in the processing of replacement metal gates used for high-k/metal-gate transistors. Since the commonly used barrier materials are nobler than Al, the Al interface in contact with the barrier can become prone to galvanic corrosion in the wet CMP environment. Using model systems of coupon electrodes and two specific barrier metals, Ta and Co, the present work investigates the electrochemical factors responsible for these corrosion effects in a moderately acidic (pH = 4.0) abrasive-free solution. The techniques of cyclic voltammetry and impedance spectroscopy are combined with strategic measurements of galvanic currents and open circuit potentials. l-ascorbic acid (AA) is employed as a surface modifying agent for controlling galvanic corrosions of Al in the Ta–Al and Co–Al bimetallic combinations. The results elaborate the chemical and electrochemical mechanisms responsible for activating and suppressing the corrosion processes in these systems.

Application and Mechanism Study of a Novel Copolymer for Filter Aids on Wet-Process Phosphoric Acid

A novel copolymer PADA which has two functions of flocculation and surface activity was synthesized in aqueous solution. The copolymer was applied to filtration aiding on wet-process phosphoric acid (WPA). The results show that PADA can increase the filtration rate of the phosphoric acid slurry and decrease the moisture of the filter cake. The mechanism of filtration aiding was studied. PADA neutralizes the surface potential of the phosphogypsum and makes the microcrystal particles flocculate to conglobation, which indicate that electrostatic neutralization and flocculation might be the action modes in the process of filtration aiding. The shortest flocculation time and largest average diameter of floccules can be obtained with the addition of 10 ppm PADA. The average pore size and porosity of the filter cake are enlarged by 0.22 μm and 15.38% respectively with the addition of PADA. The surface contact angle of the phosphogypsum is increased by 3.4° with PADA presence.

텅스텐 화학적-기계적 연마 공정에서 부식방지막이 증착된 금속 컨디셔너 표면의 전기화학적 특성평가

반도체 산업에서 회로의 고집적화와 다층구조를 형성하기 위해 화학적-기계적 연마(CMP: Chemical-Mechanical Planarization) 공정이 도입되었으며 반도체 패턴의 미세화와 다층화에 따라 화학적-기계적 연마 공정의 중요성은 더욱 강조되고 있다. 화학적-기계적 연마공정이란 화학적 반응과 기계적 힘을 동시에 이용하여 표면을 평탄화하는 공정으로, 화학적-기계적 연마 공정은 압력, 속도 등의 공정조건과, 화학적 반응을 유도하는 슬러리(Slurry), 기계적 힘을 위한 패드 등에 의해 복합적으로 영향을 받는다. 패드 컨디셔닝이란 컨디셔너가 화학적-기계적 연마 공정 중에 지속적으로 패드 표면을 연마하여 패드의 손상된 부분을 제거하고 새로운 표면을 노출시켜 패드의 상태를 일정하게 유지시키는 것을 말한다. 한편, 금속박막의 화학적-기계적 연마 공정에 사용되는 슬러리는 금속박막과 산화반응을 하기 위하여 산화제를 포함하는데, 산화제는 금속 컨디셔너 표면을 산화시켜 부식을 야기한다. 컨디셔너의 표면부식은 반도체 수율에 직접적인 영향을 줄 수 있는 스크래치(Scratch) 등을 발생시킬 뿐만 아니라, 컨디셔너의 수명도 저하시키게 되므로 이를 방지하기 위한 노력이 매우 중요하다. 본 연구에서는 컨디셔너 표면에 슬러리와 컨디셔너 표면 간에 일어나는 표면부식을 방지하기 위하여 유기박막을 표면에 증착하여 부식을 방지하고자 하였다. 컨디셔너 제작에 사용되는 금속인 니켈과 니켈 합금을 기판으로 하고, 증착된 유기박막으로는 자기조립단분자막(SAM: Self-Assembled Monolayer)과 불화탄소(FC: FluoroCarbon) 박막을 증착하였다. 자기조립단분자막은 2가지 전구체(Perfluoroctyltrichloro silane(FOTS), Dodecanethiol(DT))를 사용하여 기상 자기조립 단분자막 증착(Vapor SAM) 방법으로 증착하였고, 불화탄소막은 10 nm, 50 nm, 100 nm 두께로 PE-CVD(Plasma Enhanced-Chemical Vapor Deposition, SRN-504, Sorona, Korea) 방법으로 증착하여 표면의 부식특성을 평가하였다. 표면 부식 특성은 동전위분극법(Potentiodynamic Polarization)과 전기화학적 임피던스 측정법(Electrochemical Impedance Spectroscopy(EIS)) 등의 전기화학 분석법을 사용하여 평가되었다. 또한 측정된 임피던스 데이터를 전기적 등가회로(Electrical Equivalent Circuit) 모델에 적용하여 부식 방지 효율을 계산하였다. 동전위분극법과 EIS의 결과 분석으로부터 유기박막이 증착된 표면의 부식전류밀도가 감소하고, 임피던스가 증가하는 것을 확인하였다. Chemical Mechanical Planarization (CMP) is a polishing process used in the microelectronic fabrication industries to achieve a globally planar wafer surface for the manufacturing of integrated circuits. Pad conditioning plays an important role in the CMP process to maintain a material removal rate (MRR) and its uniformity. For metal CMP process, highly acidic slurry containing strong oxidizer is being used. It would affect the conditioner surface which normally made of metal such as Nickel and its alloy. If conditioner surface is corroded, diamonds on the conditioner surface would be fallen out from the surface. Because of this phenomenon, not only life time of conditioners is decreased, but also more scratches are generated. To protect the conditioners from corrosion, thin organic film deposition on the metal surface is suggested without requiring current conditioner manufacturing process. To prepare the anti-corrosion film on metal conditioner surface, vapor SAM (self-assembled monolayer) and FC (Fluorocarbon) -CVD (SRN-504, Sorona, Korea) films were prepared on both nickel and nickel alloy surfaces. Vapor SAM method was used for SAM deposition using both Dodecanethiol (DT) and Perfluoroctyltrichloro silane (FOTS). FC films were prepared in different thickness of 10 nm, 50 nm and 100 nm on conditioner surfaces. Electrochemical analysis such as potentiodynamic polarization and impedance, and contact angle measurements were carried out to evaluate the coating characteristics. Impedance data was analyzed by an electrical equivalent circuit model. The observed contact angle is higher than 90o after thin film deposition, which confirms that the coatings deposited on the surfaces are densely packed. The results of potentiodynamic polarization and the impedance show that modified surfaces have better performance than bare metal surfaces which could be applied to increase the life time and reliability of conditioner during W CMP.

Optimization of Slurry and Technological Parameter on Chemical Mechanical Polishing of Titanium Dioxide Film for IC

Titanium dioxide (TiO2) has shown a great potential to be used in resistive random access memory, capacitor, solar cell and sensor. However, the surface topography as-deposited TiO2 film cannot meet the requirement of IC. Therefore, TiO2 film must be flattened before apply into semiconductor device. In this paper, chemical mechanical polishing (CMP) was used for polishing TiO2 film. We studied the effect of slurry pH of polishing from the viewpoint of chemical we found the removal rate with acid slurry is lower than the removal rate obtained by alkali slurry. The effect of the process parameter such as down force, platen rotation rate were also studied in detail and found the removal rate still exist when there is no pressure and velocity, hence Preston equation was slightly modified. Final, the surface roughness was reduced from 36Aå to 1.2Aå, and the removal rate was up to 38.2nm/min.

Ultraprecision CMP for sapphire, GaN, and SiC for advanced optoelectronics materials

Chemical mechanical polishing (CMP) of sapphire, GaN, and SiC substrates, which are categorized as hard-to-process materials, is demonstrated with a colloidal silica slurry under acidic and alkaline slurry pH conditions. Atomic level surface flatness was achieved by CMP and was confirmed to be equivalent to an almost ideally minimized surface roughness. By comparing the Preston coefficients under different slurry conditions, differences in the CMP properties among the three substrate materials and difficulties in the CMP of the GaN and SiC substrates are presented. The difference in CMP properties between the (0001) and (000-1) planes of GaN and SiC due to their non-revers crystallographical symmetry is also presented. Oxidation processes that occur during CMP of GaN and SiC are also discussed. By comparing the removal rate among GaN, SiC, and their oxides, it was found that the rate-limiting step in the total CMP process for GaN and SiC was surface oxidation reaction of GaN and SiC.