Chemical Mechanical Polishing Technique Research Articles

Ultra-smooth BaTiO3 surface morphology using chemical mechanical polishing technique for high-k metal-insulator-metal capacitors

The surface roughness of barium titanate (BTO) following its implication by aerosol deposition method (ADM), is a very important characteristic affecting its potential for use in high-k metal-insulator-metal capacitors. The ADM is the best candidate to deposit ceramic films but has two major problems: macroscopic defects and rough interface effects on the BTO surface. In this work, a chemical mechanical polishing (CMP) technique is applied to obtain an ultra-smooth BTO surface morphology by the optimization of several factors including the slurry type, the head rotational speed, and the down pressure. Statistically, we were able to achieve a root mean square (RMS) value of the BTO surface of 1.746nm by utilizing a two-step polishing process, applied at a head rotational speed of 70rpm under 5kg/cm2 of down pressure; this RMS value is improved at least 8 times over previous studies. This analysis is based on representative pattern images, three-dimensional images, line profiles, histograms, and power spectra of selected BTO surface areas, further verified with data from both energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy.

An experimental investigation of double-side processing of cylindrical rollers using chemical mechanical polishing technique

Cylindrical roller bearings have been widely used in the mechanical industry due to the high radial load capacity. In some precision applications, high accuracy of cylindrical rollers, such as high profile accuracy and excellent surface quality, is strongly demanded and is even indispensable for the operational reliability of bearings. In this paper, on the basis of a lapping process, chemical mechanical polishing (CMP) technique was used to prepare cylindrical rollers with a low roundness and a nanoscale surface roughness Ra on a double-side cylindrical ultra-precision processing device, which was developed by the Ultra-precision Machining Center of Zhejiang University of Technology. Firstly, the effects of the experimental conditions, such as the rotating speeds and the down force, on the processing performance were studied. The simulation results reveal that, using the optimized rotating speeds, with the processing time going, the processing trajectory gradually distributes uniformly on the cylindrical surface of the roller along both the circular and the axial directions, and thereby, the uniform material removal can be realized; with the increase of the down force, the material removal rate (MRR) of the cylindrical roller almost linearly increases. Specially, the down force of the CMP process was set to 20 N/roller to obtain a better polishing performance. Then, on the basis of a lapping process, CMP technique was used to further improve the surface quality of the cylindrical rollers to nanoscale roughness. The results show that, after a two-step CMP process including a rough polishing step and a fine polishing step, the cylindrical surface of the rollers changes from rough and uneven state into smooth and free of micro-scratches state, and the surface roughness Ra decreases from initial 76 to 16.6 nm, and the roundness decreases from initial 0.97 to 0.40 μm. Finally, the material removal mechanism of the cylindrical rollers was investigated. During the lapping process, the material removal is predominantly driven by the mechanical abrasion from the α-alumina particles; while during the CMP process, the material removal is realized by the alternating cycles of “oxidation/complexation/passivation-abrasion-oxidation/complexation/passivation” process. In sequence, the mechanism of the roundness improvement was proposed. During the lapping and the CMP processes, the MRR at the protrudent point is larger than that at the recessed point due to the larger contact stress, and as a result, the actual surface profile of the circular section gradually reaches the average circle, and the roundness decreases.

Chemical mechanical polishing of steel substrate using colloidal silica-based slurries

AISI 52100 steel has been widely used in the mechanical industry due to its excellent mechanical properties and high availability. In some cases, an ultra-smooth surface of AISI 52100 steel is needed and is even indispensable for the satisfactory performance of devices. In this paper, chemical mechanical polishing technique was employed to prepare the ultra-smooth surface of AISI 52100 steel. Colloidal silica was used as the abrasive. The effects of pH, complexing agent such as glycine, H2O2 and benzotriazole (BTA) on the polishing performance were studied. It is revealed that, with the increase of pH, the static etching rate (SER) and the material removal rate (MRR) are both gradually reduced, and the post-CMP surface roughness Ra decreases. This is attributed to the fact that compact and passive iron oxides, especially Fe(III) oxides, gradually form on the top surface. At pH 4.00, in the presence of glycine, and with the increase of the H2O2 concentration, the SER is further suppressed, and the surface roughness Ra gradually decreases; the MRR initially dramatically increases due to the fact that, with the addition of small amount of H2O2, the porous iron oxide layer with relatively low mechanical strength can be rapidly formed on the surface. Moreover, glycine intensifies the chemical dissolution by chelating iron ions, especially Fe(II) ions, and thereby the mechanical strength of the oxide layer further weakens. Then, after reaching the peak value, the MRR gradually decreases when the H2O2 concentration further increases since the compactness of the oxide layer gradually increases. With the increase of the BTA concentration, the MRR is gradually suppressed and the surface roughness Ra decreases due to the formation of Fe-BTA passivating film on the top surface. Finally, a two-step polishing process was developed. The polishing results show that, within 20min, a rough surface of AISI 52100 steel with the Ra value of 188nm can be polished into an ultra-smooth surface with the Ra value of 1.8nm.

Chemical Mechanical Polishing of Stainless Steel as Solar Cell Substrate

Recently, stainless steel has been widely used as the solar cell substrate. In this paper, chemical mechanical polishing technique was employed to prepare the ultra-smooth 316L stainless steel surface for such application. The effects of solid content, pH, H2O2 and benzotriazole (BTA) on the polishing performance of 316L stainless steel were investigated. The results indicated that, at pH 4.00, with the increase in the H2O2 concentration, the MRR first dramatically increases due to the fact that, with the addition of small amount of H2O2, a porous outer layer mainly consisting of iron-enriched oxides with relatively low mechanical strength of the bilayer-structure oxide film is rapidly formed on the surface. After reaching the maximum value, the MRR gradually decreases since the outer layer gradually grows compact by the transformation of γ-FeOOH into α-FeOOH and even into α-Fe2O3. With the addition of BTA, the MRR can be suppressed, which is probably attributed to the formation of BTA passivating film on the top surface. Finally, a two-step polishing method was proposed, by which the ultra-smooth 316L stainless steel surface with the surface roughness Ra about 2.0 nm can be achieved within 30 min and it can be subsequently used for thin-film solar cells.

Fabrication of new Interdigital Transducers for Surface Acoustic Wave Device

We investigate high-performance interdigital transducers (IDTs) for the generation of surface acoustic waves (SAWs) on AT-cut quartz, where the metal fingers are embedded in the substrate. Three micromachining techniques are used to manufacture SAW structures, namely an inductively coupled plasma, a laser etching and a reactive ion etching. An evaporated layer of Al and a Ni thick electroplating are used to grow the metals in the micromachining structures. A chemical mechanical polishing (CMP) technique is used to remove the exceeding metal and keep a flat surface. The electrical characterizations indicate that the fabricated devices are suited for sensing proposes with a low insertion loss and a linear phase. Results are reported emphasizing the efficiency of the Ni damascene process to manufacture SAW sensors with the embedded structures.

Effects of pH and Oxidizer on Chemical Mechanical Polishing of AISI 1045 Steel

AISI 1045 steel has been widely used as the substrate for thin film deposition. In some cases, an ultra-smooth surface of AISI 1045 steel is needed and is even indispensible for the satisfactory deposition of thin film. In this paper, chemical mechanical polishing technique was employed to prepare the ultra-smooth surface of AISI 1045 steel. The effects of pH and H2O2 on the polishing performance of AISI 1045 steel were investigated. It is revealed that, with the increase of pH, the material removal rate (MRR) and the static etching rate (SER) of AISI 1045 steel gradually decrease due to the formation of passive iron oxides on the top surface, and thus the surface quality gradually improves. At pH 4.00, with the addition of H2O2, the SER of AISI 1045 steel is further suppressed; while the MRR of AISI 1045 steel first dramatically increases due to the formation of porous iron oxides with relatively low mechanical strength on the surface when the H2O2 concentration increases from 0 to 0.01 wt%, and then decreases since the porous iron oxides gradually grow compact when the H2O2 concentration further increases. The increase of the compactness of the iron oxides might be attributed to the crystallization of γ-FeOOH into α-FeOOH and even into α-Fe2O3 and the resulting polymerization of the amorphous iron oxides.

GaN-based substrates and optoelectronic materials and devices

In order to solve the problems of GaN heteroepitaxy on sapphire substrate, some techniques were explored. Freestanding GaN substrates have been made by hydride vapor phase epitaxy (HVPE), laser lift-off (LLO), and chemical mechanical polishing techniques. Wafer bending and cracking in the HVPE growth were partly settled by pulsed flow modulation method. High-crystal quality was established for 1.2 mm thick GaN substrate by X-ray diffraction measurement, in which the full width of half maximum values were 72, 110 arcsec for (102), (002) peaks. A novel micro-size patterned sapphire substrate (PSS) and a nano PSS were also fabricated. High-power vertical structure light emitting diodes (VSLEDs) have been developed by Au–Sn eutectic wafer bonding, homemade micro-area LLO, and light extraction structure preparation. The high-injection-level active region with low temperature GaN sandwiched layers was used for low-efficiency droop. The light output power of VSLED was achieved as 400 mW driven at 350 mA, and the dominant wavelength is about 460 nm. The structures and properties of strain modulated superlattices (SLs) and quantum wells as well as advanced simulation of carriers transport across the electron blocking layer were investigated in laser diodes. The hole concentration was achieved as high as 1.6 × 1018 cm−3 in AlGaN/GaN SLs:Mg by inserting an AlN layer. High-quality AlGaN epilayers and structures were grown by MOCVD. Some device structures of UV LEDs and detectors were demonstrated. The emission wavelength of 262 nm UV LED has been successfully fabricated. At last, high-quality InN and InGaN materials for solar cell were grown by boundary-temperature-controlled epitaxy and growth-temperature-controlled epitaxy. Hall-effect measurement showed a recorded electron mobility of 3,280 cm2/(V s) and a residual electron concentration of 1.47 × 1017 cm−3 at 300 K.

Preparation of room temperature terahertz detector with lithium tantalate crystal and thin film

Research on room temperature terahertz (THz) detector is essential for promoting the application of THz science and technology. Both lithium tantalate crystal (LiTaO3) and lithium tantalate thin film were used to fabricate the THz detector in this paper. Polishing process were used to reduce the thickness of LiTaO3 crystal slice by chemical mechanical polishing techniques and an improved sol-gel process was used to obtain high concentration LiTaO3 precursor solution to fabricate LiTaO3 thin film. Three dimension models of two THz detectors were set up and the temperature increasing map of two devices were simulated using finite element method. The lowest noise equivalent power value for terahertz detector using pyroelectric material reaches 6.8 × 10−9 W at 30 Hz operating frequency, which is suitable for THz imaging application.

Identification Research on CMP Multi-Zones Pressure System

In the process of very large scale integrated circuit (VLSI) manufacturing, Chemical Mechanical Polishing (CMP) technique is one of the most effective wafer global planarization techniques. The polishing quality depends not only on the slurry and polishing head structure, but also on accurately wafer polishing pressure control. However, the polishing pressure accurately control depends on a generalized pressure control system of the polishing head and multi-zones pneumatic pressure system. As the system has time-varying, nonlinear and coupling characters, it is difficult to apply theoretical modeling method for obtaining the accurate mathematical model. Therefore, this paper presents a method based on subsubmodel identification to establish the precise mathematical model of the pressure control system. The experimental results show that the method is feasible, practical and accurate.

Evaluation of Infection Resistance of Biological Implants through CMP based Micro-Patterning

ABSTRACTBiomaterials are widely used for dental implants, orthopedic devices, cardiac pacemakers and catheters. One of the main concerns on using bio-implants is the risk of infection on the materials used. In this study, our aim is to quantify the effect of controlled surface roughness on the infection resistance of the titanium based bio-materials which are commonly used for orthopedic devices and dental implants. To modify the surface roughness of the surfaces in a controlled manner, Chemical Mechanical Polishing (CMP) technique, which is extensively used in semiconductor industry for the planarization of the interlayer dielectrics and metals, is utilized. To determine the infection resistance of the created films with varying surface roughness, bacteria growth response was studied on titanium plates after CMP.

Thinning and polishing of cross-section of depth-graded WSi2/Si multilayer for linear zone plate application

A linear zone plate named multilayer laue lens (MLL) is fabricated using a depth-graded multilayer structure. The lens shows considerable potential in focusing an X-ray beam into a nanometer scale with high efficiency. In this letter, a depth-graded multilayer consisting of 324 alternating WSi2 and Si layers with a total thickness of 7.9 \mu m is deposited based on the thickness sequence according to the demands of the zone plate law. Subsequently, the multilayer sample is sliced and thinned to an ideal depth along the cross-section direction using raw abrasives and diamond lapping. Finally, the cross-section is polished by a chemical mechanical polishing (CMP) technique to remove the damages and improve the surface smoothness. The final depth of the MLL is approximately 7 μm with an achieved aspect ratio greater than 400. Results of scanning electron microscopy (SEM) and atomic force microscopy (AFM) indicate that interfaces are sharp, and the multilayer structure remains undamaged after the thinning and polishing processes. The surface roughness achieved is 0.33 nm.

Effect of Operated Parameters on Removal Rate and Surface Roughness in Precision Atomization Ultra-Polishing Process of Copper Surface

Compared with the traditional chemical mechanical polishing (CMP) technique, the precision atomization ultra-polishing (PAUP) technology has the advantages of friendly environmental and damage-free. This paper established a novel PAUP tester based on the atmospheric pressure theory, and explored the possibility of PAUP technique. Furthermore, effects of operated parameters on the material removal rate and surface roughness were investigated in PAUP process. It was found that a material removal rate of 78.302 nm/min was obtained with a surface roughness of 0.015 µm at the optimal parameters. This study provides insight into the development of the novel ultra-polishing methods and its underlying theoretical foundation.

High Precision Finishing Technique of Sapphire Substrate Surface for Photoconducting Device

Sapphire (α-Al2O3) single crystal, as an important photoconducting device substrate material, stringent surface quality requirements, i.e. surface finish and flatness, are required. The use of chemical mechanical polishing (CMP) technique can produce high quality surface finishes at low cost and with fast material removal rates. The polishing mechanism was studied in this paper, and it was pointed that there were chemical and mechanical kinetics process respectively. The chosen polishing temperature was 40 oC. SiO2 sol was chosen as abrasive and the particle size is 40nm. The pH value was determined at 11.5~12. During CMP process C6382I-W/YJ single side polisher and SUBA 600 pad were used. After polishing and cleaning of sapphire surface, the measured removal rate was above 183.3nm /min and the surface roughness by using AFM was lower than Ra 0.3 nm. From the results, it was found that using such method, the optimal sapphire surface can be gotten, which is advantaged for epitaxial growth and device making-up.

Morphology Improvement of Step Bunching on 4H-SiC Wafers by Polishing Technique

In this paper, we report a new polishing technique regarding the elimination of step bunching on the silicon carbide (SiC) surface. The step bunching generation is often observed as frequent phenomenon on the surface of SiC epilayers grown on low off-angle (0001) SiC wafers and on SiC devices after annealing to activate the dopants. We polished the step bunching surface using a chemical mechanical polishing (CMP) technique reported in a previous study, and we succeeded to improve the morphology with a flat and smooth surface which showed a small Rms value of around 0.1nm. We especially found an excellent polishing effect for the control of leakage current in reverse I-V characteristics of SiC Schottky barrier diodes (SBD).

The Study of Stress Effects in GaN Epilayers on Very Thin Sapphire Substrates Using Chemical Mechanical Polishing Technique

The wafer bonding process and chemical mechanical polishing (CMP) technique are used to remove the sapphire substrate for fabricating the thin-GaN light emitting diodes (LEDs). The stress effects in GaN epilayers on very thin sapphire substrates are analyzed by Raman spectroscopy and photoluminescence (PL). By reducing the thickness of the sapphire substrate from 450 µm to the range between 1.1 and 20.3 µm, the compressive stress in GaN epilayers will be almost released. By analyzing the main scattering signal of E2 (high) mode, the sample with thinnest sapphire of 1.1 µm exhibits 248.3 MPa stress relaxation which is obtained from the Raman shift Δω of 1.54 cm-1. By analyzing the variation of the biaxial stress with sapphire thickness, the relationship between the Raman wavenumbers ω (in cm-1) and residual sapphire thicknesses d (in µm) can be expressed by ω=569.51-1.92×exp (-d/5.81) (cm-1). Finally, an almost linear relationship between residual sapphire thickness and energy bandgap of GaN films was also observed during the CMP process.

Preparation of Silica Abrasives from Water Glass and Application in Silicon Wafer Polishing

Chemical mechanical polishing technique is more frequently adopted for planarization in integrated circuit fabrication. The silica abrasives in colloidal state are fabricated with the sodium silicate solution as raw materials through the polymerization reaction among silicic acid molecules. By continuous injection of silicic acid into the preexisting silica solution, the diameter of silica nanoparticles increases. The different sized silica nanoparticles are imaged by scanning electron microscopy, and the dried silica are characterized by X-ray diffraction and thermal analysis. The polishing test on silicon wafer with as-fabricated silica abrasives shows that the surface flatness reaches 1.1 nm roughness, however, micro scratches are still present in the surface.

Investigation on the controllable growth of monodisperse silica colloid abrasives for the chemical mechanical polishing application

With the rapid development of chemical mechanical polishing technique as well as its increasing application in IC foundry, the abrasives of slurry are required to have different specifications in terms of size and size’s distribution, which play a vital role in the material removal and defect control. In this study, we monitor in detail the growth process of colloidal silica abrasives changing from the tiny nuclei to large nanoparticles by means of the electron microscopy images. Using the procedure we develop, we are capable of producing monodisperse colloidal silica nanoparticles ranging from 60 to 130 nm in diameter, which are mostly often applied as abrasives in chemical mechanical planarization/polishing (CMP) process of integrated circuit (IC) manufacturing. The physicochemical properties of the silica synthesized by our procedure are also characterized by the X-ray diffraction (XRD) patterns and thermal analysis. The polishing test adopting the colloidal silica as abrasives is performed on silicon wafer to evaluate the CMP properties.

DC and 1/ f noise characteristics of strained-Si nMOSFETs using chemical–mechanical-polishing technique

Utilizing chemical–mechanical-polishing (CMP) technique to reduce oxide interface defects and roughness induced from SiGe virtual substrate in strained-Si nMOSFETs has been investigated. Due to the smoother SiO 2/Si interface, an additional 3.5% driving current and 11% transconductance enhancements are found in strained-Si devices with a gate length = 0.5 μm on CMP-treated SiGe virtual substrate, compared to strained-Si devices without CMP process. Moreover, strained-Si devices with CMP process exhibit the lowest 1/ f noise. Under larger gate voltage overdrive, the enhancements become more obvious indicating that the CMP process provides a smoother surface of the strained-Si/SiGe structure.

Fabrication of Periodically-Inverted AlGaAs Waveguides for Quasi-Phase-Matched Wavelength Conversion at 1.55 µm

We have improved fabrication processes of periodically inverted AlGaAs waveguides for highly efficient quasi-phase-matched wavelength conversion. In order to reduce propagation losses in waveguiding devices fabricated based on sublattice reversal epitaxy, we have introduced template planarization by chemical mechanical polishing and low-temperature regrowth technique. Corrugations at the core/clad interface and the propagation loss at 1.55 µm has been reduced to 40 nm and 9 dB/cm, respectively. First-order quasi-phase-matched second-harmonic generation was demonstrated at 1.55 µm fundamental wavelength with a 1.47-mm-long device. Obtained internal conversion efficiency is 2.2%/W which is one order of magnitude lower than the theoretical value for an ideal lossless waveguide. A significant increase in the conversion efficiency is expected with a redesign of the device and further optimization of the fabrication processes.

Investigation of material removal mechanism of silicon wafer in the chemical mechanical polishing process using molecular dynamics simulation method

Chemical mechanical polishing (CMP) technology, being the mainstream technique of acquiring global planarization and nanometer level surface, has already become an attractive research item. In the case of CMP process, the indentation depth lies in the range of nanometer or sub-nanometer, huge hydrostatic pressure induced in the local deformation area which makes the material removal and surface generation process different from traditional manufacturing process. In order to investigate the physical essence of CMP technique, the authors carry out molecular dynamics (MD) analysis of chemical mechanical polishing of a silicon wafer. The simulation result shows that huge hydrostatic pressure is induced in the local area and leads to the silicon atom transform from the classical diamond structure (α silicon) to metal structure (β silicon). This important factor results in the ductile fracture of silicon and then in the acquisition of a super-smooth surface.