Effects of OH radicals on formation of Cu oxide and polishing performance in Cu Chemical Mechanical Polishing

The amount of OH radicals generated varied according to the complexing agent or Cu ion, and the accelerating effect of OH radicals on the rate of Cu oxide formation was found in acidic pH. When Cu I ions and oxalic acid were added to H2O2-based slurry, the decreases in etch and removal rates of Cu were observed because more generation of OH radicals resulted in the formation of thicker Cu oxide compared to additive-free slurry. Therefore, proper control of the formation and dissolution of Cu oxide led to an increase in etch and removal rates.This work was supported by the KOSEF through the Research Center for Energy Conversion and Storage (RCECS), Hanhwa Chemical, Ltd., and by the Institute of Chemical Processes (ICP) in Seoul National University

Analysis of Correlation between Pad Temperature and Asperity Angle in Chemical Mechanical Planarization

Chemical mechanical planarization (CMP) is a technology widely employed in device integration and planarization processes used in semiconductor fabrication. In CMP, the polishing pad plays a key role both mechanically and chemically. The surface of the pad, consisting of asperities and pores, undergoes repeated cycles of glazing induced by polishing followed by the recovery of roughness by a conditioning process applied during CMP. As a polymer material, the pad also experiences thermal expansion from changes in temperature. Such changes can be expressed in terms of surface roughness values, but these do not fully capture the actual changes to the pad surface. In this study, the change in pad temperature occurring during CMP was analyzed with regard to its effect on the asperity angle, and the influence on CMP outcome was assessed. The changes in the surface asperities according to the steady-state pad temperature were evaluated using various measurement methods. The change in pad roughness was characterized in terms of the asperity angle, and the contact state predicted according to temperature were validated by measuring the contact perimeter, the number of contact points, and related values. Through Scanning Electron Microscope (SEM) and micro-CT analysis, it was confirmed that in the continuous polishing process and the conditioning process, the changes in asperity angle due to changes in pad temperature affect the polishing outcome

Experimental Investigation of Material Removal Characteristics in Silicon Chemical Mechanical Polishing

The material removal characteristics of a silicon wafer were experimentally investigated with respect to the chemical dissolution and mechanical abrasion of the wafer during silicon chemical mechanical polishing (CMP) using an alkali-based slurry. The silicon surface without native oxide is rapidly dissolved by the slurry containing an amine agent, which effectively leads to the reduced hardness of the loaded silicon wafer due to Si–Si bond breaking during polishing. The abrasive particles in the slurry easily remove the reacted silicon surface, and the removal rate and wafer non-uniformity for abrasive concentrations of 1.5–3 wt% are better than those for other concentrations because of the low and steady coefficient of friction (COF) owing to the evenness of abrasive particles between the wafer and pad. Also, it was found that a high slurry flow rate of 700–1000cm3/min improves wafer non-uniformity owing to the reduced temporal variation of temperature, because the slurry acts as a good cooling source during polishing. However, the removal rate remains almost constant upon varying the slurry flow rate because of the effective dissolution characteristic of the slurry with abundant amine as an accelerator, regardless of the reduction of average temperature with increasing slurry flow rate. In the break-in process used to stabilize the material removal, the viscoelastic behaviors of the pad and the ground wafer surface with native oxide and wheel marks cause a temporal change of the friction force during polishing, which is related to the removal rate and wafer non-uniformity. As a result, the stabilization of removal rate and wafer non-uniformity is achieved through a steady-state process with elevated temperature and reduced COF after a total polishing time of 60 min, based on the removal process of the wafer surface and the permanent deformation in the viscoelastic behavior of the pad

Technological Approaches in Nanopolishing for Microstructures

Polishing technology has been broadly used in manufacturing of components to enhance the surface quality at final processing stage. On the threshold for the 21th century, all of technologies are changing more rapidly than the past. One of them is the miniaturization of the smart systems that require new technological approaches in manufacturing processes. Scientists and engineers have some responsibilities to revise the terminology and expand the area of each technology from the conventional one to nanoengineering. This paper focuses on the introduction of new technological approaches in nanopolishing for microstructures that imply new additional concepts on the conventional polishing. New concepts include damage-free, planarization, nanotopography and conformalization. Damage-free means to get not only atomic level surface roughness, but also subsurface without any physical defects. As one of the emerging methods, chemical mechanical polishing (CMP) is introduced with chemical reaction on the conventional mechanical polishing. Planarization is one of the fabrication processes for semiconductor devices, to make flat from the bumpy or rugged pattern surfaces for rearrangement of ULSI below quarter microns. Representative applications are reported with IMD, STI, copper and low-k CMP. Nanotopography means nanofeatures having 0.2~20mm wave length covered between nanoroughness (10-100nm) and flatness. It influences on the deterioration of threshold voltage, dielectric breakdown and failure of CMP of thin blanket film. Final issue is pointed to the conformalization which means isotropic removal of microstructures to improve the roughness while maintaining the micro three dimensional forms. Electrorheological and magnetorheologi- cal fluid (ERF or MRF) assisted polishing techniques are summarized with their material removal mechanisms and some results

Effect of Ceria Abrasives on Planarization Efficiency in STI CMP Process

The strong Ce-O-Si bonding between CeO2 abrasives and SiO2 film surface; i.e., the chemical tooth effect, improved planarization efficiency in CMP using ceria-based slurry as a result of nonlinear behavior of the removal rate. Removal rate is a power function of pressure and relative velocity (i.e., RR = kPαV β ). In particular, the high dependency of removal rate on pressure when α >1 results in a much higher material removal rate in the upper pattern than in the lower pattern. Therefore, the planarization efficiency of ceriabased slurry is better, from initial polishing time to the completion of the polishing step, than that of conventional silica-based slurry with an exponent value of α ≈1

Effect of the Lapping Platen Groove Density on the Characteristics of Microabrasive-Based Lapping

Microabrasive-based lapping is widely used in the manufacturing of single-crystal substrates such as sapphire, SiC, and GaN. Although many studies have been conducted to improve the lapping process characteristics, most of them focused on process conditions or consumables. In this study, the effect of the lapping platen groove density on the lapping characteristics was studied using a sapphire substrate. Groove density was defined as the ratio of groove width to groove pitch, and the displacement of the lapping head was measured to calculate the oil film thickness. It was confirmed that, for groove densities below 0.30, hydroplaning occurs when the oil film thickness increases. When the oil film thickness is larger than the abrasive particle size, the material removal rate is low because the abrasive does not participate in the lapping process. When the oil film was developed, the experimental results showed a high surface roughness and poor flatness of the substrate, as only large abrasive particles participated in the lapping process. Therefore, to improve the lapping characteristics, it is important to reduce the groove density by reducing the groove pitch, which prevents the development of the oil film

Material Removal Model for Lapping Process Based on Spiral Groove Density

The increasing demand for single-crystal wafers combined with the increase in diameter of semiconductor wafers has warranted further improvements in thickness variation and material removal rate during lapping to ensure price competitiveness of wafers; consequently, the lapping process has gained the attention of researchers. However, there is insufficient research on the effect of platen grooves on the lapping process. In this study, the parameters to describe grooves were defined in order to understand their influence on the lapping process, and a material removal model was suggested based on indentation theory and subsequently experimentally validated. The results indicate that changes in groove density affect the lubrication condition at the contact interface as well as the probability of abrasive participation by varying the oil film thickness. When fabricating the groove for a lapping platen, a groove density at the critical groove density (CGD) or higher should be selected. The higher the groove density, the easier it is to avoid the CGD, and the higher is the material removal rate. The results of this study will enable engineers to design lapping platen grooves that are suitable for the production of modern semiconductor wafers