Chemical Mechanical Polishing Equipment Research Articles

The compression deformation and particles removal of PVA brushes during the post-CMP cleaning process

Abstract In advanced wafer manufacturing processes, a wet cleaning system (wet in dry out) integrated with chemical mechanical polishing equipment is the primary form of post-chemical-mechanical polishing (CMP) cleaning. This pioneering study addresses the quantitative description of the contact between a polyvinyl alcohol (PVA) sponge brush and the wafer surface and establishes a relationship between the compression deformation as a function of the pressure on the wafer surface to achieve precise control of the contact between the brush and the wafer. The physical properties of the three types of PVA sponge brushes, namely, porosity, saturated water absorption, and pore change rate, were analyzed, and the effect of particle removal was explored. Finally, the effect of the brush on removing the residual polishing liquid from the wafer surface under different compression deformation conditions was studied, and its internal mechanism was explained. A ‘√’ curve was observed between the compression deformation (stress) and particle removal effect. When the compression deformation (stress) is 0.5 mm (35.11 g), the 26 nm particles on the wafer surface after post-CMP cleaning can reach less than 10ea.

Thin Ferrite Wafer Uniformly Polished with Magnetic Attraction Method

When a ferrite substrate is used to prepare thin-film InSb Hall element chips, one surface of the ferrite wafer needs to be polished. The traditional chemical mechanical polishing (CMP) method, often used for polishing of ferrite wafers, has several problems: a long time to install and remove wafers, a little high debris rate, and high cost. Taking advantage of the fact that ferrite wafers can be magnetically attracted, a method using independent RuFeB magnets to attract and hold ferrite wafers is proposed. The polishing head holding the ferrite wafer can perform planetary rotary motion to achieve uniform polishing. The polishing head floats up and down freely on the polishing pad, without the requirements of matching and process accuracy in machining, mechanical linkage, and control. The roughness of the ferrite surface after polishing is about 0.18 μm, which meets the requirements for the substrate of InSb Hall element chips. With no debris, the efficiency of installing and removing wafers is 30 times higher than that of traditional methods. At the same time, compared with traditional CMP machine, the cost of CMP equipment made by this method is very low.

Synthesis of Zn-doped colloidal SiO2 abrasives and their applications in sapphire chemical mechanical polishing slurry

In this paper, Zn-doped colloidal SiO2 composite abrasives were synthesized by seed-induced growth method and used to polish sapphire substrates. Time of flight secondary ion mass spectroscopy and scanning electron microscopy analyses show that element zinc has been doped into colloidal SiO2, and the prepared Zn-doped colloidal SiO2 composite abrasives are all ideal spherical and have good dispersibility. Chemical mechanical polishing (CMP) performances of Zn-doped colloidal SiO2 composite abrasives on sapphire substrates were investigated using UNIPOL-1502 CMP equipment. Experimental results show that, under the same testing conditions, the surfaces of sapphire polished by Zn-doped colloidal SiO2 composite abrasives exhibit lower root mean square roughness and higher material removal rate (MRR) than those of pure colloidal SiO2 abrasive. Especially, the composite abrasive shows the maximum MRR at 1.0 wt% Zn(OH)2 content. Furthermore, the acting mechanism of Zn-doped colloidal SiO2 composite abrasives in sapphire CMP was analyzed by X-ray photoelectron spectroscopy, and analytical results show that element zinc in composite abrasives can react with sapphire substrate to form aluminum zincate (Al2ZnO4) during CMP, which promotes the chemical effect in CMP and leads to the improvement of MRR.

Preparation of Cu-doped colloidal SiO2 abrasives and their chemical mechanical polishing behavior on sapphire substrates

Cu-doped colloidal SiO2 composite abrasives were synthesized by seed-induced growth method. Time of flight secondary ion mass spectroscopy and scanning electron microscopy analyses show that element copper has been doped into colloidal SiO2, and the prepared Cu-doped colloidal SiO2 composite abrasives are all ideal spherical and have good dispersibility. Chemical mechanical polishing (CMP) performances of Cu-doped colloidal SiO2 composite abrasives on sapphire substrates were investigated using UNIPOL-1502 CMP equipment. Experimental results show that, the surface of sapphire polished by Cu-doped colloidal SiO2 composite abrasive exhibit lower surface roughness (Ra) and higher material removal rate (MRR) than that of pure colloidal SiO2 abrasive under the same testing conditions. Furthermore, the acting mechanism of Cu-doped colloidal SiO2 composite abrasive in sapphire CMP was analyzed by X-ray photoelectron spectroscopy, and analytical results show that element Cu in composite abrasives can react with sapphire substrates to form dialuminium copper tetraoxide (Al2CuO4) during CMP, which promotes the chemical effect in CMP and leads to the improvement of MRR.

Preparation of Fe-doped colloidal SiO(2) abrasives and their chemical mechanical polishing behavior on sapphire substrates.

Abrasives are one of key influencing factors on surface quality during chemical mechanical polishing (CMP). Silica sol, a widely used abrasive in CMP slurries for sapphire substrates, often causes lower material removal rate (MRRs). In the present paper, Fe-doped colloidal SiO2 composite abrasives were prepared by a seed-induced growth method in order to improve the MRR of sapphire substrates. The CMP performance of Fe-doped colloidal SiO2 abrasives on sapphire substrates was investigated using UNIPOL-1502 CMP equipment. Experimental results indicate that the Fe-doped colloidal SiO2 composite abrasives exhibit lower surface roughness and higher MRR than pure colloidal SiO2 abrasives for sapphire substrates under the same testing conditions. Furthermore, the acting mechanism of Fe-doped colloidal SiO2 composite abrasives in sapphire CMP was analyzed by x-ray photoelectron spectroscopy. Analytical results show that the Fe in the composite abrasives can react with the sapphire substrates to form aluminum ferrite (AlFeO3) during CMP, which promotes the chemical effect in CMP and leads to improvement of MRR.

선형 롤 CMP에서 플로팅 노즐을 이용한 연마 특성에 관한 연구

Conventional etching technology is in the face of problems such as dishing, erosion resulting from non-uniform removal of film. Advanced printed circuit board (PCB) requires accurate wire formation with the aid of planarization by chemical mechanical polishing (CMP). Linear roll CMP is a line contact continuous process which removes the film by pressurization and rotation while slurry is supplied to polishing pad attached to the roll. This paper focuses on the design of floating nozzle on the linear roll CMP equipment which makes the slurry supply uniformly on the roll pad. Experimental results show that removal rate using the floating nozzle increases 3 times higher than that without it and non-uniformity is less than 15%.

Kinematic Optimization for Chemical Mechanical Polishing Based On Statistical Analysis of Particle Trajectories

The abrasive effect of particles is one of the basic mechanical actions in chemical mechanical polishing (CMP). In this paper, numerical simulations of particle sliding trajectories are performed to examine the influence of the kinematic parameters on the polishing uniformity of typical rotary-type CMP equipment. The trajectory simulations are carried out based on the kinematic analysis. The results reveal that the speed ratio α and the period ratio kT0, which represent the coupling relationships among the three basic motions of CMP, are the two major factors affecting the trajectory distribution. Further, a trajectory density parameter is proposed to quantitatively evaluate the global uniformity of the trajectory distributions and to optimize the kinematic parameters for better uniformity. The statistical results of the trajectory density analysis reveal that the trajectory of the wafer edge is denser than that of the wafer central area. To obtain better trajectory uniformity, some particular values of α and kT0, that is, α = 1 and kT0=1, which imply that the basic motions have a special coupling relationship, should be excluded; the preferred kinematic parameter values for CMP are α = 0.91-0.93 and kT0=5-7. This paper provides a basic guide to the kinematic parameter settings of CMP.

Effect of contact angle between retaining ring and polishing pad on material removal uniformity in CMP process

This paper presents the effect of the contact angle between the retaining ring and the polishing pad in chemical mechanical polishing (CMP) on the profile of the material removal rate (MRR) around the wafer edge and on the within-wafer nonuniformity (WIWNU). This study demonstrates that the mechanical interaction among the polishing pad, wafer, and retaining ring influences the ability to achieve planarization from the CMP process. In particular, the purpose of this study is to understand the effect of the contact conditions between the retaining ring and the pad on the CMP process. In order to verify the mechanical aspects of the MRR near the wafer edge, retaining rings with different contact angles were prepared. Finite element analysis (FEA) verified the effect of the contact angle between the retaining ring and the polishing pad on the stress distribution around the edge of the wafer. The results of the analysis were corroborated by conducting CMP experiments with 200-mm blanket oxide wafers. As expected, the FEA results were in good agreement with the MRR profile around the edge area. Through simulations and experiments, we concluded that the contact angle is an important factor to achieve a flatter edge profile and the material removal profile around the edge of the wafer was optimum at a 0o contact angle. In particular the WIWNU was below 4% when a flat retaining ring was used. The results of this study make it possible to improve the yield of chip production by ensuring the retaining ring maintains perfect flatness without making any special design changes to the CMP equipment.

Analyzing on Nonuniformity of Material Removal in Silicon Wafer CMP Based on Abrasive Movement Trajectories

Chemical mechanical polishing (CMP) has already become a mainstream technology in global planarization of wafer. The nonuniformity of material removal on wafer surface has a main influence on surface profile of silicon wafer in CMP process. However, the formation mechanism of nonuniformity in wafer CMP has not been fully understood and the influences of CMP process variables on nonuniformity are not fully clear. The nonuniformity of material removal on wafer surface has not been fully understood and the influences of CMP process variables on nonuniformity are not fully clear in CMP process. In this paper, firstly, the equation of particle movement trajectories on wafer surface was built by the movement relationship between the wafer and the polishing pad on a single head CMP machine with line oscillation of carrier. Then the distribution of abrasive trajectories on wafer surface was analyzed at different rotational speed. By the analysis, the relationship between the movement variables of the CMP machine and the With-In-Wafer Nonuniformity (WIWNU) of material removal on wafer surface had been derived. Last, the WIWNU tests were conducted on CP-4 machine. The analysis results are in accord with experimental results. The results will provide some theoretical guide for designing the CMP equipment, selecting the movement variables in CMP and further understanding the material removal mechanism in wafer CMP.

Modeling and Analyzing on Nonuniformity of Material Removal in Chemical Mechanical Polishing of Silicon Wafer

Chemical mechanical polishing (CMP) has already become a mainstream technology in global planarization of wafer, but the mechanism of nonuniform material removal has not been revealed. In this paper, the calculation of particle movement tracks on wafer surface was conducted by the motion relationship between the wafer and the polishing pad on a large-sized single head CMP machine. Based on the distribution of particle tracks on wafer surface, the model for the within-wafer-nonuniformity (WIWNU) of material removal was put forward. By the calculation and analysis, the relationship between the motion variables of the CMP machine and the WIWNU of material removal on wafer surface had been derived. This model can be used not only for predicting the WIWNU, but also for providing theoretical guide to the design of CMP equipment, selecting the motion variables of CMP and further understanding the material removal mechanism in wafer CMP.

Advantages of point of use (POU) slurry filter and high spray method for reduction of CMP process defects

As integrated circuit devices shrink to smaller dimensions, a chemical mechanical polishing (CMP) process was required for the global planarization of the inter-metal dielectric (IMD) layer with free-defects. However, as the IMD layer gets thinner, micro-scratches are becoming a major defect. Micro-scratches are generated by agglomerated slurry, solidified and attached slurry in the pipeline of the slurry supply system. In order to prevent the agglomerated slurry particles from slurry inflow, we installed a 0.5 μm point of use (POU) filter, which is a depth-type filter and has 80% filtering efficiency for 1.0 μm size particles. Also a high spray bar of de-ionized water with high pressure was installed in the CMP equipment. Our experimental results showed that it is impossible to completely prevent defect-causing particles through the depth-type filter. Thus, we suggest that it is necessary to optimize the slurry flow rate and to install a high spray bar of de-ionized water (DIW) with high pressure, in order to overcome the weak points of a POU depth-type filter.

Design of experimental optimization for ULSI CMP process applications

As the device geometry shrinks to the deep sub-micron region, chemical mechanical polishing (CMP) planarization has become a more essential technique in advanced ULSI process. In particular, the complete global planarization of multilevel interconnections can be achieved only with the CMP process. However, it still has various problems due to the CMP equipment. In particular, among the CMP components, process variables are very important parameters in determining the removal rate and non-uniformity. In this paper, we studied the design of experiments (DOE) method in order to obtain optimized CMP equipment variables. Various process parameters, such as table and head speed, slurry flow rate and down force, have been investigated from the viewpoint of high removal rate and low non-uniformity. Through the above DOE results, we can determine the optimal CMP process parameters.

반경험적인 실험설계 기법을 이용한 CMP 공정 변수의 최적화

The rise throughput and the stability in the device fabrication can be obtained by applying chemical mechanical polishing (CMP) process in 0.18 <TEX>$\mu\textrm{m}$</TEX> semiconductor device. However, it still has various problems due to the CMP equipment. Especially, among the CMP components, process variables are very important parameters in determining the removal rate and non-uniformity. In this paper, we studied the DOE (design of experiment) method in order to get the optimized CMP equipment variables. Various process parameters, such as table and head speed, slurry flow rate and down force, have investigated in the viewpoint of removal rate and non-uniformity. Through the above DOE results, we could set-up the optimal CMP process parameters.

Improvements of CMP characteristics using slurry filter and high-spray bar of de-ionized water

As the integrated circuit device size shrinks to smaller dimensions, a chemical mechanical polishing (CMP) process was required for the global planarization of inter-metal dielectric (IMD) layer free of defects. However, as the IMD layer gets thinner, micro-scratches are becoming a major concern. Micro-scratches are generated by agglomerated slurry, solidified and attached slurry in the pipe-lines of the slurry supply system. In order to prevent the agglomerated slurry particles from slurry inflow, we installed a 0.5-μm point-of-use (POU) filter, which is a depth-type filter and has 80% filtering efficiency for the 1.0-μm size particles. Also, a high-spray bar of de-ionized water with high pressure was installed in the CMP equipment. In this paper, we studied the relationship between defect generation and pad counts to understand the exact efficiency of the slurry filter, and to determine the appropriate pad usage. Our experimental results showed that it is impossible to prevent defect-causing particles completely through the depth-type filter. Thus, we suggest that it is necessary to optimize the slurry flow rate and to install a high-spray bar of de-ionized water (DIW) with high pressure, in order to overcome weak points of the POU depth-type filter.

Effects of deionized water pressure and purified nitrogen gas on the chemical mechanical polishing process

The chemical mechanical polishing (CMP) process is widely used for the global planarization of inter-layer dielectric (ILD) for deep sub-micrometer technology. But hot-spots due to partial over-polishing generated in the edges of wafers, have become a major concern. Thus, it is very important to understand the correlation between the ILD-CMP process and various facility factors of the CMP equipment system. With a facility shortage of de-ionized water (DIW) pressure, we introduced an additional purified nitrogen (PN2) gas in the polishing-head-cleaning station to increase the cleaning effect. Our experimental results show that DIW pressure and PN2 gas factors were not related to the removal rate, but edge hot-spots on the patterned wafer had a strong relation with them. We estimated two factors (DIW pressure and PN2 gas) for the improvement of the CMP process. In particular, we obtained a uniform planarity in the patterned wafer and prevented more than 90% of wafer edge over-polishing. Finally, we suggest that the facility factors for an equipment system play an important role in the ILD-CMP process.