Study on CMP Slurry and Technique of Silicon Dioxide Dielectric for ULSI
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SiO2 is a kind of widely used dielectric material in ULSI and its chemical mechanical planarization (CMP) is one of the most difficult processes. In this paper, the CMP mechanism and the effect of abrasive on SiO2 dielectric were analyzed; the different factors of affecting the CMP were analyzed. A kind of organic alkali was chosen to act as the pH regulator and complexation agent to enhance the chemical effect. The silica sol was selected as abrasive to realize no contamination, low viscidity, proper hardness and easy to clean. The effect of different concentration of abrasive on the removal rate and surface performance were studied. Further more the influence of polishing slurry flow and surfactant on removal rate were analyzed. The final planarization was realized.Keywords:
Chemical Mechanical Planarization
Silicon dioxide
Silica abrasive plays an important role in chemical mechanical planarization (CMP) of copper. In this paper, effect of different silica abrasive concentrations on copper removal rate and planarization performance of copper was investigated. The results show that the copper removal rate was increased as the concentration of silica abrasive increase. However, excessive abrasive will lead to a decreased copper removal rate. The initial step height values of the multilayer copper wafers were all about 2500Å, and after being polished for 30s, the remaining values of step height of slurry A, B, C and D were 717 Å, 906 Å, 1222 Å and 1493 Å. It indicates that alkaline copper slurries with different abrasive concentrations all had a good planarization performance on copper patterned wafer CMP. As the abrasive concentration increased, the planarization capability was enhanced.
Chemical Mechanical Planarization
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In this work, the position of the novel slurry injection system (SIS) was optimized to achieve a more cost-effective and environmentally benign chemical mechanical planarization process using a widely-adopted ceria-based "reverse slurry". SIS was configured with different angles in order to investigate slurry dilution characteristics caused by residual pad rinsing with ultrapure water (UPW) that affected silicon dioxide removal rates. UPW dilution effect on removal rate, coefficient of friction and pad surface temperature was explained by maintaining a constant dilution ratio for each of the SIS configuration tests. Results indicated that the negative rotation angle of the SIS increased the actual slurry dilution ratio on top of the polishing pad. This generated more Ce3+ which boosted the removal rate. Application of negatively rotated SIS allowed significantly lower slurry flow rate and/or shorter polishing time leading to achieve a more environmental friendly semiconductor manufacturing process. Finally, it was confirmed that variations in SIS configuration had no impact on silicon dioxide to silicon nitride removal rate selectivity.
Chemical Mechanical Planarization
Dilution
Ultrapure water
Silicon dioxide
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The polishing process was optimized according to the polishing rate and its consistency of HE slurry with different dilution multiple on the copper wafers, it can be confirmed that: the best pressure value of HE1, HE10, HE20, HE50 type slurries was 6890Pa, the best flow rate value of the preceding three slurries was 300ml/min, the best value of the HE50 slurry was 400ml/min. Through the planarization effects of the slurries with different dilution multiple, it can be obtained that: the initial dishing and erosion heights of the samples were both 1270nm and -500nm, and the two values respectively changed to 539.3nm, -75.7nm and 796.3nm, -191.3nm after being treated by HE1 and HE10 slurries, the step height of the wafer changed from 117nm to 72nm after being treated by HE20 slurry, the step height of the wafer changed from 88nm to 71nm after being treated by HE50 slurry. It was concluded that: the HE slurry shows strong ability for step removal when the slurry is diluted by 1 times and 10 times, the HE slurry also owns high planarization ability when the slurry is diluted by 20 times and 50 times.
Chemical Mechanical Planarization
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The necessity of fixed abrasive CMP in polishing semiconductor materials processing was analyzed. Compared the shortcomings of traditional free abrasive polishing with the advantages of fixed abrasive polishing, the applications of fixed abrasive polishing technology in semiconductor processing were described. A variety of fixed abrasive polishing pad production methods were introduced. The development trend of fixed abrasive polishing was prospected.
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Chemical-mechanical polishing(Chemical Mechanical Polishing,CMP)is currently only able to provide the global planarization technology,its mechanism of polishing is currently the most popular. A survey of some models was given which consider the polishing properties of polishing liquid and polishin pads,and the relevant characteristics of each model was analyzed,at last the development and research directions of the CMP model was prospected.
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Chemical Mechanical Planarization
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The recycle of Chemical Mechanical Planarization (CMP) slurries has been actively considered in the industry to reduce the cost-of-consumables (COC) because of the sharp increase of the consumption of slurry in CMP. The main purpose of this study was to characterize the used oxide slurry physically and chemically to establish a means of reprocessing it. The characteristics of slurry were determined according to pH, solid content, specific gravity and particle size. These characteristics were affected and varied by deionized water inflow during the CMP process. The tetraethylorthosilicate removal rate was strongly dependent on the solid content and pH of slurry solutions. The solid content played a major role in determining the removal rates. Regardless of the number of polishings, the removal rate was almost the same at a solid content when it was modified by adding new slurry. The mean particle size of slurries did not change at all even in the five times recycled slurry. Even though there was a slight increase in the fraction of large particles in the range of 20 to 120 µm in the recycled slurries, no changes in thickness uniformity or defect density were observed when polishing was performed in either new or recycled slurry.
Chemical Mechanical Planarization
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A macromodel for changes in a pad surface by dressing and polishing is proposed. A polishing pad is divided into small areas and it is assumed that each area takes an “H” (= high) or “L” (= low) condition. The condition is changed by dressing or polishing, and the total chemical mechanical planarization (CMP) performance is determined by the average pad condition. The results from equations are compared with experimental data, and good correspondence is confirmed. Various CMP behaviors are well explained by the equations, such as polishing rate stabilization by dummy running, the differences in the stability time and polishing rate between in situ dressing and ex situ dressing, and polishing rate behaviors for patterned wafers. This new model can be used to predict process performances, to optimize process conditions, or to indicate the direction of consumable development.
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Recently, a comprehensive model has been developed by Luo and Dornfeld ("Material removal mechanism in chemical mechanical polishing: theory and modeling", IEEE Trans. Semiconduct. Manufact., vol. 14, pp. 112-133, May 2001) to explain the material removal mechanism in chemical mechanical planarization (CMP). Based on the model, the abrasive size distribution influences the material removal from two aspects, one, the number of active abrasives, and the other, the size of the active abrasives. In this paper, experimental evidence supporting this view of abrasive size effects is discussed. A detailed model of wafer-abrasive-pad contact is developed to explain how and where abrasive size distributions come into the comprehensive material removal model. A material removal rate formulation as a function of abrasive size distribution is proposed and verified. In the future, the application of the model to the CMP process optimization, for example, improving the nonuniformity, or obtaining minimum surface scratching and preferred material removal rate by changing abrasive size distribution, may be attempted.
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We have developed an MQO~ slurry for dielectric planarization for the first time. Our Mn2O3 slurry has 4 times the removal rate of conventional slurry. The removal rate for this slurry remains constant for between 1 wt% and 10 wt% solid concentration. Pad-conditioning-free polish was successfully realized. We demonstrated that this slurry is
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