Chemical Mechanical Polishing by Colloidal Silica Slurry
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M.Sivanandini, Dr. Sukhdeep S Dhami , Dr. B S Pabla / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 3, May-Jun 2013, pp.1337-1345 CHEMICAL MECHANICAL POLISHING BY COLLOIDAL SILICA SLURRY M.SIVANANDINI, DR. SUKHDEEP S DHAMI , DR. B S PABLA Mechanical Department, National Institute of Technical Teachers Training and Research,Chandigarh-160019 ABSTRACT Chemical Mechanical Polishing is a damage. The application of scientific technological unique process enabling technology that allows results in the domain of glass polishing with chip makers to readily drive lithographic suspensions of rare earth oxides and micro patterning steps to smaller dimensions, an ages heterogeneous suspensions with particle old, “retro” technology related to glass polishing dimensions of 0.1–0.5 μm diameter and new or and metallographic finishing, thus enabling tested abrasive ultra disperse powders (UDP) have optical lithography to work. It represents a been attempted in electronics. The Chemical situation that is a true paradigm shift from the mechanical polishing performances can be typical way in which technological advancements optimized by process parameters such as become main stream in high-technology equipment and consumables (pad, backing film, semiconductor manufacturing processes. and slurry). One of the critical consumables in the Colloidal nano-abrasives with different particle CMP process is slurry (typically containing both sizes are required for slurries in different CMP abrasives and chemicals acting together), that processes. Colloidal silica is used as polishing directly affects CMP efficiency and the yield. slurry for producing reflecting surfaces for Slight changes in slurry properties due to mirrors, lenses and the planarization of contamination, chemical degradation, abrasive computer chips. Industrial use of colloidal content or applied shear can change polish silica’s is growing steadily in both traditional performance and impact yield. Correlation of areas and ever-increasing numbers of novel slurry property measurements with evaluations of areas. Colloidal silica’s are found in fields as wafer polish rate, planarity and defectivity provides diverse as catalysis, metallurgy, electronics, insight into the root cause of degradation in glass, ceramics, paper and pulp technology, polishing. The conventional slurry consists of optics, elastomers, food, health care and abrasive particles of the solid state suspended in a industrial chromatography, polishing liquid state chemical solution [8] containing one or sophisticated microcircuit parts to outer space more of various chemicals such as oxidizers, pH and play vital role in the safe reentry of space stabilizers, metal ion complexants and corrosion vehicles and the development of Western for inhibitors [9]. An abrasive in the slurry provides that matter, world civilization. The paper both mechanical action with nanometer-sized focuses a brief overview of chemical mechanical abrasive particles and chemical action from the polishing using colloidal slurry. solution additives with a synergistic effect that causes material removal [10,11].Through chemical Keywords - Chemical Mechanical Polishing, and physical actions, the abrasive-liquid Colloidal silica, Nanoabrasives, Slurry, interactions play an important role in determining Semiconductor the optimum abrasives’ type, size, shape and concentration [12]. The slurry designed for optimal I. INTRODUCTION performance should produce reasonable removal Chemical mechanical polishing (CMP) rates, acceptable polishing selectivity with respect technology was first put forward by Monsanto [1- to the underlying layer, low surface defects after 3] in 1965. It is an indispensable process step in polishing and good slurry stability. Choosing slurry semiconductor device fabrication, common which provides good removal rates without causing technique used in wafer polishing for dynamic defects is of utmost importance in CMP. Colloidal memory, microprocessor applications and glass sized SiO2, CeO2 and Al2O3 particles are used in mechanical polishing. It is one of the key new the manufacturing of CMP slurries. They are nanotechnology fabrication processes, a true applied in different fields, but SiO2 is promising. advance that could be made to work despite Alumina particles find limited used in the enormous odds and technical difficulties early on. manufacturing of slurries for tungsten CMP; they Chemical mechanical polishing (CMP) is widely are slowly falling out of vogue because of their used in the semiconductor industry [4-7] to produce hardness[13], Today, silica particles are mirror like surfaces with no measurable subsurface predominantly used in the preparation of slurries for dielectric as well as metal CMP. The use of industrial sols–gels of silicon acid (Monsanto 1337 | P a g e M.Sivanandini, Dr. Sukhdeep S Dhami , Dr. B S Pabla / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 3, May-Jun 2013, pp.1337-1345 Comp, Dupoint, Nalco Ch et al.) and of impact on wafer material removal rates with an compositions based on aerosol type UDP SiO2 associated increase in removal rate variability. The (Siemens,Degussa) and Al2O3 (Union Carbide authors concluded that additional rotational speed Corp.) led to the development of colloidal silica. studies would be useful to maximize material Robert Walsh (Monsanto), patent and publications removal rate with decreased variability of other authors (H. Dersin, I.S. Basi, R.L. The effects of phosphoric acid addition on Lachapelle, et al.) up to the beginning of eighties slurry for chemical–mechanical planarization contributed to development in microelectronics (CMP) of copper and tantalum nitride were with the development of colloidal silica sol and investigated by [15]. Alumina or colloidal silica as silica gel. In this paper a brief review of CMP an abrasive, organic acid as a complexing agent, process using colloidal silica slurry is presented. Hydrogen peroxide (H2O2) an oxidizing agent, a film forming agent, a pH control agent and II. COLLOIDAL SILICA SLURRY additives, phosphoric acid (H3PO4) as accelerator The silica slurries are typical consumable of the tantalum nitride as well as hydrogen materials for CMP. The colloidal silica and fumed peroxide as stabilizer were used. Experiments were silica are known as the representative CMP slurry performed on G&P Technology POLI-500CEk materials. Colloidal silica polishing suspensions are chemical–mechanical polisher ,Rodel IC-1400 k- unique because they provide both dispersing action groove polyurethane pad with the head speed and as well as a chemical mechanical polishing (CMP) the table speed 40 rpm, down pressure of the head action. It is effective as an additive for the 7 psi , slurry flow rate 150 ml/min, polishing for 1 intermediate diamond polishing of metals and is min on electroplated copper, sputtered tantalum also the best polishing abrasive for eliminating nitride, PETEOS wafer with 10,000 A° thickness. subsurface and surface because of its CMP Zeta potential and particle size measurement of the polishing action. These polishes are chemically slurries were carried out by using the Brookhaven stabilized to produce a nearly “perfect suspension”; ZetaPlus instrument. An acceleration of the can also have additives that minimize the effect of tantalum nitride CMP was verified by particle aggregation of crystallization. The electrochemical curves recorded with an EG and G distribution of colloidal silica has an important 273A potentiostat. The slurry of 5.0% by wt. effect on polishing rate and polished surface abrasive, 5.0% by wt hydrogen peroxide, 0.5% by roughness. wt. phosphoric acid had good H2O2 stability and In 2001, the effects of temperature, slurry TaN acceleration and dispersion ability. Hence pH, applied pressure and polishing rotation rate on slurry including phosphoric acid was proposed. the material removal rate during chemical Hong Lei prepared novel colloidal SiO2 mechanical polishing (CMP) of 4H-silicon carbide slurry, a carboxylic acid containing a long alkyl wafers using colloidal silica slurry and chain as lubricant additive, for the chemical– polyurethane/polyester fiber polishing pads have mechanical polishing of disk substrates with NiP been studied by Neslen C.L et al [14]. The wafers plated [16]. Polishing tests were conducted with were polished for 30 or 60 mins using a Strasbaugh SPEEDFAM-16B-4M CMP equipment Precision Polishmaster with a random motion (SPEEDFAMCo. Ltd., Japan ) for four slurries, polishing armature. Polishing at wafer temperatures each with a different mean particle diameter of 15, of 230C and 650C were performed and found that 30, 50 and 160 nm, processing pressure of 70 increased temperatures had no significant g/cm2, rotating speed of 25 rpm, processing improvements in removal rate. The polishing slurry duration of 8.5 min and slurry supplying rate of pH levels for the 90 rpm study were similar to 60 300 ml/min on work pieces of 95 mm/1.25mm rpm, showed that material removal rate was not aluminum alloy substrates with NiP plated about 85 affected by pH. Increased applied pressure resulted wt. % nickel and 15 wt. % phosphorus element. in accelerated removal of wafer material. The Prepared slurry of 6 wt. % SiO2 particles with an average removal rate over the four-hour period average diameter of 30 nm, 1 wt. % ferric oxidizer using a 9.9 pH polishing slurry was 139 Å/hour