Slurry Chemicals

Sada, E., Kumazawa, H. and Lee, C.H., 1983. Chemical absorption in a bubble column loading concentrated slurry. Chemical Engineering Science, 38, 2047-2051. 

Luo, J. and Dorfeld, D. A., Material Removal Regions in Chemical Mechanical Planarization for Sub-micron Integrated Circuit Fabrication Coupling Effects of Slurry Chemicals, Abrasive Size Distribution and Wafer-Pad Contact Area, IEEE Trans. Semicond. Manuf, Vol. 16, No. 1, 2003, pp. 45-56. 

CMP is a wet process with DI water and/or polishing slurry present. During polishing, pad is under the attack of water, slurry chemicals, and abrasive particles at elevated temperature due to the friction force among wafer-particle-pad contact. This leads to changes in pad s physical and mechanical properties that influence polishing performance. 

Patri UB. Role of slurry chemicals in chemical mechanical planarization of copper [dissertation]. Potsdam (NY) Clarkson University 2005. 

Slurry Chemicals A large variety of materials (metals, alloys, insulators, semiconductors, etc.) are being polished. Each has a diffemt chemistry as far as chemical interactions with the slurry is concerned. Slurry chemicals affect primarily the chemical component, e.g., etch rate. However, chemical reactions modify the mechanical properties of the film, pad, and abrasive surfaces, which in turn affects the mechanical component. 

Concentration of Chemical Species Units of (moles/Iiter). Reaction rates are determined by both the concentrations of the reactants and the products of a reaction. Slurry chemicals either supply reactants or remove products, and hence as the concentration of the slurry chemicals increases, the reaction rates increase. Note, however, that the overall CMP process is composed of several steps and several different reactions. For any given set of process conditions, one of these steps will be limiting the total CMP removal rate. If an individual reaction is not part of this rate limiting step, the polish rate will be unaffected by changing the reaction rate. Only the reactions that are part of the rate limiting step will affect the polish rate. 

The final type of boundary layer results from chemical reactions of metal surfaces with the slurry chemicals. During metal CMP, the slurry chemicals react with the metal surface and form either solid or ionic products or both. Such reactions are considered corrosion reactions. Formation of solid species occurs on the metal surface, forming a surface layer which, to varying de-... 

Note, however, that for a given point on the surface, abrasion is not a continuous process, but rather occurs as discrete events. Because the pad has some surface roughness (on the order of 10-100 pm peak-to-peak) the pad is not in continuous contact with each point on the wafer. This concept will become more evident in the discussion of Section 4.5.1. In between the reformation of the abrasion events, the boundary layers reform. Between the time of the abrasion event and boundary layers, however, the surface is left highly exposed and reacts quickly with the slurry chemicals. As we shall see, surface reactions between abrasion events can have a strong influence on the CMP process, particularly in the case of tungsten CMP. 

CMP is analogous to the phenomena of erosion corrosion. Normally, during corrosion of a metal, a scale forms which slows further corrosion of the metal by acting as a barrier between the metal and the corrosive medium (Section 4.3). In erosion corrosion, low corrosion rates are accelerated by the removal of this scale via an erosion or wear process. The scale, wear process, and corrosive medium in erosion corrosion are analogous to the surface layer, mechanical abrasion, and slurry chemicals of the CMP process. Thus, in principle, the same electrochemical theories that are used to understand corrosion may be applied to CMP. In this section, we discuss the electrochemical theories that are important in metal CMP. In many instances we shall refer to the electrochemical behavior of copper for illustration. However, these electrochemical principles are applicable to the CMP of all metals. 

According to the Preston equation (Equation (4.1)), the polish rate varies linearly with pressure and velocity. In general, the Preston equation describes the pressure and velocity dependence of oxide CMP rate well, as shown in Figure 5.14. However, the theoretical value of the Preston coefficient, = 1/2E, does not explain the polish rate variation with other important process variables such as pad type, pad condition, slurry abrasive, and slurry chemicals. 

The slurry chemicals quickly re-form the surface layer, however, and a repetitive process of surface layer formation via chemical... 

In all these derivations, the role of the slurry chemicals during the polish process is not apparent. Even under static conditions, some of the chemicals can dissolve the material as in the case of ferric nitrate and copper or even H202/glycine and copper. This effect can, in principle, be easily included in a model description by adding a nonzero, velocity and pressure independent, intercept to the polish rate expression. In practice, it is more complicated since the relation between this nonzero intercept and static dissolution rates is not simple and is unknown due to, among other things, the effects of the polishing pad. In such cases, the role of a threshold pressure, while perhaps obvious when mechanical abrasion is the only mechanism for material removal, is not evident unless the removal rate can be broken neatly into two independent terms, one for the mechanical abrasion and the second for the chemical removal. Such is the case for the... 

During polishing, especially of metallic films, the concentration of the slurry chemicals in the liquid layers between the pad and the wafer is an important variable in determining the material removal rate. Unlike the hard abrasive powders in the slurry, the chemicals are consumed and need to be constantly replenished. The velocity of the wafer and the pad will influence the concentration as well as the rate of replenishment of the chemicals in the liquid film entrained between the pad and the wafer . Furthermore, the temperature of the film surface being polished will very likely increase as the wafer/pad velocity is increased, which, in turn, will increase the rates of the chemical reactions occurring at the film surface. Hence, one may anticipate that the removal rate will have a much stronger dependence on the velocity than that... 

The polish rate has a stronger dependence on velocity than that suggested hy Preston equation, when the slurry chemicals play a significant role in material removal during chemical-mechanical polishing as in the case of metal films. The empirical removal rate, R=KPV + BV + Rc, where K, B and Rc are constants provides a satisfactory description of all the polish rate data presented here. 

Luo, J., Domfeld, D.A., 2003. Material removal regions in chemical mechanical planarization for submicron integrated circuit fabrication coupling effects of slurry chemicals, abrasive size distribution, and wafer-pad contact area. IEEE Trans. Semicond. Manuf. 16, 45—56. 

The differential chemical reactivity of the Cu and barrier films when exposed to the slurry chemicals in the polishing environment can lead to the desired selective material removal but can also generate a variety of defects—corrosion pits, fangs due to galvanic corrosion, etc., and the underlying processes can be best investigated using a variety of electrochemical techniques, as described in the chapter authored by Dipankar Roy. 

Yoshioka, N., Hotta, Y., Tanaka, S., Naito, S. and Tongami, S., Continuous thickening of homogeneous slurries . Chemical Engineering, Tokyo, 21,66-74 (1957)... 

METASOL D3T is a preservative effective against a broad spectrum of bacteria and fungi in coatings, clay slurries, adhesives, glues, latex, emulsions, casein, and titanium dioxide slurries. Chemically, the product is tetrahydro-3,5-dimethyl-2H-l,3,5-thiadiazine-2-thione. 

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