To date, chemical mechanical planarization ͑CMP͒ models have relied heavily on parameters such as pressure, velocity, slurry, and pad properties to describe material removal rates. One key parameter, temperature, which can impact both the mechanical and chemical facets of the CMP process, is often neglected. Using a modified definition of the generalized Preston's equation with the inclusion of an Arrhenius relationship, thermally controlled polishing experiments are shown to quantify the contribution of temperature to the relative magnitude of the thermally dependent and thermally independent aspects of copper and interlayer dielectric ͑ILD͒ CMP. The newly defined Preston's equation includes a modified definition of the activation energy parameter contained in the Arrhenius portion, the combined activation energy, which describes all events ͑chemical or mechanical͒ that are impacted by temperature during CMP. Studies indicate that for every consumable set combination ͑i.e., slurry and polishing pad͒ a characteristic combined Arrhenius activation energy can be calculated for each substrate material being polished.
This study employs real-time high-frequency frictional force analysis coupled with removal rate studies to quantify the extent of frictional forces encountered during copper polish using abrasive-free slurries and to establish the time-dependent tribological attributes of the process. The study also uses spectral analysis of the frictional force data to validate and explore the subtle characteristics of the formation and extinction of the copper complex layer known to play an integral role in abrasive-free copper chemical mechanical planarization (CMP). It was found that copper removal rates are at least partially driven by coefficient of friction, which is similar to the case of interlayer dielectric (ILD) CMP. Spectral analysis suggests that the periodicity of the copper complex layer formation and abrasion is approximately 10 ms.
This study seeks to explain removal rate trends and scatter in thermal silicon dioxide and PECVD tetraethoxysilane-sourced silicon dioxide (PE-TEOS) CMP using an augmented version of the Langmuir-Hinshelwood mechanism. The proposed model combines the chemical and mechanical facets of interlevel dielectric (ILD) CMP and hypothesizes that the chemical reaction temperature is determined by transient flash heating. The agreement between the model and data suggests that the main source of apparent scatter in removal rate data plotted as rate versus pressure times velocity is competition between mechanical and thermochemical mechanisms. A method of visualizing removal rate data is described that shows, apart from any particular interpretative theory, that a smooth and easily interpretable surface underlies the apparent scatter.
This study investigates the effect of heat generation and thermal inputs on the frictional characteristics of interlayer dielectric ͑ILD͒ and copper chemical mechanical planarization ͑CMP͒ processes. A series of ILD and copper polishes were completed with controlled pad temperatures of ϳ12, 22, 33, and 45°C and various pressures and velocities. Coefficient of friction results indicated an increasing trend for ILD and copper polishing with a rise in polishing temperature. Dynamic mechanical analysis of the used polishing pads revealed links between the softening effects of the pad with rising temperatures and increased shear forces resulting from the contact of the pad and wafer during polishing. The results presented are critical for establishing pad designs with stable dynamic mechanical properties and prolonged pad life.Recent publications have provided fundamental insight concerning the role of process temperature on material removal rate during chemical mechanical planarization ͑CMP͒ of interlayer dielectric ͑ILD͒ and copper films. 1-6 These in turn have led to the development of thermal models describing the generation of heat as a result of frictional effects caused by shaft work at the pad-slurry-wafer interface. 6,7 In these cases, given that thermal effects are small in magnitude ͑i.e., up to 8°C͒ and transient in nature ͑i.e., temperature rises during the first 30 s of a 75 s polishing process, and remains constant thereafter͒, 8 it is critical to determine how sustained thermal inputs ͑i.e., in the form of external platen heating or cooling͒ affect the frictional characteristics of ILD and copper CMP processes. Information of this nature is critical for establishing pad life and designing pads with stable dynamic mechanical properties. 9 Furthermore, for ILD polish, it has been shown that removal rate ͑i.e., as represented by Preston's constant͒ and average coefficient of friction ͑defined as the ratio of shear force to normal force, both of which can be determined experimentally using the apparatus described below͒ are linearly related at slurry abrasive concentrations of 9% or larger for a variety of pad types. 9 This work is based on the premise that during planarization, temperature increases in the pad-slurry-wafer region cause the dynamic mechanical properties of CMP pads to change, thus changing the coefficient of friction. Such phenomena require a fundamental understanding of the magnitude of forces involved in the process to refine existing removal rate and lubrication models. ExperimentalPolisher.-All experiments were performed on a scaled version of a Speedfam-IPEC 472 polisher. The polisher and its associated accessories have been described in detail elsewhere. 10 To measure the shear force between the pad and the wafer during polish, a sliding table was placed beneath the polisher. The sliding table consisted of a bottom and a top plate upon which the polisher was set. As the wafer and pad were engaged, the top plate would slide with respect to the bottom plate in only one direction due to...
This study employs pressure measurements and von Mises stress simulations across surfaces of wafers in order to examine the effect of wafer-ring gap size, extent and direction of wafer bow, and the effect of thermal history on within wafer pressure nonuniformity (WWPNU). WWPNU analysis for nominally flat, thermally untreated, wafers indicates that the wafer's 'central zone' has average pressure profiles, which remain constant, while the 'edge region' exhibits a sharp pressure peak. Dependence of wafer-ring gap size for the 'central zone' of bowed and thermally untreated wafers on WWPNU indicates that pressure profiles at larger gap sizes remain constant regardless of wafer shape. The 'edge zone' shows that the extent and direction of wafer bow has no effect on average pressure and variability. The effect of wafer-ring gap size on WWPNU for thermally treated wafers indicates that heat treatment reduces, or masks, the effect of gap size on average pressure in the 'central zone' of the wafer. A major effect of thermal treatment is the increase in overall pressure variability at the 'edge zone' of wafers.
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