J. Sorooshian

Arrhenius Characterization of ILD and Copper CMP Processes

To date, chemical mechanical planarization (CMP) 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 Prestons 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 (ILD) CMP. The newly defined Prestons 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 mechanical) that are impacted by temperature during CMP. Studies indicate that for every consumable set combination (i.e., slurry and polishing pad) a characteristic combined Arrhenius activation energy can be calculated for each substrate material being polished.

Revisiting the Removal Rate Model for Oxide CMP

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.

Tribology and Removal Rate Characteristics of Abrasive-Free Slurries for Copper CMP Applications

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.

Effect of Process Temperature on Coefficient of Friction during CMP

This study investigates the effect of heat generation and thermal inputs on the frictional characteristics of interlayer dielectric (ILD) and copper chemical mechanical planarization (CMP) processes. A series of ILD and copper polishes were completed with controlled pad temperatures of ∼12, 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.

Estimating the Effective Pressure on Patterned Wafers during STI CMP

Removal rate results obtained from a 150 mm Speedfam-IPEC 472 polisher, coupled with a proven removal rate model has allowed for the determination of effective pressure (i.e., the actual pressure exerted on the structuresof a patterned wafer) during chemical mechanical planarization (CMP) of high-density plasma-filled shallow trench isolation (STI) wafers. Results showed that the ratio of derived effective pressure to applied wafer pressure was 2.2, 1.7, and 1.3 for 10, 50, and 90% density wafers, respectively. The relative consistency of these ratios indicates that the effective pressure experienced during polishing is not impacted by pattern density in a proportionate manner.

Dependence of Oxide Pattern Density Variation on Motor Current Endpoint Detection during Shallow Trench Isolation Chemical Mechanical Planarization

In this study, we evaluate the limitations associated with variable shallow trench isolation (STI) oxide pattern densities for accurate motor current endpoint detection during chemical mechanical planarization (CMP). Results indicate that repeatable motor current endpoint detection can be achieved for STI wafers with oxide pattern density variations of up to 17.4%. Furthermore, results show that a dependence exists between the STI oxide pattern density variation and motor current endpoint success during polishing. According to the findings of this study, a suitable motor current endpoint detection system could yield successful termination points for STI polishing, as well as reduce the need for polishing reworks.

Extending the flash heating removal rate model to various interlayer dielectric CMP consumables

This study extends the application of a previously presented flash heating removal rate model to a series of interlayer dielectric (ILD) chemical mechanical planarization (CMP) experiments using Freudenberg XY and perforated groove pads along with Fujimi PL-4217 fumed silica slurry. Polishing tests were conducted at platen temperatures ranging from approximately 24 to 45°C. Application of the model indicates its versatility when using different tool sets, pad types, and slurry chemistries compared to those originally used to develop the model. The flash heating removal rate model was shown to predict experimental data from this study by an average root mean square (rms) error of 164 A/min. When compared to the traditional Preston model, which predicted the data by an average rms of 300 A/min, the flash heating model provides better predictive accuracy and enables one to predict previously assumed scatter associated with removal rate in a systematic and comprehensible manner.