Scott G. Meikle

Metalorganic chemical vapor deposition of TiN films for advanced metallization

Titanium nitride (TiN) films are used extensively in advanced metallization schemes for ultralarge scale integrated applications. In the present experiments, physical properties of thin TiN films deposited using low pressure chemical vapor deposition from tetrakis‐dimethyl‐amino titanium and ammonia have been investigated. Deposited films were characterized by resistivity, stoichiometry and etch rates. It was found that bulk resistivity correlated to wet etch rates with high resistivity films having higher wet etch rates. High bulk resistivity films were unstable in atmosphere and Auger analysis showed higher relative oxygen content. It is concluded that high resistivity films are low density and thereby susceptible to ex situ contamination. Optimized films had bulk resistivity of 250 μΩ cm and wet etch rates comparable to reactively sputtered TiN.

Effects of CMP Process Conditions on Defect Generation in Low-k Materials An Atomic Force Microscopy Study

The effects of chemical mechanical planarization (CMP) process parameters and consumables on the polish rate and defects generated in various low-k materials with k values ranging from 2.2 to 3.0 were studied in detail. The process consumables and conditions evaluated include slurry material (alumina and silica), pad type (soft and hard), polish pressure, and polish time. Atomic force microscopy (AFM) images and roughness numbers were used to evaluate the post-CMP defect generation under various process conditions and revealed nano/microscratches, pits, voids, and film delamination. For a given material, the removal rate increased with increasing pressure. The dependence of defects on pressure appeared highly driven by the slurry material, pad type, and low-k material properties. Defects increased with increasing pad hardness and decreasing k values. The increasing defects with decreasing k value can be attributed to the lower elastic modulus observed with low-k materials. Removal rates exhibited both a decrease and an increase in conjunction with polish time, depending on the type of low-k material used. AFM analysis showed an improvement in global surface roughness with increasing polish time; however, an increase in localized defects such as pits was also observed. Fourier transform infrared and X-ray photoelectron spectroscopy analyses showed no change in film chemistry under the conditions studied here.

Modeling of Chemical Mechanical Polishing Processes Using a Discretized Geometry Approach

A transport-based, three-dimensional numerical modeling approach has been developed to simulate chemical mechanical polishing processes occurring in microelectronic materials processing. A unique aspect of this model is that the detailed morphology of the slurry flow domain between the wafer and polishing pad is approximated with a regularly updated sequence of geometries evenly positioned along the polishing orbit. Additionally, the modeling approach allows the use of any constitutive relationship for the rheological behavior of the polishing slurry. The local polishing rate is taken to be proportional to the local hydrodyanmic shear stress generated on the to-be-polished wafer surface. To illustrate the modeling approach, the development of planarity during polishing of a prototypical 3 X 3 array of square roughness elements was simulated. The rheology of the polishing medium was described as a power-law fluid with a Newtonian plateau, which is appropriate for an aqueous slurry of colloidal silica. Two modes of pad-to-wafer tracking during polishing are discussed. Modeling results show good agreement with typical experimental data.

The Influence of Feature‐Scale Surface Geometry on CMP Processes

The influence of feature-scale surface pattern dimensions on chemical mechanical polishing (CMP) processes has been studied through numerical simulations using a discretized geometry approach. The development of planarity for a symmetrical 3 X 3 array of square roughness elements with various lateral dimensions and spacing was simulated. Geometrical shielding of roughness elements by neighboring elements was found to cause asymmetrical surface polishing during the CMP processes. Given a specified trench spacing, a stronger doming effect was predicted for smaller sized protrusions. For a fixed feature size, the most significant doming effect was found to occur when the trench width is comparable to the gap size between the pad and the protrusion. These effects can be associated with variations in the flow pattern of the polishing slurry in the vicinity of the roughness elements.

Inhibition of Alumina Deposition during Tungsten Chemical Mechanical Planarization Through the Use of Citric Acid

The beneficial effects of citric acid in inhibiting alumina particle deposition onto silica areas during tungsten chemical mechanical planarization were investigated. The electrokinetics of alumina in the presence of citric acid and the uptake of citric acid by alumina were studied experimentally. At a pH of 4, as the citric acid concentration was increased, the zeta potential of alumina became less positive and reversed sign. Slurry dip tests and small‐scale polishing experiments were carried out and the surface cleanliness of contaminated oxide surfaces was characterized with a field emission scanning electron microscope and image analysis. It has been demonstrated that citric acid is very effective in controlling alumina contamination on oxide surfaces when added into the slurry. Electrochemical tests showed that citric acid does not significantly attack tungsten films. A mechanism for the interaction between citric acid and alumina particles has been proposed.

Substrate temperature and collimator aspect ratio effects in titanium sputtering

We investigated the relationship of substrate temperature and collimator aspect ratio to sputtered titanium thin‐film properties. Titanium films were deposited in a configuration with a collimating mesh between the target and substrate over collimator aspect ratios of 0.7–2.0 and substrate temperature ranges of 150–450 °C, respectively. We found that a morphology transition occurs with rising deposition temperature and falling collimator aspect ratio where film stress switches from compressive to tensile, roughness increases 50%, grain size doubles, and resistivity increases 20%. We propose that the transition phenomenon is based on a film growth mechanism where substrate heating and surface bombardment have competing effects on the formation of surface clusters.

Barrier layer metallization schemes for ULSI technologies

Deep sub micron high aspect ratio contacts used for ULSI require highly conformal Ti and TiN films for W contact plug technology. Collimated Ti sputtering has been shown to enhance the coverage of Ti at the bottom of the contacts which helps obtain low contact resistance. However, insufficient sidewall and bottom corner coverage results in failure of the TiN barrier during subsequent processing. Conformal CVD TiN with collimated Ti is proposed as a technology of choice for obtaining low resistance and highly reliable contacts for advanced ULSI applications.