Interlayer Dielectric Chemical Mechanical Planarization Research Articles

Correlating Coefficient of Friction and Shear Force to Platen Motor Current in Tungsten and Interlayer Dielectric Chemical Mechanical Planarization at Steady-State Conditions

Following up our earlier work that highlighted the relationship between shear force (SF) and platen motor current (PMC), in parallel with the relationship between coefficient of friction (COF) and PMC for various tungsten and interlayer dielectric (ILD) chemical mechanical planarization (CMP) cases at non-steady-state conditions, we explored whether or not PMC could be used as a reliable indicator instead of SF and COF at steady-state conditions. For the 12 cases studied, 72 distinct steps were analyzed. It was determined that PMC somewhat mirrored SF and PMC for long time (i.e. 10 s or longer) intervals after data averaging and applying a trend matching algorithm. SF and PMC trends matched only about 64% of the time (ranges between 45% to 85%) for all 72 steps, while PMC and COF trends matched 62% of the time ranging between 42% and 85%. PMC-SF and PMC-COF correlations were fairly poor at 1-sec time intervals as evidenced by much lower percent match values. Such poor correlations proved that at small time intervals, PMC was not sensitive enough to capture important information regarding myriad fluid dynamics and tribological phenomena and the instantaneous stick-slip occurrences encountered in CMP.

Correlating Coefficient of Friction and Shear Force to Platen Motor Current in Tungsten and Interlayer Dielectric Chemical Mechanical Planarization at Highly Non-Steady-State Conditions

Correlations between shear force and platen motor current (PMC), as well as those between coefficient of friction (COF) and PMC were investigated for various tungsten and interlayer dielectric (ILD) chemical mechanical planarization (CMP) cases where the processes were highly non steady-state. We chose to initially focus on non-steady-state conditions because we believed the relationships among shear force, COF and platen motor current to be clearer as opposed to steady-state conditions. Shear force, normal force and PMC data were collected from twelve different Stribeck+ curves at an acquisition frequency of 1,000 Hz and analyzed in order to determine any emerging trends. For the 12 cases, involving 8 pre-polished blanket CVD tungsten and 4 silicon dioxide blanket wafers, it was discovered that PMC closely mirrored shear force as evidenced by a high average correlation coefficient (0.955) and coefficient of determination (0.916) obtained from all runs. For COF vs. PMC, the average correlation coefficient and coefficient of determination for all cases were 0.758 and 0.608, respectively. These average values were dragged down by 5 cases in which the dominant tribological mechanism was found to be “boundary lubrication” where COF changed minimally with pseudo-Sommerfeld number.

Effect of Pad Groove Design on Slurry Injection Scheme during Interlayer Dielectric Chemical Mechanical Planarization

In this study, the effect of pad groove design on slurry injection scheme during interlayer dielectric chemical mechanical planarization was investigated. A novel slurry injection system (SIS) with multiple slurry outlets was designed to allow fresh slurry to be injected through one or multiple points. At first, the SIS with one injection point scheme was compared with the standard slurry application method on a concentrically grooved pad and an xy-groove pad. On the concentrically grooved pad, the SIS with one injection point scheme generated significantly higher oxide removal rates (ranging from 22 to 35 percent) compared to the standard slurry application method at different slurry flow rates. On the xy-groove pad, the SIS with one injection point scheme still resulted in higher removal rates (ranging from 3 to 9 percent), however, its removal rate enhancement was not as high as that of the concentrically grooved pad. In order to further improve slurry availability on the xy-groove pad, SIS with multi-injection point scheme was tested. Results showed that the SIS with multi-injection point scheme resulted in significantly higher removal rates (ranging from 17 to 20 percent) compared to the standard slurry application method. This work underscored the importance of optimum slurry injection scheme for accommodating particular pad groove designs.

Effect of Pad Surface Micro-Texture on Removal Rate during Interlayer Dielectric Chemical Mechanical Planarization Process

The effect of pad surface micro-texture on removal rate in interlayer dielectric chemical mechanical planarization was investigated. Blanket 200-mm oxide wafers were polished on a Dow® IC1000TM K-groove pad conditioned at two different conditioning forces. The coefficient of friction increased slightly (by 7%) while removal rate increased dramatically (by 65%) when conditioning force was increased from 26.7 to 44.5 N. Pad surface micro-texture analysis results showed that pad surface contact area decreased dramatically (by 71%) at the conditioning force of 44.5 N, leading to a sharp increase in the local contact pressure and resulting in a significantly higher removal rate.

Pad Wear Analysis during Interlayer Dielectric Chemical Mechanical Planarization

In this study, pad wear during interlayer dielectric (ILD) chemical mechanical planarization (CMP) was investigated using retaining rings with different materials and slot designs as well as pads with different materials at different platen temperatures. Results showed that the retaining ring slot design did not significantly affect the pad wear rate. On the other hand, the polyether ether ketone (PEEK) retaining ring exhibited a significantly lower pad wear rate (by 31%) than the polyphenylene sulfide (PPS) retaining ring. At both platen temperatures (25 and 50°C), the thermoplastic D100 pad exhibited lower pad wear rates than the thermoset IC1000 pad.

Investigating Effect of Conditioner Aggressiveness on Removal Rate during Interlayer Dielectric Chemical Mechanical Planarization through Confocal Microscopy and Dual Emission Ultraviolet-Enhanced Fluorescence Imaging

The effect of conditioner aggressiveness is investigated in interlayer dielectric polishing on three types of pad. A method using confocal microscopy is used to analyze the effect of conditioner aggressiveness on pad–wafer contact. Results show that a more aggressive conditioner produces a higher interlayer dielectric polishing rate while at the same time a pad surface with fewer contacting summits and less contact area. It is found that the ratio of the contacting summit density to the contact area fraction is more important than either parameter measured separately since the ratio determines the mean real contact pressure. Modeling results based on contact area measurements agree well with experimental results. Moreover, it is found that a more aggressive disc also generates a thicker slurry film at the pad–wafer interface. This is in agreement with our general findings regarding pad asperity height distribution obtained using confocal microscopy.

Tribological, Thermal, and Wear Characteristics of Poly(phenylene sulfide) and Polyetheretherketone Retaining Rings in Interlayer Dielectric CMP

Retaining rings made of poly(phenylene sulfide) (PPS) and polyetheretherketone (PEEK) with two different slot designs were subjected to a 4 h wear test. During the chemical mechanical planarization (CMP) process, the PPS retaining ring induced a higher coefficient of friction (COF) by ∼0.1 than the PEEK retaining rings. In addition, the PPS retaining ring exhibited a higher wear rate than the PEEK retaining rings by ∼28%. Although the retaining ring slot design did not significantly affect the COF and wear rate, retaining rings with sharp slot edges resulted in higher pad surface abruptness.

Characterization of thermoset and thermoplastic polyurethane pads, and molded and non-optimized machined grooving methods for oxide chemical mechanical planarization applications

This paper systematically studies the effect of pad material, grooving method and grooving pattern on interlayer dielectric chemical mechanical planarization. The tested polishing pads consist of thermoplastic and thermoset polyurethanes synthesized using two different processes. Grooves created using a molding technique are compared with grooves formed by mechanical cutting. The concentric groove design is also compared with the logarithmic positive spiral positive grooving design. Experimental data collected include removal rate, coefficient of friction, shear force variance, pad temperature and dynamic mechanical analyzer measurements. Scanning electron microscope images are used to correlate grooving methods with coefficient of friction and shear force variance measurements. Results show that all of the pads polish wafers in boundary lubrication mode with unique friction coefficient, shear force variance and pad temperature characteristics. Simulations using a two-step removal rate mechanism are performed to estimate the chemical and mechanical rate constants. The analysis indicates that the thermoplastic pad is more mechanically controlled than the thermoset pad and that molded grooving induces a more mechanically controlled process than non-optimized machined grooving.

Investigation of Pad Surface Topography Distribution for Material Removal Uniformity in CMP Process

This paper investigates the pad surface topography distribution and its effect on material removal uniformity using two different types of conditioners in an interlayer dielectric chemical mechanical planarization (CMP) process. The two types of conditioners are a random diamond disk and a uniform diamond disk (UDD). The pad surface was roughened by using the two diamond disks, and then the surface roughness and real contact area between the pad and the wafer were analyzed. The UDD generated a more uniform surface layer having a low standard deviation, although it had a low surface roughness. The random roughness pad showed a low material removal rate with a wide standard deviation, but the uniform roughness pad demonstrated a high removal rate with a narrow standard deviation. The uniform roughness pad improved the wettability of the pad and uniform distribution of the slurry across the pad. Therefore, the uniform roughness pad gave a more stable polishing performance than the random roughness pad.

Development of a Pad Conditioning Process for Interlayer Dielectric CMP Using High-Pressure Micro Jet Technology

Diamond conditioning was compared to an alternative method, namely high-pressure micro jet (HPMJ) conditioning, through a series of interlayer dielectric chemical mechanical planarization (ILD CMP) marathon tests. The two systems were compared individually and in combination on the basis of ILD removal rate (RR), coefficient of friction (COF), and the physical appearance of the pad surface (both on the top areas as well as inside the grooves). Results indicated that diamond conditioning alone was effective in causing RR and COF stability during extended runs, but it could not clean the slurry residues and other by-products from the surface of the pad (especially inside the grooves). Results also showed that HPMJ conditioning was able to effectively clean the pad surface, despite not providing enough energy to abrade the surface of the pad and maintain constant RR and COF during extended polishing. Based on these findings, a new pad conditioning method based on a combination of diamond and HPMJ conditioning was proposed. Results showed that this new method allowed for stable polish results in terms of RR and COF during extended marathon runs, and also yielded substantially residue-free surfaces, which could extend pad life and reduce wafer-level defect.

Mechanical properties of chemical mechanical polishing pads containing water-soluble particles

Non-porous pads containing varying amounts of embedded water-soluble particles (WSP) have been characterized and compared to porous pads for interlayer dielectric chemical mechanical planarization (CMP) applications. In situ infrared imaging of the pad shows temperatures increasing as a function of pressure and velocity. Results also indicate that pad surface temperatures can increase up to 10 °C for a 1-min polish. Thermal information proves to be a critical component in explaining the viscoelastic response of the pad as a result of CMP process temperatures. Glass transition temperatures for WSP-containing pads occur within standard CMP operating temperatures (20–40 °C). Comparative storage modulus trends demonstrate steeper decreasing slopes with increasing temperature for WSP-containing pads than the IC-1000. The gradually decreasing slope for the IC-1000 is a sign of a highly cross-linked material. WSP-containing pads also exhibit a greater energy loss due to heat as quantified by the difference in tan δ. Regardless of whether a pad is new or used, dynamic mechanical analysis results indicate similar bulk properties.

Effect of Pad Groove Designs on the Frictional and Removal Rate Characteristics of ILD CMP

Real-time coefficient of friction (COF) analysis was used to determine the extent of normal and shear forces during chemical mechanical planarization (CMP) and identify the lubrication mechanism of the process. Experiments were done on a scaled polisher using IC-1000 pads with various surface textures, and Fujimi’s PL-4217 fumed silica slurry over a wide range of applied pressures and relative pad-wafer velocities. Stribeck curves showed that pad texture dictated the overall lubrication mechanism of the system. Average COF results yielded valuable information regarding the overall range of frictional forces associated with each type of surface texture. The linear correlation between COF data and interlayer dielectric (ILD) removal rate was consistent with previously published correlation graphs involving a variety of conventional pad textures and fumed silica concentrations. Spectral analysis of real-time friction data was used to elucidate the lubrication mechanism of the process in terms of the stick-slip phenomena and to quantify the total amount of hydrodynamic chattering as a function of various pad surface textures. For a given lubrication mechanism, analysis of the spectra for various textures indicated significant differences that were attributed to the amount of slurry present in the pad-wafer interface. © 2004 The Electrochemical Society. All rights reserved.

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 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 (ILD) 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 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. © 2004 The Electrochemical Society. All rights reserved.

The Stability of Nano Fumed Silica Particles and Its Influence on Chemical Mechanical Planarization for Interlayer Dielectrics

The effects of water-soluble polymer adsorption on the stability of silica particles and its influence on chemical mechanical planarization (CMP) for interlayer dielectrics (ILD) were investigated. This study was focused on the properties of silica slurry with and without surface modification by analyzing dispersion stability and chemical mechanical planarization field evaluation. As a silica slurry for interlayer dielectric chemical mechanical planarization was prepared in the alkaline region to accelerate the chemical corrosion process of plasma enhanced tetraethlyorthosilicate (PETEOS) film, Si ions dissolved the point where it would adversely affect the colloidal stability of the silica particles. As the silica surface was modified with poly vinyl pyrrolidone (PVP) polymer, the decrease of surface potential above pH 9.0 disappears and thus resulted in an increase of the stability of silica particles dispersed in the alkaline region. Modification of the slurry with PVP reduced micro-scratches and remaining silica particles on the wafers with favorable removal rate and better uniformity.