Toshiro Doi

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 Fujimis 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.

Implications of Wafer-Size Scale-up on Frictional, Thermal, and Kinetic Attributes of Interlayer Dielectric CMP Process

The interlayer dielectric (ILD) chemical mechanical polishing (CMP) process was characterized using frictional forces, material removal rates, thermal measurements, and theory. Experiments were performed on a novel 200 mm tribometer in which friction force was acquired in two directions, giving a complete resolution of the force vector in the CMP process. A thermal study of the pad surface was conducted using an infrared video camera to simultaneously measure temperature changes. A Langmuir-Hinshelwood model with a reaction temperature based on a flash heating hypothesis was applied to the experimental data to evaluate the chemical and mechanical contributions during ILD CMP. The results obtained from the 200 mm tribometer were compared to those from a 100 mm tribometer. Results showed that the scale-up of the ILD process from 100 to 200 mm caused a transition from a mechanically limited regime, in which it was still possible to detect thermal effects, to a higher degree of mechanical limitation where it was no longer nossible to detect thermal effects.

Effect of Pad Surface Roughness on SiO2 Removal Rate in Chemical Mechanical Polishing with Ceria Slurry

The effect of pad surface roughness on SiO2 removal rate was investigated using four different slurries containing ceria (CeO2) powders of different crystallite sizes and mean particle sizes. A clear maximum was observed in the dependence of removal rate on pad surface roughness. The four ceria slurries showed a peak in blanket wafer removal rate against pad surface roughness Ra. The peak moved toward larger Ra values with decreasing ceria crystallite size. The removal rate was strongly influenced not only by pad surface roughness but also by the crystallite size of ceria in the slurry.

Development and Analysis of a High-Pressure Micro Jet Pad Conditioning System for Interlayer Dielectric Chemical Mechanical Planarization

Conventional diamond disc pad conditioning methods employed in chemical mechanical planarization (CMP) have presented several problems for integrated circuit (IC) manufacturers. These include diamond wear, which reduces pad life, and diamond fracture, which causes the semiconductor devices to be scratched by loose diamond fragments. In order to attempt to overcome these problems, a high-pressure micro jet (HPMJ) conditioning system, in which pressurized ultra pure water (UPW) ranging from 3–30 MPa is sprayed on the pad surface, is proposed and developed. This study first analyzes the extent of the kinetic energy of water droplets ejecting from the HPMJ system and its utility in conditioning the pad surface. Subsequently, CMP is used to polish interlayer dielectric (ILD) films using both conventional diamond discs as well as HPMJ conditioning methods. Results, reported in the form of coefficient of friction (COF), removal rate, pad surface roughness and pad surface quality, highlight both the advantages as well as disadvantages of the HPMJ method compared to conventional conditioning schemes.

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.

Modeling Copper CMP Removal Rate Dependency on Wafer Pressure, Velocity, and Dissolved Oxygen Concentration

A controlled atmosphere polishing system (CAP) was used to identify differences in copper chemical mechanical polishing (CMP) removal characteristics by changing oxygen partial pressure. A two-step kinetic mechanism was proposed, including a copper surface passivation layer formation and subsequent removal. A semiempirical, two-parameter model has been developed to simulate removal rates for multiple wafer pressures, pad-wafer velocities, and oxygen concentrations. The model accurately predicts removal trends with calculated root-mean-square errors of 77-125 A/min. A major advantage of the CAP system is that a point-of-use gaseous oxidant was successfully used to polish copper substrates, and slight changes in oxidant partial pressure were found to significantly affect removal rate trends.

Design and performance of a controlled atmosphere polisher for silicon crystal polishing

A controlled atmosphere polisher (CAP) was manufactured featuring a pressure-resistant chamber that hermetically contains the entire processing unit. The machine allows chamber gases to be changed. A vacuum pump or a compressor is used to maintain chamber pressure at a desired set point. When polishing under an air ambient, polish rates under partial vacuum or under pressurized conditions are significantly higher than those under conventional polishing conditions. Differences in polish rate are also seen depending on the type of gas used during polishing. This polishing method and tool have the potential of efficiently controlling and enhancing silicon polish rates.

Impact of Gaseous Additives on Copper CMP in Neutral and Alkaline Solutions Using a CAP System

A controlled atmosphere polishing (CAP) system was used to determine the effects of various chamber gases on copper chemical mechanical polishing (CMP) in the presence and absence of NH 4 OH and H 2 O 2 . Using 500 kPa oxygen or nitrogen has only slight effects on copper removal rates in the presence of 1 wt % H 2 O 2 . Polishing without H 2 O 2 , performed with controlled oxygen partial pressure, demonstrates removal rates that are 4 times higher than using nitrogen. Polishing using inert gases alone demonstrates an oxidant-starved system that reflects little dependence on wafer pressure or velocity. Addition of NH 4 OH (pH 10) to experiments using oxidizing gases, such as oxygen and air, increases removal rates up to 3×. Removal rates vary linearly with oxygen partial pressure using oxidizing gases for experiments using NH 4 OH at pH 10. A trend indicating a transition from chemical to mechanical control is observed when NH 4 OH concentration is increased at constant oxygen pressure. A copper removal mechanism in the presence of dissolved oxygen has been developed that highlights a buildup of oxidized copper at the wafer surface. The ability to perform CMP in a pressurized gaseous environment has shown that copper removal is a process of mechanical removal, dissolution of abraded material, and copper-oxygen reactions at the wafer surface.

Lapping and Polishing

Publisher Summary Lapping and polishing occur by the sliding frictions between particles and a surface. The lap or polisher travels across a work surface against which particles of sand or mud-type slurry are forced to the point of contact. The present processing technology, which belongs to the 4th generation, an improved version of the 3rd generation technology, has been applied to the fabrication of optical, electronic, and mechanical devices. A study on an automatic or computer aided machining system for both processing and ultra-precision polishing has been undertaken for practical use. Lapping and polishing are considered as two of the most outstanding processing methods because of their capability to secure high accuracy. The main difference between the lapping and polishing processes is obvious in glass lens manufacturing. Lapping produces a rough surface processed with coarse abrasives and a hard plate tool, while polishing produces a mirror-like surface processed with fine particle abrasives and soft pads. This chapter discusses principles of lapping and polishing for hard and brittle materials, like optical glass and crystals belonging to the group of ceramics, while also discussing the ultra-precision processing technique.