Yongyong He

Kinematic Optimization for Chemical Mechanical Polishing Based On Statistical Analysis of Particle Trajectories

The abrasive effect of particles is one of the basic mechanical actions in chemical mechanical polishing (CMP). In this paper, numerical simulations of particle sliding trajectories are performed to examine the influence of the kinematic parameters on the polishing uniformity of typical rotary-type CMP equipment. The trajectory simulations are carried out based on the kinematic analysis. The results reveal that the speed ratio α and the period ratio kT0, which represent the coupling relationships among the three basic motions of CMP, are the two major factors affecting the trajectory distribution. Further, a trajectory density parameter is proposed to quantitatively evaluate the global uniformity of the trajectory distributions and to optimize the kinematic parameters for better uniformity. The statistical results of the trajectory density analysis reveal that the trajectory of the wafer edge is denser than that of the wafer central area. To obtain better trajectory uniformity, some particular values of α and kT0, that is, α = 1 and kT0=1, which imply that the basic motions have a special coupling relationship, should be excluded; the preferred kinematic parameter values for CMP are α = 0.91-0.93 and kT0=5-7. This paper provides a basic guide to the kinematic parameter settings of CMP.

Modeling the Chemical-Mechanical Synergy during Copper CMP

Based on the corrosion-wear theory, a mathematical material removal model incorporating both chemical and mechanical effects during chemical-mechanical planarization (CMP) is proposed in this paper. The model not only quantifies the chemical-mechanical synergy, but also isolates each components contribution to the material removal rate. Synergetic effects on material removal rate are simulated according to the corrosion-wear map. Furthermore, the influences of process parameters and particle size are analyzed. Although the experimental verification has yet to follow, the model predictions are in good agreement with the existing models and published experimental results. In addition, the model will provide an approach for assessing dominant factors in material removal rate during CMP.

Mild thermal reduction of graphene oxide as a lubrication additive for friction and wear reduction

Recently, studies on graphene-based lubrication additives have been widely researched, but few refer to their preparation by thermal reduction which shows potential in not only significantly lowering the mass-production cost, but also the simple, nonchemical process. In this study, mild thermal reduction of graphene oxide (MRGO) has been achieved by high temperature (700 °C) treatment and the product used as a lubrication additive. It shows a relatively ordered lamellar structure and a certain level of oxygen by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analysis, and exhibits excellent tribological properties as a lubrication additive. The friction coefficient can be reduced by as much as 30% and the rubbing surfaces display few scratches at a lower additive concentration (0.5 wt%) compared with that of base oil (Poly Alpha Olefins Type 6: PAO 6) without MRGO additive under the same friction conditions. Based on the advantages of green, low-cost and simple synthesis operation, the MRGO offers significant potential application as a lubrication additive.

Aminosilanization Nanoadhesive Layer for Nanoelectric Circuits with Porous Ultralow Dielectric Film

An ultrathin layer is investigated for its potential application of replacing conventional diffusion barriers and promoting interface adhesion for nanoelectric circuits with porous ultralow dielectrics. The porous ultralow dielectric (k ≈ 2.5) substrate is silanized by 3-aminopropyltrimethoxysilane (APTMS) to form the nanoadhesive layer by performing oxygen plasma modification and tailoring the silanization conditions appropriately. The high primary amine content is obtained in favor of strong interaction between amino groups and copper. And the results of leakage current measurements of metal-oxide-semiconductor capacitor structure demonstrate that the aminosilanization nanoadhesive layer can block copper diffusion effectively and guarantee the performance of devices. Furthermore, the results of four-point bending tests indicate that the nanoadhesive layer with monolayer structure can provide the satisfactory interface toughness up to 6.7 ± 0.5 J/m(2) for Cu/ultralow-k interface. Additionally, an annealing-enhanced interface toughness effect occurs because of the formation of Cu-N bonding and siloxane bridges below 500 °C. However, the interface is weakened on account of the oxidization of amines and copper as well as the breaking of Cu-N bonding above 500 °C. It is also found that APTMS nanoadhesive layer with multilayer structure provides relatively low interface toughness compared with monolayer structure, which is mainly correlated to the breaking of interlayer hydrogen bonding.

Investigation on the galvanic corrosion of copper during chemical mechanical polishing of ruthenium barrier layer

With the development of ultra-large scale integrated circuits, ruthenium has been used as one of the most promising barrier materials for copper interconnects by replacing the conventional Ta/TaN bilayer film. However, during the polishing process of Ru/Cu structure using KIO4 slurries, the galvanic corrosion of copper could happen due to the large difference of the corrosion potentials between ruthenium and copper. This paper investigates the galvanic corrosion of copper of the Ru/Cu galvanic couple in KIO4-based slurries. The results reveal that, in KIO4 slurries without the addition of effective inhibitors, the galvanic corrosion of copper can greatly accelerate the oxidation and the corrosion of copper, and as a result, more reaction products, such as Cu(IO4)2/Cu(IO3)2 and CuO, can be rapidly formed on the copper surface, by which the material removal rate (MRR) of copper increases and the defects of copper could be aggravated. According to the theory of galvanic corrosion, two types of methods for controlling the galvanic corrosion of copper are proposed, i.e. the 1st one is using other oxidizer instead and the 2nd one is adding appropriate inhibitors. For the 1st method, KIO3 is used for demonstration and the effectiveness is verified. For the 2nd method, the combination of benzotriazole (BTA) and a non-ionic surfactant is tested. With the addition of BTA and the non-ionic surfactant, the theoretical galvanic current density decreases by one order of magnitude, and the MRR of copper slightly decreases after copper is connected to ruthenium to form a Ru/Cu galvanic couple. The passivation mechanism of BTA and the non-ionic surfactant on the copper surface can be proposed as follows: firstly the added BTA can form hydrophobic Cu-BTA complex on the copper surface; then the hydrophobic polypropylene oxide segments of the non-ionic surfactant can be effectively absorbed on the hydrophobic Cu-BTA complex as a supplement. These two parts are integrated as a complete passivating film on the copper surface to protect it from corrosion and excessive mechanical abrasion.

Plasma Nitriding of AISI 304 Stainless Steel in Cathodic and Floating Electric Potential: Influence on Morphology, Chemical Characteristics and Tribological Behavior

In direct current plasma nitriding (DCPN), the treated components are subjected to a high cathodic potential, which brings several inherent shortcomings, e.g., damage by arcing and the edging effect. In active screen plasma nitriding (ASPN) processes, the cathodic potential is applied to a metal screen that surrounds the workload, and the component to be treated is placed in a floating potential. Such an electrical configuration allows plasma to be formed on the metal screen surface rather than on the component surface; thus, the shortcomings of the DCPN are eliminated. In this work, the nitrided experiments were performed using a plasma nitriding unit. Two groups of samples were placed on the table in the cathodic and the floating potential, corresponding to the DCPN and ASPN, respectively. The floating samples and table were surrounded by a steel screen. The DCPN and ASPN of the AISI 304 stainless steels are investigated as a function of the electric potential. The samples were characterized using scanning electron microscopy with energy-dispersive x-ray spectroscopy, x-ray diffraction, atomic force microscopy and transmission electron microscope. Dry sliding ball-on-disk wear tests were conducted on the untreated substrate, DCPN and ASPN samples. The results reveal that all nitrided samples successfully produced similar nitrogen-supersaturated S phase layers on their surfaces. This finding also shows the strong impact of the electric potential of the nitriding process on the morphology, chemical characteristics, hardness and tribological behavior of the DCPN and ASPN samples.

Ruthenium and Copper CMP in periodate-based slurry with BTA and K 2 MoO 4 as compound corrosion inhibitors

The Copper (Cu) wiring and barrier layer Ru (Ruthenium) CMP is of vital importance to the performance of microchips. For fabricating Ru-Cu interconnect structures, a serious challenge is the galvanic corrosion of Cu that occurs during Ru chemical mechanical polishing (CMP). Previous work has presented a calculation approach to evaluate the galvanic corrosion of Cu in slurry with KIO4 as the oxidizer. Potassium molybdate (K2MoO4) combined with benzotriazole (BTA) acts as the inhibitor and the synergetic effect during CMP has been investigated. The work in this paper makes further improvement in the CMP performance using K2MoO4 and BTA as corrosion inhibitors for Cu and Ru. Results show that the pH value, the oxidant and inhibitor concentration could significantly affect the CMP performance. The material removal rate (MRR) selectivity between Cu and Ru has been optimized by adjusting the slurry composition. Results show that in BTA contained slurry with KIO4 as oxidant, the addition of K2MoO4 helps to obtain good MRR selectivity between Cu and Ru. BTA-K2MoO4 acts as good corrosion inhibitor for Cu and has complexation effect for Ru during CMP.