CMP Performance Research Articles

CMP for Cu Interconnect with Advanced Barrier Materials

In this paper, we discuss CMP technology for Cu interconnects with a Co seed enhancement liner (SEL) and Cu with a Ru barrier. Typical forms of galvanic corrosion for each type of barrier are also reviewed. To meet CMP performance requirements, specific polishing and cleaning processes for each CMP step were developed. The overall performance of CMP was evaluated using a variety of patterned wafers, and results are presented.

Effects of CMP Pad Conditioner Properties and Performance on Polishing Pad, Process and Wafer Removal Rate

The focus of this work is CMP pad conditioners and the impact of diamond shape, size, density and protrusion on pad cut rate, pad surface roughness and wafer removal rate. Conditioner properties such as diamond shape, density and protrusion were found to directly impact the pad cut rate and wafer removal rate. Conditioners with high variation in diamond protrusion and uneven diamond shapes exhibited high drop in pad cut rate and wafer removal rate over the test period. Conditioners with high and very aggressive diamonds led to uneven pad conditioning creating step like features on the pad. Diamonds show wearing off sharp edges and chipping of edges due to mechanical forces exerted on them during conditioning. Also diamonds on some of the tested conditioners were found to be missing or sheared off during conditioning due to the mechanical stress and weak bonding process.

The L28 STI CMP Dummy Pattern Study on Topography for Advanced Fixed Abrasive and High Selective Slurry

The STI CMP performance was major determined by the uniformity of STI step height which was characterized by the ranges of within-die (WID) and within-wafer (WIW) thickness for both silicon nitride and trench oxide surface of isolation area. Currently, for 28nm generation, two advanced approaches for STI CMP were high selective slurry (HSS) and fixed abrasive (FA) CMP. For these two approaches, the design and layout of dummy were important to overcome the effect of various pattern densities and feature sizes. Therefore this research focused on the effect of dummy type for HSS and FA CMP. The result shows HSS CMP is the most robust process in STI CMP. The nitride thickness after HSS CMP shows good uniformity, 2~3 %, and is slightly affected by dummy type and PD of test key comparing with FA CMP.

Effects of CMP Pad Conditioner Properties and Performance on Polishing Pad, Process and Wafer Removal Rate

not Available.

Potassium sorbate as an inhibitor in copper chemical mechanical planarization slurry. Part I. Elucidating slurry chemistry

The integration of an advanced inhibitor, potassium sorbate (K[CH 3(CH) 4CO 2]), in a copper CMP slurry based on hydrogen peroxide and glycine is reported. The first part of the study discusses the slurry chemistry by qualitatively describing the processes involved and proposes a mechanism for a hydrogen peroxide–glycine based slurry having sorbate anion as an inhibitor. For this purpose, the specific role of each chemical constituent in the slurry was elucidated at a fundamental level by electrochemical studies, X-ray photon spectroscopy (XPS) and contact angle measurements, all linked to the CMP performance on blanket wafers. Once the polishing mechanism was resolved the influence of the inhibitor was evaluated by CMP processing of patterned wafers.

Cu/barrier CMP Protection Film Characterization Using Electrochemical Technique

As reported in a previous paper, electrochemical data not only can provide the information about Cu corrosion protection, but also can be correlated with slurry CMP performance. In this paper, further study on thermal stability of protection film and Cu planarization efficiency are carried out. Some surface related defect studies correlated with electrochemical data are also discussed.

Methodological Study on the Recycle of Oxide-Chemical Mechanical Polishing Slurry

To investigate the recycle possibility of a slurry for the oxide chemical-mechanical polishing (oxide-CMP) applications, we introduce three kinds of re-treated methods. First, the effects of addition of silica abrasives and a diluted silica slurry (DSS) on CMP performance were investigated. Second, the characteristics of a mixed abrasive slurry (MAS) using non-annealed and annealed alumina (Al2O3) powder as an abrasive added within a DSS were evaluated to achieve improved removal rates (RRs) and to decrease within-wafer non-uniformity percent (WIWNU%). Third, the oxide-CMP wastewater was examined in order to evaluate possible ways of reusing it. We discuss the CMP characteristics of a silica slurry re-treated by mixing of an original slurry with a used slurry (MOS). As an experimental result, the possibility of using a recycled slurry for oxide-CMP was confirmed. Our proposed methods will contribute to substantial savings in slurry consumption. Furthermore, acceptable oxide-CMP characteristics can be achieved by using a two-step CMP procedure.

Cu-CMPにおけるパッド溝形状・物性とその研磨特性

Cu-CMPにおけるパッド溝形状・物性とその研磨特性

Advances in Understanding and Control of CMP Performance: Contact-Hydrodynamics at Wafer, Groove, and Asperity Scale

ABSTRACTExamining CMP at any scale, one finds coupled contact mechanics and fluid mechanics. Increasingly sophisticated experimental and computational techniques have revealed aspects of solid-solid interaction and slurry flow at the wafer and groove scale and, more recently, at the texture scale. Successful prediction of CMP performance hinges on identifying universal physics that span these scales. In this paper we first review results of novel asperity-scale experiments that characterize the pad texture both as a solid topography subject to contact deformation and as an equivalent porous medium for slurry flow. These measures reveal that much of the texture volume is inactive as flow space, a feature confirmed quantitatively by computational modeling of flow across a conditioned CMP pad surface built from 3-D microscopy images. For hydrodynamics, the findings establish active fluid volume per unit area as the property that bridges from asperity scale to wafer scale. We then derive a fundamental basis for CMP removal rate prediction based on contact and hydrodynamics, using a Sommerfeld number defined across the groove and texture length scales. The resulting equation, containing a single unknown proportionality constant, demonstrates that the often used product of downforce and table speed tracks removal rate only when the hydrodynamic state affords adequate pad-wafer contact. Departures from the Preston equation attributed in other models to chemically-limited regimes of CMP are explained in the present treatment as changes in hydrodynamic film thickness and contact area—a fact confirmed by direct measurement. Removal rate predictions are discussed for ILD, STI, and copper processes using both conventional and non-Prestonian slurries, including variations in downforce, table speed, temperature, pad properties, and groove design. Finally, the influence of regional pad-wafer hydrodynamics is illustrated by applying the contact-hydrodynamics equation to grooves specially configured to vary the slurry film thickness from wafer center to edge. Local removal rates are well predicted using locally defined values of the groove-texture Sommerfeld number, confirming the generality of the contact-hydrodynamic description at least from wafer to asperity scale. Findings are further discussed in the context of next-generation pad architectures—not only to achieve more effective pad-wafer contact and slurry delivery, but also to favorably decouple contact and fluid mechanics in CMP pad design.

A Novel Nanoparticle Additive for Enhanced Copper CMP Performance

not Available.

Dependence of Decarbonation of Cerium Precursor on Synthesized Ceria Particle and Its Influence of STI CMP Performance

not Available.

The Impact of Wafer Edge Roll-Off on CMP Performance

The impact of wafer edge roll-off on CMP performance was investigated. Distributions of removal rates at the periphery of wafers were estimated by pressure distributions of front-side surfaces of wafers calculated by FEM analysis. Results showed that the edge roll-off influenced distributions of the removal rates at periphery of the wafers when both a stacked pad and a solo pad were used. The influence was reached 4 mm from the edge of a wafer with a stacked pad, and 10 mm from the edge with a solo pad. When ROA was 1.27 μm, ratios of surface pressure near the edge compared to the center part of a wafer, were about 30% with a stacked pad and about 23% with a solo pad. Moreover, in the case of a stacked pad, we found that the influence of the wafer edge roll-off to CMP process could be compensated by adjusting a pressure of a retainer ring. Also, ranges of allowable ROA with the stacked pad were not uniform when the pressure of a retainer ring was changed from 23 kPa to 30 kPa. On the other hand, in the case of the solo pad, the ranges of allowable ROA did not change very much, which was from 0 to about 0.4 μm, even if the pressure of a retainer ring was changed.

The Effect of Cerium Precursor Agglomeration on the Synthesis of Ceria Particles and Its Influence on Shallow Trench Isolation Chemical Mechanical Polishing Performance

The level of agglomeration in the cerium precursor and its effect on the physicochemical properties of the synthesized ceria particles and how these properties influence shallow trench isolation chemical mechanical polishing (STI CMP) performance were investigated. Two different types of ceria particles were synthesized from cerium precursors of different degrees of agglomeration. The crystallinity and particle size distribution of the synthesized ceria particles were markedly different between these two types of particles. The ceria particles synthesized from agglomerated cerium precursors had a smaller crystallite size than the other particles due to the incomplete decarbonation reaction, which resulted in large agglomerations of particles. The different physical characteristics of the ceria particles resulted in remarkable discrepancies between the STI CMP performances of the ceria slurries, such as the oxide removal rate, the selectivity and the uniformity.

Electrochemical corrosion effects and chemical mechanical polishing characteristics of tungsten film using mixed oxidizers

In this paper, the effects of mixed oxidizers on tungsten-chemical mechanical polishing (W-CMP) process were studied using three different kinds of oxidizers such as Fe(NO 3) 3, KIO 3 and H 2O 2. Moreover, the interaction between the tungsten film and the oxidizer was discussed by potentiodynamic polarization test, in order to compare the CMP performances and electrochemical behavior of the tungsten film as a function of mixed oxidizers. The potentiodynamic polarization results indicated that the corrosion current densities of the 5 wt% H 2O 2 and 5 wt% H 2O 2 + 5 wt% Fe(NO 3) 3 were higher than the other mixed oxidizers. Such an electrochemical corrosion effect implies that slurries with the highest removal rate have a high dissolution rate at lower pH. Therefore, we conclude that W-CMP performances are strongly dependent on the kind of oxidizers and the amounts of oxidizer additive.

Effect of Slurry Temperature on Cu Chemical Mechanical Polishing with Different Oxidizing Agents

AbstractChemical Mechanical Planarization (CMP) has evolved as one of the most critical and significant process in the manufacturing of semiconductor devices. Copper has become the material of choice for the interconnect wiring. The effect of heat generation at the interface is realized to be significant on copper CMP process. The increase in the oxidation rate of the chemical reaction and viscoelastic properties of polishing pads due to increase in temperature at the surface results in increased removal rates and change in planarization performance. In this research, the effect of temperature on the CMP performance using two most common oxidizing agents, KIO3 and H2O2 has been investigated using the CETRTM bench-top CMP tester. The coefficient of friction at the interface of polishing using both the oxidizers at different temperatures was monitored. The generated surface roughness post CMP was evaluated for samples polished using different oxidizing agents at different slurry temperatures. The AFM study was carried out using Digital InstrumentsTM D3100 instrument. This study is aimed at understanding the effect of temperature on the CMP process performance and the relative sensitivity of two most common oxidizers used in copper CMP towards temperature.

Optimization of Psiloquest's Application Specific CMP Pads for Commercialization

AbstractThere is a need for metrology, characterization and optimization of CMP pad architecture before being put into service. psiloQuest, Inc. has developed a novel polishing pad which is made up of polyolefin material instead of conventional polyurethane. The surface of the pad has been modified to match the surface of the material under going CMP. In this research, we have optimized the PECVD tetraethylorthosilicate (TEOS) surface coating duration and pad thickness for optimum pad output. The pad was then extensively characterized using the several standard metrology techniques such as SEM, XPS and nanoindentation. The CMP performance evaluation of all the candidate pads was done using CETR CP-4TM bench top CMP tester. There was a correlation and interdependence of the pad coating time and surface chemical, micromechanical and tribological properties. However, their impact on the pad CMP performance was found to be indirect, if any. These findings were used to optimize the pad design and architecture before commercialization. The demonstrated methodology can also be implemented for parametric optimization of polishing pads with novel designs in the future.

Potential-pH Diagrams of Interest to Chemical Mechanical Planarization of Copper Thin Films

AbstractChemical mechanical planarization (CMP), which can globally planarize both silicon dioxide (the prevalent interlayer dielectric), and copper films, has become the key process in the damascene method used for producing integrated circuit (IC) devices with multilevel copper interconnects. Cu CMP is typically carried out with slurries containing oxidizing agents, complexing agents, and corrosion inhibitors as the principal chemical components. In such slurries, complexing agents enhance the solubility of copper and increase the dissolution rate of the abraded material in Cu CMP. They also assist achieving high copper removal rates during dynamic polishing conditions. The nature of the complexing agent used, the pH and the redox potential of the slurry system are among the main factors controlling the dissolution and passivation behaviors of copper during CMP. Consequently, these factors are intimately related to the key CMP performance metrics such as removal rate and planarity. In this paper, potentialpH diagrams of copper in aqueous systems containing a number of organic complexing agents including ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), oxalic acid and malonic acid are presented. The predominance regions of copper complexes under different copper and ligand activities and their implications on copper removal during CMP are discussed.

Chemical and Mechanical Characterizations of the Passivation Layer of Copper in Organic Acid Based Slurries and its CMP Performance

Chemical and Mechanical Characterizations of the Passivation Layer of Copper in Organic Acid Based Slurries and its CMP Performance

Effect of Abrasive in Cu-CMP Slurry on Global Planarization

AbstractWe investigated the mechanical effect of an abrasive in an abrasive-free-like (AFL) slurry using CMP evaluation and ζ potential evaluation. The amount of abrasive strongly influenced CMP performance. We found out the optimum amount of abrasive for optimal CMP performance. The ζ potential of the abrasive was positive, and those of the Cu and barrier metal were negative. We discussed a planarization model of the AFL slurry in detail based on the ζ potential results obtained.

The Application of Chemical Mechanical Polishing for Nickel Used in MEMS Devices

AbstractChemical mechanical planarization (CMP) has found extensive application in the fabrication of micro-electro-mechanical systems (MEMS). Nickel and Nickel based alloys are known to possess favorable properties that make them promising candidates to realize movable structures for MEMS applications. The development of CMP slurry chemistry for Ni that provides good CMP performance is the key in enabling CMP technology for Nickel based MEMS device fabrication. Unfortunately, very little work has been reported in terms of the electrochemical interaction of Ni with various CMP slurry constituents such as oxidizers, complexants and inhibitors. In this study, CMP of nickel was performed using H2O2 as oxidizer and alumina particles as abrasives. Electrochemical techniques were used to investigate the dissolution/passivation behavior of high-purity Ni under static and dynamic conditions in slurries at pH 4 with the addition of oxidizer, complexing agent and nickel salt. The affected surface layers of the statically etched Ni-disc were investigated using X-ray photoelectron spectroscopy (XPS). The Ni removal rate increased with the addition of oxidizer and further increased with the addition of complexing agent and nickel salt. The electrochemical results indicate that the surface chemistry and electrochemical characteristic of Ni play an important role in controlling the polishing behavior.