Cu Chemical Mechanical Polishing Research Articles

Study on the film forming mechanism, corrosion inhibition effect and synergistic action of two different inhibitors on copper surface chemical mechanical polishing for GLSI

As the most basic interconnection metallic material, copper (Cu) has been widely used in giant-large scale integrated circuits (GLSI). Corrosion inhibitors always play a crucial role in the Cu chemical mechanical polishing (CMP) process. The passivation of hydrogen peroxide (H2O2) alone is too weak to adequately protect against chemical corrosion on the surface of Cu film, thus, it is necessary to add corrosion inhibitors to the slurry. As a representative corrosion inhibitor, 1, 2, 4-triazole was compared with a novel corrosion inhibitor known as TT-LYK (ethanol, 2, 2′-[[(methyl-1H-benzotriazol-1-yl) methyl] imino] bis-), and their mixed inhibitor was studied in this paper. Different analytical methods such as the potentiodynamic polarization test, physical appearance phenomenon analysis, contact angle measurement and dynamic polishing experiment were used to compare their inhibition properties, and the fitting of different adsorption isotherms and static erosion tests were used to clarify the adsorption types and passivation processes respectively. The results indicated that both TT-LYK and 1, 2, 4-triazole achieved the goal of inhibiting Cu surface corrosion, but the inhibition effect of TT-LYK was slightly weaker at the same mass fraction. The corrosion protection of the two inhibitors is mainly attributable to the presence of organic inhibitor molecules on the surface of Cu by chemisorption and physisorption simultaneously. The passivation processes of both can be divided into two steps. First, the direct growth of the Cu-inhibitor passivation film occurs, followed by the redeposition of the Cu-inhibitor complex. From the results of electrochemical experiments, it can be concluded that the structure of the thin passivation film growing on the Cu surface varies with the inhibitor, and the composition of the passivation film was investigated by XPS and Raman spectrum analysis. At the same time, the surface roughness after polishing was found to decrease with the increase in inhibition effect of the inhibitors. According to the inhibition characteristics of these two inhibitors, a mixed corrosion inhibitor (TT-LYK and 1, 2, 4-triazole) was proposed in this study. Under the synergistic inhibition action, better inhibition effect and surface quality for Cu CMP were obtained. This outcome may be ascribed to the variation in the structure and density of the passivation film.

The effect of TAD based cleaning solution on post Cu CMP process

A cleaning solution has been introduced to remove the residue from Cu substrate after the Cu chemical mechanical polishing (CMP) process. In this study, the effects of complexing agents on the performance of cleaning solutions were studied depending on different functional groups and concentration based on a lift-off mechanism. The cleaning performance of the cleaning solution was assessed based on zeta potential, residual particle density, and etch rates. To prove that the cleaning is based on the lift-off mechanism, the Cu oxide layer composition and thickness were investigated by X-ray photoelectron spectroscopy. The thickness of Cu oxide increased up to 3.48nm after the Cu CMP process; however, it dramatically decreased to 0.80nm after the cleaning process. As the number of functional group for complexing agent and its concentration increased, the cleaning performance improved. In alkali condition, the amine functional group was found to be superior to other functional groups.

Planarization effect evaluation of acid and alkaline slurries in the copper interconnect process**Project supported by the Special Project Items No. 2 in National Long-Term Technology Development Plan (No. 2009ZX02308), the Doctoral Program Foundation of Xinjiang Normal University Plan (No. XJNUBS1226), the Key Laboratory of Coal Gasification, Ministry of Education, and the Inorganic Chemistry Key Disciplines of Xinjiang Normal University.

We observed and analyzed the acid and HEBUT alkaline of Cu chemical mechanical polishing (CMP) slurry to evaluate their effects. Material analysis has shown that the planarity surfaces and the removal rate of alkaline slurry are better than the acid slurry during metal CMP processes. The global surface roughness and the small-scale surface roughness by 10 × 10 μm2 of copper film polished by the SVTC slurry are 1.127 nm and 2.49 nm. However, it is found that the surface roughnesses of copper films polished by the HEBUT slurry are 0.728 nm and 0.215 nm. All other things being equal, the remaining step heights of copper films polished by the SVTC slurry and HEBUT slurry are respectively 150 nm and 50 nm. At the end of the polishing process, the dishing heights of the HEBUT slurry and the SVTC slurry are approximately both 30 nm, the erosion heights of the HEBUT slurry and the SVTC slurry are approximately both 20 nm. The surface states of the copper film after CMP are tested, and the AFM results of two samples are obviously seen. The surface polished by SVTC slurry shows many spikes. This indicates that the HEBUT alkaline slurry is promising for inter-level dielectric (ILD) applications in ultra large-scale integrated circuits (ULSI) technology.

습식표면처리 및 열 사이클에 따른 Cu/SiNx계면접착에너지 평가 및 분석

반도체 미세구리배선 적용을 위하여 구리배선의 습식 표면처리 및 열 사이클에 따른 구리 박막과 실리콘질화막 도포층 사이의 계면접착에너지를 4점굽힘시험을 통해 정량적으로 평가하였다. 구리배선을 화학적 기계적 연마한 후 습식 표면처리를 통하여 구리 박막과 실리콘질화막의 계면접착에너지는 <TEX>$10.57J/m^2$</TEX>에서 <TEX>$14.87J/m^2$</TEX>로 증가하였다. <TEX>$-45{\sim}175^{\circ}C$</TEX>범위에서 250사이클 후, 표면처리를 하지 않은 시편의 계면접착에너지는 <TEX>$5.64J/m^2$</TEX>으로, 표면처리를 한 시편은 <TEX>$7.34J/m^2$</TEX>으로 감소하였으며, 모든 시편의 박리계면은 구리 박막과 실리콘질화막 계면으로 확인되었다. X-선 광전자 분광법으로 계면 결합 상태를 분석한 결과, 화학적 기계적 연마 공정 후 구리배선의 표면 산화물이 습식표면처리에 의해 효과적으로 제거된 것을 확인하였다. 또한, 열 사이클 처리동안, 구리 박막과 실리콘질화막의 큰 열 팽창 계수 차이로 인한 열응력으로 인하여 구리 박막과 실리콘질화막 계면이 취약해지고, 계면을 통한 산소유입에 따른 구리 산화층이 증가하여 계면접착에너지가 저하된 것으로 판단된다. Effects of wet chemical treatment and thermal cycle conditions on the quantitative interfacial adhesion energy of <TEX>$Cu/SiN_x$</TEX> thin film interfaces were evaluated by 4-point bending test method. The test samples were cleaned by chemical treatment after Cu chemical-mechanical polishing (CMP). The thermal cycle test between Cu and <TEX>$SiN_x$</TEX> capping layer was experimented at the temperature, -45 to <TEX>$175^{\circ}C$</TEX> for 250 cycles. The measured interfacial adhesion energy increased from 10.57 to <TEX>$14.87J/m^2$</TEX> after surface chemical treatment. After 250 thermal cycles, the interfacial adhesion energy decreased to <TEX>$5.64J/m^2$</TEX> and <TEX>$7.34J/m^2$</TEX> for without chemical treatment and with chemical treatment, respectively. The delaminated interfaces were confirmed as <TEX>$Cu/SiN_x$</TEX> interface by using the scanning electron microscope and energy dispersive spectroscopy. From X-ray photoelectron spectroscopy analysis results, the relative Cu oxide amounts between <TEX>$SiN_x$</TEX> and Cu decreased by chemical treatment and increased after thermal cycle. The thermal stress due to the mismatch of thermal expansion coefficient during thermal cycle seemed to weaken the <TEX>$Cu/SiN_x$</TEX> interface adhesion, which led to increased CuO amounts at Cu film surface.

웨이퍼 레벨 3D Integration을 위한 Ti/Cu CMP 공정 연구

Cu 본딩을 이용한 웨이퍼 레벨 적층 기술은 고밀도 DRAM 이나 고성능 Logic 소자 적층 또는 이종소자 적층의 핵심 기술로 매우 중요시 되고 있다. Cu 본딩 공정을 최적화하기 위해서는 Cu chemical mechanical polishing(CMP)공정 개발이 필수적이며, 본딩층 평탄화를 위한 중요한 핵심 기술이라 하겠다. 특히 Logic 소자 응용에서는 ultra low-k 유전체와 호환성이 좋은 Ti barrier를 선호하는데, Ti barrier는 전기화학적으로 Cu CMP 슬러리에 영향을 받는 경우가 많다. 본 연구에서는 웨이퍼 레벨 Cu 본딩 기술을 위한 Ti/Cu 배선 구조의 Cu CMP 공정 기술을 연구하였다. 다마싱(damascene) 공정으로 Cu CMP 웨이퍼 시편을 제작하였고, 두 종류의 슬러리를 비교 분석 하였다. Cu 연마율(removal rate)과 슬러리에 대한 <TEX>$SiO_2$</TEX>와 Ti barrier의 선택비(selectivity)를 측정하였으며, 라인 폭과 금속 패턴 밀도에 대한 Cu dishing과 oxide erosion을 평가하였다. The wafer level stacking with Cu-to-Cu bonding becomes an important technology for high density DRAM stacking, high performance logic stacking, or heterogeneous chip stacking. Cu CMP becomes one of key processes to be developed for optimized Cu bonding process. For the ultra low-k dielectrics used in the advanced logic applications, Ti barrier has been preferred due to its good compatibility with porous ultra low-K dielectrics. But since Ti is electrochemically reactive to Cu CMP slurries, it leads to a new challenge to Cu CMP. In this study Ti barrier/Cu interconnection structure has been investigated for the wafer level 3D integration. Cu CMP wafers have been fabricated by a damascene process and two types of slurry were compared. The slurry selectivity to <TEX>$SiO_2$</TEX> and Ti and removal rate were measured. The effect of metal line width and metal density were evaluated.

Effects of Slurry in Cu Chemical Mechanical Polishing (CMP) of TSVs for 3-D IC Integration

In this paper, the optimization of Cu chemical-mechanical polishing (CMP) performance (dishing) for the removal of thick Cu-plating overburden due to Cu plating for deep through silicon via (TSV) in a 300-mm wafer is investigated. Moreover, backside isolation oxide CMP for TSV Cu exposure is examined. To obtain a minimum Cu dishing on the TSV region, a proper selection of Cu slurries is proposed for the current two-step Cu-polishing process. First, a bulk of Cu is removed with the slurry of high Cu removal rate and second, the Cu surface is planarized with the slurry of high Cu passivation capability. The Cu dishing can be improved up to 97% for the 10-μm-diameter TSVs on a 300-mm wafer. The dishing/erosion of the metal/oxide can be reduced with respect to a correspondingly optimized Cu-plating overburden for TSVs and redistribution layers. Cu metal dishing can be drastically reduced once the Cu overburdens are increased to a critical thickness. For backside isolation oxide CMP for TSV Cu exposure, the results show that the Cu studs of TSVs with a larger TSV diameter still keep in a plateau-like shape after CMP.

Pad Conditioning for Scratch-Free, Cu Chemical-Mechanical Polishing (CuCMP)

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Effect of Functional Groups of Complexing Agents on the Performance of Cu CMP Slurry

Complexing agents in Cu chemical mechanical polishing (CMP) slurry have an important role for enhancing Cu removal rate. To understand the effects of complexing agents on the performance of Cu CMP slurry, selected complexing agents which have different functional groups were investigated. It was observed that the Cu dissolution rate was varied with the change of types and numbers of functional groups of complexing agents. By using UV-visible analysis, the changes of complex form with pH were monitored and expected reaction mechanisms were proposed. The effect of Cu oxide formation was also monitored by the coulometric reduction method (CRM) analysis. Based on CRM analysis, the evaluation of Cu oxide thickness which formed on the Cu surface during the dissolution was conducted and the relationships between formed Cu oxide thickness on the surface and Cu dissolution rate were discussed.

Galvanic Corrosion Control in Chemical Mechanical Polishing of Cu Interconnects with Ruthenium Barrier Metal Film

We investigated galvanic corrosion in Cu interconnects with ruthenium (Ru) barrier metal films that occurred in Cu chemical mechanical polishing (CMP) and Ru-CMP steps. When conventional CMP slurries were used in the same polishing conditions, severe dishing was found to occur in Ru barrier interconnects. This dishing was attributed to the electrochemical potential difference between Cu and Ru in the CMP slurries. Thus, we reduced this potential difference in the slurry from 400 to 2 mV, and we suppressed dishing just after Cu-CMP from 27 to 9 nm. As a result, by using Ru slurry with a controlled corrosion potential, we minimized final dishing after Ru-CMP to 25 nm which was lower than that of conventional Ta barrier interconnects.

Influence of Chemical-Mechanical Polishing Process on Time Dependent Dielectric Breakdown Reliability of Cu/Low-k Integration

AbstractThe effects of defects caused by Cu chemical-mechanical polishing (CMP) on time-dependent dielectric breakdown (TDDB) in a damascene structure incorporating a low-k interlevel dielectric layer were investigated experimentally. Comb line capacitor structures were prepared with one of three types of defects (rough Cu surface corrosion, Cu depletion, or crevice corrosion) and stressed at 3.2 to 6.2 MV/cm at 140°C. The first two defects had an insignificant effect on the TDDB characteristics while crevice corrosion at the edges of wires significantly degraded them. Investigation of the effects of Cu oxidation during post-CMP cleaning on the TDDB characteristics revealed that the formation of a non-uniform oxide layer accompanying deionized water rinsing was due to the dissolution of Cu oxide during the post-CMP cleaning process. When a barrier metal slurry containing a soluble inhibitor was used, non-uniform oxide formation on the Cu surfaces during post-CMP cleaning degraded the TDDB characteristics. These results demonstrate the importance of uniform Cu oxidation during post-CMP cleaning for improving the TDDB characteristics.

Influence of CMP Slurries and Post-CMP Cleaning Solutions on Cu Interconnects and TDDB Reliability

We investigated Cu/low-k integration to test the time-dependent dielectric breakdown (TDDB) reliability of Cu interconnects. We described the relationship between TDDB lifetime and defects possibly caused by the Cu chemical-mechanical polishing (CMP) process, such as rough copper surface corrosion, crevice corrosion, and scratches, using Cu/silicon oxycarbide interconnects. Although rough copper surface corrosion has an insignificant effect on the TDDB lifetime, crevice corrosion at the edges of wires does cause TDDB degradation. We also found that a structure’s TDDB lifetime was affected by the kind of post-CMP cleaning solutions used when barrier metal slurries do not contain benzotriazole (BTA). These results indicate that two types of processes for post-CMP cleaning should be used. It is best to use solutions that do not have strong oxidized copper dissolution ability but can remove particles when a barrier metal slurry with an inhibitor other than BTA is used. Also good are solutions with a strong oxidized copper dissolution ability that have been optimized to prevent Cu corrosion when a barrier metal slurry with BTA is used. To improve TDDB reliability, care must be taken with regard to the combination of the barrier metal slurry and the post-CMP cleaning solution.

Copper voids improvement for the copper dual damascene interconnection process

The mechanism of copper (Cu) voids formation from electro-chemical plating (ECP) followed by Cu chemical mechanical polishing (CMP) are studied in Cu dual-damascene interconnection. The formation of Cu voids at metal lines is the main problem that causes not only the failure of via-induced metal-island corrosion but also yield loss. The galvanic theory and Cu lifting mechanism are proposed to explain the dependence of Cu-void performance on the Cu grain size and the benzotriazole (BTA, C 6H 5N 3) flow rates. In the integration process of Cu interconnects, it is found that the smaller Cu grain size in ECP conditions and less BTA flow rate in CMP processes cannot only reduce the number of Cu voids but also improve the wafer yield.

Evaluation of Mercaptobenzothiazole Anticorrosive Layer on Cu Surface by Spectroscopic Ellipsometry

Mercaptobenzothiazole (MBT) anticorrosive layer on copper surface prepared in MBT solutions was analyzed by spectroscopic ellipsometry (SE). The results showed that MBT anticorrosive layer was formed on Cu2O layer in the MBT solution at temperatures higher than 50 °C. Additionally, it was confirmed that MBT anticorrosive layer was formed in the MBT solution at room temperature by adding about 20 wt % acetone to the solution. From polishing experiments of MBT anticorrosive layer and benzotriazole (BTA) layer, it was revealed that MBT anticorrosive layer was physically stronger than BTA layer. It is considered that dishing amount in Cu chemical-mechanical polishing (CMP) can be reduced by using MBT. However, MBT anticorrosive layer was not formed in the MBT solution including Hydrogen peroxide (H2O2) suggesting that slurry should be composed without H2O2 in order to use MBT for Cu CMP.

Enhancement of Post-Cu-Chemical Mechanical Polishing Cleaning Process for Low-k Substrate

The introduction of low-dielectric-constant (low-k) materials as interlayer dielectrics (ILD) to support Cu interconnects causes poor slurry removal efficiency and watermark generation in post Cu-chemical mechanical polishing (CMP) cleaning because low-k dielectric films are hydrophobic. To address these problems, the authors performed basic studies using low-k (SiOC) blank (unpatterned) substrates. Our studies have revealed that it is important to control the wettability of the SiOC surface by using a surfactant-spiked cleaning solution in order to effectively remove the large number of slurry particles adhering to the SiOC surface due to hydrophobic interaction. For watermark generation, our study has found that even the combination of ultrapure water (UPW) spin rinsing and spin drying causes a watermark to be generated on a clean SiOC surface. It is revealed that watermark generation is attributed mainly to oxygen diffusion into microdroplets left on the SiOC surface after spin drying. Fourier transform IR (FTIR) analysis indicates this watermark to be composed of silicon oxides or silicon hydrates. The authors have also proven that watermark generation can be suppressed by using ultrapure water with N2 gas dissolved to its saturated concentration (N2-UPW).

Dominant Factors in TDDB Degradation of Cu Interconnects

The field acceleration factor (/spl gamma/) for the E-model of time-dependent dielectric breakdown (TDDB) in various Cu interconnect structures has been studied. The /spl gamma/ for pSiCN structures is larger than that of pSiN structures and independent of the kind of interlayer dielectric material or other processes used to make it. The relationship between the breakdown electric field strength (E/sub BD/) and the TDDB lifetime has been investigated. It has been demonstrated that the TDDB lifetime can be predicted from experimentally measured E/sub BD/ and /spl gamma/. An E/sub BD/ of at least 4.2 MV/cm is necessary to assure ten-year reliability under 0.2 MV/cm operation. Moreover, the important factors influencing the TDDB lifetime for Cu interconnects have been discussed. These include the Cu chemical-mechanical polishing (CMP), the post-CMP annealing, line edge roughness, and fine line effect.

光放射圧を利用したCu-CMP加工に関する研究(第2報)

光放射圧を利用したCu-CMP加工に関する研究(第2報)

Influence of Cu-Ion Migration and Fine-Line Effect on Time-Dependent Dielectric Breakdown Lifetime of Cu Interconnects

The time-dependent dielectric breakdown (TDDB) of sub-half-micron Cu interconnects was investigated with respect to the waiting time between Cu chemical mechanical polishing (CMP) and barrier dielectric deposition. Breakdown voltage and TDDB lifetime between adjacent Cu wires decrease markedly if the waiting time in air exceeds 5 days. This is due to Cu-ion migration phenomenon on the CMP surface. The degradation can be improved by keeping the samples in a N2 box or adopting post-CMP cleaning. This TDDB degradation has been observed for various Cu barrier dielectrics in this study. In addition, a “fine-line effect” on Cu TDDB lifetime has been discovered. As Cu wire width becomes smaller, the TDDB lifetime also decreases because of the intensification of the electric field at the CMP surface.

Reduction Characteristics of Iodate Ion on Copper: Application to Copper Chemical Mechanical Polishing

Potentiodynamic and potentiostatic polarization, and the rotating disk electrode technique were used to study the reduction characteristics of iodate (IO3−) ion on copper (Cu). Depending on the relative concentrations of IO3− and H+ two pH regimes were observed. The cathodic current in the first regime (pH > ,3) was controlled by H+ diffusion from the solution to the metal surface. In the second regime (pH > 3 and up to 10−2 m IO3− concentration) the cathodic current was found to be under mixed control, involving reaction control via the electrochemical reduction of IO3− and transport control via the diffusion of I2(aq). It was concluded that IO3− was an effective oxidant for Cu chemical mechanical polishing (CMP) with strongly acidic (pH 3) slurries.

Effects of hydrogen peroxide and alumina on surface characteristics of copper chemical–mechanical polishing in citric acid slurries

The roles of H 2O 2 and alumina on the changes of metal removal rate, surface passivation and surface morphology in citric acid (CA) base slurry in simulated Cu chemical–mechanical polishing (CMP) was investigated. X-ray photoelectron spectroscopy (XPS) analysis indicated that H 2O 2 assisted oxide formation while citric acid promoted anodic dissolution of copper in various slurries that contained 1 wt.% Al 2O 3. Atomic force microscopy (AFM) revealed that Al 2O 3 abrasive particles modified the surface morphology by inducing surface deformation. The results of open circuit potential (OCP) and removal rate measurements clearly demonstrated that there existed a synergistic effect due to the chelating and oxidizing agents in Cu CMP.

In situ characterization of Cu CMP slurry and defect reduction using IR thermal camera

In order to choose appropriate property of Cu chemical–mechanical polishing (CMP) slurry, we used IR thermal camera to distinguish this slurry that belonged to Preston or non-Preston. The adoption of the IR thermal camera is to choose suitable non-Preston Cu CMP slurry in situ and find out optimal changing timing of step endpoint. Additionally supplementing robust CMP machine, appropriate Cu film quality and pre-treatment, we could obtain a total defect number is less than 10 1 order and achieve excellent Cu CMP performance. Such Cu CMP technology resulting in Cu damascene process work and make sure 0.13 μm and beyond 100 nm Cu process to be reliable and practical.