High Planarization Efficiency Research Articles

Overview and Potential Solutions of Current and Future Challenges in CMP

This talk is dedicated to the special session in honor of Prof. Babu Shrink of critical dimensions and stringent technology specifications are posing several planarization challenges in technology development (TD) and high-volume manufacturing (HVM) phases of current and advanced technology nodes. In this talk, we will focus on process challenges related to achieving (a) minimum defects (b) high planarization efficiency with less than 1nm dishing (c) tighter WIW and WID uniformities (d) ultra-smooth post-CMP surface roughness in the order of sub-nanometer. In addition, identifying appropriate endpoint control techniques combined with advanced process control strategies to provide good process margin will also be discussed. Addressing the above challenges in a cost-effective manner is vital for HVM. Root cause analysis and probable working models will be discussed for high-risk process challenges. Based on our understanding, a jist shall be provided about challenges associated with future technology nodes in logic and memory industries, with focus on how (a) technical understanding, (b) change in CMP ecosystem, and (c) AI can help solving technology development and high-volume manufacturing problems.

Surface Engineering of SiC through Nanogrinding and CMP

Processing silicon carbide (SiC) wafers to achieve an epi-ready quality finish typically requires many lapping and a very long chemical mechanical polishing (CMP) steps. In this paper, we report the thinning down of 6” SiC wafers to sub-nanometer surface finish in less than two hours. Three process steps (rough grinding, nanogrinding and CMP) are involved. Rough grinding thins down the wafer with fast feed rate and maintain excellent flatness. Nanogrinding allows the surface finish to improve down to a few nanometers. The last CMP step provides high planarization efficiency. Overall the throughput of SiC processing is substantially increased over current market solutions.

The stability of a novel weakly alkaline slurry of copper interconnection CMPfor GLSI * * Project supported by the Major National Science and Technology Special Projects (No. 2016ZX02301003-004-007), the Professional Degree Teaching Case Foundation of Hebei Province, China (No. KCJSZ2017008), the Natural Science Foundation of Hebei Province, China (No. F2015202267), and the Natural Science Foundation of Tianjin, China (No. 16JCYBJC16100).

Chemical mechanical polishing (CMP) is one of the important machining procedures of multilayered copper interconnection for GLSI, meanwhile polishing slurry is a critical factor for realizing the high polishing performance such as high planarization efficiency, low surface roughness. The effect of slurry components such as abrasive (colloidal silica), complexing agent (glycine), inhibitor (BTA) and oxidizing agent (H2O2) on the stability of the novel weakly alkaline slurry of copper interconnection CMP for GLSI was investigated in this paper. First, the synergistic and competitive relationship of them in a peroxide-based weakly alkaline slurry during the copper CMP process was studied and the stability mechanism was put forward. Then 1 wt% colloidal silica, 2.5 wt% glycine, 200 ppm BTA, 20 mL/L H2O2 had been selected as the appropriate concentration to prepare copper slurry, and using such slurry the copper blanket wafer was polished. From the variations of copper removal rate, root-mean square roughness (Sq) value with the setting time, it indicates that the working-life of the novel weakly alkaline slurry can reach more than 7 days, which satisfies the requirement of microelectronics further development.

In Situ Electrochemical Behavior of Aluminum Chemical Mechanical Polishing at Low Down Pressure in Environmentally Friendly and Weakly Alkaline Slurry

The lower pressure tendency in chemical mechanical polishing (CMP) process requires a lower adhesive inhibitor with environmentally friendly corrosion properties to replace the conventional benzotriazole (BTA) inhibitor for aluminum (Al) CMP. Open circuit potential test, potentiodynamic polarization curve test, linear sweep voltammetry and potential drop investigated by in-situ electrochemical mechanical polishing (ECMP) platform were used to reveal the controlled evolution process of corrosion inhibitor films at low pressure during Al CMP. The comparison between BTA and 1,2,4-triazole (TAZ) shows that TAZ has lower current density, wider potential inhibition interval, and high planarization efficiency, although TAZ has lower adhesion on Al surface. Finally, the surface roughness of Al after CMP with TAZ in weakly alkaline slurry at pressure of 1 psi was observed by atomic force microscopy (AFM) with a value of 0.19 nm. This studies demonstrated that the conventional BTA can be replaced by environmentally friendly corrosion inhibitor TAZ, which is a promising alternative candidate to the Al CMP at low down pressure.

Mechanisms and Development of Ceria-Based, Fast Oxide Slurries

Recent developments in vertical integration schemes including 3D-NAND flash memory have introduced a significant need for fast oxide slurries (1). Specifically, the new staircase CMP process requires exceptionally large step heights to be polished in a timely manner. Balancing low defectivity and high planarization efficiency with extremely fast bulk oxide removal rates is a difficult but crucial set of requirements. Ceria-based slurries with fine-tuned chemistries are well suited to meet these challenges. Mechanisms for ceria-based slurries polishing behavior on oxide surfaces have been the subject of investigation for a number of years now. A careful examination of these proposed mechanisms can drive the design and development of next generation fast oxide slurries.

Nano-Sized Chemical Release Capsules Enable High Planarization Efficiency CMP Processes

As semiconductor device sizes decrease, next generation CMP slurries must achieve planarization on increasingly more complicated material surfaces with higher aspect ratio structures. While incremental improvements to CMP performance using the traditional homogenous mixtures of abrasives and chemical components continue to be obtained, new approaches to CMP slurry formulations are needed to meet future device requirements. GE&R has developed novel techniques to economically synthesize CMP slurries containing nano-capsules. Nano-capsules use typical metal oxide nanoparticles, where the pores of the particle are loaded with a chemical payload, and then coated with a polymer to encapsulate the chemical payload. When the nano-capsule contacts the wafer surface during CMP, the polymer coating is torn away and the chemical payload is released only in a localized area. A variety of metal oxide base particles (including GE&R silica) and different chemical payloads are possible, opening the door for improved selectivity mechanisms and high planarity processes.

Nano-Sized Chemical Release Capsules Enable High Planarization Efficiency CMP Processes

General Engineering & Research, L.L.C. (GE&R) has developed slurries containing nano-sized chemical release capsules (nano-CRC) which provide highly controlled processing and efficient planarization. Instead of the traditional mixture of solid nanoparticles and chemicals, nano-CRC based slurries consist of a core-shell nanoparticle where the mechanical and chemical components are combined into a single entity (Figure 1). When the nanoparticle contacts the wafer surface during CMP, the polymer coating is torn away and the chemical payload is released in an area localized to where it is needed. Various abrasive particles are possible (SiO2, Al2O3, etc.) as well as different chemical payloads. In this research effort, nano-CRC particles made from various sized (20nm – 200nm) porous colloidal silica abrasives were loaded with glycine, and then coated with a polymer to encapsulate the glycine. Slurries containing these nano-CRC particles were tested on the copper CMP process. All wafers were polished in house on a Strasbaugh 6EC CMP tool using IC1000 polishing pad and Kinik Diagrid conditioning stone, with wafer downforce of 3psi, head/platen speed of 60/60 rpm and 150ml/min slurry flowrate. All slurries contained 4wt% silica nanoparticles. The nano-CRC slurry surface removal mechanism consists of a simultaneous mechanical abrasion in combination with a localized release of the chemical payload. These slurries do not require any other stabilizers, surfactants, inhibitors, etc., however, because of this, electrophoretic influences can be significant. The nano-CRC interaction with the surface is influenced by solution chemistry, such as pH and oxidizer concentration, which determines the zeta potential of the capsules and the charge on the wafer surface film. The polymer coating on the nano-CRC is thin enough that the capsules typically retain the colloidal properties of the base particle, i.e. the iso-electric-point (IEP) of the silica based nano-CRC slurries is pH~2. Acidic nano-CRC slurries provide good material removal rates (MRR) of copper films (IEP pH~9), however, alkaline solutions provide little to no removal of the copper surface due to the copper surface and nano-CRC particles being similarly charged and repelling each other. Oxidizer concentration in the slurry also affects copper oxide film formation and may inhibit the copper-glycine complex if used in excess. Figure 2 shows the MRR vs. H2O2 concentration for 40nm silica nanoparticles (no loading or polymer coating) and 40nm nano-CRC (glycine loading and polymer coating) slurries, where the MRR of the nano-CRC slurry is very sensitive to H2O2 concentration. The particle size also influences CMP performance. Figure 3 shows the Cu CMP MRR and planarization efficiency (PE) (ratio of step height removed to thickness removed), for slurries containing bare silica particles and the nano-CRC particles. The PE was calculated using a feature with 50um line spacing and 50um line width. Interestingly, of the bare silica slurries, the 80nm particle size provided the highest MRR, however, no improvement in MRR was observed with the 80nm nano-CRC slurry. The 40nm nano-CRC slurry shows both the highest MRR~200nm/min and PE>90%. Both the porosity and the hardness of the particles, which varies with particle size, may influence the CMP performance. Further optimization, particularly increasing the porosity of the nanoparticles, is expected to provide nano-CRC slurries with even higher MRR and high PE. Figure 1

A study on exploring the alkaline copper CMP slurry without inhibitors to achieve high planarization efficiency

Benzotriazole (BTA), a widely used inhibitor, is added to the slurry to eliminate step height. However, it is carcinogenic compound and presents challenges in post CMP cleaning. In this paper, we have solved this problem by using a unique alkaline macromolecular organic chelating agent with the high activation energy (named FA/O) to complex cupric ion. A model is proposed to illuminate why the slurry is free of inhibitors and predict that a high removal rate difference between the convex and concave areas can help eliminate step height. Dissolution rate results indicate that there is almost no reaction between FA/O chelating agent and copper ions in the static alkaline conditions, and films, including Cu2O, CuO and Cu(OH)2 formed in the alkaline solution, hardly dissolve protecting the copper from reacting in the recessed regions. On the contrary, the FA/O-based slurry without BTA gives a very high copper polish rate compared to the static dissolution rate, and it yields a considerably higher planarization efficiency (PE) of 88.4% than that (27.5%) of the glycine-based slurry without BTA, which achieves the equal performance with the addition of BTA to the glycine-based slurry (90.4%). Here the different reaction mechanism between the glycine based acidic slurry and FA/O chelating agent based alkaline slurry has been discussed.

Chemically Impregnated Abrasives Provide High Planarization Efficiency Copper CMP Slurry

As device sizes decrease, next generation CMP slurries must achieve planarization on increasingly higher aspect ratio structures. Current copper CMP slurries have a limited planarization efficiency (PE) (ratio of step height removed to thickness removed). Without an improvement in PE, CMP is going to become an increasingly expensive and limiting step in the semiconductor manufacturing process. This research is focused on developing a copper CMP slurry containing nano-sized contact release capsules (nano-CRC). Nano-CRC based slurries consist of a core-shell nanoparticle where the mechanical and chemical components are combined into a single entity. Nano-CRC particles made from porous colloidal silica abrasives were impregnated with glycine, and then coated with a polymer to encapsulate the glycine. Initial results have yielded simultaneously high PE and high material removal rate, which will improve planarity and decrease processing costs.

Chemically Impregnated Abrasives Provide High Planarization Efficiency Copper CMP Slurry

As device sizes decrease, next generation CMP slurries must achieve planarization on increasingly higher aspect ratio structures. Current copper CMP slurries have a limited planarization efficiency (PE) (ratio of step height removed to thickness removed). Without an improvement in PE, CMP is going to become an increasingly expensive and limiting step in the semiconductor manufacturing process. Current commercial CMP slurries consist of homogenous mixtures of abrasives (typically metal oxide nanoparticles) and chemical components. While incremental improvements to CMP performance using this paradigm continue to be obtained, new approaches to CMP slurry formulations will be needed to meet future device requirements.General Engineering & Research, L.L.C. is developing a copper CMP slurry containing nano-sized contact release capsules (nano-CRC). Instead of the traditional mixture of solid nanoparticles and chemicals, nano-CRC based slurries consist of a core-shell nanoparticle where the mechanical and chemical components are combined into a single entity (Figure 1). When the nanoparticle contacts the wafer surface during CMP, the polymer coating is torn away and the chemical complexing agent (glycine) is released in an area localized to where it is needed. In this research effort, nano-CRC particles made from porous colloidal silica abrasives were impregnated with glycine, and then coated with a polymer to encapsulate the glycine. Upon shearing contact with the wafer surface during CMP, the polymer coating is torn away and the glycine is released. The following development goals for a nano-CRC based slurry were met: 1) Chemical payload (glycine) encapsulated in the nanoparticle pores2) Stable polymer coating that prevented leakage of payload3) Polymer coating soft enough to be torn away by the shearing forces during CMP to release the payload4) Well dispersed particles that were free from agglomeration5) Cost effective manufacturing method for competitive CMP slurry pricingTo date, no known CMP slurry technologies have attempted to combine the mechanical and chemical components of the slurry into a single entity. Initial results have yielded simultaneously high PE and high material removal rate (MRR), which will improve planarity and decrease processing costs. Table 1 summarizes the copper CMP results of the nano-CRC slurry compared to benchmark commercial CMP slurries. Commercial slurries were diluted as recommended by the manufacturer, and a similar abrasion loading concentration was used for the nano-CRC slurry (equivalent of 4wt% abrasive). Commercial Slurry A is an example of a chemical only slurry which is inexpensive but has only moderate performance (substantial etch rate, low MRR and low PE). Commercial Slurry B has better performance with a negative etch rate and a MRR of 23 nm/min and a PE of 43%. The best performing nano-CRC prototype was able to match the Slurry B etch rate and provide a 16 nm/min increase in MRR and a 24% increase in PE. PE is a key factor in determining the surface quality after CMP (dishing) and the development of a class of very high PE CMP slurries will strongly impact future CMP utility. Another consequence of high MRR and PE is their effect on the cost, time and waste stream of the CMP process. The volume of slurry (Vol) needed to planarize a 200nm step height (ΔS) was calculated according to the following equation: Vol = (F ∙ ΔS)/ (MRR ∙ PE) (Table 1). The nano-CRC slurry is predicted to require just 0.3 gal of slurry to achieve planarization compared to 0.8 gal of Slurry B, a 62% reduction in both slurry volume and time to planarize. With further optimization, even greater improvements in the Cu CMP process is anticipated resulting in a product with a very high return on investment for semiconductor manufacturers.

A new weakly alkaline slurry for copper planarization at a reduced down pressure

This study reports a new weakly alkaline slurry for copper chemical mechanical planarization (CMP), it can achieve a high planarization efficiency at a reduced down pressure of 1.0 psi. The slurry is studied through the polish rate, planarization, copper surface roughness and stability. The copper polishing experiment result shows that the polish rate can reach 10032 Å/min. From the multi-layers copper CMP test, a good result is obtained, that is a big step height (10870 Å) that can be eliminated in just 35 s, and the copper root mean square surface roughness (sq) is very low (< 1 nm). Apart from this, compared with the alkaline slurry researched before, it has a good progress on stability of copper polishing rate, stable for 12 h at least. All the results presented here are relevant for further developments in the area of copper CMP.

Achievement of high planarization efficiency in CMP of copper at a reduced down pressure

We report improved planarization efficiency (ratio of step height reduction and removed layer thickness) in chemical–mechanical planarization (CMP) of copper lines at a down pressure of 2 psi. The CMP slurry used to achieve these results contains fumed silica particles (abrasive), β-alanine (surface complexing agent) and H 2O 2 (oxidizer), combined with dissolution inhibiting ammonium dodecyl sulfate (ADS) and/or low concentrations (≤1 mM) of benzotriazole (BTAH) at a solution pH of 4.0. When only ADS or BTAH is used, Cu dissolution rate is reduced, but at the cost of somewhat low planarization efficiency. Combination of ADS (typically 3 mM) and BTAH (≤1 mM) in the slurry significantly improves both the surface polish rates and the planarization efficiency. The processed surface (examined by optical profilometry) is noticeably defect-free for this particular system. The mechanisms of surface dissolution and passivation are discussed, and contact angle data are used to elucidate the surface passivating nature of the inhibitor films. The results presented here are relevant for further developments in the area of low pressure CMP of Cu lines overlying fragile low-k dielectrics in the new interconnect structures.

Mechanically Induced Growth Rate Differential for Copper Layers Electroplated in Presence of Organic Additives

Electrochemical mechanical deposition (ECMD) planarizes copper films as they are plated on patterned wafer surfaces. The technique involves electrochemical deposition (ECD) and simultaneous sweeping of the cathode surface with a pad. Pad sweeping gives rise to a mechanically induced current suppression (MICS) phenomenon if plating is performed in electrolytes containing accelerator and suppressor additives as well as ions. In this work we studied the MICS phenomenon by partially sweeping blanket wafer surfaces with a small pad and investigating effects of the bath chemistry and wafer surface derivatization on the copper growth rates at the swept and unswept regions of the surface. It was found that, at a given suppressor concentration, copper growth rate differential between the two regions was reduced with increasing accelerator concentration in the bath. Derivatization of the wafer surface in an accelerator-containing solution followed by ECMD in a suppressor-containing bath gave the largest growth differential between the swept and unswept surface portions, suggesting high planarization efficiency. Adsorption-desorption kinetics of the organic additives used in this work were obtained under ECD conditions and found to support the proposed mechanism of MICS.

Cu Planarization in Electrochemical Mechanical Planarization

The electrochemical mechanical planarization (Ecmp) process is a revolutionary planarization technology uniquely combining removal rate controlled by charge with superior planarization efficiency in the near no-shear regime. A planarization mechanism for Ecmp is proposed to explain the high planarization efficiency. Meanwhile, the effects of applied voltage on removal rate and planarization efficiency are discussed. The electrical feature allows Ecmp to be a planarization process with removal rate independent of downforce, enabling a wide removal rate window and high planarization efficiency.

Effect of Surface Passivation Removal on Planarization Efficiency in Cu Abrasive-Free Polishing

Selective removal of surface passivation on protruded Cu film is a critical factor of Cu planarization. For a stress-free Cu abrasive-free polishing (Cu AFP) process, due to the lack of mechanical abrasion by abrasives, a polishing pad is used instead of abrasives to remove surface passivation during Cu planarization. Thus, the planarization efficiency in Cu AFP relates to the efficiency of surface passivation removed by a pad. Comparing Cu oxides with a non-native Cu-BTA (Cu-Benzotriazole) monolayer used as surface passivation, this study found that an oxide-free Cu surface should be required in Cu AFP. When Cu oxides function as surface passivation in Cu AFP, they are removed with greater difficulty by a pad resulting in low planarization efficiency. Contrary to Cu oxides, high planarization efficiency can be obtained with non-native Cu-BTA as surface passivation in Cu AFP.

High Planarization Efficiency and Wide Process Window Using Electro-chemical Mechanical Planarization (EcmpTM)

AbstractEcmpTM is a revolutionary planarization technology uniquely combining removal rate controlled by charge with superior planarization efficiency in the near no shear regime. In addition, the electrochemical removal mechanism has excellent within-wafer profile control. Multiple electrical zones configuration combined with a precise end-point control by electric charge, make it more predictable to control the remaining thickness and profile of copper film. The factors affecting the planarization such as the concentration and the efficiency of the inhibitors will be discussed in this paper. Meanwhile a planarization mechanism for Ecmp will be proposed to match the high planarization efficiency. The effects of applied voltage on removal rate and planarization efficiency will be presented in this paper. The electrical feature allows Ecmp to be a planarization process with removal rate independent of down force, enabling a wide removal rate window based on applied voltage.

Superpolishing for Planarizing Copper Damascene Interconnects

We demonstrate a superpolishing electrolyte, which consists of acid additives in conventional Cu polishing electrolytes (H 3 PO 4 ). for efficiently planarizing Cu damascene features. The significant additive concentration gradient in features, resulting in a selective Cu dissolution rate within features, is explored as a major mechanism that yields such electrolytes with high planarization efficiency. Moreover, another additive. polyethylene glycol as a suppressor, is also employed to reduce oxygen bubbling on polished films. Consequently, a smooth surface with a complete step height elimination is obtained in a 70 μm trench after electropolishing.

Chemical Mechanical Polishing for Surface Smoothing

Chemical Mechanical Polishing (CMP) has become a more and more important process for planarization in IC technology. For planarization, stacked pads with a hard top pad (for high planarization efficiency) and a softer sub pad (for acceptable uniformity) are used. In this work, the focus is to investigate CMP using a soft poromeric pad. Possible applications could be to create rounded structures for microptical devices or corner rounding to reduce stress in microstructures. Surface profile evolution during CMP of both inlaid and protruding pattern of line arrays completely etched in silicon dioxide is investigated. It is found that there is an exponential dependence of the step height in the arrays on the polish time. Also, wide silicon areas were open through the silicon dioxide. It is found that the soft pad allows polishing on the open silicon areas. Due to the selectivity of the slurry between silicon and oxide, the step height increases even though the silicon areas are situated below the oxide.