Semiconductor packaging migrated from wire bond to flip chip level interconnect to meet size, weight, and electrical performance requirements. Pure Sn and lead-free tin alloys have become common materials for flip chip attachment in electronics. Alloys containing Sn and Ag are the most common. The mechanical strength, wetting, and fatigue resistance of these alloys and pure Sn is either comparable to or surpasses lead alloys. Electroplating with lead-free alloys is the most desirable technique due to its low cost and usefulness in building fine pitch solder bumps [1]. The new generation of lead-free plating systems targets faster deposition rates, better uniformity with-in die and longer bath life. The co-deposition of elements may be complicated by the large difference in the electrode potentials of tin and alloying metals (e.g. silver, bismuth). To produce uniform and dense deposits, lead-free solder plating baths include organic additives that are typically separated for two groups with different functions: surfactants that significantly affect the plating rate and control the uniformity of deposit; and grain refiners [2]. The bath components must be maintained within specific concentration ranges to keep the bath operational and to avoid producing poor quality electrodeposited alloys. In some cases, the analytical results for bath components are needed more frequently to provide feedback to dosing systems [3]. To develop the most accurate and repeatable analytical methods, the interactions between lead-free plating bath components were studied and understood [3, 4]. This enabled ECI to develop more efficient analytical techniques for analysis of lead-free plating bath components. To further improve analytical methods performance, the effect of changes in the concentration of organic components on the structure of the deposits was studied and will be reported in this document. For development of new analytical methods, ECI utilized a traditional electrochemical cell with three electrodes connected to a potentiostat. Automated delivery of organic additives was used for improved consistency in mixing of standard solutions. Various parameters and steps of analysis were also evaluated for potential reduction of the analysis time. This presentation provides detailed information related to the behavior of organic additives under specific electrochemical and hydrodynamic conditions. The concentration of inorganic components and silver complexing agent are determined via non-reagent and express spectroscopic analytical methods. These techniques enable completion of analysis within 5 minutes. The document concludes with a discussion of analytical results for several organic additives at different concentration levels.

Replacement of tin-lead solder bumps by a suitable lead-free material for flip chip attachment has become an urgent necessity due to the impending ban on the use of lead in electronics. Alloys containing Sn and Ag as well as pure Sn are the most common for the replacement of Sn-Pb. The mechanical strength, wetting, and fatigue resistance of these alloys and pure Sn is comparable or surpass that of Sn-Pb”. Electroplating with lead-free alloys is the most desirable technique due to its low cost and usefulness in building small dimension bumps. However, the co-deposition of elements is complicated by the large difference in the electrode potentials of each element. Besides metal ions, these plating baths include organic additives, chelating agents, and acids. For appropriate plating bath performance, these components must be kept within specific concentration ranges. This is achieved through the use of dedicated chemical analyzers and dosers [1]. Most of these systems use multiple analytical methods that typically include electrochemical techniques. The introduction of new electroplating processes requires the development of new analytical methods. Before a new analytical electrochemical method is developed, the interactions between bath components should be investigated and understood. For this purpose, we utilized an electrochemical cell with three electrodes connected to a potentiostat/galvanostat. We studied the responses of organic components under varying electrochemical and hydrodynamic conditions as well as at different concentrations of bath components. Fig. 1 shows the electrochemical responses of organic additives used in commercial lead-free plating baths [2]. All tests were performed with the working and counter platinum electrodes and a low maintenance Ag/AgCl double junction reference electrode. Optimized electrochemical analysis parameters enable the determination of a wide range of concentrations of organic plating additives without interference from other bath components. Analysis of organic additives can be performed with relatively simple fluidics that include a single electrochemical cell with accurate temperature control. Typical analysis steps include fast electrode conditioning in support electrolyte, several injections of plating solution to determine changes in plating rate, and then subsequent calculation of the concentrations. This presentation will provide more information related to the electrochemical behavior of organic additives and inorganic components. Results of Electrochemical Impedance Spectroscopy investigations will also be presented. Results of electrochemical analyses will be correlated to data obtained with an HPLC analytical technique. The presentation will be concluded with a discussion of analytical results for each organic additive at different concentration levels. References: Pavlov, D. Lin, E. Shalyt, I. Tsimberg, “Electrochemical Analysis of Semiconductor Plating Baths”, MAM Conference, Milano, Italy, March 18-21, 2018 Foyet, M. Clauss, W. Zang-Beglinger, J. Woertink, Y. Qin, J. Prange, P. Lopez, , “Electroplating baths of silver and tin alloys”, US Patent, US9512529B2 Figure 1

Cobalt made an inevitable move into more and more applications as device features shrink. It has largely been replacing tungsten in prior forays: for encapsulating and for high-aspect-ratio fill. Cobalt now has a new target in its sights: copper interconnect [1]. Copper replaced aluminum about 20 years ago and had been successfully utilized in numerous semiconductor manufacturing nodes. However, when the IC industry moved beyond the 10 nm node, copper interconnects became more compact, causing an increase in the resistance-capacitance delay. One way to solve the problem is to utilize a cobalt metallization alternative that provides resistance benefits over conventional technology without compromising reliability and yield [2]. In this electroplating process, a super-filling relies on depletion of protons inside feature, leading to increased current efficiency for Cobalt. Depletion of protons in this case leads to reduction of suppression efficiency and further enhancement of cobalt deposition as compared to field [3, 4]. These publications agree that a successful super-filling requires tight pH control. This presentation reveals results of advanced method that allow to reach 0.005 pH repeatability required for electroplating process. While this cobalt plating process is maturing, tighter process control is required to provide more accurate and precise data as well as faster analysis data generation. Previously developed analytical methods [5, 6] had been refined and improved to address challenges of the modern industrial cobalt plating processes. New, efficient analytical techniques were also developed. These methods can also report additional properties of a plating solution (conductivity and pH) critical for bath performance. Fig 1. shows the electrochemical responses of different proprietary organic additives used in commercial cobalt plating baths. Optimized electroanalytical and hydrodynamic parameters enable the determination of a wide range of concentrations of organic additives without interference from other bath components, as well as from bath pH and temperature. Analysis of organic additives can be performed with relatively simple fluidics that include a single mini electrochemical cell with accurate temperature control. Typical analysis steps include fast electrode conditioning in support electrolyte, several or single injection of plating solution to determine changes in plating rate, and then subsequent calculation of the concentrations. One of the newly developed methods is non-reagent spectroscopic analysis of boric acid. This method can also be combined with non-reagent analysis of cobalt providing very fast analysis of both components. Fig. 2 shows correlation of obtained and expected values for wide range of boric acid concentrations. This presentation will provide more detailed information related to the electrochemical behavior of organic additives and inorganic components. The results of Electrochemical Impedance Spectroscopy investigations and Raman spectroscopy will also be presented. The presentation will be concluded with a discussion of analytical results for all bath components during electroplating process. References: B. Moyer, “The Cobalt Waive Continues”, Electronic Engineering Journal (internet publication), July 16, 2018 Natalia V. Doubina, Matthew A. Rigsby, Jonathan David Reid, “Chemistry additives and process for cobalt film electrodeposition”, US Patent, US 9777386B2 Matthew A. Rigsby, Lee J. Brogan, Natalia V. Doubina, Yihua Liu, Edward C. Opocensky, Tighe A. Spurlin, Jian Zhou and Jonathan D. Reid, “The Critical Role of pH Gradient Formation in Driving Superconformal Cobalt Deposition”, J. Electrochem. Soc. 2019 volume 166, issue 1, D3167-D3174 J. Wu, F. Wafula, S. S. Branagan, H. Suzuki and J. van Eisden, “Mechanism of Cobalt Bottom-Up Filling for Advanced Node Interconnect Metallization”, J. Electrochem. Soc. 2019 volume 166, issue 1, D3136-D3141 M. Pavlov, D. Lin, E. Shalyt, X. Yan, “Electrochemical behavior and Analysis of Organic Additives in Cobalt Damascene Baths”, 230th ECS Meeting PRiME, Honolulu, Hawaii, October 2-7, 2016 M. Pavlov, E. Shalyt, X. Yan, D. Lin, “Process Metrology of Cobalt Damascene Interconnect”, 2016 IEEE IITC and AMC Conference, San Jose CA, May 23-26 Figure 1

Despite advances in optical interconnect, metal interconnect remains the dominant technology, however the type and diversity of metal structures is rapidly changing. Wire-bonding cannot meet required interconnect density and is being replaced with electrodeposition-based flip chip technology. Modern packaging scheme required high diversity of interconnects within the same device: RDL, mircobump, pillar, TSV, tall (mega) pillar, etc. using sequential deposition of different metals such as Cu, Ni, SnAg/Sn, Au. Diverse challenging requirement leads to evolution of chemistries and process control approaches. Many 20th century chemistries were limited to 1 organic additive for Cu process. Today, up to 4 individual additives are used to dial the process. While most of semiconductor front end processing enjoys the luxury of single-use chemistry, it is not yet considered a viable option for electrodeposition. The same electrolyte can be used for processing over 1000 parts in replenishment mode. Maintaining performance under these conditions requires close monitoring of component breakdown and contaminants accumulated in the processes. There is also a real possibility for disproportional trends for individual components of replenishment package. It is no longer enough to monitor just main 3–6 components of the bath. Successful high volume metallization for advanced packaging requires comprehensive metrology/process control. Presentation will provide specific examples of metrology and process control strategy for various metallization solution with emphasize on breakdown products and contaminants. There is no single technology which can cover diversity of metrology needs. CVS is a versatile technology which can be used not only for control of main additives but also to monitor breakdown products of accelerator, suppressor, leveler, Cu(I) contaminants, H2O2 contaminant and even leached photoresist. In case of Ni chemistry, it is useful to monitor breakdown products of sulfamate. UV-Vis spectroscopy shines at monitoring of leached photoresists, Fe(III), breakdown products of sulfamate as well as control of many main components: Cu, Ni, Co, Au, additives. ICP is the best for ultra low level of metal contaminants which can harms deposition process, as well as low level of some target components, like Tl in Au. Novel approach is developed to track additive turnover process based on ICP results. HPLC is valuable to characterize multiple breakdown products of organic additives, while ion chromatography helps to track transformation of ions, such as oxidation of sulfite to sulfate in Au solution. Surface tension aids monitoring of surfactants and their degradation. It is important to differentiate between R&D study and robust “fit-to-purpose” practical process control. While Ion Chromatography approach would be more appropriate for academic study and perhaps process development, simple robust methods like titration, specific gravity are preferable for industrial process control. Similarly, HPLC is a great scientific tool but CVS, spectroscopy and titration are better fit and safer alternative for in-fab operation. Presentation will provide specific examples and comparative analysis of different analytical methods.

The capability of analyzing all components in modern copper electroplating baths using non-reagent methods is demonstrated. The concentration of copper in new plating baths is significantly lower than in traditional baths. This article presents the results of our most recent study of the behavior of organic additives at low copper concentrations. The analytical results of our new methods for all bath components are presented.

Abstract Copper electroplating processes are widely used in semiconductor manufacturing, particularly during the packaging stage [1]. Copper deposition is used to build various structures including TSV, RDL, Pillars, and Micro and Mega Bumps. Those processes utilize plating solutions that contain inorganic components and organic additives [2]. During the electroplating process, the additives can partially transform into compounds that are so-called breakdown products. The presence of such breakdown products can interfere with the electrochemical analysis of organic additives. This article presents results of plating tests that show the influence of freshly produced breakdown products on analysis of organic additives. In addition, several options to eliminate this effect are presented.

With miniaturization of semiconductor devices, the size of electroplated features is continuously reduced in the damascene process. Most recently, copper electroplating technology application has been extended in 14 nm, 10 nm, and 7 nm nodes. This advancement has caused significant changes in bath compositions. While new organic additive packages were introduced, the inorganic component concentrations were significantly altered as well. The composition of plating baths used in sub 14 nm nodes was recently described [1, 2]. These publications specified relatively low concentrations of copper between 1 and 10 grams per liter, sulfuric acid between 2 and 15 grams per liter, and 30-150 ppm chloride ions. Such electrolyte also includes organic additives traditionally used in copper electroplating baths (Suppressor, Accelerator, and Leveler). Suppressors are polymeric in nature (e.g. polyethylene glycol, polypropylene glycol, etc.). Accelerators are typically sulfur-containing compounds such as dimercaptopropane sulfonic acid, and bis-(3-sulfopropyl) disulfide (SPS). Levelers are designed to work on protruding features, and typically nitrogen contained compounds, e.g. Janus Green B. Before a new analytical electrochemical method is developed, the interactions between bath components at low copper concentrations should be investigated and understood. For this purpose, we utilized an electrochemical cell with three electrodes connected to a potentiostat/galvanostat. We studied responses of organic components at different electrochemical and hydrodynamic conditions as well as at different concentrations of copper. Fig. 1 shows electrochemical responses of organic additives in solutions with different copper concentrations. All tests were performed with the working platinum electrode set at a constant cathodic current of -10 mA and 10-2500 RPM. As this graph indicates, the copper concentration plays a key role in the electrodeposition process. Reduction in copper concentration causes significant changes of plating potential, which is consistent with observations made in another publication [2]. Injection of Suppressor (PEG) into the solution changes plating overpotential in a similar way to reduction of copper concentration. It is critical to note that addition of Suppressor into solutions with different copper concentration causes almost the same shift in plating potential (Fig. 2). In Fig. 2, the voltages for 1 g/l and 5 g/l copper solutions were adjusted to match the initial potential for a solution with 10 g/l of copper. Unlike the Suppressor effect, Accelerator (SPS) and Leveler (JGB) effects are clearly dependant on the changes in the copper conentrations. Accelerator component transient response shows slower and weaker depolarizatrion at the lowest concentration of copper, while the Leveler polarization effect is stronger at lower copper concentration. Understanding the interactions between bath components at low copper concentrations enables the design of accurate electrochemical methods of analysis for each organic component. This presentation will reveal more information related to the electrochemical behavior of organic additives and inorganic components. Results of EIS investigations will also be represented. The presentation will be concluded with a discussion of analytical results for each organic additive at different concentration levels. References: J. Zhou, J. Reid, “Low copper electroplating solutions for fill and defect control”, US Patent Application, US 13/753,33 J. Zhou, E. Opocensky, J. Reid, “Low Cu electrolyte for advanced damascene plating”, Semiconductor Technology International Conference (CSTIC), 2015 Figure 1

Abstract Nickel electroplating is widely used in semiconductor manufacturing, primarily during the packaging stage. It is not used as a final coating, but instead as a barrier layer to prevent formation of copper–tin intermetallic compounds that affect the reliability of solder joints. The nickel is deposited from baths containing nickel salt (in relatively high concentrations), boric acid, and other ions. The quality of the deposited nickel is highly dependent on the composition of the plating bath. Metallic contaminants are acceptable when their concentrations are below approximately 30 ppm. Copper, lead, zinc, and cadmium, even in relatively small quantities (higher than 30 ppm) produce a dull, black, or skip plate condition in the low-current-density areas. These metals may be removed from the plating solution by low-current-density dummy plating, but a sensitive and accurate analytical method must be used to determine when to treat the bath. Copper is considered a main contaminant due to its higher concentrations in the bath and its most detrimental effect on the nickel deposit. To prevent plating defects, the bath contaminants must be monitored.

The copper dual damascene process has been used in semiconductor manufacturing since it was introduced by IBM in mid-1990. Since then, copper interconnects shrunk dramatically following the principles of Moore’s law. Currently, there are questions regarding the extendibility of the copper dual damascene flow as the IC industry moves beyond the 10 nm node. Copper interconnects are becoming more compact at each node, causing an increase in the resistance-capacitance delay. Furthermore, voids that occur in heavily scaled vias severely impact yield. Leading semiconductor manufacturers are exploring novel metallization methods to solve these issues. One way to solve the problem is to identify metallization alternatives that provide resistance benefits over conventional technology without compromising reliability and yield. Cobalt is considered as a potential replacement candidate for copper.Cobalt plating baths typically contain cobalt salt, boric acid, and organic additives . We have recently developed new analytical techniques for complete analysis of cobalt damascene plating baths. Electrochemical methods are used to study behavior and analyze multiple organic additives present in cobalt plating baths , while other bath components can be effectively analyzed with traditional titration and/or spectroscopic methods. Fig. 1 shows the effects of commercial Suppressor and Accelerator additives used for cobalt plating. The voltammograms indicate decreased plating rate when Suppressor additive is injected into the VMS electrolyte. VMS stands for Virgin make-up solution, which contains only inorganic components. The injection of Accelerator into the electrolyte with Suppressor causes increased plating rate. Fig. 2 shows response curves of Suppressor and Accelerator. All responses are reproducible and allow accurate determination of organic additives in plating baths. This article will also reveal the effects of other bath components on the plating properties of cobalt. We will also present statistical results of electrochemical analysis of both organic additives. Figure 1

The thickness of a palladium coating on copper (or another substrate) is measured chronopotentiometrically by passing a cathodic current through a predetermined area of the coating in contact with an electrolytic solution and measuring the potential as a function of time. Protons from the electrolytic solution are electrochemically reduced to palladium hydride at cathodic potentials less negative than required for evolution of hydrogen gas. As formation of the PdH0.58 beta-phase throughout the Pd coating is completed, the cathodic potential increases rapidly to a cathodic potential plateau corresponding to evolution of hydrogen gas on the PdH0.58 surface. This voltage step in the cathodic potential provides an end point time for the measurement. The absolute thickness of the Pd coating is calculated from the integrated cathodic charge passed up to the end point time. (C) 2014 The Electrochemical Society. All rights reserved.

As copper plated features in semiconductors continue to decrease in size, it is increasingly critical to their manufacturers to receive the most accurate information about the composition of plating solutions. With miniaturization of plating features, the modern plating chemistries are also being modified to provide defect-free filling. These modifications typically affect organic additive systems, while the inorganic components remain the same with an option of concentration change. For appropriate control of the plating bath, some organic additive systems require analysis of multiple individual components. Typical plating composition includes three organic additives commonly named Suppressor, Accelerator, and Leveler. In this testing, four organic components system have been analyzed. This article focuses on novel approaches in electrochemical analysis of copper plating solutions used in Wafer Level Packaging (WLP). Results obtained for four organic additives are reported.

Through-silicon via (TSV) technology is gaining popularity in 3D packaging and 3D integrated circuits. TSV baths are formulated with highly stable electrolytes that contain copper and sulfuric acid. Other components introduced into the bath in relatively small amounts are organic additives and chloride ions. This article will focus on a non-reagent metrology to efficiently monitor these components. The chloride concentration is determined from the chloride oxidation current using specific voltammetric parameters. Similar to analysis of suppressor, the measurement is made directly in the undiluted plating bath. Results for non-reagent analysis for acid and copper were reported earlier. Electrochemistry and spectroscopy are employed in on-line monitoring of various TSV baths. The concentrations of organic additives are determined from the rate of the copper deposition. The new techniques differ from conventional CVS procedures. The advantages of these newly developed electrochemical procedures are speed (results are obtained within one minute), accuracy and reproducibility. Our new non-reagent techniques do not use special reagents for analysis and require only standard solution used for automatic system calibration and validation.

Electrodeposition in all industries switches to less hazardous components in compliance to regulations. Unique trend of semiconductor industry includes emphasize on process control which enables extension of electrolyte life time and decrease of bleed and feed ratio.

Transition of interconnect technology to copper elevated challenges for polymer removal. Electrolyte has to provide efficient removal of organic material while preserving Cu surface with controlled regrowth of copper oxide. Spectroscopy in combination with electrochemical method can provide comprehensive characterization of electrolyte for concentration of major components (H2O2, H2O, organic, pH). In addition, local electrochemical analysis provides information on copper oxide removal/regrowth.

Abstract not Available.

Abstract not Available.