Improving Copper Electrodeposition in the Microelectronics Industry (original) (raw)
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Journal of Applied Electrochemistry, 2011
A quantitative study of the impact of key Cu plating parameters on the voiding propensity of solder joints with Cu electroplated in a commercially available plating solution (CAPS) is performed first on 0.3 cm 2 Cu rotating disk electrode. It is shown that similar to samples plated in a generic plating solution (GPS) containing bis(3-sulfopropyl) disulfide, polyethylene glycol, and Clions, void-prone samples are deposited predominantly at higher overpotentials, in the range from positive to-0.20 V. In the second part, a Hull cell with 46 cm 2 cathode is used to scale up the voiding study in both, GPS and CAPS. It is demonstrated that plating conditions could be chosen in a way to generate both, void-prone and void-proof Cu on the same cathode panel. Thus, the controlled voiding propensity illustrated for the first time in a prototype of industrial Cu plating helps in realizing the sporadic nature of the voiding phenomenon.
Effect of plating current density and annealing on impurities in electroplated Cu film
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2005
This study uses secondary-ion-mass spectrometry to examine the effects of plating current density and annealing temperature on the nature of electroplated copper ͑Cu͒ films. The experimental results reveal that high levels of impurities, such as C, O, S, and Cl, are incorporated into Cu deposits at the lower current density region while superfilling occurs. The C and O impurities can be released from the plated films by thermal annealing, while S and Cl cannot. This work proposes a possible mechanism based on bond strength to explain the phenomena. Rapid C and O desorption is observed when the films are first cycled to 220°C immediately after electroplating. The activation energy of C desorption is found to be approximately 9.8 kJ/ mol. For Cu electroplating, this investigation suggests that high plating current density and an adequate annealing temperature are required to reduce impurities.
The Impact of Organic Additives on Copper Trench Microstructure
Journal of The Electrochemical Society, 2017
Organic additives are typically used in the pulse electrodeposition of copper (Cu) to prevent void formation during the filling of high aspect ratio features. In this work, the role of bath chemistry as modified by organic additives was investigated for its effects on Cu trench microstructure. Polyethylene glycol (PEG), bis(3-sulfopropyl) disulfide (SPS), and Janus green b (JGB) concentrations were varied in the Cu electrodeposition bath. Results indicated a correlation between the JGB/SPS ratio and the surface roughness and residual stresses in the Cu. Electron backscattering diffraction (EBSD) and transmission Kikuchi diffraction (TKD) were used to study the cross-sectional microstructure in the trenches. Finer grain morphologies appeared in trenches filled with organic additives as compared to additive-free structures. Cu trench (111) texture also decreased with increasing organic additive concentrations due to more pronounced influence of sidewall seed layers on trench features. Twin density in the microstructure closely tracked calculated stresses in the Cu trenches. A comprehensive microstructural analysis was conducted in this study, on an area of focus that has garnered little attention from the literature, yet can have a major impact on microelectronic reliability. Since it replaced aluminum in the 1980's, copper (Cu) has become the primary material for microelectronic interconnects for its low electrical resistance. 1 However, copper's high coefficient of thermal expansion (CTE) compared to the surrounding materials, such as silicon, in these multi-material systems can result in many thermo-mechanical stresses/ defects. 2-4 Preferentially oriented Cu microstructures with large twin densities have been shown to improve reliability of interconnects by increasing thermal stability, mechanical
Controlling factors affecting the stability and rate of electroless copper plating
Materials Letters, 2004
The purpose of this article is to focus on the electroless copper plating step from tartarate or ethylenediaminetetraacetic (EDTA) baths used in through hole plating (THP) of printed circuit boards (PCBs). The effect of bath operating conditions (temperature, pH and agitation) and bath additives (pyridine, cytosine, thiourea, benzotriazole (BT) and 2-mercaptobenzothiozole (2MBT)) on plating rate, bath stability, morphology and etching rate of the coating has been studied. It has been found that all the organic additives studied except thiourea not only stabilize electroless copper baths but also enhance the plating rate from 1.1 to 1.8 mg/(cm 2 h) in the tartarate bath at 30 jC and from 5.4 to 10.5 mg/(cm 2 h) in the EDTA bath at 50 jC. Mild air agitation increases the bath stability 20 times that of bath without aeration. The additives were found to modify the crystal structure with the production of small grain size, dense, tightly adherent and etching resistant copper deposit.
Effect of Post-CMP Cleaning On Electrochemical Characteristics of Cu and Ti in Patterned Wafer
Korean Journal of Materials Research, 2009
The effects of post-CMP cleaning on the chemical and galvanic corrosion of copper (Cu) and titanium (Ti) were studied in patterned silicon (Si) wafers. First, variation of the corrosion rate was investigated as a function of the concentration of citric acid that was included in both the CMP slurry and the post-CMP solution. The open circuit potential (OCP) of Cu decreased as the citric acid concentration increased. In contrast with Cu, the OCP of titanium (Ti) increased as this concentration increased. The gap in the OCP between Cu and Ti increased as citric acid concentration increased, which increased the galvanic corrosion rate between Cu and Ti. The corrosion rates of Cu showed a linear relationship with the concentrations of citric acid. Second, the effect of Triton X-100 ® , a nonionic surfactant, in a post-CMP solution on the electrochemical characteristics of the specimens was also investigated. The OCP of Cu decreased as the surfactant concentration increased. In contrast with Cu, the OCP of Ti increased greatly as this concentration increased. Given that Triton X-100 ® changes its micelle structure according to its concentration in the solution, the corrosion rate of each concentration was tested.
Effects of Minor Elements in Cu Leadframe on Whisker Initiation From Electrodeposited Sn/Cu Coating
IEEE Transactions on Electronics Packaging Manufacturing, 2007
Drastically different tendencies of whisker initiation have been observed from the same Sn/Cu coating electrodeposited on two different Cu leadframe materials, CUFE and CUCR. After long-term storage at room temperature, no whisker initiation was observed on the coating on CUCR, whereas long whiskers with a maximum length of more than 200 m were formed on the coating on CUFE. FE-STEM and FE-TEM microstructural observations of vertical sections of each Cu leadframe with the coating showed that the cross-sectional morphologies of Cu-Sn intermetallic compounds (IMCs) formed at the interface between the coating and the leadframe were as follows: a wedge-shaped structure for the Sn/Cu-CUFE sample and a comb-tooth structure for the Sn/Cu-CUCR sample. Energy dispersive X-ray (EDX) analysis results confirmed that the formation morphologies of the Cu-Sn IMC were affected by minor elements in the Cu leadframes. Fe particles with a large diameter of mainly 50-200 nm precipitated nonuniformly in the CUFE leadframe, which had Fe, Zn, and P as minor elements. Conversely, very small Cr-rich particles, 10-20 nm in diameter, were precipitated in the CUCR leadframe, which had Cr, Sn, and Zn as minor elements. The Fe particles suppressed the growth of the Cu-Sn IMC by acting as obstacles to IMC formation, whereas grain boundaries in the Sn/Cu coating acted as preferential IMC formation sites. The combination of these two effects is thought to produce the wedge-shaped cross-sectional structure of the IMC. On the other hand, the Cr-rich particles did not have such a prominent suppression effect on Cu-Sn IMC growth: only the grain boundaries in the Sn/Cu coating affected the IMC formation site. As a result, IMC with a comb-tooth structure was formed in the Sn/Cu-CUCR sample. The difference in whisker initiation tendency was inferred to be due to the difference in compressive stress on the basis of the Cu-Sn IMC formation morphology in the Sn/Cu coating. Therefore, the stresses were finally measured by X-ray diffraction to determine the correlation between whisker initiation tendency and the morphology of Cu-Sn IMC formation. Based on the results, a model for controlling whisker initiation in Sn/Cu-coated Cu leadframe systems is presented. Index Terms-Compressive stress, Cu-Sn intermetallic compound (IMC), electrodeposited Sn/Cu coating, electron microscopy, minor elements in the Cu leadframe, whisker initiation, X-ray diffraction (XRD) stress measurement.