Huiqin Ling

High-performance Si-based 3D Cu nanostructured electrode assembly for rechargeable lithium batteries

In this work, we report the synthesis of a Si/Cu nanocone-array (NCA) electrode via a facile ambient electrodeposition method with subsequent magnetron sputtering deposition. The close connection between the Cu NCA and the silicon layer facilitates the charge transfer in the system and supports a binder-free technique of preparing lithium ion battery (LIB) anodes. The void spaces between Si cylinders allow not only greater alleviation of the strain caused by the Si expansion during lithiation but also a significantly enhanced rate performance due to the increasing electrode/electrolyte contact area, and shortening path lengths for electronic and Li+ transport. Such engineered electrodes exhibit a long cycle life up to 2000 cycles and can be very promising for high-performance anode applications.

Electrodeposition and characterization of copper nanocone structures

In this work, large-scale Cu nanocone arrays were synthesized by a one-step electrodeposition method without any template. The surface morphologies of Cu deposits prepared under different fabrication conditions have been observed. The as-prepared Cu nanocones grow preferentially along the direction. The formation mechanism of the nanocone structure can be explained by the screw dislocation driven growth theory. In addition, this electrodeposited Cu film with nanocone structure exhibits a superhydrophobic property after chemical modification.

Through silicon via filling by copper electroplating in acidic cupric methanesulfonate bath

Copper electrodeposition in acidic cupric methanesulfonate bath with organic additives is discussed in this paper. The influence of poly(ethylene glycol) (PEG) and bis-(3-sodiumsulfopropyl disulfide) (SPS) on copper deposition were studied by means of linear sweep voltammetry, cyclic voltammetry and chronoamperometry. These electrochemical analysises revealed a competition of PEG and SPS on electrode surface site. The swiftness of SPS chemisorption and the subsequent displacement by the passivating film of PEG exerted an extra wave at small overpotential on the negative-going sweep. The following polarization curve indicated the firmness of the passivating film. All these features of additives in acidic cupric methanesulfonate bath suggested a novel method to achieve superconformal or bottom-up filling which was proved by actual TSV plating.

Collaborative effect between additives and current in TSV via filling process

Deep via filling is one of key technologies of 3D packaging. Vias are commonly filled by electroplating. Since cupric transportation in vias is limited by diffusion, Current density is one of the most influential factors for copper plating in vias. We investigated new additive of accelerator, suppressor and leveler. Simulation of the competitive adsorption ability of accelerator and suppressor at different potential was studied. It was found that accelerator has more powerful adsorption ability than suppressor at high potential. Suppressor would form a passivating layer at the surface in the electroplating process, but the layer is easily disrupted by accelerator at high potential. We also investigated vias filling at different current density to prove our assumption. 0.4ASD was the best condition which got a fulfilled via without voids or seams. Conformal growth performance was attained at low current density and large current density would sealed the opening quickly, leaving seam at the bottom.

Simulation of electric field uniformity in through silicon via filling

There are many factors which will affect the final result of TSV filling, such as ratio of the additives including accelerator, suppresser, leveler and so on. Complicated environment is also hard to control exactly. If we want to form the “bottom up” in the plating, there must be comprehensively consideration of all factors. Many studies have focused on the effect of additives on the plating uniformity. But in industrial production, the macro-uniformity is the primary consideration. In this paper, we are talking about the most important factor-the electric field. ANSYS is used to simulate the electric field distribution in order to find the most Optimal parameters. Considering some major factors in electroplating, an optimization model is suggested by simulation. And the non-uniformity is reduced to below 10%. Based on this, we have simulated the electroplating of microholes in the beginning of TSV filling. The uniformity of the electric field inside the hole is mainly determined by the adsorption of chemical additives, especially for the suppressor. Deeper of the adsorbed position of suppressor, better “bottom up” trend in the process of electroplating.

Investigation of competitive adsorption between accelerator and suppressor in TSV copper electroplating

In TSV copper electroplating, the goal is to achieve superfilling deposition. In order to reach the bottom-up in TSV copper electroplating, some additives (accelerator suppressor and leveler) are added into the electroplating bath. To know the relationship between additives in the plating solution is very important. In the present work, by means of linear sweep voltammetry (LSV) and cyclic voltammogram (CV), it is found that there is a competition between the accelerator and the suppressor. At the less negative potential, the accelerator shows a strong adsorption property, and the suppressor plays its role in the relatively more negative potential area, which shows a competitive adsorption relationship between the accelerator and the suppressor during the process of bottom-up filling.

The effect of polyethylene glycols upon copper electrodeposition in methanesulfonate electrolytes

The effect of polyethylene glycols upon copper electrodeposition in methanesulfonate electrolytes is discussed in this paper. By means of linear sweep voltammetry and electrochemical impedance spectroscopy, it is found that polyethylene glycols in methanesulfonat electrolytes have very different behavior from that in traditional sulfuric electrolytes. PEG can adsorb on electrode surface in absent of chloride ion. The presence of chloride would destroy PEG adsorption to the electrode surface. The impedance shows that PEG can inhibit the reactions Cu2+→Cu+ and Cu+→Cu. The special effect of PEG in methanesulfonate electrolyte is probably related to methanesulfonic radical.

Pure Bottom-up filling process for efficient TSV metallization

TSV (Through Silicon Via) is an enabling technology for 3D WLP (Wafer Level Packaging) and 3D integration. TSV is a very hot topic for semiconductor industry today. One of the key processes for TSV is the electroplating process. The quality and rate of electroplating are two critical parameters for TSV filling, which can be significantly improved by Bottom-Up filling with much thinner overburden. Also, bottom up plating is a critical process to thin overburden. In this study, the copper plating of TSVs with the diameter and the depth in the ranges of 2.5-30 μm and 50-300 μm, respectively, was investigated. A nearly 100% bottom up plating recipe was developed in order to achieve void-free and seamless filling. The performance of this plating recipe was evaluated by vertical and top-down cross-sections images of filled TSVs using optical microscopy and X-ray inspection. The influence of the suppressor and cupric ion concentrations on Bottom-Up filling were investigated. Pure Bottom-Up filling can be achieved with a strong enough suppressor and high copper concentration. The strength of suppressor determines the required amount of copper concentration. The influence of diffusion time to different via diameter were also discussed. The copper concentration can be up to 120g/L in Methylsufonic Acid (MSA). The void-free and seamless copper deposition results with via diameter from 2.5μm-25μm or aspect ratio up to 20 can be achieved.

Through-silicon via filling process using pulse reversal plating

Though silicon vias filled by pulse reversal current, and influences of frequency of pulse current and reverse current density are investigated. Chronopotentiometry was applied to analyze the principle of these effects. It was found that when frequency is too high, the reverse current was mainly consumed in process of charge-discharge of electric double layer; it cannot play the role of dissolving copper deposit on surface of via and orifice. For pulse reversal plating, low frequency is required. Generally frequency less than 40Hz is suitable in this system. High reverse current density could suppress copper growth on surface and at the orifice. It is beneficial for bottom-up via filling. However, if reverse current is too high, plating speed could be serious inhibited. In our study, 1:2 is the best ratio of forward and reverse current density.

Influence of leveler concentration on copper electrodeposition for through silicon via filling

Through silicon via technology is one of the critical and enabling technologies for 3D packaging. 300μm deep vias with a diameter of 50μm were filled by copper electroplating with CuSO4 and H2SO4 as base electrolyte. Chloride ions, accelerator and leveler were added. The effect of leveler concentration on filling performance was studied. Electrochemical measurements were used to investigate the cathode process and the action of additives. It was found that mass transportation of copper in via became the slowest step in deep vias, small current is necessary to obtain void free deposit and only conformal growth was obtained. And with increasing of leveler concentration filling performance became better.