TSV Filling Research Articles

Acceleration Kinetic of Copper Damascene by Chloride, SPS, and Cuprous Concentration Computation in TSV Filling

Copper electrodeposition occurs in two steps and a practical electrodeposition normally needs several additives that require kinetic parameters for the calculation of current density and the concentration of intermediates. The copper electrodeposition was considered as a surface reaction, the exponential part of Butler-Volmer equation contributes to the value of reaction rate constant while the exchange current density relates to both the reaction rate constant and the surface concentration of cupric and cuprous ions. Two models for the adsorption of an additive or two additives on electrode surface were supposed. Using cyclic voltammetric stripping and chronoamperometry method, the electron bridge performance of chloride and the interaction of chloride with SPS were quantitatively compared with the non-additive copper electrodeposition.

Communication—Conical TSV Filling within 30 Seconds

Super bottom up filling of TSVs is achieved by using a new leveler NM. The leveler was characterized by CVS method, its inhibition role was exhibited at different rotating rates and concentrations. NM electrolyte built up TSVs from the bottoms and almost no deposition on the TSV walls. The electrolyte containing NM leveler was effective at a high current density for both periodic pulse reverse (PPR) current, and direct current (DC). The 2 μm diameter and 16 μm depth conical TSVs required 30 s for full filling by two steps which were the PPR current step and the DC step.

Parameters Analysis of TSV Filling Models of Distinct Chemical Behaviours of Additives

Four types of via-filling models are developed in this paper, considering distinct chemical behaviour of additives used in the TSV electroplating. The surface convection, surface diffusion and the effect of the curvature are considered in the equation of the coverage of additives, which is solved by a weak form of the PDEs. The simulation results of the different models are compared. Sensitivity analyses of the important parameters in the four models are conducted. Thus, the influences of parameters on the via-filling process are investigated. Conclusions are drawn based on the analysis of the developed numerical models.

Communication—Halide Ions in TEG-Based Levelers Affecting TSV Filling Performance

A leveler is one of the key additives for the defect-free filling of Through Silicon Via. The convection dependent behavior of a leveler is required to achieve successful gap-filling of Cu. Levelers occasionally contain charged functional groups and the counter anions. The charged functional groups obviously determine the characteristics of the leveler, and counter anions also influence the electrochemical behavior and Cu gap-filling. In this study, we synthesize levelers that have two quaternary ammoniums and different counter anions. The electrochemical behavior of the synthesized levelers and the effect of the counter anions on Cu gap-filling are described.

Optimizing TSV Fill Phases for Improved Fill Rate, Process Stability and Void Performance

This paper will explore the differences between the theoretical optimal electrochemical polarization conditions within the via during the key phases of gap filling (e.g. nucleation, conformal filling, and the transition to bottom-up filling), and compare to the actual conditions of conventional processing. The gaps between the optimal and actual conditions identify opportunities for innovation to significantly reduce fill time, provide supreme stability of the bath and minimize overburden thickness. The paper describes several such innovations.

Optimizing TSV Fill Phases for Improved Fill Rate, Process Stability and Void Performance

Through Silicon Via integration provides enabling technology as the semiconductor industry continues to implement 2.5D and true 3D device and system packages. The drive for improved performance and the foray into the era of the Internet of Things promises a continued need for TSV advancement including different barrier/seed schemes and aggressive aspect ratios. While the industry has developed fairly robust gap filling processes for conventional interposer and via middle features in the range of 5X50µm and 10X100µm, continued scaling of aspect ratio ensures that TSV plating will require new innovations to provide a stable process free of killer voids such as seam and pinch off voids. Reliability performance will demand a reduction and/or elimination of the microvoid formation between grains. Additionally, the costs associated with TSV integration will continue to drive the need for faster fill and thinner overburden in order to minimize cost of ownership. For this reason, the continued optimization of plating conditions is critical and includes factors such as control of the current density at via bottom during nucleation and initiation of gap filling, sidewall grain orientation, degree of sidewall suppression, additive diffusion rate, etc. This paper will explore optimal electrochemical polarization conditions within the via during the key phases of gap filling, such as nucleation, conformal filling, and the transition to bottom-up filling. As an example, the plating process begins with the nucleation of plated copper onto the seed layer. This phase targets the formation of a high density of nucleation sites in order to form a uniform and conformal initial layer of ECD copper. The theoretical optimal conditions include uniform seed layer from top to bottom, full concentration of additives present homogenously throughout the via at time zero, and uniform current density at each point along the via sidewall and via bottom. Additionally, the field area must be polarized to a high degree. In actual practice, the seed layer is typically thinner toward the bottom of the via and can often be discontinuous. For conventional TSV fill, the diffusion of the plating chemistry takes time and by design the diffusion rate of the various additives is different. Current density is unlikely to be uniform the entire length of the sidewall due to variations in seed thickness. Despite this gap between the theoretical optimal condition and the actual conditions, continued management of additive activity and waveform has enabled the development of a robust gap filling process. However, the opportunity for further innovation remains with respect to the various the phases of fill: Immersion –> Nucleation; Nucleation –> Mixed Growth Phase; Mixed Growth –> Bottom-Up Dominated Fill; Bottom-Up Dominated Fill –> Top Off; Top Off –> Overburden. This paper will discuss optimal conditions at each phase and present results of several innovations from Applied Materials which take advantage of the gaps between phases and provide improvements such as: significant fill time reduction, supreme stabilization of electrochemical activity against bath aging, and improvements in the formation of microvoids between grains.

Highly Adhesive Displacement Plated Cu Seed on Cowb Barrier for All-Wet TSV Fill Process

Fabrication of TSV is one of key technology for 3D-ICs. For realizing conformal barrier layers against Cu diffusion with a low temperature process is important to achieve highly reliable TSVs. Electroless plated metals such as Co-alloy and Ni-alloy are considered to have a high potential as a barrier layer. We succeeded in conformal electroless plating of CoWB on SiO2, using DMAB as a reducing agent after forming self-assembled monolayer (SAM) of silane coupling agent (APTES) on SiO2 [1-2], assisted with Pd nanoparticle catalyst. The adhesion strength of CoWB decreased with an increase in film thickness [1], which might be due to an increase in film intrinsic stress. Electroless Cu plated film using reducing agent on the CoWB layer showed a very poor adhesion property. In this study, we studied to form electroless Cu seed layer with a high adhesion strength by displacement reaction without reducing agent, and furthermore examined the barrier and seed formation into a high aspect ratio TSVs. The electroless CoWB plating bath composed of cobalt sulfate and tungstic acid as a metal salt, citric acid as a complex agent, DMAB as a reduction agent. The Cu displacement plating bath composed of sulfuric acid and copper sulfate, and its pH was 3.5. The adhesion strength was evaluated by the stud-pull test. Table 1 shows the adhesion strengths of various films such as CoWB (70nm) only, displacement plated Cu on CoWB, electroless Cu plated with reducing agent (glyoxylic acid) on CoWB. The adhesion strength of the 70 nm CoWB film was 20MPa. That of displacement plated Cu/CoWB was 50 MPa. The adhesion strength of electroless plated Cu with reducing agent was very poor. We succeeded in obtaining a high adhesion strength by Cu displacement plating. Figure 1 shows the displacement plated Cu seed layer on 80 nm electroless CoWB layer in TSV. The diameter is 3 μm and aspect ratio is 10. Displacement plated Cu film was formed almost uniformly from top to bottom of TSV. The sidewall and bottom coverages of Cu/CoWB bilayer in TSV was 70 to 80 % against that of the flat area. At the bottom of TSV, Cu(40nm)/CoWB(40nm) bilayer was formed succesfully without delamination. We succeeded in the formation of highly adhesive electroless plated Cu seed layer on CoWB layer. Further study of complete fill of TSV with ECP Cu is in progress.

TSV Fillings and Electrochemical Measurements of the Dialyl-amine Additive with Cl− and Br−

The TSV filling using the dialyl-amine and the Br− and Cl− halogen ions to a copper electrodeposition bath is reported. The TSV bottom acceleration and TSV outside inhibition have been measured by an electrochemical method using the rotating disk electrode and numerical computation of the fluid dynamics. A perfect TSV filling is achieved with 1 ppm P(DAMA[HBr]/SO2) + 1 ppm of Br− and the electrodeposited morphology is fine and bright. This shows acceleration at the lower rotation speeds of the rotating disk electrode and an inhibition at the higher speeds, if compared to 1 ppm P(DAMA[HCl]/SO2) + Cl−1 ppm. Br− 1 ppm shows a stronger inhibition at the higher rotation speeds, if compared to Cl−1 ppm. The addition of SPS in addition to Br− 1 ppm shows acceleration at the lower speeds. No voids formed at the higher current density of 3.5 mA/cm2 with SPS.

Optimized TSV Module for High Performance 2.5D Device Packaging

3D-IC has been increasingly adopted by the industry owing to its promise of higher device speed and package bandwidth, improved power consumption, reduced form factor, and lower cost for important applications over a wide range of industrial segments including image sensors, logic-memory and logic-logic integration, MEMS, integrated optical interposers and LEDs. This presentation is a systematic study of multiple experimental factors affecting the electrical performance, reliability and scalability of TSVs. Electrical modeling and simulation was used to determine the key factors influencing singal transmission and return losses in TSVs at high (>1 GHz) frequencies. A variety of process modules and steps for the fabrication of through silicon vias were then systematically optimized to ensure high performance. The modules evaluated include TSV etch, TSV fill, chemical mechanical polishing (CMP), pad finish, bonding schemes, wafer thinning, via reveal, passivation, wiring and bumping. One example is the improvement of TSV profile and sidewall roughness through the optimization of DRIE parameters and wet chemical methods to reduce silicon sidewall roughness from that of a typical Bosch etch to less than 10nm which is critical for adhesion of barrier/seed layer and the final reliability of 2.5D packaging. Scalability of void-free via fill process with respect to TSV diameter and depth was addressed by using highly conformal barrier layers. Adhesion of Cu to the barrier layer was also improved upon detailed analysis to prevent delamination and improve reliability. A bottom up plating chemistry with significantly low impurity content was utilized to mitigate voids, seams and excessive overburden in the TSV. Its impact on stress and delamination issues and subsequent reliability failures was studied in details. The annealing process following TSV formation is systematically studied with varying conditions and characterized with metrology and electrical tests to investigate its effect on microstructure and material properties. The process parameters were tuned for CMP of Cu, adhesion and barrier layer without causing corrosion or delamination between adjacent layers. Process requirements for these modules in TSV process are closely related. This presentation will review the process module development in the context of their effects on the integrated TSV parameters (performance, reliability and scalability). We will also provide an in-depth discussion on process module optimization, electrical and mechanical characterization and cost reduction methodologies.

TSV Filling By NiW Alloys Electroplating

not Available.

Control of Adhesion Strength and TSV Filling Morphology of Electroless Barrier Layer

In this study, we investigated to control adhesion property of the electroless plated barrier layer on SiO2 by addition of saccharin and its deposition profile in a high aspect ratio TSV with inhibitor and saccharin. We achieved high adhesion strength of barrier layer by addition of suitable amount saccharin. Furthermore, we succeeded in the formation of thin continuous electroless barrier layer for a high aspect ratio TSV with addition of both inhibitor and saccharin. The proposed highly adhesive and conformal electroless barrier layer formation would provide a highly reliable all-wet TSV filling process.

The Effect of Polymer Additives on TSV Filling by Copper Electroplating

not Available.

Control of Adhesion Strength and TSV Filling Morphology of Electroless Barrier Layer

not Available.

Characterization of the Organic Components in a Commercial TSV Filling Chemistry

not Available.

The Effect of Polymeric Additives on TSV Filling by Copper Electroplating

not Available.

Conformal Electroless Deposition of Barrier and Cu Seed Layers for Realizing All-Wet TSV Filling Process

not Available.