Copper Seed Layer Research Articles

Improved Adhesion of Direct Copper Seed Layer by Medium-Vacuum Sputtering Using Vacuum Ultraviolet Light

A sputtering method is used to form the seed layer for copper electric plating. In general, copper sputtering has weak adhesion to resin, so titanium sputter is combined to increase the adhesion strength. However, etching in the lithography process requires two types of processes, titanium and copper metal. Adhesion strength was improved by performing vacuum ultraviolet (VUV) treatment as a pretreatment for medium-vacuum sputtering. We discovered the relationship between the hydroxyl groups on the resin surface and the adhesion strength by the chemical modification XPS method. Furthermore, by XPS analysis of the peeled copper interface, the adhesion mechanism between the resin and copper due to VUV irradiation was estimated. We evaluated the absorption properties in the vacuum ultraviolet region of a thinly polished glass epoxy resin. We investigated the behavior of functional groups at the interface and considered the effect of vacuum ultraviolet light in the depth direction.

Consideration of Improved Adhesion of Direct Copper Seed Layer by Medium-Vacuum Sputtering Using Vacuum Ultraviolet Light

A sputtering method is used to form the seed layer for copper electric plating. In general, copper spatter has weak adhesion to resin, so titanium spatter is combined to increase the adhesion strength. However, etching in the lithography process requires two types of processes, titanium and copper metal. We have reported the improvement of adhesion of copper sputter to glass epoxy resin by medium vacuum sputtering equipment in 242nd ECS meeting. Adhesion strength was improved by performing vacuum ultraviolet treatment as a pretreatment for medium-vacuum sputtering. We discovered the relationship between the hydroxyl groups on the resin surface and the adhesion force by the chemical modification XPS method. Furthermore, by XPS analysis of the peeled copper interface, the adhesion mechanism between the resin and copper due to UV irradiation was estimated. We evaluated the absorption properties in the vacuum ultraviolet region of a thinly processed glass epoxy resin. We investigated the behavior of functional groups at the interface and considered the effect of vacuum ultraviolet rays in the depth direction.

Consideration of Improved Adhesion of Direct Copper Seed Layer by Medium-Vacuum Sputtering Using Vacuum Ultraviolet Light

A sputtering method is used to form the seed layer for copper electric plating. In general, copper sputtering has weak adhesion to resin, so titanium sputter is combined to increase the adhesion strength. However, etching in the lithography process requires two types of processes, titanium and copper metal. Adhesion strength was improved by performing vacuum ultraviolet (VUV) treatment as a pretreatment for medium-vacuum sputtering. We discovered the relationship between the hydroxyl groups on the resin surface and the adhesion strength by the chemical modification XPS method. Furthermore, by XPS analysis of the peeled copper interface, the adhesion mechanism between the resin and copper due to VUV irradiation was estimated. We evaluated the absorption properties in the vacuum ultraviolet region of a thinly polished glass epoxy resin. We investigated the behavior of functional groups at the interface and considered the effect of vacuum ultraviolet light in the depth direction.

Improved Adhesion of Copper Seed Layer Using Vacuum Ultraviolet Light for Direct High-Speed Sputtering

The dry process is progressing in the manufacturing process of semiconductor packages. The semi-additive process for forming the rewiring layer is required to be finer and more reliable than ever. The interface between the insulating resin and the copper wiring is being smoothed in order to reduce transmission loss during high-frequency communication. The conventional electroless plating method using the anchor effect is disadvantageous for smoothing. Therefore, a sputtering method is used to form the seed layer. In general, copper spatter has weak adhesion to resin, so titanium spatter is combined to increase the adhesion strength. However, etching in the lithography process requires two types of processes, titanium and copper.We investigated the improvement of copper sputtering adhesion to glass epoxy resin by a high-speed sputtering device. Adhesion strength was improved by performing plasma treatment and vacuum ultraviolet treatment as pretreatment for high-speed sputtering. Surface modification was analyzed and evaluated by XPS. We report on the process and evaluation method that contribute to the dryness of the packaging process.

Investigation of Metal Co-evaporated Copper Seed Layers for Copper-Plated Heterojunction Solar Cells

For the reduction of optical loss and contact material cost in silicon heterojunction (SHJ) solar cells, copper plating has been considered as a suitable metallization technique. However, a plated copper contact on an indium-tin-oxide (ITO) generally has low a reliability of adhesion. For this reason, proper seed layer materials are required for adhesive copper plating. As a requirement for a suitable seed layer material, the contact resistance between the seed and the ITO is also important, as well as the adhesion, because high series resistance results in a low fill factor. In this research, we deposited a seed layer by co-evaporating copper with other metals (Cu-X). The contact resistivity (ρ c ) of the Cu-X deposited on ITO was evaluated by using the transfer length method (TLM). In order to confirm the influence of the work function of the Cu-X, we measured the contact potential difference (CPD) by using photoemission in an air system (PAS). Moreover, phase and we analyzed the crystallite size by using X-ray diffraction (XRD) measurement.

Study of Seed-Layer Stability on Copper Electrolytic Bath

In microelectronic field, 3D interconnects are processed by copper electrodeposition using a copper seed-layer to ensure the electrical contact. A uniform and homogeneous seed-layer is necessary to guarantee full filling of structures without any defect. This research work is focused on the seed-layer stability in electrolytic copper bath and its dissolution rate, during the idle time just before the plating.

Study of Seed-Layer Stability on Copper Electrolytic Bath

For years, the effectiveness of the Damascene process has allowed the semiconductor industry to successfully keep the pace with the aggressive scaling of Moore’s law. However, ever increasing costs have raised the need for alternative technologies bringing advantages in terms of performance gain, time to market and cost competitiveness. Thus, 3D chip stacking technologies have now become a field of extensive research [1-2]. The today improvements are mainly devoted on the current process optimization or the development of new methods to elaborate barriers, seed-layers and fillings compatible with technological advances and the more and more aggressive via aspect-ratio [3]. Generally made in copper by CVD, PVD, ALD or electrografted technics, the seed-layer plays an important role during the via filling. Its principal criteria are to be uniform in term of thickness and continuous to ensure a good electrical contact during the electrochemical process [4]. During the filling process, the wafers and thus the seed-layer are first pre-wetted using DI water or etching solutions and then immerged in the copper bath. Traditionally an idle time is maintain before applying the current density, to favour the species exchange. However, few studies have an interest for the reaction during this idle time and in more general consideration for the copper seed-layer stability on the copper electrolytic bath. Hence, the copper seed-layer is dissolved in the plating bath due to electrochemical reaction with the oxygen dissolved in the bath [5-7]. In this research work, the stability of the seed-layer and its dissolution rate are studied combining in-situ and ex-situ technics (figure 1). Open circuit potential versus time is an interesting approach for this study, allowing direct information on the surface modification during the idle time. Quartz microbalance measurements complete the analyses, giving direct information of weigh lost resulting from dissolution. As ex-situ characterization technics, SEM-EDS, XPS and RBS measurement were performed to characterize the surface states and the chemical composition after the idle time. Several parameters are particularly highlighted as the bath composition and its concentration and the rotation rate of the substrate. [1] T.P. Moffat, D. Wheeler et al., IBM J. Res. Dev., 49, 19 (2005) [2] P.M. Vereecken, R.A. Binstead, H. Deligianni, P.C. Andricacos, IBM J. Res. Dev, 49, 3 (2005) [3] M. Datta, Electrochemical processing technologies and their impact in microelectronic packaging in Microelectronic Packaging, edited by M. Datta, T. Osaka and J.W. Schultze, CRC Press edition (2005) [4] Part II Chip metallization in Microelectronic Packaging, edited by M. Datta, T. Osaka and J.W. Schultze, CRC Press edition (2005) [5] R. Schumacher et al, J. Electroanal. Chem. 219 (1987) 311-3174 [6] K.Y. Electrochimica Acta, 38, 14 (1993) 2121-2127 [7] A.G. Zelinsky et al, Corrosion Science 46 (2004) 1083–1093 Figure 1

Electrografted Copper Seed Layer for High Aspect Ratio TSVs Interposer Metallization

Nowadays, Through Silicon Vias (TSV) with High Aspect Ratio (HAR > 8:1) are seriously mandatory in the 3D Integrated Circuits in order to maintain semiconductor performance trends into new technological advances. Consequently, successful integration of HAR TSVs requires solving key challenges in terms of technical (layer continuity, step coverage, adhesion) and industrial (scale-up to 300mm diameter wafer) developments. In this paper, one proposes to discuss those questions by means of the integration of an electrografting (eG) seed layer on a high conformal, but low conductive MOCVD TiN copper diffusion barrier. On the one hand, one studies the impact of different electrochemical parameters on eG Seed layer properties. On the other one, the encountered difficulties are presented and solutions are proposed to integrate eG Seed layer at a large scale i.e. on a specific industrial 300mm diameter wafer plating chamber.

Study on the Corrosion Characteristics of Sputtered Barrier-Free Cu(MoN) Copper Seed Layers

Study on the Corrosion Characteristics of Sputtered Barrier-Free Cu(MoN) Copper Seed Layers

Electrografted Copper Seed Layer for High Aspect Ratio TSVs Interposer Metallization

After many years of developments, 3D Integrated Circuits have emerged as a potential key enabler for maintaining semiconductor performance trends. Through Silicon Vias (TSVs) sit at the foundation of the 3D-IC revolution for extending semiconductor integration into a new phase. Integrated device manufacturers and fabless design houses need small, high-density, fine-pitch vias for improving signal integrity and Si real-estate savings, without possibility to wait for very thin wafer processing and handling technologies to become a mainstream. Deep TSVs with Aspect Ratio (AR) greater than 10:1 elegantly fulfill those requirements. But they cannot be manufactured with acceptable yield/cost using traditional dry processes for liner, barrier and seed deposition. Conventional dry techniques show basic shortcomings and impose high capital investments. Beyond that, physical limitations of directional dry techniques prevent the deposited layer from reaching good step coverage or even continuity inside the vias, which is required to perform void-free gap filling with electroplated copper.To overcome those limitations, alternative wet solutions based on electrografting (eG) and chemical grafting (cG) technologies were developed. These latter are two fundamental molecular engineering technologies, delivering high-quality films (continuous, adherent and uniform) for high aspect ratio (HAR) TSVs. This paper will focus on the integration of eG copper seed as a mature solution for TSVs with HAR, to overcome PVD Copper limitations in those dimensions.Electrografting is based on surface chemistry formulations and processes. It is applied to conductive and semi-conductive surfaces, and enables self-oriented growth of thin coatings of various materials, initiated by in-situ chemical reactions between specific precursor molecules and the surface. Contrary to electro-deposition which requires a potential supply throughout deposition to fuel the redox processes, electrografting is an electro-initiated process which requires a charged electrode only for the grafting step, but not for the thickening. As eG is mainly a cathodic process, it can generally be applied to various metallic and semiconducting surfaces without any concern over oxide formation. In a first approach, electrografting was used for polymer deposition on various conductive and semi conductive substrates. In this case, the grafting occurs via a direct electron transfer from the cathode to the electro-active monomers in solution (Figure 1). Mechanisms of radical polymerization show that polymer electrografting is an electro-induced grafting process followed by a purely chemical propagation step (polymerization). The first electro-induced step is crucial to form the chemical bond between the polymer and the surface. A specific organic precursor (B) is used both to form a first primer grafted layer and to initiate the polymerization of the vinyl monomer (A) in solution. The termination step of the polymerization leads to the grafting of macromolecular chains (-[A-A-A]n-B) onto the first primer grafted layer. Based on the polymer electrografting concept, formulation and processes have been developed to graft metal layers onto various type of conductive and semi-conductive surfaces. In opposite, for instance, to copper electrodeposition which has to be performed on conductive layer to avoid terminal effect induced by resistive copper diffusion barrier layers, copper electrografting technology can interestingly be achieved on highly resistive substrates.A bath containing specific organics and copper has previously been developed to deposit the Cu seed layer. It has been shown that electrografted copper seed can directly be applied to various dry-deposited diffusion barriers (Ta, TaN, Ti, TiN, TiW) without any adhesion promoter in between.This paper deals with the integration of eG Seed layer on a conformal MoCVD TiN copper diffusion barrier on 8:1 aspect ratio TSVs. First, detailed mechanism of the electrografting process will be discussed. Secondly, the influence of the electrical barrier resistivity (PVD TiN, Ni vs MoCVD TiN) on the plating properties into the via will be presented for both experiments done at coupon level and up scaled in an industrial 300mm diameter wafer reactor. Plating differences will be considered in term of growth initiation and step coverage for these two experimental configurations. Fine tuning of the process parameters at the 300mm scale will then be examined to achieve a conformal, uniform and adherent copper seed layer in order to successfully respond to the high AR copper filling challenge in the TSV applications. Finally, void-free filling, integration in a conventional 3D process flow and electrical characterizations on high aspect ratio TSV middle daisy chains are ongoing. As a perspective to decrease the cost of TSV metallization, the entire wet metallization process flow including isolation, copper diffusion barrier, copper seed and copper fill steps will be developed at the end of this paper.

Deposition of a Continuous and Conformal Copper Seed Layer by a Large-Area Electron Cyclotron Resonance Plasma Source with Embedded Lisitano Antenna

To deposit copper seed layer on ultra large scale integration devices, a large-area (O 378 mm) electron cyclotron resonance plasma has been generated by using permanent magnets-embedded Lisitano antenna. The plasma source operates in the pressure range of 0.2–1.5 mTorr with microwave power range of 500–2,000 W. By using a Langmuir probe, the electron density and temperature have been measured near the DC sputter target position. Measurements indicate argon plasmas having electron densities of ~5 × 1010/cm and electron temperatures of 5 eV with 750 W microwave power at gas pressures of 0.5 mTorr. Using this plasma source and a DC sputter, we obtained excellent conformal copper seed layer with high aspect ratios of 12:1. This is in contrast with conventional methods using magnetron sputter, which has aspect ratios of 2–3:1. Also, improvements are observed in the smoothness (root mean square roughness of 1.345 nm), uniformity (2.5 % at 300 mm wafer), and sidewall symmetricity (more than 95 %) of the copper seed layer.

Ultrastable and Atomically Smooth Ultrathin Silver Films Grown on a Copper Seed Layer

An effective method to deposit atomically smooth ultrathin silver (Ag) films by employing a 1 nm copper (Cu) seed layer is reported. The inclusion of the Cu seed layer leads to the deposition of films with extremely low surface roughness (<0.5 nm), while it also reduces the minimum thickness required to obtain a continuous Ag film (percolation thickness) to 3 nm compared to 6 nm without the seed layer. Moreover, the Cu seed layer alters the growth mechanism of the Ag film by providing energetically favorable nucleation sites for the incoming Ag atoms leading to an improved surface morphology and concomitant lower electrical sheet resistance. Optical measurements together with X-ray diffraction and electrical resistivity measurements confirmed that the Ag film undergoes a layer-by-layer growth mode resulting in a smaller grain size. The Cu seeded Ag growth method provides a feasible way to deposit ultrathin Ag films for nanoscale electronic, plasmonic and photonic applications. In addition, as a result of the improved uniformity, the oxidation of the Ag layer is strongly reduced to negligible values.

Scaling of Copper Seed Layer Thickness Using Plasma-Enhanced ALD and Optimized Precursors

Two recently developed precursors, AbaCus and Super AbaCus, are evaluated for use in ultralow temperature copper deposition by plasma enhanced atomic layer deposition. Film adhesion, platability, and process window evaluation demonstrate the strong capability of these precursors to overcome current metallization challenges.

Formation of Copper Seed Layers and Copper Via Filling with Various Additives

Recently, the demand for the miniaturization of printed circuit boards has been increasing, as electronic devices have been sharply downsized. Conventional multi-layered PCBs are limited in terms their use with higher packaging densities. Therefore, a build-up process has been adopted as a new multi-layered PCB manufacturing process. In this process, via-holes are used to connect each conductive layer. After the connection of the interlayers created by electro copper plating, the via-holes are filled with a conductive paste. In this study, a desmear treatment, electroless plating and electroplating were carried out to investigate the optimum processing conditions for Cu via filling on a PCB. The desmear treatment involved swelling, etching, reduction, and an acid dip. A seed layer was formed on the via surface by electroless Cu plating. For Cu via filling, the electroplating of Cu from an acid sulfate bath containing typical additives such as PEG(polyethylene glycol), chloride ions, bis-(3-sodiumsulfopropyl disulfide) (SPS), and Janus Green B(JGB) was carried out. The desmear treatment clearly removes laser drilling residue and improves the surface roughness, which is necessary to ensure good adhesion of the Cu. A homogeneous and thick Cu seed layer was deposited on the samples after the desmear treatment. The 2,2'-Dipyridyl additive significantly improves the seed layer quality. SPS, PEG, and JGB additives are necessary to ensure defect-free bottom-up super filling.

Vapor Deposition of Highly Conformal Copper Seed Layers for Plating Through-Silicon Vias (TSVs)

Through-silicon vias (TSV) will speed up interconnections between chips. Manufacturable and cost-effective TSVs will allow faster computer systems. In this paper, we report the successful formation of seed layers for plating copper TSVs with aspect ratios greater than 25:1. Following the rapid atomic layer deposition (ALD) of a conformal insulating layer of silica inside the silicon vias, manganese nitride (Mn4N) is deposited conformally on the silica surface by chemical vapor deposition (CVD). Mn4N forms an effective copper diffusion barrier and provides strong adhesion between the silica and the subsequently-deposited copper. Conformal copper or copper-manganese alloy films are then deposited by an iodine-catalyzed direct-liquid-injection (DLI) CVD process. Diffusion of manganese during post-deposition annealing further enhances the barrier and adhesion properties at the copper/dielectric interface.

Vapor Deposition of Highly Conformal Copper Seed Layers for Plating through-Silicon Vias, Including Silica Insulator and Manganese Nitride Barrier and Adhesion Layers

not Available.

Room Temperature Copper Seed Layer Deposition by Plasma-Enhanced Atomic Layer Deposition

AbaCus, a newly developed fluorine-free precursor has been used for room temperature copper deposition using plasma enhanced chemical vapor deposition (PEALD). This process has been characterized and the film properties investigated in term of composition, deposition rate, resistivity, grain size and platability. Integration results with completely filled structures obtained demonstrate a high potential for use in advanced interconnect technologies.

Room Temperature Copper Seed Layer Deposition by Plasma-Enhanced Atomic Layer Deposition

not Available.

Ultra-Low Temperature Deposition of Copper Seed Layers by PEALD

Two novel fluorine-free precursors have been developed and evaluated for use in ultra-low temperature copper deposition by PEALD. Manufacturable PEALD processes have been demonstrated, and processing conditions correlated to film composition, growth rate, resistivity and step coverage. Preliminary integration results indicate that both of these precursors have potential for use in advanced interconnect systems.

Ultra-Low Temperature Deposition of Copper Seed Layers by PEALD

not Available.