[Show abstract][Hide abstract] ABSTRACT: In order to enable an oxide-free Cu-to-Cu bonding in a (dual) damascene process, 3-aminopropyltrimethoxysilane- and decanethiol-derived self-assembled monolayers are selectively deposited in a dielectric-Cu based metal–insulator–metal (MIM) capacitor used as a test vehicle, which represents a dual damascene architecture environment. A two-steps SAM coating sequence is investigated for this purpose. In a first step, a “sacrificial” SHSAM is deposited on the Cu areas at the bottom of the vias. In a second step, a “barrier” NH2SAM is deposited on the dielectric areas in the field region and via’s sidewalls. This deposition sequence followed by the selective thermal ablation of the “sacrificial” SAM vs. the “barrier” SAM, enable an oxide-free Cu-to-Cu connection at via’s bottom. The differential in thermal stability between the amino and thiol SAMs has been studied by water contact angle and cyclic voltammetry. While the sacrificial SAM is selectively desorbed by thermal ablation already at ∼200 °C, the barrier SAM on the dielectric sidewall and field regions withstands a thermal budget as high as ∼350 °C. The substrate-selective SAMs depositions are revealed by XPS chemical characterization on the Cu and dielectric areas of the MIM structures supported by the SEM visualization of the Au nanoparticles that selectively decorate the NH2 functionalities of the barrier SAM.
[Show abstract][Hide abstract] ABSTRACT: Barrier reliability in 3D through-Si via (TSV) Cu interconnections requires particular attention as these structures come very close to the active devices and Cu diffusion into the silicon substrate would significantly affect device performance. This work focuses on a via-middle process flow, which implies processing of the 3D-TSV after the front-end-of-line (FEOL) process, but before the back-end-of-line (BEOL) interconnect process. This results in several high temperature processing steps after TSV fabrication, including a final device wafer sintering step, generally in the 400 °C range. Thus, it becomes essential to study the stability of the TSV Cu-barrier at these temperatures to ensure a reliable integration of 3D TSV in CMOS wafers. TSV aspect ratios can vary as function of the integration scheme, for instance in a via-last or via-middle flow, and thus barrier continuity requires conformality which guarantees the presence of a diffusion barrier until the bottom of the TSV. Target conformality can either be obtained by PVD, typically for TSV A.R. ⩽ 10:1. We report on the thermal stability of Ta, and Ti barriers and we show that 5 nm PVD Ta barriers are thermally stable, while PVD Ti-barriers require thicknesses above 5 nm to guarantee their thermal stability.
[Show abstract][Hide abstract] ABSTRACT: NMP is a commonly used solvent for removing positive photoresist in 3D applications, especially in electroplating and (micro-) bumping. However, the negative photoresists are more and more preferred in these applications. Unfortunately, NMP is inefficient for negative photoresist and it is not considered in Europe as an ESH solvent anymore. In this paper a comparative study was carried out in order to identify a solvent that is ESH friendly and a one-size-fits-all solution for stripping negative-tone and thick positive-tone photoresist (2-22 μm) for (micro-) bumping, electroplating and TSV etch applications. The study was performed at tool level.
Solid State Phenomena 04/2012; 187:223-226. DOI:10.4028/www.scientific.net/SSP.187.223
[Show abstract][Hide abstract] ABSTRACT: Exposure of TSVs from the backside in 3D-SIC is a multistep process [1-. Two steps in this process flow (thinning module) are potentially a high risk for particle contamination: wafer edge trimming and wafer thinning by grinding.
Solid State Phenomena 04/2012; 187:265-268. DOI:10.4028/www.scientific.net/SSP.187.265
[Show abstract][Hide abstract] ABSTRACT: Power and substrate domains are strategically isolated or unified in heterogeneous 3D integration. In-tier probing circuitry provides accessibility to power delivery and substrate networks in a deep tier of a 3D chip stack and capability of diagnosing intra/inter tier coupling. A two-tier demonstrator was successfully tested in a 130 nm CMOS, 3D-SIC Cu TSV technology.
3D Systems Integration Conference (3DIC), 2011 IEEE International; 01/2012
[Show abstract][Hide abstract] ABSTRACT: In this paper, we report on the processing and the electrical characterization of a 3-D-wafer level packaging through-silicon-via (TSV) flow, using a polymer-isolated, Cu-filled TSV, realized on thinned wafers bonded to temporary carriers. A Cu/Sn micro-bump structure is integrated in the TSV process flow and used for realizing a two-die stack. Before TSV processing, the Si wafers are bonded to temporary carriers and thinned down to 50 μm. The actual TSV and micro-bump process uses 3 masks, two Si-deep-reactive ion etching steps and a polymer liner as a dielectric. The dimensions of the TSV structure are: 35 μm <sup>Ø</sup>TSV, 5 μm thick polymer liner, 25-μm-Ø Cu TSV, 50 μm deep TSV, and a 60 μm TSV pitch.
IEEE Transactions on Components, Packaging, and Manufacturing Technology 07/2011; 1(6-1):833 - 840. DOI:10.1109/TCPMT.2011.2125791 · 1.18 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The establishment of a cost-effective Through Silicon Vias (TSV) fabrication process integrated to a CMOS flow with industrially available tools is of high interest for the electronics industry because such process can produce more compact systems. We present a 300 mm industry-compliant via-middle TSV module, integrated to an advanced highk/metal gate CMOS process platform. TSVs are fabricated by a Bosch process after contact fabrication and before the first metal layer. The target for copper diameter is 5 µm and via depth in the silicon substrate is 50 µm. Dense structures have a pitch of 10 µm. The vias are filled with TEOS/O3 oxide to reduce via-to-substrate capacitance and leakage, a Ta layer to act as Cu-diffusion barrier and electroplated copper. Copper is thermally treated before CMP to minimize copper pumping effects. The processing is integrated as part of a 65 nm node CMOS fabrication module and validated with regular monitoring of physical parameters. The module was tested in device lots and also integrated to a thinning and backside passivation flow.
Electronic Components and Technology Conference (ECTC), 2011 IEEE 61st, Lake Buena Vista, FL; 05/2011
[Show abstract][Hide abstract] ABSTRACT: In this paper we will highlight key integration issues that were encountered during the development of the 3D-stacked IC Through Silicon Via (TSV) module and present solutions to achieve a robust copper TSV. Electrical performance of the obtained TSV module is discussed based on a lumped RC model for 3D ring oscillators containing TSVs between bottom and top tiers.
[Show abstract][Hide abstract] ABSTRACT: In this paper key design issues and considerations of a low-cost 3-D Cu-TSV technology are investigated. The impact of TSV on BEOL interconnect reliability is limited, no failures have been observed. The impact of TSV stress on MOS devices causes shifts, further analysis is required to understand their importance. Thermal hot spots in 3-D chip stacks cause temperature increases three times higher than in 2-D chips, necessitating a careful thermal floorplanning to avoid thermal failures. We have monitored for ESD during 3-D processing and have found no events take place, however careful further monitoring is required. The noise coupling between two tiers in a 3-D chip-stack is 20 dB lower than in a 2-D SoC, opening opportunities for increased mixed signal system performance. The impact on digital circuit performance of TSVs is accurately modeled with the presented RC model and digital gates can directly drive signals through TSVs at high speed and low power. Experimental results of a 3-D Network-on-Chip implementation demonstrate that the NoC concept can be extended from 2-D SoC to 3-D SoCs at low area (0.018 ) and power (3%) overhead.
[Show abstract][Hide abstract] ABSTRACT: As scaling becomes increasingly difficult, 3D integration has emerged as a viable alternative to achieve the requisite bandwidth and power efficiency challenges. However mechanical stress induced by the through silicon vias (TSV) is one of the key constraints in the 3D flow that must be controlled in order to preserve the integrity of front end devices. For the first time an extended and comprehensive study is given for the stress induced by single- and arrayed TSVs and its impact on both analog and digital FEOL devices and circuits. This work provides a complete experimental assessment and quantifies the stress distribution and its effect on front end devices. By using a combined experimental and theoretical approach we provide a framework that will enable stress aware design and the right definition of keep out zone and ultimately save valuable silicon area.
Electron Devices Meeting (IEDM), 2010 IEEE International; 01/2011
[Show abstract][Hide abstract] ABSTRACT: The trend for future integrated circuits (IC) is decreasing in size beyond the conventional limits. The recent transition from aluminum to copper as the interconnect material for IC is due to copper's higher resistance to electromigration and its lower resistivity. Unfortunately, copper has high mobility in Si and SiO2 and may cause destruction of electrical connections on the chip. Hence, there is a significant necessity in finding ultra thin, thermally stable, high quality and good adhered diffusion barriers. The most widely used barrier is pure Ta films or layer stacks consisting of Ta and TaN. These have excellent conformality, very good uniformity and high thermal stability. But The continuous scaling down of the interconnect dimensions lead to an essential decrease in the barrier layer effective thickness to less than 5nm; coupled with the replacement of silicon oxide by advanced low-k dielectrics it demand further improvements of the diffusion barrier performance. For that reason Self-assembled monolayers (SAMs), with thicknesses of 2nm or less, have been propose for copper diffusion barrier application. By tailoring the structure of these monomolecular organic films, atomic scale properties can be controlled and selective surfaces and interfaces can be engine as desired for a specific application. In the presented work, the quality of an amino-terminated SAM barrier (NH2SAM) is tested. A high density and the absence of pinholes in the barrier layer are essential for a good barrier performance. First, the macroscopic quality of the NH2SAM barrier has been characterized by Water contact angle (CA) and High resolution AFM (HR-AFM). Secondly, the density and the presence and/or absence of pinholes have been tested by Ellipsometry and Cylic Voltametry (CV). Finally, the intrinsic barrier performance in form of Time- dependent dielectric breakdown (TDDB) lifetime has been extracted from planar capacitor structures that permitted to measure the leakage/Cu diffusion through barrier in the vertical direction. The Contact angle of layers formed at different deposition times show a variation of the hydrophilic SiO2 substrate to hydrophobic already with 1min deposited NH2SAM layer. A 15min deposited NH2SAM (~1nm), results in a continuous and pinhole free layer observed by HR-AFM. The refraction index (η) calculated by ellipsometry, indicates an increase in the density of the layer with the deposition time. On the other hand, cyclic voltametry shows inhibition of the electrochemical reduction of Fe3+ specimen to Fe2+ when NH2SAM are formed on ~2nmSiO2/Si electrodes. A decrease in the capacitive current is observed by increasing the layer thickness and density. The intrinsic barrier performance of the NH2SAM barrier by TDDB is demonstrated with an increase of 10 times the capacitor lifetime by comparing with no barrier system.
[Show abstract][Hide abstract] ABSTRACT: New challenges for wafer metrology solutions have evolved with 3D-IC manufacturing technology. 3D-IC technology allows stacking single chips, electrically connecting them in the vertical direction, and then forming a chip structure with significant advantages over traditional chips. However, before the 3D–stacking of IC’s becomes a mainstream process numerous metrology issues need to be solved. In this paper we discuss the critical in-line metrology needs during bonding and thinning of the device wafers before stacking. We show how TSV depth variations, glue layer defects and grinding issues require monitoring for a successful 3D integration.
Proceedings - Electronic Components and Technology Conference 01/2011; DOI:10.1109/ECTC.2011.5898631
[Show abstract][Hide abstract] ABSTRACT: Barrier reliability in 3D Through-Si Via (TSV) Cu interconnections requires particular attention as these structures come very close to the active devices and Cu diffusion into the silicon substrate would significantly affect device performance. This work focuses on a via-middle process flow, which implies processing of the 3D-TSV after the front-end-of-line (FEOL) process, but before the back-end-of-line (BEOL) interconnect process. This results in several high temperature processing steps after TSV fabrication, including a final device wafer sintering step, generally in the 400°C range. Thus, it becomes essential to study the stability of the TSV Cu-barrier at these temperatures to ensure a reliable integration of 3D TSV in CMOS wafers. We report on the thermal stability of Ta and Ti barriers and we show that 5nm Ta barriers are thermally stable, while Ti-barriers require thicknesses above 5nm to guarantee their thermal stability.
Interconnect Technology Conference and 2011 Materials for Advanced Metallization (IITC/MAM), 2011 IEEE International; 01/2011
[Show abstract][Hide abstract] ABSTRACT: Two different material-selective Self assembled monolayers (SAMs) were successfully deposited on Cu and SiO2 structures that mimic the Dual Damascene integration scheme. A two-step SAM coating process is presented. First, a “sacrificial” SAM is deposited at the Cu bottom and secondly, a “barrier” SAM at the SiO2 surface. The order in the SAMs deposition sequence and the differential thermal release of the thiol “sacrificial” SAM vs. the amino “barrier” SAM, allows an oxide-free Cu-to-Cu connection at the vias bottom. While the sacrificial SAM is selectively released by thermal ablation, the barrier SAM remains intact on the dielectric sidewall and field regions, ready for the subsequent copper metallization.
[Show abstract][Hide abstract] ABSTRACT: Among the many 3D technology options that are being explored today, the 3D-stacked IC approach has become a mature and economically viable technology and provides the highest density for 3D interconnects to date. One approach for IC stacking pursued by imec is the integration of Through Silicon Vias with extreme wafer thinning and backside processing on full CMOS wafers. This has been successfully demonstrated for the first time in a 300mm production line, and the compatibility of thin wafer handling with backside processing has been evaluated.
Proceedings - Electronic Components and Technology Conference 01/2011; DOI:10.1109/ECTC.2011.5898650
[Show abstract][Hide abstract] ABSTRACT: In this paper, we report on the development of Cu pillars and their impact on the subsequent thinning process for 3D applications. As the Cu pillars have a height of tens of microns (typically between 50–100µm), controlling the total thickness variation (TTV) after wafer thinning is becoming even more challenging. The Cu pillars are processed after completion of the Back End of Line (BEOL) with a target thickness of 50µm for a diameter of 80µm and a pitch of 200µm. The key challenge for D integration is the control of the wafer TTV after back grinding in order to allow TSV reveal. After optimization of the temporary wafer bonding in presence of high topography induced by 50µm high Cu pillars, a TTV after thinning below 5µm is achieved, which is comparable to the TTV obtained after wafer thinning without topography.
[Show abstract][Hide abstract] ABSTRACT: Thin wafer handling has become a very challenging topic of emerging 3D technologies, and temporary wafer bonding to a carrier support wafer is one way to guarantee the required mechanical stability and rigidity to the thin wafer during subsequent backside processing. The temporary bonding approach followed by Imec is based on the adhesive material HT10.10 from Brewer Science (WaferBond<sup>®</sup> HT-10.10). The thermal and chemical stability of the temporary adhesive layer has been fully assessed and characterized in a 300mm production line, and for the first time we report on the full integration of thin wafer handling with backside processing on 300mm CMOS wafers.
3D Systems Integration Conference (3DIC), 2010 IEEE International; 12/2010
[Show abstract][Hide abstract] ABSTRACT: We describe the design challenges for a low-cost 130nm 3D CMOS technology with 5μm diameter at 10μm pitch Cu-TSV. We investigate electrical, thermal and thermo-mechanical issues encountered in 3D. The electrical yield and ESD of TSVs is reviewed and designers are advised how to ensure yield and reliability. For thermal and thermo-mechanical we'll indicate based on experimental characterization, the importance of extending the chip package co-design flow with thermo-mechanical simulations of the chip stack. We propose a new design flow which leverages information captured by smart samples.