Divinylsiloxane Bisbenzocyclobutene Research Articles

High-Density Patterned Array Bonding through Void-Free Divinyl Siloxane Bis-Benzocyclobutene Bonding Process.

Divinylsiloxane-bis-benzocyclobutene (DVS-BCB) has attracted significant attention as an intermediate bonding material, owing to its excellent properties. However, its applications are limited, due to damage to peripheral devices at high curing temperatures and unoptimized compressive pressure. Therefore, it is necessary to explore the compressive pressure condition for DVS-BCB bonding. This study demonstrates an optimization process for void-free DVS-BCB bonding. The process for obtaining void-free DVS-BCB bonding is a vacuum condition of 0.03 Torr, compressive pressure of 0.6 N/mm2, and curing temperature of 250 °C for 1 h. Herein, we define two factors affecting the DVS-BCB bonding quality through the DVS-BCB bonding mechanism. For strong DVS-BCB bonding, void-free and high-density chemical bonds are required. Therefore, we observed the DVS-BCB bonding under various compressive pressure conditions at a relatively low temperature (250 °C). The presence of voids and high-density crosslinking density was examined through near-infrared confocal laser microscopy and Fourier-transform infrared microscopy. We also evaluated the adhesion of the DVS-BCB bonding, using a universal testing machine. The results suggest that the good adhesion with no voids and high crosslinking density was obtained at the compressive pressure condition of 0.6 N/mm2. We believe that the proposed process will be of great significance for applications in semiconductor and device packaging technologies.

Silicon-Integrated Hybrid-Cavity 850-nm VCSELs by Adhesive Bonding: Impact of Bonding Interface Thickness on Laser Performance

The impact of bonding interface thickness on the performance of 850-nm silicon-integrated hybrid-cavity vertical-cavity surface-emitting lasers (HC-VCSELs) is investigated. The HC-VCSEL is constructed by attaching a III–V “half-VCSEL” to a dielectric distributed Bragg reflector on a Si substrate using ultrathin divinylsiloxane-bis-benzocyclobutene (DVS-BCB) adhesive bonding. The thickness of the bonding interface, defined by the DVS-BCB layer together with a thin SiO2 layer on the “half-VCSEL,” can be used to tailor the performance, for e.g., maximum output power or modulation speed at a certain temperature, or temperature-stable performance. Here, we demonstrate an optical output power of 2.3 and 0.9 mW, a modulation bandwidth of 10.0 and 6.4 GHz, and error-free data transmission up to 25 and 10 Gb/s at an ambient temperature of 25 and 85 °C, respectively. The thermal impedance is found to be unaffected by the bonding interface thickness.

Silicon-integrated short-wavelength hybrid-cavity VCSEL.

We demonstrate a short-wavelength hybrid-cavity vertical-cavity surface-emitting laser (VCSEL) heterogeneously integrated on silicon. A GaAs-based "half-VCSEL" has been attached to a dielectric distributed Bragg reflector (DBR) on a silicon wafer using ultra-thin divinylsiloxane-bis-benzocyclobutene (DVS-BCB) adhesive bonding, thereby creating a cavity with the standing-wave optical field extending over the silicon- and GaAs-based parts of the cavity. A 9 µm oxide aperture diameter VCSEL with a threshold current of 1.2 mA produces 1.6 mW optical output power at 6.0 mA bias current with a wavelength of ~845 nm.

Ultra-thin DVS-BCB adhesive bonding of III-V wafers, dies and multiple dies to a patterned silicon-on-insulator substrate

Heterogeneous integration of III-V semiconductor materials on a silicon-on-insulator (SOI) platform has recently emerged as one of the most promising methods for the fabrication of active photonic devices in silicon photonics. For this integration, it is essential to have a reliable and robust bonding procedure, which also provides a uniform and ultra-thin bonding layer for an effective optical coupling between III-V active layers and SOI waveguides. A new process for bonding of III-V dies to processed silicon-on-insulator waveguide circuits using divinylsiloxane-bis-benzocyclobutene (DVS-BCB) was developed using a commercial wafer bonder. This “cold bonding” method significantly simplifies the bonding preparation for machine-based bonding both for die and wafer-scale bonding. High-quality bonding, with ultra-thin bonding layers (<50 nm) is demonstrated, which is suitable for the fabrication of heterogeneously integrated photonic devices, specifically hybrid III-V/Si lasers.

Low-Threshold Heterogeneously Integrated InP/SOI Lasers With a Double Adiabatic Taper Coupler

We report on a heterogeneously integrated InP/silicon-on-insulator (SOI) laser source realized through divinylsiloxane-bis-benzocyclobutene (DVS-BCB) wafer bonding. The hybrid lasers present several new features. The III-V waveguide has a width of only 1.7 μm, reducing the power consumption of the device. The silicon waveguide thickness is 400 nm, compatible with high-performance modulator designs and allowing efficient coupling to a standard 220-nm high index contrast silicon waveguide layer. In order to make the mode coupling efficient, both the III-V waveguide and silicon waveguide are tapered, with a tip width for the III-V waveguide of around 800 nm. These new features lead to good laser performance: a lasing threshold as low as 30 mA and an output power of more than 4 mW at room temperature in continuous-wave operation regime. Continuous wave lasing up to 70°C is obtained.

Vapor phase reactions in polymerization plasma for divinylsiloxane-bis-benzocyclobutene film deposition

Vapor phase reactions in plasma polymerization of divinylsiloxane-bis-benzocyclobutene (DVS-BCB) low-k film depositions on 300mm wafers were studied using mass spectrometry, in situ Fourier transform infrared, and a surface wave probe. Polymerization via Diels-Alder cycloaddition reaction was identified by the detection of the benzocyclohexene group. Hydrogen addition and methyl group desorption were also detected in DVS-BCB monomer and related large molecules. The dielectric constant k of plasma polymerized DVS-BCB with a plasma source power range up to 250W was close to ∼2.7 of thermally polymerized DVS-BCB, and increased gradually over 250W⁠. The electron density at 250W was about 1.5×1010cm−3⁠. The increase of the k value at higher power was explained by the decrease of both large molecular species via multistep dissociation and incorporation of silica components into the polymer. It was found that the reduction of electron density as well as precursor residence time is important for the plasma polymerization process to prevent the excess dissociation of the precursor.

Aqueous-Base-Developable Benzocyclobutene (BCB)-Based Material Curable in Air

A positive-tone and aqueous-base-developable benzocyclobutene (BCB)-based dielectric material curable in air is described in this paper. The prepolymer is made from divinylsiloxane bisbenzocyclobutene (DVS-bisBCB) and BCB-acrylic acid. The formulation contains antioxidants that allow the prepolymer to cure in air and a diazonaphthaquinone to make it photosensitive. Patterned films have high resolution, and via openings are scum-free without a descum operation. Whether cured in nitrogen or in air, the prepolymer produces a film with optical, electrical, thermal, and mechanical properties desirable for many microelectronic applications, such as packaging applications and as a planarization or insulation layer in display applications

Highly thermal-stable, plasma-polymerized BCB polymer film

A new plasma-enhanced organic monomer-vapour polymerization (plasma polymerization) method has been developed. It was used to make a divinyl siloxane bis-benzocyclobutene (DVS-BCB) polymer film for Cu dual-damascene interconnects that had high thermal stability and a low dielectric constant, k = 2.6. The method consists of the vaporization of organic monomers, transportation of monomers in the gas phase, and polymerization by plasma to make the polymer film. The method eliminates polymer oxidation of DVS-BCB during the polymerization in high vacuum, which improves the film's thermal stability. The thermal stability of plasma-polymerized BCB (p-BCB) exceeded 400°C because of the higher deposition temperature, and the film had a high resistance to Cu diffusion at 400°C annealing. The narrow-pitched Cu/BCB damascene lines showed a 35% reduction in line capacitance compared with Cu/SiO2 ones. The p-BCB is shown to be a strong candidate for Cu/low-k interconnects.

Overview of Photo-definable Benzocyclobutene Polymer.

Benzocyclobutene (BCB) polymer was developed at Dow Chemical in the late 1980's for microelectronics packaging and interconnect applications. Photo-definable BCB formulation was commercialized in 1994. The Dielectric polymer films produced from BCB formulations possess many desirable properties[1] [2] [3] [4] for microelectronic applications; for example, low dielectric constant and dissipation factor, low moisture absorption, rapid curing and low temperature cure without generating by-products, minimum shrinkage in curing process, and no Cu migration issues. Derived from these properties, applications have been developed in: bumping/wafer level packaging [5][6], Ga/As chip ILD [7], optical wave guide [8], flat panel display [9], and lately in BCB-coated Cu foil for build-up board [10]. This article summaries the chemistry, the relevant properties and the typical process of photo definable divinylsiloxane bisbenzocyclobutene (DVS-BCB) commercialized by Dow Chemical as CYCLOTENETM resin system.

Damascene copper interconnects with polymer ILDs

On-chip interconnects with copper metallization and polymer interlevel dielectrics (ILDs) have the lowest R-C delay, lowest parasitic coupling and highest electromigration resistance of currently proposed room temperature material sets. Patterning of such interconnect structures requires either damascene patterning (chemical-mechanical planarization (CMP) of copper deposited into trenches and via reactive ion etching (RIE) into the polymer) or elevated temperature RIE patterning of the copper. In this paper we present the dual damascene patterning of copper on low dielectric constant polymers like divinylsiloxane bisbenzocyclobutene (DVS bis BCB) and parylene- n. In particular, we present and discuss various RIE polymer etch masks and CMP polish stops that have been utilized in this work (such as PECVD silicon nitride, PECVD silicon dioxide and tantalum) and the results with different pads and slurries. Emphasis is placed on achieving a planar copper CMP with a minimum amount of polish stop and polymer ILD erosion, as well as attaining low contact resistance. Difficulties in achieving these desirable features with relatively soft low dielectric constant polymers are presented, with contact resistivity in the mid 10 −9 Ω-cm 2 having been achieved to date.

Investigation of the Cu/BCB and Cu/PPQ interfaces by photoelectron spectroscopy

Polyphenylquinoxaline (PPQ) and divinylsiloxane bis-benzocyclobutene (BCB) are of great technological interest concerning the fabrication of electronic multilayer devices. Both polymers own similar electrical properties but differ in their adhesion behavior towards copper. Photoelectron spectroscopy utilizing x-ray and ultraviolet radiation has been used to study the electronic structure of the Cu/PPQ and Cu/BCB interfaces. Thin layers of the polymers were produced by spin coating and their surface topologies were examined using atomic force microscopy. The metallization was done by evaporation and the gradual growth of the interface region was examined in situ after every metallization cycle. In both cases a reactive interface region with a low oxygen content is found. The difference in the adhesion between the two systems towards copper is discussed with respect to the differences of the interfaces formed during the metallization.

Organic Polymer Dielectrics in Microelectronic Technologies: Reliability Requirements, Testing, and Qualification

ABSTRACTThis work reviews the dependence of reliability testing results on material processing and properties for polymeric materials used in high density interconnection technologies.Specific data are presented for CyclotenesTM 3022 resins containing divinylsiloxane bisbenzocyclobutene, (CAS 117732-87-3). Silane coupling agents discussed in this study are 3-aminopropyltriethoxysilane (CAS 01760-24-3)(APTES) and 3-methacryloxypropyl trimethoxysilane (CAS 02530-85-0) (MOP-TMS).

Adhesion of Cyclotene™ (BCB) Coatings on Silicon Substrates

AbstractThis work examines the adhesion of coatings derived from divinylsiloxane bisbenzocyclobutene, mixed stereo and positional isomers of 1,3-bis(2-bicyclo[4.2.0]octa-1,3,5-trien-3-ylethenyl)-1,1,3,3-tetramethyl disiloxane (CAS 117732–87–3), on oxidized silicon substrates treated with silane coupling agents.This material, commercially available as Cyclotene™ 3022, can be used in the construction of high performance electronic circuits, such as multichip modules. Silane coupling agents examined in this study were 3-aminopropyltriethoxysilane (CAS 01760-24-3)(APTES)(, vinyltriethoxysilane (CAS 00078–08–0)(VTES), and 3-methacryloxypropyl trimethoxysilane (CAS 02530–85–0) (MOP-TMS).Measurement of the interfacial adhesion was performed using microindentation. Bond strengths obtained by this method exceed 200 MPa for the most effective coupling agents. However, these high bond strengths were not found to correlate with acceptable adhesive performance in all cases. In addition to the choice and preparation of the coupling agent, process related chemical exposure has been found to be a key element in the observed adhesive performance. The effect of the cure schedule for the thermoset coating has also been found to be a controlling factor. A short cycle test vehicle was developed consisting of a single 20 gIm polymer layer etched with anisotropic sidewalls. This test vehicle was used to evaluate the efficacy of the coupling agents during process exposures and subsequent thermal shock testing. A solution of MOP-TMS pre-hydrolyzed in methanol was found to produce the most reliable interface with high bond strength.

Advances in the Thermal-Oxidative Stabilization of Divinyl Siloxane Bis-Benzocyclobutene Polymer Coatings

This paper discusses the nonhermetic performance of polymer thin film coatings derived from 1,3-bis(2-bicyclo[4.2.0]octa-1,3,5-trien-3-ylethenyl)-1,1,3,3-tetramethyl disiloxane (mixed isomers, CAS 117732-87-3), known also as divinyl siloxane bis-benzocyclobutene or DVS bis-BCB. The stability of the dielectric constant and the mechanical properties have been examined before and during high temperature exposures of the polymer films to air for extended periods of time at high and low humidity. Infrared absorbance spectra and dielectric constant measurements have been correlated. Formulations of the DVS bis-BCB prepolymer with a polymeric oxidation inhibitor are predicted to yield polymer films which display less than a 10% change in the dielectric constant after 40 years in air at 85°C. These films have excellent potential for use as the dielectric coating layer in nonhermetic packaging applications for Multi Chip Module (MCM) circuits.

Cure Technology for Controlled Stress in Thin Benzocyclobutene Coatings

AbstractThe stress at room temperature in many typical polymer coatings used for microelectronic dielectrics is near 40 MPa. Polymer coatings derived from divinylsiloxane bisbenzocyclobutene (BCB), (CAS 117732-87-3), have a stress level of ca. 38 MPa after a conventional thermal oven cure. In this work, a novel approach based on curing the BCB polymeric network in the vitrified state has been used to achieve far field stresses of 24 MPa in the final coatings. This represents a 36% reduction in the far field stress of BCB coatings cured at 250 °C. The cure methodology and compatibility with device process design are discussed.

Mechanical Behavior of Benzocyclobutene Films on Silicon Substrates

AbstractThe evolution of the stress in coatings derived from divinylsiloxane bisbenzocyclobutene, mixed stereo and positional isomers of 1,3-bis(2-bicyclo[4.2.0]octa-1,3,5-trien-3-ylethenyl)-1,1,3,3-tetramethyl disiloxane (CAS 117732-87-3), has been measured on silicon substrates with an optically levered beam during thermal cycles. The stress at room temperature in gelled coatings varies between ca. 15 MPa and 45 MPa depending on the cure schedule. The progression of the polymer's glass transition temperature is correlated with the evolution of the structural state observed with FTIR. A method is presented for predictably controlling substrate curvature during multilayer processing.

Observation of Glass Transition Temperatures in Polymeric Thin Films by Wafer Curvature Measurements

ABSTRACTWafer bending measurements have been used to study the glass transition temperature, Tg, of thin coatings of polystyrene and polycarbonate on Si wafers. The observed values of Tg agree with DSC and TMA measurements on bulk samples. The evolution of the substrate curvature has been used to examine the behavior of Tg in thin epoxy films and coatings derived from divinylsiloxane bisbenzocyclobutene, mixed stereo and positional isomers of 1, 3-bis(2-bicyclo[4.2.0]octa-1, 3, 5-trien-3-ylethenyl)-1, 1, 3, 3-tetramethyl disitoxane (CAS 117732–87–3). The dependence of the Tg of the epoxide coatings is studied as a function of the cross-linking. The evolution of the Tg in the benzocyclobutene coating is found to be a monotonie function of the level of conversion of the polymer network.

Real-Time FT-IR Studies Of The Reaction Kinetics For The Polymerization Of Divinyl Siloxane Bis-Benzocyclobutene Monomers

ABSTRACTThe thermal polymerization reaction of divinyl siloxane bis-benzocyclobutene (DVS bis-BCB) was monitored in-situ with FT-IR spectroscopy in order to follow specific chemical changes and determine the reaction order and rate constants at temperatures from 150° to 210°C. FT-IR spectra were obtained at regular intervals throughout the reaction with a Nicolet 170SX spectrophotometer.Monomeric DVS bis-BCB contains mixed stereo and positional isomers of 1,3- bis(2-bicyclo[4.2.0]octa-1, 3, 5-trien-3-ylethenyl)-1, 1, 3, 3-tetramethyl disiloxane (CAS 117732-87-3). It polymerizes via Diels-Alder cycloaddition reactions between vinyl groups and an intermediate o-quinodimethane formed by first-order, thermally initiated ring openings of the benzocyclobutene rings. Gaseous byproducts are not produced; therefore, the cure is easier to manage than are cures for polyimides which evolve water in polycondensation reactions. The DVS bis-BCB has four reactive elements per monomer unit and, thus, polymerizes into a very highly cross linked and solvent resistant network.With the FT-IR methodology, the reaction was easily monitored through the points of gel formation and vitrification. With the exception of DSC (i.e., calorimetry) which does not sense specific chemistry, other methods were not successful in following the reaction after a gel was formed. We have found that the polymerization was first-order until vitrification occurs; the gelation alone had no apparent effect on the reaction rate.DVS bis-BCB is under development at Dow as high performance dielectric material for multilayer interconnect coating applications for the microelectronics industry. Methodology reported here is employed in developing effective cure management strategies.