E. O. Shaffer

Development of a Low‐Dielectric‐Constant Polymer for the Fabrication of Integrated Circuit Interconnect

For faster, smaller, and higher performance integrated circuits, a low dielectric constant insulator is required to replace silicon dioxide. Here the properties of a new dielectric—SiLK resin, a solution of a low-molecular-weight aromatic thermosetting polymer—are reviewed and examples of its application in the fabrication of interconnect structures, such as the one shown in the Figure, are given.

Silk Polymer Coating with Low Dielectric Constant and High Thermal Stability for Ulsi Interlayer Dielectric

A novel polymer has been developed for use as a thin film dielectric in the interconnect structure of high density integrated circuits. The coating is applied to the substrate as an oligomeric solution, SiLK*, using conventional spin coating equipment and produces highly uniform films after curing at 400 °C to 450 °C. The oligomeric solution, with a viscosity of ca. 30 cPs, is readily handled on standard thin film coating equipment. Polymerization does not require a catalyst. There is no water evolved during the polymerization. The resulting polymer network is an aromatic hydrocarbon with an isotropie structure and contains no fluorine. The properties of the cured films are designed to permit integration with current ILD processes. In particular, the rate of weight-loss during isothermal exposures at 450 °C is ca. 0.7 wt.%/hour. The dielectric constant of cured SiLK has been measured at 2.65. The refractive index in both the in-plane and out-of-plane directions is 1.63. The flow characteristics of SiLK lead to broad topographic planarization and permit the filling of gaps at least as narrow as 0.1 μm. The glass transition temperature for the fully cured film is greater than 490 °C. The coefficient of thermal expansivity is 66 ppm/°C below the glass transition temperature. The stress in fully cured films on Si wafers is ca. 60 MPa at room temperature. The fracture toughness measured on thin films is 0.62 MPa m ½ . Thin coatings absorb less than 0.25 wt.% water when exposed to 80% relative humidity at room temperature.

Adhesion Energy Measurements of Multilayer Low-K Dielectric Materials for ULSI Applications

Currently, the IC industry is researching the integration of a variety of materials to meet the low dielectric constant requirement for improved back-end of line (BEOL) interconnect performance. One critical dimension for successful ntegration of these new materials is maintaining mechanical integrity through multilayer processes. This includes both cohesive and adhesive fracture resistance. The latter adds additional complexity in that adhesive toughness is a function of the adherend materials and the processes used to join them. Hence, many good dielectric materials may be rematurely eliminated from further research not because of inherently poor adhesion but because of the necessity to optimize processing strategies. In this paper, we use the modified Edge Liftoff Test (m-ELT) to quantify the mechanical adhesion of multilayer blanket coatings. A specific example is used to demonstrate the utility of combining the m-ELT with surface analysis to optimize the reliability of low-K dielectric resins for use in ULSI applications. The system studied consists of a Cyclotene ™ 5021(BCB) low-K material integrated with CVD aluminum for single level, damascene structures. The effects of liner layer metallurgy and surface plasma treatments are measured. Surface analysis is done on the failed parts to understand the location of the failure. In this way recommendations for process optimization can be made.

Material and process studies in the integration of plasma-promoted chemical-vapor deposition of aluminum with benzocyclobutene low-dielectric constant polymer

The integration of low-temperature plasma-promoted chemical-vapor deposition (PPCVD) of aluminum, using dimethylethylamine-alane (DMEAA) as the source precursor, with benzocyclobutene (BCB) low-k polymers has been investigated to explore the feasibility of BCB-based Al metallization for sub-quarter-micron integrated circuitry. The study examined the thermal, chemical, and structural compatibility of PPCVD Al interconnects with the BCB polymer, including the feasibility of barrierless aluminum–BCB multilevel metallization stacks. Studies were conducted on a range of BCB surfaces, consisting of untreated (UNT), reactive-ion etched (RIE), and SiO2-capped BCB (SiO2–BCB) surfaces. The purpose was to mimic the actual BCB surfaces encountered during damascene processing. Each BCB surface was treated with argon or hydrogen plasma prior to aluminum processing to ensure reduction in the barrier to aluminum formation, leading potentially to enhanced Al nucleation mechanisms. In all cases, the direct deposition of Al...

Integration of chemical vapor deposition Al interconnects in a benzocyclobutene low dielectric constant polymer matrix: A feasibility study

Results are presented from a proof-of-concept study that examined the integration of damascene-processed thermal chemical vapor deposited (TCVD) aluminum (Al) interconnects in a benzocyclobutene (BCB) polymer matrix. In a first phase, the study identified baseline deposition conditions for the formation of structurally and chemically compatible blanket Al/titanium nitride (TiN)/BCB stacks on two types of blanket BCB substrates utilized to simulate the actual surfaces encountered in typical damascene processing: (1) blanket BCB films capped with a silicon dioxide SiO2 layer (SiO2-BCB), and (2) plasma reactive ion etched blanket BCB films. The TiN diffusion barrier was grown in two stages. A first (bottom) layer was deposited by physical vapor deposition (PVD), followed by a CVD-grown top layer. The resulting TCVD Al/CVD TiN/PVD TiN/BCB stacks were stable under thermal stressing up to 325 °C for 1 h. In a second phase, an optimized TCVD Al process flow was developed for void-free filling of TiN-coated 320-n...

Nanoscale Elastic Imaging of Aluminum/Low-k Dielectric Interconnect Structures

A new characterization tool based on ultrasonic force microscopy (UFM) has been developed to image the nanometer scale mechanical properties of aluminum/low-k polymer damascene integrated circuit (IC) test structures. Aluminum and polymer regions are differentiated on the basis of elastic modulus with a spatial resolution ≤10 nm. This technique reveals a reactive-ion etch (RIE)-induced hardening of the low-k polymer that is manifested in the final IC test structure by a region of increased hardness at the aluminum/polymer interface. The ability to characterize nanometer scale mechanical properties of materials used for IC back-end-of-line (BEOL) manufacture offers new opportunities for metrological reliability evaluation of low-k integration processes.

Interconnect Process Technology Using Perfluorocyclobutane (PFCB)

A novel polymer dielectric derived from tris-perfluorocyclobutene(PFCB) monomer has been investigated as a thin film dielectric. The dielectric constant of this material has been measured at 2.35. PFCB is applied from a hydrocarbon solvated solution using conventional spin coating equipment onto the substrate and produces highly uniform films after curing at 300 °C. This paper describes the processing and properties of films derived from PFCB, and examines the interactions between the polymer and metals at the interfaces. In particular, the interfaces formed by the deposition of Cr or Co onto PFCB are unchanged after 30 minutes at 390 °C. The interface formed by the application of the polymer onto Ta is similarly unaffected by high temperatures. The interfaces formed by the deposition of Ta or Ti onto the polymer surface did not remain intact, with substantial quantities of the metals permeating the polymer after high temperature exposures. This behavior is discussed relative to the thermo-physical properties of the metal fluorides.

Nanoscale elastic imaging: a new metrology tool for low-k dielectric integration

A new characterization tool based on ultrasonic force microscopy (UFM) has been developed to image the nanoscale mechanical properties of metal/low-k polymer damascence test structures. Metal and polymer regions are differentiated on the basis of elastic modulus with a spatial resolution /spl les/10 nm. This technique reveals a RIE-induced hardening of the low-k polymer at the metal/polymer interface and offers new opportunities for metrological reliability evaluation of low-k integration processes.

Development of TaSiN diffusion barriers for Cu/SiLK metallization schemes

Diffusion barrier optimization and compatibility studies were undertaken with respect to the integration of Cu/TiSiN stacks on SiLK low-k dielectric films. First-pass testing optimized TiSiN film composition and evaluated process compatibility with SiLK. TiSiN/SiO/sub 2/ stacks were used for baseline comparisons. Second-pass testing evaluated thermal stability of TiSiN/Cu/TiSiN/SiLK stacks against Cu diffusion and the stability of the TiSiN/SiLK interface. At temperatures up to 450/spl deg/C no variations in stack composition or interfacial morphology were evidenced.

Mechanical Properties of Cured SiLK Low-K Dielectric Films

SiLK (trademark of The Dow Chemical Company) semiconductor dielectric is a low-k organic polymer, based on the synthesis of crosslinked polyphenylenes by the reaction of poly functional cyclopentadienone- and acetylene-containing materials1. SiLK dielectric is used for high performance integrated circuits with subtractive Al/W 2–4 or Cu damascene 5–7 wiring technology. The properties of cured SiLK enable integration with current interlayer dielectric (ILD) processes: for example, high thermal stability, high Tg, low dielectric constant, no fluorine, spin-on application, good adhesion and mechanical durability, low moisture absorption, and solvent resistance. Some of these properties are listed in Table 1.