Robert A. DeVries

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.

Benzocyclobutenes as styrene monomer scavengers and molecular weight “stabilizers” in atactic and syndiotactic polystyrenes

Syndiotactic polystyrene (SPS) is a semicrystalline polymer with a melting point of 270°C. At processing temperatures of 300°C or higher, SPS begins to decompose with loss of molecular weight and the formation of styrene monomer. Under these conditions, atactic polystyrene also decomposes. One approach to controlling this generation and buildup of styrene and the molecular weight loss during processing is to add a compound that will react with styrene and/or with the polymer decomposition products at the processing conditions. This report describes the use of three benzocyclobutene (BCB) compounds (ethylene bis-BCB, divinyl disiloxane bis-BCB, and a copolymer of styrene and 4-vinyl BCB) during SPS and atactic polystyrene processing. The conclusions are: 1. BCB moieties, when extruded with SPS at the 2 wt % level, caused a substantial decrease in residual styrene compared with a control SPS; 2. BCB compounds, when extruded with SPS, resulted in high molecular weight fractions. The result with the divinyl disiloxane bis-BCB was especially dramatic; and 3. BCB functionalized materials may find utility as additives in SPS during processing to minimize loss of molecular weight and buildup of styrene.

Digital Optical Imaging Of Benzocyclobutene (Bcb) Thin Films On Silicon Wafers

A practical, low-cost research system for the fluorescent optical imaging of BCB (DVS-bisBCB) thin films has been used for the first time to evaluate coating quality on spin coated silicon wafers. In general, DVS-bisBCB thin films are easily produced defect free with a high degree of planarization. Various features of the coating are enhanced visually by the fluorescence making detection, digital storage, and quantification easier. Examples of features found in defective coatings made intentionally by a process to generate several common thin film defects are variations in film thickness, foreign particles, pinholes, and residual polymer in vias. The fluorescent bands of the normally transparent resin are easily excited in the near UV with a mercury lamp, causing a semi-opaque visible emission which could be observed by conventional imaging hardware. The BCB fluorescent quantum yield, or efficiency, is similar to fluorescent dyes so that only a small amount of BCB need be present in a substrate to allow optical inspection. This strong fluorescent property of DVS-bisBCB polymer, not possessed by many polyimide resins, could reduce labor costs of manual inspections and improve multichip module (MCM) processing yields. This digital imaging technique has potential for further development as a cost-effective automated optical inspection (AOI) method.