Electrostatic actuators based on microelectromechanical systems ͑MEMS͒ have many attractive features for use as variable capacitors in high-frequency applications. The devices consist of two electrodes, one fixed and the other movable. In this study, a curved, cantilever beam was used as the movable electrode. A novel process has been developed for fabricating an all-gold, curved beam. The cantilever beams were curved due to an intrinsic stress gradient in the metal. Electroplating and conventional lithography were used to metallize the cantilever beam electrodes. The internal stress gradient in the gold was obtained by changing the electroplating conditions during fabrication. Stiction during release and operation of the variable capacitors was alleviated by treating the gold with an alkane thiol self-assembled monolayer. The intrinsic stress gradient and the stress-induced bending moment were calculated using a generalized model for the stress gradient in the films. Compared to bimetallic, cantilever beams, the curvature of the all-gold beam was found to be independent of temperature. This implies that the operation of the single-metal variable capacitor will be more reproducible and stable with temperature than a comparable bimetallic device.

Polymers are widely used in the microelectronics industry as thin-film interlevel dielectrics layers between metal lines, as passivation layers on semiconductor devices and in various packaging applications. As multiple layers of polymer and patterned metal are constructed, the ability of these polymers to planarize topographical features becomes increasingly important. In this study, the degree of planarization (DOP) for five commercially available polymers has been examined for three different structural configurations with the intent of simulating practical applications. Specifically, this study investigates single layer planarization, multiple coat planarization, and planarization of metal lines patterned on a polymer base. This study also examines the effects of orientation of the metal structure to polymer flow during spin casting and location on the wafer. The polymers were selected to investigate different polymer chemistries frequently used in the microelectronics industry. The underlying structures were fabricated using standard photolithography and electroplating techniques. Feature dimensions include 25-200 m line spacings and widths with the polymer overcoat thickness being twice the height of the underlying structures.

Bimetallic thin films are of interest for use in microelectromechanical systems (MEMS) for the fabrication of sensors and actuators. The coefficient of thermal expansion (CTE) mismatch between the two metal films of the bimetallic structure can be used to attain the desired level of deflection or actuation in the MEMS device. Gold/aluminum and gold/zinc films have desirable properties for use in bimetallic films because of their differences in CTE. The stress-temperature behavior of these bimetal configurations has been studied. The effect of deposition technique and recrystallization of the metal films on the total stress and strain of the bimetallic films has been investigated. It has been shown that the formation of intermetallic compounds between the metal layers changes the mechanical properties of composite films. The intermetallic compounds are often undesirable because of their uncontrolled composition and poor mechanical properties. The degree of formation of the intermetallic compounds in the gold/aluminum bimetallic films can be reduced by use of a diffusion barrier between the two metals. It is shown that aluminum oxide is an effective diffusion barrier, and it can be easily fabricated. Stress-strain measurements and chemical depth profiling of the bimetallic films with the diffusion barrier have been used to quantify the reduction in the formation of the intermetallic compounds.

High-density packaging and interconnection applications frequently involve the use of polyimide-based materials as interlevel dielectrics for multilevel interconnection schemes. Surface planarity after each polymer layer is very important to the fabrication of multilayer structures. Highly nonplanar surfaces were observed in a multilayer test structure, fabricated using a thermally cured polyimide (Ultradel 7501). In this study, the effect of a novel cure technique involving electron beam (e-beam) exposure on multilayering and planarization behavior in Ultradel 7501 is investigated. Planarization measurements were conducted on different feature sizes and at various locations on the wafer in order to investigate the effect of solvent exposure, time and area of contact between multiple layers. The degree of planarization was found to improve from 206% for a thermally cured case to +15% for an e-beam cured sample. Analysis of the solvent induced polymer swelling and its effect on multilayer planarization of Ultradel 7501 is presented.

Thin films (0.2 μm to 1.8 μm) of photosensitive and nonphotosensitive BCB were fabricated and the degree of planarization (DOP) and dielectric properties were investigated. It was found that a high DOP for wide spaces (>20 μm spaces with 1 μm of BCB) was possible with nonphotosensitive BCB but not photosensitive BCB because of the cross-linking reaction during the photo-process. Thin films (as thin as 0.2 μm) exhibited dielectric properties similar to thick films. The dielectric properties of the photosensitive BCB were slightly higher than nonphotosensitive BCB. Low loss properties were observed at all thickness.