Mark Buehler

A 90-nm logic technology featuring strained-silicon

A leading-edge 90-nm technology with 1.2-nm physical gate oxide, 45-nm gate length, strained silicon, NiSi, seven layers of Cu interconnects, and low-/spl kappa/ CDO for high-performance dense logic is presented. Strained silicon is used to increase saturated n-type and p-type metal-oxide-semiconductor field-effect transistors (MOSFETs) drive currents by 10% and 25%, respectively. Using selective epitaxial Si/sub 1-x/Ge/sub x/ in the source and drain regions, longitudinal uniaxial compressive stress is introduced into the p-type MOSEFT to increase hole mobility by >50%. A tensile silicon nitride-capping layer is used to introduce tensile strain into the n-type MOSFET and enhance electron mobility by 20%. Unlike all past strained-Si work, the hole mobility enhancement in this paper is present at large vertical electric fields in nanoscale transistors making this strain technique useful for advanced logic technologies. Furthermore, using piezoresistance coefficients it is shown that significantly less strain (/spl sim/5 /spl times/) is needed for a given PMOS mobility enhancement when applied via longitudinal uniaxial compression versus in-plane biaxial tension using the conventional Si/sub 1-x/Ge/sub x/ substrate approach.

AFM Measurements of Interactions Between CMP Slurry Particles and Substrate

Atomic force microscopy (AFM) studies of interactions between slurry particles and substrates treated by chemical mechanical polishing (CMP) processes were carried out. To conduct adhesion measurements, the particles present in a CMP system were first attached to the surface of a silicon wafer covered with thin polymer film having high affinity for both particles and the silicon wafer. A silica glass sphere was attached to the AFM cantilever with an appropriate spring constant. The sphere represented the surface of the material being polished and was used as received or covered with a layer of copper. The sphere can be modified with various materials in future research. The AFM force volume mode, which uses the collection of the force-distance curves over selected surface areas, was used for the adhesion measurements. The adhesion in the systems studied was strongly dependent on the pH value of the aqueous environment, and the concentration and type of surfactants added.

Measurement of Interactions between Abrasive Silica Particles and Copper, Titanium, Tungsten and Tantalum

Colloidal probe technique has been widely employed to measure the adhesion between micro- and nanosize objects using atomic force microscopy (AFM). However, majority of studies concerns model systems, which do not incorporate real abrasive particles. The approach applied allows measuring adhesion between real CMP nanoparticles and different surfaces. Thin polymer film with high affinity to the particles was used to anchor the particles to a surface. Hollow glass bead (20-30 μm) representing flat surface was attached to soft AFM cantilever. Application of large hollow bead and the cantilever with small spring constant allows measuring the interactions with high sensitivity. Titanium, tungsten and tantalum metals were sputtered on the bead surface. The effect of different factors such as pH value, concentration and type of a surfactant on adhesion between surfaces of metals and silica slurry has been studied. Character and intensity of interactions at the moment of contact have been evaluated from experimental force-distance curves.

Polymer Anchoring Layer for Atomic Force Microscopy Studies of Nanoparticle–Substrate Interactions

An immiscible polymer blend of poly(glycidyl methacrylate) and poly(vinylpyridine), PGMA/PVP, was used as an anchoring layer to attach silica nanoparticles to an oxidized silicon wafer surface. The stability of the arrays of colloidal particles was studied in pH 4 and pH 10 buffer solutions, deionized (DI) water, and nonionic surfactant solution. The array was determined to be stable. Attachment of the nanoparticles to one‐component homogeneous PGMA and PVP films was also studied in order to determine the role of each polymer in the anchoring layer. Virtually no particles were adsorbed on the surface modified with PGMA. The nanoparticles could be adsorbed on PVP, but the integrity of the polymer layer was destroyed in the environment used for adsorption, i.e., a dispersion of nanoparticles at pH 10. Measurement of adhesion between the nanoparticles attached to the anchoring layer and the glass substrate were performed in aqueous media having different pH values using a colloidal probe atomic force microscopy (AFM) technique. In Commemoration of the Contributions of Professor Valery P. Privalko to Polymer Science.