Chris C. Yu

Acoustical method and system for detecting and controlling chemical‐mechanical polishing (CMP) depths into layers of conductors, semiconductors, and dielectric materials

A method and system for controlling the depth of removal by polishing of a selected material on a supporting underlayer where it is desired to terminate removal of the selected material, such as tungsten, at the material-underlayer interface. In accordance with this novel method and system, the selected material such as a surface metallization layer is polished to initiate removal thereof in the direction of the material-underlayer interface. A microphone is positioned at a predetermined distance from the wafer to sense acoustical waves generated when the depth of material removal reaches a certain determinable distance from the interface to thereby generate output detection signals. These output detection signals are amplified and then applied to a spectrum analyzer which operates to analyze the sound intensity-versus-frequency characteristic of the acoustical waves received by the microphone. The spectrum analyzer operates to drive a CMP computer which in turn controls the operation of a CMP polishing machine. The CMP polishing motor terminates polishing of the selected material a predetermined time after a desired output signals are received from the spectrum analyzer. The present invention is also directed to a method and system or measuring the thickness of certain materials by comparing acoustical signals in a spectrum analyzer with frequency characteristics of known materials of certain layer thicknesses.

Dishing effects in a chemical mechanical polishing planarization process for advanced trench isolation

We report the first detailed study of dishing effects in chemical mechanical polishing (CMP) of oxide films, observed during the development of an advanced CMP‐only trench isolation process. The degree of dishing has been determined for field widths ranging from 0.3 μm to 4 mm and was found to be highly pattern geometry (field width) sensitive, increasing from ∼0 nm at a field width of 5 μm and below to 200 nm at 4 mm. Although this dishing effect makes complete planarization in a large field oxide region (on the order of 1 mm) difficult, it poses no serious problem for trench isolation in narrow field regions due to its reduced effect at small field geometries.

Antireflection coatings for advanced semiconductor device metallization using laser reflow and chemical mechanical planarization

We have investigated titanium tungsten (TiW), titanium nitride (TiN), and chemical vapor deposited (CVD) tungsten (W) films as antireflection coatings (ARC) on aluminum (Al) alloy films to widen the laser planarization process window for contact via filling. ARCs lowered the minimum laser fluence required to accomplish complete contact filling and the maximum laser fluence before the onset of optical ablation, resulting in a significant increase in the process window. This increase closely correlated with the optical and thermal properties of the ARCs. The observed increase in resistivity of laser processed Al films due to intermixing with the ARCs does not preclude its use as via stud metal. A newly developed Al plug technology utilizing chemical mechanical polishing to remove the laser processed film from the surface is presented.

Texturization of polycrystalline silicon films using excimer-laser processing for memory device applications

We report the first systematic investigation of texturizing polycrystalline silicon films utilizing an excimer laser to achieve an increased cell capacitance for high‐density memory‐device applications. The degree of surface roughness after laser processing was found to be sensitive to polycrystalline silicon deposition temperature and laser fluence. In the laser‐fluence range of 0.2 to 0.7 J/cm2, the reflectivity of polycrystalline silicon films varied from ∼10% to 80%. A significant increase in the degree of surface roughness was achieved at optimized conditions. This, in turn, resulted in an increased effective surface area of the polycrystalline silicon film used as the capacitor‐storage node. Primary capacitance‐voltage measurements indicated a 10% increase in the cell capacitance, and current‐voltage characterizations showed no device degradation due to laser processing.

The combination of high‐temperature sputtering with excimer laser planarization for submicrometer contact via filling

We have systematically investigated the use of high‐temperature sputtering in conjunction with excimer laser planarization for planarizing Al alloy surfaces and filling submicrometer, high aspect ratio (∼1–3) contact vias. In general, the process window for the complete contact filling increased significantly with the increasing sputtering temperature, and decreased with shrinking contact/via geometry. Better as‐deposited metal step coverage and profile obtained at higher sputtering temperatures were identified as the key parameters contributing to this significant improvement in the process window. The process window achieved by this combined process is significantly wider than that obtained by high‐temperature sputtering alone. In addition, the poor surface morphology generally observed for the Al alloy films sputtered at elevated temperatures is significantly improved due to recrystallization during laser reflow.