Phillip W. Carter

Anion Effects on Cu–benzotriazole Film Formation Implications for CMP

We examine the effect of different anions in solutions containing benzotriazole (BTA) on the Cu removal rate during chemical mechanical planarization (CMP). In solutions containing both Cl - and BTA, the Cu removal rate is nearly a factor of twenty lower than in solutions containing either Cl - or BTA alone. As-grown BTA films from solutions containing different anions are characterized using atomic force microscopy, ellipsometry, Raman spectroscopy, mass spectrometry, and open-circuit-potential measurements. Films grown from halide-containing solutions are found to be considerably thicker than those grown from other anions. The difference in Cu removal rate correlates well with the different as-grown film thicknesses.

Chemical Mechanical Polishing of Tantalum Aqueous Interfacial Reactivity of Tantalum and Tantalum Oxide

The surface reactivity of tantalum metal and its associated oxide in aqueous environments was explored using electrochemical impedance spectroscopy (EIS) and potentiodynamic electrochemical dc tests in combination with tantalum blanket wafer removal rates produced by chemical mechanical polishing. The EIS data indicated that the transient tantalum oxide films formed during polishing are thinner and have a lower charge-transfer resistance at pH 2 compared to pH 10. The thinner film at pH 2 is attributed to easier mechanical removal of the tantalum oxide at low pH compared to high pH. Polishing experiments showed tantalum blanket wafer removal rates 6 to 20 times greater at pH 2 compared to pH 10 for three different oxidizing agents. In addition, there was a measurable induction time before material removal via polishing at pH 10 where pH 2 showed no significant induction time. The mechanical removal of the surface oxide, not charge-transfer, is postulated to be the rate limiting step in tantalum polishing conditions utilizing low downforces, low abrasive concentrations, and a soft pad within the pH range 2-10. The ease of mechanical removal at low pH may result from enhanced interactions of tantalum surface functionalities with abrasive or solution species.

A Method for Measuring Frictional Forces and Shaft Vibrations during Chemical Mechanical Polishing

A technique for determining friction forces during chemical mechanical polishing has been developed using a noncontact displacement sensor to measure polishing shaft deflections. Shaft deflections were calibrated to the shear forces acting on the substrate surface allowing in situ measurement of drag force and coefficient of friction (COF). Power spectrum data of the shaft displacements revealed a broad feature near 70 Hz. The drag force, COF, and shaft vibration intensity vary as a function of slurry, substrate, pad, and process downforce. The shaft vibration response was found to be largely decoupled from the mean drag force and COF measurements. The vibration intensity was correlated to blanket silicon dioxide removal rate for a variety of ceria-based slurries in cases where the drag force and COF values did not differentiate between conditions. In addition, a high intensity vibration response observed on blanket oxide substrates was associated with unusual pattern wafer behavior where high-density features were planarized at a higher rate compared to low-density features.

Characterization and Use of Quinones as Selective Oxidizers of Tantalum in CMP Applications

The reversible oxidation-reduction reaction of 9,10-anthraquinone-l,8-disulfonic acid potassium salt (1,8-AQDSA-K) was characterized using mass spectrometry and UV-visible spectrophotometry. Quinone derivatives such as anthroquinone disulfonic acid (AQDSA) or its salts were found to promote selective oxidation of tantalum in chemical mechanical planarization when used in slurry formulations. In general, additives with a redox potential between tantalum and copper resulted in a high selectivity of tantalum to copper removal in barrier applications. The details of representative redox reactions and kinetics are presented for AQDSA.