No abstract

A high pressure CO 2 -based post-etch-residue removal method is described. Tetramethylammonium hydroxide ͑TMAH͒ mixtures containing methanol and water were used as cosolvents with CO 2 . The effect of process parameters such as temperature, time, and cosolvent composition on the residue removal was investigated. X-ray photoelectron spectroscopy and scanning electron microscopy were used to characterize the samples. A 12% w/w of a 4:1 volumetric mixture of 25% TMAH in methanol and deionized water in CO 2 at 3000 psi and 70°C was effective in removing the residue; under these conditions, more than one phase was observed in the CO 2 -based mixture. Mechanisms that account for the film and residue removal are proposed.

Photoresist and post etch residue removal were studied as functions of the cleaning-mixture-phase state. Solutions of tetramethylammonium bicarbonate (TMAHCO 3 ) in methanol were used as cosolvents with CO 2 . The phase behavior of this mixture was studied at temperatures between 25 and 70°C and TMAHCO 3 /CH 3 OH mole ratios of 0.127 and 0.02. At a cosolvent flow rate of 0.0262 mol/h, the single-phase mixture was more efficient for photoresist and etch residue removal than the two-phase mixture. Blanket plasma deposited fluorocarbon films were used to investigate the removal mechanism. The removal process was reaction rate limited and depended on the temperature and active species concentrations. This novel cleaning mixture displayed minimal reaction with SiO 2 and Coral™ films.

High-pressure CO2 -based fluids have recently been proposed for post plasma etch residue removal as an environmentally benign alternative to current liquid-based methods. Specifically, CO2 -tetramethylammonium bicarbonate (TMAHCO3) methanol mixtures have been used to remove photoresist residues from a CORAL low-dielectric constant film. In this work, detailed studies are performed to improve the understanding of the residue removal mechanism using these mixtures. Attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and interferometry are used for in situ and ex situ monitoring during the cleaning process; model residue films are used to facilitate interpretation of results from these studies. The role of CO2 and the additives in the mixture is also delineated. The primary cleaning mechanism appears to be attack of the interface between the residue and the capping layer by OH− ions generated by dissociation of TMAHCO3 . Methanol promotes dissociation of the bicarbonate, while the role of CO2 is to promote diffusion of the additives to the interface.

High pressure CO2 based cleaning mixtures have recently been proposed as an environmentally benign approach for postplasma etch residue removal. These mixtures must remove etch residues without damaging the low-k dielectric film that will be used to isolate interconnect structures in future generation devices. In this work, the compatibility of a CO2-based mixture with a porous low-k film is evaluated. Positronium annihilation lifetime spectroscopy (PALS) is used to monitor the change in pore size and film chemistry in a porous methyl silsesquioxane film after treatments under several different elevated pressure conditions. Spectroscopic ellipsometry and infrared spectroscopy are used to complement the PALS technique in order to better understand cleaning mixture effects on the dielectric film. CO2–TMAHCO3–methanol mixtures cause negligible changes in pore dimensions and bulk composition of the film. The high pressure treatments cause a small decrease in positronium formation which may be attributed to contamination in the high pressure system.