Bottom-up fill of Cu in deep submicrometer via holes was achieved through electroless plating alone for the first time. We investigated the effect of addition of inhibitor molecules to electroless Cu plating solution, and found that sulfopropyl sulfonate ͑SPS͒ was highly effective in promoting the bottom-up fill. The tendency for bottom-up filling was enhanced by shrinkage of the hole diameter. This suggests that the diffusion flux of SPS molecules to the bottom of holes was more suppressed for smaller holes. Thus, the Cu deposition rate near the hole bottom is larger than that outside the hole, leading to bottom-up filling.

The bottom-up fill of copper in fine via holes is reported in electroless copper plating with the addition of bis͑3-sulfopropyl͒ disulfide ͑SPS͒. When the concentration of SPS in the plating bath was varied from 0.05 to 0.5 mg/L with a plating time of 10 min, the ratio of the Cu thickness at the bottom of the hole (T b ) to that at the surface (T s ), called the bottom-up ratio, increased from 1.05 to 2.8 for a 1.0 m hole. The bottom-up ratio increases with SPS concentration and decreases with an increase in hole diameter. X-ray diffraction structure analyses and cross-sectional transmission electron microscopy observations indicated that the grain size of Cu film was reduced by the SPS addition, but Cu͑111͒ texture was enhanced by the SPS addition. Bottom-up fill may be attributed to a higher SPS concentration at the surface than at the bottom of the holes due to SPS incorporation in the Cu film and diffusion-limited flux of SPS molecules into fine holes.Copper ͑Cu͒ is used widely as an interconnection metal in ultralarge-scale integration ͑ULSI͒ circuits due to its lower resistivity and superior resistance against electromigration compared to conventional aluminum alloys. The present damascene copper interconnections are fabricated by electroplating on a sputtered Cu seed layer. To produce void-free and seamless fill for high-aspect-ratio trenches and via holes, superfill or bottom-up fill, in which the deposition rate at the bottom of the hole is higher than at the surface, is necessary. Cu electroplating baths containing additives, such as chloride ion, polyethylene glycol ͑PEG͒, bis͑3-sulfopropyl͒ disulfide ͑SPS͒, 3-mercapto-1-propanesulfonate ͑MPSA͒, or Janus Green B ͑JGB͒, have yielded desirable plating characteristics. 1-8 Inhibition to Cu deposition in the Cl-PEG-SPS system is due primarily to the combination of PEG and chloride ions, 2-5 with acceleration attributed to SPS. However, a major premise of the superfill deposition of electroplating is a continuous sputtered Cu seed layer. Because a shrinkage in dimensions occurs for next generation interconnections, forming a continuous sputtered Cu film on the sidewalls of fine via holes becomes more difficult as sputtering suffers from poor step coverage. Consequently, copper electroless plating and chemical vapor deposition ͑CVD͒ are the most promising processes for the formation of a seed layer for electroplating. 9-15 Bottom-up filling of submicrometer features by iodine-catalyzed CVD was reported by Shim et al., 9 Hwang and Lee, 10 and Josell et al.,11 but adhesion between the copper film and the barrier metal layer was poor and the deposition rate was slow. Copper electroless plating, which does not require a sputtered Cu seed layer, is an efficient means of filling high aspect ratio holes and has became increasingly important. 12-15 However, when the hole diameter is less than 70 nm, filling the highaspect-via-hole with normal electroless plating is difficult.Many studies report bottom-up fill of Cu in electroplating baths using additives, but few r...

Electroless plated copper can be deposited on a TaN surface initiated by displacement plating when the surface oxide layer is removed by wet chemical etching. For application to ultra-large-scale integrated (ULSI) interconnection technology in which very thin TaN barrier films are used, it is essential to form a stable TaN film with minimal native oxide thickness. In this study, TaN films with various N/Ta atomic ratios were fabricated by reactive sputtering and native oxide growth on the surface was investigated by x-ray photoelectron spectroscopy, high resolution Rutherford backscattering spectrometry, and x-ray diffraction (XRD). It was found that when the N/Ta atomic ratio in the film was lower than 1.2, surface oxidation of the TaN film advanced with time. When the ratio was higher than 1.2, oxidation of the TaN film stopped at 1 ML. The XRD spectra indicated that when the N/Ta atomic ratio was between 0.82 and 1.25, face-centered-cubic TaN films were formed and the resistivity increased with an increase in the N/Ta ratio. Thus, a TaN film with a N/Ta ratio of 1.25 ratifies the minimal surface oxide thickness as well as low-resistivity requirements, and is appropriate for ULSI Cu interconnections using electroless Cu deposition.

The effects of additives, such as Cl À , thiourea, benzotriazole, bis(3-sulfopropyl)-disulfide (SPS), and mercaptonicotinic acid, upon the hole filling characteristic of electroless Cu plating were investigated. With the addition of thiourea, the Cu deposition rate was suppressed and the hole filling characteristic became anti-bottom-up filling with the presence of voids. With the addition of SPS, bottom-up Cu filling was achieved and the bottom-up tendency increased with an increase in SPS concentration. The mechanism of anti-bottom-up filling and bottom-up filling with the addition of thiourea or SPS is attributed to the diffusion flux of thiourea being higher than that of Cu 2þ -EDTA complex, and the diffusion flux of SPS being lower than that of Cu 2þ -EDTA complex.

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