Solid State Phenomena Vol. 346

Abstract: Cleaning of semi-damascene structures after direct metal etch (DME) are becoming more challenging as the size of features are getting smaller and number of materials increase in advanced nodes. Typical DME residues in-between Ru lines, generated during/after semi-damascene patterning by DME, mainly consist of Ti-based residues whereas there are TiN layers present as etch stop layer (ESL) below the SiN HM and underneath Ru lines. Wet cleaning of Ti-based residues selective to TiN and Ru in a decent process time is necessary. Undercut of TiN during wet cleaning results in collapsing of the SiN HM and/or Ru lines. We present a novel FOTOPUR^® R solution designed to clean Ti-based residues selective to Ru and TiN. Moreover, the new chemistry can further extend the process window without collapsing the Ru lines.

Abstract: As semiconductor devices continue to scale, it is important to evaluate alternative metals on narrower wiring or via structures. Ruthenium (Ru) is one promising candidate because of its lower resistivity compared to the conventional metals such as copper (Cu), cobalt (Co) and tungsten (W) on narrow space. To prevent leakage problems between metal layers caused by residues on the bottom and sidewalls after the metal patterning process, a cleaning process for Ru metal lines is necessary. Although the industry standard using Ammonia Peroxide Mixture (APM) is effective for removing residues, it was ineffective for Ru semi-damascene stack. Therefore, a new cleaning method involving UV treatment followed by APM, which was tested on metal pitch 18 nm patterned structure, was developed. This method showed promising results and is expected to be used in manufacturing of future semiconductor devices.

Abstract: The effect of various chemical solutions and mixtures on the etch characteristics, roughness change, and surface composition of NiAl, Al, and Ni films were investigated. Both HCl solution (1.82%) and NH₄OH (0.6 and 1.45%) solutions were found to have a detrimental effect on NiAl film in terms of material etching (4-point probe results) and surface roughness change (AFM). Within the concentration range applied, adding H₂O₂ into the HCl or NH₄OH solutions resulted in a significant increase of the etching of the NiAl film. A correlation was observed between the magnitude of etching and increase in surface roughness suggesting that a preferential etching occurred, most likely of grain boundary. Experimental results showed that in the case of 1.82% HCl-H₂O₂ mixture, NiAl surface can be protected up to 240 s of immersion with the use of a corrosion inhibitor such as triazole (TA).

Abstract: We demonstrate that a uniform recess of polycrystalline Mo can be achieved using a two-step method: metal oxidation with isotropic oxygen plasma that forms a layer of MoO₃ and selective etching of this oxide layer. The oxidation step fully defines the recess depth, and its uniformity is ensured by the low facet dependence of plasma oxidation. We have extensively studied the oxidation of patterned Mo nanowires (30 nm width) in isotropic oxygen plasma and achieved uniform oxide layers of predefined thickness by controlling radio-frequency (RF) power, gas pressure, and exposure time. We showed that using highly selective oxide etching, we can perform multiple etching cycles with a typical etch rate of 1-2 nm per cycle, depending on the RF power. Due to plasma isotropy, this approach can be implemented for a controlled uniform etching of large vertical stacks of metal nanostructures.

Abstract: We achieved the controlled recess of molybdenum (Mo), which is alternative interconnect material for copper (Cu), by wet chemical etching. This wet etching process includes two main steps which are chemical oxidation of Mo and its subsequent dissolution, respectively. Firstly, Mo nanowires (NWs) are uniformly oxidized with potassium permanganate (KMnO₄) solution in acetone. Secondly, the Mo oxide is dissolved using an aqueous solution of HCl. Mo NWs are characterized through transmission electron microscopy (TEM) imaging after each of the above steps. Cyclic etching experiments including oxidation and dissolution of Mo showed that Mo recess is linear and can be controlled for each cycle, where the etching produced the smooth Mo surface. This controlled Mo recess is crucial for the fabrication of next-generation metal interconnects.

Abstract: In this paper, we investigate the use of a wet cleaner developed to dissolve residues left after plasma etching selectively to aluminum in new applications such as the removal of various resilient ionic and halides-based surface contaminants. The compromise between efficiency and selectivity of this fluorinated acid cleaner makes it an interesting chemistry for many cleaning steps during wafer manufacturing. Two new applications were investigated: the selective removal of fluoride-based defects on aluminum pads and surface decontamination of various ionic metals with low substrate consumption. These studies showed very encouraging results in beakers level tests, but also on partly industrial equipment, opening new possibilities for this cleaner. Indeed, “water lily” defects removal seems to be possible with a low aluminum consumption in TechniClean IK73. Decontamination study carried out in static bath and in single wafer tool showed rather similar results, enabling static bath protocol and ionic metals removal to be validated and VPD-ICPMS results, after a short process time in a single wafer tool were very promising with metal levels close to the lower limit of detection of all elements tested.