Metal etching and cleaning in chemical solutions

About a week ago

Controlled etching of metals represents one of the challenges encountered during integration of advanced CMOS devices. Etching of metals in chemical solution(s) can be applied in the fabrication of 3D NAND flash memory, back-end of line interconnects, or simply it can be used for removal of the backside of wafers.


The scaling of Back-End of Line (BEOL) towards 5 nm node requires integrating complex stacks and multiple patterning schemes to meet challenging process specifications. One of the many challenges encountered during integration of advanced nodes structure is controlled etching of materials, including metals. For instance, wet etching of metals can be applied in the fabrication of a three-dimensional stacked word-line NAND flash memory, where the metal in the word-line stack is etched under a controlled way. A wet recess also finds its application in back-end of line interconnect, in particular, for fully self-aligned via (FSAV) processing steps. In FSAV processing, after the CMP step a topography is created by a controlled wet etching (recess) of the metal. The properties of the metals to be etched and the type of chemicals have an important effect on the etching results such as the metal surface roughness and surface chemistry, and etch uniformity.

Description of the work:

The objective of this project is to study the effect of chemical solutions (and mixtures), including aqueous and solvent-based, on (a) the etch rate of various materials, (b) the change of surface properties (roughness, surface chemistry) and (c) the etch mechanism by means of characterization.

  • Etch rate quantification of metals and metal oxides: focus on ruthenium (Ru), molybdenum (Mo), tungsten (W), and their oxides, TiN, TaN.  The effect of additives including corrosion inhibitors on material etching will also be investigated.
  • Evaluation of the change in properties of dielectric films, hardmask materials caused by the chemicals and etch rate of various metals and liner materials.

    Main characterization techniques include:
  • Four-point probe to measure sheet resistance (metals)
  • Scanning electron microscopy (SEM)
  • Rutherford backscattering spectrometry (RBS) (metal thickness).
  • Ultraviolet-Visible spectroscopy (UV-VIS)
  • Spectroscopic ellipsometry (SE) to determine thickness and refractive index (certain metal oxides, dielectric films).
  • Atomic force microscopy (AFM) to assess surface roughness and morphology (metals, dielectrics).
  • Fourier transform infrared spectroscopy (FTIR) to determine functional groups and bonding structure (organics, dielectric films).
  • Inductively coupled plasma mass spectroscopy (ICP-MS) for etch rate quantification (metals) (optional).
  • X-ray photoelectron spectroscopy (XPS) to quantify surface composition and bonding structure.
  • Other surface characterization techniques if required. 

A more detailed background of the project can be obtained by email or by telephone.

Type of project: Combination of internship and thesis

Duration: 6 months

Required degree: Master of Science, Master of Engineering Technology

Supervising scientist(s): For further information or for application, please contact: Quoc Toan Le (

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