With film thicknesses approaching a few monolayers in semiconductor processes, the chemical state and the cleanliness of the surfaces become critical in determining the outcome of many semiconductor processes. Currently available molecular analytical techniques with sufficient surface sensitivity such as XPS and ToF-SIMS lack the spatial resolution to analyze nanoscale defects and residues. While electron microscopy-based EDX can identify many atomic elements, they cannot provide chemical bonding information, which is needed to assess more accurately the nature and origin of the defects. In this paper, a relatively new hyperspectral technique called infrared photo-induced force microscopy (IR PiFM), which combines atomic force microscopy (AFM) and infrared (IR) spectroscopy with ~ 5 nm spatial resolution, is introduced. By utilizing a state-of-the-art tunable broadband IR laser, truly nanoscale PiF-IR spectra that agree with bulk FTIR spectra can be acquired without contact, i.e., it is non-contaminating and non-destructive, on films as thin as ~ 1 nm. PiF-IR spectra can be used to search existing IR databases to unambiguously identify the chemical species (both organic and inorganic molecules) of sub-20 nm defects and sub-monolayer residues via their IR signatures. Examples of defects and residues analyzed by IR PiFM system for 8” wafers and standard 6” photomasks are presented. For both types of samples, the system can automatically navigate to defect locations per defect map to acquire both topographical and chemical map images of the defects. PiF-IR spectra acquired on the defects and residue can be searched against Wiley’s KnowItAll IR database for potential matches.
With the advent of 45nm and below technology nodes and EUV lithography, the need to identify the chemical composition of defects is of paramount importance. The defects of concern range from 10nm to 500nm, which the current batch of molecular analytical tools cannot address adequately since the indications are that most of the defects detected on photomasks are organic in nature. In this paper, a relatively new nanoscale technique called infrared photoinduced force microscopy (IR PiFM), which combines atomic force microscopy (AFM) and infrared (IR) spectroscopy with ~ 5 nm spatial resolution, is introduced. By utilizing a state-of-the-art tunable broadband IR laser (tunable from ~550 to < 4000 cm-1 with ~ 3 cm-1 spectral width over the entire range), truly nanoscale PiF-IR spectra that agree with bulk FTIR spectra can be acquired; PiF-IR spectra can be used to search the existing IR database to unambiguously identify the different chemical species (both organic and inorganic molecules) of sub-20 nm defects and monolayer residues via their IR signatures. PiFM images at fixed wavenumbers associated with the different chemical species provide chemical mapping in real space with ~ 5 nm spatial resolution, clearly illuminating multi-component defects and existence of residues. The paper will show how the nanoscale hyperspectral PiFM data can provide unambiguous and speedy feedback to process engineers engaged in advanced lithography.
Self-assembled molecules (SAM) are used as an inhibitor in conjunction with atomic layer deposition (ALD) for selective area deposition. Given the extremely thin film and the pattern density involved in this type of process, currently available analytical tools have difficulty in analyzing the quality and selectivity of each processing step. For example, while FTIR may provide evidence of SAM coverage, it cannot assure the quality of coverage, especially on a scale relevant to current processing requirements. Similarly, electron microscopes that can provide excellent spatial resolution and elemental analysis cannot determine the quality of the ultrathin thin organic and selective inorganic deposition layers. In this paper, a relatively new technique called photo-induced force microscopy (PiFM), which combines atomic force microscopy (AFM) and infrared (IR) spectroscopy with sub-10nm spatial resolution, is used to analyze the deposition of SAM layer and subsequent alumina deposition on metal/SiO2 test patterns (80nm being the smallest pitch). PiFM spectra can unambiguously identify the different chemical species (SAM, SiO2, and alumina) via their IR signatures. PiFM images at fixed wavenumbers associated with the different chemical species provide chemical mapping in real space with sub-10nm spatial resolution, clearly illuminating how selective different processing steps are. The paper will show how the nanoscale hyperspectral PiFM data can provide unambiguous and speedy feedback to process engineers engaged in selective deposition.
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