Probing surface and bulk chemistry in resist films using near edge x-ray absorption fine structure (original) (raw)
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Utilizing Near Edge X-ray Absorption Fine Structure to Probe Interfacial Issues in Photolithography
ACS Symposium Series, 2004
Control of the shape, critical dimension (CD), and roughness is critical for the fabrication of sub 100 nm features, where the CD and roughness budget are approaching the molecular dimension of the resist polymers 1. Here we utilize near edge X-ray absorption fine structure (NEXAFS) to provide detailed chemical insight into two interfacial problems facing sub-100 nm patterning. First, chemically amplified photoresists are prone to surface phenomenon, which causes deviations in the pattern profile near the interface. Striking examples include T-topping, closure, footing, and undercutting. NEXAFS was used to illustrate that the surface extent of deprotection in a model resist film can be different than the bulk deprotection. Second, line edge roughness becomes increasingly critical with shrinking patterns, and may be intimately related to the line edge deprotection profile. A NEXAFS technique to surface depth profile for compositional gradients is described with the potential to provide detailed chemical information about the resist line edge.
X-ray absorption spectroscopy to probe interfacial issues in photolithography
Proceedings of SPIE, 2003
We utilize near edge X-ray absorption fine structure spectroscopy (NEXAFS) to provide detailed chemical insight into two interfacial problems facing sub-100 nm patterning. First, chemically amplified photo-resists are sensitive to surface phenomenon, which causes deviations in the pattern profile near the interface. Striking examples include T-topping, closure, footing, and undercutting. NEXAFS was used to examine surface segregation of a photo-acid generator at the resist/air interface and to illustrate that the surface extent of deprotection in a model resist film can be different than the bulk extent of deprotection. Second, line edge roughness becomes increasingly critical with shrinking patterns, and may be intimately related to the line edge deprotection profile. A NEXAFS technique to surface depth profile for compositional gradients is described with the potential to provide chemical information about the resist line edge.
Langmuir, 2005
Near-edge X-ray absorption fine structure spectroscopy (NEXAFS) is utilized to provide insight into surface chemical effects in model photoresist films. First, NEXAFS was used to examine the resist/air interface including surface segregation of a photoacid generator (PAG) and the extent of surface deprotection in the film. The concentration of PAG at the resist-air interface was higher than the bulk concentration, which led to a faster deprotection rate at that interface. Second, a NEXAFS depth profiling technique was utilized to probe for compositional gradients in model resist line edge regions. In the model line edge region, the surface composition profile for the developed line edge was dependent on the post exposure bake time. Figure 8. A schematic of the experiments used to generate a model line edge region. NEXAFS depth profiling was conducted on the developed bilayer sample, stage 5 from above.
Nanotechnology, 2018
We report on the near edge x-ray absorption fine structure (NEXAFS) spectroscopy of hybrid organic-inorganic resists. These materials are nonchemically amplified systems based on Si, Zr, and Ti oxides, synthesized from organically modified precursors and transition metal alkoxides by a sol-gel route and designed for ultraviolet, extreme ultraviolet (EUV) and electron beam lithography. The experiments were conducted using a scanning transmission x-ray microscope (STXM) which combines high spatial-resolution microscopy and NEXAFS spectroscopy. The absorption spectra were collected in the proximity of the carbon edge (∼290 eV) before and after in situ exposure, enabling the measurement of a significant photo-induced degradation of the organic group (phenyl or methyl methacrylate, respectively), the degree of which depends on the configuration of the ligand. Photo-induced degradation was more efficient in the resist synthesized with pendant phenyl substituents than it was in the case of...
The Journal of Physical Chemistry B, 2005
Soft X-ray absorption microscopy was applied to image and characterize molecular patterns produced by electron irradiation of aliphatic and aromatic thiol-derived self-assembled monolayers (SAMs) on Au substrates. The measurements were performed at all relevant absorption edges. The fabricated patterns could be clearly imaged with a lateral resolution better than 150 nm, which, for example, allowed us to distinguish a fine structure of 1 µm features. The X-ray absorption microspot spectra derived from different areas of the SAM patterns provided specific chemical information on pristine and irradiated areas and unexpected features in these patterns. The quality of the microspot spectra is comparable with that of the analogous X-ray absorption spectra acquired with standard equipment from homogeneous SAMs. In particular, a chemical transformation of the functional tail groups within the irradiated areas of the patterned aromatic SAMs could be directly monitored.
NEXAFS measurements of the surface chemistry of chemically amplified photoresists
2003
Near edge x-ray absorption fine structure (NEXAFS) spectroscopy was used to quantify the surface composition profile (top 1 nm to 6 nm) of model chemically amplified photoresists with various photo-acid generators. These materials are prone to interfacial and surface chemical changes that cause deviations in the desired lithographic pattern such as T-topping and closure. If interfacial excess or depletion of the photo-generated acid occurs, either from atmospheric contamination, evaporation, or segregation within the film, the resulting compositional heterogeneity will affect the interfacial photoresist structure, composition, and deprotection kinetics. A significant technical challenge lies in measuring the surface composition and extent of reaction with depth resolution at interfaces. Electron yield NEXAFS allows measurement of the surface chemical composition, particularly for carbon, fluorine, oxygen, and nitrogen. When exposed to vacuum ultraviolet x-rays (soft x-rays), the top surface of the material releases electrons that can be measured with a high pass grid analyzer electron yield detector. By varying the negative voltage bias at the entrance grid to the electron yield detector, it is possible to differentiate the kinetic energy of electrons escaping from depths up to 6 nm into the film. This measurement capability becomes increasingly important with the drive towards sub-100 nm lithography. As the photoresist film thickness continually decreases and the interfacial regions dominate the behavior of the material, it is crucial to understand both their physical and chemical nature.
Advances in Resist Technology and Processing XXI, 2004
The performance of chemically amplified photoresists, including next generation thin film 157 nm fluorinated copolymers and blends, is affected by such phenomena as polymer/substrate and polymer/air interfacial (surface energy) effects, blend miscibility, small molecule diffusion in thin films, permeability of airborne contaminants, and interactions with products from the deprotection reaction. Using near edge x-ray absorption fine structure (NEXAFS) spectroscopy, it is possible to simultaneously probe the surface and bulk chemistry of chemically amplified photoresists to determine possible causes of pattern degradation, including post exposure delay induced material failure, blend component and small molecule diffusion/segregation to the photoresist surface, and interactions between components of the photoresist formulation and developer. The surface and bulk chemistry of model photoresists were analyzed in the NEXAFS vacuum chamber, equipped with in situ processing capabilities for exposure, controlled dosing of a model contaminant gas (NMP or water vapor), and heating, to quantify component segregation and identify surface phenomena that may be responsible for pattern degradation. For model 157 nm blend films, it was found that there is segregation of one component to the surface of the photoresist film, in excess of the composition of that component in the blend. For polymer blends the more hydrophobic or lower surface tension species will typically wet the film surface when heated in air. Segregation of photo-acid generator has also been demonstrated and the effect of reducing film thickness investigated. As photoresist film thickness continually decreases and the photoresists become increasingly sensitive to environmental contaminants, the interfacial and surface regions dominate the behavior of the material and it is crucial to understand both their physical and chemical nature.
Highly spatially resolved chemical metrology on latent resist images
2022
Patterning photoresist with extreme control over dose and placement is the first crucial step in semiconductor manufacturing. However, how can the activation of modern complex resist components be accurately measured at sufficient spatial resolution? No exposed nanometre-scale resist pattern is sufficiently sturdy to unaltered withstand inspection by intense photon or electron beams, not even after processing and development. This paper presents experimental proof that infrared atomic force microscopy (IR-AFM) is sufficiently sensitive and gentle to chemically record vulnerable yet valuable lithographic patterns in a chemically amplified resist after exposure prior to development. Accordingly, IR-AFM metrology provides long-sought insights into changes in the chemical and spatial distribution per component in a latent resist image, both directly after exposure and during processing. With these to-be-gained understandings, a disruptive acceleration of resist design and processing is ...
Highly spatial-resolved chemical metrology on latent resist images
2022
Patterning photoresist with extreme control over dose and placement is the first crucial step in semiconductor manufacturing. But, how to accurately measure the activation of modern complex resists components at sufficient spatial resolution? No exposed nanometre-scale resist pattern is sufficiently sturdy to unaltered withstand inspection by intense photon or electron beams, not even after processing and development. This paper presents experimental proof that Infra-Red Atomic Force Microscopy (IR-AFM) is sufficiently sensitive and gentle to chemically record the vulnerable-yet-valuable lithographic patterns in a chemically amplified resist after exposure, prior to development. Accordingly, IR-AFM metrology provides the long-sought-for insights in changes in the chemical and spatial distribution per component in a latent resist image, both directly after exposure as well as during processing. With these to-be-gained understandings, a disruptive acceleration of resist design and pro...