Treatments of polymer films using either a MHz atmospheric pressure plasma jet (APPJ) or an atmospheric pressure surface micro-discharge (SMD) plasma are investigated. While the typical approach to determine relevant reactive species is to correlate surface effects with gas phase species measurement, this does not capture potential synergistic or other complex effects that may be occurring. Activation energy and directionality of the etching process can characterize what is occurring at the surface for these processes in more detail. The APPJ source shows an apparent activation energy of ∼0.18 eV at 8 mm distance and up to ∼0.34 eV at 16 mm distance for a temperature range of 20-80°C tested with thin polymer films. The APPJ source shows directional etching at 8 mm distance with less anisotropy the more distance is increased. The SMD source has an apparent activation energy of ∼0.8-0.9 eV at a distance of 3 mm. The SMD also only shows isotropic etching behavior. However the SMD surface chemistry changes significantly to less oxidation with increased temperature while the APPJ source induced modifications remain very similar with temperature change. The lower apparent activation energy of the APPJinduced etching reactions as compared with low pressure work (0.5 eV) and observation of line-of-sight contribution to etching suggests the involvement of a directional species at closer distances facilitating the etching which falls off with increasing distance. The high activation energy of the SMD suggests that species with less capability for etching is responsible compared to the APPJ and low pressure plasma. The high surface oxidation from low temperature SMD treatments shows that the surface is being oxidized but not sufficiently to reach the desorption step of the etching process.

The development of new photoresists for semiconductor manufacturing applications requires an understanding of the material properties that control the material's plasma etching behavior. Ion bombardment at ion energies of the order 100 s of eV is typical of plasma-based pattern-transfer processes and results in the formation of a dense amorphous carbon (DAC) layer on the surface of a photoresist, such as the PR193-type of photoresist that currently dominates the semiconductor industry. Prior studies have examined the physical properties of the DAC layer, but the correlation between these properties and the photoresist etching behavior had not been established. In this work, the authors studied the real-time evolution of a steady-state DAC layer as it is selectively depleted using an admixture of oxygen into an argon plasma. Observations of the depletion behavior for various DAC layer thicknesses motivate a new model of DAC layer depletion. This model also correlates the impact of the DAC layer thickness with the etch rate of the bulk photoresist. The authors find that up to a 40% depletion of the DAC layer thickness does not have a significant impact on the bulk photoresist etch rate. However, further depletion results in an exponential increase in the etch rate, which can be up to ten times greater at full depletion than for the fully formed DAC layer. Thus, with these trends the authors show that the photoresist etch rate is controlled by the thickness of the DAC layer. Furthermore, thickness loss of the DAC layer in an O2-containing plasma coincides with a chemical modification of the layer into an oxygen-rich surface overlayer with properties that are intermediate between those of the DAC layer and the bulk photoresist. Support for this interpretation was provided via x-ray photoelectron spectroscopy characterization. Atomic force microscopy was used to gauge the impact on surface roughness as the DAC layer is formed and depleted. The trends established in this work will provide a benchmark in our development of new photoresists, which will be suitable for pattern transfer processes that will ultimately be a part of enabling smaller semiconductor device feature sizes and pitches.

Thin layers of polypropylene (PP) have been treated by argon low‐temperature plasmas in an inductively coupled plasma setup. The etched thickness of PP was monitored in situ by means of single‐wavelength ellipsometry. The ellipsometric model of the polymer surface exposed to plasma consists of a UV‐modified layer, a dense amorphous carbon layer because of ion bombardment, and an effective medium approximation layer, which accounts for moderate surface roughness. The etching behavior has been compared to a model based on argon ion beam irradiation experiments. In this approach, surface processes are described in terms of etching yields and crosslinking probabilities as a function of incident fluxes and energies of Ar ions and UV photons. The ion beam model fits well with the plasma etching results.

No abstract

Extreme ultraviolet (EUV) lithography has emerged as the next generational step in advancing the manufacturing of increasingly complex semiconductor devices. The commercial viability of this new lithographic technique requires compatible photoresist (PR) materials that satisfy both the lithographic and etch requirements of good feature resolution, chemical sensitivity, a low line edge roughness, and good critical dimension uniformity. Achieving the decreased feature pitches of modern processing nodes via EUV lithography places a limit on the available photoresist thickness for a pattern transfer process. Therefore, etch processes are required to maximize the etching selectivity of a hard mask material, such as SiO2, to an EUV photoresist. In this work, the authors evaluated the ability of an atomic layer etching (ALE) process to maximize the SiO2/EUV PR etching selectivity. Through the flexible parameter space available in an ALE process, the authors evaluated the etching behaviors as a function of the ALE parameters of ion energy, etch step length, fluorocarbon (FC) deposition thickness, and precursor gas type. The authors found that the interaction between the energetic argon ion bombardment and a deposited FC layer produces a modified surface layer on the PR material that can strongly control the PR etch rate and even produce an etch stop under some conditions. Under the same processing conditions, the etching behavior of SiO2 continues unimpeded, thus resulting in a high overall SiO2/PR etching selectivity. Secondary characterization using x-ray photoelectron spectroscopy and atomic force microscopy was used to support the conclusions derived from the ellipsometric modeling based on the surface chemistry evolution and determine the impact of the ALE process on the surface roughness of the EUV PR, respectively. Additionally, attenuated total reflection Fourier-transform infrared spectroscopy was used to track the impact on specific functional groups within the PR composition from both the argon ion bombardment and FC deposition components of the ALE process. The ALE-based PR etching concept established in this work serves as a foundation for both the understanding of the impacts of an ALE process on an EUV PR material and for future works, employing an ALE process for PR-based pattern transfer.