Competitive effect between roughness and mask pattern on charging phenomena during plasma etching

In plasma etching process, the edge roughness and mask pattern usually play a significant role in the deformation of holes under the influence of charging effect. The competitive effect between these two factors has been investigated, focusing on the surface charging in a hexagonal array, with various values of roughness parameters (amplitude (A) and wavelength (W)) and distances between holes (L). A series of classical particle dynamic simulations of surface charging, surface etching and profile evolution were used to investigate the effect of roughness and pattern on charging. This study showed that various roughness and patterns (represented by different values of L) can significantly influence surface distributions of the electric-field (E-field) and the etching rates on the mask surface. The simulations also showed that (1) the shape of the pattern array influences the mask hole profile during etching process, i.e. a hexagonal array pattern tends to deform the profile of a circular mask hole into a hexagonal hole; (2) pattern roughness is aggravated during etching process. These factors were found to be significant only at a small feature pitch and may be ignored at a large feature pitch. Possible mechanisms of these results during etching process are discussed. This work sheds light on the ways to maintain pattern integrity and further improve the quality of the pattern transfer onto the substrate.

Fabricating Elastomeric Photomask with Nanosized-Metal Patterns for Near-Field Contact Printing

When an elastomeric photomask is used for near-field contact printing, the high deformability of the elastomer mask plate enables gap-free full contact with the substrate, minimizing the effect of diffraction. This image-transfer technique provides sub-50 nm resolution and depth-of-focus-free lithographic capability with cost-efficient equipment. However, the method’s application is limited due to the lack of a wellestablished protocol for fabricating a nanoscale mask pattern on an elastomeric substrate, which remains a major technical challenge in the field of near-field contact printing. In this study, we present a reliable protocol for fabricating a metal-embedded polydimethylsiloxane (PDMS) photomask. Our fabrication protocol uses conventional nanofabrication processes to fabricate nanosized chromium mask patterns and then transfers the chromium patterns to an elastomeric mask plate using a sacrificial Ni layer. Our protocol provides a high flexibility mask pattern design, and highly stable metal patterns during transferring process. By careful optimizing the experimental parameters, we determined a perfect pattern transfer ratio, which avoided any mechanical failure of the metal pattern, such as debonding or wrinkling. We then fabricated a PDMS photomask and confirmed its nanoscale patterning resolution, with the smallest feature 51 nm in width under a 400-nm light source. We anticipate that our fabrication protocol will enable the application of cost-efficient and high-resolution near-field photolithography.

METHOD FOR CALCULATION OF MASK SPECIFICATION CONTRIBUTION TO LITHOGRAPHIC BUDGETS

In this work we consider the contribution of tolerances on the mask pattern quality to the error budgets of lithographic operations. A method for developing a photomask specification based on the lithography modeling is proposed.

Selective Area Epitaxy of GaAs/Ge/Si Nanomembranes: A Morphological Study

We demonstrate the feasibility of growing GaAs nanomembranes on a plastically-relaxed Ge layer deposited on Si (111) by exploiting selective area epitaxy in MBE. Our results are compared to the case of the GaAs homoepitaxy to highlight the criticalities arising by switching to heteroepitaxy. We found that the nanomembranes evolution strongly depends on the chosen growth parameters as well as mask pattern. The selectivity of III-V material with respect to the SiO2 mask can be obtained when the lifetime of Ga adatoms on SiO2 is reduced, so that the diffusion length of adsorbed Ga is high enough to drive the Ga adatoms towards the etched slits. The best condition for a heteroepitaxial selective area epitaxy is obtained using a growth rate equal to 0.3 ML/s of GaAs, with a As BEP pressure of about 2.5 × 10−6 torr and a temperature of 600 °C.