Materials Science & Engineering

Permanent URI for this communityhttp://hdl.handle.net/1903/2260

Browse

Subject: search.filters.subject.plasma etching

Search Results

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Plasma-Photoresist Interactions for Realizing Advanced Pattern Transfer Processes
    (2020) Pranda, Adam; Oehrlein, Gottlieb S; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Photoresist (PR) materials undergo significant physical and chemical modification from the ions, vacuum ultraviolet (VUV) photons, and reactive species that comprise a plasma etch process. The modifications of these materials, which are an integral component in the manufacturing process of semiconductor devices, has key implications on the control of the etching and roughening behaviors that are vital for establishing selective pattern transfer processes that maintain feature fidelity at increasingly smaller feature sizes and pitches. In the initial chapters of this dissertation, we focus on establishing a fundamental understanding of the relationship between PR modification and the resulting etching behavior under an inert argon plasma process. To establish the key relationships, we utilize a combination of in situ ellipsometry supported by x-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy to develop an ellipsometric model that interprets the correlation between the PR layer structure, which develops due to energetic ion bombardment in a plasma process, and the corresponding etching behavior. From this analysis, we find that energetic ion bombardment produces a dense amorphous carbon (DAC) layer on the PR surface that reduces the overall PR etch rate with increasing thickness. Secondary characterization via atomic force microscopy (AFM) also shows corresponding development of surface roughness. Expanding the scope to reactive plasma chemistries containing fluorocarbon (FC) species, we find that the FC species interact with the DAC layer to produce an FC-rich modified layer on the surface. In the latter part of this dissertation, we apply our findings regarding the PR surface modification to address an industrial need to improve the etch selectivity of silicon dioxide (SiO2) to PR by minimizing the thickness loss of an extreme ultraviolet (EUV) PR under an atomic layer etching (ALE) process by systematically evaluating the ALE processing parameters. We find that cyclic ion bombardment of a deposited FC layer leads to the development of a modified layer that significantly reduces PR loss while simultaneously maintaining SiO2 etching, thus producing a high SiO2/PR etching selectivity. Lastly, we examine another industrial challenge concerning the extent of off-normal ions affecting the etching uniformity of PR samples.
  • Thumbnail Image
    Item
    Nanomechanical Properties and Buckling Instability of Plasma Induced Damaged Layer on Polystyrene
    (2012) Lin, Tsung-Cheng; Phaneuf, Raymond J; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In this thesis we report on an investigation of an elastic buckling instability as a driving force for the roughening of polystyrene, a model resist, during Ar+ plasma etching. Polystyrene films etched by pure Ar+ plasma with different ion energies were characterized using both atomic force microscopy topography and force curve measurements. By using height-height correlation function in analyzing the AFM measured topography images, we find that surface corrugation of etched polystyrene film surfaces all display a dominant wrinkle wavelength (ë), which is a function of ion energy. Next, we characterized the mechanical properties of these samples using AFM force curve measurements in an controlled ambient environment. We analyzed the measured force curves using a systematic algorithm based on statistical fitting procedures, and taking into account the adhesive interaction, in order to determine the effective elastic modulus of the films. We find that the effective elastic modulus (EBL) of the etched samples increases monotonically with increasing ion energy, but the changes are rather subtle as compared to the elastic modulus (EPS) of the unetched one. In order to test the validity of a buckling instability as the mechanism for surface roughening in our polystyrene-Ar plasma system, the elastic modulus of individual layer (i.e. ion-damaged layer plus unmodified foundation) needs to be determined. We present a determination of the damaged layer elastic modulus (EDL) from the effective elastic modulus of the damaged layer/polystyrene bilayer structure (EBL), based upon a finite element method simulation taking into account the thickness and elastic modulus of the damaged layers. We extract the damaged layer elastic modulus versus etching ion energy initially within the approximation of a spherical tip in contact with a flat sample surface. We next extend our model, by considering a periodic corrugated film surface, with its amplitude and wavelength determined by AFM, to take into account the effect of roughness induced by plasma exposure. The damaged layer elastic modulus extracted from these two approximations gives of quantitative agreement, and thus evidence for the correlation between buckling instability and plasma-induced roughening.
  • Thumbnail Image
    Item
    INFLUENCE OF POLYMER STRUCTURE ON PLASMA-POLYMER INTERACTIONS IN RESIST MATERIALS
    (2010) Bruce, Robert Lawson; Oehrlein, Gottlieb S; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The controlled patterning of polymer resists by plasma plays an essential role in the fabrication of integrated circuits and nanostructures. As the dimensions of patterned structures continue to decrease, we require an atomistic understanding underlying the morphological changes that occur during plasma-polymer interactions. In this work, we investigated how plasma surface modifications and the initial polymer structure influenced plasma etch behavior and morphological changes in polymer resists. Using a prototypical argon discharge, we observed polymer modification by ions and vacuum ultraviolet (VUV) radiation from the plasma. A thin, highly dense modified layer was formed at the polymer surface due to ion bombardment. The thickness and physical properties of this ion-damaged layer was independent of polymer structure for the systems examined here. A relationship was observed that strongly suggests that buckling caused by ion-damaged layer formation on a polymer is the origin of roughness that develops during plasma etching. Our results indicate that with knowledge of the mechanical properties of the ion-damaged layer and the polymer being processed, plasma-induced surface roughness can be predicted and the surface morphology calculated. Examining a wide variety of polymer structures, the polymer poly(4-vinylpyridine) (P4VP) was observed to produce extremely smooth surfaces during high-ion energy plasma etching. Our data suggest that VUV crosslinking of P4VP below the ion-damaged layer may prevent wrinkling. We also studied another form of resists, silicon-containing polymers that form a SiO2 etch barrier layer during O2 plasma processing. In this study, we examined whether assisting SiO2 layer formation by adding Si-O bonds to the polymer structure would improve O2 etch behavior and reduce polymer surface roughness. Our results showed that while adding Si-O bonds decreased etch rates and silicon volatilization during O2 plasma exposure, the surface roughness became worse. Enhanced roughening was linked to the decrease in glass transition temperature and elastic modulus as Si-O bonds were added to the polymer structure. For polymers used as resists it is required that the mechanical properties of the ion-damaged layer and the polymer be taken into account to understand their roughening behavior.
  • Thumbnail Image
    Item
    INVESTIGATION OF AMORPHOUS HYDROGENATED Si AS A RESIST FOR VACUUM-COMPATIBLE LITHOGRAPHY OF HgCdTe/CdTe FILMS
    (2005-04-13) Jacobs, Randolph N; Salamanca-Riba, Lourdes; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The vision of achieving a completely in-vacuum process for fabricating HgCdTe Infrared detector arrays is contingent on the availability of a vacuum-compatible lithography technology. One such technology for vacuum-lithography involves the use of amorphous hydrogenated Si (a-Si:H) as a dry photoresist. The basic concept has recently been demonstrated whereby a-Si:H resists were deposited via plasma enhanced chemical vapor deposition (PECVD), and then patterned using an excimer laser. The patterns were then hydrogen plasma developed to remove unirradiated areas. Finally, an Ar/H2 electron cyclotron resonance (ECR) plasma was used to transfer patterns to underlying Hg1-xCdxTe film layers. This thesis presents a continued investigation of a-Si:H as a resist material wherein the resists are deposited using an Ar-diluted silane precursor. To determine the best conditions for the technique, the effects of different laser fluences, and exposure environments were studied. Analysis via transmission electron microscopy (TEM) reveals that the excimer-exposed surfaces are polycrystalline in nature, indicating that the mechanism for pattern generation in this study is based on melting and crystallization of the exposed areas. To reduce undesirable surface roughness induced by laser irradiation, a step-wise crystallization/dehydrogenation technique is demonstrated. Fundamental aspects of pattern transfer (via ECR plasma etching) to CdTe and HgCdTe films are also demonstrated, where etch selectivities of 8:1 and 16:1 (respectively) are observed. These values represent a significant improvement to etch selectivities obtained using commercially available organic resists. To address concerns regarding possible damage to HgCdTe caused by the a-Si:H dry lithography process, preliminary studies were carried out using double-crystal rocking curve X-Ray diffraction and high-resolution TEM. The results indicate no evidence of microstructural damage to the HgCdTe film. Other characterization techniques used throughout this thesis include Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and stylus profilometry. The implementation of the a-Si:H dry lithography process represents a crucial step toward achieving totally integrated fabrication of HgCdTe IR detector arrays. In addition this lithography technique is both low temperature and contamination-free, so that other semiconductor microfabrication processes could potentially benefit from its use.