Fluorocarbon Film Deposition Research Articles

MEMS Process by Film Transfer Using a Fluorocarbon Anti-Adhesive Layer

A low cost and low temperature microelectromechanical systems (MEMS) transfer process is presented. The process is based on adhesion control of molded electroplated Ni microstructures on the donor wafer by using a plasma deposited fluorocarbon film. Adhesive bonding of the microstructures on the target wafer using BCB sealing enables mechanical tearing off from the donor wafer. This proposed process has allowed us to realize from 7 μm down to 700 nm thick Ni patterns on Si, Pyrex glass wafers and Kapton foils. Multiple transfers lead to Ni stacked microstructures. We demonstrated the interest of a simple film transfer process for the elaboration of 3D microstructures.

From Superamphiphobic to Amphiphilic Polymeric Surfaces with Ordered Hierarchical Roughness Fabricated with Colloidal Lithography and Plasma Nanotexturing

Ordered, hierarchical (triple-scale), superhydrophobic, oleophobic, superoleophobic, and amphiphilic surfaces on poly(methyl methacrylate) PMMA polymer substrates are fabricated using polystyrene (PS) microparticle colloidal lithography, followed by oxygen plasma etching-nanotexturing (for amphiphilic surfaces) and optional subsequent fluorocarbon plasma deposition (for amphiphobic surfaces). The PS colloidal microparticles were assembled by spin-coating. After etching/nanotexturing, the PMMA plates are amphiphilic and exhibit hierarchical (triple-scale) roughness with microscale ordered columns, and dual-scale (hundred nano/ten nano meter) nanoscale texture on the particles (top of the column) and on the etched PMMA surface. The spacing, diameter, height, and reentrant profile of the microcolumns are controlled with the etching process. Following the design requirements for superamphiphobic surfaces, we demonstrate enhancement of both hydrophobicity and oleophobicity as a result of hierarchical (triple-scale) and re-entrant topography. After fluorocarbon film deposition, we demonstrate superhydrophobic surfaces (contact angle for water 168°, compared to 110° for a flat surface), as well as superoleophobic surfaces (153° for diiodomethane, compared to 80° for a flat surface).

Deposition of Fluorocarbon Films by RF Magnetron Sputtering at Varying Target-Substrate Distance

The target-substrate distance has a significant effect on the morphology and the relative deposition rate of fluorocarbon films deposited by RF magnetron sputtering. The films were deposited on regenerated cellulose substrate using a polytetrafluoroethylene (PTFE) target, with argon as the working gas. The surface and fracture cross-section morphologies of the deposited films were examined by scanning electron microscopy (SEM). The average thickness of the fluorocarbon films and the relative deposition rates were calculated for varying target-substrate distances. The films had island-like structures composed of nanoscale particles, and the surfaces were not flat. The density of the particles increased and their size decreased with increase of the target-substrate distance in the range 30 to 80 mm. The relative deposition rate increased at first and then decreased with increased target-substrate distance: the optimal target-substrate distance was 50-60 mm.

MEMS Process by Film Transfer Using Fluorocarbon Anti-Adhesive Layer

A low cost and low temperature MEMS transfer process is presented. The process is based on adhesion control of molded electroplated Ni microstructures on donor wafer by using plasma deposited fluorocarbon film. Adhesive bonding of the microstructures on the target wafer using BCB sealing enables mechanical tearing out from the donor wafer. This proposed process has allowed us to realize from 7 µm down to 700 nm thick Ni patterns on Si, Pyrex glass wafers and Kapton foils. Multiple transfers lead to Ni stacked microstructures. Because this process is simple and only involves a low temperature (250°C) heating of the host wafer, it is highly versatile and suitable for various applications and brings new perspectives towards 3D integration of MEMS/NEMS.

Chamberless plasma polymerization of fluorocarbon thin films

Fluorocarbon thin films were prepared and investigated using atmospheric pressure plasma jet. This atmospheric pressure plasma jet deposited fluorocarbon films without unfavorable contamination in plasma source. The atmospheric pressure plasma, generated with RF frequency power at 13.56 MHz, was fed with hexafluorobenzene (C 6F 6) as the deposition precursor and helium as the carrier gas. After deposition, the fluorocarbon films were analyzed for chemical characteristic, elemental composition, and surface morphology. The chemical structures and surface properties of the films were evaluated by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) analyses. By reason of the XPS and FTIR data, atmospheric pressure plasma deposited fluorocarbon films are similar to original aromatic ring in chemical structure. This investigation demonstrates that atmospheric pressure plasma jet affords good control over fluorocarbon film properties.

Comparison of fluorocarbon film deposition by pulsed/continuous wave and downstream radio frequency plasmas

Fluorocarbon (FC) films have been deposited using pulsed and continuous wave (cw) radio frequency (rf) plasmas fed with hexafluoroethane (C 2F 6), octafluoropropane (C 3F 8), or octafluorocyclobutane (C 4F 8). The effects of feed gases used, discharge pressure, rf power, substrate positions and discharge modes (pulsed or cw) on the deposited films are examined. Film properties are determined using X-ray photoelectron spectroscopy, atomic force microscopy, and static contact angle measurements. The contact angles of FC films are well related to their compositions and structures. Feed gases used, discharge pressure, rf power, substrate positions and discharge modes strongly affect the morphology of the resulting film, as revealed by atomic force microscopy. Optical emission spectrometry measurements were performed to in-situ characterize the gas-phase compositions of the plasmas and radicals’ emission intensities during film deposition. Correlations between film properties, gas-phase plasma diagnostic data, and film growth processes were discussed. The film growth in pulsed or downstream plasmas was controlled by the surface migration of radicals, such as CF 2 towards nucleation centers, which result in the deposition of FC films with less cross-linked nature and rougher surfaces. These results demonstrate that it is possible to control film compositions and surface structure by changing deposition parameters.

MEMS packaging process by film transfer using an anti-adhesive layer

A low cost and low temperature thin film packaging process based on the transfer of an electroplated Nickel 3D cap is proposed. This process is based on adhesion control of a thick molded cap Ni film on the carrier wafer by using a plasma deposited fluorocarbon film, on mechanical debonding and on adhesive bonding of the microcaps on the host wafer with BCB sealing rings. Mechanical characterizations show that the transferred microcaps have a high stiffness, a low stress and a high adhesion. Because this process is simple and only involves a low temperature (250°C) heating of the host wafer, it is highly versatile and suitable for the encapsulation of micro and nano devices, circuits and systems elaborated on a large range of substrate materials.

Micro Pirani vacuum gauges manufactured by a film transfer process

A low cost and low temperature transfer process of electroplated Ni microstructures is presented. The process is based on adhesion control of molded Ni microstructures on donor wafer by using plasma deposited fluorocarbon film. Low temperature adhesive bonding of the microstructures on the target wafer using BCB sealing enables mechanical tear out from the donor wafer. Interest of this process is demonstrated here in the case of micro pressure sensors based on the Pirani principle. Suspended Ni electroplated microwires of 0.55 to 1.2 length, 10 μm width and 700 nm to 10 μm thickness were characterized into pressure dependant chamber. These sensors exhibit good sensitivity in the range of 0.1 to 100 mbar. The presented results thus demonstrate the interest of a simple film transfer process for elaboration of 3D microstructures.

Comparison of CH, C3, CHF, and CF2 Surface Reactivities during Plasma-Enhanced Chemical Vapor Deposition of Fluorocarbon Films

The overall character of films deposited using plasma-enhanced chemical vapor deposition relies on the interactions of gas-phase molecules with the depositing film surface. The steady-state surface interactions of CH, C3, CHF, and CF2 have been characterized at the interface of depositing fluorocarbon (FC) films using the imaging of radicals interacting with surfaces (IRIS) technique. IRIS measurements show that the relative gas-phase densities of CH, C3, CHF, and CF2 in mixed FC plasmas depend on the CH2F2/C3F8 ratio. Similar results are found using optical emission spectroscopy to monitor the production of excited-state plasma species. The effects of plasma parameters, such as the feed gas composition and substrate bias on the radical surface, were measured. Under all conditions, the surface reactivity for CH radicals is near unity, whereas those for C3, CHF, and CF2 exhibit very low surface reactivity but also show some dependence on experimental parameters. Under some conditions, CF2 and CHF are generated at the surface of the depositing film. Surface reactivity measurements indicate that CF2, CHF, and C3 may contribute to FC growth only when adsorbing at reactive sites at the film surface. Moreover, the low surface reactivities of singlet species such as C3, CF2, and CHF may be related to the electronic configuration of the molecules.

Chemistry in long residence time fluorocarbon plasmas

The densities of radicals and neutrals in fluorocarbon (FC) plasmas have been investigated in an inductively coupled plasma system to understand the predominant gain and loss mechanisms of dissociative products and their interaction with chamber surfaces. The input parameters varied in this experiment are the source to chuck gap and the F: C ratio of the feed gas. The densities of F, CF2, CF3, CF4, C2F4, SiF4, COF2, CO, and CO2 are measured and analyzed. In addition, two different forms of C4F8, the standard cyclic c and a radical linear l structures are observed in C4F8 containing plasmas. l-C4F8 is shown to be the primary dissociation product of c-C4F8 and, thus, cannot be neglected from calculations of the loss rate of c-C4F8 to electron collisions. This implies that the typically cited dissociative products of c-C4F8 (primarily C2F4) can have dual production channels: one from l-C4F8 and the other directly from c-C4F8. Furthermore, the measured density of CF4 shows strong correlation to the loss of F to the surfaces, indicating its primary production mechanism is from surface recombination. Similarly, CF3 is mainly produced from deposited FC film on chamber surfaces and lost to electron impact reactions. The etch products resulting from etch of the quartz window are shown, and an overall neutral density model is developed.

Surface modification of materials by dielectric barrier discharge deposition of fluorocarbon films

Dielectric barrier discharges have been used to deposit fluorocarbon (FC) films on various materials, such as paper, glass, and silicon substrates. The primary monomers used for plasma polymerization were difluoromethane (CH 2F 2), octafluoropropane (C 3F 8), and octafluorocyclobutane (C 4F 8). FC films were characterized using Fourier transform infrared spectroscopy, atomic force microscopy, static contact angle measurements, and scanning electron microscopy. Surface and structural properties of deposited films are strongly dependent on the plasma compositions and plasma parameters. FC films deposited on paper are to enhance its barrier properties and to achieve hydrophobic surfaces. Contact angle studies reveal that a minimum FC film thickness of about 200 nm on paper is required to completely cover surface and near-surface fibers, thereby providing the paper with long term hydrophobic character. In the C 3F 8 and C 4F 8 systems, the contact angles of the deposited films do not change appreciably with plasma parameters and are strongly dependent on the substrate roughness. Hydrogenated FC films deposited with CH 2F 2 plasmas show the relatively low contact angles due to the existence of CH X ( x = 1–3) groups.

Plasma deposition of fluorocarbon thin films using pulsed /continuous and downstream radio frequency plasmas

Fluorocarbon (FC) films deposited in continuous wave (cw) and pulsed difluoromethane radio frequency (r.f.) plasmas were characterized using Fourier transform infrared spectroscopy and atomic force microscopy. The effects of varying r.f. power, cw/pulsed discharge mode, and the distance of the substrate from the coil on the deposition rate, film structure, and surface roughness were investigated. These cw and pulsed deposition systems were characterized in-situ by means of optical emission spectroscopy. Emission intensities of H α, H β, H 2 and carbon-containing species in the coil region and downstream plasmas as a function of plasma parameters were measured. The hydrogen excitation temperature obtained from the relative emission intensities of H α and H β lines shows a clear dependence on the r.f. power and the substrate position. Correlations between film properties, gas-phase plasma diagnostic data, and film growth processes were discussed. Experimental results indicate that the film growth within the coil region in cw plasmas is controlled by the synergistic effect between energetic ions and low-energy species. The film growth in pulsed and downstream plasmas is controlled by the growth of coalesced nuclei via surface diffusion of adsorbed species, which results in the deposition of FC films with relatively rough surfaces.

Study of 193nm photoresist degradation during short time fluorocarbon plasma exposure III. Effect of fluorocarbon film and initial surface condition on photoresist degradation

The effect of fluorocarbon film and surface pretreatments on roughness formation of 193nm photoresist (PR) during short time fluorocarbon plasma exposure was investigated. The present work complements two earlier reports by this group on surface modifications of 193nm PR during plasma etching. The authors employed a shutter approach to minimize initial plasma transient effects on processing of PR surfaces. Surface chemical conditions after plasma etching were observed by x-ray photoelectron spectroscopy. The authors investigated the effect of deposited fluorocarbon film and pretreatments using several gas chemistries on PR roughening. Pretreated samples exhibited smaller roughness after plasma etching as compared to specimens processed without pretreatment. Three main mechanisms were identified for surface roughness reduction after pretreatment: (a) the formation of a fluorinated surface layer—having a large amount of fluorine on the PR surface at the beginning of the etch reduces PR surface roughening, (b) the improvement of durability of the PR under plasma exposure by removal of the ester group, and (c) a rapid fluorination and a reduction in the PR etch rate during the initial etch period due to the formation of a protective film on the top of the PR. The authors conclude from this work that the initial surface chemical state is an important factor that determines the degree of surface roughness formation for 193nm PR during the initial etch period.

Plasma enhanced CVD of fluorocarbon films by low-pressure dielectric barrier discharge

Low-pressure dielectric barrier discharge (DBD) plasmas have been used to deposit polymerized fluorocarbon (FC) films on silicon substrates. The effects of discharge pressure and frequency of power supply on the film quality have been systematically investigated. The deposited films were characterized by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and static contact angle measurements. Experimental results show that FC films with a less crosslinked structure may be deposited at a relatively high pressure. Increasing the frequency of power supply leads to a significant increase in the deposition rate. All deposited FC films with a uniform microstructure show the hydrophobic property. Decreasing the frequency of power supply or increasing the deposition pressure results in the deposition of FC films with the extremely low surface roughness. The relationship between plasma parameters and the analyzed properties of deposited FC films is discussed.

Study of 193nm photoresist degradation during short time fluorocarbon plasma exposure. I. Studies of modified layer formation

The mechanism of modified layer formation for 193nm photoresist (PR) during a short time (up to ∼10s) fluorocarbon plasma exposure was investigated. We employed a shutter approach to achieve rapidly steady-state plasma condition when processing PR surfaces. The time evolution of the optical constants and the thickness of the modified layer on the PR surface were obtained using two layer optical modeling of ellipsometric data for the processed PR material. This enabled us to determine the time-resolved etching rate of the PR and the kinetics of modified layer formation. The change in the surface chemical composition of the PR materials was determined by x-ray photoelectron spectroscopy (XPS). A graphitic layer with a higher refractive index as compared to the bulk PR material was formed on the PR surface within a few (∼3s) seconds of plasma exposure. The XPS data revealed that before a fluorinated surface developed, cleavage at ester groups of the side chain in the polymer and dangling bond formation took place, leading to cross-linking. To investigate the influence of the oxygen content of the polymer on surface roughness formation, we compared the surface evolution of oxygen-rich 193 and 248nm PRs, which have a smaller oxygen content. Remarkable differences in the etching behavior during the initial plasma interaction period were observed for the two materials. Whereas for 193nm PR, etching was observed immediately and the material exhibited higher surface roughness, for the 248nm PR material fluorocarbon film deposition took place initially. Once a fluorinated surface had developed, steady-state etching took place, but the 248nm PR exhibited lower surface roughness than the 193nm material. XPS measurements showed that when comparing the fluorine content of the surface layer to the oxygen content, the fluorine content was relatively more important for the 248nm PR than for the 193nm PR. For the latter, oxygen in the side groups of the bulk PR enhanced the PR etching rate initially and led to a rapid surface roughness formation. This coincides with the development of a fluorinated surface.

The characterization of fluorocarbon films on NiTi alloy by magnetron sputtering

Fluorocarbon films were deposited on nickel–titanium (NiTi) alloy substrate by radio-frequency (RF, 13.56 MHz) magnetron sputtering using a polytetrafluoroethylene (PTFE) target. The deposition parameters of fluorocarbon films including the RF power, the working gas pressure and Ar flow rate were systematically studied. The structure of the deposited films was studied by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). The surface morphology of the deposited films was measured by atomic force microscopy (AFM). The mechanical properties of the deposited films were characterized by a nanoindenter. C–F x and C–C units were found in the deposited fluorocarbon films, which corresponded to the results of XPS. The surface roughness of the fluorocarbon film was 7.418 nm (Ra).

Fluorine-doped SiO 2 and fluorocarbon low- k dielectrics investigated by SIMS

In this work, we present secondary ion mass spectrometry (SIMS) investigations of the incorporation of fluorine into thin SiO 2 films adapted as low- k dielectrics in the metal-oxide-semiconductor (MOS) devices. The insulating SiOF oxides with the thickness ranging from 1 up to 15 nm have been prepared by plasma-enhanced chemical vapor deposition (PECVD) and/or by reactive ion etching (RIE) methods on 〈1 0 0〉 oriented p-Si substrates with the use of either CF 4 or CHF 3 source of the plasma. SIMS experiments were performed using ultra-low energy (1 keV) argon ion beam and quadrupole mass analyzer. Depth profiles of the resulting dielectric films illustrate: (i) the incorporation of F into the SiO 2 matrix is accomplished by either the CHF 3 or CF 4 plasmas; (ii) no etching of SiO 2 matrix is observed by using of CHF 3; (iii) CHF 3 is a source of fluorocarbon film deposition on top of the SiO 2 that prevents the SiO 2 etching; and (iv) fluorine quantifications done based on implantation criteria give the maximum concentrations within the films from 6.0 × 10 18 to 2.4 × 10 20 atoms/cm 3 depending on the different fluoridation conditions. The F concentration in SiO 2 increases with the r.f. power of CF 4 or with decreasing a gas pressure of CHF 3 plasma.

Growth of Fluorocarbon Films by Low-Pressure Dielectric Barrier Discharge

Plasma polymerized fluorocarbon (FC) films have been deposited on silicon substrates from dielectric barrier discharge (DBD) plasma of C4F8 at room temperature under a pressure of 25∼125 Pa. The effects of the discharge pressure and frequency of power supply on the films have been systematically investigated. FC films with a less cross linked structure may be formed at a relatively high pressure. Increase in the frequency of power supply leads to a significant increase in the deposition rate. Static contact angle measurements show that deposited FC films have a stable, hydrophobic surface property. All deposited films show smooth surfaces with an atomic surface roughness. The relationship between plasma parameters and the properties of the deposited FC films are discussed.

Studies of fluorocarbon film deposition and its correlation with etched trench sidewall angle by employing a gap structure using C4F8∕Ar and CF4∕H2 based capacitively coupled plasmas

A high-aspect ratio, small gap structure that provides a sample surface region without direct ion bombardment has been used to study surface chemistry aspects of fluorocarbon (FC) film deposition and to simulate FC film deposition on trench sidewalls during plasma-based pattern transfer. As on the sidewalls of microscopic trenches being etched, thin FC layers form by arrival of reactive neutrals on the shadowed surface portions of the small gap structure. The deposition rates, composition, and chemical bonding of FC films formed in the small gap structure were determined by ellipsometry and x-ray photoemission spectroscopy as a function of process conditions for C4F8∕Ar and CF4∕H2 discharges produced in a dual frequency (40.68∕4MHz) capacitively coupled plasma reactor. Actual trench features were also produced using photoresist patterned organosilicate films for the same plasma processes. Scanning electron microscopy of the trenches shows a characteristic sidewall slope angle for different process conditions. We find that plasma process conditions producing lower FC film deposition rates on the shielded surface of the gap structure yield more vertical trench sidewalls. This relationship confirms the relevance of the small gap structure approach to the examination of trench sidewall chemistry. Since the present approach produces macroscopic samples of gap-deposited FC films, it enables direct surface chemical characterization of a material that is analogous to sidewall deposited films and allows to avoid the difficulties connected with direct measurements of microscopic samples. The lack of ion bombardment for the shielded deposition increases the retention of the chemical structure of the FC film precursors for the deposited films, which promises to be useful for obtaining mechanistic insights on film precursors.

Effects of X-ray radiation on the surface chemical composition of plasma deposited thin fluorocarbon films

Different thin fluorocarbon (FC) films were deposited on Si(111) using plasma polymerisation and then exposed to X-ray radiation. Changes in the chemical composition of the deposited fluorocarbon films as a function of irradiation time were investigated in situ using X-ray photoelectron spectroscopy. The evaluation of the C1s and F1s core level induced emission as a function of exposure to X-ray radiation (Mg Kα, hν = 1253.6 eV) reveals changes in the surface chemical composition of the FC polymer structure. The presented results indicate a high defluorination under X-ray irradiation. Additionally, binding energy shifts of the F1s and C1s peaks during the exposure associated with surface charging effects were observed. With ongoing exposure the surface charging decreases continuously and the FC surfaces become more conductive due to changes in the polymer structure. Different models have been used to describe the decomposition kinetics and surface composition.