M. Anderle

Anomalous diffusion of fluorine in silicon

The diffusion of ion implanted F in Si has been studied by the use of secondary ion mass spectroscopy and thermal desorption spectroscopy. In the dose range studied (below amorphization threshold), F exhibits an anomalous out‐diffusion behavior which is characterized by the depletion of F in Si substrate at temperatures ≥550 °C with complete suppression of diffusion deeper into the bulk of Si. F species which migrate to the surface react with native oxide and Si to form volatile Si oxyfluoride and Si fluoride, which then evaporate from the surface. There is clear evidence that the formation of Si oxyfluoride correlates strongly with the thermally activated anomalous migration of F. While the driving force for the anomalous F migration has not yet been identified, it appears that the electric field is not a dominant mechanism.

Damage of ultralow k materials during photoresist mask stripping process

Plasma-based ashing of photoresist masks after pattern transfer is a common processing step in the fabrication of integrated circuits. In this work we investigated damage mechanisms of nanoporous ultra low k (ULK) materials with different overall porosities due to the ashing process. Oxygen-, nitrogen- and hydrogen-based photoresiststripping using direct and remote plasma processes were examined. Ellipsometry, x-ray photoelectron spectroscopy,secondary ion mass spectroscopy, and transmission electron microscopy were utilized to study the damage layer thickness, physical (pore morphology), and chemical modifications of the nanoporoussilica thin films after exposure to the O 2 -, N 2 - or H 2 -based ashing processes. As a result of the plasma exposure, carbon groups in nanoporoussilica can be removed from the ULK layers which is also accompanied by material densification. We find severe ashing damage of ULK materials after O 2 -based ashing using both direct and remote discharges. N 2 and H 2 discharges also damage ultralow k materials for direct plasma ashing processes which are accompanied by low energy ion bombardment of the substrates. The introduction rate and degree of the ULK materials modifications correlates with the overall porosity. We show that the pore interconnectivity is one of the key parameters that determine ashing damage. ULK damage is greatly reduced for remote N 2 or H 2 discharges, but the resist removal rates are impractically low if the substrate is at room temperature. We show that both acceptable photoresist stripping rates and ULK damage levels can be achieved for remote H 2 plasma ashing processes if the substrate temperature is 250 ° C and higher.

Subatmospheric chemical vapor deposition ozone/TEOS process for SiO2 trench filling

Ozone/TEOS thermal chemical vapor deposition (CVD) has been investigated for SiO2 deposition on Si, using a cold‐wall research reactor equipped to determine the effects of precursor concentration, deposition temperature (300–500 °C), and pressure (30–200 Torr) on deposition rates, etch rates, and step coverage in the regime of subatmospheric CVD (SACVD). Deposition rates first increase with substrate temperature then reach a maximum and finally decrease distinctly at higher temperatures, with the latter reflective of reactant depletion in the gas phase. Wet etch rates decrease at higher deposition temperature and higher ozone/TEOS ratio, indicating improved film quality under these conditions. Elevated deposition temperatures significantly improves step coverage in high‐aspect‐ratio trenches, but decreases deposition rates. Deposition rates increase and then saturate with TEOS concentration, suggesting rate‐limited behavior associated with lack of ozone.

Role of implantation‐induced defects in surface‐oriented diffusion of fluorine in silicon

Open‐volume defects introduced in Si(100) crystals during fluorine implantation were investigated by variable‐energy positron beam depth profiling. The behavior of the implantation‐induced lattice defects upon high temperature annealing and their role in the surface‐oriented diffusion of F impurities were examined. The defects become mobile and undergo recovery at temperatures below 550 °C, i.e., well before the onset of fluorine diffusion as seen by secondary ion mass spectroscopy (SIMS) profiling. This behavior suggests that after irradiation and annealing the fluorine occupies substitutional sites to which positrons are insensitive. The anomalous F diffusion seen in SIMS has been explained through a two‐step diffusion mechanism, in which the diffusion kinetics is determined by dissociation of the substitutional F into an interstitial F and a vacancy, followed by a rapid diffusion of the interstitial F and the vacancy through the crystal to the surface.

Structural and compositional study of B–C–N films produced by laser ablation of B4C targets in N2 atmosphere

Abstract In this work, we report on a structural and compositional characterization of B–C–N thin films deposited by laser reactive ablation of a B4C target, in low-pressure (5 Pa) nitrogen atmosphere. For target ablation, a KrF excimer laser (λ=248 nm, τ=20 ns) has been used, at the fluences of 6 and 12 J/cm2. Films have been deposited on silicon 〈100〉 substrates at room temperature. Scanning electron miroscopy (SEM), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and Fourier transform-infrared spectroscopy (FT-IR) characterization techniques were used to analyze the composition and the structure of the deposited films. The film results to be a mixture of sp2/sp3 BN and sp2/sp3 nitrogenated C phases. The concentration of the different BN phases depends on the used laser fluence for the deposition of the film.

Investigation of surface modifications of 193 and 248nm photoresist materials during low-pressure plasma etching

Plasma-based pattern transfer of lithographically produced nanoscale patterns in advanced photoresist materials is often accompanied by photoresist surface roughening and line edge roughening due to factors which are not well understood. We have studied the evolution of surface roughening in prototypical 193 and 248nm photoresist materials during plasma processing as a function of plasma operating parameters. We used real-time ellipsometry and mass spectrometry, along with atomic force microscopy, x-ray photoemission spectroscopy and time-of-flight secondary ion mass spectrometry in an effort to understand the morphological and chemical changes of the photoresist materials as a function of plasma–surface interactions parameters, e.g., maximum ion energy, total energy flux, and plasma chemistry, and photoresist material. A comparison of 248nm photoresist with 193nm photoresist shows that significantly more surface roughness is introduced in the 193nm photoresist for most plasma processing conditions invest...

Influence of C4F8/Ar-based etching and H2-based remote plasma ashing processes on ultralow k materials modifications

The authors evaluated photoresist (PR) stripping processes that are compatible with ultralow dielectric constant (ULK) materials using H2-based remote plasmas generated in an inductively coupled plasma reactor. The materials used were 193 nm PR and nanoporous SiCOH-based ULK (JSR LKD 5109). PR ashing rates and ULK damage (carbon depletion) were measured for H2, H2/N2, and H2/Ar discharges as a function of substrate temperature over the range of 200–275 °C. They employed ellipsometry, x-ray photoelectron spectroscopy (XPS), optical emission spectroscopy, and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) for analysis. For their H2 remote plasmas and a substrate temperature in the range of 200–275 °C, the PR ashing rate varied from 270 to 880 nm/min, whereas 3–5 nm of ULK damage was measured for 20 s remote plasma exposure. As a useful process metric, they defined ashing efficiency as the thickness of PR removed over the thickness of ULK simultaneously damaged. PR stripping processes can be optim...

Mechanical and tribological properties of CNx films deposited by reactive pulsed laser ablation

We report the tribological, mechanical, structural and compositional characteristics of CNx films deposited by excimer laser (XeCl, ? = 308 nm, TFWHM = 30 ns) ablation of a graphite target in N2 at ...

Real-time process and product diagnostics in rapid thermal chemical vapor deposition using in situ mass spectrometric sampling

Mass spectrometry has been exploited for rapid real‐time sensing of both reactant and product species in single‐wafer rapid thermal chemical vapor deposition (RTCVD) of polycrystalline Si from SiH4. Active mass spectrometric sampling at pressures to 5 Torr is achieved using two‐stage differential pumping of a sampling aperture in the exhaust stream, leading to response times as short as ∼3 sec to concentration and pressure changes in the reactor during a process carried out in ∼30 sec. In addition to reactant species, gaseous reaction byproducts have been identified and differentiated from cracking fragments of the reactant through relative intensities of mass fragments as a function of wafer temperature (i.e., reaction rate). For RTCVD of poly‐Si from SiH4, carried out in the range 450–800 °C at 5 Torr in 10% SiH4/Ar, mass spectra reveal not only the time dependence of reactant (monitored by SiH2+, 30 amu), but also—at higher temperatures—reactant depletion and product generation (from H2+, 2 amu). These...

Integration of benzocyclobutene polymers and silicon micromachined structures using anisotropic wet etching

Integration of thick, low-k dielectric benzocyclobutene (BCB) film with deep etched structures in silicon allows the fabrication of microelectromechanical systems (MEMS) devices with low parasitic loss. A fabrication process is developed for integration of 1-μm-thick BCB low-k dielectric film and 200-μm-deep anisotropically etched grooves in silicon with potassium hydroxide (KOH). In order to protect the low-k film during the highly corrosive, long, high-temperature KOH etching process, gold (Au) is used as an etch mask. Chromium (Cr) is used to improve the adhesion of Au to the underlying BCB layer. Metal-BCB adhesion is the key parameter in this masking design. Partial cure of BCB at 210 °C for 40 min with appropriate surface treatment (adhesion promoter) prior to metallization and full cure at 250 °C for 1 h after metallization, together with Cr/Au sputtering at 200 °C, improves the adhesion dramatically. The adhesion strength of metal films to BCB was experimentally verified in a qualitative manner. V...