G.-R. Yang

High deposition rate parylene films

The deposition rate of polymeric parylene films is shown to be a sensitive function of temperature and pressure. By keeping the substrate temperature below room temperature, we obtain more than one order of magnitude higher deposition rates than those obtained at room temperature. It is suggested that the higher deposition rates are due to the increased condensation of the monomer on the surface during growth. These results are consistent with a physical-chemical model of the kinetics of polymer-film formation.

Vapor deposition of parylene‐F by pyrolysis of dibromotetrafluoro‐p‐xylene

Structural characteristics of poly(tetrafluoroparaxylylene) (PA‐F) films deposited directly from C6H4(CF2Br)2 precursor have been studied using Fourier transform infrared spectroscopy (FTIR) and x‐ray photoelectron spectroscopy (XPS). Zn was used as the catalyst and the vapor pyrolysis of precursor was carried out between 350 and 400 °C. It is shown that the FTIR and XPS spectra of the PA‐F films deposited from the precursor are comparable to those made from the conventional dimer route. Dissociation of the PA‐F films does not occur up to an annealing temperature of 500 °C. Both Zn and Br contaminants were observed in the XPS spectra. However, we found that the Br contamination disappears after annealing to an elevated temperature (≥350 °C), while Zn impurities still remain in the film.

CHEMICAL INTERACTIONS AT TA/FLUORINATED POLYMER BURIED INTERFACES

In this letter, we study Ta/parylene-F (PA–F) buried interfaces using x-ray photoelectron spectroscopy. We found that the Ta–F bond was formed at the Ta/PA–F interface after depositing a layer of thin Ta film (<50 A). For the Ar+ or O2 plasma pretreated PA–F surface, in addition to the Ta–F bond, a Ta–C bond was observed at the buried interface after Ta metallization. The Ta–C bond may be responsible for the enhancement of Ta/PA–F adhesion.

IMPROVED GROWTH AND THERMAL STABILITY OF PARYLENE FILMS

Experimental results for the deposition of low dielectric constant Parylene-N and Parylene-F films are explained by a mechanism based on bulk phase diffusion reaction in the film. The deposition rate of Parylene-F decreases significantly as time increases and ultimately achieves steady state. Very favorable agreement with experiments at a substrate temperature of −10 °C is obtained for parylene-F with a rate constant of kf=5×10−5/s, and a diffusion coefficient Df=1.3×10−8 cm2/s. In contrast, the much higher rate constant at room temperature for Parylene-N films is kf=0.16/s and the predicted deposition rate is constant after a very small period of time (tss<4/kf=25 s). This prediction is confirmed by the experiments. The model predicts correctly that low deposition temperatures improve both the deposition rate and thermal stability of Parylene films. Our experiments confirm this prediction and one obtains both high growth rates and high molecular weight films at lower deposition temperatures. Furthermore,...

INTERACTION OF AMORPHOUS FLUOROPOLYMER WITH METAL

The bonding structure of an amorphous fluoropolymer, AF 1600, with Al, Ag, Au, and Cu were examined using x‐ray photoelectron spectroscopy. 100 A thick films of AF 1600 were deposited on various metal films. AlF3 was found at the AF 1600/Al interface. F detached from the −CF3 functional group of the AF 1600, diffused into the Al/Al2O3 matrix and formed AlF3. The diffusion depth of F is estimated to be ≳150 A. An Al film was evaporated onto an AF 1600 film. The Al film was then mechanically peeled off and the remaining polymer surface examined. AlF3 was again found. For the spin‐on AF 1600 film on Ag, Au, and Cu, no chemical reaction between the metal and the polymer were found.

XPS and AFM study of chemical mechanical polishing of silicon nitride

Abstract In this paper, the effect of chemical–mechanical polishing (CMP) of silicon nitride films was investigated using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Silicon nitride films with different deposition methods (PECVD and LPCVD) and two different silica-based slurries were studied. The surface chemical structure of as-deposited LPCVD film is slightly better than that of as-deposited PECVD film, and the surface morphologies (RMS roughness ∽0.3 nm for LPCVD film, and 1.9 nm for PECVD film) are much different. After CMP, the LPCVD film was more dramatically oxidized, and the surface became rougher for the process conditions used. The PECVD film was less dramatically oxidized, a subsilicon nitride (SiNx) appeared on the surface, and the surface became smoother. These results suggest that the quality of as-deposited nitride film, as well as the CMP process conditions, impact significantly on the quality of the polished surface.

Study of silver diffusion into Si(111) and SiO2 at moderate temperatures

Diffusion of Ag from epitaxial layers into Si(111) is studied under an anneal of 450–500 °C using the secondary ion mass spectrometry depth profiling tool. The measurements yielded values of the diffusion constant (0.80–1.6 × 10−15 cm2/s) which fall short of literature values extrapolated from higher‐temperature Arrhenius laws. Diffusion of Ag into SiO2 was also measured directly. The observed diffusivity of 1.0 × 10−15 cm2/s is a factor of ∼ 105 smaller than expected from previous determinations of the diffusivity of Ag+ in SiO2 obtained from anneals in forming gas. The discrepancy may be due to changes in the local electrostatic environment in the absence of acceptor levels in SiO2 from dissolved gases which are absent in vacuum.

X-ray photoelectron spectroscopy study of Al/Ta2O5 and Ta2O5/Al buried interfaces

Buried interfaces of thin Al/Ta2O5 and Ta2O5/Al films were studied using the x-ray photoelectron spectroscopy technique. The peak decomposition technique was employed to identify the composition and chemical states at the interface region. It was observed that there is an “intermixing layer” at the Al/Ta2O5 interface, where Ta2O5 has been reduced to lower binding energy states due to the reaction of Al with Ta2O5 during deposition. On the other hand, the Ta2O5/Al interface is relatively stable, consisting of Ta2O5 and Al2O3 interfacial layers. Based on a uniform multilayer structure model, the thickness of the interfacial layers was estimated by using the relative photoelectron intensities.

Surface reaction and stability of Parylene N and F thin films at elevated temperatures

The morphology and chemical structure of Parylene F and Parylene N films annealed in air, N2, and vacuum were examined. The decomposition temperatures of Parylene N in air, N2, and vacuum were determined to be 175,350, and 425°C, respectively. The decomposition temperatures of Parylene F in air and N2 were determined to be 400 and 500°C, respectively. For both materials, the decomposition process with and without the presence of O is different. In the case of Parylene N, O diffuses into the materials and reacts with the C in the polymer. In the case of Parylene F, no reaction products with O are observed on the surface. Annealing at the decomposition temperature resulted in the decomposition of -CF2- functional groups to -CF- functional groups in the Parylene F. Thicker films,< μ, of either material cracked during annealing while films <0.5 μ, remained smooth and transparent. Pinholes were also observed in the Parylene F film deposited using the Gorham method after annealing.

Secondary ion mass spectrometry study of the thermal stability of Cu/refractory metal/Si structures

Evidence is presented for the blocking of Cu diffusion into SiO2 and Si by Ta and Ta/W barriers. The anneal was performed at 450 °C for 30 min. Here, W is rejected as a potential barrier for Cu technology. A Cr layer as thin as 200 A is shown to limit diffusion into Si to ∼600 A. The study also demonstrates the utility and versatility of secondary ion mass spectrometry for evaluating potential diffusion barriers, and the need for such corroborative characterization in light of the lesser sensitivity of Rutherford backscattering spectroscopy.