Agnieszka Walkiewicz-Pietrzykowska

Reactivity of Alkylsilanes and Alkylcarbosilanes in Atomic Hydrogen‐Induced Chemical Vapor Deposition

A number of alkylsilanes and alkylcarbosilanes of widely different molecular structure are characterized in terms of their ability to the formation of amorphous hydrogenated silicon-carbon (a-Si:C:H) film in atomic hydrogen-induced chemical vapor deposition. The compounds containing only the Si-C bonds or four-membered carbosilane rings appear to be inactive, while those with the Si-Si or Si-H bonds are capable of the a-Si:C:H film-formation. The reactivity of the latter group of compounds is characterized by the deposition yield parameter determined at the constant and variable feeding rates. Based upon the reactivity data a mechanism for the initiation step is proposed.

Mechanism of the Initiation Step in Atomic Hydrogen-Induced CVD of Amorphous Hydrogenated Silicon–Carbon Films from Single-Source Precursors

A number of alkylsilanes and alkylcarbosilanes of widely different molecular structure are characterized in terms of their ability to form amorphous hydrogenated silicon–carbon (a-Si:C:H) films in atomic hydrogen-induced chemical vapor deposition (AHCVD). The compounds containing only Si–C and C–H bonds in the molecular skeleton appear to be inactive, while those with Si–Si or Si–H bonds are capable of a-Si:C:H film formation. The reactivity of the latter group of compounds is characterized by determining the AHCVD′s rate constants. For most of the investigated source compounds AHCVD was found to be a non-thermally activated process. Based upon the values of the rate constant and the identified low-molecular-weight and oligomeric products of AHCVD, a mechanism of the initiation step, as well as the nature of resulting film-forming precursor are proposed.

Mechanical and Tribological Properties of Thin Remote Microwave Plasma CVD a-Si:N:C Films from a Single-Source Precursor

Silicon carbonitride (a-Si:N:C) films produced by remote plasma chemical vapor deposition (RP-CVD) were investigated. Tetramethyldisilazane as a single-source precursor and (H2+N2) upstream gas mixture for plasma generation were used. The influence of the upstream gas composition on the structure, density, mechanical and tribological properties of the films deposited on p-type Si (001) wafers (both heated—Ts=300°C and unheated—Ts=30°C) are reported. The H2 RP-CVD process was found to result in the formation of outstanding low friction (μ≈0.04) and high hardness (H=27-31 GPa) a-Si:N:C films exhibiting promisingly high H/E values.

Mechanism of Amorphous Silica Film Formation from Tetraethoxysilane in Atomic Oxygen‐Induced Chemical Vapor Deposition

Atomic oxygen-induced chemical vapor deposition (AOCVD), using tetraethoxysilane (TEOS) as single-source compound, was investigated to get insight into the mechanism of silica film growth. In particular, an effort was made to elucidate the chemical nature of silica film-forming precursors. AOCVD, selected as a model process suitable for mechanistic study, has been examined in terms of the effects of atomic oxygen concentration, of the contents of the ground and excited state oxygen atoms in atomic oxygen fraction, and of thermal activation. The growth rate of silica film does not depend on the composition of the atomic oxygen fraction, but is proportional to the total concentration of atomic oxygen fed into the CVD reactor. In the light of the apparent activation energy (E a ) values calculated from the Arrhenius plots of the substrate temperature dependencies of film growth rate, the mechanism of AOCVD is related to the concentration of atomic oxygen. The near zero E a value found at low concentration of atomic oxygen (1.5 × 10 1 cm -3 ) implies that AOCVD is not a thermally activated process; diffusion of the precursors from the gas phase to the substrate seems to be the ratelimiting factor of AOCVD under these conditions. Apparently negative E a values observed for high concentrations of atomic oxygen(≥9.7 × 10 14 cm -3 ) indicate that the adsorption of the precursors onto the growth surface is the main factor controlling the rate of AOCVD. Reaction products of the gas-phase conversion of TEOS, investigated by high-resolution gas chromatography/mass spectrometry, revealed the presence of linear and cyclic siloxane oligomers, containing the -(EtO) 2 SiO- repeating unit. The structure O identified oligomers, results of the study of TEOS reactions with atomic oxygen, the structure of the deposited film, chemiluminescence spectra of the gas-phase products in the CVD reactor, and the results of step coverage tests, point to diethoxysilanone (a high reactivity intermediate) and hexaethoxydisiloxane (a high surface mobility, low reactivity intermediate) as the major precursors of silica film growth.

Hard and High-Temperature-Resistant Silicon Carbonitride Coatings Based on N-Silyl-Substituted Cyclodisilazane Rings

l,3-bis(dimethylsilyl)-2,2,4,4-tetrametyhylcyclodisilazane was used as a single-source precursor for the production of silicon carbonitride (SiCN) thin-film coatings by remote microwave hydrogen plasma chemical vapor deposition (RP-CVD). The effect of the substrate temperature (Ts) on the rate and yield of the RP-CVD process, chemical composition, chemical structure, and surface morphology of the resulting film is reported. The temperature dependencies of the thickness-based growth rate and growth yield of the film imply that for the low substrate temperature range (35 ≤ T S < 200°C), film growth is limited by adsorption of film-forming precursors, whereas in the high substrate temperature range (200 ≤ T s ≤ 400°C), film growth is independent of the temperature and RP-CVD is a mass-transport limited process. The increase of the substrate temperature from 35 to 400°C causes the elimination of organic moieties from the film and the formation of the Si-C network, which contains incorporated N-silyl-substituted cyclodisilazane molecular skeletons of the precursor linked with the network via the Si-C bonds. The microscopic examination revealed that the films are defect-free materials of excellent morphological homogeneity and exhibit small surface roughness, which vary in a narrow range of values. The SiCN films deposited at various substrate temperatures were characterized in terms of their density, adhesion to a substrate, hardness, elastic modulus, and friction coefficient. The film properties are strongly influenced by the compositional and structural parameters represented, respectively, by the contents of nitrogen and Si-C bonds; the latter described by the relative integrated intensity of the Si-C infrared band. The reasonable relationships between the film properties and the mentioned compositional and structural parameters have been determined.

Type of precursor and synthesis of silicon oxycarbide (SiOxCyH) thin films with a surfatron microwave oxygen/argon plasma

Siliconelike thin films (i.e., SiOxCyHz) were prepared in a microwave plasma enhanced chemical vapor deposition reactor from structurally different organosilicon precursors [i.e., hexamethyldisiloxane (HMDSO), dimethylsilane (DMS), and tetramethylsilane (TMS)]. The films were deposited at room temperature by using different oxygen/argon ratios in the plasma gas. By changing the type of precursor and the relative concentration of oxygen in the plasma, thin films with different compositions (i.e., O∕C ratio) and properties are obtained. In general, raising the oxygen concentration in the plasma produces the progressive removal of the organic moieties from the films whose composition and structure then approach those of silicon dioxide. The deposition rate was highly dependent on the type of precursor, following the order HMDSO⪢DMS>TMS. The polarizabilities, optical band gaps, and surface free energy of the films also depended on the thin film composition and structure. It is proposed that the Si–O bonds exi...