Hot Filament CVD System Research Articles

Effect of methane concentration on mechanical properties of HFCVD diamond-coated cemented carbide tool inserts

CVD diamond-coated cemented carbide inserts are on the verge of becoming the next generation of tools used for high-speed hard-cutting processes. Good adhesion of the diamond coating, and consistency on the micro-level of the CVD process are the current challenges which to a certain extent prevent these coated tools from becoming an off-the-shelf product. In this work, we report preliminary results of the effect of methane concentration variation on the surface roughness, adhesion, residual stress, and turning performance for diamond-coated inserts. Cemented carbide inserts with 5% cobalt were coated with diamond films using an inexpensive hot filament CVD system. The methane concentration in the reaction mixture was varied from 1 to 9%. The results suggest that the optimal mechanical performance of diamond-coated inserts can be achieved when diamond is deposited at a methane concentration of about 3%.

Method for achieving high selectivity and resolution in selectively deposited diamond films

A process for depositing CVD diamond selectively on silicon is presented. Using standard photolithography techniques, wafers are patterned with 0.6 μm resist features. Chromium is then deposited through electron beam evaporation and lifted off of the desired growth areas with acetone. After scratching with 0.5 μm diamond powder, the chrome film is etched off and diamond deposited in a hot filament CVD system. Micrographs demonstrating a high degree of selectivity and micron-scale resolution are presented. These include contiguous, single crystallite wide lines and square arrays of individual nuclei with 10 μm periodicity

Simulation of homoepitaxial growth on the diamond (100) surface using detailed reaction mechanisms

One-dimensional reactive-flow simulations of a hot-filament CVD-system including detailed surface reaction mechanisms for homoepitaxial diamond growth are carried out. A growth model for the diamond (100) surface based on elementary chemical reactions steps is introduced. This surface reaction scheme includes the incorporation of the CH 3 radical in the diamond lattice. Homoepitaxial growth on the (100) surface is modelled for a wide range of experimental reactor parameters. The experimental growth rates are compared with simulations for two different surface reaction schemes. It is found that the scheme based on growth at monoatomic steps on the reconstructed (100) surface is more realistic. It shows qualitative agreement with experimental data, whereas the more simple mechanism for an unrealistic unreconstructed (100) surface cannot explain the surface temperature dependence of the growth rate correctly.

Deposition of Diamond Films in a Closed Hot Filament CVD System.

A closed system hot filament chemical vapor deposition (CVD) reactor has been used to deposit diamond films on silicon substrates. A fixed charge of hydrogen gas is fed into the deposition system until the desired deposition pressure level is reached. A solid graphite cylindrical rod held above the tungsten filament was the carbon source. System parameters for diamond film growth have been determined. The diamond structure of the films has been verified by x-ray diffraction (XRD). Morphology typical of CVD diamond films has been observed in scanning electron microscopy (SEM). The quality of the diamond films has been evaluated by micro-Raman spectroscopy.

Methyl radical production in a hot filament CVD system

The absolute concentration of methyl radicals is measured in a hot filament chemical vapor deposition system for a range of filament temperatures and input gas compositions by using ultrasensitive optical absorption with a multi-element detector at wavelengths near 216 nm. The results yield effective activation energies for CH 3 production and indicate that CH 3 production is dominated by the gas-phase atomic hydrogen abstraction reaction when the input gas contains CH 4 and H 2. We find that passing ≈ 1% tert-butyl peroxide in H 2 over a hot filament is also an efficient CH 3 source, and has an activation energy similar to the activation energy for the production of CH 3 from CH 4.

Deposition of diamond films with controlled nucleation and growth using hot filament CVD

Abstract High quality diamond films have been deposited by sequentially switching between high and low oxygen feed to a hot filament CVD system with constant hydrogen and methane flow rates. Since a high oxygen feed is effective in etching non-diamond components in a growing diamond film, a computer can be used to control the switching between a high oxygen-content gas mixture, which is used for etching, and a low oxygen-content gas mixture, which is used for deposition, in order to achieve a higher growth rate of diamond deposition without sacrificing the diamond quality. SEM photographs and Raman spectra show that by decreasing the period of each cycling time, better diamond films are obtained. Using a cycling time of less than one minute, diamond films of the same high quality are deposited at a higher growth rate. A short cycling time is necessary to remove undesirable non-diamond components in time, in order to grow high quality diamond films at high rates by the hot filament CVD method. The high oxygen-content cycle of the CVD process reduces the density of secondary nucleation and leads to diamond films with larger grain sizes and clearer crystal facets.