Study On The Effect Of Gas Phase Chemistry On Diamond Film Growth By Hot Filament CVD

In this article,the effect of deposition pressure,carbon source and gas flow rate on diamond film growth by hot filament chemical vapor deposition were studied.Methane,acetone and hydrogen were used as reaction gas.In order to analysis the relationship between the changes of redical and diamond film growth,the OES was used to diagnose the plasma state.The effect of different gas flow rate on the diamond film deposition in confined space was studied under a self-made confinement space deposition device.The study of diamond film deposition at low temperature was studied while keeping the temperature of substrate at 660 ?.The whole results were characterized by scanning electron microscope,Raman spectroscopy.Research showed:(1)In the hydrogen and methane system,the lower deposition pressure can get higher active group concentration,energy,deposition rate,and secondary nucleation,the size of grain was nanoscale,but the content of non diamond phase is higher.With the increase of pressure,the electron temperature and growth rate decreased,the grain size increases.The reason is the relative ratio of active hydrogen atoms and carbon groups increases madethe power of etching improved,and the quality of films increased.(2)Compare with the carbon source acetone and methane at equal volume fraction,the deposition rate of acetone system was significantly higher than which in the methane system.When compare with the acetone and methane at equal carbon number fraction,the volume fraction of acetone is one third of methane.At this situation,the acetone also occupied the advantage obviously,shwoed higher deposition rate and quality of the diamond film.The lower cracking energy of acetone and stronger selective etching effect of OH and atomic O,these two reason made sure that higher deposition rate and quality.At the same time,no matter the acetone or the methane system,the deposition rate increases and the film quality decreases with the increase of carbon source concentration.(3)In the hydrogen and acetone system,the reaction gas pressure was kept constant,and the gas flow rate was increased by increasing the gas intake.Set the flow rate range at 86-590 sccm,the film growth rate and quality increased firstly with the gas flow rate increased and then decreased.Due to the large volume of the reaction chamber,the state of the air flow has not changed significantly.Based on this,we placed the hot filament,reactive gas,and substrate wafer are in a self-made slit confinement space,so that the variation range of the air flow increased.With the air flow rate increased,the deposition rate increased greatly at first,then it decreased.In the restricted mode,the deposition rate was significantly increased,and the maximum rate of 6.31 ?m/h was obtained at the gas flow rate of 230 sccm while ensuring good quality.The grain size of diamond was micro level at low gas flow rate,and nano level would obtain at the high flow rate.This result provides a relatively high speed method for the preparation of micron-nano composite membranes by hot filament CVD.(4)Pure aluminum sheet was used to measure the temperature and monitor the substrate temperature at 660°C.With the condition that the water cooling effect of the substrate table is constant.With the smaller distance between hot filament and substrate,and the power of hot filament,the growth mode tends to be higher secondary nucleation and wuch of small crystal clustered together and grow up;while at larger distance and higher power,active carbon-containing groups tend to participate in the continued growth of the original diamond grains.For medium and large scale,the optimal combination of conditions for this experiment is a distance of 5mm and a hot filament power of 288 W,but the average deposition rate is only 1.37?m/h.Using the confined space growth mode at 660°C,the deposition rate was significantly increased to 1.94 ?m/h.Raman spectroscopy results showed that the film quality was qualified.