Preparation Of Ultra-broadband Antireflection Coating By PECVD

Plasma enhanced chemical vapor deposition as an optical thin-film deposition techniques gradually has been used to prepare a dense high-quality optical films of large area and high-damage threshold, such as optical filters, antireflective coating. The optical coating are deposited on silicon and K9glass substrate by PECVD for discussing the optical characteristics of low-index, high-index, gradient index films and analyzing the influence of different process parameters on the refractive index, index profile, extinction coefficient. The article systematically discusses the design methods of ultra-broadband antireflection coatings which are prepared by PECVD. The results are as follows:1) SiO2film is deposited on silicon substrate by PECVD. The test results show that increasing C2F6flow may reduce the refractive index of the thin film while the reaction precursor of SiH4and N2O contained. The refractive index and extinction coefficient of coating are1.37and4*10-4respectively at550nm when the temperature is300℃, RF power is200W, pressure is20Pa and the flow rate of SiH4, N2O4and C2F6are60sccm,40sccm,30sccm respectively. This fluoridation silicon oxide flim can be used as a kind of low-index optical thin film material.2) SiNx:H film is deposited by PECVD on silicon and K9glass substrate. The test results show that the highest refractive index among the Si3N4:H film is1.93with the extinction coefficient less than10-5. With the increase in the SiH4flow, the refractive index will increase while the amorphous silicon component will introduce more increase in the extinction coefficient. With the increase in the N2flow, the composition will tend to Si3N4film.3) MATLAB simulation results show that inhomogeneous coating can smooth the transmittance curve of antireflection coating. The SiOxNy as graded-index films are deposited with reaction precursor of SiH4, N2O, and N2flow. The SiH4flow rate is fixed on40sccm. The ratio of N2and N2O flow changes from50:0to0:50gradually. The test results show that the index change between1.46and1.97as the ratio of N2and N2O flow increasing. 4) Ultra-broadband antireflection coating of which the bandwidth span from450nm to900nm is designed by MATLAB with Fourier transform method, mixed design method, genetic algorithm. The design peak transmittance is99.7%and the average transmittance is98.8%. When the actual ultra-broadband antireflection coating which make up of SiOF, SiNx and SiOxNy is deposited on both side of K9glass by PECVD, its peak transmittance and average transmittance are98.9%and of96.8%respectively.