光学玻璃基底原子层同质材料沉积薄膜光谱及激光诱导损伤特性研究

Spectral and Laser-Induced Damage Characteristics of Atomic Layer Deposited SiO_(2) Films on Fused Silica Glass

通过原子层沉积技术在熔石英玻璃表面制备了同质材料的单层SiO_(2)薄膜,对光学薄膜的物理化学性质和强激光辐照下的激光诱导损伤性能进行了深入研究。实验中采用双叔丁基氨基硅烷(BTBAS)和臭氧(O_(3))作为反应前驱体,在熔石英光学元件表面进行了SiO_(2)薄膜的原子层沉积工艺研究,以不同沉积温度条件制备了一系列膜样品。首先对原子层沉积特性和薄膜均匀性展开了研究,发现薄膜生长厚度与沉积循环次数之间符合线性生长规律,验证了制备薄膜的原子级逐层生长特性,并且表面沉积膜层的均匀性很好,其测得膜厚波动不超过2%。然后针对不同温度条件下沉积的SiO_(2)薄膜,对其粗糙度及各类光谱特性展开了研究,对比结果表明:样品的表面粗糙度在镀膜后有轻微的降低;薄膜样品在200~1000 nm范围内具有出色的透过率,均超过90%并逐渐趋近于93.3%,且其透射光谱与在裸露熔石英衬底上测得的光谱没有明显差异;镀膜前后荧光光谱和傅里叶变换红外光谱的差异证实了原子层沉积SiO_(2)膜中点缺陷(非桥键氧、氧空位、羟基等)的存在,这将会影响薄膜耐损伤性能。最后对衬底和膜样品进行了紫外激光诱导损伤测试,损伤阈值的变化表明熔石英元件表面沉积薄膜后的激光损伤性能有所降低,其零概率损伤阈值从31.8 J·cm^(-2)减小到20 J·cm^(-2)左右,与光谱缺陷情况表征相符合。薄膜中点缺陷部位会吸收紫外激光能量,导致局域温度升高,进而出现激光诱导损伤现象并降低抗激光损伤阈值。在选定的沉积温度范围内,较高温度条件下沉积的SiO_(2)薄膜其激光诱导损伤性能更好,可以控制沉积温度条件使得元件的抗损伤性能更为接近衬底本身,后续有望通过其他反应参数的优化来获得薄膜抗损伤性能的进一步提升。

In this paper,single-layer SiO_(2) films of homogeneous material were deposited on the surface of fused silica glasses by atomic layer deposition(ALD)technology.The physical and chemical properties of the optical films and the laser induced damage performance under laser irradiation were deeply researched.Bis-tert-butylaminosilane(BTBAS)and ozone(O_(3))were chosen as reaction precursors in the experiment,and ALD prepared a series of film samples under different temperature conditions.Firstly,a study on the characteristics of ALD and the uniformity of the films was carried out.It was found that the film growth thickness and the number of deposition cycles conformed to the linear growth,which verified the atomic layer-by-layer growth characteristics of the ALD.The uniformity of the deposited film on the surface is fine,while the error does not exceed 2%.Then,for the SiO_(2) films deposited at different temperatures,the roughness and various spectral characteristics have been tested.The comparison results show that the surface roughness of the sample is slightly decreased after coating.The ALD film samples have excellent transmittance in the range of 200 to 1000 nm,both exceeding 90%and gradually approaching 93.3%,and their transmission spectrum is not significantly different from the spectrum measured on a bare fused silica substrate.The difference between fluorescence spectrum and Fourier transform infrared(FTIR)spectrum before and after coating confirms the existence of point defects(non-bridging oxygen,oxygen vacancies,hydroxyl,etc.)in the SiO_(2) films deposited by ALD,which will affect the film damage resistance performance.Finally,ultraviolet laser-induced damage tests were performed on the substrate and film samples.Results of damage performance show that the laser induced damage threshold of the thin film deposited on the surface is reduced,and the zero-probability damage threshold is decreased from 31.8 J·cm^(-2) to about 20 J·cm^(-2),which is consistent with the characterization of spectral defects.The point defect in the film will absorb ultraviolet laser energy,causing the local temperature to rise,and then the threshold of laser damage resistance is reduced while the phenomenon of laser-induced damage occurs.Within the selected deposition temperature range,SiO_(2) films deposited at higher temperature seem to have better damage performance.The deposition temperature conditions can be controlled to make the samples’damage performance closer to the substrate itself.It is expected that the optimization of other reaction parameters will further improve the film damage performance.