CCD蓝敏技术

Methods for Blue Enhancement of CCDs

Ｃ Ｃ Ｄ 用于天文领域已经有近２０ａ （ 年） 的历史， 随着 Ｃ Ｃ Ｄ 技术的发展， 作为重要参数之一的量子效率也得到极大提高， 已经有许多效率在蓝端超过９０ ％ 的芯片应用于天文观测。本文介绍了提高 Ｃ Ｃ Ｄ 蓝端量子效率的多种方法， 包括电极减薄、 Ｌｕｍｏｇｅｎ 镀膜、 Ｃ Ｃ Ｄ 减薄、紫外预照、电子预注入和增透膜等技术等等。可以看到， 采用 Ｃ Ｃ Ｄ 减薄、电荷注入和选择合适的增透膜可以使量子效率接近１００ ％

CCDs have become the most important astronomical detector for UV,visible and NIR imaging and spectroscopy at most observatories throughout the world.But the quantum efficiencies in the blue region of general CCDs are very low.Increasing the sensitivity in this region is desirable when the CCDs are used in astronomy. There are two ways to improve QEs of frontside illuminated CCDs.Deposition of a very thin polysilicon gate allows transmittance of shorter wavelength photons, and frontside coating a completed device with lumogen absorbs lower wavelength photons and re-emits them near the peak sensitivity of the CCD. The substrate of the CCD can be thinned to allow direct illumination of the epilayer.After a CCD is thinned, a silicon oxide film grows naturally on the backside due to contact with air,and positive charge creates a potential well at the backside.Any photons absorbed within this region produce photoelectrons that have only a small chance of migrating to the frontside collection wells.UV Photons are significantly affected since the absorption depth of silicon decreases rapidly with wavelength.Therefore the backside surface must be treated after CCD thinning. UV flood and flash gate are two common methods of builiding up a negative charge layer near the backside of the CCD to directly photogenerate electrons toward the frontside well. Another significant quantum efficiency degradation of back illuminated CCDs is due to their large back surface reflection loss.The thinning process creates a mirror-like a surface with an extremely high specular reflectivity.This reflection loss approaches 60% in the near UV,greatly reducing the CCDs effective quantum efficiency.The application of thin film antireflection coating on to the CCD back surface can significantly reduce this loss. After optimizing,100% QE enhancement may be realized at UV band.