微结构显微光学无损检测方法(特邀)

Non-destructive Test Methods of Microstructures by Optical Microscopy(Invited)

微纳尺度的微结构可调制光场,提高传感器的灵敏度,是新一代功能器件或传感器件中广泛使用的重要结构特征。包含微细加工在内的先进制造技术的快速发展,对多种型式微纳尺度微结构的无损测量技术提出了紧迫的需求。本文从多维视角论述了国内外行业发展中出现的微结构种类、型式,围绕具有高精度无损检测特质的光学显微技术,阐述了国内外仍在继续发展的微结构无损检测四种主流方法,分析了这些方法的技术特点、适用对象,给出了典型样品的检测结果,其中部分结果是首次发表。结果表明,暗场显微机器视觉法,是振幅型颗粒、凹坑、划痕等有害微结构的有效检测方法,可以实现大尺度样品的快速检测;共焦显微成像和低相干显微干涉法是“相位”型微结构的最佳检测方法,可以得到微结构的三维形貌;光谱反演-过焦扫描法与近红外显微干涉法,是应高深宽比微结构无损检测需求而发展起来的新方法,前者可以快速测得线宽和深度,后者可以测得物镜视场范围内高深宽比微结构的三维形貌,二者可以相互验证与补充。

The micro and nano scale microstructure can modulate the light field and increase the sensitivity of the sensor,is an important structure widely used in a new generation of functional devices or sensor devices.With the rapid development of advanced manufacturing technology including micromachining,laser direct writing and lithography,there is an urgent demand for nondestructive measurement technology of various types of micro and nano scale microstructure.In order to show much more knowledge about metrology of micro-structure as far as possible,this paper reviews the types of micro-structure in the development of industry in China and abroad.Focusing on the optical microscopy technology with the characteristics of high-precision nondestructive testing,this paper reviews four major methods of microstructure nondestructive testing that are still developing in China and abroad:dark-field microscopy with machine vision,confocal axial scanning microscopy,coherence spectral inversion combined with through-focus scanning optical microscopy,and low-coherence interferometric microscopy.This paper reviews the technical characteristics of these four methods,the test results of typical samples with these methods are individually given,some of which are published for the first time.These nondestructive testing methods are based on the diffraction-limited imaging principle of the optical microscope.The theoretical model of imaging can be unified,and the light intensity distribution function of the image field is given in this paper.The optical configurations of four major optical microscopes are all shown in the paper.The results show that the dark field microscopic imaging method is an effective method to detect harmful microstructures such as intensity-type particles,pits and scratches.Through the two-dimensional rapid scanning of the sample in the sample plane perpendicular to the optical axis,the rapid detection of largescale samples can be realized,some measurement maps of large-scale fused silica flat and thin film transistor display screen are given in this paper;Confocal microscopic imaging and low coherence microscopic interferometry are the best detection methods of phase-type microstructure.They both need to make relative motion between the optical microscope and the sample to complete the vertical scanning,which can obtain the three-dimensional tomography of the microstructure sample.Three dimensional topography detection results of two-type gratings by confocal microscopy are provided and three dimensional topography of super-lens by white light low-coherence interferometric microscope is also given.We also review the theoretical reason of the bat effect on step type microstructure result.If the nearinfrared light source is used with penetration ability to silicon-based materials instead of white light source,and in the meantime,the active compensator is used to compensate for the modulation aberration of detection beam induced by microstructure,the silicon-based microstructure with a high aspect ratio can be detected.By the way,some maps of three-dimensional tomography of MEMs microstructure on Sisubstrate are given.The combination method of coherence spectral inversion and through-focus scanning optical microscopy is also effective on the measurement of high aspect ratio microstructure.The coherence spectral inversion method is used to obtain the height of the microstructure with a low numerical aperture microscope.In the meantime,the through-focus scanning method is used to obtain the critical dimension with a large numerical aperture microscope.Coherence spectral inversion combined with through-focus scanning optical microscopy and near-infrared interferometric microscopy is new methods developed to meet the needs of nondestructive testing of high aspect ratio microstructure.The former can quickly measure the linewidth and depth,and the latter can measure the three-dimensional tomography of high aspect ratio microstructure in the field of view of the objective lens.They can verify and supplement each other.In this paper,we describe the advantage and disadvantage of the above four major methods of microstructure nondestructive testing in detail from the multi angle of view,and discuss the new variability from the four major methods.