微电子与微电子机械系统(MEMS)中的现代光学测试技术

ADVANCED OPTICAL MEASUREMENT TECHNOLOGY IN THE SEMICONDUCTOR AND MEMS

介绍了微电子和微电子机械系统 (MEMS)中几种常用的变形和形貌测量方法以及相关的测量设备。其中相移云纹干涉技术用于微电子器件的面内位移测量 ,灵敏度可达到纳米量级。显微栅线投影技术用于MEMS的离面变形和形貌测量 ,灵敏度可达 0 .1微米。

Mechanical test of materials and structures commonly used in micro-electro-mechanical systems (MEMS) is an essential step towards the achievement of optimal design and reliability of the micro mechanical components. The measurement of the occurring mechanical quantities, such as forces and deformations, requires the development of new testing procedures. Non-contact and whole-field optical measuring and inspection methods are a unique technology for the measurement of the shape and deformation of MEMS materials and components. In recent years, substantial research has been carried out on micro-sensors, micro-mirrors, micro-motors, micro-pumps, micro- valves, micro-actuators, micro-lenses, and so on. The diameter of spherical lens is about 250 μm, the size of micro-motor is no more than 800 μm, an inlet port size is only 80 μm. Under Scanning Electronic Microscope (SEM) and Atomic Force Microscope (AFM) sub-micron displacement can be resolved. But, to loading on the sample is more difficult and the deformation measurement range is limited. Optical methods are introduced for the small sample testing of MESM materials and structures in this paper. The methods are based on the laser interferometry, phase shifting, digital image correlation and image processing etc. Using a LWDM (long working distance microscope) and digital speckle correlation method (DSCM) the stretching strain of a thin copper wire (diameter 0.1 mm) can be determined. The proposed technique is also applicable for measuring other MEMS materials that may be even smaller or thinner than that used in this paper. The interference of light beams of equal path difference is used for the measurement of the Young's modulus of a micro-beam. An optical wedge which consists of an optical plate and a micro-beam which forms part of a micro-accelerometer is illuminated by a collimated monochromatic sodium light beam. Loading on the micro-beam is accomplished by a loading-pin mounted on a 3-axis translation-stage and the resulting interference fringe pattern is observed using a CCD camera connected to a computer. Loadings are recorded using a high sensitive load cell that measures loads of up to 200 g with a resolution of 0.01 g. This paper also describes the use of optical fringe projection method for 3-D surface profile measurement of small objects. In this method, sinusoidal linear fringes are projected on the object surface by a sinusoidal grating phase shifting projector and a LWDM. The image of the fringe pattern is captured by another LWDM and a CCD camera and processed by phase-shifting techniques. A simple procedure is described which enables calibration of the optical set-up for subsequent quantitative measurement of unknown object shapes and deformations. The method developed can also be applied to the measurement of the warpage of a small component under thermal loading. This method is relatively simple and accurate, and is capable of conducting fully automated measurements. The deformation of a micromirror (100 μm × 100 μm) driven by an electrostatic force is measured by comparing the profiles between deformed and undeformed. The maximum displacement of micro mirror is no more than 2 microns. Thus, the rotation angle of the micromirror is less 2 degrees. Experimental results obtained demonstrate the feasibility of the proposed method to be used for evaluating the contouring of the microstructure.