Research On High-precision Wafer Bonding Alignment Method Based On Moiré Fringes

Compared with traditional 2D integrated circuits,3D integrated circuits have lower cost,smaller size and higher performance,which is an ideal direction to break through Moore’s Law in the future.As a key technology to realize 3D integrated circuits,wafer bonding technology has become a popular research direction in integrated circuits due to its advantages of high integration and low cost.The accuracy and speed of the alignment process in the wafer bonding process directly determine the yield and performance of 3D integrated circuits.The use of alignment marks combined with digital image processing algorithms in the alignment process is an easy-to-implement,low-cost,high-efficiency method.Method of precision.Studying the alignment marks and corresponding image processing algorithms in wafer bonding and alignment has very important theoretical research and engineering application value for improving the efficiency and accuracy of wafer bonding equipment and reducing equipment costs.The thesis considers the wafer bonding alignment process as the research object in the wafer bonding equipment.Through the detailed analysis of the alignment process in the wafer bonding equipment,combined with the actual situation of the bonding machine and the auxiliary wafer is proposed—special raster markings for alignment and a detailed description of how it works and the calculation process.Through mathematical inference,simulation analysis and actual experiments of building a test bench,it is verified that the special alignment mark proposed in the paper is suitable for the wafer bonding alignment process and is highly accurate.The main contents of the paper are as follows:1)By analyzing the specific work of the wafer bonding process of the bonding equipment,the alignment process directly related to the bonding alignment is split,and the reasons for choosing the alignment mark and digital image processing for auxiliary alignment are explained.The causes of moire fringes and their effect of amplifying the relative displacement between gratings are analyzed in detail.2)The introduction of digital gratings shows that the superposition of digital gratings and optical gratings can produce moire fringes,and the displacement analysis of the gratings can be carried out.The extraction,filtering and solution of Moiré signal are deduced in detail.3)To further improve the accuracy of the moire fringe solution without changing the hardware conditions,a super-resolution network based on a convolutional neural network and imaging principle is extracted,which can enlarge the picture by a certain multiple.Experiments show that the network has stronger performance than previous superresolution networks and can get clearer images.4)To further verify the feasibility of the marking proposed in the paper,an experimental bench is designed,and the performance of the testing bench is verified and improved.Many experiments have been conducted to confirm that the markers and methods proposed in this paper can achieve the same accuracy as widely recognized methods on the market and are more suitable for wafer bonding alignment.It is also verified that the calculation accuracy will improve after using the super-resolution network.