A challenge in the semiconductor industry is 3-D inspection of the miniaturized solder bumps grown on wafers for direct die-to-die bonding. An inspection mechanism proposed earlier requires the projection of a binary fringe grating to the inspected surface from an inclined angle. For high speed and accuracy of the mechanism, the projection optics has to meet these requirements: (1) it allows a tilt angle between the inspected surface and the projector's optical axis; (2) it has a high bandwidth to let high-spatial-frequency harmonics contained in the binary grating pass through the lens and be projected onto the inspected surface properly; (3) it has a high modulation transfer function; (4) it has a large field of view; and (5) it has an adequate depth of field that matches the depth range of the inspected surface. In this paper, we describe a projection optics design, consisting of a fringe grating and several pieces of spherical lens, that addresses the requirements. To reduce the lens aberrations, the grating is laid out with an angle chosen specifically to make the grating, the lens, and the average plane of the inspected surface intersect in the same line. Performance analysis and tolerance analysis are shown to demonstrate the feasibility of the design.
With the continuous effort of the electronic industry in miniaturizing device size, the task of inspecting the various electrical parts becomes increasingly difficult. For instance, solder bumps grown on wafers for direct die-to-die bonding need to have their 3D shape inspected for assuring electrical contact and preventing damage to the processing equipments or to the dies themselves in the bonding process. Yet, the inspection task is made difficult by the tiny size and the highly specular and textureless nature of the bump surfaces. In an earlier work we proposed a mechanism for reconstructing such highly specular micro-surfaces as wafer bumps. However, the mechanism is capable of recovering 3D positions only. In this paper we describe a new mechanism that recovers surface orientations as well which are as important in describing a surface. The mechanism is based upon projecting light from a point or parallel light source to the inspected surface through a specially designed binary grid. The grid consists of a number of black and transparent blocks, resembling a checker board. By shifting the grid in space a number of times in a direction not parallel to either boundary of the grid elements, and each time taking a separate image of the illuminated surface, we could determine the surface orientations of the inspected surface at points which appear in the image data as grid corners. Experimental results on real objects are shown to illustrate the effectiveness of the proposed mechanism.
A challenge in the semiconductor industry is the 3D inspection of solder bumps grown on wafers for direct die-to-die bonding. In an earlier work we proposed a novel mechanism for reconstructing wafer bump surface in 3D, which is based upon projecting a binary pattern to the surface and capturing image of the illuminated scene. By shifting the binary pattern in space and every time taking a separate image of the illuminated surface, each position on the illuminated surface will be attached with a binary code in the sequence of images taken. 3D information about the bump surface can then be obtained over these coded points via triangulation. However, when a binary pattern is projected onto the inspected surface through projection lenses, the high order harmonics of the pattern are often diminished because of the lens' limited bandwidth. This will lead to blurring of the projected fringe boundaries in the captured image data and make differentiation between dark and bright fringes there difficult. In addition, different compositions of the target surface, some metallic (the solder surface) and some not (the substrate surface of the wafer), have different reflectance functions (including both the specular and lambertian components). This makes fringe boundary detection in the image data an even more challenging problem. This paper proposes a solution to the problem. It makes use of the spatial-temporal image volume over the target surface to tackle the issue of inhomogeneous reflectance function. It is shown that the observed intensity profile across the images of a fixed point has the same up-and-down profile of the orignal binary gratings, regardless of the reflectance on the target surface, from which edges can be detected using classical methods like the gradient based ones. Preliminary study through theoretical analysis and empirical experiments on real image data demonstrate the feasibility of proposed approach.
A challenge in the semiconductor industry is the 3D inspection of solder bumps grown on wafers for direct die-to-die bonding. In an earlier work we proposed a mechanism for reconstructing wafer bump surface in 3D, which is based upon projecting a binary grating to the surface with an inclined angle. For the purpose of 3D reconstruction with high speed and accuracy, the requirements for the projection lens system are the followings: (1) having a tilted angle between the projection plane and the optical axis; (2) having high bandwidth to let high-spatial-frequency harmonics contained in the binary grating pass through the lens and be projected onto the inspected surface properly; (3) having high Modulation Transfer Function (MTF); (4) having large Field of View (FOV); and (5) having a large Depth of Field (DOF) that corresponds to the depth range or height of the
inspected surface. The above requirements lead to great challenges in the design of the projection lens system. In this paper, we describe a design consisting of a grating and several pieces of spherical lens, that addresses the requirements. To reduce the lens aberrations, the grating is laid out with a tilting angle specifically to make the grating, the lens, and the image plane intersect at the same line. Such a system can project a high spatial-frequency binary grating onto the inspected surface properly. Simulation results, including performance analysis and tolerance analysis, are shown to demonstrate the feasibility of the design.
As the electronic industry advances rapidly, the shrunk dimension of the device leads to more stringent requirement on process control and quality assurance. For instance, the tiny size of the solder bumps grown on wafers for direct die-to-die bonding pose great challenge to the inspection of the bumps’ 3D quality. Traditional pattern projection method of recovering 3D is about projecting a light pattern to the inspected surface and imaging the illuminated surface from one or more points of view. However, image saturation and the specular nature of the bump surface are issues. This paper proposes a new 3D reconstruction mechanism for inspecting the surface of such wafer bumps. It is still based upon the light pattern projection framework, but uses the Ronchi pattern - a pattern that contrasts with the traditionally used gray level one. With the use of a parallel or point light source in combination with a binary grating, it allows a discrete pattern to be projected onto the inspected surface. As the projected pattern is binary, the image information is binary as well. With such a bright-or-dark world for each image position, the above-mentioned difficult issues are avoided. Preliminary study shows that the mechanism holds promises that existing approaches do not.