Kinematic Prediction and Experimental Demonstration of Conditioning Process for Controlling the Profile Shape of a Chemical Mechanical Polishing Pad

The uniformity of the wafer in a chemical mechanical polishing (CMP) process is vital to the ultra-fine and high integration of semiconductor structures. In particular, the uniformity of the polishing pad corresponding to the tool directly affects the polishing uniformity and wafer shape. In this study, the profile shape of a CMP pad was predicted through a kinematic simulation based on the trajectory density of the diamond abrasives of the diamond conditioner disc. The kinematic prediction was found to be in good agreement with the experimentally measured pad profile shape. Based on this, the shape error of the pad could be maintained within 10 μm even after performing the pad conditioning process for more than 2 h, through the overhang of the conditioner.

Investigation of Dressing Characteristics of Single Crystal Diamond in CMP

Diamond conditioners, or dressers, are commonly used to dress polishing pads that are applied to the chemical mechanical polishing of silicon wafers for integrated circuits. Although the diamond conditioner has regular distribution diamond grits, they differ in shape and can be oriented differently because the shape of diamond grits is generally cubo-octahedral. Therefore, the dressing behaviors on the polishing pad are unpredictable. In this work, the fundamental characteristics of dressing are investigated by a single crystal diamond with various shapes (each resulting in point-cutting, line-cutting, and face-cutting), a rake angle of-50°, and cutting faces in the (100) and (111) planes. For the purpose of analysis, plowing ratio is defined as the sum of the areas of the two side ridges divided by the groove area. This ratio can be used to evaluate the contribution of plowing and cutting actions from the dressing. Experimental results reveal that a groove with ridges on both side walls is formed as the diamond is moved over the pad. The profile of the scratch correlates with the shape of the diamond. In summary, cutting dominates when point-cutting is responsible for the dressing. On the contrary, plowing plays a major role with respect to line-cutting. The cutting action tends to dominate when the dressing is completed by face-cutting a (111) plane. Alternatively, the wear tends to be dominated by the plowing action if the dressing is conducted via face-cutting a (100) plane.

Friction Phenomenon in Chemical Mechanical Polishing of Oxide Film

The friction phenomenon was investigated to explore the relationship between the diamond conditioner, polishing pad and wafer of oxide film in the chemical mechanical polishing (CMP) process. Two kinds of diamond conditioners (disk-A and disk-B) were used. Diamond disk-A used was traditional diamond conditioner containing random shaped diamond grits. Diamond disk-B used was made by sculpturing a sintered polycrystalline diamond to form identically shaped cutting tips. Experimental results reveal that friction force between disk and pad increases with dressing load. But friction force decreases with sliding speed due to increase of sliding speeds resulting in an increase of interface temperature. The coefficient of friction between wafer and pad initially increases with the dressing load, and then it starts to drop slowly with further increases of the dressing load. It was found that removal rate of the oxide film correlates well with the variation of the coefficient of force. In addition disk-B can produce a higher wafer removal rate under a low dressing load.

Blade Diamond Disk for Conditioning CMP Polishing Pad

A diamond conditioner or dresser is needed to regenerate the asperity structure of the pad and recover its designed ability in chemical mechanical polishing (CMP) process. In this paper a new design of diamond conditioner is made by shaping a sintered matrix of polycrystalline diamond (PCD) to form teethed blades. These blades are arranged and embedded in epoxy resin to make a designed penetration angle, called the blade diamond disk. The dressing characteristics of pad surface textures are studied by comparison with conventional diamond conditioner. It is found that the height variation of the diamond tip of blade diamond disk is significantly smaller than the conventional diamond disk. The dressing rate of blade diamond disk is lower than that of the conventional diamond disk, and hence the pad life is prolonged. As a result, reduction of the cost CMP is expected. In addition the pad surface roughness Ra of about 3.79μm is less than Ra of about 4.15μm obtained after dressing using a conventional diamond disk.