Relationships between Contact Image Analysis Results for Pad Surface Texture and Removal Rate in CMP

Abstract

In chemical mechanical polishing (CMP) process, the removal rate is affected by the actual contact conditions between the wafer and the polishing pad. Further, the free abrasives in the slurry attack the wafer at the regions of actual contact. The polishing pad is one of the most important consumable materials in CMP since the pad surface texture changes during wafer polishing and substantially influences the actual contact conditions. Therefore, methods for quantitative evaluation of the pad surface texture have been proposed by various research institutes. We have developed a novel method for the quantitative evaluation of the polishing pad surface texture; this method is based on contact image analysis using an image rotation prism. We have proposed the use of four effective evaluation parameters: the number of contact points, the contact ratio, the maximum value of the minimum spacing of the contact points, and the half-width of the peak of the spatial fast Fourier transform (FFT) of a contact image. We determine the changes in the polishing pad surface texture on the basis of the proposed evaluation parameters in serial batch polishing tests. In particular, we focus on the relationships between the proposed evaluation parameters and the removal rate, which changes with an increase in the number of batch polishing tests. The evaluation parameters are linearly correlated with the removal rate. Hence, the removal rate is improved not only with an increase of the number of contact points and the contact ratio but also with a decrease in the size of the cohesion regions and the spacing between the contact points.Progress in science and technology depends substantially on innovations in the semiconductor industry. For example, silicon wafers used for semiconductor device fabrication should have highly flat surfaces, and because of the continuous downsizing of such devices, 1 nanometer-scale planarization becomes important. Therefore, there is an increasing demand for chemical mechanical polishing (CMP) techniques.Recently, it was found that the material removal rate in wafer polishing is affected by the actual contact conditions between the wafer and the polishing pad. 2, 3 The actual contact conditions affect both the mix effects of chemical mechanical factors of the slurry and the viscoelastic deformation of the pad. Additionally, the free abrasives in the slurry attack the wafer at the regions of actual contact. 3 Therefore, it is important to identify the optimum contact conditions under which the slurry can effectively act on the wafer and the removal rate can be improved.The polishing pad is one of the most important consumable materials used in CMP since its surface texture has a substantial influence on the actual contact conditions. 4 Therefore, it is extremely important to develop methods for the quantitative evaluation of the actual contact conditions between the wafer and the polishing pad and to examine the effects of these conditions on the CMP characteristics.With this background, we have developed ...

Chemical mechanical polishing: Theory and experiment

“…The precision of the model is determined by the above assumptions. In fact, the actual contact ratio is very small (<1%) [54,57].…”

Influence of Pad Surface Asperity on Removal Rate in Chemical Mechanical Polishing of Large-Diameter Silicon Wafer Applied to Substrate of GaN-Based LEDs

“…The contact image analysis method suggests the following four evaluation parameters (other details can be found in our previous paper (8) ):…”

“…In this section, we will integrate the results of the consecutive polishing experiment (8 inch silicon wafer) depicted in the previous section, the double-sided polishing experiment (12 inch silicon wafer) according to the authors' stepped-conditioning method, (7) and the consecutive batch double-sided polishing experiment (12-inch silicon wafer). (8) We will then introduce the overall relationship between the pad surface condition evaluation parameters and the removal rate. Figure 6 shows the relationship between each evaluation parameter and the removal rate.…”

“…In addition, we even managed to commercialize the apparatus. (6)(7)(8)(9) In this paper, we will show an outline of a contact image analysis method along with the validity of the evaluation parameters used. We will state the changes in the removal rate in the consecutive polishing of a large-diameter silicon wafer (8 inches) using a single-sided polishing apparatus.…”

Kinematic Optimization for Chemical Mechanical Polishing Based On Statistical Analysis of Particle Trajectories

“…Some researchers [20], [21] have investigated the number of active particles, whereas others [22], [23] have conducted some experimental studies on the contact ratio of the pad asperities. Based on these studies, it can be predicted that the effective particle number is more than 1,000,000.…”