LSIパターンからの反射光の偏光特性を利用した異物検出法の開発

LSIウェハ上異物の自動検出技術の研究

抄録

The major cause of defects in the initial process for manufacturing high-integration LSI circuits lies in contaminants which arise during the manufacturing process. Therefore, the accurate assessment of the presence of such contaminants and application of measures to deal these contaminants at an early stage is of great importance. The present research was undertaken with the purpose of developing automatic inspection techniques for the detection of minute contaminants on patterned wafer surfaces during the production process by optically distinguishing the contaminants from the background pattern.
This paper describes an optical technique for revealing the presence of contaminants by utilizing differences in the polarization characteristics of the light scattered from the pattern and from the contaminants. The approach to development of this technique consisted in investigating the appropriate conditions with respect to illumination and polarization analysis for emphasizing (a) the scattered light from contaminants and (b) the reflected light from the background pattern, then illuminating the sample in accordance with the conditions (a) and (b), and detecting the contaminants by computation on the basis of comparison between the two detected signals corresponding to (a) and (b) which generate from the same point of the sample.
This study has proved the following two results. (1) As regards the above conditions (a): in order to obtain a proportional relationship between the size of the contaminant particles and the detected signal indicating the scattered light from these particles, the inclination angle w₁ of the illuminating light must not exceed 5 degrees. As regards the above conditions (b): increasing the illumination angle w₂ tends to increase the result of the comparative computation of the detected signal from the contaminant. (2) Varying the illumination angle w₂ does not cause any great variations in the result of the comparative computation of the detected signal from the pattern.
On the basis of the above facts, experiments to distinguish the contaminants from the pattern were conducted using an experimental apparatus with the settings w₁=2° and w₂=30°. The results of these experiments indicated that contaminant particles as small as 1μm in diameter can be detected and confirmed the effectiveness of the present method.
The present method is new in that objects (i.e., contaminants) can be optically distinguished from the background (i.e., the pattern) by comparative computation with respect to two detected signals from the sample.