As the semiconductor design rules shrink down, process margins are getting narrower, and thus, it is getting more important than ever to monitor pattern profile and detect minor structure variation. A breakthrough technology has been introduced as a solution to this concern. The new technology converts the fluctuation of polarization ingredient, which is caused by form birefringence, into light intensity variations as an optical image. This technology, which is called Pattern Edge Roughness (PER) inspection mode, is proved to be effective for 55nm production process. We also studied the possibility of the macro inspection method for half pitch 32nm technology node through FDTD method.

In recent years, the number of manufacturing processes is increasing in pursuit of device pattern miniaturization. Complicated processes such as SAQP have been introduced, increasing the number of control parameters. Nevertheless, the demand for production yield enhancement is as high as ever. To detect CD changes, fixed-point measurement by using CD-SEM or scatterometry tools is typically performed, but these time-consuming measurement methods are not suitable for high-density, across-a-wafer measurement or for detecting CD anomalies that randomly occur. To address these issues, we have developed a technology that enables high-precision CD measurement of more than 100,000 points per wafer within a few minutes. It enables monitoring various CD defects in various processes such as holes and L/S patterns after photolithography, L/S patterns after SAQP/SADP, and fine hole diameters after etching. It can also measure CD imbalances after SAQP processes. In addition, it enables precisely obtaining intra-shot CD distribution based on the distribution over the entire surface of a wafer. We evaluated this technology using actual device wafers. CD imbalances of SAQP on DRAM process wafers were measured, within a few minutes across a wafer, at an accuracy of |X|+3σ<0.5 nm. CD changes at the outermost area of the wafer were captured by CD measurement of 27 nm hole patterns on a DRAM process wafer. Random CD defects were captured by CD measurement of 38 nm hole patterns on a DRAM process wafer. These defects affect device yield but were not detectable by using conventional inspection tools.

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We have developed the new technology to measure focus variations in a field or over the wafer quickly for exposure tool management. With the new technology, 2-dimensional image(s) of the whole wafer are captured with diffraction optics, and by analyzing the image signal(s), we are able to get a focus map in an exposure field or over the entire wafer. Diffraction-focus curve is used instead of a CD-focus curve to get the focus value from the image signal(s). The measurements on the production patterns with the production illumination conditions are available. We can measure the field inclination and curvature from the focus map. The performance of the new method was confirmed with a test pattern and production patterns.

In the automatic macro inspection, a diffraction light method is very effective. However, this method needs a shorter wavelength illumination for finer wafer patterns. A wavelength of 193 nm will be needed for half pitch 55 nm. Light source and optics for such shorter wavelength is large and expensive, and chemical clean environment is needed. Therefore, the equipment size and costs will increase dramatically. In order to solve this problem and to comply with the process of half pitch 55 nm and below, we have developed the breakthrough technology. The key is the image of polarization fluctuation caused by a wafer pattern structure. The polarized light is affected by the variation of the wafer pattern structure due to a dose or focus shift. The new technology converts the polarization fluctuation into the gray level of the image. At a result, the sensitivity for the dose or focus shift was enough to detect process errors.