Measurement of critical dimensions and vertical shape of features in semiconductor manufacturing is a critical
task. Optical scatterometry proved capable of providing such measurements. In this paper, a software tool to
model scatterometry was developed. Rigorous coupled wavelength analysis (RCWA) is used as a physical
model. This software does not use fitting coefficients of any specific equipment and therefore is useful in
understanding, analysis and optimization of measurements of specific patterns and potential sensitivity of
methods and systems to process variation. Special attention was given to improve the accuracy and
throughput of simulation; results of comparison to another software proved advantages of the developed
For advanced process control, a sampling plan for critical dimension measurement is optimized through empirical considerations concerning the nature of error and a statistical approach. The metric of the optimization is the accuracy of lot mean estimation. In this work, critical dimension errors are classified into static and dynamic components. The static component is defined as the error which repeats through lots while keeping its tendency, and the dynamic as the error whose tendency changes by lot. In the basic concept of our sampling plan, sampling positions and size are determined from the static and dynamic error, respectively. The balance of sampling number of wafer, field and pattern is obtained under the restriction of total sampling size by a statistical theory with some assumptions. Based on the concept, we could make a sampling plan for 65 nm CMOS lithography.
Scatterometry, a non-destructive optical metrology, provides information on cross-sectional pattern profiles, including pattern height, sidewall angle and linewidth. Compared with other non-destructive metrology tools, such as the atomic force microscope (AFM) and CD-SEM, scatterometry offers the advantages of high throughput and superior repeatability. We have applied scatterometry to the monitoring of the depth of Shallow Trench Isolation (STI) for the analysis of complicated stack. We obtained sufficient measurement accuracy by optimizing a model.
In addition, we propose the application of scatterometry to post-lithography monitoring for advanced process control (APC). A regression model was established to derive effective dose and focus from the change of photoresist profile monitored by means of scatterometry. In our experiment using an ArF scanner, we obtained sufficient measurement repeatability of dose and focus.
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.