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Scatterometery is an emerging metrology technique for measuring critical dimensions (CD), profiles, and thicknesses within diffraction gratings printed on semiconductor film stacks. A 28 scatterometer was used to measure diffraction gratings on two films stacks: 1) Front end of line logic gate stack, and 2) Resist on anti-reflective coating (ARC) on Silicon. The CD measurements of the scatterometer were compared to critical dimension scanning electron microscope (CD-SEM), atomic force microscope (AFM), and cross-section scanning electron microscope (X-SEM) measurements. The correlation between scatterometer and CD-SEM measurements was analyzed using the Mandel technique of Archie and Banke' where AFM and X-SEM measurements were used to characterize the "real" properties of the grating. Initial results indicated that the measured CD value by scatterometer and CD-SEM were linearly correlated with a sizeable offset. Further analysis of the correlation shows that the offset was pronounced at grating sidewall angles approaching 90". The effect of sidewall angle on CD-SEM to scatterometer correlation and results for precision and accuracy on the scatterometer are discussed relative to in-line stepper focus control. SummarySemiconductor device performance is controlled by the critical dimension of features printed by lithographic and etch processes. Conventionally, the critical dimension scanning electron microscope (CD-SEM) is used for process control; however, the scatterometer is another technique that has recently become available. The two systems work on entirely different principles.The CD-SEM uses a focused electron beam that is rastered over an area of interest, where by secondary and backscattered electrons are generated everywhere the beam imparts the sample2. The generated electrons are then collected, giving a waveform (1-D) or image (2-D) of intensity versus position which can be analyzed using different algorithms to extract critical dimensions3. The operating conditions of the CD-SEM are such that higher magnifications are used for critical dimension measurements; therefore, measurements are performed over small segments of device features.The scatterometer works on the principle of light diffracted from an array of features.4i5 At several angles the 28 scatterometer measures the intensity of the Oth order diffraction intensity, which will vary depending on the film stack and diffraction grating spacing.6 Rigorous modeling of the optical behavior of the grating as a function of angle can be used to predict the intensity profile for most film stacks and grating spacings. By comparing the measured intensities to the modeled data, film thickness, critical dimension, and sidewall profile information can be determined using the scatterometer. Due to the laser spot size and other optical considerations, 0-7803-6252-7/00/$10.0002000 IEEE

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