Characterization of photo masks by X3D AFM

Abstract:
In this presentation we show the results from AFM measurements on photo masks to determine sidewall angles and height values. The images were obtained in the adaptive scanning modes where the data points are determined by the feedback system of the AFM to achieve the highest data reliability. In the deep trench (DT) mode the depth information is received fast without sidewall information. In the critical dimension (CD) mode the information about three dimensional data is obtained by an additional dither of a specially shaped AFM tip. The results show the high accuracy of the measurements to help the development of new photo masks. In the DT measurements the depth values at 3 sites show a short term and long term repeatability (3s ) of below 1%. The short term repeatability can even be improved when the measurement is repeated with the “slow scan axis” disabled, meaning the AFM is measuring the same line for several times. The sidewall angle measurements were performed on calibrated standards. Here repeatability of below 1 degree could be achieved. Tip wear is one of the concerns during AFM measurements. In this presentation we show examples of high and low tip wear which helps to decide which probe material can be used for the respective measurement.