METROLOGY OF SUBWAVELENGTH PHOTORESIST GRATINGS USING OPTICAL SCATTEROMETRY

The widths and overall profiles of dielectric grating lines can be det ermined by measuring the intensity of diffracted laser light from the sample over a specified range of incident beam angles. This technique, known as 2-theta scatterometry, is able to accurately and precisely m easure photoresist structures in the subhalf micron regime. Moreover, a 2-theta scatterometer is capable of making measurements in a rapid a nd nondestructive manner. To test this technique we measured five iden tically processed wafers with nominal 0.5 mu m line/0.5 mu m space gra ting patterns. Each wafer comprised gratings in a Shipley 89131 negati ve photoresist exposed in a matrix of incremental exposure doses and f ocus settings. The scatterometry results were consistent with cross-se ctional and top-down scanning electron microscopy (SEM) measurements o f the same structures. The average deviation of 11 scatterometer linew idth measurements from top-down SEM measurements, over a broad exposur e range, is 14.5 nm. In addition, the repeatability (1 sigma) of the 2 -theta scatterometer is shown to be excellent: 0.5 nm for consecutive measurements and 0.8 nm for day-to-day measurements. (C) 1995 American Vacuum Society.