Pattern Placement Measurements Research Articles

An electron optical metrology system for pattern placement measurements

The demands on the uncertainties of pattern placement and overlay measurements in lithography are constantly growing due to the continuing reduction of feature size which allows higher density integration. Although nowadays optical projection lithography plays the dominant role in lithography and will continue to do so in the near future other technologies will be developed further in order to replace optical lithography soon after the beginning of the next century. A pattern placement metrology instrument should be able to perform measurements on the masks used today as well as on future types of lithography masks. The PTB has developed a new pattern placement metrology instrument using a high-resolution electron beam probe. The electron optical metrology system consists of a low-voltage scanning electron microscope with a large vacuum chamber and a 300 mm x-y-positioning stage, controlled by vacuum laser interferometry. The design principles of the instrument will be described and a comparison of measurements with those of an optical mask measuring system will be presented.

Pattern placement metrology on x-ray masks

Metrology is a key function in the evaluation of new manufacturing technology and processes. Meeting the pattern placement requirements for the 256 Mbit DRAM technology with 0.25 μm minimum feature size on 1:1 x-ray masks is a development challenge. Pattern placement measurements on structures in the range between 0.25 μm and 15 μm are reported using the Leitz LMS 2000 slightly modified to be able to handle x-ray masks automatically without using a special mask holding frame.

X-Ray Mask Technology Utilizing an Optical Stepper

An X-ray mask with half of a 64-Mbit dRAM chip whose minimum feature size was 0.3 µm wide was developed using a W absorber on a SiN membrane. To precisely control the W film stress, Ar+ ions were implanted into the W film prepared by chemical vapor deposition (CVD). To evaluate mask-to-mask overlay accuracy except that due to electron-beam-writing error, pattern placement measurement marks were delineated by optical exposure. It was found that the overlay accuracy between two masks with different pattern densities could be 0.08 µm (3σ) which is very nearly the limit of measurement accuracy.