Proceedings Article | 17 December 2003
KEYWORDS: Etching, Phase shifts, Quartz, Photomasks, Metrology, Interferometers, Phase measurement, Deep ultraviolet, Process control, Scanning electron microscopy
The phase shift effect in Alternating Phase Shift Masks (AAPSMs) and chrome-less phase shift masks is created by etching trenches directly into the quartz substrate. Since the phase shift is critically dependent on the etch depth, the quartz etch process must be tightly controlled. In the absence of an etch stop for the process, an integrated metrology solution is desirable on the mask tech tool. Traditional methods for measuring etch depth or phase shift, such as interferometry, profilometry, AFM, and SEM, are expensive, slow, and/or destructive. In addition, traditional methods cannot measure quartz etch depth without removing the resist and in some cases the chrome mask, making them unsuitable for integration into the etch process. This paper will present measurements of trench depth and phase shift on quartz phase shift mask using the n&k Analyzer 1512-RT. The n&k Analyzer measures reflectance (R) and transmittance (T) from 190-1000nm, which is analyzed according to the Forouhi-Bloomer dispersion relations to simultaneously determine n, k, film thicknesses, trench depth, and phase shift. The measurement is non-destructive and fast, typically taking 2-3 seconds per measurement point. No special test structures are required for the measurement. In addition, the n&k Analyzer can measure quartz etch depth with the chrome mask, ARC layers, and resist still intact. The n&k Analyzer measurements show good correlation with 193nm interferometer measurements, and good repeatability. The small footprint, ease of use, measurement speed, and the ability to measure quartz depth in the presence of chrome and resist make the n&k Analyzer an ideal candidate for integrated metrology applications on mask etch tools for advanced proces control (APC). The Applied Materials' Tetra II phootmask etch system has the unique capability to accommodate integrated metrology modules through the factory interface. Applications of APC with integrated phase shift measurements will be discussed.
