Laser pattern generators ALTA 3500 and 3700 are widely used for 0.18 micron and above technology nodes in photomask manufacturing. They have low butting, high throughput and high position accuracy, with some weaknesses such as, corner rounding, no proximity effect correction and poor CD linearity when compared to E-beam pattern generators. Optical Proximity Correction (OPC) software was thus created to extend the productivity of laser pattern generators. For contact holes serifs are typically added at the four corners to enhance pattern fidelity. However, the serifs or scattering bars can significantly increase the data size. In our study, we generated serifs for contact holes but applied different exposure strategies: (1) lumping serifs together with the main pattern; (2) exposing serifs and main pattern separately with same dosage; (3) exposing serifs and main pattern separately with different dosages. We examined the results of each approach in terms of contact hole quality, throughput, and inspection results.
Mask profile of chromeless phase-shifting lithography (CPL) defined by OCD has been investigated. In CPL masks, unbalanced bombardments caused by different ion accelerations lead to the formation of micro-notch structures. A better understanding of micro-notch structures is essential for quality gating of mask processes to improve of CPL mask profiles. By measuring 12 of 16 elements of Mueller matrix, we are able to set up a model to simulate the depth of micro-notch structure profile which shows good correlation with TEM images. Moreover, values of CD, quartz etching depth and side wall angle acquired by OCD are presented and compared with those obtained by SEM, TEM and AFM, respectively.
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