Evaluation and countermeasures verification of haze on ArF PSM

Haze is a defect such as particle that is generated on the photomask during exposure, consequently reducing the lifetime of the photomask. Therefore, various investigation has been done to clarify the root causes of haze, and countermeasures have been taken according to the causes. However, in recent years, it has been discovered that there is a new mode of haze caused by the photomask material itself. The molybdenum, derived from MoSi phase shift films, was generated as particles such as molybdenum oxide and ammonium molybdate during ArF exposure. In this paper, the results of the verification evaluation of the hypothetical cause of molybdenum haze and countermeasures are reported. Based on the hypothesis that the cause of molybdenum haze may be molybdenum ion residue dissolved in the photomask cleaning solution, as a result of verification evaluation using an Accelerated irradiation Test Bed (ATB), a large amount of haze occurred on the quartz part of the photomask, so the hypothesis was likely to be correct. Therefore, a phase shift film with a protection layer was devised to prevent the MoSi film from being exposed to the cleaning solution. The photomasks made of this new phase shift film had more than four times the haze resistance of the conventional photomasks and had less CD change after irradiation. In addition, the processability and lithography performance of the new structure photomask were the same as that of the conventional photomask, and it was confirmed that they were a promising photomask.