Detection of Progressive Transmission Loss Due to Haze withGalileor~(TM)Mask DUV Transmittance Mapping Based on NonImaging Optics

摘要

In this paper, we expand on our earlier work~(1,2)reporting the use of high sensitivity DUV transmission metrology as ameans for detection of progressive transmission loss on mask and pellicle surfaces. We also report a use case forincoming reticle qualification based on DUV transmission uniformity. Traditional inspection systems rely on algorithms to locate discrete defects greater than a threshold size (typically >100nm), or printing a wafer and then looking for repeating defects using wafer inspection and SEM review. Thesetypes of defect inspection do not have the ability to detect transmission degradation at the low levels where it beginsto impact yield. There are numerous mechanisms for transmission degradation, including haze in its early, thin filmform, electric-field induced field migration, and pellicle degradation. During the early development of haze, it behaves as a surface film which reduces 193nm transmission and requirescompensation by scanner dose. The film forms in a non-uniform fashion, resulting from non-uniformity of exposureon the pattern side due to varying dose passing through the attenuating layers. As this non-uniformity evolves, thereis a gradual loss of wafer critical dimension uniformity (CDU) due to a degradation of the exposure dosehomogeneity. Electric-field induced migration also appears to manifest as a non-uniform transmission loss,typically presenting with a radial signature. In this paper we present evidence that a DUV transmission measurement system, GalileoTm, is capable of detectinglow levels of transmission loss, prior to CDU related yield loss or the appearance of printing defects. Galileo is anadvanced DUV transmission metrology system which utilizes a wide-band, incoherent light source and non-imagingoptics to achieve sensitivities to transmission changes of less than 0.1%. Due to its very high SNR, it has a fastMAM time of less than 1 sec per point, measuring a full field mask in as little as 30 minutes. A flexible userinterface enables users to easily define measurement recipes, threshold sensitivities, and time-based tracking oftransmission degradation. The system measures through pellicle under better than class 1 clean air conditions.