As the minimum feature size of electronic devices shrinks to less than 0.25 μm, it is critically important that we reduce the defects that occur in lithography processes. Moreover, as the defects to be controlled become ever smaller, this makes them increasingly difficult to detect by conventional fault detection equipment. In order to detect these minute defects in the context of shrinking device geometries, it is essential that we develop a clear understanding of the behavior of micro defects in developer. In principle, there are three ways in which these defects might be dealt with: (1) defects can be prevented from occurring in the first place, (2) defects can be prevented from adhering to the device, or (3) defects can be eliminated after they occur. Our recent work has mainly been concerned with the first and most effective approach of preventing defects from occurring in the first place, and this motivated the present study to investigate the mechanisms by which defects occur. We believe that defects occur in chemically amplified (CA) resists that are insufficiently unprotected at boundary regions between unexposed and exposed areas or in unexposed areas, so that the de-protection reaction in the resist suns to different degrees of completion due to varying exposure doses. In this study we investigate the number of defects in various developers, and determine the size distribution of the defects. Based on analysis of the behavior of defects from their size distribution in develop we conclude that: (1) the size of defects increases when the exposure dose is reduced by appropriate Eops, (2) defects originate in the boundary area between unexposed and exposed areas, and (3) a portion of CA resist polymer that is insufficiently deprotected is dispersed in the developer, coalesces and is deposited in a form that is not very soluble, and is manifested as relatively large particle defects.
Reducing defects in the semiconductor photolithography process has become increasingly critical. Many kinds of defects can occur during photolithography, such as missing contact holes or pattern collapses that occur during developing. As the pattern size becomes finer, the exposure wavelength has been shortened from 248-nm to 193-nm, and then to 157-nm. In addition, the resin structure and the chemical characteristics of the resist material have changed greatly. Changing the resist material from I-line to 248-nm created the problem of satellite defects peculiar to chemically amplified resist. Previous studies have suggested that a satellite defect is a complex salt of PAG, quencher, and TMAH, and is soluble in water.1) Because the resist material for 157-nm lithography is highly hydrophobic and is used for making ultra-thin films, defect evaluations of it are necessary. This paper evaluates the defects arising with various kinds of 157-nm lithography resist. Just as with 248-nm resist, a deposition defect peculiar to CAR occurs with 157-nm resist, but it occurs more frequently than with 248-nm resist. Unique defects appear with 157-nm resist, but their appearance and frequency seem to depend on the resist structure. The number of missing contact holes increases when the contact angle to ultra-pure water on the 157-nm resist film raise. It is necessary to elucidate on the mechanism that the unique defect occur in 157-nm resist.
As semiconductor design rules become increasingly complex, there is growing demand for a reduction in defects in lithography processes, and the process that contributes most to such defects is believed to be the developing process. The control of defects occurring in chemically amplified resist due to changes in the resist structure has been growing in complexity. Today, when the exposure source is about to undergo a transition from KrF (248 nm) to ArF (193 nm), the controlled objects in defect inspection decrease in size, becoming smaller than the particle size that can be handled by inspection machines. For defect control against the background of the increasing miniaturization anticipated in the future, it will be necessary to gain an understanding of the behavior of ultra micro defects contained in developers. This report concerns the consideration of defect behavior in developing fluid resulting from the quantification of defects occurring due to resist dissolution in the developing fluid, and from defect behavioral analysis performed on the developing fluid.
Reduction of defects after development is a critical issue in photolithography. A special category of post development defects is the satellite defect which is located in large exposed areas generally in proximity to large unexposed regions of photoresist. We have investigated the formation of this defect type on ESCAP and ACETAL DUV resists with and without underlying organic BARCs, In this paper, we will present AFM and elemental analysis data to determine the origin of the satellite defect. Imaging was done on a full-field Nikon 248nm stepper and resist processing was completed on a TEL CLEAN TRACK ACT 8 track. Defect inspection and review were performed on a KLA-Tencor and Hitachi SEM respectively. Results indicate that the satellite defect is generated on both BARC and resist films and defect counts are dependent on the dark erosion. Elemental analysis indicates that the defects are composed of sulfur and nitrogen compounds. We suspect that the defect is formed as a result of a reaction between PAG, quencher and TMAH. This defect type is removed after a DIW re-rinse.
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