For lithography technology to support the scaling down of semiconductor devices, 193-nm immersion exposure
processing is being introduced to mass-production at a rapid pace. At the same time, there are still many unclear areas
and many concerns to be addressed with regards to defects in 193-nm immersion lithography. To make 193-nm
immersion lithography technology practical for mass production, it is essential that the defect problems be solved.
Importance must be attached to understanding the conditions that give rise to defects and their transference in the steps
between lithography and etching processes.
It is apparent that double patterning (DP) will be the mainstream technology below 40nm node. It can be assumed that
the risk of the defect generation will rise, because the number of the litho processing steps will be increased in DP.
Especially, in the case of Litho-Etch-Litho-Etch (LELE) process, the concept of defect transfer becomes more important
because etch processing is placed between each litho processing step.
In this paper, we use 193-nm immersion lithography processing to examine the defect transference from lithography
through the etching process for a representative 45nm metal layer substrate stack for device manufacturing. It will be
shown which types of defects transfer from litho to etch and become killer defects.
As a promising way to scale down semiconductor devices, 193-nm immersion exposure lithography is being developed
at a rapid pace and is nearing application to mass production. This technology allows the design of projection lens with
higher numerical aperture (NA) by filling the space between the projection lens and the silicon wafer with a liquid
(de-ionized water). However, direct contact between the resist film and water during exposure creates a number of
process risks. There are still many unresolved issues and many problems to be solved concerning defects that arise in
193-nm immersion lithography.
The use of de-ionized water during the exposure process in 193-nm immersion lithography can lead to a variety of
problems. For example, the trapping of microscopic air bubbles can degrade resolution, and residual water droplets left
on the wafer surface after immersion exposure can affect resolution in the regions under those droplets. It has also been
reported that the immersion of resist film in de-ionized water during exposure can cause moisture to penetrate the resist
film and dissolve resist components, and that immersion can affect critical dimensions as well as generate defects.
The use of a top coat is viewed as one possible way to prevent adverse effects from the immersion of resist in water, but
it has been reported that the same problems may occur even with a top coat and that additional problems may be
generated, such as the creation of development residues due to the mixing of top coat and resist. To make 193-nm
immersion lithography technology practical for mass production, it is essential that the above defect problems be solved.
Importance must be attached to understanding the conditions that give rise to residual defects and their transference in
the steps between lithography and the etching/cleaning processes.
In this paper, we use 193-nm immersion lithography equipment to examine the transference (traceability) of defects that
appear in actual device manufacturing. It will be shown that defect transfer to the etching process can be significantly
reduced by the appropriate use of defect-reduction techniques.
Semiconductor manufacturing technology has progressed remarkably in recent years. This progress has been accompanied by demands to reduce the feature size used in photolithography processing, resulting in a reduction of the exposure wavelength from 248 nm (KrF laser) to 193 nm (ArF laser). ArF immersion lithography is now being actively researched and developed with the aim of implementing the 45-nm technology node. Chemically amplified (CA) resists have been introduced to cope with these reduced feature sizes, making it all the more important to reduce defects produced in the lithography process. In recent years, the behavior of defects in a CA resist has been clarified by studies involving various microprobe analysis techniques. Basically, it has been reported that water-soluble defects such as "satellites" and water-insoluble defects such as "resist residues" are generated by various factors. Furthermore, the reduction in pattern sizes has led to the identification of new types of resist-related defects such as "missing-hole" defects in contact-hole (C/H) patterns and "bridging" defects in line-and-space (L/S) patterns. Although the satellite, resist-residue, and missing-hole problems have been addressed by implementing new ideas such as extended rinse times, improved development recipes, and the introduction of post-development rinse stages and improved rinse recipes, it cannot be said that these measures are sufficient in terms of processing throughput or effectiveness. In this paper, we investigate the effect of adding chemical additives to the de-ionized water (DIW) rinse used in the development rinse process. Our studies confirm that these additives significantly reduce the quantity of minute defects generated on the wafer without degrading lithography performance, and thus help to improve process throughput. We also investigate the application of this method to immersion lithography, and confirm that this additive procedure also reduces the quantity of defects in immersion lithography processes.
Exposure wavelength is being reduced significantly, along with design rule reductions. The sub-100-nm node process is currently underway with 193-nm lithography. The problems that need to be solved for the shift in wavelength from 248-nm to 193-nm lithography are those attributed to resist materials, such as plasma resistance, SEM (scanning electron microscope) shrink, and problems attributed to processes, such as pattern collapse and deposition defects (Fig. 1). Although thin films are preferable to improve resist resolution limits, pattern collapse is more likely to occur in 193-nm and 157-nm processing due to DIW (deionized water) rinse surface tension during the drying step after development. This is because of the increased A/R (aspect ratio) of the resist used to improve etching durability and lower the rigidity of 193-nm resist compared to the 248-nm resist. We had focused on controlling the capillary effect between the resist pattern and the rinse solution to avoid swelling. We evaluated the method with the use of DIW with additives rinse, and named its process “FIRM (Fishing-up by improved rinse materials)”. In this paper, we report the effectiveness of the FIRM treatment for each resist by using a dispenser of track system. We had confirmed the pattern collapse within the wafer, the process margin, CD (critical dimension) variation, CDU (CD uniformity), Defect test and, the effectiveness of the FIRM treatment in the etching process. Results indicated that the FIRM process could be used in mass production. Additionally, we had investigated application of this method to the sub-65-nm node process. We created a 55-nm line (Pitch 200-nm), with A/R = 4.47 by overdosing and performed the FIRM treatment. We were able to confirm that the FIRM treatment improved the results while all patterns had collapsed after a standard development. We believe that the FIRM treatment will be applicable to the 65-nm node.
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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