In immersion lithography, importance is placed on technology for controlling coating along the edge of the wafer. In the
case of a top-coat process, it has been observed that the top coat can peel off during immersion exposure due to weak
adhesion to the substrate, a characteristic of top-coat films. The peeling of the film is thought to adversely affect
immersion-exposure equipment and the wafer surface by the formation of defects due to the contamination of the
immersion-exposure tool and by residual particles. Nikon Corporation and Tokyo Electron Ltd. (TEL) have performed
joint research and development in response to these problems. TEL has studied rinsing technology for the wafer edge
section and established coating processes and control techniques that rinse the edge section to remove foreign matter and
that control the cutting position of each film in the edge section. TEL has developed new processes and hardware to
remove foreign matter introduced into the immersion-exposure tool, and has shown that this technology can help prevent
contamination of exposure equipment. Nikon has established efficient on-body periodic rinsing as a new technology for
exposure equipment that can reduce defect.
The demand for more highly integrated semiconductor devices is driving efforts to reduce pattern dimensions in semiconductor lithography. It has been found that 193-nm immersion lithography can achieve smaller patterns without having to modify the infrastructure used for existing state-of-the-art 193-nm dry lithography. As a result, 193-nm immersion lithography is a promising technology for use in mass production processes. Recently, the scanning speed of the exposure stage has been increasing in order to achieve high throughput for mass production. Currently, the topcoat process is one of the promising candidates for this high speed scanning process. On the other hand, the non topcoat resist process is being tested from a C.O.O. (cost of ownership) point of view. However, there are some important points that become apparent, such as specific defect countermeasures and wafer bevel control.
Nikon and TEL developed the novel immersion exposure tool and coater/developer system application technology in order to solve these immersion specific issues.
In this paper, we examine the process performance using novel immersion exposure tool and coater/developer system.
It has been found that 193nm immersion lithography technology can achieve smaller patterns without any
modification to the technology infrastructure of existing state-of-the-art 193nm dry lithography. This has made 193nm
immersion lithography a promising technology for mass production processes. Recently, scanning speed of the exposure
stage has been increasing in order to achieve high throughput for mass production. At present, the adoption of a topcoat
is one of the promising candidates for this high speed scanning process. On the other hand, the demand for a non-topcoat
process is being pursued from a C.O.O. (cost of ownership) point of view but there are still issues being revealed and
concerns to be solved. In this report, feasibility of a comprehensive process for high scanning ArF immersion lithography was discussed. As for the topcoat process, a high receding contact angle topcoat, such as TC-A (JSR), is proving to be a good candidate for mass production using high scanning speed immersion lithography. TC-A has a similar defectivity and lithographic performance to TCX041 (JSR). On the other hand, the feasibility of a non-topcoat process was also investigated. CD uniformity, defectivity and lithography performance of AIM5120JN and AIM5570JN (JSR) data indicate that the non-topcoat process can be adopted for mass production process. An immersion cluster comprised of a high volume production immersion exposure tool, S610C (NIKON) having 1.3 NA and CLEAN TRACKTM LITHIUSTM i+ (TEL) track system were used in this study.
The demand for even denser semiconductor devices is driving efforts to reduce pattern dimensions in semiconductor
lithography. It has been found that 193-nm immersion lithography technology can achieve smaller patterns without
having to modify the infrastructure technology of existing state-of-the-art 193-nm dry lithography. This has made
193-nm immersion lithography a promising technology for next-generation mass production processes. It is now under
full-scale development and is about to enter a commercial stage applicable to mass production.
In 193-nm immersion lithography, the space between the optical projection system and silicon wafer is filled with
liquid thereby immersing the resist film in de-ionized water during exposure. This generates a number of concerns, such
as the penetration of moisture into the resist, the leaching of resist components into deionized water, and the presence of
residual moisture, all of which can lead to defects that can affect post-processing. It has been reported; however, that
rinse processing before and after exposure can be effective in reducing such defects [1]. Also, the trend toward finer
patterns has resulted in large aspect ratios that can lead to pattern collapse, but the application of a surfactant has been
found to ease this problem. Controlling the drying process after rinsing has also been found to reduce residue adhering to
the resist.
The stability of process data is considered to be a crucial factor in the adapting of 193-nm immersion lithography to
mass production. In this report, we obtain long-term data on defects and critical dimension (CD), examine this data for
process stability, and discuss the applicability of 193-nm immersion lithography to mass production.
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.
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.
In 157-nm resists, fluorine atom is added into the polymers in order to improve the transmittance at the exposure wavelength. It is considered that the fluorine atom increases the hydrophobicity of the resists and that the number of defects during development process increases. We evaluated the development defects focusing on the missing contact holes on 157-nm resists. We used different types of 157-nm resists based on such as monocyclic fluoropolymer type, tetrafluoroethylene-norbornene type, and siloxane type. A KrF and ArF resist were also studied for comparison. We measured the number of the missing contact holes for 2500nm 1:2 hole pattern exposed using a KrF stepper. The number of the missing contact holes is higher for the 157-nm resists than that for the KrF or ArF resist. The contact angle of de-ionized water on the resist film of the 157-nm resists was found to be higher than that of the KrF and ArF resists. We examined the number of missing contact holes for various types of resist polymer and the blocking level, and found that the large contact angle, which corresponds to the high hydrophobicity of the resist film, induces the large number of the missing contact holes. The origin of the missing contact holes is the micro bubbles in the developer solution induced by the dissolved nitrogen. For the 157-nm resists, the wettability between resist surface and developer solution is insufficient due to the high hydrophobicity of the resists. Therefore, the micro bubbles are not easily released from the resist surface, and the number of the micro bubbles increases. In order to reduce the number of the missing contact holes, we tried the surfactant-containing developer solution and also tried the nitrogen-degassed developer solution. In both developers, we found that the number of the missing contact holes is reduced by less than half.
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