**6. Acknowledgment**

The author would like to acknowledge DuPont, JSR, and Mitsui Chemicals for supplying G2 fluids and purification units. The author also thanks colleagues for their cooperation.

### **7. References**

414 Recent Advances in Nanofabrication Techniques and Applications

the scanning speed of 800 mm/sec. This result exhibits that the nozzle can reduce the amount of residual fluid sufficiently and can suppress the fluid darkening. In conclusion, the issue of dissolved oxygen was solved by the immersion nozzle designed for a G2 fluid.

> 0 2 4 6 8 10 Wafer No.

Fig. 24. Fluid absorbance between a lens and a wafer during the scan. The absorbance induced by dissolved oxygen is low enough even at the scanning speed of 800 mm/sec.

There are some remaining challenges to realize high-index immersion lithography. As described in the second subchapter, the quality of LuAG material does not reach the target specification. Especially, the absorbance of LuAG would be a critical issue. While the intrinsic absorbance of LuAG is lower than the target absorbance, further reduction of

On the other hand, there still remain a few issues to be studied in an immersion system using a G2 fluid. Although fluid absorbance can be kept low enough, dose homogeneity through a fluid layer should be confirmed. Defect study should be done with various resists.

For the extendability of high-index immersion lithography, the research activity on new

It has been discussed the feasibility on a high-index immersion system of 1.55 NA using LuAG and a G2 fluid. Although the IBR correction of LuAG is feasible, the quality of LuAG is not enough and the acceleration of its development is desired. The immersion system using a G2 fluid is being developed without serious issues. It was demonstrated that fluid absorbance can be kept low enough through an in-line purification unit and an oxygen removal unit. Lens contamination can be suppressed by addition of a small amount of water into a G2 fluid. Some issues arising with residual fluid, such as fluid darkening due to reentry of oxygen-rich residual fluid, were solved. By accepting residual fluid on a wafer,

EUVL is the orthodox candidate of the next generation lithography but still needs real verifications in various items. If EUVL is delayed, high-index immersion lithography will be at the leading edge lithography. It is a common knowledge that strong supports from the

It is preferable to examine them with a preproduction tool using a G2 fluid.

materials such as G3 fluids and high-index resists is needed.

the scanning speed and the throughput can be raised.

800mm/sec 500mm/sec 300mm/sec

Scanning speed

0

0.0001

0.0002

Absorbance of fluid layer

**4. Remaining challenges** 

impurities is required.

**5. Conclusion** 

induced by dissolved oxygen

0.0003

0.0004


**21** 

*Germany* 

**Double Patterning for Memory ICs** 

In order to continue technology shrink roadmaps and to provide year by year smaller chips with more functionality, nearly all of the leading edge semiconductor companies have adopted double patterning process technologies in their fabrication lines to bridge the time until next generation EUV lithography reaches production maturity. Double patterning technology can be classified into two major main streams, however its implementation and especially the details of the process integration vary strongly among the semiconductor

Therefore the given schemata will focus on the key principles. We will not stress material combinations, but point out particular challenges, show some detailed analyses, and sketch

The most straightforward approach of doing double patterning is splitting a given pattern into two parts by separating neighbouring patterns (see figure 1a). By doing this the minimum pitch of each split will be enlarged and becomes again printable with standard ARF immersion exposure tools. At the first lithography step, a photo mask containing only the blue part of the pattern will be used. As one can easily see from figure 1b, the pitch of blue only pattern is about two times larger than in the original layout. However, in order to achieve a good optical contrast during imaging as well as to get sufficient (photo resist) process window for the

patterning, the pattern will usually be biased on the mask as shown in figure 1c.

Fig. 1. Example of decomposing an irregular structure for double patterning processing.

company and every manufacturer found his own optimum.

**2. Double patterning by litho-etch-litho-etch** 

**1. Introduction** 

solutions.

Christoph Ludwig and Steffen Meyer

*Q-CELLS SE, Bitterfeld-Wolfen* 

