A new inorganic EUV resist with high-etch resistance
Markos Trikeriotis a, Marie Krysak a, Yeon Sook Chung a, Christine Ouyang a, Brian Cardineau b, Robert Brainard b, Christopher K. Ober a, Emmanuel P. Giannelis a, Kyoungyong Cho c
a Dept. of Materials Science and Engineering, Cornell University, Ithaca, NY 14853;
b College of Nanoscale Science and Engineering, University at Albany, Albany, NY 12203;
c SEMATECH, Albany, NY 12203
ABSTRACT
极品女人Performance requirements for EUV resists will necessitate the development of entirely new resist platforms. As outlined in the ITRS, the new resists for EUVL must show high etch resistance (to enable pattern transfer using thinner films), improved LER and high nsitivity. A challenge in designing the new resists is the lection of molecular structures that will demonstrate superior characteristics in imaging and etch performance while maintaining minimal absorbance at EUV wavelengths. We have previously described the u of inorganic photoresists in 193 nm and e-beam lithography. The inorganic photoresists are made of HfO2 nanoparticles and have shown etch resistance that is 25 time
s higher than polymer resists. The high etch resistance of the materials allow the processing of very thin films (< 40 nm) and will push the resolution limits below 20 nm without pattern collap. Additionally, the small size of the nanoparticles (< 5 nm) leads to low LER while the absorbance at EUV wavelengths is low. In this prentation we show that the inorganic resists can be applied to EUV lithography. We have successfully achieved high resolution patterning (<30 nm) with very high nsitivity and low LER.
Keywords: EUV lithography, inorganic photoresist, hafnium oxide, zirconium oxide, nanoparticles, etch resistance
1.INTRODUCTIONwps打印预览
Currently, Extreme Ultra-Violet (EUV) lithography is considered an upcoming next generation patterning system1. Despite remaining challenges with the EUV system, alternative lithographic techniques, such as double patterning, nanoimprint and lf-asmbly, either cannot achieve the required resolution or have other issues that limit their applicability. As a result, EUV lithography and improved photoresists for this patterning technology are important goals in the ITRS roadmap.
推开又来打一字The desired performance characteristics of EUV photoresists will require the development of entirely
new photoresist platforms. As pattern sizes reach the sub-20 nm range, it is necessary to u thinner films to prevent pattern collap from high aspect ratios. An aspect ratio of 2:1 would require films within the 30-40 nm range. However, photoresist films that are comprid of organic materials cannot sufficiently resist the etch process as thinner films2. Therefore, extremely high etch resistant structures must be studied and developed to allow pattern transfer to the underlying substrate.
Given the relatively low intensity of current EUV sources, the next generation photoresists will need to demonstrate high nsitivity and optimum absorbance. At 13.5 nm which is the wavelength ud in EUV lithography, the absorption of all materials is very strong and only dependent on their atomic composition and density3. For example, elements that are commonly ud in photoresists at other wavelengths, such as fluorine, are highly absorbing at 13.5 nm making them problematic for EUV applications. Other elements including carbon, silicon, zirconium or hafnium have very high transmission. A challenge in designing new photoresists for EUV lithography is the lection of molecular structures that have optimum absorbance.
Extreme Ultraviolet (EUV) Lithography III, edited by Patrick P. Naulleau,
Obert R. Wood II, Proc. of SPIE Vol. 8322, 83220U · © 2012 SPIE
In order to fulfill the requirements that were mentioned above, in this study we prent a next generation photoresist material bad on hybrid organic/inorganic nanoparticles. The nanoparticles are comprid of a hafnium oxide or zirconium oxide core that is surrounded by organic ligands. Previous work at Cornell University has studied the application of the inorganic photoresists in DUV, 193 and e-beam lithography4. The studies also revealed that the nanoparticle films exhibit exceptionally high etch resistance due to their thermal and chemical stability5. Additionally, the hybrid nature of the nanoparticle films enables the control of the film absorbance in order to optimize their lithographic performance. By controlling the ratio of the organic and inorganic content of the films it is possible to regulate the film density and therefore its absorbance. Additionally, Hf and Zr have different absorption coefficients at 13.5 nm and this gives additional flexibility in the photoresist formulation in order to fine-tune the film absorbance.
2.MATERIALS AND METHODS
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2.1Materials巢湖龟山
All chemicals were purchad from Sigma Aldrich unless otherwi indicated, and ud without further purification. All solvents were reagent grade and purchad from Sigma Aldrich unless noted otherwi.
2.2Synthesis of Nanoparticles
Hafnium oxide nanoparticles stabilized with carboxylic acid ligands were prepared by a controlled hydrolysis reaction. Hafnium isopropoxide was dissolved in an excess of carboxylic acid solvent at 65°C followed by the slow addition of a water/carboxylic acid mixture. After stirring for 21 h the product is precipitated by addition of water. This precipitate was centrifuged at 8,000 g for 5 min and then dissolved in acetone and reprecipitated with water twice. The final product, a white powder, was obtained after drying under vacuum. The same approach is ud to prepare zirconium oxide nanoparticles starting from zirconium isopropoxide as a precursor.
2.3Photoresist formulation and thin film preparation
Photoresist solutions were prepared by adding proper amounts of the nanoparticle powder to PGMEA followed by the addition of the photoactive compound or any other additives. Any aggregates or dust were removed by filtration using a 0.2 μm filter membrane. To prepare thin films for lithography experiments the photoresist solution was spin coated directly on unprimed Si wafers and then baked to remove any excess solvent.
2.4Lithographic processing
EUV experiments were carried out at Lawrence Berkeley National Laboratory using the SEMATECH BMET. After exposure the films were developed manually using a custom-made organic developer. DUV (254 nm) testing was carried out at the Cornell Nanoscale Science and Technology Facility (CNF), using an ABM contact aligner equipped with a mercury lamp UV source. For pattern transfer experiments a PlasmaTherm PT72 etcher was ud.
3.RESULTS AND DISCUSSION
Our previous work with inorganic photoresists was focud on the hafnium oxide system with methacrylic acid as the organic ligand (HfMAA). Using this system and with the addition of a photoradical initiator, we were able to demonstrate high resolution negative tone patterns. The same films can also be patterned in positive tone when an additional PEB step is added and aqueous TMAH is ud as the developer. To expand the potential of the inorganic photoresists ZrMAA films were also tested on both positive and negative tone under DUV exposure. Furthermore, both positive and negative tone patterns were obtained from HfMAA and ZrMAA films using a PAG as a photoactive compound. The results are demonstrated in Figure 1.
The dual tone capability of the inorganic nanoparticle films and the various formulations that give hig
h quality patterns demonstrate the flexibility of this versatile inorganic photoresist. In fact, any combination of Hf or Zr nanoparticles with a photoradical initiator or a PAG will give both positive and negative tone patterns. The same system is patternable under DUV, 193, e-beam and EUV exposure. Additionally, other carboxylic acids also give nanoparticle films that are patternable while alternative, non-caboxylate ligands are also under study in collaboration with prof. R. Brainard and his group at the University at Albany.
Figure 1. Positive and negative tone DUV patterns using the inorganic photoresist with a PAG additive: A) HfMAA,
positive tone, B) HfMAA, negative tone, C) ZrMAA, positive tone and D) ZrMAA, negative tone.
The same resist formulations that were patterned using DUV at Cornell were then tested under EUV exposure at the LBNL. Many combinations of nanoparticles and different photoactive compounds were tested at both positive and negative tone, but the ones that showed the best performance were the ZrMAA nanoparticles with PAG. Figure 2 shows two reprentative SEM images of negative tone patterns that were printed with this system. Image analysis was carried out using the SuMMIT software which showed that the patterns on Figure 2A are 32 nm wide with a LER = 5.9 nm while the patterns on Figure 2B are 26 nm with LER = 3.8 nm.
The results demonstrate the high resolution capabilities of the inorganic photoresist but what is even more remarkable is the photoresist’s nsitivity. The patterns shown on Figure 2 were created after exposure at 5.6 mJ/cm2 and 4.2 mJ/cm2 respectively. That is the highest reported nsitivity of any EUV resist that has been tested to date. Given the relatively low intensity of current EUV sources, the nsitivity of the photoresist is very important so that the whole EUV成语你画我猜
中秋节的资料
processing can be cost effective.
Figure 2. Negative tone patterns after EUV exposure of the ZrMAA photoresist with a PAG additive: A) 32 nm lines at 5.6 mJ/cm2 and B) 26 nm lines at 4.2 mJ/cm2.
To obtain the high resolution patterns shown in Figure 2 the film thickness of the photoresist had to be reduced to 40 nm. Even thinner films, around 30 nm thick, are required in order to improve the resolution below 20 nm half-pitch. As a result the etch resistance of the photoresist material has to be exceptionally high to allow pattern transfer. Figure 3 demonstrates the etch rate of the HfMAA film
compared to polyhydroxystyrene (PHOST). Both films were etched using a SF6/O2 mixture while the HfMAA film was also initially treated with O2 plasma for 30c to remove the organic ligands. As a result the etch rate of the hafnium film is 0.17 nm/c or 10.2 nm/min which is 25 times slower than the etch rate of the PHOST film under the same conditions.
补血药The etching of patterned films was also studied in order to examine the pattern transfer into the Si substrate. Figure 3 shows an SEM cross-ction image of the transferred patterns after SF6/O2 etching. A small layer of remaining HfMAA film is still prent while the pattern has been deeply etched into the Si substrate. Before etching with SF6/O2, the film was treated with O2 plasma in order to increa its inorganic content and improve its etch resistance. Thermal treatment was also studied as an alternative but the quality of the patterns was affected and as a result the pattern transfer was not successful. On the other hand, the successful pattern transfer that is demonstrated on Figure 3 means that the O2 plasma treatment does not affect the quality of the patterns.
4.CONCLUSIONS
This paper expands our previous work on inorganic photoresists by applying them to EUV lithography. The HfMAA and ZrMAA nanoparticles described in this study can be ud to form versati
le photoresists that have dual tone capability and work with either radical photoinitiators or PAG additives. The photoresists have been previously applied to DUV, 193 and e-beam lithography and this study also shows their potential as EUV resists. The ZrMAA films were patterned at negative tone using a do of 4.2 mJ/cm2, the lowest reported to date for a EUV photoresist. The inorganic photoresists have also shown superior etch resistance to polymer photoresists and their successful pattern transfer was demonstrated using SF6/O2. Further studies are now underway in order to improve the patterning resolution and optimize
the positive tone patterning under EUV exposure.
Figure 3. Top: Film thickness versus etching time for HfMAA and PHOST films. Remaining film thickness was measured after various time intervals during etching with SF 6/O 2. Bottom: SEM cross-ction image showing the transferred pattern in the Si substrate.
ACKNOWLEDGEMENT
The authors gratefully acknowledge international SEMATECH for funding, as well as The Cornell Nanoscale Science and Technology Facility (CNF), Cornell Center of Materials Rearch (CCMR) and the Center of X-Ray Optics (CXRO) at the Lawrence Berkeley National Laboratory for u of the
ir facilities.
