Andreas Frommhold

Dynamic absorption coefficients of chemically amplified resists and nonchemically amplified resists at extreme ultraviolet

Abstract. The dynamic absorption coefficients of several chemically amplified resists (CAR) and non-CAR extreme ultraviolet (EUV) photoresists are measured experimentally using a specifically developed setup in transmission mode at the x-ray interference lithography beamline of the Swiss Light Source. The absorption coefficient α and the Dill parameters ABC were measured with unprecedented accuracy. In general, the α of resists match very closely with the theoretical value calculated from elemental densities and absorption coefficients, whereas exceptions are observed. In addition, through the direct measurements of the absorption coefficients and dose-to-clear values, we introduce a new figure of merit called chemical sensitivity to account for all the postabsorption chemical reaction ongoing in the resist, which also predicts a quantitative clearing volume and clearing radius, due to the photon absorption in the resist. These parameters may help provide deeper insight into the underlying mechanisms of the EUV concepts of clearing volume and clearing radius, which are then defined and quantitatively calculated.

Chemically amplified phenolic fullerene electron beam resist

Molecular resist materials for electron beam lithography have received significant interest as a route to reducing line width roughness and improving resolution. However, they have often required the use of hazardous solvents in their processing. A new family of fullerene based negative tone chemically amplified e-beam resists, using industry compatible solvents, has been developed. A sensitivity of ∼40 μC cm−2 was achieved at 20 keV. Isolated features with a line width of 13.6 nm as well as ∼20 nm lines on a 36 nm pitch have been patterned, whilst one variant has demonstrated resolution to 15 nm half-pitch at slightly higher dose.

Positive-tone chemically amplified fullerene resist

With continuing efforts to achieve higher lithographic resolution there has been on-going interest in the development of low molecular weight resists, such as molecular glasses. Here we present the initial results of a study into the development of a positive tone two component chemically amplified resist based on methanofullerene derivatives (MF) with acid labile groups (tert-butyl acetate (tBAC); tert-butoxycarbonyl (tBOC)). Mono, di, tris and hexa adducts of MFtBAC together with mono and di adducts of MF-tBOC have been evaluated with several photoacid generators. Sensitivities as high as 11 μC/cm2 have been achieved in some cases and sub-100 nm features have been patterned.

High aspect ratio etching using a fullerene derivative spin-on-carbon hardmask

As lithographic resolution has increased to meet the demand for smaller devices it has been necessary to use extremely thin photoresist films to mitigate aspect ratio related resist feature collapse during development. Even with high etchdurability photoresists, usable photoresist thickness limits etch depth, and it is becoming increasingly difficult to transfer the pattern directly from the photoresist to the substrate. As feature sizes have diminished the use of multilayer etch stacks has been increasingly investigated to further increase aspect ratio. Typically, a thick layer of amorphous carbon is deposited by chemical vapor deposition, and then coated with thin silicon and resist layers. To improve manufacturability it would be beneficial to use spin-on-carbon in the bottom layer. Here we introduce a fullerene based spin-on carbon with high etch-durability. Sub 50 nm features with aspect ratios in excess of 15:1 have been produced in silicon using ICP etching.

Performance of negative tone chemically amplified fullerene resists in extreme ultraviolet lithography

Abstract. With extreme ultraviolet lithography (EUVL) emerging as one of the top contenders to succeed from optical lithography for the production of next generation semiconductor devices, the search for suitable resists that combine high resolution, low line edge roughness (LER) and commercially viable sensitivity for high volume production is still ongoing. One promising approach to achieve these goals has been the development of molecular resists. Here we report our investigations into the EUV lithographic performance of a molecular fullerene resist showing resolution down to 20-nm half-pitch with interference lithography with a LER of >5  nm and sensitivity of about 20  mJ/cm2.

Spin-on carbon based on fullerene derivatives as hardmask materials for high-aspect-ratio etching

Abstract. The advance of lithographic resolution has made it necessary to adopt extremely thin photoresist films for the fabrication of “2× nm” structures in order to mitigate problems such as resist collapse during development but limiting achievable etch depths at the same time. By using multilayer hardmask stacks, a considerable increase in achievable aspect ratio is possible. We have previously presented a fullerene-based spin-on carbon hardmask material capable of high-aspect-ratio etching. We report our latest findings in material characterization of an original and a modified formulation. By using a higher adduct derivative fullerene, the solubility in industry-friendly solvents and thermal stability could be improved. The etching performance and materials characteristics of the new higher-adduct fullerene hardmask were found to be comparable to those of the original hardmask.

Dynamic absorption coefficients of CAR and non-CAR resists at EUV

The dynamic absorption coefficients of several CAR and non-CAR EUV photoresists are measured experimentally using a specifically developed setup in transmission mode at the XIL beamline of the Swiss Light Source. The absorption coefficient α and the Dill parameters ABC were measured with unprecedented accuracy. In general the α of resists match very closely with the theoretical value calculated from elemental densities and absorption coefficients, whereas exceptions are observed. In addition, through the direct measurements of the absorption coefficients and dose-to-clear values, we introduce a new figure of merit called Chemical Sensitivity to account for all the post-absorption chemical reaction ongoing in the resist, which is also predicts a quantitative clearing volume, and respectively clearing radius, due to the photon absorption in the resist. These parameters may help in deeper insight into the underlying mechanisms of EUV concept of clearing volume and clearing radius are then defined and quantitatively calculated.

Towards 11nm half-pitch resolution for a negative-tone chemically amplified molecular resist platform for extreme-ultraviolet lithography

We have synthesized a new resist molecule and investigated its high-resolution capability. The material showed resolved line-spaces with 14 nm half-pitch (hp) and the potential to pattern 11 nm hp features. Line edge roughness values as low as 3.15 nm were seen in optimized formulations. The dose-to-size is estimated at around 20-30 mJ/cm2. The role of the molecule in the patterning process was studied by comparing it with structurally similar compounds. Furthermore we present first results from exposures of our materials at the Berkeley Micro Exposure Tool. Finally it is also demonstrated that the material works as a resist in 100 kV electron beam lithography as well.

Optimization of fullerene-based negative tone chemically amplified fullerene resist for extreme ultraviolet lithography

While the technological progress of Next Generation Lithography (NGL) steadily continues, further progress is required before successful insertion in high volume manufacturing is possible. A key issue is the development of new resists suitable to achieve higher lithographic resolution with acceptable sensitivity and line edge roughness. Molecular resists have been a primary focus of interest for NGL because they promise high resolution and small line edge roughness (LER), but no suitable resist candidate has emerged yet that fulfills all of the industry’s criteria. We have previously shown first extreme ultraviolet lithography (EUVL) exposures for a new fullerene derivative based three-component negative tone chemically amplified resist with suitable properties close to or within the target range of the resist metrics as set out in the International Technology Roadmap for Semiconductors for 2016. Here we present the results of our efforts to optimize the EUVL performance of our resist system especially with regards to LER.

Chemically amplified fullerene resists, spin-on fullerene hardmasks and high aspect ratio etching

As resolution requirements increase there is a need for high performance ultra thin resists, which has led to significant interest in molecular resists. We have previously described a fullerene based resist whose electron beam lithography properties include sparse resolution of ~12 nm, half pitch ~20 nm, sub 5 nm linewidth roughness (LWR), sub 10 μC/cm2 sensitivity, and high etch durability. The material shows extremely wide process latitude and LWR <;2 nm in sparse features. Initial results of exposure via EUV lithography indicate a resolution capability of at least 30 nm half pitch. As resist films have become thinner to mitigate aspect ratio related pattern collapse, etching has become more challenging. We have studied the ICP plasma etching of high-resolution patterns in sub 40 nm thickness films of the fullerene resist. Silicon structures of 20 nm width and more than 100 nm height have been demonstrated. Additionally we have developed a fullerene based spin-on-carbon for use in a tri-layer etching scheme allowing aspect ratios greater than 19:1 to be achieved in room temperature ICP etching of sub 30 nm patterns. The same trilayer scheme has also been deployed for colloidal lithography fabrication of sub 100 nm silicon pillars with aspect ratios >;17:1.