Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Single layer resist prototype

The objective of Infineon’s work on 157nm Single Layer Resist Development within UV2Litho was to provide a resist material for a sub 60nm DRAM ground rule, tested on the AT:1600. This material finally should have been commercially available and production worthy in terms of parameters that are not related to the imaging capabilities of the used exposure tool. In order to speed up resist development for 157nm, Infineon started a joined development project with a commercial resist supplier (Clariant Corporation). This very close scientifically based collaboration opened a unique chance to actively steer and speed up the project development in order to provide a functioning resist on time. Clariant acted as a subcontractor within the German funded BMBF. Due to the decreasing interest in worldwide industry towards 157nm Lithography and the move towards 193nm Immersion Lithography instead, the prototype resist constituted Infineon’s final activity within UV2Litho concerning resist activities.

As part of a new generation of more transparent 157 nm resist platforms, a series of novel resists have been developed that have higher transparency and contrast. Using a new protecting group strategy, encouraging results have been obtained with fluorinated resin platforms based on norbornenes and cycloolefines These new resist systems show absorbance values as low as 1/µm at 157nm, have improved contrast, and have neither significant dark erosion nor do they switch to negative tone behaviour within the dose range studied.

It has been shown that the BOCME group has a combination of properties that make it well-suited as a protective group for fluoroalcohol moieties.

Two types of BOCME substituted materials were described, BOCME-F1 and BOCME-TFR, both of which are accessible through direct polymerisation and polymer modification. The BOCME-TFR polymers were found to give very transparent resins, which upon formation with a PAG could give resins with absorbances as low as 1.07micron at 157nm.

Both the BOCME-F1 and the BOCME-TFR platforms were able to resolve small features upon exposure with 157nm light. The BOCME-TFR resin with low nominal protection was able to achieve resolution of 70nm for 1:1 and 50nm 1:1.5 L/S features at a dose of 91mJ/cm² (NA 0.85, Alt. PSM, low sigma). By lowering the amount of base it is possible to increase lithographic sensitivity up to 8-9 mJ/cm². This is done at the cost of feature profiles and top rounding, but intermediate levels of base are expected to yield materials having a good compromise between the two. Indeed a PED latitude of at least 20min in an FSI track can be easily achieved. Resist systems based upon BOCME-TFR have good PED latitude and excellent PEB temperature latitude and give good performance on either an organic BARC or SiON. Using the high NA exposure capability (0.9 NA) in highly pure and stable cleanroom atmosphere, features as small as 55nm lines and spaces were resolved for dense line patterns using advanced resist formulations.

Blends of BOCME-F1 and BOCME-TFR give resins that have an intermediate absorption between the two types of resins. Using this blend approach, it was possible to resolve relaxed pitches down to 60nm L/S. For oxide etch conditions, such blends can give improved plasma etch resistance, but it was found that the BOCME-TFR platform by itself is sufficiently etch resistant to give selectivity only slightly inferior to that of the 248nm resist Deep UV RESIST. For chlorine etches, the selectivity of the BOCME-TFR was unexpectedly found to exceed that of the Deep UV RESIST standard. Last not least, hardmask etch capabilities have been proven for L/S patterns with relaxed CD and pitch.

Due to the high and varying airborne contamination level at the different exposure sites, it is difficult to define one single layer resist prototype for all tools. To our knowledge, the AZ® EXP FX 2000P formulation behaves best under the cleanroom conditions at INVENT in Albany. With respect to the declining interest in 157nm lithography and the early project closure, a further optimisation of this prototype has not been carried out.

More information on the UV2LITHO project can be found at:

Reported by

Infineon Technologies AG, R&D
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