Three-layer system CSAR/PMMAcoMA/PMMA

A further variant for the structure of three-layer systems uses 950k PMMA as bottom resist, AR-P 617 as middle layer and CSAR 62 as top resist. There is no mixing during the coating, thus ensuring a defined layer buildup. AR-P 617 can be coated on all PMMA’s (50k – 950k) without any problems, besides, the coating with AR-P 6200 (CSAR 62) is successful as well since anisole does not dissolve AR-P 617.

T-gates with three-layer system CSAR/PMMAcoMA/PMMA

T-gate structures are often required for the fabrication of electronic components (MEMS, HEMTs). Corresponding nanostructures can be realized via e-beam lithography in multi-layer processes. Generally, resist layers with different sensitivities like e.g. PMMAs with varying molecular weight distributions are coated on top of each other, irradiated with electrons and then developed in one step.

CSAR 62 – Mechanism of action

By comparison with PMMA resists, CSAR 62 is characterized by a higher sensitivity and a significantly better plasma etch resistance. The main components of the resist are poly(α-methylstyrene-co-chloromethacrylic acid methyl ester), an acid generator and the safer solvent anisole. The higher sensitivity results from the addition of halogen atoms to the polymer chain.

AR-P 617 Two layer lift-off system

An alternative version of the structure of two layer systems emanates from only one resist: AR-P 617 (PMMAcoMA 33). At increasing temperature, AR-P 617.08 becomes linearly more sensitive.

PMMA e-beam resist, positive and negative in the case of overexposure, suitable for bridge structures

PMMA resists work positively under standard conditions. The long polymer chains are broken into small fragments by the irradiation process. PMMA 950k with a molar mass of 950 000 g/mol is primarily reduced to a molar mass of about 5000 g/mol. These short-chain polymers are readily soluble in the developer, which is not the case for the polymer with the initial high molar mass.

PMMA e-beam resist with flat gradation for three-dimensional structures

It is advantageous for the fabrication of three-dimensional structures if the gradation (contrast) is low. A resist with very high contrast will always generate perpendicular resist flanks. Smallest changes of the dose induce a rapid shift from undeveloped to the completely developed state. If the gradation is low, the dose difference between the undeveloped and the completely developed state is accordingly high.

Temperature resistance of e-beam polymers

Layers and structures of e-beam polymers possess different temperature resistance properties. PMMA layers are generally the most stable.

CSAR 62 nanostructures written at 100 kV

Applying an acceleration voltage of 100 kV has the advantage that the proximity effect due to electron backscattering can be avoided.

CSAR 62 single layer lift-off system

With our new development e-beam resist AR-P 6200 (CSAR 62), very fine structures like e.g. 10 nm wide trenches can be manufactured with very high contrast (> 14) and comparably high sensitivity.

CSAR 62 for thick films

Layers with a thickness of 1.5 μm were produced using AR-P 6200.18, thick. As shown by investigations at the KIT (IMT, Dr. Lothar Hahn), allows this layer thickness to generate very regular trenches with a width of 300 nm at a period of 300 nm (see Fig. 1).