Writing time

The minimum necessary exposure time for a certain area, at a given exposure dose, can be calculated by the following correlation: Area * dose = Duration of exposure * beam current.

SCALPEL

A further mask-based technology is SCALPEL (Scattering with Angular Limitation Projection Electron-beam Lithography). Due to the interposed mask, certain parts of the electron beam are shadowed. The scattering layer strongly deflects incident electrons. A great advantage of this procedure as compared to electron absorption is less loading and less heating of the mask.

Raster and vector scan principle

Raster scan principle is a procedure in which the electron beam is led line by line over the exposure area, comparable to the beam guidance in an electron microscope. The structures are exposed by switching the electron beam on and off while continuously moving the substrate (XY regulation).

Proximity effect

A part of the high-energy electrons which impact on the substrate is stopped and cannot be conducted at all or only very slowly toward ground, especially in the case of insulating substrates such as quartz. The substrate and respectively the resist charges itself negatively and the electron beam is deflected uncontrollably from the desired position during exposure.

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.

Solution

In contrast to photolithography, the solution of e-beam lithography is practically unlimited by wavelength. Electrons of an energy of 25keV have a wave length of < 0,01 nm. The maximum resolution thus is crucially determined by the beam diameter.

Loading

A part of the high-energy electrons which impact on the substrate is stopped and cannot be conducted at all or only very slowly toward ground, especially in the case of insulating substrates such as quartz. The substrate and respectively the resist charges itself negatively and the electron beam is deflected uncontrollably from the desired position during exposure.

PPA for two layer applications

Report on the two layer system, respectively lift-off: AR P-617 (250nm) with PPA (30nm), development followed by vapor coating of Al (40nm).

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.