2. type of polymer
general information - 2. type of polymer
Allresist offers a large variety of different types of resists
which cover a wide range of possible applications
PMMA resists are composed of polymethacrylates with different molecular weight (50K, 200K, 600K, and 950K) dissolved in chlorobenzene (AR-P 631…671) or the safer solvents anisole (AR-P 632…672), ethyl lactate (AR-P 639 … 679) or 1-methoxy-2-propyl acetate (AR-P 6510). All resists work in a positive manner. The polymer 50K is characterised by a 20 % higher sensitivity as compared to the 950K polymer. The glass transition temperature of PMMA films is about 105 °C, and polymers are temperature-stable up to 230 °C. PMMAs are characterised by an excellent resolution. For example, 6 nm lines with an aspect ratio of 10 can be obtained for AR-P 679.02. Special resists are the resists of the AR-P 6510 PMMA series which allow to generate very thick films (62 - 250 μm) for LIGA technologies.
Copolymer resists like AR-P 617 are composed of copolymers on the basis of methylmethacrylate and methacrylic acid (PMMA/MA 33 %), dissolved in the safer solvent 1-methoxy-2-propanol. The CSAR 62 (AR-P 6200) is based on styrene acrylates which are dissolved in the safer solvent anisole. Copolymer resists are positive-working and exhibit a 3-4 fold higher sensitivity as compared to PMMA resists. Copolymer layers are furthermore temperature-stable up to 240 °C; the glass transition temperature for AR-P 617 is around 150 °C and approximately 148 °C for CSAR 62. Above a wavelength of 260 nm, PMMA and copolymer layers are optically transparent. Since these resists also absorb at 248 nm, irradiation with deep UV and structuring is possible, even though with a lower sensitivity.
Novolac-based e-beam resists like AR-P 7400, AR-N 7500, 7520, 7700 and 7720 can generally be developed under alkaline-aqueous conditions and are distinguished into positive and negative-tone e-beam resists. In addition to novolac, they contain organic or amine-based crosslinking agents and/or acid generators. AR-N 7500 furthermore contains positive-working naphthoquinone diazides. Novolac-based e-beam resists are about twice as resistant during plasma etching as PMMA resists and are used for the generation of structures with e-beam lithography or for mask production. A few e-beam resists can also be patterned with mix & match procedures which combine e-beam and UV exposure (7400, 7520, 7700). The fine structures are written in the resist layer using an electron beam, followed by exposed to UV light (i-line) of the larger structures and a development step as usual. For very thin films of AR-P 7400 and AR-N 7520, a maximum resolution of < 30 nm can be obtained.
Chemically enhanced e-beam resists are AR-N 7700 and 7720. These resists which contain radiation-sensitive acid generators and always require a crosslinking bake after exposure provide a high resolution and allow for structural resolutions of 50 -100 nm, with very high sensitivity. Due to its specifically adjusted low contrast, AR-N 7720 is particularly well suited for three-dimensional structures like diffractive optics or holograms. Refractive indices are 1.48 for PMMAs, 1.49 for copolymers AR-P 617 and 1.54 for CSAR, while refractive indices are in a range of 1.60 - 1.61 for novolac-based e-beam resists.
Customer-specific e-beam resists
The broad range of Allresist e-beam resists covers almost all applications of e-beam lithography. If however special demands should exist (specific film thickness or a particular contrast), are we able to realise also requested experimental samples cost-efficiently within a short time.