Medusa 82 – the alternative to HSQ-resists, storage stability

Our research team successfully developed a negative resist with high resolution and plasma etching stability in oxygen. Already with the first samples, it was possible to achieve the properties of HSQ.

For this purpose, aptitude tests were carried out at Raith GmbH. The area dose was approx. 1250 μC/cm² (30 kV); the resolution of single lines about 11 nm (Fig. 1). Development was performed in aqueous-alkaline manner in a strong TMAH solution. Even higher resolutions are possible if specially adapted developers are used.

High resolution test with Medusa 82 (SX AR-N 8200.03/1), 50 nm, SB 10 min @120°C, 30kV, 90s AR 300-44), Raith GmbH

Further tests demonstrated not only improved process stability as compared to HSQ, but also higher storage stability.

Repetition of high resolution assay with Medusa 82 layers stored for 22 days

Coated substrates are characterized by excellent storage stability. While for HSQ, standby-times of only a few hours may already be relevant and can lead to a deterioration of results, studies with 22-day-old layers of Medusa 82 show neither a decrease in sensitivity, nor a reduction of the maximum possible resolution or the achievable contrast.

	AR 300-44	0.26n	AR 300-73	0.70n
storage time (days)	contrast	dose (uC/cm2)	contrast	dose (uC/cm2)
0	4.7	690	4.6	785
22	3.8	690	3.8	785

Also developers with higher TMAH concentration can be used for Medusa 82, e.g. AR 300-73. With comparably good contrast, the sensitivity is slightly lower as compared to a development with AR 300-44 (0.26 n TMAH). The stored samples again show a nearly identical behaviour.

The research on Medusa 82 is continued within the scope of a scientific project. The aim of these experiments is an increase of the sensitivity by maintaining the very good etch stability and the excellent resolution to a large extent. Besides, by addition of photosensitive components, we aim at an application as photo resist. Please ask for the status quo if you are interested.