Introduction
Since the first naphthoquinone photosensitizer 2,1,5-diazonapthoquinone (DNQ) was reported by Oscar in 1944, more and more naphthoquinone photosensitizers were extensively applied to the photoresist.[1] The naphthoquinone photosensitizers play a key role in the field of lithography and especially DNQ groups are important for the photosensitive coating. DNQ is the key photoactive components of resists and widely used in the fabrication of integrated circuits as common materials. Photoresists are light sensitive materials that release molecular nitrogen undergoing a ring contraction (Wolff rearrangement) when exposed to radiation. In the photolithography process, the photoresist of DNQ solution is applied on the surface of a cleaned substrate sequentially forms a uniform thin film by spin coating. After this, the mask printed with the target pattern is put in between the photoresist layer and the light source to conduct the exposure. More importantly, the photoresists can serve as a protection layer to keep materials intact in the subsequent fabrication process.
Figure 1. The application of DNQ photosensitizer
Effect Factors of Photolithography Process by Naphthoquinone Photosensitizers
With the increasing demand for portable electronic products in our daily life, including mobile phones, computers, portable medical equipment and so on, more and more attention was put on the semiconductor industry. Meanwhile, people put forward higher requirements for processing technology of the photolithography process. Therefore, it is very necessary for us to understand the factors that affect photolithography process by naphthoquinone photosensitizers.
The photolithography process is significantly affected by operational conditions, such as the temperature of naphthoquinone photosensitizers. In order to choose the best conditions, the effects of temperature were tested preliminarily. Meanwhile, to keep constant all experimental factors except the excitation wavelength, we get the qualitatively different irradiation spectra. After analyzing the spectra, the results suggest that the compounds were not thermally stable and gradually decay when gradually warmed up to equilibrate at room temperature. It should be noted that the spectra have changed observably in the UV and in the visible regions.
The photolithography process also affects by the concentration of naphthoquinone photosensitizers.[2] The spectra at the end of the irradiation significantly changed when increasing the concentration of naphthoquinone photosensitizers. The spectra suggest that there is a weak color band at low concentration while the band notably increased at a high concentration compared to dilute solution. In addition, some relatively long-lived intermediate species were produced at high concentration that could be able to interact with the ground state DNQ, sequentially subtract photosensitive material to the overall system.
Except for the temperature and concentration, the solvent is also important for the photolithography process. The spectra were measured in different solvents and the other factors are the same. The spectra suggest that the clear signal was shown in polar solvents while there is almost no signal in the non-polar solvents.[3]
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References
- Cipolloni M.; et al. Effects of solvent, excitation wavelength, and concentration the photobehavior of some diazonaphthoquinones. J. Org. Chem. 2011, 25: 205-220.
- Bienvenu C.; et al. Photosensitized oxidation of 5-methyl-2-deoxycytidine by 2-methyl-1,4-naphthoquinone: characterization of 5-(hydroperoxymethyl)-2-deoxycytidine and stable methyl group oxidation products. J. Am. Chem. Soc. 1996, 118: 11406-11411.
- Luo C.; et al. Review of recent advances in inorganic photoresists. RSC Adv. 2020, 10(14): 8385-8395.
