The effect of X-ray irradiation on the novella type photoresist

As a result of the rapid development of lithography, it enables semiconductor technology to design more devices in the same area, which therefore makes electronic products faster, more functional, and hold more components. The photoresist, playing an important role in lithography, constantly develops with light wavelength used for exposure, from early entire wavelengths to present optical and non-optical lithography. The light sources of optical lithography have moved from the early 436 nm and 365 nm wavelength to short-wavelength light gradually. It is a big issue to find a suitable photoresist under the exposure of 0.578 nm X-ray light source. In this paper we first proposed to use DNQ / Novolak photoresist sold in the market for the 0.578 nm X-ray lithography. Due to the good resolution of NQ / Novolak photoresists, we obtained a 30 nm line width as shown in Figure 1.In the experiment, it was discover that the exposure amount of X-ray can determine if the photoresist is positive or negative; in low doses, when the photoresist film thickness is increased with the reduced exposure time, and a critical level is reached, the Novolak liquid will become positive photoresist after it is exposed in certain time. The high-dose X-ray beam will make Novolak resin bond break and result in free radicals, which, through resin crosslinking, can improve the internal strength, and reduce developer solubility so the Novolak liquid can become to be a negative photoresist as shown in figure 2. By using synthesized DNQ / Novolak photoresist, under X-ray exposure, we can reduce process line width, and explore principles of photoresist imaging analysis under the different exposure doses.