Interfacial effects on sensitization of chemically amplified extreme ultraviolet resists

Abstract

With the improvement of lithography resolution in horizontal direction, the thickness of resist films becomes thin to avoid the pattern collapse. The thinning of resist films is an important issue in the development of next-generation lithography process. In this study, the interfacial effects on the sensitization of chemically amplified extreme ultraviolet (EUV) resists were investigated using a Monte Carlo method on the basis of their sensitization mechanism. The chemically amplified resist is a standard resist used for the fabrication of semiconductor devices. In chemically amplified resists, thermalized electrons reduce sensitizer molecules upon exposure to EUV radiation. The low-energy secondary electron dynamics at the vacuum-resist and resist-underlayer interfaces strongly affected the distribution of decomposed sensitizers. In particular, the resist bulk layer almost disappeared at 20 nm pitch in the specific cases. The control of interfaces becomes important in the development of next-generation lithography process.

Effects of underlayer absorption coefficient on bridging risk in chemically amplified resist process for extreme ultraviolet lithography

“…The boundary condition between the resist layer and the underlayer for secondary electrons was assumed to be the total transmission. 27) The reaction radii of PAG and PDQ with thermalized electrons were set to be the same as that of triphenylsulfonium triflate. 33) The sum of PAG and PDQ concentrations (total sensitizer concentration) was 0.2 (molecule) nm −3 .…”

“…[17][18][19][20][21][22][23][24][25] Among them, the low-energy electron dynamics at the interfaces is an important factor. [26][27][28] When there is little difference between the bulk potentials of the resist layer and underlayer, the secondary electrons generated in both layers can cross their interface. 26) In this study, the secondary electron dynamics in a resist-underlayer system was investigated assuming lineand-space resist patterns to assess the effects of the underlayer absorption coefficient on the bridging risk.…”

Defect risks at interfaces of chemically amplified resists in extreme ultraviolet lithography process

“…21) From these viewpoints, the suppression of stochastic defects at the interfaces has been investigated. However, the short-range backexposure effects of low-energy secondary electrons [22][23][24][25] should be taken into account to control the vertical profiles of resist patterns in addition to the factors described previously. In this study, the sensitization and reaction processes induced in chemically amplified EUV resists were calculated for eight combinations of boundary conditions using a Monte Carlo method to estimate the dependence of defect risks 26) on the conditions of resist interfaces.…”

“…Figure 1 shows schematics of the assumed boundary conditions for low-energy secondary electrons. 23) BC VR and BC RU represent the boundary conditions at the resist interfaces with vacuum and an underlayer, respectively. A long arrow and a pair of short arrows indicate the total transmission and the total reflection of low-energy secondary electrons at the interface, respectively.…”

Shielding effect of underlayer against secondary electrons generated in substrate in extreme ultraviolet lithography

“…5,6) In the EUV resist process, we do not generally consider the reflection of EUV photons at the substrate, because the refractive index of typical substrates such as Si is close to 1.0 and similar to the refractive index of the resist unlike in the case of deep UV and vacuum UV. In the EUV resist process, we should be concerned about the secondary electrons generated in the substrate, 7,8) similarly to the electron beam (EB) resist process, [9][10][11][12] although not only secondary electrons but also primary electrons are included in the EB resist process. The span of the effect of electrons generated in the substrate is different by four orders of magnitude between EB and EUV because of their energy difference.…”