| AVS 63rd International Symposium & Exhibition | |
| Plasma Science and Technology | Thursday Sessions |
| Session PS-ThA |
| Session: | Plasma Chemistry and Plasma Surface Interactions |
| Presenter: | Adam Pranda, University of Maryland, College Park |
| Authors: | A. Pranda, University of Maryland, College Park Z. Tomova, University of Maryland, College Park S. Gutierrez Razo, University of Maryland, College Park J.T. Fourkas, University of Maryland, College Park G.S. Oehrlein, University of Maryland, College Park |
| Correspondent: | Click to Email |
Multicolor photolithography is an alternative to extreme ultraviolet (EUV) lithography in attaining device feature sizes below 10nm. The use of this technique requires modification of existing acrylate-based photoresists in order to enable selective photochemistry with multiple wavelengths of light. In the following work, we establish the viability of multicolor photoresists by comparing their plasma etching behavior to industry-standard 193nm and 248nm photoresists.
The 193nm and 248nm photoresist polymers commonly used in industry are abundant in C-H bonds that scission when exposed to high energy ions that are characteristic of plasma etching. The rapid removal of volatile hydrogen- and oxygen-based carbon products results in the formation of a dense amorphous carbon (DAC) overlayer in the nm range. Steady-state etching of the bulk photoresist entails the constant removal and reformation of this overlayer, and the DAC layer acts as an etch-inhibiting layer on top of the bulk resist. The overall density of the overlayer will determine the etching behavior of the underlying photoresist.
In this work, we define a baseline for comparing multicolor photoresists by investigating the relationships between chamber conditions, formation of the DAC overlayer, and the resultant etch yields for a poly(methyl methacrylate)-based 193nm photoresist polymer (PR193) and a polystyrene-based 248nm photoresist polymer (PR248) using an inductively-coupled plasma (ICP) reactor as well as an electron cyclotron wave resonance (ECWR) reactor. The thickness and refractive index of both the DAC overlayer and bulk photoresist layer were monitored in real-time using in-situ ellipsometry.
We observe a correlation between the ambient chamber oxygen concentration, magnitude of the DAC overlayer refractive index (reflective of material density), and photoresist steady state etch rate. In the absence of ambient oxygen, the primary steady-state etching mechanism is physical sputtering. In the presence of ambient oxygen, the etching mechanism has contributions from physical and chemical sputtering, the latter mainly through adsorbed oxygen on the sample surface. Removal of carbon from the overlayer is enhanced by chemical sputtering, resulting in a less dense DAC overlayer which yields a higher steady state etch rate compared to the oxygen-deficient condition. These observations are useful as a baseline for evaluating the behavior of multicolor photoresists and provide a benchmark to guide which photoresists to synthesize to achieve the desired etching behavior.
The authors gratefully acknowledge the financial support of this work by the National Science Foundation (NSF CMMI-1449309).