Since they have been introduced to substitute poly(hydroxystyrene) based 248nm photoresists (PR), 193nm photoresists
based on acrylate chemistry have raised issues regarding their dry etch resistance. These resists undergo severe
degradations during typical dry etch processes involved in gate patterning, resulting in strong film loss, resist chemical
modifications, critical surface roughening and also linewidth roughness (LWR). Other studies have shown that applying
plasma treatments to 193nm photoresist patterns prior to the other plasma etching processes is a way to minimize PR
degradation. Among these plasma treatments, the HBr plasma cure is known to reinforce the 193nm photoresist etch
resistance and to reduce the resist LWR.
In this study, we propose to go further in the understanding of cure plasma treatments impact on a 193nm model resist
polymer (from Rohm & Haas Electronic Materials) using real time in-situ ellipsometry experiments correlated to several
characterization techniques such as in-situ X-Ray Photoelectrons Spectroscopy (XPS), Fourier Transformed Infrared
Spectroscopy (FTIR) and Dynamic Mechanical Analysis (DMA).
The impact of Ar and HBr cure plasma treatments on 193nm PR is investigated and compared. Both treatments lead to
surface and also bulk modifications of the resist films. XPS analyses show that the 10 first nanometers of the resist film
are graphitized after only 20s plasma treatment, resulting in a higher carbon content and therefore indicating a better
etch resistance following the Ohnishi parameter. Besides this superficial modification, FTIR show that the resist film
can be completely modified after HBr cure plasma treatment with the removal of lactone and leaving groups present in
the polymer. The same kinds of modifications are observed with Ar cure plasma treatment but only the first 80nm of the
resist film are chemically modified. A significant decrease of the glass transition temperature is also observed with both
treatments and is related to lactone and leaving group units that remain in the film
Finally, we show that the resist etch resistance is indeed improved if the resist is previously cured. However, in the case
of Ar plasma treatment, the etch resistance is only improved while etching the first 80nm chemically modified resist.
The effectivity of 193nm photoresists as dry etch masks is becoming more and more critical as the size of integrated
devices shrinks. 193nm resists are known to be much less resistant to dry etching than 248nm resists based on a
poly(hydroxystyrene) polymer backbone. The decrease in the resist film budget implies a better etch resistance to use
single layer 193nm photoresists for the 65nm node and beyond. In spite of significant improvements made in the past
decade regarding the etch resistance of photoresists, much of the fundamental chemistry and physics that could
explain the behaviour of these materials has to be better understood. Such knowledge is necessary in order to propose
materials and etch processes for the next technology nodes (45nm and below).
In this paper, we report our studies on the etch behaviour of different 193nm resist materials as a function of etch
chemistry. In a first step, we focus our attention on the interactions between photoresists and the reactive species of a
plasma during a dry etch step. Etch experiments were carried out in a DPS (Decoupled Plasma Source) high density
chamber. The gas chemistry in particular was changed to check the role of the plasma reactive species on the resist. O<sub>2</sub>,
Cl<sub>2</sub>, CF<sub>4</sub>, HBr and Ar gas were used.
Etch rates and chemical modifications of different materials were quantified by ellipsometry, Fourier Transformed
Infrared Spectroscopy (FTIR), and X-Ray Photoelectrons Spectroscopy (XPS). We evaluated different materials
including 248nm model polymer backbones (pure PHS or functionalized PHS), and 193nm model polymers (PMMA
and acrylate polymers) or resist formulations. Besides the influence of resist chemistry, the impact of plasma parameters