Impact of HBr and Ar cure plasma treatments on 193nm photoresists

Abstract

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.