Novel polymeric antireflective coating (PARC) for better uniformity control of critical dimension

Abstract

A novel polymeric bottom anti-reflective coating (PARC) process has been developed for O.25tm Flash device on the severe topology with KrF lithography. The refractive index, n, and the extinction coefficient, k, of PARC can be tuned to match the optical properties of substrates. The CD uniformity range within wafer is O.O27m and the variation is O.OO7tm for the polymer BARC. However, the data from organic ARC is O.O47tm and O.O24tm for the CD uniformity and variation, respectively. The PARC is a uniform and conformal layer of thin film, which significantly improves the CD uniformity of critical layers such as poly Si gate and other features over topography. Since PARC is a highly conformal film, it can be deposited very uniformly across topography. The thickness of PARC is very uniform on the poly Si/TEOS oxide stack of polysilicon gate of a O.25im Flash device with highly topology. In contrast, the thickness of BARC varies from place to place. While the thickness of BARC is very thick in the trough, it becomes quite thin at the top. Such a variation not only decreases the photo process latitude, but also creates a problem for the etch process. Furthermore, the etching rate of PARC is about 200% higher than BARC, so that there is less resist loss during BARC open step.

A new method to characterize conformality of BARC coatings

“…A planarizing coating produces a global flat surface and minimizes concerns related to photoresist DOF, but the difference in BARC thickness will cause a difference in reflectivity and a plasma etching bias when etching the BARC layer. On the other hand, as the exposure wavelength of the lithography scanner or stepper is decreased, there is an increase in reflected light from the underlying films [2]. Uniformity of BARC thickness is an important factor in finely controlling reflectivity.…”

“…Traditionally, the conformality or degree of planarization of a BARC is calculated by a simple equation that includes terms for the maximum top thickness, the minimum bottom thickness, and the step height as related to coating over topography [1,2,6,8,9]. Though this single point method gives a rough estimation of the conformality, it cannot represent the whole coating coverage and does not take into account the effects of material properties.…”