As feature sizes continue to the 45nm and 32nm nodes, significant challenges will continue to arise in both
front-end-of-line (FEOL) and back-end-of-line (BEOL) applications. The reduced thickness, as well as the
reduced etch resistance, of the photoresist (PR) makes it nearly impossible to use the PR as both an imaging
and a pattern transfer layer. This etch challenge has led device manufacturers and vendors to explore the
use of multi-layer (trilayer) stacks. Multilayer stacks are typically comprised of a thick via-filling organic
layer that will provide adequate etch resistance while etching into low-k and ultra-low-k dielectrics. A
silicon-containing layer is then applied on top of the via-filling layer, which will provide improved
imaging, as well as etch resistance for the organic layer. The PR is then applied on top to complete the
multilayer stack. While many challenges have presented themselves in multilayer stacks, new challenges
such as rework and cleaning have arisen. As low-k and ultra-low-k dielectrics become more prevalent,
traditional oxygen ashing processes for the removal of PR and anti-reflective coatings can cause damage to
the dielectric layer due to the chemical and physical structures of the materials involved. While some
processes have been developed to replace damaged dielectric material during ashing and etching through
silyation, alternate processes are being developed where entirely wet stripping processes can remove
multilayer stacks. One advantage of an entirely wet removal process is that it can prevent damage caused
by ashing or etching, and the wet stripper is developed so it does not attack the dielectric films. While an
entirely wet removal process has potential advantages, it still must be proven that these processes can
remove residues that are left after etch processes, sufficient removal of particles are obtained, and any
material loss of the dielectric layer meets the requirements of the customer and the International
Technology Roadmap for Semiconductors (ITRS). Other challenges are presenting themselves, as many
customers would like to move from batch-type wet rework or cleaning processes to single wafer tool
It is the intent of this paper to not only identify new wet cleaning materials that can be used to remove
multilayer materials by means of an entirely wet process, but also to find single wafer tool processes that
produce fewer particles (defects) and cause no dielectric material loss.
Spin on bottom anti-reflective coatings were introduced to the semiconductor industry about 20 years ago to help control substrate reflectivity, improve critical dimension (CD) control, and, most importantly, improve depth of focus window, thus improving throughput and yields. Bottom anti-reflective coating (BARC) materials are either inorganic or organic in nature. Inorganic BARCs are chemical vapor deposition (CVD) films that work on the principal of destructive interference to eliminate reflectivity and demand tight thickness control in the BARC layer. In contrast, organic BARCs are generally spin-on polymeric materials that reduce substrate reflectivity by absorbing exposure radiation to provide greater latitude in thickness control. As an added benefit, organic spin-on BARCs also provide a level of planarization efficiency prior to photoresist deposition to improve depth of focus and process window in the photolithography step. As the feature sizes continue to shrink, etching becomes very challenging due to thin ArF photoresist (PR) layers which are much less etch resistant compared to KrF photoresists. The reduced thickness, as well as the reduced etch resistance, of the PR makes it nearly impossible to use the PR as both an imaging and a pattern transfer layer. This has lead to the development of a new class of spin-on “hybrid” BARC materials which not only have improved etch selectivity to the PR due to inorganic functionality but also have the absorbing properties, and hence offer greater process latitude. Hybrid BARC (H-BARC) materials enable the BARC layer to act as both an anti-reflective coating and as a pattern transfer layer in standard etch-back integration schemes. Due to the polymeric functionality associated with H-BARCs, these materials have exceptional gap-fill and planarization properties and can also be used in via-first dual damascene applications where similar etch characteristics between interlayer dielectric materials and the via-fill BARC enable better CD control.
This paper will focus on the benefits of ENSEMBLE ARC materials, a new class of spin-on hybrid BARC materials, which can be used in either standard BARC applications or in via-first dual damascene applications which require that the BARC act both as an anti-reflective coating and as a via-fill material to assist in CD control during trench etch processes. This paper demonstrates lithography with 193-nm resists, resist compatibility, via-fill performance, optical properties, and etch rates with different plasma recipes.
A novel spin-bowl-compatible bottom anti-reflective coating (BARC) for i-line applications is presented in this study. The BARCs were prepared from a titanate sol-gel material, which exhibits excellent spin-bowl compatibility with a wide variety of solvents. A variable angle spectroscopic ellipsometer measurement on the titanate BARC gives an n (real refractive index) value of 1.71 and a k (imaginary refractive index) value of 0.40. The titanate BARC shows good compatibility with resist solvents and excellent photolithography performance with resolution down to 0.35 μm. No metal contamination was observed with this BARC when gate oxide integrity (GOI) testing was performed on different size capacitors.