The Risk of Pattern Collapse for Structures in Future Logic Devices

Abstract

Pattern collapse has long been known in photoresist patterning where the resist patterns merge or collapse during rinsing and drying steps [. The forces responsible for this collapse were identified as capillary forces during the drying process. Structures such as titanium nitride DRAM cylinders [ and silicon Flash shallow trench isolation (STI) lines have also been observed to be pattern collapse sensitive due to increase in aspect ratio of the features. Micro-electromechanical systems (MEMS) devices also show a similar phenomenon, but on a larger length scale, and is referred to as stiction [. For the technology nodes <14 nm, back-end-of-line (BEOL) low-k structures are also on the verge to show pattern collapse behavior. Whether a structure is sensitive to pattern collapse or not depends on several parameters, which will be analyzed in this paper.

Effect of Surface Energy Reduction for Nano-Structure Stiction

“…U T becomes inevitably positive at h=0 and h=L, so U T can be negative only in the case that the total energy has a minimum value in equilibrium. dU E / dh + dU S / dh = 0 [6] The height limit (h') is obtained by the equation [3], [5] and [6].…”

“…Although micro-electromechanical systems (MEMS) devices also have been faced with the stiction issue which is a term derived from "static friction", it is supposed that MEMS "static friction" is caused not only by capillary forces but also adhesion forces, electrostatic forces, van der Waals' forces and hydrogen bonding (3)(4). Supposedly, the release of the stiction is influenced by the correlation between the elastic restoring forces and the adhesion forces (5).…”

Pattern Collapse-Free Drying with Sacrificial Gap Fill Polymers

“…The challenge of collapse free drying is well documented [1,2,3] and increasingly problematic as the impact of liquid surface tension capillary forces affect a growing number of pattern levels, especially in advanced memory designs. Initial work on preventing pattern collapse during drying of high-aspect-ratio (HAR) etched features focused on reducing the capillary force by lowering the surface tension of the rinse liquid, typically by application of isopropyl alcohol (IPA) [4,5] to displace water.…”

Fixed Charge Control of Silylated Surface for Stiction-Free Drying with Surface Energy Reduction Process

“…In the micro-electromechanical systems (MEMS) process, other solutions have been reported to avoid stiction [3,4,5]. We have proposed that a surface energy reduction process (SERP) for the semiconductor process is more effective for avoiding stiction than an IPA drying process [6,7].…”