<title>Single closed contact for 0.18-micron photolithography process</title>

Abstract

With the rapid advances of deep submicron semiconductor technology, identifying defects is converted into a challenge for different modules in the fabrication of chips. Yield engineers often do bilinap on a memory circuit array (SRAM) to identify the failure bits. This is followed by a wafer stripback to look for visual defects at each deprocessei layer for feedback to the Fab. However, to identify the root cause of a problem, Fab engineers must be able to detect similar defects either on the product wafers in process or some short ioop test wafers. In the photolithography process, we recognize that the detection of defects is becoming as important as satisfying the Critical dimension (CD) of the device. For a multi-level metallization chemically mechanical polish backend process, it is very difficult to detect missing contacts or via at the masking steps due to metal grain roughness, film color variation and/orprevious layer defects. Often, photolithography engineer must depend on Photo Cell Monitor (PCM) and short ioop experiments for controlling baseline defects and improvement.In this paper, we discuss the fmdings on the Poly mask PCM and the Contact mask PCM. We present the comparison betweenthe Poly mask and the Contact mask ofthe I-line Phase Shifted Via mask and DUV maskprocess for a O.l8micron process technology. The correlation and the different type ofdefects between the Contact PCM and the Poly Mask are discussed. The Contact PCM was found to be more sensitive and correlated to contact failure at sort yield better. We also dedicate to study the root cause of a single closed contact hole in the Contact mask short loop experiment for a 0. 18 micron process technology. A single closed contact defect was often caused by the developer process, such as bubbles in the line, resist residue left behind, and the rinse mechanism. We also found surfactant solution helps to improve the surface tension of the wafer for the developer process and this prevents Ieliminates a single dosed contact hole defects. The applications and effects of using different subsirates like SiON, different thickness ofOxides, and Poly in the Contact Photo Mask is shown. Finally, some defect troubleshooting techniques and the root cause analysis are also discussed.

A systematic study of missing via mechanism and its solutions

“…As we know that the color variation within a thin film, such as inter-metal dielectric (IMD) or just the photoresist or BARC means thickness variation of the thin films, which produces interference patterns. Such "core" can possibly be related to the particles in the developer cup or particles generated by inadequate developing process [4][5]. But the fact that the particle in developer cup is usually found randomly throughout the wafer indicates that the particle, which is detected at the edge of the wafer, is related to the developing process.…”