Effect of Retainer Ring Pressure in Ceria Based CMP

Abstract

Consumable of Chemical mechanical polishing (CMP) process for global planarization can be divided by pad, conditioner, and slurry. Wafer is applied to pressure on the pad with Slurry. Among the abrasives contained the slurry, although ceria has a low concentration, the removal rate is higher than the silica on inter-layer dielectric (ILD)/inter-metal dielectric (IMD) CMP process. Removal rate (RR) increased by Preston’s equation in proportion to the pressure and rpm (RR=KPV). Where K is a Preston’s constant, P is the main pressure, and V is the relative velocity. Yield improvement method in the semiconductor is a large uniform area after CMP process. In other words, wafer edge area should be minimized. It is important to control uniform pressure distribution. Head structure can be divided by main pressure for removal and retainer ring pressure for prevention out of course. In this research, pressure distribution is demonstrated by controlling the different pressure wafer pressure and retainer ring in a single pressure structure. Removal rate changed by different pressure due to pad deformation. Relative pressure difference changed from 150 to 30 g/cm2 to demonstrate for the reason. In case of the low pressure (1, 2psi), the smaller relative pressure difference increases the uniformity, but the removal rate is decreased. In the high pressure (3, 4 psi), the removal rate and uniformity are not big changes according to relative pressure difference. But parameters of temperature and coefficient of friction are not same. This research investigated the mechanism of how to affect the ceria in ILD/IMD CMP through each parameter.Figure 1. Removal rate according to relative pressure difference of retainer ring, (a) low pressure, and (b) high pressure. Figure 1