The Effect of Pad Properties on Planarity in a CMP Process
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The Effect of Pad Properties on Planarity in a CMP Process Hoyoung Kim, Dong-Woon Park, Chang-Ki Hong, Woo-Sung Han and Joo-Tae Moon Process Development Team, Semiconductor R&D Center, Samsung Electronics Co., Ltd. San #24 Nongseo-Ri, Giheung-Eup, Yongin-City, KOREA
ABSTRACT This study presents the effect of pad properties, such as elastic modulus and surface roughness, on planarity in a CMP process. A systematic method to measure planarization length, which represents the die-scale planarity in a quantitative manner, has been proposed. It has been shown that the planarization length is highly dependent on the bulk modulus of the pad. The effect of elastic modulus and roughness of the pad on dishing amount, which represents the feature-scale planarity, has been shown. Dishing amount is determined by the elastic modulus of the superficial layer of the pad, which is typically tens of microns thick, rather than by the bulk elastic modulus of the pad. A double layer pad model has been proposed based on the observed results, which can explain that the dishing amount is reduced by increasing elastic modulus of the pad superficial layer, or by decreasing the surface roughness of the pad.
INTRODUCTION Uniformity and planarity are the representative parameters which characterize CMP performance. As the device shrinks, the importance of planarity has been increased owing to its pattern dependency. The planarity is known to be affected by pad properties, slurry, polishing pressure, etc. [1] Especially, many studies have been done on the relationship between pad properties and planarity such as dishing, erosion, step height reduction [2-4]. In those studies, the nonlinear behavior of polyurethane pad makes it difficult to get reliable model. The purpose of this study is to examine the effect of pad properties on planarity including nonlinear behavior of pad. Planarity has been classified into two regions. One is the die-scale which is in the order of several millimeters, and the other is the feature-scale which is in the order of tens of microns. Planarization length and dishing have been selected as the representative parameter of each region and compared through some experiments.
RESULTS AND DISCUSSION Pad properties In this experiment, four kinds of pads which are IC1000 pad (Rodel Co.), IC1000/Suba IV stack pad (Rodel Co.), soft pad (Pad A) and hard pad (Pad B) were used. Pad A and Pad B were specially designed to observe the effect of pad elastic modulus and surface roughness on planarity. Pore sizes of these two pads were twice larger than that of IC1000 pad and their elastic moduli were controlled by pore density (Table I).
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Table I. Density and pore diameter of each pad IC1000 Pad A Pad B 0.75 0.69 0.93 30~40 60~80 60~80
Density Pore Diameter
Unit g/cm3 ㎛
The elastic mod
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