Curing Study of Hydrogen Silsesquioxane Under H 2 /N 2 Ambient
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CURING STUDY OF HYDROGEN SILSESQUIOXANE UNDER H2/N2 AMBIENT HUEY-CHIANG LIOU, EVAN DEHATE, JERRY DUEL, AND FRED DALL Dow Corning Corporation, Semiconductor Fabrication Materials, Midland, MI 48686-0994 ABSTRACT Thin film properties of hydrogen silsesquioxane (HSQ) cured at different temperature under N2 and H2/N2 ambients have been studied. In this study, it was found that compared to an N2 ambient, film curing in an H2/N2 ambient will impact HSQ properties when the temperature is 400°C – 500°C. H2/N2 ambient can be used to minimize the dielectric constant while increasing modulus of the films. The data indicates that H2 can minimize the oxidation of the HSQ films and maintain the dielectric properties. INTRODUCTION As the geometry of microelectronic devices continues to shrink, new materials with low dielectric constant (k) and gap fill capability are being sought after by the semiconductor industry [1]. These new materials are used as an interlayer dielectric to enhance the performance of integrated circuits (ICs) by reducing the resistance-capacitance (RC) delay and which, in turn, increases the signal propagation speed. Recently, hydrogen silsesquioxane (HSQ) films have attracted attention in the semiconductor industry due to low dielectric constant (k < 3.0), ease of processing, good planarization properties and excellent gap fill capability in deep submicron features [2]. The general chemical composition of HSQ before curing is (HSiO3/2)n and a representative molecular structure is shown in Figure 1. From the infrared spectrum, it has been shown that HSQ consists random network linkage based on the eight-corner H8Si8O12 structure [3]. When thermally processed, the bonds in HSQ break and its molecular structure is rearranged/redistributed into an amorphous film with more network bonding. H Si O
Figure 1. The simulation of HSQ molecule.
A large reduction of SiH bonds occurrs when the cure temperature is greater than 350°C in an N2 ambient or lower than 350°C in an O2 ambient [3-4]. The reaction is faster at higher cure temperatures. It was also found that when the loss of hydrogen exceeds a certain percentage of the initial value, polar -OH groups are incorporated into the film and increase the dielectric constant [5]. In addition, increasing the concentration of O2 in the curing ambient will magnify this effect. Therefore, HSQ might achieve more desirable film properties, e.g. k < 3, if the
D5.12.1
Table 1. The curing conditions of HSQ in a quartz furnace Gas Ambient Start Temp.(°C) Cure Temp. (°C) Cure Time (hr.) A1, A2, A3 40 350 1.0 40 40 40
A1, A2, A3 A1, A2, A3 A1, A2, A3
400 450 500
1.0 1.0 1.0
Ambient: A1-N2, A2-5%H2/95%N2 , A3-10%H2/90%N2
presence of H2 can react with O2 to reduce the oxidization of HSQ. It might also be possible that the presence of H2 can participate in the reactions whose net effect is to minimize the loss of SiH bonds while still allowing film densification, thus improving the mechanical strength. Therefore, in an attempt to produce low k films with higher density and bette
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