Category: VLSI and ULSI Technology Effect of supercritical drying on sol-gel deposited silica aerogel thin films at different temperatures Anil Gaikwad, Yogesh Mhaisagar, Jigar Bhavsar and Ashok Mahajan * Department of Electronics, North Maharashtra University, Jalgaon (MS)- 425 001, India. * E-mail: ammahajan@nmu.ac.in Abstract-Now a days silica aerogel thin films are attracted more attention as an interlayer dielectric (ILD) application in ULSI technology due to the lowest dielectric constant. In present work, we report the successful deposition of silica aerogel thin films on Si wafer by sol-gel technique. Further, in order to introduce porosity the deposited thin films were dried at supercritical condition with different temperatures. Elipsometric study shows that the refractive index (RI) of as deposited film is observed to 1.44 whereas RI of super critically dried thin films is observed to be decreased to 1.29 for the film dried at 40 o C. The film thickness observed to be decreased from 200nm to 129nm with increase in supercritical drying temperature. The dielectric constant of the films is observed to be lowered to 2.8 for the film dried at 40 o C temperature. The pore volume and porosity of the films increased up to 0.25 and 37% respectively with increase in drying temperature while the density of the films is decreases with increasing temperature. Index Terms—silica aerogel thin film, super critical drying, RI, elipsometry, sol-gel, ULSI. I. INTRODUCTION In recent years, advancement in fabrication process results in revolution in the technology that helps in scaling the device size towards nanoregime with increase in device speed and device density on single chip. This leads to introduction of new issues like RC delay, cross talk and power consumption in Back End of Line (BEOL) process [1]. To overcome these issues it is essential to replace the conventional SiO 2 layer with new ILD materials having low dielectric constant. As per the International Technology Roadmap for Semiconductors (ITRS) [2] it is expected that devices requires an ILD materials with lower k values. It is observed that introduction of porosity is the superior way to achieve lower k value of the ILD materials [3]. As the dielectric constant of porous low-k films is mainly dependent on the porosity of the films, raising the porosity with closed pores and its uniform distribution in the film has become the most important factor in porous low-k films preparation [4]. Silica aerogel thin films dried by a supercritical process is the promising candidate realized as k value below < 2 shows applicablity as ILD material for ULSI technology in nanoelectronics [5]. Currently, their are two main technological routes in use to deposit the low-k dielectric materials, spin-on technique or plasma enhanced chemical vapour deposition (PECVD) technique. The spin-on technique (or spin-coating, SOD) consists of the deposition of a solution by centrifugation followed by steps of baking and thermal treatments in order to eliminate solvents and consolidate the layer by crosslinking [6-8]. Generally aerogels are prepared by the supercritical drying and by ambient pressure drying method [9-11], here we used supercritical drying method to prepare silica aerogel thin films. In present work the silica aerogel thin films were deposited by using sol-gel spin on technique. To obtain the silica aerogel thin films we dried the thin films at supercritical conditions at different temperatures in autoclave. This manuscript has four sections, second section describes the experimental details used for the deposition of SiO 2 and drying of the deposited films at different temperatures. The results are discussed in third section and fourth section concludes the conclusion of work. II. EXPERIMENTAL DETAILS The p-type (100) single side polished (SSP) Si Wafers, with resistivity ~1-10 ohm-cm, have been used as substrates. These substrates were cleaned using dilute HF, Trichloroethylene, Acetone and Methanol followed by De- Ionized water. The coating solution was prepared by mixing Tetraethylortho silicate (TEOS) as a source of Si with ethanol, deionized water and acid catalyst at room temperature with a molar ratio of 1:4:2:0.5 of TEOS: Ethanol: H2O: HF respectively. After stirring the solution for 1 hour sol was dispensed on p-type pre-cleaned Si (100) substrate before the gel point is reached and spun on spin coater at 3000 rpm. Experimental Process flow for the deposition of silica aerogel thin films is shown in Fig. 1. FIG.1. Process flow for deposition of silica aerogel thin films. The spin coated thin films later on dried at supercritical conditions using CO 2 as supercritical fluid (for CO 2 very low V. K. Jain and A. Verma (eds.), Physics of Semiconductor Devices, DOI: 10.1007/978-3-319-03002-9 , _ Environmental Science and Engineering, Ó Springer International Publishing Switzerland 2014 9 3