Morphological and Structural Evolution of an Ultra-low-k Dielectric During the Porogen Removal
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0914-F02-04
Morphological and Structural Evolution of an Ultra-low-k Dielectric During the Porogen Removal Diane Rebiscoul1, Héléne Trouvé2, Bruno Remiat3, Laurence Clerc4, Didier Louis4 , and Gerard Passemard5 1 LETI, CEA, 17 rue des Martyrs, Grenoble, France, 38054, France 2 Rohm and Haas Electronic Material LLC, Grenoble, France, 38054, France 3 LITEN, CEA, 17 rue des Martyrs, Grenoble, Isere, 38054, France 4 LETI, CEA, 17 rue des martyrs, Grenoble, Isere, 38054, France 5 LETI, STmicroelectronic, 17 rue des Martyrs, Grenoble, Isere, 38054, France
ABSTRACT The use of porous ultra-low-k materials between interconnections for sub 45nm technologies has introduced some barrier diffusion and mechanical problems. In order to avoid the problems caused by the porosity, a hybrid dense material (porogen and matrix) can be used in an alternate integration scheme. In this approach, the porogen is removed after CMP steps by a thermal cure or UV assisted thermal cure. In this work, we have first characterized the impact of the temperature and the duration of the thermal cure on the material. The crosslinking degree increases and the porogen amount decreases with increasing cure temperature. The most important impact of the curing duration happens between 350°C and 400°C. The increase of the curing duration leads to an increase of the porogen loss and a decrease of the refractive index. Secondly, in order to assess the structure of the layer as a function of the depth, the material was etched in a 0.05% HF solution and then characterized. According to the temperature and duration of the cure, the etch-rate can vary as a function of the material depth. This variation is related to a complex gradient inside the material. INTRODUCTION Reducing the RC delay is becoming an important challenge for high performance interconnects for sub 45nm technologies. It will require the use of low capacitance and low resistance materials such as low-k materials and copper. The introduction of porosity inside the material is a way to decrease the dielectric constant. Meanwhile, the porosity can lead to the diffusion of the CVD barrier layer inside the pores [1] and to low mechanical properties [3,4] which can be a problem during the mechanical polishing step [4]. In order to avoid these issues, a hybrid dense material containing a silsesquioxane matrix and a porogen, i.e. Solid First™ ILD approach proposed by Calvert and Gallagher, can be used as the integration scheme. The porogen is then removed after the metallization and mechanical polishing steps by a thermal, UV [5] or supercritical CO2 [6] cure liberating the porosity. Standard processes used during the integration can be performed at temperatures above 350°C; consequently the material morphology and structure can be modified. In this paper we propose to study the impact of the temperature and the duration of the cure on a hybrid spin-on methylsilsesquioxane (MSQ) material. In a first part, the hybrid material’s morphology and structural evolution was characterized by ellipsometry, X-ray r
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