Material Properties and Process Compatibility of Spin-on Nano-foamed Polybenzoxazole for Copper Damascene Process
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Material Properties and Process Compatibility of Spin-on Nano-foamed Polybenzoxazole for Copper Damascene Process Takashi Enoki, Kenzo Maejima, Hidenori Saito, and Akifumi Katsumura Fundamental Research Laboratory, Research Department, Sumitomo Bakelite Co., Ltd., 495, Akiba-cho, Totsuka-ku, Yokohama, 245-0052, JAPAN ABSTRACT
We have developed nano-foamed OxD which has good properties such as dielectric constant=2.2, homogeneous distributed nano pores, smooth surface based on polybenzoxazole chemistry and nano-foaming technology. The nano-foamed OxD also has excellent thermal stability, chemical stability and etching property. The developed nano-foamed OxD is one of good candidates for copper damascene structure to achieve shrinking dimensions of future semi-conductor devices.
INTRODUCTION
In shrinking dimensions of future semi-conductor devices, lower dielectric constant (k) material is strongly required in Cu/low k damascene structure. According to the International Technology Roadmap for Semiconductors (ITRS) 2001, ultra low-k interlayer dielectric materials (k < 2.4) will be needed around 2005 [1]. Because the k value of air is one, nano-foaming with air is possible solution to provide lower k material. Polybenzoxazole [2] is one of excellent heat resistant polymers and is synthesized via cyclization of its precursor (poly(o-hydroxy)amide) by polycondensation between bis-o-amino-phenol and dicarboxylic acid derivative monomers (Scheme 1.). H2N S1 HO
OH
S2
+
Bis-aminophenol O C HN
COOH
HOOC
NH2
polycondensation Dicarboxylic Acid Cyclization
O NH C
S2
S1 HO
(Spin-on
OH
Cure)
Precursor (Varnish) N
N
S2
S1 O
O
Polybenzoxazole (OxD) Scheme 1. Chemistry of Polybenzoxazole. S1 and S2 = Spacers
The precursor shows good solubility to several organic solvents, which allows us
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spin-on application. Once the polybenzoxazole is obtained by cyclization from spun-on precursor by heat, it becomes insoluble and shows high thermal stability. We have designed a spin-on nano-foamed OxD (Oxazole Dielectrics) by taking advantage of polybenzoxazole chemistry considering nano-foaming process [3,4]. In this work, we will report material and process properties of nano-foamed OxD which are important to consider Cu damascene process. We will discuss pore size, surface roughness, thermal stability, chemical stability, process compatibility such as etching property and so on. EXPERIMENTAL DETAILS OxD precursor varnishes were spin coated onto silicon wafers to form films from 0.4 um to 1.0 um thick. The films were cured for 1 hour at 250oC and 1 hour at 425oC in N2 atmosphere. The thickness and refractive index of the films were measured with a spectrometric reflectance tool, n & k analyzer 1500 (n&k Technology, Inc.). All the electrical measurements were done using Hg probe (Automatic Mercury Probe CV System SSM 495, Solid State Measurements Co.,Ltd.). Surface roughness of the film was analyzed by atomic force microscopy (AFM), Nano Scope IIIa (Digital Instruments). Determination of pore size was ex
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