Thin Solid Films 458 (2004) 309–313 0040-6090/04/$ - see front matter  2003 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2003.11.309 Submicronic etching of borophosphosilicate glass using NF and NF y He 3 3 radio frequency glow discharge N. Mekkakia Maaza*, A. Boudghene Stambouli Laboratoire des Dispositifs Microelectroniques Avancees, Electrical Engineering Faculty, Department of Electronics, USTO, ´ ´ BP 1505 El M’Naouar, (31000) Oran, Algeria Received 9 December 2002; received in revised form 14 October 2003; accepted 27 November 2003 Abstract The etching of borophosphosilicate glass (BPSG) in NF and NF yHe radio frequency (RF) glow discharge has been 3 3 characterized. The etch rates, BPSGyresist selectivity and etch profile have been investigated along with the reactor geometry, namely the inter electrode distance, by which the process can be optimized. The results shows that the etch rates of BPSG are 650 nmymin at RF power of 500 W, pressure of 0.3=10 Pa and 60 sccm flow rate of NF gas. The selective etching BPSGy 2 3 resist has also been examined and was significantly enhanced from a value of 1.2 to 2 under 16% of Helium injection into NF 3 discharge at high pressure of 0.9=10 Pa. The increase of inter electrode distance of the reactor improves the selectivity value 2 but reduces the BPSG etch rate. The BPSG etch profile became isotrope for inter electrode distance value of 5=10 m and y2 higher. The best value of the selectivity was obtained for an inter electrode distance of 15=10 m. For completeness of the y2 process anisotropic etching was achieved, the obtained tapered sidewall was characterized as having an angle of 388 with the normal surface.  2003 Elsevier B.V. All rights reserved. Keywords: Etching; Contacts; Glow discharge; Silicon oxide 1. Introduction With the increase of the integration level and the reduction of the transistor geometry, contact holes and vias in the silicon dioxide become more and more difficult to cover by a metal layer that is applied to make contact with the silicon substrate. This difficulty resides in the non-uniform deposit and the rupture of the strip of the set down metal on the contact hole. In order to permit a metallic deposit without rupture of the strip, it is necessary to taper the sidewall of these opening contacts. Borophosphosilicate glass (BPSG) has been devel- oped in the VLSI technology to replace the silicon dioxide like insulating dielectric between the polysilicon and the first level of metal. The utilization of the BPSG permits the reduction of the surface roughness and produces a tapered sidewall of contact holes that drag *Corresponding author. Tel.yfax: q213-41-422-981. E-mail addresses: nmekakia@univ-usto.dz (N. Mekkakia Maaza), aboudghenes@yahoo.com (A. Boudghene Stambouli). an excellent recovery by metal w1x. One of the mostly used techniques consists to etch the BPSG in two steps: The first step consists of etching the BPSG layer isotropically on its half thickness, whereas in the second one, the BPSG layer is etched anisotropically on its remaining half thickness. The isotropic etching of BPSG is obtained in a radio frequency (RF) glow discharge. The etch process will be characterized for various parameters of the discharge (RF power, flow rate, chamber pressure) and those of the reactor such as the inter electrode distance. The objective aimed in this work is to optimize the isotropic etching step of the doped silicon oxide and to study the series of anisotropic step for the best operating conditions. The gas used during this work is nitrogen trifluoride (NF ). Its utilization in dry etching has become impor- 3 tant particularly in applications that require high etch rate. It also offers the advantage to have the ability to liberate free active fluorine species in the plasma without formation of polymers. NF gas is used as an alternate 3