Anisotropic Etching of Heavily Doped Polysilicon by a Hot Cl 2 Molecular Beam
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ANISOTROPIC ETCHING OF HEAVILY DOPED POLYSILICON BY A HOT 012 MOLECULAR BEAM T. Ono, S. Hiraoka, and K. Suzuki Central Research Laboratory, Hitachi, Ltd., Kokubunji, Tokyo 185, Japan ABSTRACT Anisotropic etching of n+ poly-Si is achieved using a hot C12 molecular beam and a sidewall protection technique. A hot molecular beam is produced by a free jet expansion of a gas heated in a furnace. A nitrogen radical beam is used to prevent the sidewall etching. The etch rate of n+ poly-Si is 4.3 nm/min at the anisotropic etching condition. INTRODUCTION Damages caused by high energy charged particles during a plasma process for VLSI are becoming serious problems as the integration density increases. The dielectric breakdown of a SiO2 layer and radiation-induced traps have been reported [1,2]. Aiming at a damage free process, we are developing a new etching technique using a hot molecular beam. A hot molecular beam is produced by a free jet expansion of a gas heated in a furnace. This etching has been proven to be damage free. In addition, anisotropic etching of undoped poly-Si has been achieved by a hot C12 molecular (Cl2*) beam
[3]. The purpose of this paper is to widen the application of hot molecular beam etching by introducing sidewall protection to this etching process. Sidewall protection is commonly used in plasma etching to improve the degree of anisotropy [4], but this is the first report of its use in hot molecular beam etching. We apply sidewall protection to achieve anisotropic etching of n+ poly-Si. This is impossible if only a C12* beam is used. EXPERIMENTAL Figure 1 shows the apparatus to produce a hot molecular beam. Here, C12 gas flows through a graphite tube and expands into a vacuum. The
inside diameter of the graphite tube is 2 mm. This tube is heated in a quartz furnace. The furnace temperature is controlled by a tungsten wire Joule heating from 4600C up to 8300C. The C12 flow rate is 5 sccm
Mat. Res. Soc. Symp. Proc. Vol. 201. V1991 Materials Research Society
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QUARTZ TUNGSTEN TUBE WIRE
1H[ -------
/L.L-
CLAMPING PLATE
4
-ClCOVER
5-
50mm
-H
2
GRAPHITE TUBE
Fig.1 Furnace structure and substrate for hot molecular beam etching
ELECTRODE PINHOLE (0.5 mm)
GLASS E-NVELOPE h4)
20 mm Fig.2 Discharge tube to produce N radical beam
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