The Formation of Rugged Surface Polycrystalline Silicon Using Cl 2 /O 2 Plasmas: The Role of Oxygen
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THE FORMATION OF RUGGED SURFACE POLYCRYSTALLINE THE ROLE OF OXYGEN. SILICON USING C12 /02 PLASMAS: N. OZAWA, N. IKEGAMI, Y.MIYAKAWA, AND J. KANAMORI VLSI R&D Center, Electronic Devices Group, OKI Electric Industry Co.,Ltd, 550-1, Higashiasakawa, Hachioji, Tokyo193, Japan ABSTRACT The formation of rugged surface polycrystalline silicon (poly-Si) using C12/02 plasmas in which 02 concentration is 0-10 % has been investigated. Phosphorus doped poly-Si (n+ poly-Si) surface is rugged by the plasma etching under the condition that 02 concentration are 1-5 % at 10 Pa, but is not rugged at 1.3 Pa. On the other hand, undoped poly-Si surface is not rugged in C12 /0-10 %02 plasmas at 10 Pa. Oxygen and phosphorus play an important role in the ruggedness of n+ poly-Si. The ruggedness mechanism has been investigated using scanning electron microscope, optical emission and mass spectrometry. The ruggedness mechanism is spectroscopy suggested that in C12 plasmas added a small amount of oxygen, nWpoly-Si is etched selectively at the grain boundaries which contain more phosphorus than in grains. The Cl emission intensity and n÷ poly-Si etch rate reach maximum in C12/3 %02 plasma at 1.3 Pa. Oxygen has a possibility of promoting SiCIx dissociation and increasing Cl radicals. INTRODUCTION Higher device packing density requires sufficient storage capacity in spite of a reduction of storage node area. Recently, in order to enhance the storage capacity in 64 megabit DRAMs, applying rugged surface polycrystalline silicon (poly-Si) to storage electrodes has been widely the two typical processes has investigated [1-3]. In these investigations, been proposed. One is low pressure chemical vapor deposition(LPCVD) another is plasma etching process [3]. process [1,2], rugged surface poly-Si is formed using SiH 4 In LPCVD process, which is equivalent to the transition in the range of 560-575*C, In the temperature from amorphous phase to crystalline phase [2]. plasma etching process, rugged surface poly-Si is formed by anisotropic poly-Si etching utilizing dispersed resist micro-particles as an etchingmask. It was reported that silicon surfaces were roughed by exposuring C12/02 plasmas [4]. Tomas has suggested that the roughening seems unlikely to have resulted from SiOH formation and so it is possible that oxide masking could be occurring. In this paper, we present a new formation process of rugged surface poly-Si using C12/02 plasma etching without etching-mask and investigate the etching mechanisms. EXPERIMENTAL A magnetron reactive ion etching(RIE) system and an electron cyclotron resonance (ECR) plasma system were used for etching poly-Si. Compared with magnetron RIE system, ECR plasma system is able to Mat. Res. Soc. Symp. Proc. Vol. 236. @1992 Materials Research Society
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Permanent Magnet Ad
Magnetron (2.45GHz) Quartz Chamber Magnetic Coil O.E..S.
Matching pump
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0-MS
Box 13.56MHz
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Figure 1 A schematic diagram of magnetron RIE system
RF(2MHz)
Pump
Figure 2 A schematic diagram of ECR plasma system
make a discharge a
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