Pressure Dependence on the Electrical Properties of SiO 2 Gate Oxide Formed by Inductive Coupled Plasma Oxidation
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Pressure Dependence on the Electrical Properties of SiO2 Gate Oxide Formed by Inductive Coupled Plasma Oxidation Beom-jong Kim , Dong-chan Kim, Yoon-jae Kim., Han-jin Lim, Ju-eun Kim, Wook-yeol Yi, Dae-hyun Kim, Bong-hyun Kim, Young-wan Kim, Sung-ho Kang, Yung-seok Kim, Woo-jun Lee, Seok-woo Nam and Chil-hee Chung Process Development Team, Semiconductor R&D Center, Samsung Electronics Co., Ltd San#16, Banwol-Dong, Hwasung-City, Gyeonggi-Do, Korea, 445-701 ABSTRACT We investigated the pressure dependence of the inductive coupled plasma (ICP) oxidation on the electrical characteristics of the thin oxide films. Activation energies and electron temperatures with different pressures were estimated. To demonstrate the pressure effect on the plasma oxide quality, simple N type metal-oxide-semiconductor (NMOS) transistors were fabricated and investigated in a few electrical properties. At higher pressure than 200mTorr, plasma oxide has a slightly higher on-current and a lower interfacial trap density. The on-current gain seems to be related to the field mobility increase and the lower defective interface to the electron temperature during oxidation. INTRODUCTION Recent trend of semiconductor is not only high density but also low energy consumption. For this reason, the device size is getting smaller and the gate electrode is replaced by metal electrode. These size shrinkage and metal gate introduction forces the gate oxide to be ultrathin and grown at low temperature. Furthermore, the thin oxide grown at low temperature is required to have the good quality as a gate oxide. Plasma oxidation is one of the candidates for low temperature process and many researches on plasma oxide have been released recently [1-3]. Therefore, it is important to understand the relationship between the plasma characteristics and the electrical properties of oxide. In this work, we focused on the pressure effects on the plasma oxidation and some electrical properties as a gate oxide. EXPERIMENT Gate oxides were grown by ICP method with different pressure conditions. All process parameters except the pressure were fixed and the pressures were 20, 100, 200, 400mTorr. To define the process characteristics of each condition, we measured the electron temperature using optical emissions spectrometer (OES). For the analysis of electrical properties, we fabricated several simple NMOS transistors through the traditional process. The size of NMOS transistor is 100 µm by 100 µm and the poly silicon was used as a gate electrode. DISCUSSION
Figure 1 shows the activation energy of the oxide with pressure from 20mTorr to 400mTorr. The activation energy at 20mTorr is 0.03eV and it increases linearly with pressure up to 0.14eV at 400mTorr.
Figure 1. Activation energy of oxide grown with pressure It is supposed that this pressure dependence could be related to the energy and the mean free path of oxygen ions participating during the oxidation. At lower pressure, the molecule and ion density is reduced, but the mean free path of the ions is longer enough to reach
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