Microscopic Structure and Electrical Activity of 4H-SiC/SiO2 Interface Defects : an EPR Study of Oxidized Porous SiC
Microscopic Structure and Electrical Activity of 4H-SiC/SiO2 Interface Defects : an EPR Study of Oxidized Porous SiC
复制标题
4H-SiC/SiO2 界面缺陷的微观结构和电活性：氧化多孔 SiC 的 EPR 研究
DOI：
--
复制
发表时间：
2004
期刊：
影响因子：
--
通讯作者：
W. J. Choyke
中科院分区：
文献类型：
--
作者：
H. J. von Bardeleben;J. Cantin;Y. Shishkin;R. Devaty;W. J. Choyke
通过电子顺磁共振波谱研究了多孔n型4H-SiC中与氧化相关的缺陷。在干氧中 1000°C 氧化后观察到两个主要中心。第一个是各向同性的，g 因子为 2.0028 ；它归因于氧化物中的碳相关中心。第二个中心是各向异性的，具有 C3v 或 C1h 对称性，具体取决于其相对于 c 轴的方向。其 g 因子为 g//c=2.0024 和 g⊥c=2.00315 以及 gxx=2.0031、gyy=2.0028、gzz=2.0023。从其中心和配体超精细相互作用来看，它归因于界面 SiC 侧的类似 Pb 的碳悬挂键中心：(Pbc)。 Pbc 具有电活性并引入深能级。两个缺陷的浓度估计为[C]=10 18 cm -3 和[PbC]=10 12 cm -2 。引言 4H-SiC/SiO2 和 6H-SiC/SiO2 的氧化物和界面结构一直是众多实验和理论研究的对象[1]。与Si的情况一样，可以通过SiC的高温氧化获得SiO2成分的热氧化物。氧化动力学与 Si 情况不同，取决于研究最多的 (0001) 表面的碳或硅面[2]。界面结构也与Si情况不同，4H-SiC是否可以形成原子突变界面或者是否无法避免SiOxCy过渡层仍然是一个悬而未决的问题[3]。这些问题对于可接受的 MOSFET 结构的可行性非常重要[4]。我们通过 EPR 光谱研究了界面和氧化物中缺陷的性质和浓度。该技术先前已被证明对于 Si/SiO2 界面缺陷研究极其有用[5]。对于 (111)Si 界面，它允许识别和表征所谓的 Pb 中心，这是该结构中已识别的主要缺陷。多孔硅是一种具有高内表面积的单晶硅，尽管其强度较低，但由于 Pb 中心的超精细结构解析良好，因此使用多孔硅可以提供额外的信息[6]。在之前对块状 SiC/SiO2 样品的 EPR 研究中 [7-10]，已经研究了与氧化和氧化后退火相关的缺陷。观察到一个缺陷，其特征是具有 g=2.0024 (4H-SiC) 的各向同性单线 EPR 光谱；根据 g 值，初步将其归因于非晶 SiO2 层中的 C 悬空键缺陷。在界面的结晶部分没有观察到缺陷。我们在此介绍氧化多孔 4H-SiC 的 EPR 研究结果。第一批结果最近已发布[11,12]。实验通过光辅助电化学溶解块体n型掺杂4H-SiC基底来制备多孔层。详细信息请参见参考文献[13]。获得厚度为数十μm的层。根据溶解条件，可以获得具有不同孔隙结构的样品。图1显示了具有三角形孔结构的样品的横截面。高等材料科学论坛在线：2004-06-15 ISSN：1662-9752，Vols。 457-460，第 1457-1462 页 doi:10.4028/www.scientific.net/MSF.457-460.1457 © 2004 Trans Tech Publications Ltd，瑞士保留所有权利。未经 Trans Tech Publications Ltd（www.scientific.net）书面许可，不得以任何形式或任何方式复制或传播本文的任何内容。 (Semanticscholar.org-11/03/20,15:23:27) 电流密度形成了 V 形孔结构（图 2）。三角形孔样品的内表面估计为100m 2 /cm 3 。下面给出的 EPR 结果与特定的孔隙结构无关。所有样品均在密闭炉中在干氧（32mbar）下于1000℃氧化10分钟。此外，一些样品还在 NO 气体下进行了热处理（1050°C/5..200 分钟）。 EPR 测量是在 9 GHz 和 35 GHz、4K 至 300K 之间的各种温度下对 5x5 mm 2 尺寸的样品进行的。图1.具有三角形孔结构的n型4H-SiC多孔层的横截面SEM图像图2。具有 V 形孔结构的 n 型 4H-SiC 多孔层的横截面 SEM 图像 对于 (11-20) 和 (1100) 平面中的磁场旋转，测量了光谱的角度变化。由于与线宽相比与较小的 g 因子各向异性相关的几个光谱的重叠，已对总光谱进行了计算机辅助分解。结果与讨论 在图 3 中，我们展示了在具有三个高对称方向的三角形孔隙结构的氧化层中观察到的典型 X 波段 EPR 光谱。光谱是各向异性的，由多条仅部分解析的谱线组成。该光谱已在许多不同的样品以及两个微波频率下进行了研究。 3442 3444 3446 3448 3450 3452 90° 54° //c E P R 信号 (arb .u .) 磁场 B (G) 12125 1213
The oxidation related defects in porous n-type 4H-SiC have been studied by electron paramagnetic resonance spectroscopy. Two main centers are observed after a 1000°C oxidation in dry oxygen. The first one is isotropic with a g-factor of 2.0028 ; it is attributed to a carbon related center in the oxide. The second center is anisotropic with C3v or C1h symmetries depending on its orientation relative to the c-axis. Its g-factors are g//c=2.0024 and g⊥c=2.00315 and gxx=2.0031, gyy=2.0028, gzz=2.0023. From its central and ligand hyperfine interactions it is attributed to a Pb like carbon dangling bond center at the SiC side of the interface:(Pbc). The Pbc is electrically active and introduces a deep level. The concentrations of the two defects are estimated to [C]=10 18 cm -3 and [PbC]=10 12 cm -2 . Introduction The oxide and interface structure of 4H-SiC/SiO2 and 6H-SiC/SiO2 have been the object of numerous experimental and theoretical studies[1]. As in the case of Si a thermal oxide of SiO2 composition can be obtained by high temperature oxidation of SiC. The oxidation kinetics are different from the Si case and depend on the carbon or silicon face for the most studied (0001) surface[2]. The interface structure is also different from the Si case and it is a still open question whether an atomically abrupt interface can be formed for 4H-SiC or whether a transition layer of SiOxCy can not be avoided[3]. These issues are important for the feasibility of acceptable MOSFET structures[4]. We have investigated the nature and concentration of the defects at the interface and in the oxide by EPR spectroscopy. This technique has been shown previously to be extremely useful for interface defect studies in Si/SiO2[5]. For (111)Si interfaces it had allowed the identification and characterization of the so called Pb center, which is the dominant identified defect in this structure. The use of porous silicon, which is a monocristalline form of Si with a high internal surface area has given additional information due to the well resolved hyperfine structures of the Pb center in spite of their low intensity[6]. In previous EPR studies on bulk SiC/SiO2 samples [7-10] oxidation and postoxidation anneal related defects have been investigated. One defect characterized by an isotropic single line EPR spectrum with g=2.0024 (4H-SiC) was observed; based on the g-value it had been tentatively attributed to a C dangling bond defect in the amorphous SiO2 layer. No defect at the cristalline part of the interface had been observed. We present here the results of an EPR study of oxidized porous 4H-SiC. First results have been published already recently [11,12]. Experimental The porous layers were prepared by photo assisted electrochemical dissolution of bulk n-type doped 4H-SiC substrates. For details see ref.[13]. Layers with a thickness of several tens of μm were obtained. Depending on the dissolution conditions samples with different pores structures can be obtained. Figure 1 shows a cross section of a sample with triangular pore structure. At higher Materials Science Forum Online: 2004-06-15 ISSN: 1662-9752, Vols. 457-460, pp 1457-1462 doi:10.4028/www.scientific.net/MSF.457-460.1457 © 2004 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-11/03/20,15:23:27) current densities a chevron like pore structure is developed (fig.2). The internal surface of the triangular pore samples has been estimated to 100m 2 /cm 3 . The EPR results presented below are independent of the particular pore structure. All samples were oxidized in a closed furnace under dry oxygen(32mbar) at 1000°C for 10minutes. Some samples were in addition submitted to a thermal treatment under NO gas (1050°C/ 5..200min). The EPR measurements were performed on 5x5 mm 2 sized samples at 9 GHz and 35 GHz at various temperatures between 4K and 300K. Fig.1. Cross sectional SEM image of a n-type 4H-SiC porous layer with triangular pore structure Fig.2. Cross sectional SEM image of a n-type 4H-SiC porous layer with chevron like pore structure The angular variations of the spectra have been measured for a rotation of the magnetic field in the (11-20) and (1100) planes. Due to the overlap of several spectra related to a small g-factor anisotropy as compared to the linewidth a computer assisted decomposition of the total spectrum has been performed. Results and Discussion In fig.3 we show typical X-band EPR spectra observed in an oxidized layer with triangular pore structure for three high symmetry orientations. The spectrum is anisotropic and composed of multiple lines only partially resolved. This spectrum has been studied in a number of different samples as well as at two microwave frequencies. 3442 3444 3446 3448 3450 3452 90° 54° //c E P R S ig n a l (a rb .u .) Magnetic Field B (G) 12125 1213