Si-TaSi₂共晶自生复合场发射材料的研究

【作者】 韩民；

【导师】 张军；

【作者基本信息】 西北工业大学 ， 材料加工工程， 2004， 硕士

【摘要】 Si-TaSi₂共晶自生复合材料作为半导体金属共晶材料（SEM）之一，具有较低的功函数、良好的电传输特性和自生肖特基结等特点。本文采用切克拉斯基法（CZ法）和电子束区熔法（EBFZM）两种定向凝固方法制备该共晶自生复合材料；借助金相技术、电镜技术、图象处理技术等多种分析测试手段，考察了Si-TaSi₂共晶定向凝固组织和及其相应的工艺规范。 本文探讨了CZ法工艺参数对材料凝固组织的影响，确定了制备该复合材料的最佳工艺参数。在晶转12r／min，埚转6r／min，提拉速率12cm／h，埚升速率1.2cm／h工艺条件下，纤维平均间距为9～10μm，平均直径1.79um，平均密度为0.925×10⁶rod／cm²，平均横向面积为8～10μm²，平均体积分数为2.328％，满足场发射材料的要求。凝固速率在8～20cm／h范围内，随凝固速率R的增加，纤维直径d和纤维间距λ都减小，前者符合线性关系，后者符合λ∝R^-0.5关系。随凝固速率的增加TaSi₂纤维体积分数基本不变。 在较好控制固液界面和较低的生长速率定向生长条件下，纤维相TaSi₂生长过程有其独特的规律性，通常可以将其生长过程分为启动、竞争、稳定三个典型阶段。研究纤维相和基体相之间的位相关系发现，纤维相表面光滑，与基体相界面分明，证明两相形成低能界面，其位相关系为[111]_si//[0001]_TaSi2，（220）_si//（2（?）00）_TaSi₂。考察纤维参数在不同生长阶段的分布规律发现，从顶部到中段纤维密度增大，从中部到根部纤维密度基本不变化。同一晶片上纤维沿径向分布有差异，边缘纤维密度高，中心部位纤维密度低。纤维横向截面形状表现多样。材料的场发射性能良好，其发射开启场强约为4.4V／um，F—N曲线表明该材料的电子发射主要是由隧道效应引起的。 利用EBFZM法，本文研究了区熔工艺和凝固组织之间的关系。结果表明，在区熔速率R=0～0.3mm／min范围内两相很难形成规则共晶，其中基体相定向生长，第二相混乱生长，弥散分布于基体中。区熔速率R=0.6mm／min，Si—TaSi₂共晶体两相形成规则共晶。纤维相生长经历了启动生长、竞争生长、稳定生长过程。比较EBFZM和CZ法生长的共晶体纤维相分布发现，前者纤维相分布更均匀，纤维细且长，但取向性没前者好。更多还原

【Abstract】 As one of the semiconductor-metal eutectic material (SEM), the rod-like eutectic in-situ composite of Si & TaSi2 has lower work function , excellent electrical transport and the schottky junctions, which was grown-in during the crystal growth step. Therefore, in this paper, two directional solidification methods, Czochralski method and electron-beam floating zone melting method, were used to obtain such material. The directional solidifition microstructures of Si-TaSi2 system was performed using NEOPHOT-1, AMRAY- 100B SEM and JEM-2000CX TEM analysis technique.The effect of the technique parameters to the microstructure of the eutectic in-situ composite was discussed firstly. On these basis, the. optimum process parameters were founded. With a seed rotation rate of 12rpm, a crucible rotation rate of 6 rpm, a seed puller rate of 12cm/h and a crucible rise rate 1.2cm/h, the average inter-rod spacing was 9-10 um, the average rod diameter was 1.79um, the average rod density was 0.925 X 106 rod/cm2 and the volume fraction was 2.3277%. These parameters all meet the requirement of field emission material. When the solidification rate was changed from 8 to 20 cm/h, with the increase of solidification rate R, the fibre diameter (d) and the inter-rod spacing (A ) both decreased. The former followed linearity rule and the latter followed the rule of λεr-0.5 The volume fraction was steadiness when the solidification rate increased. On condition of controlling solid-liquid interface preferably and keeping low directional solidification rate, there were particular phenomena in TaSi2 fibre development process. Generally, it can be divided into three typical steps. The first was star-up period, the second was competition period, the third was stabilization period. As the relationship of phase interface between Si matrix and TaSi2 fibre was studied, it resulted that the interface between the two phases was evidently. This proved that the low energy inter-face was formed. The ruleof two phase was [111]Si//[0001]TaSi2, (220) Si//(2200)Tasi2. The two coupling phasewas firstly developed in the low-energy surface. In the course of studying the fibre parameter in different development period, it was discovered that the rod density increased from the top to the middle of the boule. But it did nearly not changed from the middle to the bottom. In the same wafer, the fibre parameter was different along the radial. It was high at the edge and low in the center section. The fibre traverse section was multiplicity. The result showed that the composite had excellent fieldemission characters. The star-up field intensity was 4.4v/um and the F-Ncurve indicated that the electron emission was leaded by tunnel effect.The connection of microstructure and floating zone melting process was studied . The result indicated that the two phases in eutectic had difficulty in growing regularly on condition that the floating zone melting rate was in the scope of 0~0.3mm/min. The matrix phase was directional grown and the other phase was grown with no order. It was dispersed in the matrix phase . At the rate of 0.6mm/min, the two phases of Si-TaSi2 system was grown eutectic regularly. The fibre phase was developed in star-up process, competition process and stabilization process. Compared with the fibre distribution by CZ method and EBFZM method, it was discovered that the former was uniformity and slim, the latter was better for alignment.更多还原