锰的硅化物薄膜在Si(100)-2×1表面生长的STM研究

STM study of growth of manganese silicide thin films on a Si(100)-2×1 surface

锰的硅化物在微电子器件、自旋电子学器件等领域具有良好的应用前景,了解锰的硅化物薄膜在硅表面的生长规律是其走向实际应用的关键步骤之一.本文采用分子束外延方法在Si(100)-2×1表面沉积了约4个原子层的锰薄膜,并利用超高真空扫描隧道显微镜研究了该薄膜与硅衬底之间在250—750℃范围内的固相反应情况.室温下沉积在硅衬底表面的锰原子与衬底不发生反应,薄膜由无序的锰团簇构成;当退火温度高于290℃时,锰原子与衬底开始发生反应,生成外形不规则的枝晶状锰硅化物和富锰的三维小岛;325℃时,衬底上开始形成平板状的MnSi小岛;525℃时,枝晶状锰硅化物完全消失,出现平板状的MnSi_(1.7)7大岛;高于600℃时,富锰的三维小岛和平板状的MnSi小岛全部消失,仅剩下平板状的MnSi_(1.7)大岛.这些结果说明退火温度决定了薄膜的形态和结构.在大约600℃退火时岛的尺寸随着退火时间的延长而逐渐增大,表明岛的生长遵从扩散限制的Ostwald熟化机理.

Manganese silicides are promising candidates for microelectronics and spintronics materials.A good understanding of their growth mechanisms is a crucial step toward their practical applications.In this paper,a Mn film of～4 monolayer is deposited on a Si（100）-2×1 surface by molecular beam epitaxy.The solid reaction between the Mn film and the silicon substrate in a temperature range of 250—750℃is studied using scanning tunneling microscopy.At room temperature,the as-deposited Mn atoms do not react with the silicon atoms and the film consists of disordered Mn clusters.When the sample is annealed at a higher temperature than 290℃,the Mn begins to react with the Si and forms small three-dimensional（3D） islands of Mn-rich silicides and silicide islands of dendritic shapes.When the annealing temperature reaches 325℃,small tabular islands,which correspond to MnSi,start to grow on the Si substrate.At an annealing temperature of 525℃,silicide islands with dendritic shapes all disappear;meantime several large tabular islands,which correspond to MnSi_（1.7）,are formed.When the annealing temperature is higher than 600℃,3D islands and small tabular islands all disappear while large tabular islands remain there.These results demonstrate that the morphology and the structure of the film strongly depend on annealing temperature.The average size（area） of the remaining islands increases with the increase of annealing time.Time dependence of the averaged island area indicates that the growth of the islands follows the diffusion limited Ostwald ripening mechanism.