Silicon Self-Diffusion Using Isotopically Enriched ^<28>Si Epitaxial Layers

在氧化、离子注入等硅大规模集成电路工艺中，点缺陷（空位和硅自间隙）存在于非热态。随着设备尺寸的不断缩小，这些过程的控制变得越来越重要。一般来说，半导体中点缺陷的行为可以用自扩散来研究。然而，由于硅的半衰期很短，在硅中进行自扩散实验是非常困难的。本文利用同位素富集的^<30>SiH_4气源测定了Si自扩散系数，阐明了点缺陷在Si自扩散中的作用。主要研究成果如下：(1)首次成功生长出同位素纯的^<30>Si外延层。（ii）利用^<30>Si/天然Si的异质结构，利用SIMS估算天然Si中^<30>Si的浓度分布，确定了850 ~ 1050℃温度下Si的自扩散系数。（iii）研究了掺杂对Si自扩散的依赖（费米能级效应），明确了点缺陷对Si自扩散的影响。制备了三种不同的Si衬底（重度As掺杂Si=3x10^<19>cm^<-3>，重度B掺杂Si=2x10^<19>cm^<-3>，和重度B掺杂Si=1x10^<16>cm^<-3>）。Si在外源p型Si中的自扩散系数是本征Si的2倍，而在外源n型Si中的自扩散系数与本征Si的自扩散系数基本相同。在外源n型硅中，由于费米能级效应，存在多余的空位。然而，目前的研究结果表明，在较低温度下（850、900℃），由于重n型掺杂对Si自扩散系数的影响很小，空位对Si自扩散的作用很小。阐明了低温区硅自扩散以空位为主的普遍观点是站不住脚的。

In Si LSI process such as oxidation, ion implantation and so on, point defects (vacancy and Si self-interstitial) exist in non-thermal state. With the shirink of device dimension, control of these processes becomes more and more important. Generally, the behavior of point defects in semiconductor can be investigated by self-diffusion. However, it is very difficult to perform the experiment on self-diffusion in Si because of its very short half life. In this work, we determined Si self diffusion coefficient using isotopically enriched ^<30>SiH_4 gas source and clarified the role of point defects in Si self-diffusion. Main results of the work are as follows. (i) We succeeded to grow the isotopically pure ^<30>Si epitaxial layers for the first time. (ii) Using the hetero-structures of ^<30>Si/ natural Si, Si self diffusion coefficient was determined at temperatures of 850-1050℃ by estimating the ^<30>Si concentration profiles in natural Si with SIMS.(iii) Doping dependence on Si self diffusion (Fermi level effect) was investigated and clarified the role of point defect on Si self diffusion. Three different Si substrates (heavily As doped Si=3x10^<19>cm^<-3>, heavijy B doped Si=2x10^<19>cm^<-3>, and B doped Si=1x10^<16>cm^<-3>) were prepared. Si self-diffusion coefficient in extrinsic p-type Si is twice larger than that of intrinsic Si, while self diffusion coefficient in extrinsic n-type Si is almost same as that of intrinsic Si. In extrinsic n-type Si, excess vacancies exist due to the Fermi level effect. However the present results indicate that the role of vacancy on Si self-diffusion is very small at lower temperatures (850, 900℃) because of little influence of heavily n-type doping on self-diffusion coefficient. It clarifies that the general opinion-vacancy is dominant in Si self-diffusion at lower temperature region-cannot hold.