超淺接面製程及鈦鈷堆疊結構形成矽化鈷之特性研究

Abstract

本論文主要討論以不同製程製備超淺接面之特性，及以鈦鈷（Ti/Co）堆疊結構形成矽化鈷（CoSi2）的材料特性。以一種同時具有離子佈植（ion implantation）及擴散（diffusion）優點的固態擴散方式製作超淺接面，p+n接面二極體的反向偏壓漏電流密度小於0.2nA/cm2。 除此之外，實驗中將另以非晶化佈植方式及低能量離子佈植技術製作淺接面，發現由於離子佈植造成的缺陷，使得p+n接面二極體的反向偏壓漏電流密度高達10nA/cm2以上。 在接面深度方面，非晶化離子佈植方法，由於可以避免通道效應（channeling effect），可以得到較淺的接面深度~ 40 nm；然而深度和非晶化矽離子佈植的能量成正比，這是因為非晶化離子佈植能量會增加TED（Transient-enhanced diffusion）的效應，使得接面深度較深。低能量離子佈植有較深的接面，是因為通道效應影響較嚴重；另外，當覆蓋一層LP-TEOS後，由於LP-TEOS防止了硼原子擴散出矽晶片表面，得到了一個較大的硼濃度梯度，增加了硼擴散的深度；另外，OED（Oxygen Enhanced Diffusion）的影響也可能使接面深度加深。 在鈦鈷堆疊結構形成矽化鈷方面，鈦鈷堆疊結構不僅有較大的快速熱退火製程範圍，在熱穩定性方面也有不錯的改善；然而，由於鈦原子會和鈷原子形成合金，因而影響鈷原子擴散到矽表面形成矽化鈷的速率，使得在相同快速退火條件下，得到較薄的矽化鈷薄膜厚度。

This thesis studies the characterization of ultra-shallow junctions with different formation methods and the material characterization of CoSi2 with Ti-capped staked structure. As the dimension scales down, the short channel effects become more serious. The formation of ultra-shallow junctions is essential to minimizing the punch-through and short channel effects. This thesis presents a method to fabricate ultra-shallow junctions that combine the merits of ion implantation and diffusion. Specifically, in the diffusion from implanted oxide (DIO) method, low energy ion implantation is used to highly dose a very thin screening oxide. In a subsequent RTP step, the dopants then diffuse into the underlying silicon, and ultra-shallow junctions are formed. Leakage current density of the resultant p＋n junction is found to be less than 0.2 nA/cm2 and junction depth is 0.0375μm. In addition to DIO, Si pre-amorphization ion implantation（PAI）, and the low energy ion implantation（LEI） are also tried to form p＋n ultra-shallow junctions. However, both of these methods have more than two orders of reverse junction leakage current than DIO. This is because that ion implantation produces more defects. The junction depths for LEI are 0.07μm because TED, oxide enhanced diffusion, larger boron concentration gradient, energy contamination and channeling effect. The junctions depths for PAI are only 0.05μm, because pre-amorphization can mitigate diffusion speed and channeling effect. CoSi2 is a promising alternative for TiSi2. Ti-capped CoSi2 have been found to depict wider RTA process window, better thermal stability, and smaller reverse junction leakage, compared to the conventional COSi2. This is because Ti atom can reduce native oxide between cobalt and silicon and diffuse into grain boundary of CoSi2 to retard the agglomeration. Abstract（Chinese) ……………………………………………………I Abstract（English）……………………………………………………III Acknowledge………………………………………………………………V Contents……….…………………………………………………………VI Table ＆ Figure Captions……….……………………………………VII Chapter 1 Introduction 1.1 Formation of ultra-shallow junctions………………………1 1.2Other methods to fabricate ultra-shallow junctions…….2 1.3 Characterizations of Ti-capped cobalt salicide.…3 1.4 Thesis organization…………………………………..…5 Chapter 2 Formation of ultra-shallow junctions 2.1 Introduction………………………………………………….6 2.2 Experiment procedure 2.2.1 Formation with diffusion from implanted oxide.6 2.2.2 Ultra-shallow junctions with Si Pre-amorphization ion implantation…............................7 2.2.3 Low energy ion implantation……………………….8 2.3 Junctions depths, sheet resistance and junctions leakage 2.3.1 Junctions depths and sheet resistance…………8 2.3.2 p＋n junctions leakage current…………………13 2.4 Reverse junctions leakage characteristics…………15 2.5 Summary……………………………………………………..18 Chapter 3 Characterizations of Ti-capped cobalt salicide 3.1 Introduction……………………………………………..20 3.2 Experiment procedure…………………………………..21 3.3 Sheet resistance with different stacked structure….22 3.4 Electric characteristics of Ti-capped Co-salicide junction……………................................24 3.5 Summary………………………………………………………………..25 Chapter 4 Conclusions………………………………………………………….26 Reference Figures & Tables