标题: 利用萧特基源极与汲极接面改善锗通道金氧半场效电晶体之性能
Enhancing the Performance of Germanium Channel MOSFET with Schottky S/D
作者: 曾主元
Tzeng, Juu-Yuan
简昭欣
Chien, Chao-Hsin
电子工程学系 电子研究所
关键字: 锗;萧特基;锗化物;金氧半电晶体;Ge;Schottky;Germanide;MOSFET
公开日期: 2013
摘要: 此论文中,首先我们分析金属与锗接面特性。将镍金属溅镀在锗基板上,讨论在不同金属沉积后退火温度下产生的镍锗合金/锗其二极体的电性与物性分析。在摄氏两百度一分钟氮气内的条件下退火后的镍锗合金/n型二极体得到开关电流比有五个数量级;经由电流电压方法(Current-Voltage method)可得到电子萧特基能障(Schottky barrier for electron)为0.56电子伏特,理想因子(ideality factory)为1.07。由于费米能阶钉札(Fermi-level pinning)靠近价带(valance band)导致电洞萧特基能障偏小且无法调节的现象,使得镍锗合金/p型二极体从实验数据上可以得到一个欧姆接面特性;我们利用磷(Phosphorus)载子隔离(Dopant Segregation)的方式有效在镍锗合金/者接面建立较高的电洞萧特基能障。本次实验淬取出最大的开关电流比约四个数量级和电洞萧特基能障为0.57电子伏特。利用三氧化二矽/二氧化锗/锗形成闸极介电层的锗金氧半电容(MOSCAP),搭配前述的实验制作出金属源极/汲极接面(Metal S/D)金氧半电晶体。并利用电导方法(conductance method)来萃取介面缺陷电荷密度,并发现介面缺陷电荷密度可经由300度30分钟氢气氮气混合之热退火可被降低;介面缺陷电荷密度的值在热退火后下降了40%。而在热退火后我们也发现了平带电压往正的方向移动以及较小的电压迟滞现象。
其次,我们成功制作出镍锗合金的萧特基n型金氧半电晶体;在光罩通道长度为10 m的元件拥有三个数量级的开关电流比和317 mV/dec的次临界摆幅;接着利用摄氏300度30分钟氢气氮气混合之热退火可将特性改善为四个数量级的开关电流比和173 mV/dec的次临界摆幅。在这元件中金属源极/汲极接面有效的降低电阻值进而提高操作电流,相比传统利用布植制程的元件可有效从电阻方面改进。氢气氮气混合之热退火可改善元件介面缺陷电荷密度和次临界摆幅,但镍锗合金对于热预算的要求是值得关切的。
最后,我们成功制作出镍锗合金的n型金氧半电晶体利用载子隔离,并比较和讨论使用不同的载子活化温度与载子布植能量的元件特性;在摄氏500度一分钟氮气退火条件下光罩通道长度为10 m的n型元件拥有四个数量级的开关电流比和147 mV/dec的次临界摆幅;不同布植能量下我们猜测足够情况下使用较低的能量可以减少损伤造成的漏电路径,在活化足够的情况下使用较低的退火温度可以减少热预算改善元件特性。
In this thesis, firstly, Ni/Ge junctions are formed by depositing Ni via sputtering and with different post metal annealing (PMA) temperatures. We electrically and physically analyze the NiGe/Ge junctions. The Ni/n-Ge contact with RTA at 200 °C has an effective electron barrier height (ΦBn) of 0.56 eV and an ideality factory of 1.07. Moreover, an Ion/Ioff ratio ~105 is obtained. It is obvious that for Ni/p-Ge the control sample without dopant segregation (DS) shows the ohmic contact behavior due to the strong Fermi level pinning (FLP) near the valence band and the resultant tiny ΦBp. The rectifying behavior is obtained by implanting phosphorus dopants into NiGe and the following RTA. Phosphorus atoms are supposed to segregate near at the NiGe/p-Ge interface through RTA. The extracted highest value of effective ΦBp is ~0.57 eV and an Ion/Ioff ratio ~3x104 is obtained. MOS capacitor of Al2O3/GeO2/p-Ge stack is fabricated and employed to examine the surface interface state density (Dit) near the midgap by conductance method at room temperature.
Secondly, we investigate the effect of FGA on the metal-S/D PMOSFET characteristics. The on/off ratio of our NiGe/Ge junction and SB-PMOSFET (W/L = 100m/10m) reaches 3.5 and ~3 orders of magnitude, respectively. Better subthreshold swing (173mV/dec) can be obtained after FGA. For PMOSFETs, the on/off ratio of junction is improved using the metal source/drain, RTOTAL is decreased compared with that of the conventional PMOSFET. Pros and cons of FGA at 300 °C for 30 min on PMOSFET are summarized according to our experimental data. Positive VFB shift and subthreshold swing is obtained after FGA. However, the additional thermal budget may damage the NiGe junction because of the agglomeration of NiGe.
Finally, we investigate the effect of dopant energy and drive-in annealing temperature on the characteristics of NiGe/Ge junction and device. The on/off ratio of our SB-NMOSFET (W/L = 100m/10m) is 2×104; subthreshold swing ~147mV/dec is obtained with an implant energy of 10 keV and a 400C drive-in annealing. For NMOSFETs, the on/off ratio of device is improved as the implant energy is reduced; RTOTAL of the NMOSFET subject to 500 C annealing is lower than that subject to 400 C annealing. Moreover, we show that the performance of NiGe Schottky S/D NMOSFET is more superior than that of the conventional device. Finally, our results exhibit high performance Ge NMOSFET with NiGe Schottky S/D has the potential for the future Ge MOSFET realization.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT070050150
http://hdl.handle.net/11536/73632
显示于类别:Thesis