鋁與鍺摻雜對二氧化鋯閘極介電層之影響及通道摻雜對n型鍺電晶體之影響研究

Studies on the Effect of Al- and Ge-incorporation on ZrO2 Gate Dielectric and Effect of Channel Doping on Ge n-MOSFET

許嘉麟(Chia-Lin Hsu)

指導教授 ： 崔秉鉞

國立交通大學/電機學院/電子工程系所/碩士(2018年)

摘要

在本篇論文中，我們探討摻雜鋁與鍺對二氧化鋯閘極介電層之影響。我們發現在二氧化鋯閘極中摻雜鋁會延遲結晶，因而抑制累積區的電容值表現，但同時也會降低閘極漏電流與遲滯現象，亦不會劣化界面；而在二氧化鋯中摻雜鍺，相較於純的二氧化鋯閘極，則不會對電性有太大的改變。另外，我們針對摻雜鋁之二氧化鋯閘極，在不同的金屬沉積後退火溫度下，作不同結構與不同摻雜濃度的比較。並從中找出最佳的結構與摻雜濃度。
為了能深入了解摻雜鋁對二氧化鋯閘極介電層結晶現象的影響，我們製作不同厚度及更高沉積後退火溫度的試片。我們發現，在二氧化鋯的閘極中摻雜鋁，會增加二氧化鋯的結晶臨界厚度與臨界溫度，因此延緩結晶的現象。
整體而言，在漏電對等效氧化層的趨勢中，純的二氧化鋯閘極還是有較好的表現；摻雜鋁的二氧化鋯閘極則是有更低的漏電流。而在二氧化鋯中摻雜鋁跟摻雜鍺都能有效的降低遲滯現象，且不會劣化介面。
接著，我們探討通道摻雜對n型鍺電晶體的影響。我們製作不同通道摻雜濃度的鍺電晶體，並量測其電性，其中包含轉換特性曲線、輸出特性曲線、介面缺陷及邊緣缺陷的評估與遷移率。在之前發表的文獻中提出，隨著通道濃度漸濃到1e18時，導通電流及電子遷移率似乎會有嚴重衰減的現象。但依據本篇研究中的量測結果，隨著通道濃度漸濃，受到離子植入後增加的介面缺陷之庫倫散射的影響，導通電流及電子遷移率只有些微的下降。
對於那些導通電流與遷移率的有嚴重衰減現象的元件，我們提出可能的猜測與解決方式。我們猜測電性嚴重衰減的現象，是由於高能量的離子植入後，產生大量晶格缺陷，導致介面與閘極的劣化，進而有更嚴重的庫倫散射效應，同時也不排除是因晶圓本身品質不佳所造成。另外，相較於矽電晶體，庫倫散射及表面粗糙散射在鍺電晶體中嚴重許多。因此若能改善鍺基板與閘極介面，例如增加適當的熱製程，或使用更高品質的晶圓，勢必能讓鍺電晶體有更好的表現。

關鍵字

鍺 ； 閘極介電層 ； 氧化鋯 ； n型電晶體 ； 通道摻雜

並列摘要

In this thesis, the properties of Al- and Ge-doped ZrO2 dielectric stacks on Ge devices are investigated thoroughly. It is found that the doping of Al suppresses the crystallization of ZrO2, resulting in the reduce of accumulation capacitance; however, it also reduces the leakage current and promotes the hysteresis performance without the deterioration of interface state density. In contrast, the Ge-doped samples exhibit similar performance as the samples with pure ZrO2. On the other hand, the effects of different structures and several Al doping concentrations with various post-metal annealing (PMA) temperatures are also discussed and evaluated, and the best condition is proposed and suggested.
In order to further understand the influence of the incorporation of Al into ZrO2 as gate dielectric, the samples with thicker physical thickness and higher PMA temperatures are fabricated. It is discovered that the doping of Al will increase the critical crystallization temperature and the onset crystallization thickness of ZrO2, which accounts for the retardation of crystallization.
Overall, the pure ZrO2 samples still exhibit better J_G-EOT behavior, while the Al-doped samples own lower leakage current. In addition, all the Al- and Ge- doped samples have better hysteresis than the pure ZrO2 ones without the deterioration of the interfacial layer.
Next, Germanium (Ge) n-MOSFETs with various channel doping concentration are fabricated, and the effects of channel doping are fully discussed and investigated. The overall electrical properties are evaluated, including transfer and output characteristics, the number of interface traps and border traps, and the channel mobility. In previously proposed researches, it is found that the on-current and mobility will severely degrade when the substrate doping concentration reaches 1e18. However, in this thesis, only slight deterioration of on-current and mobility is observed at the higher doping concentration, probably due to the Coulomb scattering of interface trap densities generated after implantation.
Then, for the samples with severe on-current and mobility degradation, the possible speculation and solution are proposed. it is suspected that the severe degradation may result from the extra Coulomb scattering caused by the defects generated at the interface after implantation with high energy. In addition, the quality of Ge wafer may also be a concern. On the other hand, it is discovered that the Coulomb scattering and the surface roughness scattering are more serious in Ge n-MOSFET compared to silicon. As a result, if the interface and substrate of Ge n-MOSFET can be improved more with appropriate thermal budget or high-quality wafer, it is possible to achieve better performance.

並列關鍵字

Ge ； gate dieletric ； Zirconium oxide ； n-MOSFET ； channel doping

參考文獻

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