氮化鈦/氧化鋁鉿/氮化鈦金氧金電容之電性分析與電壓電容係數物理模型

Abstract

在本篇論文中，我們採用摻雜鋁金屬之二氧化鉿之高介電材料作為金屬-氧化物-金屬(MIM)電容的介電質，摻雜兩種比例的鋁金屬，分別為10%與14.7%。試片厚度分為三種:15nm、25nm、35nm。鋁摻雜為10%且厚度為15nm的試片，在3V頻率為1MHz的量測條件下，得到電容密度約13.6 fF/μm2，其所對應的介電常數約為23；而鋁摻雜為14%且厚度為15nm的試片中，電容密度約為11.3 fF/μm2而其所對應的介電常數約為19.5。兩者相比，鋁摻雜濃度越低（即鉿元素含量較高），介電常數較高，所得到的電容密度也較高。本篇論文之電容密度達到2013年 ITRS的規格。而在改良漏電流方面，於1V的偏壓下，兩種不同鋁摻雜量且厚度皆為15nm的試片，其漏電流分別為1.88×10-8 (A/cm2) 及1.72×10-8 (A/cm2)。漏電流機制，於非常低電場下呈現歐姆傳導機制(Ohmic conduction)；中等電場下呈現蕭基發射傳導機制(Schottky Emission)；高電場則呈現Frenkel-Poole傳導機制。 降低電容電壓係數(VCC)為金氧金電容之一大挑戰，在本篇論文中，我們製作的鋁摻雜14%且厚度35nm的試片，其VCC僅有259(ppm/V2)，然而，造成VCC現象之基本機制目前尚無定論，由已知的實驗結果顯示，VCC與本身材料種類、薄膜厚度有關。本篇論文提出一個修改過的物理模型，藉由邊界缺陷電容值與量測頻率和偏壓之間的關係式，也可經由適當的轉換，成為自矽基底表面的穿隧距離和自氧化鋁鉿之導帶邊緣的缺陷能階深度。以一穿透梯形位能障礙的彈性直接穿隧物理模型為理論基礎，我們能夠藉由一平滑的三維網線，來描述在氧化鋁鉿的邊界缺陷之空間與能階分佈。而所萃取之結果介於1×1015~3×1017 (cm-3eV-1)之間，且與VCC成正相關。推測此種邊界缺陷是VCC的成因之ㄧ。最後，我們也討論了此方法的限制。

In this thesis, we use HfAlO as the dielectric layer in MIM capacitors. HfAlO films with two different Al percentages were deposited. The Al percentages are 10% and 14.7%. The thickness of samples is divided into three kinds of thickness: 15nm, 25nm, and 35nm. The capacitance density is 13.6 fF/μm2 with 10% Al content and the dielectric constant is about 23 at 3V and 1MHz. The capacitance density is 11.3 fF/μm2 with 14.7% Al content and the dielectric constant is about 19.5. The lower Al percentage is (Hf content is higher), the higher capacitance density is. The capacitance density meets the requirement of 2013 ITRS. The leakage current densities of the samples with 15nm-thick HfAlO and 10% and 14.7% Al content are 1.88×10-8 and 1.72×10-8 (A/cm2) at 1V bias, respectively. The leakage current mechanism is identified to be Ohmic Conduction at low electric field, Schottky Emission Conduction at moderate electric field, and Frenkel-Poole conduction at high electric field. The lowest parabolic voltage coefficient of capacitance (VCC-□) in this thesis is about 259(ppm/V2) with Al content of 14% Al content and thickness of 35nm. A physical model considering the pre-existing border traps was proposed to account for the VCC-□. From the frequency and electrode bias voltage dependences the spatial and energy distribution from Si substrate surface and from HfAlO conduction band edge could be extracted, respectively. The orders of the magnitude of the extracted border trap volume densities are around 3×1017 (cm-3eV-1), which have positive correlation with the VCC-□. Increasing the Al content can reduce the trap density and the VCC-□. The limitations of detectable space and energy depth of the physical model are also discussed briefly.