單層及多層金屬薄膜與p型銻化鎵接觸之特性分析

Abstract

隨著元件尺寸的不斷微縮，產生的物理極限使得矽基互補式金屬氧化物半導體(CMOS)，難以繼續提升其元件效能。近年來許多新的替代材料，以及元件結構新技術的引進，讓電晶體的效能有了新的進步方向。其中三五族化合物半導體比起矽有更高的載子遷移率，使其元件在低電壓供給下，能夠有高的電流表現，提升效能。而比起其他三五族半導體材料，銻化鎵擁有較高的塊材電洞遷移率，其電洞遷移率約為1000 cm 2/Vs，及其能障約為0.72eV，是適合取代矽應用於p-MOSFETs 的材料。 為了達到三五金氧半電晶體的高效能，其中主要的挑戰是形成低電阻之汲極/源極接面(S/D)，然而銻化鎵與金屬接觸介面的技術仍未完整建立，由於銻化鎵可達之低摻雜濃度和高退火活化溫度，在銻化鎵p-MOSFET之製程中，金屬與銻化鎵的合金為S/D的自我對準製程是必要的。 本論文研究金屬薄膜與銻化鎵接觸之材料反應機制，以及電性分析。金屬薄膜的選擇為單層金屬Ni、Ti、Co和雙層金屬Ti/Ni、Ni/Ti，在200~600°C ∕30秒 快速熱退火處理後，以TEM/EDS、XRD 和 AFM進行材料分析，並以圓形傳輸線模型結構萃取特徵接觸電阻。 在研究中發現，高溫退火下，接觸電阻會因相分離的產生而大幅上升。本研究得到銻化鎵與金屬薄膜之最低接觸電阻5.3×〖10〗^(-5) Ω-cm2，為Ti/Ni 與GaSb接觸，退火條件為500°C∕30秒，其中微晶的TiNi 反應層產生，並與銻化鎵基板接觸。研究結果得知，為達到低電阻之金屬/銻化鎵合金S/D的形成，製程上需要低的熱預算，並維持足夠低的溫度以避免相分離產生。

As the scaling of device continued shrinking, the Si-based complementary metal-oxide-semiconductor (CMOS) has faced difficulties in enhance the device performance due to the physical limitation. For the past few years, the introduction of alternative materials and device structures are expected to improve the device performance. III–V compound semiconductor materials have higher carrier mobility compared with Si, which lead to the higher device performance at low power supply. Among the III–V compound semiconductor materials, GaSb has the bulk hole mobility of ~1000 cm2/Vs, higher than that of most other III–V compounds, as well as a sufficiently large band gap (0.72 eV), which is promising to replace Si as the materials of the transistors. One of the main challenges to achieve the high performance of III-V pMOSFETs is the low-resistance source and drain (S/D) formation. However, the fabrication of high-performance GaSb-based pMOSFETs is difficult owing to the metal/GaSb source/drain contact technologies. Because of the low dopant solubility and high temperature of dopant activation annealing of GaSb, self-aligned metal S/D formation process is necessary for the fabrication process of GaSb-based p-MOSFETs.

In this work, the reaction mechanisms and electrical properties of metal films contacts on p-GaSb were characterized. Ni, Co and Ti were used to be materials of the single-layer metal films and the combinations of Ti/Ni and Ni/Ti were used for the multi-layer metal films. The metal-GaSb alloys formed at the interface of the contacts by rapid thermal annealing process (200~600°C / 30s) have been characterized using transmission electron microscopy/energy dispersive spectromter (TEM/EDS), x-ray diffraction (XRD) and atomic force microscopy (AFM). The specific contact resistance of the contacts of metal films on p-GaSb were extracted by circular transmission line model (CTLM). The specific contact resistance increased extremely when the samples were annealed at high temperature due to the phase separation at the interface of contact. The lowest specific contact resistance was measured as 5.3×〖10〗^(-5) Ω-cm2 at the contact of Ti/Ni on p-GaSb annealed at 500°C / 30s compared with other samples. These results indicated that in order to develop the metal-GaSb alloys S/D with low parasitic resistance, the processing temperature should be controlled specifically lower than the temperature of phase separation.