Alignment of Ge dots on Si (001) substrateith two-dimension hole array

自我聚集鍺點已經被廣泛研究，因為其潛在著許多應用，最近許多文獻討論，如何來控制鍺點的定位，因為對大多數電子元件而言，這是技術是必備的。一個可能的方法來製作有序鍺點是利用微影及自我聚集成長技術的整合。在這方面的研究裡，我們成功展現於具有二維孔洞陣列結構之矽(001)基板上成長有序排列及大小一致性的鍺點。同時，我們也針對不同週期、深度、孔洞陣列的形貌進行探討，其對鍺點有序排列所造成的影響。 在研究過程中，所有樣品均藉由超高真空化學氣相沉積(UHV-CVD)系統於600℃下進行成長。矽模板製作是藉由e-beam 顯影及反應性離子蝕刻(RIE)系統。在成長鍺點之前，我們會先成長一層矽緩衝層，目的是為了減緩蝕刻時，所造成的表面不平整。我們製作的樣品尺寸及表面形貌將藉由掃描電子顯微鏡(SEM)及輕敲式原子力顯微鏡(AFM)所量測。論文中的電子束顯微鏡所量測的孔洞陣列是由e-beam 顯影及反應性離子蝕刻所形成，這些圖形尺寸大小約為200奈米，所有的圖案均沿著[110]晶面方向排列。於圓型二維孔洞陣列下所成長的鍺點將藉由輕敲式原子力顯微鏡量測，其洞深度大約20奈米，週期分別為300、350、400奈米。圓頂型的鍺點將形成於洞內{110}面的四個交角。此外，有序排列的程度將隨週期降低而增加。這邊我們定義落在洞內{110}面交角的點為有序點(這邊我們先忽略在隆起部之金字塔形的點，之後會進行討論)。而有序百分比(有序點數量/所有點數量)和孔洞陣列之週期成線性關係。其中最佳的情況為300奈米下的75%。接下來於相同週期下(300奈米)不同深度下(分別為4、23、31奈米)的AFM圖形進行討論。其有序百分比依然和深度呈現性關係，並且隨著週期增加而增加，而最佳的情況為深度31奈米的97%。 雖然良好二維有序排列的圓頂型鍺點已被達成，但如果我們考慮隆起部之金字塔型的鍺點，可以發現其鍺點呈現兩個不同大小的分佈。在不同洞外貌的(圓形、方形、菱形)的樣品AFM圖形中。對圓形而言，在隆起部會出現金字塔型之鍺點，其鍺點呈現兩個不同大小的分佈。對方形而言，沒有金字塔型鍺點在隆起部，但洞內鍺點呈現不規則形狀，並非圓頂形。對菱形而言，在隆起部並沒有金字塔型鍺點，且洞內鍺點均為圓頂形。在週期300奈米、深度31奈米、菱形的樣品中，鍺點平均直徑約為85奈米、標準差約為3.5奈米。此外鍺點面密度約約為4×109/cm2，其和平面密度有相同數量級。 因此，我們可以藉由調變矽基板上所製作二維孔洞陣列的週期及深度來達成鍺點的有序定位。同時，藉由菱形圖案的製作改善鍺點的大小一致性。其鍺點大小及密度分別為85奈米及4×109/cm2。Self-assembled Ge dots have been extensively investigated because of its potential applications. Recently many reports discussed on the control of Ge dot position which is necessary for most electronic applications. One approach to fabricate ordered Ge dots is to integrate lithography and self-assembly growth techniques. In this study, we demonstrated well-aligned Ge dots with uniform size distribution on Si (001) with two-dimension hole array. The influence of the period, the depth, and the shape of the hole array on alignment of Ge dots was investigated. All samples in this work were grown by UHVCVD system at 600℃. The Si (001) templates were fabricated by e-beam lithography and reactive ion etching (RIE). Before the growth of Ge dots, a Si buffer layer was grown to eliminate the roughness introduced during etching. The dimension and surface morphology were investigated by scanning electron microscope (SEM) and tapping mode atomic force microscope (AFM). The SEM images of 2D hole array (circle, square, and diamond) fabricated by e-beam lithography and RIE. The dimensions of these patterns are about 200nm. All of these patterns are along the [110] direction. The AFM images after growth of the Ge dots on circle-shaped hole array. The hole depth is ~20nm and the period is 300nm, 350nm, and 400 nm, respectively. As it can be seen the dome-shaped Ge dots nucleate at the intersection of {110} planes inside the hole array. Besides, the degree of alignment of dots increases with decreasing the period. Here we defined the dots located at the intersection of {110} planes as the “aligned dots” (we ignored the pyramid-shaped dots on ridges and discussed it later). The relation between alignment percentage (number of aligned dots/number of all dots) and the period of hole array is linear. The highest alignment percentage is 75% of the 300nm-period sample. The AFM images of the samples with same period of hole array (300nm) but different hole depth (4nm, 23nm, and 31nm). The alignment percentage also increases linearly with the hole depth. The highest alignment percentage is 97% of the 31nm-depth sample. Although the 2D well-aligned dome-shaped Ge dots has been achieved, the size distribution is bimodal if we take the pyramid-shaped dots on ridges into account. The AFM images of the samples with different hole shape (circle, square, and diamond). For the circle case, there are pyramid-shaped dots on ridges and the size distribution is bimodal. For the square case, no pyramid-shaped dots observed on ridges. However, the dots inside the hole are irregular rather than rounded dots. As for the diamond case, there are no pyramid-shaped dots on ridges and the dots inside the hole are dome-shaped. The size distribution of Ge dots of the sample with 300nm-period, 31nm-depth, and diamond-shaped hole array. The average diameter is 85nm and the standard deviation is 3.5nm. Besides, the dot density is ~4×109/cm2 which is comparable to the Ge dots grown on blanket Si substrate. lignment of Ge dots on Si (001) substrate with two-dimension hole array was achieved by modulating the period and depth of the hole array. The size uniformity of dots can be improved by diamond-shaped pattern. The average diameter and areal density is 85nm and 4×109/cm2, respectively.口試委員會審定書………………………………………………………….……....... i謝……………………………………………………………………………...……iii文摘要……………………………………………………………………….......... iv文摘要……………………………………….………………………………..……vi錄………………………………………………………………………..……….…ix目錄…………………………………………………………………..……………xii目錄…………………………………………………………………………....…xvii一章 導論……………………………………………..……………………………1.1前言……………………………………………………………………..…………1.2論文架構…………………………………………………………………………...3二章 基本原理介紹……………………………………………………….……….4.1量子點介紹………………………………………………….……………….……4.2.1量子點應用………………………………………………...…………………4.1.2製作量子點的方法…………………………………………………...………6.2異質磊晶成長模型介紹……………………...……………………………………8.2.1三種異質磊晶成長模型………………………………………………………8.2.2Ge/Si異質磊晶……………………………………..…………………………9.3 有序排列………………………………………………...………………………10.3.1量子點有序排列(alignment) ………………………………..………………10.3.2量子點大小一致性(uniformity) ………………………………….…………12.4化學能模型(chemical potential model) …………………………………………13三章 製程介紹……………………………………………………………………15.1樣品製作過程……………………………………………………………………15.1.1光阻塗佈(spin coating) …………………………………………..…………15.1.2電子束直寫(e-beam direct write) ………………...…………………………15.1.3 顯影(develop) ………………………………………………………………15.1.4RIE製程…………………………………………………...…………………16.1.5 去光阻(PR-remover)製程...………………...………………………………18.1.6 長晶製程……………………………………………………………………18.1.7 製程流程……………………………………………………………………19.2量測儀器介紹……………………………………………………………………20.2.1 掃描式電子顯微鏡(Scanning Electron Microscope，SEM) ….……………22.2.2 原子力顯微鏡(Atomic Force Microscpoic，AFM) …………………..……22四章 實驗結果介紹………………………………………………………………23.1 鍺點在平面成長情形…………………………………………………...............24.1.1不同溫度下所成長的鍺點…………………………………….……………24.1.2不同流量下所成長的鍺點………………………………………………….26.2二維孔洞陣列……………………………………………………………………27.2.1微影後之二維孔洞陣列………………………………………….…………27.2.2 RIE蝕刻後之二維孔洞陣列…………………………………………..……29.2.3 同步高溫處理(in-situ heat treatment)後之二維孔洞陣列………...………31.2.4成長緩衝層(Buffer)後之二維孔洞陣列……………………………………35.3鍺點(Ge dots)在二維孔洞陣列成長情形………….……………………………38.3.1不同週期下成長情形……………….………………………………………38.3.2不同深度下成長情形………………………….……………………………41.3.3不同形狀下成長結果………………………….……………………………43.4量化分析…………………………………………………………………………46.4.1鍺點排列………………………………………….…………………………46.4.2鍺點大小…………………………………………….………………………48.4.3鍺點密度…………………………………………………………….…………52.5鍺點在二維孔洞陣列下成長情形(橫截面) ………………………………….…54.6鍺點在二維孔洞陣列空乏區成長情形…………………………………………55.7小結………………………………………………………………………....……56五章 模擬結果討論………………………………………………………....……58.1化學能模型(chemical potential model) …………………………………………58.1.1化學能模型介紹……………………………………………………….……58.2模擬結果……………………………………………………...…………….……62.2.1不同週期之模擬結果………………………………………………….……62.2.2不同深度之模擬結果………………………………………………….……65.2.3不想理效應模擬結果……………………………………………….………68.3小結…………………………………………………..………………….……….69六章 結論及未來工作………………………………...…………………….……70.1結論……………………………………………………………………...……….70.2未來工作…………………………………………………..…………….……….71.2.1 拉曼(Raman) …………………………………………...………….……….71.2.2 表面原子重組……………………………………………..……….……….72考文獻…………………………………………………………………….……….7