Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/7157
標題: 奈米結晶氮化矽薄膜電致發光特性之研究
Electroluminescence from nc-SiNX:H
作者: 石倍宗
Shih, Pei-Tzong
關鍵字: nanocrystal silicon;奈米結晶矽;hydrogenated amorphous silicon nitride;photoluminescence;氫化非晶氮化矽;光致發光
出版社: 電機工程學系所
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摘要: 
本論文設計三個實驗,將電漿加強式化學氣相沉積系統(PECVD),在電漿功率、壓力及基板溫度不變的條件下,在Ar、H2氣體稀釋的環境之中,沉積出非晶氮化矽薄膜。分別控制三種參數,反應氣體SiH4/NH3不同流量比例改變薄膜N/Si比例、高溫爐管回火時間改變奈米結晶矽尺寸以及薄膜厚度觀察對於發光特性影響。再經高溫爐管回火處理,使薄膜中因部分矽氮原子結合鍵結成Si3N4,而多餘的矽原子聚集結晶並被Si3N4所包圍而分離且限制其結晶大小,形成結晶大小均勻且數量多的奈米結晶氮化矽薄膜。再量測此材料的光致發光(PL)特性,以探討薄膜的N/Si比例對PL光譜強度之影響,進而再將之以電子元件形式製作,達成電致發光。
腔體壓力、SiH4/Ar/H2、電漿功率、沉積溫度分別固定為1 torr、12 /160 /80 sccm、5 W及250℃,SiNx薄膜沈積厚度固定為100 nm,經高溫爐管回火處理1.5小時。
實驗一,單層非晶氧化矽薄膜中氮的控制以6種NH3流量參數為控製變因,流量從12、24、36、48、60到72 sccm。實驗二,固定NH3流量為60 sccm,改變爐管回火時間為1、1.5、2小時。實驗三,則改變薄膜沉積厚度為5、20、50、100 nm。
薄膜分析方面,矽氧氮鍵結由傅立葉轉換紅外線光譜(FTIR)測量。薄膜的N/Si比例、結晶結構及尺寸由能量散佈光譜(AES)、拉曼散射光譜(Raman)。發光特性由光致發光光譜(PL)量測。
AES量測結果顯示,從流量12到流量72 sccm的薄膜中,N/Si原子比例隨NH3的流量漸漸增加從0.42倍減少到0.69倍,在當NH3和SiH4的比例大於5倍以上之後,薄膜中的N/Si比例開始下降至0.65倍。比較回火處理前之FTIR頻譜圖,結果顯示NH3流量比例愈大,薄膜中則有較大的Si-N訊號,氮原子的比例較高。由於NH3流量較大而稀釋的緣故,Si-H鍵結群訊號較弱,這是形成薄膜中Si少H多的情形。回火後的試片的FTIR光譜發現回火讓薄膜重新排列,H鍵結的消失表示回火趕走了氫,讓薄膜結構發生了變化。比較回火處理前後之拉曼光譜圖,改變NH3流量從12 ~ 72 sccm的試片,在回火前,主要為非晶矽的訊號。回火後,所有試片的拉曼光譜在520 cm-1處都有明顯強列的單晶矽結晶訊號,相對應的光致發光光譜也有很強的訊號。証實光致發光的機制來自於電子電洞對在矽奈米結晶矽中的復合發光。
由PL光譜中我們可得知N/Si比例由0.42變化至0.69可以增加nc-SiNx薄膜的PL光譜強度,造成發光強度變化的主因是由於結晶比例之變化所造成。比較不同回火時間對於發光的影響,我們則推測在每一條件的試片都有其對應最佳的回火時間,使得薄膜重新排列成最佳發光特性之薄膜。然而,隨著薄膜厚度增加可使峰值強度增加。但卻非一直成正比,在厚度為50 nm和100 nm的試片比對之下,厚度為50 nm的試片反而有較高的發光強度。

Abstract

In this thesis, we design three experiments. The amorphous silicon nitride (SiNX) films were deposited by plasma-enhanced chemical vapor deposition (PECVD), while the RF power, deposition conditions of pressure, substrate temperature, and diluting gas Ar/H2 flow rate for a-SiNX:H films were fixed. We control three kinds of parameters separately, different SiH4/NH3 gas ratio to modulate the nitrogen to silicon atom ratio (N/Si), different annealing time to modulate the size of nc-Si and different film thickness to observe the relation between thickness and light emitting property. After post annealing, a part of nitrogen and silicon atoms are bonded and formed Si3N4, so that the other silicon atoms are crystallized, bonded together, and separated from Si3N4. The crystal size of these silicon atoms are also confined to form a nanocrystal embedded in silicon nitride film with uniform size and great number of crystals. We measure the photoluminescence (PL) property to study the influence the N/Si ratio to PL spectrum, and then apply to make a electric device to reach the goal, electroluminescence.
The deposition conditions of pressure, SiH4/Ar/H2 flow rate, RF power, substrate temperature were fixed at 1 torr、12 /160 /80 sccm、5 W及250℃, respectively. The thickness of the silicon nitride films and the annealing duration are fixed the same at 100 nm and 1.5 hours.
Experiment one, The NH3 flow, which is used to control the nitrogen ratio in the amorphous silicon nitride, was changed from 12, 24, 36, to 48 sccm. Experiment two, the annealing duration was changed from 1, 1.5, to 2 hours, while fixing the NH3 flow at 60 sccm. Experiment three, the thickness of the films was changed from 5, 20, 50, to 100 nm. The structure bonding are measured by Fourier Transform Infrared spectrometer. The N/Si ratio of nc-SiNx film and crystal structure and size are measured by Auger Electron Spectroscopy and Raman spectrum. And the light emitting property was measured by PL spectrum.
The result of AES spectrum indicates that N/Si atom ratio increases from 0.42 to 0.69 times. After the proportions of NH3 and SiH4 are increased to more than 5 times, N/Si atoms ratio begins to decrease to 0.65 times. The FTIR spectrum before annealing indicates that there is a larger Si-N intensity and much higher nitrogen atom ratio with increasing the NH3 flow. Due to the larger flow volume of NH3, Si-H groups becomes weaker, this is how there is little Si and more hydrogen atoms in the films. The FTIR spectrum of the films after being annealed indicated that annealing enables the film to rearrange, the disappearing of Si-H and N-H bonding indicates that annealing gets rid of hydrogen atoms, making the structure of the films to be changed. Compare the Raman spectrum before and after annealing, the samples before annealing are composed of amorphous silicon. After annealing, the Raman spectrum of all the samples got a great intensity at 520 cm-1where is the position of single crystal. That also indicates that the light emitting mechanism comes from the recombination of electron hole pairs in nc-Si.
From the spectrum of photoluminescence, we know that the photoluminescence intensity can be increased with increasing the N/Si ratio in the films. Causing the main reason that luminous intensity changes mainly is because the change of the proportion of crystallization. Comparing the affect of different annealing time to the light emitting property, we presume that each sample has its best annealing duration to rearrange that cause better light emitting properties. However, as we know, the intensity of peak increases with the increasing of the film thickness. But it’s not always a direct proportion. The sample of 50 nm has higher emitting intensity than the sample of 100 nm.
URI: http://hdl.handle.net/11455/7157
其他識別: U0005-2908200616105200
Appears in Collections:電機工程學系所

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