改善孔洞型二氧化矽低介電薄膜製程中的熱處理程序

Improvement of Heat Treatment Process for Manufacturing Porous Silica Low-k Films

鄭智陽(Chih-Yang Cheng)

指導教授 ： 萬本儒

國立臺灣大學/工學院/化學工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.10048

摘要

本研究的目標是改善低介電薄膜製程中的熱處理程序，希望降低溫度及縮短時間以減少對電子元件產生的熱積存，避免元件性質劣化，並提升製程效率。研究中主要針對先前研究的熱處理程序(450°C鍛燒5小時，升溫速率1°C/min，不含降溫共10小時50分)做改善，另外，探討加入電漿或紫外光程序對熱處理程序的效果。
熱處理程序有二個目的，第一是移除薄膜中的有機物包含模板試劑TPAOH及界面活性劑Tween 80，以產生孔洞降低k值；第二是使薄膜中的Si-OH進行縮合反應形成Si-O-Si鍵結，藉此提升薄膜機械強度，同時，減少薄膜中Si-OH含量降低k值。
首先，為了降低溫度，本研究藉由熱重分析探討移除有機物及Si-OH進行縮合反應的溫度。實驗顯示有機物於350°C移除完畢，此外，Si-OH縮合反應於鑑定的溫度範圍100°C至800°C都會進行。基於熱重分析的結果，本研究將持溫溫度由原本的450°C降為350°C，並探討升溫速率對薄膜性質的影響。由氮氣吸脫附的鑑定，發現升溫速率越快，孔隙度越大，然而，k值皆大於2不滿足未來工業需求。進一步探討薄膜中Si-OH含量與k值的關係，研究發現高溫(400°C或450°C)持溫相較於350°C持溫，能使薄膜中Si-OH縮合反應進行更完全，降低薄膜中Si-OH含量，使k值小於2。
為了進一步降低熱處理溫度，本研究探討低溫(約50°C -80°C)電漿或紫外光加入熱處理程序的可行性，分別在軟烤或鍛燒後加入電漿或紫外光程序，結果顯示前者因有機物移除過快但薄膜強度不足而崩塌，而後者未能有效提升薄膜中Si-OH的縮合程度。
本研究使用直接放入400°C鍛燒5小時的溫度程序，可得薄膜k值1.95，硬度1.1Gpa，彈性係數11.18Gpa，符合未來工業需求(k值<2，硬度>1Gpa，彈性係數>10Gpa)。相較於先前研究的熱處理程序節省5小時50分，並將持溫溫度降低50°C。

關鍵字

孔洞型低介電薄膜 ； 熱處理程序 ； 縮合反應 ； 電漿程序 ； 紫外光程序

並列摘要

The goal of this research is to improve heat treatment process for manufacturing low dielectric films. The original heat treatment process was calcined at 450°C for 5hr with temperature rising rate 1°C/min and the total period was 10hr 50min (which didn’t include period of cooling). In order to reduce thermal budget of the electronic components which could prevent them from damaging, two ways including lowering temperature and reducing process period were applied. Besides, the effects of introduction of plasma or ultraviolet process into heat treatment have been discussed in details.
There are two purposes for heat treatment process. Firstly, organics such as TPAOH(structure directing agent) and Tween 80(surfactant) can be removed from the films to produce pore and lower k value. Secondly, Si-OH condensation reaction can be promoted to form Si-O-Si bond in the films to enhance mechanical strength and reduce the amount of Si-OH to lower k value.
In order to lower temperature of heat treatment, by research of thermogravimetric analysis, it has been investigated for at which temperature the organics can be removed and Si-OH condensation reaction can proceed. It was found that the organics would be removed at 350°C and Si-OH condensation reaction would proceed in the investigated range, from 100°C to 800°C. Therefore, the calcination temperature in this research was changed from 450°C to 350°C. Besides, different temperature rising rates were applied. The nitrogen adsorption/desorption analysis revealed that the porosity would get larger as temperature rising rate increased. However, k values were all larger than 2 which didn’t meet the requirements of future IC industry. IR studies indicate that more amount of Si-OH remaining in the films than that calcined at 450°C was the main cause. Plasma and ultraviolet exposing was introduced after the calcination at 350°C; nevertheless, Si-OH condensation still could not be improved effectively. On the other hand, while plasma or ultraviolet process was introduced after soft baking to improve heat treatment, it was found that films would collapse. The reason was that the organic templates for making the pores were removed before Si-OH condensation occurred. The mechanical strength of pore walls were too weak to be held.
Based on the experimental results (i.e. NMR, thermogravimetric analysis and so on), it can be concluded that sufficient temperature(i.e. 400°C or 450°C) and process period in heat treatment were two critical points to promote Si-OH condensation reaction and lower k values. The reason for insufficient Si-OH condensation or collapsing of films as plasma or ultraviolet were applied was their low processed temperature (i.e. 50°C-80°C). In this research, the film calcined at 400°C for 5 hours (which was directly put into the furnace at 400°C and the average temperature rising rate was 21°C/min) possesses a k value of 1.95, a hardness of 1.1Gpa and an elastic modulus of 11.18Gpa which could meet the requirements of future IC industry (k<2,hardness>1Gpa,elastic modulus>10Gpa). In addition, it could save 5hr 50min and lower 50°C compared to original heat treatment process.

並列關鍵字

Porous low-k films ； Heat treatment process ； Condensation reaction ； Plasma process ； Ultraviolet process

參考文獻

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