濺鍍薄膜之光學常數與界面應力

The optical properties and interface stresses of the sputtered dielectric thin films

李坤憲(Kun-Hsien Lee)

指導教授 ： 李正中

國立中央大學/理學院/光電科學研究所/博士(2011年)

摘要

針對濺鍍之光學薄膜，本論文提出一套新的方法，在不影響薄膜的光學特性前提下，消除多層膜的殘留應力。射頻離子束濺鍍殘留應力值高達1.5GPa以上之SiNx薄膜，以離子束電壓1300V、離子束電流110mA所製鍍的單層SiN1.06薄膜，厚度250nm的殘留應力值為-2.18GPa，將此單層等分切割成四層製鍍時，其殘留應力值降為-1.38GPa，定性地驗證介電質薄膜存在著界面應力。
磁控濺鍍SiO2及Nb2O5薄膜於玻璃基板與塑膠PET基板上，薄膜的光學常數存在著差異性：SiO2、Nb2O5於PET上的折射率均分別高於其被製鍍在玻璃基板上的折射率值，而塑膠基板上的薄膜殘留應力會小於玻璃基板的殘留應力，可能是由於有機物受到電漿激發造成斷鍵，因而與薄膜分子產生化合或混合的反應，使殘留應力減小。在多層膜的實驗中，玻璃基板上的SiO2Nb2O5界面為張應力，可以作為消除應力之用，Nb2O5SiO2界面則為壓應力；在PET基板上SiO2Nb2O5和Nb2O5SiO2皆為壓應力。不論何種基板，愈上層的界面，其造成撓曲量都有增加的趨勢。
利用射頻濺鍍SiO2、Ta2O5光學薄膜堆疊高反射鏡，在單層膜的實驗中，發現殘留應力隨著切層數呈倒W形的趨勢，這是由於在切層時，子層可能尚未成膜，因此本徵壓應力會較成膜時大，當界面應力無法抵銷子層的本徵應力時，殘留壓應力會增加，如同等分切割成二層與四層製鍍單層膜之情形；而界面應力的影響若能大過於子層的本徵應力時，殘留壓應力就會減小，如同等分切割成三層與五層製鍍單層膜之情況；兩層HL的切層實驗證明能有效減低應力的切法為(H, 1/3L*3)，因此利用(H, 1/3L*3)切法製鍍11層高反射鏡時，總殘留應力為-0.423GPa，與未切之高反射鏡比較，可減小其應力值約17.6%，且切層方法並未影響材料之光學常數。

關鍵字

光學常數 ； 薄膜 ； 濺鍍 ； 界面應力 ； 切層消除應力

並列摘要

A novel method is proposed to reduce the residual stress of multilayers without altering their optical constants. The residual stress of SiNx thin films deposited by RF ion-beam sputtering exceeds 1.5GPa. For example, the residual stress of single SiN1.06 layer deposited at ion-beam voltage of 1300V and current of 110mA is -2.18Gpa while its thickness is 250nm. If the single layer is divided equally into four parts to be fabricated, the stress decreases to the value of -1.38GPa due to the contribution of the interface stresses.
SiO2 and Nb2O5 thin films deposited by DC pulsed magnetron sputtering on both glass and PET substrates are investigated. The optical constants of films on PET differ from those on glass substrate. The refractive index of SiO2 and Nb2O5 on PET is higher than that on glass, respectively. It is due to the organic material of plastic substrate de-bonding by the plasma excitation. They are chemisorbed or mixed with the adatoms resulted in the increase of the refractive index and the decrease of the residual stress. After the analysis of the multilayer stress, the result shows the interface stress of SiO2Nb2O5 on glass is tensile but that of Nb2O5SiO2 is compressive. On PET substrate, the interface stresses of SiO2Nb2O5 and Nb2O5SiO2 are both compressive. The deflection of the upper interface is larger than that of the lower interface.
The high reflectance mirror is made up of multilayered stack of SiO2 and Ta2O5 deposited by RF ion-beam sputtering. In single layer stress measurement, the residual stress curve with the cutting layer number presents inverse W shape. This is because of the competition between the residual stress and interface stress of each sub-layer. In the experiments of HL stack and (HL)^5L, the total residual stress is reduced by the use of cut method of (H, 1/3L*3). If the cut method is (H, 1/3L*3), the residual stress of (HL)^5H stack is -0.423GPa which is lower than that fabricated by the traditional method and the reduction ratio of the residual stress is approximately 17.6%. The result of optical spectrum shows that the use of cut methods does not influence the optical constants of layers.

並列關鍵字

reduction of stress ； Sputtering ； thin film ； optical constants ； interface stress

參考文獻

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