六甲基二矽氮烷與氧氣製備之封裝膜阻水阻氣特性研究

Abstract

本研究利用低溫電漿輔助化學氣相沉積法開發低溫、可撓有機/無機混成抗水、氧封裝膜。藉由前驅氣體流量及製程參數的調配來調控混成膜之成分與特性，所沉積之薄膜並具良好覆蓋性，可避免水氧側漏。本研究所使用的前驅氣體為六甲基二矽氮烷(hexamethyldisilazane, HMDSZ)以及氧氣(O2)。使用玻璃、PI、以及矽晶圓(Silicon wafer)三種基板，製程溫度為室溫，HMDSZ 單體流量選定10sccm及20sccm 配合O2 流量為0~200sccm，電漿功率則設定在15W~60W 之間。 我們由傅式光譜儀(Fourier transform infrared spectroscopy, FTIR)，來觀察混成膜鍵結，發現在1073cm-1 這個波長下的Si-O-Si 鍵結，隨著氧氣流量的升高而增加，代表無機鍵結隨著氧氣分量增加而逐漸增加。並由水接觸角( Contact angle)觀察到HMDSZ 薄膜表面隨著氧氣分量愈來愈多呈現愈來愈親水，亦應證Si-O-Si成分漸增。再透過原子力顯微鏡(atomic force microscopy, AFM) 來量測其薄膜表面粗糙度，發現沒有通入氧氣的HMDSZ 薄膜的粗糙度大約是0.5nm，通入氧氣後則將粗糙度降低到大約0.1nm，透過AFM 的圖也可以發現，表面的微小顆粒在通入氧氣後明顯的數量變為較少。由可見光至近紅外穿透光譜得知，無論有無氧氣通入，混成膜於可見光之平均穿透率都保持在90%左右。接著由奈米壓痕儀(nanoindentator)量測混成膜之機械性質，隨著氧氣流量比例增加，楊氏係數與硬度均隨之上升，代表製程中Si-O-Si 鍵結的生成，使得薄膜的無機性質增加。同時我們在上述的量測皆觀察到，在通入氧氣的製程中，若提升製程電漿功率可達到和增加氧氣流量比例同樣的效果。 最後經由鈣測試法(calcium test) 量測其水氣穿透率(water vapor transmission rate, WVTR)以及氧氣穿透率(oxygen transmission rate, OTR)。我們觀察到，沒有通入氧氣製程的HMDSZ 薄膜，WVTR 約在大於10-3g/m2day，OTR 大約等於0.3cc/m2-day。通入適當比例氧氣流量後明顯讓薄膜阻水氣性質有顯著的提升，不過通入過多氧氣流量卻因μm 等級的微小顆粒產生，使得薄膜阻水氣性有劣化的現象。在調變製程功率的觀察上，我們也發現到同樣的現象。經量測，氧氣及HMDSZ單體流量比例為2.5，製程功率為30W 時，厚度0.5μm 的薄膜之WVTR 降到6.8 10-5 g/m2-day，OTR 降至2.11 10-2 cc/m2-day。當混成膜厚度增加至3μm 時，水氣穿透率為8.4 10-6 g/m2-day，氧氣穿透率為2.64 10-3 cc/m2-day。

Thin film encapsulation technology with excellent permeation barrier property is highly desirable for organic electronic and flexible electronic applications. During the last decade, several organic / inorganic multilayer composite encapsulation technologies have been demonstrated. The inorganic sub-layer serves as the permeation barrier, while the organic sub-layer, typically polymeric material, is used to decouple the inorganic sub-layers and prevent the defect propagation. However, the process for preparing multilayer composite is usually expensive and complicated. In order to reduce the process complexity, a single-layer organic-inorganic hybrid material is pursued to combine the functions of inorganic and organic sub-layers. The single-layer SiOxNyCz is deposited from a mixture of hexamethyldisilazane (HMDSZ) and oxygen by plasma enhanced chemical vapor deposition (PECVD) at room-temperature. Three types of substrates, including glass, polyimide foil and silicon wafer, are used for property characterization. The effect of oxygen to HMDSZ flow rate ratio is studied. Fourier transform infrared spectra show that the intensity of Si-O-Si absorption band at wavenumber of 1073cm-1 increases as the oxygen flow rate is raised. The contact angle of a droplet of water on the film surface decreases from >80° to 30° when O2/HMDSZ flow rate ratio increases from 0 to 10. Both imply that the addition of oxygen in the source gases can enhance the inorganic content of the resulting film. The surface topography is evaluated by atomic force microscopy. The roughness decreases monotonically (from 0.5 nm to 0.1 nm) with the increase of oxygen flow rate. The mechanical property is then determined by the nanoindentation. We observe a positive correlation between the Young’s modulus and the oxygen flow rate. In addition, we observe that there is a similar trend as we enhance the power of process with the increasing of the O2/HMDSZ flow rate ratio. While several film properties strongly depend on the O2/HMDSZ flow rate ratio and process power, the optical transmittance in the visible light regime remains 90% in all cases. Ca-test is used to evaluate the barrier properties of the hybrid SiOxNyCz layers. Thin film deposited from pure HMDSZ has a water vapor transmission rate (WVTR) of >10-3 g/m2day and oxygen transmission rate(OTR) of 0.3cc/m2-day . The WVTR decreases first and then increases again when oxygen flow rate is raised. The degradation of the barrier property at high O2/HMDSZ flow rate ratio may caused by the formation of particles embedded inside the hybrid film. Similar trend is observed when the deposition power increases. Optimal WVTRs of 6.8´10-5 g/m2-day and 8.489 10-6 g/m2-day, OTRs of 2.11 10-2 cc/m2-day and 2.64 10-3 cc/m2-day, are obtained for a 500nm-thick and an 3000nm-thick SiOxNyCz thin films deposited at the condition of O2/HMDSZ flow rate ratio = 2.5, and process power = 30W.