以微波電漿化學氣相沉積法在矽晶上沉積三元矽氮化碳薄膜的結構與特性

Abstract

本研究以微波電漿化學氣相沉積法在矽晶上以CH4和N2為氣體源，成功的合成出結晶態之三元矽氮化碳薄膜。部份矽基材以三種過飽和溶液分別為腺嘌呤、鑽石膏及氮化矽進行超音波振盪12小時前處理；其餘基材則以外加矽源，無基材前處理的條件進行沉積。所得沉積薄膜的表面形貌以原子力顯微鏡和掃描式電子顯微鏡來觀察；薄膜的組成以歐傑電子顯微鏡和電子能譜化學分析儀來估計；以陰極螢光光譜儀和光子激發光譜儀來分析薄膜能隙；並以X射線繞射光譜來決定其晶體結構；以奈米壓痕儀來分析薄膜的機械性質；由電流-電壓(I-V curve)曲線來分析薄膜的場發射特性。 由實驗的結果所得結論可分為兩大部份： (A) 在外加矽源且無基材前處理條件下，基材無須前處理即能重複成長組成及表面形貌皆均勻之薄膜，薄膜晶粒形狀主要為3~10mm之長方形柱狀晶，在柱狀晶上並成長出晶粒較小的六面柱狀晶，薄膜之成份原子比例為[Si] : [C] : [N] = 7:3:9；薄膜能隙以PL和CL量測約在3.01 eV~3.87 eV之間，晶體結構由X射線繞射分析可能具α-Si3N4，β-Si3N4及tetragonal Si3N4三種結構；薄膜之奈米壓痕硬度可達55-60 GPa。 (B) 無外加矽源條件下，以氮化矽前處理的基材在沉積後有較高的成核密度，由結果顯示各種前處理所得的沉積薄膜再現性低，且晶粒間成份變化大。在薄膜之晶體結構和能隙的結果上，除了沒有PL的能隙訊號峰且與α-Si3N4，β-Si3N4及tetragonal Si3N4比對的晶體結構契合性較低，其他與(A)所得結果相似；矽氮化碳薄膜之場發射特性在電場強度為22V/mm時，電流密度為3.3mA/cm2優於鑽石薄膜，而與部分類鑽碳膜相當，具有優異的場發射特性。

Tenary crystalline Silicon carbon nitride films have been successfully synthesized on Si wafer by MPCVD with CH4 and N2 as source gases. Some of the Si substrates were pretreated by scratching the surface with various solutions suspending with adenine, diamond paste or Si3N4 powders. The other Si substrates were deposited by adding additional Si sources without substrate pretreatments. The morphologies of the deposited films were examined by AFM and SEM. The film compositions were estimated by AES and ESCA. The bandgaps of the resultant films were investigated by CL and PL spectroscopy. The crystal structures were determined by XRD. The mechanical properties of the film were evaluated by nanoindentation technique. The field emission properties of the films were characterized by I-V measurement. From the experimental results, the conclusions can be divided into two parts： (A) For the conditions of adding additional Si sources and without substrate pretreatments, the deposited films possess good uniformity in morphology and compositions, and consist of 3~10 mm rectangle-shaped crystals attached with smaller hexagonal-shaped crystallites. The average atomic ratio of the resultant films is [Si]:[C]:[N]=7:3:9. The bandgaps as measured by PL and CL are around 3.01 eV and 3.87 eV, which are in the spectrum of the visible light range. The results of XRD show that the crystal structures of the films may consist of a-Si3N4, b-Si3N4and tetragonal Si3N4 types structures. The nano-hardness of the films is about 55~60 GPa. (B) For the conditions of adding no additional Si sources but subjecting to various substrate pretreatments, the substrates pretreated by scratching with Si3N4 solution (or called "P3") show a higher nucleation density. The pity about the rest of the results is that the reproducibility of the films is very poor under various pretreatment processes and deposition conditions. The bandgaps and crystal structures of the resultant films are similar to that in part (A), except no PL signals and poorer matching of XRD patterns with a-Si3N4, b- Si3N4and tetragonal Si3N4 types structures. As to field emission properties of the films, the results show that a field emission current density can go up to 3.3 mA/cm2, under a field intensity of 22 V/mm which is much better than that for diamond films and is compatible with that for diamond-like-carbon films.