射頻磁控濺鍍法在矽晶片上沉積三元Si-C-N薄膜及其特性分析

Abstract

本研究是以射頻磁控濺鍍法，使用燒結碳化矽靶材，在氬氣及氮氣的氣氛下，於矽晶片上沉積Si-C-N三元薄膜。並探討不同的製程參數對薄膜性質的影響。薄膜的特性分析是以電子能譜化學分析技術 (ESCA) 及傅立葉轉換紅外線光譜技術 (FTIR) 分析薄膜的組成及鍵結，原子力顯微技術 (AFM) 觀察薄膜的表面形貌，X射線繞射光譜決定薄膜的晶體結構，奈米壓痕技術分析薄膜的機械性質，並量測電流-電壓曲線來分析薄膜的電子場發射特性。 由實驗之結果顯示，當RF功率為100 W，或工作壓為50 mTorr時，所沉積出之薄膜的氧含量在41 at.%以上，而當RF功率在300 W以上或工作壓在10 mTorr以下時，薄膜中之氧含量則下降至8 at.%以下，且其薄膜組成原子比由高矽含量變成 [Si]：[C]：[N]=1：1：1。這是因為降低工作壓及增加RF功率會使得電漿內的粒子能量增強，而使得濺射及沉積效率更佳，並屏障氧的影響。在薄膜中檢測到Si-N、Si-O、C–C、C=C、C-N及C=N之鍵結，而並沒有Si–C鍵的訊號。薄膜為非晶質結構，且其表面粗糙度會隨基材負偏壓之增加而下降，當基材未加負偏壓時，薄膜表面的粗糙度為1.4 nm，而當偏壓增加至-100 V時，則下降至0.3 nm。這是因為負偏壓增加使得原子遮蔽效應減弱之故。在薄膜的機械性質方面，高氧含量之薄膜其性質不佳，而當氧含量在8 at.%以下時，薄膜之奈米硬度為16~18 GPa，推導模數為102.1~153.2 GPa。在電子場效發射特性方面，高氧含量之薄膜，並無明顯之電子場效發射現象。而低氧含量之薄膜，其起始電場強度在5~10 V/μm之間，最大之場效發射電流密度在10~37μA/cm2之間，但其場效發射電流會有衰減之問題。另外，其起始電場強度會隨著基材偏壓之增加而上升，這可能是薄膜表面有效之場效發射面積或表面粗糙度會隨基材偏壓增加而減少之故。

In this study, the ternary Si-C-N thin films were prepared on Si wafer by the radio frequency (RF) magnetron sputtering method using the sintered SiC as target under Ar and N2 atmosphere. Electron spectroscopy for chemical analysis (ESCA) and Fourier transform infrared spectrometry (FTIR) were used to determine the chemical compositions and bonding types of the films. The surface morphology of the deposited films was examined by atomic force microscopy (AFM). The crystal structures were analyzed by XRD. The mechanical properties of the films were estimated by nano-indentation technique. The field emission properties of the films were characterized by I-V measurement. The result shows that the oxygen content of the films depends on RF power and working pressure. The oxygen content can be above 41 at.%, under 100 W RF power or under 50 mTorr working pressure. Under 10 mTorr working pressure or under 300 W RF power, the oxygen content of the films becomes less than 8 at.%, and the Si content of the films decreases from high values to become [Si] : [C] : [N]=1 : 1 : 1. The reason is due to the fact that the energy of the excited particles in the plasma will be higher by decreasing the working pressure or increasing the RF power. In consequence, the sputtering and deposition yields will be improved and the shielding the oxygen from contact with the substrate will be more effective. The films were detected to possess Si–N, Si–O, C–C, C=C, C-N and C=N bonds, except Si–C bond. The films are amorphous in structure, and their surface roughness decreases as increasing negative bias voltage of the substrate. The roughness of the films is about 1.4 nm without bias application, and becomes 0.3 nm at –100 V bias voltage. This is due to weakening in the atomic shielding effect as increasing the negative substrate bias. As to the mechanical property of the films, it generally shows a poor properties at higher oxygen contents. The nano-hardness and the reduced modulus of the films with oxygen contents below 8 at.% are about 16 ~ 18 GPa and 102.1 ~ 153.2 GPa, respectively. On field emission property, the films with high oxygen contents indicate no obvious electron field emission phenomenon. The films with oxygen contents below 8 at.% show that the turn-on field intensity and the maximum current density are about 5 ~ 10 V/μm and 10 ~ 37 μA/cm2, respectively; however, it suffers decay problem in field emission property. Furthermore, the turn-on field intensity is deteriorated with increasing bias voltage of the substrate, it may relate to a decrease in the effective emission area or surface roughness of films as increasing the substrate bias.